In this article, Small Area Estimation under a Multivariate Linear model for repeated measures data is considered. The proposed model aims to get a model which borrows strength both across small areas and over time. The model accounts for repeated surveys, grouped response units and random effects variations. Estimation of model parameters is discussed within a likelihood based approach. Prediction of random effects, small area means across time points and per group units are derived. A parametric bootstrap method is proposed for estimating the mean squared error of the predicted small area means. Results are supported by a simulation study.

Examensarbetets mål är att ta fram en ny konstruktion för montering av temperaturgivare i värmepumpar. Arbetet begränsas till att omfatta de givare som idag är monterade på rör och den nya konstruktionen är tänkt att användas med en givare från en ny leverantör.

En undersökning av hur givarna är monterade idag har genomförts i Boschs egna värmepumpar men även i konkurrenters värmepumpar. Dessa undersökningar har varit till stor hjälp för att bättre förstå problemet och för att planera till de tester som sedan utförts.

För att på ett bra sätt avläsa temperaturen med givarna krävs att de monteras på ett bra sätt. En testrigg har byggts för att på ett bra sätt kunna jämföra och utvärdera olika lösningar mot varandra. De lösningar som har testats är bland annat de som hittades i undersökningen av värmepumparna men också några egna idéer.

Efter testerna har resultaten utvärderats och med detta som grund har förbättringar av existerande lösningar eller nya lösningar arbetats fram i form av skisser.

Ett clips som en konkurrent använder har efter testerna uppvisat relativt bra resultat men den stora fördelen med clipset är att det är väldigt lätt att montera och kräver inga verktyg. På grund av tidsbrist har vissa tester inte kunnat utföras för att säkerställa att detta clips uppfyller alla krav som ställs på ett nytt monteringssätt.

A popular way to reduce weight in industrial products without compromising the strength or stiffness is to replace components made of metal by plastics that have been reinforced by glass fibers. When fibers are introduced in a plastic, the resulting composite usually becomes anisotropic, which makes it much more complex to work with in simulation software. This thesis looks at modeling of such a composite using the multi-scale material modeling tool Digimat.

An injection molding simulation of a brush cutter casing made of a short fiber reinforced plastic has been performed in order to obtain information about the glass fiber orientations, and thus the anisotropy, in each material point. That information has then been transferred over from the injection mesh to the structural mesh via a mapping routine. An elasto-viscoplastic material model with failure has been employed and calibrated against experimental data to find the corresponding material parameters. Lastly, a finite element analysis simulating a drop test has been performed. The results from the analysis have been compared with a physical drop test in order to evaluate the accuracy of the methodology used. The outcome has been discussed, conclusions have been drawn and suggestions for further studies have been presented.

The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.

This is a Masters Thesis report of a project carried out at Scania AB in Södertälje. The project concerns rationalizing Chassis calculations for use in truck Frame design. The subject for analysis is a six-wheeled articulated truck, and the load cases under study is Lateral Loading, Frame Torsion and Vertical Load on Kingpin. Making robust deformation and stress models with a calculation time sufficiently short and accuracy consistently high for efficient design work is an arduous task. This report presents several approaches to tackle this type of problem. By means of simplifying contemporary modeling approaches and methods and automating the setup process, a method that enables short calculation iterations on a chassis frame of a truck is achieved. This is done using the Catia GAS framework in conjunction with several other licences commonly used by designers.

This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and also to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close-packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Fatigue crack growth testing has been performed, both using conventional isothermal testing methods and also using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are however only presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, in order to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance in the understanding of the crack driving force under different testing conditions.

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.

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.

The work consists of a construction process in order to improve the adjustment and indication of a grease dosing unit used in a dual-line lubrication system. The work is performed on behalf of and in consultation with Assalub AB in Åtvidaberg.

The grease dosing unit is a part of a dual-line central lubrication system and is often used in exposed and strenuous environments. Therefor it is important that the unit’s function and adjustment is easy and trustworthy and that the indication is clear and facilitates functional checks. The adjustment device used for adjustment and indication today does not cater Assalubs requirements. The present construction has no reliable adjustment, can give rise to leakage and has an indication which is difficult to see from some angles. This work therefor aims to develop and improve the design of the adjustment device so that the reliability and life expectancy increases and functional checks is simplified.

The work resulted in a concept with a reliable adjustment unit with well visible flags for indication and a simple adjustment unit was developed. Based on this concept CAD-models and production drawings was produced and delivered, and a prototype was made for function testing.

In the presented work, two studies using ComputationalFluid Dynamics (CFD) have been conducted on a generictruck-like model with and without a trailer unit at a speed of 80km/h. The purpose is to evaluate drag reduction possibilitiesusing externally fitted devices. A first study deals with a flapplaced at the back of a rigid truck and inclined at seven differentangles with two lengths. Results show that it is possible todecrease drag by 4%. In a second study, the flap has been fittedon the tractor and trailer units of a truck-trailer combination.Four settings were surveyed for this investigation, one of whichproved to decrease drag by up to 15%. A last configurationwhere the gap between the units has been closed has also beenevaluated. This configuration offers a 15% decrease in drag.Adding a flap to the closed gap configuration decreases drag by18%. New means of reducing aerodynamic drag of heavy-duty(HD) vehicles will be important in the foreseeable future inorder to improve the fuel economy. The possibilities of reducingdrag are prevalent using conceptual design.

The aim of this paper is to investigate the influence of the internal fluid flow characteristics of a special hydraulic solenoid valve, developed by Öhlins Racing AB, on its overall dynamic behavior. This valve is a two stage hydraulic pressure control valve and is typically mounted on each shock absorber of an on-road vehicle, allowing the implementation of semi-active suspension functionality. This technology is referred as CES (Continuously Controlled Electronic Suspension). The CES valve allows continuously controlling the vehicle shock absorbers damping characteristic by proportionally adjusting the metering geometry offered to its damping element, i.e. hydraulic oil. The electronic valve actuation and control, obtained through an electromagnetic solenoid, is based on the input from several vehicle dynamics sensors, such as accelerometers, gyroscopes and other displacement sensors. The CES valve’s unconventional design significantly influences the fluid flow, making the use of numerical modeling essential to discover its physical behavior and to support further product development. In this paper, a CFD (Computational Fluid Dynamics) analysis on the main and pilot stages of the hydraulic valve is discussed. This 3D numerical analysis is used to extract critical physical variables, affecting the valve behavior, such as flow coefficients and pressure distributions on the moving elements, i.e. flow forces. This information is coupled with a detailed lumped parameter model of the hydraulic valve, which solves for the valve moving element dynamics considering the action of the main external forces. Moreover, the 1D model allows predicting the valve critical pressure/flow characteristics. It is shown how the coupling of 3D modeling results with the CES valve 1D model strongly improves the whole valve dynamics numerical predictions over traditional methods for considering the effect of fluid inertia and discharge in lumped parameter simulations. Comparisons with measurement both on single regions of the CES hydraulic valve and on the entire valve are discussed in order to validate the various phases of numerical modeling.

In this work a cooling system connected to a reactor pressure vessel has been studied using the CFD method for the purpose of investigating the strengths and shortcomings of using CFD as a tool in similar fluid flow problems within nuclear power plants. The cooling system is used to transport water of 288K (15°C) into a nuclear reactor vessel filled with water of about 555K (282°C) during certain operating scenarios. After the system has been used, the warm water inside the vessel will be carried into the cooling system by buoyancy forces. It was of interest to investigate how quickly the warm water moves into the cooling system and how the temperature field of the water changes over time.

Using the open source CFD code OpenFOAM 2.3.x and the LES turbulence modelling method, a certain operating scenario of the cooling system was simulated. A simplified computational domain was created to represent the geometries of the downcomer region within the reactor pressure vessel and the pipe structure of the cooling system. Boundary conditions and other domain properties were chosen and motivated to represent the real scenario as good as possible. For the geometry, four computational grids of different sizes and design were generated. Three of these were generated using the ANSA pre-processing tool, and they all have the same general structure only with different cell sizes. The fourth grid was made by the OpenFOAM application snappyHexMesh, which automatically creates the volume mesh with little user input.

It was found that for the case at hand, the different computational grids produced roughly the same results despite the number of cells ranging from 0,14M to 3,2M. A major difference between the simulations was the maximum size of the time steps which ranged from 0,3ms for the finest ANSA mesh to 2ms for the snappy mesh, a difference which has a large impact on the total time consumption of the simulations.

Furthermore, a comparison of the CFD results was made with those of a simpler 1D thermal hydraulic code, Relap5. The difference in time consumption between the two analyses were of course large and it was found that although the CFD analysis provided more detailed information about the flow field, the cheaper 1D analysis managed to capture the important phenomena for this particular case. However, it cannot be guaranteed that the 1D analysis is sufficient for all similar flow scenarios as it may not always be able to sufficiently capture phenomena such as thermal shocks and sharp temperature gradients in the fluid.

Regardless of whether the CFD method or a simpler analysis is used, conservativeness in the flow simulation results needs to be ensured. If the simplifications introduced in the computational models cannot be proved to always give conservative results, the final simulation results need to be modified to ensure conservativeness although no such modifications were made in this work.

Cyclic plastic response of the austenitic heat resistant steel Sanicro 25 has been studied during strain controlled low cycle fatigue tests performed at ambient and at elevated temperature. Simultaneously with the cyclic hardening/softening curves hysteresis loops during cyclic loading were analyzed using generalized statistical theory of the hysteresis loop. The probability density distribution function of the internal critical stresses, the effective saturated stress and their evolution during cycling were derived for various strain amplitudes. The internal dislocation structure and the surface relief at room and at elevated temperature were studied and correlated with the cyclic stress–strain response and the evolution of the probability density function of the internal critical stresses.

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.

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.

This paper uses two examples, from cross country skiing and badminton, to illustrate the idea of using musculoskeletal simulation as a tool to understand and ultimately optimize sports performance. The results show that the analysis provides insight into the performances that cannot be obtained by other means, and it is advocated that this insight ultimately can lead to better coaching. The importance of “know-why” over “know-how” is stressed, and it is hypothesized that this may enable athletes to learn difficult techniques faster.

Aluminium is a widely used material, which is found in a number of products e.g. thin aluminium bands that is the base material in many heat exchangers. Rolling processes are used to produce these thin aluminium bands, in order to get the right properties and to get the aluminium easier to roll, heat treatment is needed. This heat treatment of aluminium ingots prior to the rolling is in focus in this work, where computational fluid dynamics and computational heat transfer techniques is used to predict the heating process in a hot air pre-heating furnace. The used approach includes steady state computational fluid dynamics simulations combined with transient computational heat transfer simulations. The simulation results in form of spatial and temporal distributed aluminium ingot temperature was compared with temperature measurement in a thermocouple prepared ingot in the actual pre-heating furnace. Simulation results correspond well with the measurements and there are small differences. Results of the described simulation approach open the possibility to predict spatial and temporal temperature distribution in these kinds of pre-heating processes.

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.

When designing a complex product, many groups are concurrently developing different parts or aspects of the product using detailed simulation models. Multidisciplinary design optimization (MDO) has its roots within the aerospace industry and can effectively improve designs through simultaneously considering different aspects of the product. The groups involved in MDO need to work autonomously and in parallel, which influence the choice of MDO method. The methods can be divided into single-level methods that have a central optimizer making all design decisions, and multi-level methods that have a distributed decision process.

This report is a comprehensive summary of the field of MDO with special focus on structural optimization for automotive applications using metamodels. Metamodels are simplified models of the computationally expensive detailed simulation models and can be used to relieve some of the computational burden during MDO studies. The report covers metamodel-based design optimization including design of experiments, variable screening, metamodels and their validation, as well as optimization methods. It also includes descriptions of several MDO methods, along with a comparison between the aerospace and automotive industries and their applications of MDO.

The information in this report is based on an extensive literature survey, but the conclusions drawn are influenced by the authors’ own experiences from the automotive industry. The trend goes towards using advanced metamodels and global optimization methods for the considered applications. Further on, many of the MDO methods developed for the aerospace industry are unsuitable for the automotive industry where the disciplines are more loosely coupled. The expense of using multi-level optimization methods is then greater than the benefits, and the authors therefore recommend single-level methods for most automotive applications.

When closed-loop hydraulic control systems first began to appear in industry, the applications were generally those in which very high performance was required. While hydraulic servo systems are still heavily used in high-performance applications such as the machine-tool industry, they are beginning to gain wide acceptance in a variety of industries. Examples are material handling, mobile equipment, plastics, steel plants, mining, oil exploration and automotive testing

Closed loop servo drive technology is increasingly becoming the norm in machine automation, where the operators are demanding greater precision, faster operation and simpler adjustment. There is also an expectation that the price of increasing the level of automation should be contained within acceptable limits.

Bolted joints are frequently used in aeroplanes, but there is no commonly accepted method for how to carry out fatigue calculations for tensile loaded bolted joints. In this master thesis, the effect of various parameters on the fatigue life of bolted joint will be studied. An important part of the thesis is to investigate what data is currently available at the company, and which tests that is required to fill up the gaps in the fatigue database.

A literature survey of different models for performing fatigue calculations for tensile loaded bolted joints showed, as mentioned above, that no common method exists. In general, the method to solve the problem is based on advice and guidance from various experts at the company, and usage of data etc. from different articles in the subject.

The parametric study showed that methods could be formulated for some parameters, while others parameters needed more testing before methods could be formulated with confidence. These gaps in the fatigue database need to be filled by more testing before the methodology to be implemented for calculating the fatigue life for tensile loaded bolted joints. A continuation study, for further investigating of factors that may influence the fatigue life, is also proposed.

The aim of this thesis is to investigate how a biological structure changes its shape and boundary under different cases of load if flow of nutrients is included, since nutrient flow has not been taken into account in previous studies.

In order to simulate such a scenario we construct a model by using topology optimization (the SIMP model) and a balance law which is suitable for biological structures. Moreover, the model is derived by using an analogy with the dissipation inequality and Coleman-Noll’s procedure. The model can be interpreted as bone or some other biological structure, where the growth and remodeling partly occurs due to nutrient flow.

The theory is first investigated by selecting an MBB beam with a special boundary condition for the nutrient concentration and inflow of nutrients, and then with a bone-like model.

For the analysis with different loads we have observed that the structure becomes thicker were the load is applied. Parameters like beta (β) (reflecting the relation between nutrients and material) and nutrient concentration (c) seem to play an important role in nutrient transport and building of the structure. The result for larger values of β and nutrient concentration (c) gives a thicker structure in the entire domain. We also made an assumption of Fick’s law of diffusion. Fick’s law of diffusion describes the flux from high concentration to low concentration. This phenomenon is observed in analysis with different nutrient concentrations (c): we can see that the structure tends to be built up where the concentration is high and continues to be built in the direction from high to low concentration. In analyses with mu-value (μ), which represents cost of material, the result gives a thinner structure for larger values of μ.

The mechanical behavior of a new single-crystal nickel-based superalloy for industrial gas turbine (IGT) applications is studied under creep and out-of-phase (OP) thermomechanical fatigue (TMF) conditions. Neutron diffraction methods and thermodynamic modeling are used to quantify the variation of the gamma prime (γ′) strengthening phase around the γ′ solvus temperature; these aid the design of primary aging heat treatments to develop either uniform or bimodal microstructures of the γ′ phase. Under creep conditions in the temperature range 1023 K to 1123 K (750 °C to 850 °C), with stresses between 235 to 520 MPa, the creep performance is best with a finer and uniform γ′ microstructure. On the other hand, the OP TMF performance improves when the γ′ precipitate size is larger. Thus, the micromechanical degradation mechanisms occurring during creep and TMF are distinct. During TMF, localized shear banding occurs with the γ′ phase penetrated by dislocations; however, during creep, the dislocation activity is restricted to the matrix phase. The factors controlling TMF resistance are rationalized.

This paper presents the results on the development of theoretical methods of evaluation and prediction of mechanical properties of Zr-Nb alloys over a range of strain rates from 10(-3) to 10(3) s(-1). The mechanical behavior of coarse-and ultrafine-grained Zr-1Nb (E110) was investigated numerically. The ranges of strain rates and temperatures in which the mechanical behavior of Zr-1Nb alloy can be described using modified models of Johnson-Cook and Zerilli-Armstrong were defined. The results can be used in engineering analysis of designed technical systems for nuclear reactors.

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.

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.

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.

Advancements in simulation tools and computer power have made it possible to incorporate simulation-based structural optimization in the automotive product development process. However, deterministic optimization without considering uncertainties such as variations in material properties, geometry or loading conditions might result in unreliable optimum designs. 

In this thesis, the capability of some established approaches to perform design optimization under uncertainties is assessed, and new improved methods are developed. In particular, vehicle structural problems which involve computationally expensive Finite Element (FE) simulations, are addressed.

The first paper focuses on the evaluation of robustness, given some variation in input parameters, the capabilities of three well-known metamodels are evaluated. In the second paper, a comparative study of deterministic, reliability-based and robust design optimization approaches is performed. It is found that the overall accuracy of the single-stage (global) metamodels, which are used in the above study, is acceptable for deterministic optimization. However, the accuracy of performance variation prediction (local sensitivity) must be improved. In the third paper, a decoupled reliability-based design optimization (RBDO) approach is presented. In this approach, metamodels are employed for the deterministic optimization only while the uncertainty analysis is performed using FE simulations in order to ensure its accuracy.

In the fifth paper, two new sequential sampling strategies are introduced that aim to improve the accuracy of the metamodels efficiently in critical regions. The capabilities of the methods presented are illustrated using analytical examples and a vehicle structural application.

It is important to accurately represent physical variations in material properties since these might exert a major influence on the results. In previous work these variations have been treated in a simplified manner and the consequences of these simplifications have been poorly understood. In the fourth paper, the accuracy of several simple methods in representing the real material variation has been studied. It is shown that a scaling of the nominal stress-strain curve based on the Rm scatter is the best choice of the evaluated choices, when limited material data is available.

In this thesis work, new pragmatic methods for non-deterministic optimization of large scale vehicle structural problems have been developed. The RBDO methods developed are shown to be flexible, more efficient and reasonably accurate, which enables their implementation in the current automotive product development process.

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.

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.

This master thesis was provided by Scania AB. The objective of this thesis was to modify an application in the free Computational Fluid Dynamics software OpenFOAM to be able to handle spray and wall film modeling of a Urea Water Solution together with Conjugate Heat Transfer. The basic purpose is to widen the knowledge of the vaporization process of a Urea Water Solution in the exhaust gas after treatment system for a diesel engine by using OpenFOAM. First, urea has been modeled as a very viscous liquid at low temperature to mimic the solidication process of urea. Second, the development of the new application has been done. At last, test simulations of a simple test case are performed with the new application. The results are then compared with simplied hand calculations to verify a correct behavior of certain exposed source terms. The new application is working properly for the test case but to ensure the reliability, the results need to be compared with another Computational Fluid Dynamics software or more preferable, real experiments. For more advanced geometries, the continued development presented last in this thesis is highly recommended to follow.

A TBC subjected to TMF loading may spall off after a sufficiently large number of cycles. This is a consequence of a combination of general fatigue damage growth and strong internal stresses caused by oxidation in the bondcoat/topcoat interface. Further, at the ends of the coating there are stress singularities, at which early fatigue cracks tend to develop. This can, however, be avoided or delayed by making the coating end chamfered. This work investigates the influence of coating end chamfer on the fatigue life of an APS TBC.

The static and low cycle fatigue properties of four pearlitic grey iron alloys intended for brake discs are investigated. The effect of alloying a base composition with 0.1 wt% and 0.3 wt% niobium is compared to a 0.3 wt% addition of the more conventional alloying element molybdenum. The results show that the static properties remain unaffected for an Nb content of 0.1 wt% while an addition of 0.3 wt% Nb or 0.3 wt% Mo increases the strength compared to the base alloy without Nb and Mo. The fatigue life on the other hand remains more or less unaffected by the alloying, although the stress levels are substantially higher for the compositions with 0.3 wt% Mo or 0.3 wt% Nb. Thus, the experiments show that graphite is very important for the low cycle fatigue life. It is also seen that crack propagation controls more than 90% of the life. Full scale brake dynamometer crack tests also gave a similar fatigue life of the different brake disc alloys independent of the composition.

High-chromium steels have high strength properties, corrosion properties and resistance to neutron irradiation, thereby are considered as promising steels for nuclear reactors of generation IV. The deformation and damage of high chromium steels in a wide temperature range was studied by numerical simulation method. A model was proposed to predict the deformation and damage of high chromium steels under quasi-static loading within the temperature range from 295 to 1100 K. It is shown that the ductility of high-chromium steels increases proportionally to temperature in the range from 750 to 1100 K due to the growth of alpha-phase precipitates.

Inelastic deformation and damage at the mesoscale level of ultrafine grained (UFG) light alloys with distribution of grain size were investigated in wide loading conditions by experimental and computer simulation methods. The computational multiscale models of representative volume element (RVE) with the unimodal and bimodal grain size distributions were developed using the data of structure researches aluminum and magnesium UFG alloys. The critical fracture stress of UFG alloys on mesoscale level depends on relative volumes of coarse grains. Microcracks nucleation at quasi-static and dynamic loading is associated with strain localization in UFG partial volumes with bimodal grain size distribution. Microcracks arise in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength.

This article presents the results of modelling of the mechanical behaviour of biocompatible Zr-Nb and Ti-Nb alloys in the range of strain rates from 10(-3) to 10(3) s(-1) at temperatures from 297 K to 1273 K. Modification of the micro-dynamical model was proposed for the description of Zr-1Nb ultrafine grained and coarse grained alloys. It was shown that the phase transition HCP -amp;gt; BCC alloy Zr-Nb at elevated temperatures leads to a sharp changing in the resistance to plastic flow and kinetics of growth of damage. The results can be used for engineering analysis of designed constructive elements of technical and biomedical applications.

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.

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.

Many different test methods are currently used to characterise the output of artificial muscle materials but few studies report the full range of possible force and displacements that can be generated by a given material when activated with a given input stimulus but when operated against different external loads. The measurement of the loading and unloading force extension curves in tension in both the un-activated and activated states is investigated as a means for efficiently characterising the full range of outputs for three different types of artificial muscles: pneumatically operated braided muscle and thermally operated shape memory alloy spring and twisted / coiled polymer fiber. A graphical method of analysis was applied whereby the force-extension curves obtained before and after actuator activation were plotted on the same axes. By overlaying the external loading conditions, the graphical method provided the equilibrium starting and finishing forces and displacements and successfully predicted the isotonic strokes, isometric forces and combined force and displacement generated when the actuator was operated against an external spring. Complications in the interpretation of the force-stroke curves were encountered as all three artificial muscles displayed a degree of loading-unloading hysteresis and non-ideal mechanical behavior. (C) 2019 Elsevier B.V. All rights reserved.

Griffiths' model of flow-through elastic tubes makes it possible to relate the elastic properties of the flow-controlling zone to the pressure/flow relation of the urethra. In this work the pressure function p(A) = P_mo + K_n Aⁿ, where A is cross-sectional area, P_mo the minimal opening pressure, and K_n and n parameters describing urethral distensibility, describes the elastic properties of the flow-controlling zone. By curve-fitting in the pressure/flow plot, the three parameters p_mo, K_n, and n can be estimated analytically. Using this model it is possible to identify three different biomechanical changes that may cause obstruction. First, p_mo may be elevated. Second, the urethra can be distended to a certain area only, corresponding to high values of K_n and n. Third, the urethra can be distended but a higher-than-normal pressure increase above P_mo is needed, K_n is high, and n is low. With this model it is possible to quantify urethral function for both scientific and clinical purposes.

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.

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.

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.

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.