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  • 101.
    Pacheco Roman, Oscar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Evaluation of Finite Element simulation methods for High Cycle Fatigue on engine components2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This document reflects the results of evaluating three computational methods to analyse the fatigue life of components mounted on the cylinder block; two currently in use at Scania and one that has been further developed from its previous state.

    Due to the cost of testing and the exponential increase in computational power throughout the years, the cheaper computational analyses have gained in popularity. When a component is mounted in a fairly complex assembly such as an engine, simplifications need to be made in order to make the analysis as less expensive as possible while keeping a high degree of accuracy.

    The methods of Virtual Vibrations, VROM and VFEM have been evaluated and compared in terms of accuracy, computational cost, user friendliness and general capacities. Additionally, the method VFEM has been further developed and improved from its previous state.

    A in-depth investigation regarding the differences of the methods has been conducted and improvements to make them more efficient are suggested herein. The reader can also find a decision matrix and recommendations regarding which method to use depending on the general characteristics of the component of interest and other factors.

    Two components, which differ in complexity and mounting nature, have been used to do the research.

  • 102.
    Palmert, Frans
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thermomechanical fatigue crack growth in a single crystal nickel base superalloy2019Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 122, s. 184-198Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermomechanical fatigue crack growth in a single crystal nickel base superalloy was studied. Tests were performed on single edge notched specimens, using in phase and out of phase thermomechanical fatigue cycling with temperature ranges of 100-750°C and 100-850°C and hold times at maximum temperature ranging from 10s to 6h. Isothermal testing at 100°C, 750°C and 850°C was also performed using the same test setup. A compliance-based method is proposed to experimentally evaluate the crack opening stress and thereby estimate the effective stress intensity factor range ΔKeff for both isothermal and nonisothermal conditions. For in phase thermomechanical fatigue, the crack growth rate is increased if a hold time is applied at the maximum temperature. By using the compliance-based crack opening evaluation, this increase in crack growth rate was explained by an increase in the effective stress intensity factor range which accelerated the cycle dependent crack growth. No significant difference in crack growth rate vs ΔKeff was observed between in phase thermomechanical fatigue tests and isothermal tests at the maximum temperature. For out of phase thermomechanical fatigue, the crack growth rate was insensitive to the maximum temperature and also to the length of hold time at maximum temperature. The crack growth rate vs ΔKeff during out of phase thermomechanical fatigue was significantly higher than during isothermal fatigue at the minimum temperature, even though the advancement of the crack presumably occurs at the same temperature. Dissolution of γ′ precipitates and recrystallization at the crack tip during out of phase thermomechanical fatigue is suggested as a likely explanation for this difference in crack growth rate.

    Fulltekst tilgjengelig fra 2021-01-25 17:11
  • 103.
    Palmert, Frans
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Busse, Christian
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Fatigue crack growth behaviour of an alternative single crystal nickel base superalloy2018Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 109, s. 166-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fatigue crack growth behaviour of a single crystal nickel base superalloy was studied at three different temperatures (20 degrees C, 500 degrees C and 750 degrees C) and three different crystallographic orientations. At the highest testing temperature, the influence of hold time at maximum load was also evaluated. Under some of the testing conditions, crystallographic crack growth occurred along {1 1 1} planes, which were non-perpendicular to the loading direction. The propensity for crystallographic cracking was observed to be strongly temperature dependent with a maximum occurring at the intermediate testing temperature of 500 degrees C. During non-crystallographic, Mode I crack growth the crack tended to avoid the gamma particles and propagated preferentially through the gamma matrix.

  • 104.
    Perge, Christophe
    et al.
    ENS Lyon.
    Lindström, Stefan B
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Taberlet, Nicolas
    ENS Lyon.
    Gibaud, Thomas
    ENS Lyon.
    Manneville, Sebastien
    ENS Lyon.
    Large amplitude oscillatory stress and fatigue in colloidal gels2015Inngår i: Proceedings of 10th Annual European Rheology Conference, 2015Konferansepaper (Annet vitenskapelig)
  • 105.
    Persson, Nils-Krister
    et al.
    University of Borås.
    Maziz, Ali
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biosensorer och bioelektronik. Linköpings universitet, Tekniska fakulteten.
    Öberg, Ingrid
    University of Borås.
    Christiansson, Isabella
    University of Borås.
    Stålhand, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Jager, Edwin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biosensorer och bioelektronik. Linköpings universitet, Tekniska fakulteten.
    Next generation Smart Textiles - morphing and actuating devices2017Konferansepaper (Fagfellevurdert)
  • 106.
    Rashid, Asim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Finite Element Modeling of Contact Problems2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Contact is the principal way load is transferred to a body. The study of stresses and deformations arising due to contact interaction of solid bodies is thus of paramount importance in many engineering applications. In this work, problems involving contact interactions are investigated using finite element modeling.

    In the first part, a new augmented Lagrangian multiplier method is implemented for the finite element solution of contact problems. In this method, a stabilizing term is added to avoid the instability associated with overconstraining the non-penetration condition. Numerical examples are presented to show the influence of stabilization term. Furthermore, dependence of error on different parameters is investigated.

    In the second part, a disc brake is investigated by modeling the disc in an Eulerian framework which requires significantly lower computational time than the more common Lagrangian framework. Thermal stresses in the brake disc are simulated for a single braking operation as well as for repeated braking. The results predict the presence of residual tensile stresses in the circumferential direction which may cause initiation of radial cracks on the disc surface after a few braking cycles. It is also shown that convex bending of the pad is the major cause of the contact pressure concentration in middle of the pad which results in the appearance of a hot band on the disc surface. A multi-objective optimization study is also performed, where the mass of the back plate, the brake energy and the maximum temperature generated on the disc surface during hard braking are optimized. The results indicate that a brake pad with lowest possible stiffness will result in an optimized solution with regards to all three objectives. Finally, an overview of disc brakes and related phenomena is presented in a literature review.

    In the third part, a lower limb donned in a prosthetic socket is investigated. The contact problem is solved between the socket and the limb while taking friction into consideration to determine the contact pressure and resultant internal stress-strain in the soft tissues. Internal mechanical conditions and interface stresses for three different socket designs are compared. Skin, fat, fascia, muscles, large blood vessels and bones are represented separately, which is novel in this work.

    Delarbeid
    1. Least-squares stabilized augmented Lagrangian multiplier method for elastic contact
    Åpne denne publikasjonen i ny fane eller vindu >>Least-squares stabilized augmented Lagrangian multiplier method for elastic contact
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In this paper, we propose a stabilized augmented Lagrange multiplier method for the finite element solution of small deformation elastic contact problems. We limit ourselves to friction–free contact with a rigid obstacle, but the formulation is readily extendable to more complex situations.

    Emneord
    Lagrange multiplier, stabilization, contact, augmented Lagrangian
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-124568 (URN)
    Tilgjengelig fra: 2016-02-03 Laget: 2016-02-03 Sist oppdatert: 2016-02-04bibliografisk kontrollert
    2. An Efficient Sequential Approach for Simulation of Thermal Stresses in Disc Brakes
    Åpne denne publikasjonen i ny fane eller vindu >>An Efficient Sequential Approach for Simulation of Thermal Stresses in Disc Brakes
    2012 (engelsk)Konferansepaper, Publicerat paper (Annet vitenskapelig)
    Abstract [en]

    In this paper an ecient approach to simulate thermal stresses due to tem-perature variations in disc brakes is presented. In the approach thermal and stress analysis are performed sequentially. The frictional heat analysis is based on the Eulerian method, which requires signicantly low computational time as compared to the Lagrangian approach. The nodal temperature history is recorded at each time step and is used in a sequentially coupled stress analysis, where a temperature dependent elasto-plastic material model is used to compute the stresses in the disc brake. The results show that during hard braking, high compressive stresses are generated on the disc surface in circumferential direction which cause plastic yielding. But when the disc cools down, the compressive stresses transform to tensile stresses. Such thermoplastic stress history may cause cracks on disc surface after a few braking cycles. These results are in agreement with experimental observations available in the literature.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-94281 (URN)
    Konferanse
    15th Nordic Symposium on Trbology, NORDTRIB,Trondheim, Norway, 12-15 June
    Tilgjengelig fra: 2012-09-17 Laget: 2013-06-20 Sist oppdatert: 2016-02-16bibliografisk kontrollert
    3. Sequential simulation of thermal stresses in disc brakes for repeated braking
    Åpne denne publikasjonen i ny fane eller vindu >>Sequential simulation of thermal stresses in disc brakes for repeated braking
    2013 (engelsk)Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 919-929Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper, an efficient sequential approach for simulating thermal stresses in brake discs for repeated braking is presented. First, a frictional heat analysis is performed by using an Eulerian formulation of the disc. Then, by using the temperature history from the first step of the sequence, a plasticity analysis with temperature dependent material data is performed in order to determine the corresponding thermal stresses. Three-dimensional geometries of a disc and a pad to a heavy truck are considered in the numerical simulations. The contact forces are computed at each time step taking the thermal deformations of the disc and pad into account. In such manner, the frictional heat power distribution will also be updated in each time step, which in turn will influence the development of heat bands. The plasticity model is taken to be the von Mises yield criterion with linear kinematic hardening, where both the hardening and the yield limit are temperature dependent. The results show that during hard braking, high compressive stresses are generated on the disc surface in the circumferential direction which cause yielding. But when the disc cools down, these compressive stresses transform to tensile residual stresses. For repeated hard braking when this kind of stress history is repeated, we also show that stress cycles with high amplitudes are developed which might generate low cycle fatigue cracks after a few braking cycles.

    sted, utgiver, år, opplag, sider
    Sage Publications, 2013
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-94283 (URN)10.1177/1350650113481701 (DOI)
    Tilgjengelig fra: 2013-04-26 Laget: 2013-06-20 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    4. Thermomechanical Simulation of Wear and Hot Bands in a Disc Brake by adopting an Eulerian approach
    Åpne denne publikasjonen i ny fane eller vindu >>Thermomechanical Simulation of Wear and Hot Bands in a Disc Brake by adopting an Eulerian approach
    2013 (engelsk)Inngår i: EuroBrake 2013 Conference Proceedings, FISITA , 2013Konferansepaper, Publicerat paper (Annet vitenskapelig)
    Abstract [en]

    In this paper frictional heating of a disc brake is simulated while taking wear into account. By performing thermomechanical finite element analysis, it is studied how the wear history will influence the development of hot bands. The frictional heat analysis is based on an Eulerian formulation of the disc, which requires significantly lower computational time as compared to a standard Lagrangian approach. A real disc-pad system to a heavy truck is considered, where complete three-dimensional geometries of the ventilated disc and pad are used in the simulations. A sequential approach is adopted, where the contact forces are computed at each time step taking the wear and thermal deformations of the mating parts into account. After each brake cycle, the wear profile of the pad is updated and used in subsequent analysis. The results show that when wear is considered, different distributions of the temperature on disc are obtained for each new brake cycle. After a few braking cycles two hot bands appear on the disc surface instead of only one. These results are in agreement with experimental observations.

    sted, utgiver, år, opplag, sider
    FISITA, 2013
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-94284 (URN)978-0-9572076-0-8 (ISBN)
    Konferanse
    EuroBrake 2013, Chassis Brakes International, Dresden, Germany, June 17-19, 2013
    Tilgjengelig fra: 2013-06-20 Laget: 2013-06-20 Sist oppdatert: 2016-03-07bibliografisk kontrollert
    5. Multi-Objective Optimization of a Disc Brake System by using SPEA2 and RBFN
    Åpne denne publikasjonen i ny fane eller vindu >>Multi-Objective Optimization of a Disc Brake System by using SPEA2 and RBFN
    2013 (engelsk)Konferansepaper, Publicerat paper (Annet vitenskapelig)
    Abstract [en]

    Many engineering design optimization problems involve multiple conflicting objectives, which today often are obtained by computational expensive finite element simulations. Evolutionary multi-objective optimization (EMO) methods based on surrogate modeling is one approach of solving this class of problems. In this paper, multi-objective optimization of a disc brake system to a heavy truck by using EMO and radial basis function networks (RBFN) is presented. Three conflicting objectives are considered. These are: 1) minimizing the maximum temperature of the disc brake, 2) maximizing the brake energy of the system and 3) minimizing the mass of the back plate of the brake pad. An iterative Latin hypercube sampling method is used to construct the design of experiments (DoE) for the design variables. Next, thermo-mechanical finite element analysis of the disc brake, including frictional heating between the pad and the disc, is performed in order to determine the values of the first two objectives for the DoE. Surrogate models for the maximum temperature and the brake energy are created using RBFN with polynomial biases. Different radial basis functions are compared using statistical errors and cross validation errors (PRESS) to evaluate the accuracy of the surrogate models and to select the most accurate radial basis function. The multi-objective optimization problem is then solved by employing EMO using the strength Pareto evolutionary algorithm (SPEA2). Finally, the Pareto fronts generated by the proposed methodology are presented and discussed.

    sted, utgiver, år, opplag, sider
    The American Society of Mechanical Engineers, 2013
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-94285 (URN)10.1115/DETC2013-12809 (DOI)978-0-7918-5590-4 (ISBN)
    Konferanse
    ASME 2013 International Design Engineering Technical Conferences (IDETC) and Computers and Information in Engineering Conference (CIE), Portland, USA, August 4-7, 2013
    Merknad

    Paper No. DETC2013-12809, pp. V03BT03A029; 10 pages.

    Tilgjengelig fra: 2013-06-20 Laget: 2013-06-20 Sist oppdatert: 2016-02-04bibliografisk kontrollert
    6. Overview of Disc Brakes and Related Phenomena - a review
    Åpne denne publikasjonen i ny fane eller vindu >>Overview of Disc Brakes and Related Phenomena - a review
    2014 (engelsk)Inngår i: International Journal of Vehicle Noise and Vibration, ISSN 1479-1471, Vol. 10, nr 4, s. 257-301Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Disc brakes have evolved over time to be a reliable method of decelerating and stopping a vehicle. There have been different designs of disc brake systems for different applications. This review gives a detailed description of different geometries of the components and the materials used in a disc brake system. In spite of all the improvements, there are still many operational issues related to disc brakes that need to be understood in greater detail and resolved. There has been a lot of research going on about these issues and at the same time different methods are being proposed to eliminate or reduce them. There has also been intensive fundamental research going on about the evolution of the tribological interface of the disc-pad system. One major purpose of the present paper is to give a comprehensive overview of all such developments.

    sted, utgiver, år, opplag, sider
    Inderscience Enterprises, UK, 2014
    Emneord
    Disc brakes; disc geometry; pad geometry; disc pad tribology; brake fade; brake noise; vehicle noise; vehicle braking
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-124566 (URN)10.1504/IJVNV.2014.065634 (DOI)
    Tilgjengelig fra: 2016-02-03 Laget: 2016-02-03 Sist oppdatert: 2016-02-16bibliografisk kontrollert
    7. Simulation of internal mechanical conditions in the lower limb donned in a transtibial prosthetic socket
    Åpne denne publikasjonen i ny fane eller vindu >>Simulation of internal mechanical conditions in the lower limb donned in a transtibial prosthetic socket
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    This paper investigates the internal mechanical conditions in a transtibial cross-section while in contact with a prosthetic socket. The nite element model considers the nonlinear behaviors of individual soft tissues instead of lumping them together. The contact problem is solved between socket and limb while taking the friction into consideration to determine the contact forces and resultant internal stress-strain in the limb. Simulation results are presented for three dierent socket designs; total contact, total surface-bearing and hydrostatic sockets. Inuence of higher blood pressure on internal mechanical conditions is also explored.

    Emneord
    Prosthetic socket, internal mechanical conditions, transtibial socket, interface pressure, stress distribution
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-124567 (URN)
    Tilgjengelig fra: 2016-02-03 Laget: 2016-02-03 Sist oppdatert: 2016-02-04bibliografisk kontrollert
  • 107.
    Rodríguez María, Jaime
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Modelling of the mechanobiological adaptation to vascular occlusion in the arterial tree2016Student paper other, 10 poäng / 15 hpOppgave
    Abstract [en]

    It is known that there are many cardiovascular diseases caused by the alterations in the blood vessels, that affect most of the world population. The knowledge of the mechanobiological behavior of blood vessels is used for understanding how cardiovascular diseases could affect the human body. So, by studying the growth and remodeling (G&R) of the arterial tree, it is possible to predict how these diseases will develop and consequently, how they can be treated or even prevented.

    The human body naturally tries to find the optimum steady-state by changing either the production of the constituents of the arteries or the flow rate through blood vessels. This effect is the phenomenon that is going to be studied in this thesis and these three main factors have to be taken into account when reproducing the diseases’ effects: the so-called transmural pressure, the blood flow rate, and the biomechanics of the constituents which form the arterial wall. Therefore, through numerical simulations the variation of these factors can be predicted, although always with a reliability supported by experimental data. 

  • 108.
    Ryberg, Ann-Britt
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Combitech AB, Trollhättan, Sweden.
    Metamodel-Based Multidisciplinary Design Optimization of Automotive Structures2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Multidisciplinary design optimization (MDO) can be used in computer aided engineering (CAE) to efficiently improve and balance performance of automotive structures. However, large-scale MDO is not yet generally integrated within automotive product development due to several challenges, of which excessive computing times is the most important one. In this thesis, a metamodel-based MDO process that fits normal company organizations and CAE-based development processes is presented. The introduction of global metamodels offers means to increase computational efficiency and distribute work without implementing complicated multi-level MDO methods.

    The presented MDO process is proven to be efficient for thickness optimization studies with the objective to minimize mass. It can also be used for spot weld optimization if the models are prepared correctly. A comparison of different methods reveals that topology optimization, which requires less model preparation and computational effort, is an alternative if load cases involving simulations of linear systems are judged to be of major importance.

    A technical challenge when performing metamodel-based design optimization is lack of accuracy for metamodels representing complex responses including discontinuities, which are common in for example crashworthiness applications. The decision boundary from a support vector machine (SVM) can be used to identify the border between different types of deformation behaviour. In this thesis, this information is used to improve the accuracy of feedforward neural network metamodels. Three different approaches are tested; to split the design space and fit separate metamodels for the different regions, to add estimated guiding samples to the fitting set along the boundary before a global metamodel is fitted, and to use a special SVM-based sequential sampling method. Substantial improvements in accuracy are observed, and it is found that implementing SVM-based sequential sampling and estimated guiding samples can result in successful optimization studies for cases where more conventional methods fail.

    Delarbeid
    1. Multidisciplinary design optimisation methods for automotive structures
    Åpne denne publikasjonen i ny fane eller vindu >>Multidisciplinary design optimisation methods for automotive structures
    2017 (engelsk)Inngår i: International Journal of Automotive and Mechanical Engineering, ISSN 2229-8649, Vol. 14, nr 1, s. 4050-4067Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Multidisciplinary design optimisation (MDO) can be used as an effective tool to improve the design of automotive structures. Large-scale MDO problems typically involve several groups who must work concurrently and autonomously in order to make the solution process efficient. In this article, the formulations of existing MDO methods are compared and their suitability is assessed in relation to the characteristics of automotive structural applications. Both multi-level and single-level optimisation methods are considered. Multi-level optimisation methods distribute the design process but are complex. When optimising automotive structures, metamodels are often required to relieve the computational burden of detailed simulation models. The metamodels can be created by individual groups prior to the optimisation process, and thus offer a way of distributing work. Therefore, it is concluded that a single-level method in combination with meta-models is the most straightforward way of implementing MDO into the development of automotive structures. If the benefits of multi-level optimisation methods, in a special case, are considered to compensate for their drawbacks, analytical target cascading has a number of advantages over collaborative optimisation, but both methods are possible choices.

    sted, utgiver, år, opplag, sider
    Pekan, Malaysia: Universiti Malaysia Pahang Publishing, 2017
    Emneord
    Multidisciplinary design optimisation, single-level optimisation methods, multilevel optimisation methods, automotive structures
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-140876 (URN)10.15282/ijame.14.1.2017.17.0327 (DOI)
    Tilgjengelig fra: 2017-09-14 Laget: 2017-09-14 Sist oppdatert: 2018-02-26bibliografisk kontrollert
    2. A metamodel-based multidisciplinary design optimization process for automotive structures
    Åpne denne publikasjonen i ny fane eller vindu >>A metamodel-based multidisciplinary design optimization process for automotive structures
    2015 (engelsk)Inngår i: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 31, nr 4, s. 711-728Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Automotive companies continuously strive to design better products faster and more cheaply using simulation models to evaluate every possible aspect of the product. Multidisciplinary design optimization (MDO) can be used to find the best possible design taking into account several disciplines simultaneously, but it is not yet fully integrated within automotive product development. The challenge is to find methods that fit company organizations and that can be effectively integrated into the product development process. Based on the characteristics of typical automotive structural MDO problems, a metamodel-based MDO process intended for large-scale applications with computationally expensive simulation models is presented and demonstrated in an example. The process is flexible and can easily fit into existing organizations and product development processes where different groups work in parallel. The method is proven to be efficient for the discussed example and improved designs can also be obtained for more complex industrial cases with comparable characteristics.

    sted, utgiver, år, opplag, sider
    Springer, 2015
    Emneord
    Multidisciplinary design optimization (MDO); metamodel-based design optimization (MBDO); automotive structures
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-88135 (URN)10.1007/s00366-014-0381-y (DOI)000360859000004 ()
    Tilgjengelig fra: 2013-01-30 Laget: 2013-01-30 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    3. Spot weld reduction methods for automotive structures
    Åpne denne publikasjonen i ny fane eller vindu >>Spot weld reduction methods for automotive structures
    2016 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 53, nr 4, s. 923-934Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Spot welds are commonly used to join steel sheets in automotive structures. The number and layout of these spot welds are vital for the performance of the structure. However, reducing the number of spot welds will cut both production time and cost. This article presents three different methods of reducing the number of spot welds in automotive structures: ranking-based selection, topology optimization and size optimization of a parameterized model. The methods are compared in a simple example and it is found that the latter two methods have the best potential of reducing the number of spot welds. Topology optimization requires less preparation and computational effort as compared to size optimization of a parameterized model. However, the method is primarily suitable for studies where load cases involving linear systems are judged to be most important. Otherwise, size optimization of a parameterized model is probably a better choice. The topology optimization approach is successfully demonstrated in a full-scale industrial application example and confirms that the method is useful within contemporary product development.

    sted, utgiver, år, opplag, sider
    SPRINGER, 2016
    Emneord
    Spot weld optimization; Multidisciplinary design optimization (MDO); Topology optimization; Size optimization; Metamodels; Automotive structures
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-127430 (URN)10.1007/s00158-015-1355-4 (DOI)000373023800018 ()
    Merknad

    Funding Agencies|Vinnova FFI project

    Tilgjengelig fra: 2016-05-01 Laget: 2016-04-26 Sist oppdatert: 2017-11-30
  • 109.
    Ryberg, Ann-Britt
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Combitech AB,Trollhättan, Sweden.
    Domeij Bäckryd, Rebecka
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    A metamodel-based multidisciplinary design optimization process for automotive structures2015Inngår i: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 31, nr 4, s. 711-728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Automotive companies continuously strive to design better products faster and more cheaply using simulation models to evaluate every possible aspect of the product. Multidisciplinary design optimization (MDO) can be used to find the best possible design taking into account several disciplines simultaneously, but it is not yet fully integrated within automotive product development. The challenge is to find methods that fit company organizations and that can be effectively integrated into the product development process. Based on the characteristics of typical automotive structural MDO problems, a metamodel-based MDO process intended for large-scale applications with computationally expensive simulation models is presented and demonstrated in an example. The process is flexible and can easily fit into existing organizations and product development processes where different groups work in parallel. The method is proven to be efficient for the discussed example and improved designs can also be obtained for more complex industrial cases with comparable characteristics.

  • 110.
    Ryberg, Ann-Britt
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten. Combitech AB, Sweden.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Spot weld reduction methods for automotive structures2016Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 53, nr 4, s. 923-934Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spot welds are commonly used to join steel sheets in automotive structures. The number and layout of these spot welds are vital for the performance of the structure. However, reducing the number of spot welds will cut both production time and cost. This article presents three different methods of reducing the number of spot welds in automotive structures: ranking-based selection, topology optimization and size optimization of a parameterized model. The methods are compared in a simple example and it is found that the latter two methods have the best potential of reducing the number of spot welds. Topology optimization requires less preparation and computational effort as compared to size optimization of a parameterized model. However, the method is primarily suitable for studies where load cases involving linear systems are judged to be most important. Otherwise, size optimization of a parameterized model is probably a better choice. The topology optimization approach is successfully demonstrated in a full-scale industrial application example and confirms that the method is useful within contemporary product development.

  • 111.
    Schlauer, Christian
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    The effect of machining on residual stresses and low cycle fatigue life of Inconel 718 gas turbine discs2002Rapport (Annet vitenskapelig)
  • 112.
    Sharifimajd, Babak
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    A Continuum Framework for Modeling the Excitation–Contraction Coupling of Smooth Muscle2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Excitation-contraction coupling of smooth muscle refers to a chain of coupled physiological processes which convert a stimulus to a mechanical response. These processes can be disassociated into ionic transport during cell membrane excitation, activation of myosin light chains, and muscle contraction caused by actin-myosin interaction (filament sliding). This thesis concerns the development of a framework which allows to model the smooth muscle excitation-contraction coupling constitutively by applying the principle of virtual power and dissipation inequality. In doing so, the transport of ions through membrane channels is characterized by an ionic flux and an ionic supply, both governed by an electrochemical potential energy. By letting the Helmholtz free energy to be dependent on the myosin light chain configurations during contraction, the myosin light chain activation process, i.e., myosin phosphorylation, is included. The activation process links the membrane excitation to the filament sliding. A contractile element is presented to replicate the active deformation caused by the filament sliding within the smooth muscle cell. This deformation is coupled to the overall deformation of the muscle tissue by assuming a distinct principal alignment for the contractile elements.

    By employing this framework, an electro-chemo-mechanical model is derived by which the mechanical response of smooth muscle to an electrical stimulus is determined. This model is evaluated by comparing the model response to the experimental isometric stress data obtained from rat uterine smooth muscle tissue. By implementing this model in a finite element program, human uterine contractions during labor are simulated. This simulation determines important clinical factors, e.g., intrauterine pressure and provides the opportunity to investigate the effect of physiological and structural parameters on the uterine contractility.

    Finally, a methodology to accommodate individualized parameters from intrauterine pressure measurements is established. This methodology allows to develop models with potentials of being used clinically to diagnose difficulties during labor and delivery.

    Delarbeid
    1. A continuum model for skeletal muscle contraction at homogeneous finite deformations
    Åpne denne publikasjonen i ny fane eller vindu >>A continuum model for skeletal muscle contraction at homogeneous finite deformations
    2013 (engelsk)Inngår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 12, nr 5, s. 965-973Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The contractile force in skeletal muscle models is commonly postulated to be the isometric force multiplied by a set of experimentally motivated functions which account for the muscle’s active properties. Although both flexible and simple, this approach does not automatically guarantee a thermodynamically consistent behavior. In contrast, the continuum mechanical model proposed herein is derived from fundamental principles in mechanics and guarantees a dissipative behavior. Further, the contractile force is associated with a friction clutch which provides a simple and well-defined macroscopic model for cycling cross-bridges. To show the performance of the model, it is specialized to standard experiments for rabbit tibialis anterior muscle. The results show that the model is able to capture important characteristics of skeletal muscle.

    sted, utgiver, år, opplag, sider
    Springer, 2013
    Emneord
    Skeletal muscle, Contractile element, Dissipation inequality, Strain-energy function, Continuum model
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-85805 (URN)10.1007/s10237-012-0456-x (DOI)000324378900008 ()
    Forskningsfinansiär
    Swedish Research Council
    Tilgjengelig fra: 2012-11-28 Laget: 2012-11-28 Sist oppdatert: 2018-01-03bibliografisk kontrollert
    2. A continuum model for excitation–contraction of smooth muscle under finite deformations
    Åpne denne publikasjonen i ny fane eller vindu >>A continuum model for excitation–contraction of smooth muscle under finite deformations
    2014 (engelsk)Inngår i: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 355, s. 1-9Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The main focus in most of continuum based muscle models is the muscle contraction dynamics while other physiological processes governing muscle contraction, e.g., the cell membrane excitation and the activation, are ignored. These latter processes are essential to initiate contraction and to determine the amount of generated force, and by excluding them, the developed model cannot replicate the true behavior of the muscle in question. The aim of this study is to establish a thermodynamically and physiologically consistent framework which allows to model smooth muscle contraction by including cell membrane excitability and kinetics of myosin phosphorylation, along with dynamics of smooth muscle contraction. The model accounts for these processes through a set of coupled dissipative constitutive equations derived by applying the first principles. To show the performance of the derived model, it is evaluated for two different cases: a mechanochemical study of pig taenia coli cells where the excitation process is excluded, and a complete excitation–contraction process of rat myometrium. The results show that the model is able to replicate important aspects of the smooth muscle EC process acceptably.

    sted, utgiver, år, opplag, sider
    Elsevier, 2014
    Emneord
    Smooth muscle excitation–contraction, Smooth muscle continuum model, The membrane model, Hodgkin-Huxley model, Hai-Murphy model
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-100778 (URN)10.1016/j.jtbi.2014.03.016 (DOI)000337865100001 ()
    Tilgjengelig fra: 2013-11-12 Laget: 2013-11-12 Sist oppdatert: 2018-01-03bibliografisk kontrollert
    3. Simulating uterine contraction by using an electro-chemo-mechanical model
    Åpne denne publikasjonen i ny fane eller vindu >>Simulating uterine contraction by using an electro-chemo-mechanical model
    2016 (engelsk)Inngår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, nr 3, s. 497-510Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.

    sted, utgiver, år, opplag, sider
    Springer, 2016
    Emneord
    Excitation-contraction model of uterine smooth muscle; Uterus contraction; Intrauterine pressure; Uterine electrical activity
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121013 (URN)10.1007/s10237-015-0703-z (DOI)000376014800002 ()26162461 (PubMedID)
    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2018-01-03bibliografisk kontrollert
    4. Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements
    Åpne denne publikasjonen i ny fane eller vindu >>Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements
    2017 (engelsk)Inngår i: International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, E-ISSN 2040-7947, Vol. 33, nr 1, s. 1-11Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    There are limited experimental data to characterize the mechanical response of human myometrium. A method is presented in this work to identify mechanical parameters describing the active response of human myometrium from the in vivo intrauterine pressure measurements. A finite element model is developed to compute the intrauterine pressure during labor in response to an increase in the intracellular calcium ion concentration within myometrial smooth muscle cells. The finite element model provides the opportunity to tune mechanical parameters in order to fit the computed intrauterine pressure to in vivo measurements. Since the model is computationally expensive, a cheaper meta-model is generated to approximate the model response. By fitting the meta-model response to the in vivo measurements, the parameters used to determine the active response of human myometrial smooth muscle are identified.

    sted, utgiver, år, opplag, sider
    John Wiley & Sons, 2017
    Emneord
    human uterine smooth muscle mechanics, intrauterine pressure, parameter identification, response surface methodology
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121014 (URN)10.1002/cnm.2778 (DOI)000393964900001 ()26915913 (PubMedID)2-s2.0-84962638845 (Scopus ID)
    Merknad

    At the time of the thesis presentation this publication was in status Manuscript.

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2018-01-03bibliografisk kontrollert
  • 113.
    Sharifimajd, Babak
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Stålhand, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simulating uterine contraction by using an electro-chemo-mechanical model2016Inngår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, nr 3, s. 497-510Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.

  • 114.
    Sharifimajd, Babak
    et al.
    Institute of Solid Mechanics, Department of Mechanical Engineering, Braunschweig University of Technology, Braunschweig, Germany.
    Ölvander, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Maskinkonstruktion. Linköpings universitet, Tekniska fakulteten.
    Stålhand, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements2017Inngår i: International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, E-ISSN 2040-7947, Vol. 33, nr 1, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There are limited experimental data to characterize the mechanical response of human myometrium. A method is presented in this work to identify mechanical parameters describing the active response of human myometrium from the in vivo intrauterine pressure measurements. A finite element model is developed to compute the intrauterine pressure during labor in response to an increase in the intracellular calcium ion concentration within myometrial smooth muscle cells. The finite element model provides the opportunity to tune mechanical parameters in order to fit the computed intrauterine pressure to in vivo measurements. Since the model is computationally expensive, a cheaper meta-model is generated to approximate the model response. By fitting the meta-model response to the in vivo measurements, the parameters used to determine the active response of human myometrial smooth muscle are identified.

  • 115.
    Shetty, Sandeep
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten. Painted Body and Closures, Volvo Car Corporation.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    An evaluation of simple techniques to model the variation in strain hardening behavior of steel2017Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, nr 3, s. 945-957Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is important to consider variations in material parameters in the design of automotive structures in order to obtain a robust and reliable design. However, expensive tests are required to gain complete knowledge of the material behavior and its associated variation. Consequently, due to time and cost constraints, simplified material scatter modeling techniques based on scatter data of typical material properties provided by the material suppliers are used at early design stages in simulation-based robustness studies. The aim of this paper is to study the accuracy of the simplified scatter modeling methods in representing the real material variation. The simplified scatter modeling methods are evaluated by comparing the material scatter obtained by them to the scatter obtained by complete tensile tests, which are obtained after detailed timeconsuming experimental investigations. Furthermore, an accuracy assessment is carried out based on selected responses from an axially-crushed, square tube made from DP600 steel.

  • 116.
    Simonsson, Kjell
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Micromechanical modelling of the constitutive behaviour of a material during a martensitic transformation2002Inngår i: IUTAM Symposium on Micro- and Macrostructural Aspects of Thermoplasticity: Proceedings of the IUTAM Symposium held in Bochum, Germany, 25–29 August 1997, 2002, Vol. 62, s. 345-354Konferansepaper (Fagfellevurdert)
  • 117.
    Singh, Subrat
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Veditherakal Shreedhara, Sreehari
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    CAE modelling of cast aluminium in automotive structures2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In the automobile industry, there is a big push for the automotive car manufacturers to base engineering decisions on the results of Computer Aided Engineering (CAE) solutions, and to transform the prototyping and testing, from a costly iterative process to a final verification and validation step. The variability in components material properties and environmental conditions together with the lack of knowledge about the underlying physics of complex systems often make it impractical to make reliable predictions based on only deterministic CAE models. One such area is the CAE modelling of cast aluminium components. These cast aluminium components have gained a huge relevance in the automobile industries due to their commendable mechanical properties. The advantage of the cast aluminium alloys are being a well-established alloy system in manufacturing processes, their functional integrity and relatively low weight. However, the presence of pores and micro-voids obtained during the manufacturing process constitutes a specific material behaviour and establishes a challenge in modelling of the cast materials. Furthermore, the low ductility of the materialdemands for the advanced numerical model to predict the failure.

    The main focus of this master thesis work is to investigate modelling technique of a cast aluminium alloy component, a spring tower, for a drop tower test and validate the predicted behaviour with the physical test results. Volvo Car Corporation currently uses a material model provided by MATFEM for cast aluminium parts which are explored in this thesis work, to validate the material model for component level testing.

    The methodology used to achieve this objective was to develop a boundary condition to perform component level tests in the drop tower and to correlate these with the obtained results found by using various modelling techniques in the explicit solver LS-DYNA. Therefore, precise and realistic modelling of the drop tower is crucial because the simulation results can be influenced by major design changes. A detailed finite element model for the spring tower has been developed from the observations made during the physical testing. The refined model showed good agreement with the existing model for the spring tower and observations from physical tests.

  • 118.
    Spagnoli, A.
    et al.
    University of Parma, Parma, Italy.
    Terzano, M.
    University of Parma, Parma, Italy.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Barber, J. R.
    University of Michigan, AnnArbor, MI, USA.
    Shakedown in an elastic-plastic solid with a frictional crack2016Inngår i: Procedia Structural Integrity vol. 2 / [ed] Francesco Iacoviello, Elsevier, 2016, Vol. 2, s. 2667-2673Konferansepaper (Fagfellevurdert)
    Abstract [en]

    When subjected to periodic loading, elastic systems containing contact interfaces might exhibit frictional slip which ceases after some loading cycles. In such cases, it is said that the system shakes down. For elastic discrete systems presenting complete contacts, it has been proved that Melan’s theorem, originally proposed for elastic-plastic problems, offers a sufficient condition for the system to shake down, provided that the contact is of an uncoupled type. In the present paper, the application of Melan’s theorem is speculated for systems involving plasticity and friction. A finite element example of an elastic-plastic solid containing a frictional crack is discussed.

  • 119.
    Spagnoli, A.
    et al.
    University of Parma, Italy.
    Terzano, M.
    University of Parma, Italy.
    Barber, J. R.
    University of Michigan, MI 48109 USA.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Non-linear programming in shakedown analysis with plasticity and friction2017Inngår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 104, s. 71-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Complete frictional contacts, when subjected to cyclic loading, may sometimes develop a favourable situation where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. Its resemblance to shakedown in plasticity has prompted scholars to apply direct methods, derived from the classical theorems of limit analysis, in order to assess a safe limit to the external loads applied on the system. In circumstances where zones of plastic deformation develop in the material (e.g., because of the large stress concentrations near the sharp edges of a complete contact), it is reasonable to expect an effect of mutual interaction of frictional slip and plastic strains on the load limit below which the global behaviour is non dissipative, i.e., both slip and plastic strains go to zero after some dissipative load cycles. In this paper, shakedown of general two-dimensional discrete systems, involving both friction and plasticity, is discussed and the shakedown limit load is calculated using a non-linear programming algorithm based on the static theorem of limit analysis. An illustrative example related to an elastic-plastic solid containing a frictional crack is provided. (C) 2017 Elsevier Ltd. All rights reserved.

  • 120.
    Storgärds, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    High Temperature Fatigue Crack Growth in a Ni-based Superalloy: Modelling Including the Interaction of Dwell Times2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Safe life of gas turbines is always of major concern for manufacturers in order to ensure passenger safety and stable continuous power output. An increasing amount of resources have been put into research and development to assure that all safety aspects are covered in the design of new turbines and to ensure that enough frequent service intervals are scheduled to avoid complications. Many of these issues require good knowledge of material properties and of how to use these in the design process. Some of these relate to fatigue which is of major concern in all parts of a development programme. However, while some fatigue problems have been extensively studied, some have not. One example is crack growth with influence of dwell times at elevated temperature in combination with cyclic loading. Such loading conditions have been shown to give a different cracking behaviour compared to rapid cyclic loading, increasing the growth rate significantly with respect to the number of load cycles. Improved models for predicting this behaviour is therefore of major interest for gas turbine manufacturers, and could substantially increase the reliability. As a result, more research is needed in order  solve these problems.

    The work presented in this dissertation has focused on how to predict life under the above-mentioned circumstances. The materials used in high temperature gas turbine applications are often nickel-based superalloys, and in this work the most common one, Inconel 718, has been studied. Mechanical experiments have been performed under operation like conditions in order to receive material data for the subsequent modelling work. The modelling approach was chosen such that the underlying physics of the dwell time cracking have been incorporated on a phenomenological basis, creating a model which can be physically motivated as well as used for industrial applications. The main feature of the modelling work has been to track material damage which is received from dwell times, how this interacts with cyclic loading and how it affects the crack growth rate, thus creating a load history dependent model.

    The outcome of this work has resulted in a model which is both easy to use and which has shown to give good correlation to available experimental data. Key components such as calibration for cheap and easy parameter determination, validation on complex engine spectra loadings, three dimensional crack growth, overload influences, material scatter, thermo-mechanical fatigue crack growth and the impact of high cycle fatigue loadings, are all covered in the presented work, both as experimental findings and as continuous development of the modelling concept.

    The dissertation consists of two parts. In the first an introduction with the theory and background to crack growth with dwell times is given, while the second part consists of 10 papers.

    Delarbeid
    1. High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    Åpne denne publikasjonen i ny fane eller vindu >>High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    2013 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 48, s. 178-186Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650°C. For such components, the main load cycle is typically defined by the start-up and shut-down of the engine. In this main loading cycle, hold times at high temperature are commonly present in critical components. These high temperature hold times may greatly increase the fatigue crack growth rate with respect to the number of cycles unless other beneficial factors such as for example initial overloads are present. The latter can be caused by abnormal service conditions but can also occur on a more regular basis and are then typically observed in components with strong thermal transients during engine start-up. In this paper, focus has been placed on the effect of overloads on the hold time fatigue crack growth behaviour and its subsequent description. More specifically, crack propagation in Inconel 718 has been studied at the temperatures 550°C and 650°C with and without an overload at the start of the cycle. The effect of initial overloads was found to be substantial. A simple model for describing the effect of these loading conditions has also been developed based on the concept of the damaged zone, present around the crack tip. Irregular crack fronts and unbroken ligaments left on the fracture surfaces seen in complementary microscopy studies seem to support this approach. Furthermore, the stress state in front of a crack tip in a 2D model was investigated both with and without an initial overload. The results were related to the observed crack growth retardation behaviour found in the material testing.

    sted, utgiver, år, opplag, sider
    Elsevier, 2013
    Emneord
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling, Finite Element modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-85931 (URN)10.1016/j.ijfatigue.2012.10.018 (DOI)000315617500020 ()
    Tilgjengelig fra: 2013-03-13 Laget: 2012-12-03 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    2. Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    Åpne denne publikasjonen i ny fane eller vindu >>Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    2013 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, s. 124-130Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650 °C. The main load cycle for such components is typically defined by the start-up and shut-down of the engine. It generally includes hold times at high temperatures, which have been found to have a potential for greatly increasing the fatigue crack growth rate with respect to the number of load cycles. However, these effects may be totally or partly cancelled by other load features, such as overloads or blocks of continuous cyclic loading, and the actual crack propagation rate will therefore depend on the totality of features encompassed by the load cycle. It has previously been shown that the increased crack growth rate found in hold time experiments can be associated with a damage evolution, where the latter is not only responsible for the rapid intergranular crack propagation during the actual hold times, but also for the increased crack growth during the load reversals. In this paper, modelling of the hold time fatigue crack growth behaviour of Inconel 718 has been carried out, using the concept of a damaged zone as the basis for the treatment. With this conceptually simple and partly novel approach, it is shown that good agreement with experimental results can be found.

    sted, utgiver, år, opplag, sider
    Elsevier, 2013
    Emneord
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-85933 (URN)10.1016/j.ijfatigue.2013.03.004 (DOI)000318831300013 ()
    Tilgjengelig fra: 2012-12-03 Laget: 2012-12-03 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    3. A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    Åpne denne publikasjonen i ny fane eller vindu >>A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    2014 (engelsk)Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 118, s. 17-30Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Modelling of high temperature fatigue crack growth in Inconel 718 under the interaction of fast cyclic loading and hold times at maximum load has been conducted. A model, based on the concept of a damaged zone in front of the crack tip has been applied for three different temperatures, 550, 600 and 650 ◦C, with good agreement for both calibration and validation tests. A statistical evaluation of 22 tests in total was also conducted, which shows that the developed model gives a reasonable scatter factor at a probability of failure of 0.1 %.

    sted, utgiver, år, opplag, sider
    Elsevier, 2014
    Emneord
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling, Statistics
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104809 (URN)10.1016/j.engfracmech.2014.02.005 (DOI)000334819600002 ()
    Tilgjengelig fra: 2014-02-27 Laget: 2014-02-27 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    4. Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    Åpne denne publikasjonen i ny fane eller vindu >>Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    2014 (engelsk)Inngår i: Advanced Materials Research, ISSN 1662-8985, Vol. 891-892, s. 759-764Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Gas turbine operating cycles at high temperatures often consist of load reversals mixed with hold times; the latter occurring either as cruise for aero engines or at continuous power output for land based turbines, but also at low frequency loading conditions, e.g. slow “ramp up” of engine thrust. The hold time conditions cause the crack to grow by intergranular fracture due to material damage near the crack tip, thus rapidly increasing the crack growth rate. Since the damaged zone will affect the crack propagation rate due to cyclic loadings as well, the complete load history of a component therefore has to be considered. The crack propagation model presented in this paper is based on the damaged zone concept, and considers the history effect in the form of damaged zone build up during hold times, and subsequent destruction as the crack propagates onwards by rapidly applied load reversals. By incorporating crack closure for handling different R-values, an aero engine component spectrum is evaluated for a surface crack at 550 C. The result shows a good correlation to model simulation, despite the complexity of the load spectrum.

    sted, utgiver, år, opplag, sider
    Trans Tech Publications Inc., 2014
    Emneord
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104812 (URN)10.4028/www.scientific.net/AMR.891-892.759 (DOI)000337767700118 ()
    Tilgjengelig fra: 2014-02-27 Laget: 2014-02-27 Sist oppdatert: 2016-05-18bibliografisk kontrollert
    5. Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    Åpne denne publikasjonen i ny fane eller vindu >>Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    2015 (engelsk)Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 55, nr 3, s. 559-568Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Crack length evaluations for cyclic loading and sustained loading at high temperature and a mix of both have been conducted on Inconel 718 surface crack specimens at 550 C-a similar to. The choice of method for evaluating the crack length is seen to have a non-negligible impact on the resulting crack propagation rate values. In this paper, some aspects regarding how to evaluate such testing when using the potential drop technique are presented, with the aim of giving a firm explanation on how to proceed for the best possible result.

    sted, utgiver, år, opplag, sider
    Society for Experimental Mechanics (SEM), 2015
    Emneord
    Fatigue crack propagation; Fatigue test evaluation; Sustained load; Dwell time effects; Crack length evaluation; Potential drop
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-117241 (URN)10.1007/s11340-014-9963-2 (DOI)000351444300007 ()
    Merknad

    Funding Agencies|Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

    Tilgjengelig fra: 2015-04-22 Laget: 2015-04-21 Sist oppdatert: 2017-12-04
    6. Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    Åpne denne publikasjonen i ny fane eller vindu >>Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    2016 (engelsk)Inngår i: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    High temperature materials subjected to elevated temperature have been shown to be sensitive to dwell times, giving an increased crack growth rate. The interaction between these dwell times and rapid cyclic loads have been shown to constitute a complex problem. Many models have been developed for 1D conditions, but the application to general 3D conditions has seldom been seen, although this is the most common case in most structures. In this paper a model for taking care of the interaction between these load modes in general 3D crack growth has been developed. The model uses 1D results for extension to general 3D, thus providing for local crack front evolution with a minimum of numerical simulations. The model has been implemented for usage with finite element calculations and several different tests are simulated and compared with experimental results for the nickel based superalloy Inconel 718 at 550◦C. The simulation results show crack shapes in agreement with experimental fracture surfaces and time to failure.

    Emneord
    Sustained load, Crack growth modelling, Crack tunnelling, Ni-based superalloy, High temperature
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121004 (URN)10.1016/j.tafmec.2015.11.008 (DOI)000369204600002 ()
    Merknad

    Funding agencies:  Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

    Vid tiden för disputation förelåg publikationen som manuskript

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    7. Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Åpne denne publikasjonen i ny fane eller vindu >>Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Vise andre…
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012501-012501Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Testing and simulation of aero-engine spectra with dwell times are reported in this paper. The modeling concept used is built on linear elastic fracture mechanics (LEFM) and provides a history-dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra: (1) cyclic loads, (2) combined sustained load and cyclic loads, and (3) slow load ramps and cyclic loads, all for surface cracks at 550 °C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121005 (URN)10.1115/1.4031155 (DOI)000371127900012 ()
    Merknad

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish Research Programme TURBO POWER

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    8. Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Åpne denne publikasjonen i ny fane eller vindu >>Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Vise andre…
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012502-012502Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper, scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550 °C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provide for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests, an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analyzing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other are of significant proportions.

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121007 (URN)10.1115/1.4031157 (DOI)000371127900013 ()
    Merknad

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish research programme TURBO POWER

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    9. Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    Åpne denne publikasjonen i ny fane eller vindu >>Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012503-012503Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Thermomechanical fatigue (TMF) crack growth modeling has been conducted on Inconel 718 with dwell time at maximum load. A history dependent damage model taking dwell damage into account, developed under isothermal conditions, has been extended for TMF conditions. Parameter determination for the model is carried out on isothermal load controlled tests at 550–650 °C for surface cracks, which later have been used to extrapolate parameters used for TMF crack growth. Further, validation of the developed model is conducted on a notched specimen subjected to strain control at 50–550 °C. Satisfying results are gained within reasonable scatter level compared for test and simulated number of cycles to failure.

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121008 (URN)10.1115/1.4031158 (DOI)000371127900014 ()
    Merknad

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish research programme TURBO POWER

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    10. Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Åpne denne publikasjonen i ny fane eller vindu >>Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Vise andre…
    2015 (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Sustained load have been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on sustained load and the interaction of load cycles, overloads, and temperature, but few studies have been carried out for vibrations and how these affect the dwell time crack growth. Vibrations of different kinds are frequently seen in engine components, and present in combination with sustained loads a more realistic loading situation than the latter itself. An investigation of how a vibrational load affects the dwell time cracking and how to incorporate it in a modelling context is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical testing has been conducted at 550◦C for surface cracks with and without the interaction of engine vibrations on sustained load, here represented by a superimposed high cycle fatigue (HCF) load. Subsequent investigation of the fracture behaviour was performed by Scanning Electron Microscope (SEM) and the modelling work has been conducted by incorporating the HCF load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical tests.

    Emneord
    Hold time effects, Dwell times, Sustained load, Crack growth modelling, Inconel 718, High temperature
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121009 (URN)
    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2015-09-02bibliografisk kontrollert
  • 121.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Ind Turbomachinery, Sweden.
    Mansson, Tomas
    GKN Aerosp Engine Syst, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    SCATTER IN DWELL TIME CRACKING FOR A NI-BASED SUPERALLOY IN COMBINATION WITH OVERLOADS2015Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A004Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper scatter in crack growth for dwell time loadings combination with overloads has been investigated. Multiple Jsts were performed for surface cracks at 5500C in the commonly sed high temperature material Inconel 718. The test specimens -iginate from two different batches which also provides for a disission of how material properties affect the dwell time damage rnd overload impact. In combination with these tests an investiation of the microstructure was also carried out, which shows 9w it influences the growth rate. The results from this study show tat, in order to take overloads into consideration when analysing,ectrum loadings containing dwell times, one needs a substantial mount of material data available as the scatter seen from one atch to the other is of significant proportions.

  • 122.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012502-012502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550 °C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provide for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests, an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analyzing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other are of significant proportions.

  • 123.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy2015Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Sustained load have been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on sustained load and the interaction of load cycles, overloads, and temperature, but few studies have been carried out for vibrations and how these affect the dwell time crack growth. Vibrations of different kinds are frequently seen in engine components, and present in combination with sustained loads a more realistic loading situation than the latter itself. An investigation of how a vibrational load affects the dwell time cracking and how to incorporate it in a modelling context is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical testing has been conducted at 550◦C for surface cracks with and without the interaction of engine vibrations on sustained load, here represented by a superimposed high cycle fatigue (HCF) load. Subsequent investigation of the fracture behaviour was performed by Scanning Electron Microscope (SEM) and the modelling work has been conducted by incorporating the HCF load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical tests.

  • 124.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Månsson, Tomas
    GDN Aerospace Engine Systems, Trollhättan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Influence of Superimposed Vibrational Load on Dwell Time Crack Growth in a Ni-Based Superalloy2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, s. 301-310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sustained loads have for some Ni-based superalloys been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on the interaction of load cycles, overloads, and temperature. However, vibrations of different kinds are to some extent always present in engine components, and an investigation of how such loads affect the dwell time cracking, and how to incorporate them in a modelling context, is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical crack propagation testing has been conducted at 550 °C for surface cracks with and without the interaction of superimposed vibrational loads. Subsequent investigation of the fracture behaviour was performed by scanning electron microscopy and the modelling work has been conducted by incorporating the vibration load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical test results.

  • 125.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading2016Inngår i: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High temperature materials subjected to elevated temperature have been shown to be sensitive to dwell times, giving an increased crack growth rate. The interaction between these dwell times and rapid cyclic loads have been shown to constitute a complex problem. Many models have been developed for 1D conditions, but the application to general 3D conditions has seldom been seen, although this is the most common case in most structures. In this paper a model for taking care of the interaction between these load modes in general 3D crack growth has been developed. The model uses 1D results for extension to general 3D, thus providing for local crack front evolution with a minimum of numerical simulations. The model has been implemented for usage with finite element calculations and several different tests are simulated and compared with experimental results for the nickel based superalloy Inconel 718 at 550◦C. The simulation results show crack shapes in agreement with experimental fracture surfaces and time to failure.

  • 126.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Mansson, Tomas
    GKN Aerosp Engine Syst, Sweden.
    MODELLING OF CRACK GROWTH WITH DWELL TIME FOR AERO ENGINE SPECTRA LOADINGS IN A NI-BASED SUPERALLOY2015Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Testing and simulation of aero engine spectra with dwell Imes are reported in this paper. The modelling concept used built on LEFM and provides a history dependent evolution 2scription of dwell damage and its interaction with cyclic load. he simulations have been carried out for three spectra, 1) cyclic ?ads, 2) combined sustained load and cyclic loads and 3) slow ad ramps and cyclic loads, all for surface cracks at 550 C for nconel 718. All simulations show reasonable good agreement ith experimental results. Prediction of multiple tests of several atches is also provided to show statistical scatter

  • 127.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012501-012501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Testing and simulation of aero-engine spectra with dwell times are reported in this paper. The modeling concept used is built on linear elastic fracture mechanics (LEFM) and provides a history-dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra: (1) cyclic loads, (2) combined sustained load and cyclic loads, and (3) slow load ramps and cyclic loads, all for surface cracks at 550 °C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.

  • 128.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012503-012503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermomechanical fatigue (TMF) crack growth modeling has been conducted on Inconel 718 with dwell time at maximum load. A history dependent damage model taking dwell damage into account, developed under isothermal conditions, has been extended for TMF conditions. Parameter determination for the model is carried out on isothermal load controlled tests at 550–650 °C for surface cracks, which later have been used to extrapolate parameters used for TMF crack growth. Further, validation of the developed model is conducted on a notched specimen subjected to strain control at 50–550 °C. Satisfying results are gained within reasonable scatter level compared for test and simulated number of cycles to failure.

  • 129.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    THERMO-MECHANICAL FATIGUE CRACK GROWTH MODELLING IN A NI-BASED SUPERALLOY SUBJECTED TO SUSTAINED LOAD2015Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Thermo-mechanical fatigue (TMF) crack growth modelling as been conducted on Inconel 718 with dwell time at maximum;ad. A history dependent damage model taking dwell damage uto account, developed under isothermal conditions, has been xtended for TMF conditions. Parameter determination for the lodel is carried out on isothermal load controlled tests at 55050 C for surface cracks, which later have been used to extrapole parameters used for TMF crack growth. Further, validation the developed model is conducted on a notched specimen sub?cted to strain control at 50-550 C. Satisfying results are gained ithin reasonable scatter level compared for test and simulated umber of cycles to failure.

  • 130.
    Stålhand, Jonas
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Holzapfel, Gerhard A.
    Graz University of Technology, Austria.
    Length adaptation of smooth muscle contractile filaments in response to sustained activation2016Inngår i: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 397, s. 13-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Airway and bladder smooth muscles are known to undergo length adaptation under sustained contraction. This adaptation process entails a remodelling of the intracellular actin and myosin filaments which shifts the peak of the active force-length curve towards the current length. Smooth muscles are therefore able to generate the maximum force over a wide range of lengths. In contrast, length adaptation of vascular smooth muscle has attracted very little attention and only a handful of studies have been reported. Although their results are conflicting on the existence of a length adaptation process in vascular smooth muscle, it seems that, at least, peripheral arteries and arterioles undergo such adaptation. This is of interest since peripheral vessels are responsible for pressure regulation, and a length adaptation will affect the function of the cardiovascular system. It has, e.g., been suggested that the inward remodelling of resistance vessels associated with hypertension disorders may be related to smooth muscle adaptation. In this study we develop a continuum mechanical model for vascular smooth muscle length adaptation by assuming that the muscle cells remodel the actomyosin network such that the peak of the active stress-stretch curve is shifted towards the operating point. The model is specialised to hamster cheek pouch arterioles and the simulated response to stepwise length changes under contraction. The results show that the model is able to recover the salient features of length adaptation reported in the literature.

  • 131.
    Stålhand, Jonas
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    McMeeking, Robert M.
    Department of Mechanical Engineering & Materials Department, University of California Santa Barbara, CA 93106, USA / School of Engineering, University of Aberdeen, Kings College, Aberdeen, AB24 3UE, UK.
    Holzapfel, Gerhard A.
    Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria / Norwegian University of Science and Technology (NTNU), Faculty of Engineering Science and Technology, 7491 Trondheim, Norway.
    On the Thermodynamics of Smooth Muscle Contraction2016Inngår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 94, s. 490-503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cell function is based on many dynamically complex networks of interacting biochemical reactions. Enzymes may increase the rate of only those reactions that are thermodynamically consistent. In this paper we specifically treat the contraction of smooth muscle cells from the continuum thermodynamics point of view by considering them as an open system where matter passes through the cell membrane. We systematically set up a well-known four-state kinetic model for the cross-bridge interaction of actin and myosin in smooth muscle, where the transition between each state is driven by forward and reverse reactions. Chemical, mechanical and energy balance laws are provided in local forms, while energy balance is also formulated in the more convenient temperature form. We derive the local (non-negative) production of entropy from which we deduce the reduced entropy inequality and the constitutive equations for the first Piola-Kirchhoff stress tensor, the heat flux, the ion and molecular flux and the entropy. One example for smooth muscle contraction is analyzed in more detail in order to provide orientation within the established general thermodynamic framework. In particular the stress evolution, heat generation, muscle shorting rate and a condition for muscle cooling is derived.

  • 132.
    Suresh, Shyam
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Lindström, Stefan B
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Torstenfelt, Bo
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    An Evolution-Based High-Cycle Fatigue Constraint in Topology Optimization2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We develop a topology optimization method including high-cycle fatigue as a constraint. The fatigue model is based on a continuous-time approach, which uses the concept of a moving endurance surface as a function of the stress history and back stress evolution. The development of damage only occurs when the stress state lies outside the endurance surface. Furthermore, an aggregation function, which approximates the maximum fatigue damage, is implemented. As the optimization workflow is sensitivity-based, the fatigue sensitivities are determined using an adjoint sensitivity analysis. The capabilities of the presented approach are tested on numerical models where the problem is to maximize the stiffness subject to high-cycle fatigue constraints.

  • 133.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Implicitly and Explicitly ConstrainedOptimization Problems for Training of Recurrent Neural Networks2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Training of recurrent neural networks is typically formulated as unconstrained optimization problems. There is, however, an implicit constraint stating that the equations of state must be satisfied at every iteration in the optimization process. Such constraints can make a problem highly non-linear and thus difficult to solve. A potential remedy is to reformulate the problem into one in which the parameters and state are treated as independent variables and all constraints appear explicitly. In this paper we compare an implicitly and an explicitly constrained formulation of the same problem. Reported numerical results suggest that the latter is in some respects superior.

  • 134.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Multiplicity of the maximum eigenvalue in structural optimization problems2016Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 53, nr 5, s. 961-965Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many problems in structural optimization can be formulated as a minimization of the maximum eigenvalue of a symmetric matrix. In practise it is often observed that the maximum eigenvalue has multiplicity greater than one close to or at optimal solutions. In this note we give a sufficient condition for this to happen at extreme points in the optimal solution set. If, as in topology optimization, each design variable determines the amount of material in a finite element in the design domain then this condition essentially amounts to saying that the number of elements containing material at a solution must be greater than the order of the matrix.

  • 135.
    Thore, Carl-Johan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Alm Grundström, Henrik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Game formulations for structural optimization under uncertainty2019Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider structural optimization (SO) under uncertainty formulated as a mathematical game between two players -- a "designer" and "nature". The first player wants to design a structure that performs optimally, whereas the second player tries to find the worst possible conditions to impose on the structure. Several solution concepts exist for such games, including Stackelberg and Nash equilibria and Pareto optima. Pareto optimality is shown not to be a useful solution concept. Stackelberg and Nash games are, however, both of potential interest, but these concepts are hardly ever discussed in the literature on SO under uncertainty. Based on concrete examples of topology optimization of trusses and finite element-discretized continua under worst-case load uncertainty, we therefore analyze and compare the two solution concepts. In all examples, Stackelberg equilibria exist and can be found numerically, but for some cases we demonstrate nonexistence of Nash equilibria. This motivates a view of the Stackelberg solution concept as the correct one. However, we also demonstrate that existing Nash equilibria can be found using a simple so-called decomposition algorithm, which could be of interest for other instances of SO under uncertainty, where it is difficult to find a numerically efficient Stackelberg formulation.

  • 136.
    Thore, Carl-Johan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Alm Grundström, Henrik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Torstenfelt, Bo
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Penalty regulation of overhang in topology optimization for additive manufacturing2019Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 60, nr 1, s. 59-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several filter approaches that introduce additive manufacturing-related overhang constraints in topology optimization exist. However, a drawback of these is that exact satisfaction of overhang constraints produces sharp inward corners resulting in stress singularities. The present paper therefore modifies such filter approaches by a penalty formulation, where the choice of penalty factor regulates how closely the overhang constraint is satisfied. By appropriately choosing certain weight factors in the penalty function, the cost of support structures is also reflected in the formulation in a simple and computationally inexpensive way. The method is demonstrated by parameter studies using the classical MBB beam, using both structured and unstructured meshes.

  • 137.
    Thore, Carl-Johan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Holmberg, Erik
    Saab AB, Linkoping, Sweden.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    A general framework for robust topology optimization under load-uncertainty including stress constraints2017Inngår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a worst-case approach for topology optimization under load-uncertainty based on a general problem formulation involving maxima of quadratic functions of an uncertain load vector as both objective and constraints. The problem is reformulated as a non-linear semi-definite program which can be solved efficiently. An important special case of the general problem formulation is worst-case compliance minimization under worst-case stress constraints which is illustrated by numerical examples. (C) 2017 Elsevier B.V. All rights reserved.

  • 138.
    Thore, Carl-Johan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Holmberg, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Large-scale robust topology optimization under load-uncertainty2015Inngår i: Advances in Structural and Multidisciplinary Optimization - Proceedings of the 11th World Congress of Structural and Multidisciplinary Optimization(WCSMO-11) / [ed] Qing Li, Grant P Steven and Zhongpu (Leo) Zhang, 2015, s. 255-260Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Structures designed by topology optimization (TO) are frequently sensitive to loads different from the ones accounted for in the optimization. In extreme cases this means that loads differing ever so slightly from the ones it was designed to carry may cause a structure to collapse. It is therefore clear that handling uncertainty regarding the actual loadings is important. To address this issue in a systematic  manner is one of the main goals in the field of robust TO. In this work we present a deterministic robust formulation of TO for maximum stiffness design which accounts for uncertain variations around a set of nominal loads. The idea is to find a design which minimizes the maximum compliance obtained as the loads vary in infinite, so-called uncertainty sets. This naturally gives rise to a semi-infinite optimization problem, which we here reformulate into a non-linear, semi-definite program. With appropriate numerical algorithms this optimization problem can be solved at a cost similar to that of solving a standard multiple load-case TO problem with the number of loads equal to the number of spatial dimensions plus one, times the number of nominal loads. In contrast to most previously suggested methods, which can only be applied to small-scale problems, the presented method is – as illustrated by a numerical example – well-suited for large-scale TO problems.

  • 139.
    Venkatesan, Sreedhar
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Banglore Hanumantha Raju, Hariprasad
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Probabilistic Analysis of Brake Noise: A Hierarchical Multi-fidelity Statistical Approach2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Computer Aided Engineering driven analysis is gaining grounds in automotive industry. Prediction of brake noise using CAE techniques has become populardue to its overall low cost as compared to physical testing. However, the presence of several uncertain parameters which affect brake noise and also the lack of basic understanding about brake noise, makes it difficult to make reliable decisions based on CAE analysis. Therefore, the confidence level in CAE techniques has to be increased to ensure reliability and robustness in the CAE solutions which support design work. One such way to achieve reliability in the CAE analysis isinvestigated in this thesis by incorporating the effects of different sources of uncertainty and variability in the analysis and estimating the probability of designfailure (probability of brake noise above a certain threshold). While incorporating the uncertainties in the CAE analysis ensures robustness, it is computationally intensive. This thesis work aims to gain an understanding about a brakenoise - creep groan, and to bring robustness into the CAE analysis along with reduction in computational time. A probabilistic analysis technique called hierarchical multi-fidelity statistical approachis explored in this thesis work, to estimate the probability of design failure or design robustness at a faster rate. It incorporates the stochasticity in the input parameters while running simulations. The method involves application of a hierarchy of approximations to the system response computed with variations in mesh resolution or variations in number of modes or changing solver time step,etc. And finally it uses the probability theory, to relate the information provided by approximate solutions to get the target failure estimation.Through this method, reliable data regarding the probability of design failure was approximated for every simulation and at a reduced computational time.Additionally, it provided information about critical parameters that influenced brake noise which was meritorious for design management. Estimation of probability of design failure by this method has been proved to be reliable in the case of brake noise according to the simulation results and the method can be considered robust.

  • 140.
    Vikström, Simon
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thuresson, Robin
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Finite element analysis of winding sequence for cable drums2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This project concerns large cable drums made of steel. Cable drums are cylindrical structures used to transport different kinds of cables or wires. The ones in focus in this work are used to transport very stiff and heavy cables to offshore sites in the oil industry. To reduce weight in structures is always of great interest, and for cable drums, that are designed according to standards, there is much that can be improved.

    The aim of this project is to predict the loads acting on a drum during the winding of cables. This was accomplished by performing explicit finite element simulations of the winding sequence. Modeling and meshing were done using LS-PrePost and ANSA, and the winding was simulated using LS-DYNA. LS-PrePost was also used to analyze the results, together with mETApost.

    A number of simplifications and delimitations have been made in order to make the simulation possible within the time frame of the project. Simplified models of both the cable and the drum have been used. Winding velocities in real life are really slow, so in order to reduce simulation times, the winding velocity had to be increased while still avoiding dynamic effects. From this, contact forces between the drum and the cable could be obtained. The contact forces were investigated with respect to different friction values between the cable and the drum, for the cable itself and also for different cable stiffnesses.

    The results obtained from the simulations provide contact force distributions for different parts of the drum. Much fewer rows and layers of cable were winched than in real life, and it is therefore hard to see any clear trends in the obtained forces. However, one important result of the contact forces, is that a previously used assumption, namely that the pretension of the cable only applies loads to a small fraction of the drum, was a bit too conservative. According to the simulations it actually gets distributed over the whole drum.

    It is hard to draw any conclusions from the obtained contact forces, due to the small size of the simulations. The conclusion one can draw from this report, is that it is fully possible to use finite element tools to simulate the winding sequence of cable drums and this report presents a methodology on how to achieve this. LS-DYNA handles the contact definitions in an adequate way and is, according to the authors, a strong candidate for future work in this area. 

  • 141.
    Wärner, Hugo
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Robert
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Filosofiska fakulteten. Linköpings universitet, Tekniska fakulteten.
    Chai, Guocai
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Calmunger, Mattias
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Influence of Ageing on Thermomechaical Fatigue of Austenitic Stainless Steels2019Inngår i: Structural Integrity Procedia / [ed] Elsevier, Elsevier, 2019Konferansepaper (Fagfellevurdert)
123 101 - 141 of 141
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