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  • 1.
    Gustafsson, Erik
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
    Strömberg, Niclas
    Mechanical Engineering, Jönköping University, Jönköping, Sweden.
    Successive Response Surface Methodology by using Neural Networks2007In: Proceedings of 7th World Congress on Structural and Multidisciplinary Optimization, Seoul, Korea, 2007Conference paper (Other academic)
  • 2.
    Hofwing, Magnus
    et al.
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Strömberg, Niclas
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Robustness of residual stresses in castings and an improved process window2009In: Proceedings of the 35th Design Automation Conference, August 30-September 2, San Diego, USA 2009, The American Society of Mechanical Engineers , 2009, p. 1081-1091, article id DETC2009-86454Conference paper (Refereed)
    Abstract [en]

    In this work the robustness of residual stresses in finite element simulations with respect to deviations in mechanical parameters in castings is evaluated. Young's modulus, the thermal expansion coefficient and the hardening are the studied parameters. A 2D finite element model of a stress lattice is used. The robustness is evaluated by comparing purely finite element based Monte Carlo simulations and Monte Carlo simulations based on linear and quadratic response surfaces. Young's modulus, the thermal expansion coefficient and the hardening are assumed to be normal distributed with a standard deviation that is 10% of their nominal value at different temperatures. In this work an improved process window is also suggested to show the robustness graphically. By using this window it is concluded that least robustness is obtained for high hardening values in combination to deviations in Young's modulus and the thermal expansion coefficient. It is also concluded that quadratic response surface based Monte Carlo simulations substitute finite element based Monte Carlo simulations satisfactory. Furthermore, the standard deviation of the responses are evaluated analytically by using the Gauss formula, and are compared to results from Monte Carlo simulations. The analytical solutions are accurate as long as the Gauss formula is not utilized close to a stationary point.

  • 3.
    Hofwing, Magnus
    et al.
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Strömberg, Niclas
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Simulation of residual stresses in stamping dies2008In: Proceedings of the IDDRG 2008 Conference : Best in class stamping, 16-18 June 2008, Olofström, Sweden / [ed] Nader Asnafi, Olofström: Industriellt utvecklingscentrum i Olofström AB , 2008, p. 765-776Conference paper (Refereed)
    Abstract [en]

    In the past stamping dies have in principle been designed by rules of thumb and intuition. As the sheet metals in the vehicle industry have got increased mechanical properties in recent years the demands on the stamping dies have increased. For instance increase in stiffness is desirable in order to better control spring-back. The most simple way to satisfy this new demand would be to make the stamping dies even more heavy in order to be able to handle the new sheet metals. Since there are restrictions of the weight of the stamping dies in the stamping machines and since the overhead cranes usually have reached the limit of what they can handle, this is not a desirable solution. Another approach, in order to increase the stiffness without increasing the weight is to use topology optimization. Recently in a master thesis at Volvo Car Corporation a conceptual design of a stamping die has been done by topology optimization. In that work no consideration is taken to the fact that the stamping die is casted. Casting implies that residual stresses possibly are produced during the solidification and cooling process. The residual stresses might affect the fatigue life and the risk of failure of the stamping die.

    In this work the residual stress state after casting is analyzed for the original stamping die as well as the optimized stamping die from the master thesis discussed above. The analyses are performed using an uncoupled approach, where one thermal analysis is followed by a quasi-static elasto-plastic analysis. The thermal analysis simulates the solidification and cooling during the casting process, while the quasi-static elasto-plastic analysis uses the temperature history, obtained from the thermal analysis, in order to build up residual stresses. The thermal analysis includes the release of latent heat. Furthermore, the material properties included in the heat equation (density, conductivity, specific heat) are given as temperature dependent properties for the mould as well as the casting. In the quasi-static elasto-plastic analysis the plasticity is described by the von Mises yield surface in combination with isotropic hardening and the mechanical properties (thermal expansion coefficient, Young's modulus, yield stress, hardening parameter, Poisson's ratio) are given as temperature dependent properties. The simulations show high levels of residual stresses.

     

  • 4.
    Hofwing, Magnus
    et al.
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Strömberg, Niclas
    Tekniska Högskolan, Högskolan i Jönköping, JTH, Maskinteknik.
    Tapankov, M.
    Department of Mechanical Engineering Jönköping University P.O. Box 1026, 551 11 Jönköping.
    Optimal Polynomial Regression Models by using a Genetic Algorithm2011In: Proceedings of the Second International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering / [ed] Y. Tsompanakis & B.H.V. Topping, Stirlingshire: Civil-Comp Press , 2011, article id 39Conference paper (Other academic)
    Abstract [en]

    Different regression models are commonly used to approximate the behavior of an unknown response in a given design domain. The regression models are usually obtained from a design of experiments, the corresponding responses and the constitution of the regression model. In this work a new approach is proposed, where the constituents of a polynomial regression model are of arbitrary order. A genetic algorithm is used to find the optimal terms to be included in the so-called optimal polynomial regression model. The objective for the genetic algorithm is to minimize the sum of squared errors of the predicted responses. In practice the genetic algorithm generates an optimal set of exponents of the design variables for the specified number of terms in the regression model, where each term is a product of a regression coefficient and the design variables. Several example problems are presented to show the performance and accuracy of the optimal polynomial regression model. Results show an improved performance for optimal polynomial regression models compared to traditional regression models.

  • 5.
    Ireman, Peter
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Klarbring, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    A model of damage coupled to wear2003In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 40, no 12, p. 2957-2974Article in journal (Refereed)
    Abstract [en]

    The present paper presents a model of damage coupled to wear. The damage model is based on a continuum model including the gradient of the damage variable. Such a model is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. Thereby, the well-known mesh-dependency observed for local damage models is removed. Another feature is that the boundary conditions can be used to introduce couplings between bulk damage and processes at the boundary. In this work such a coupling is suggested between bulk damage and wear at the contact interface. The model is regarded as a first attempt to formulate a continuum damage model for studying crack initiation in fretting fatigue. The model is given within a thermodynamic framework, where it is assured that the principles of thermodynamics are satisfied. Furthermore, two variational formulations of the full initial boundary value problem, serving as starting points for finite element discretization, are presented. Finally, preliminary numerical results for a simple one-dimensional example are presented and discussed. It is qualitatively shown how the evolution of damage may influence the wear behaviour and how damage may be initiated by the wear process. © 2003 Elsevier Science Ltd. All rights reserved.

  • 6.
    Ireman, Peter
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Klarbring, Anders
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    Finite element algorithms for thermoelastic wear problems2002In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 21, no 3, p. 423-440Article in journal (Refereed)
    Abstract [en]

    In the present paper three algorithms are applied to a finite element model of two thermoelastic bodies in frictional wearing contact. All three algorithms utilize a modification of a Newton method for B-differentiable equations as non-linear equation solver. In the first algorithm the fully-coupled system of thermomechanical equations is solved directly using the modified method, while in the other two algorithms the equation system is decoupled in one mechanical part and another thermal part which are solved using an iterative strategy of Gauss-Seidel type. The two iterative algorithms differ in which order the parts are solved. The numerical performance of the algorithms are investigated for two two-dimensional examples. Based on these numerical results, the behaviour of the model is also discussed. It is found that the iterative approach where the thermal subproblem is solved first is slightly more efficient for both examples. Furthermore, it is shown numerically how the predicted wear gap is influenced by the bulk properties of the contacting bodies, in particular how it is influenced by thermal dilatation. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

  • 7.
    Klarbring, Anders
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Christensen, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Pang, J.S.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Formulation and Comparison of Algorithms for Frictional Contact Problems1999In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 42, p. 145-173Article in journal (Other academic)
  • 8.
    Lundvall, Olle
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Strömberg, Niclas
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    A flexible multi-body approach for frictional contact in spur gears2004In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 278, no 3, p. 479-499Article in journal (Refereed)
    Abstract [en]

    In the present paper, a large rotational approach for dynamic contact problems with friction is proposed. The approach is used for modelling a spur gear pair with shafts and bearings. The model is obtained by superposing small displacement elasticity on rigid-body motions, and postulating tribological laws on the gear flanks. The finite element method is used to model the elastic properties of the gear pair. Shafts and bearings are represented by linear springs. The tribological laws of the contact interface are Signorini's contact law and Coulomb's law of friction. An important feature of the approach is that the difficulties of impacting mass nodes are avoided. The governing equations of the model are numerically treated by use of the augmented Lagrangian approach. In such manner the geometry of the gear flanks are well represented in the numerical simulations. It is possible to study accurately the consequences of different types of profile modifications as well as flank errors. In this work, the dynamic transmission error is studied. For instance, it turns out that the effect from profile modification is less significant for the transmission error when frictional effects are included.

  • 9.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Mechanics .
    A method for structural dynamic contact problems with friction and wear2003In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 58, no 15, p. 2371-2385Article in journal (Refereed)
    Abstract [en]

    A method for structural dynamic contact problems with friction and wear is suggested. The method is obtained by including wear in the non-smooth contact dynamics method of Moreau. A comparison of the method to the discrete energy-momentum method of Simo and Tarnow is also outlined briefly. The fully discrete equations are treated using the augmented Lagrangian approach, where a non-smooth Newton method is used as the equation solver. Two two-dimensional examples are solved by the method. It is investigated how solutions of contact, friction and wear are influenced by inertia. It is shown that the quasi-static assumption might be questionable for solving contact problems with friction and wear. © 2003 John Wiley and Sons, Ltd.

  • 10.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    An Assessment of Continuum Model for Cracking in Uranium Dioxid1998Other (Other (popular science, discussion, etc.))
  • 11.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Finite Element Treatment of Thermoelastic Wear Problems1999In: Intl Symposium on Impact and Friction of Solids, Structures and Machines,1998, 1999Conference paper (Other academic)
  • 12.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Finite element Treatment of Thermoelastic Wear Problems1999In: IUTAM-Symposium on Unilaterial Multibody Dynamics,1998, 1999Conference paper (Other academic)
  • 13.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    Finite Element Treatment of Two-dimensional Thermoelastic Wear Problems1999In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 1777, p. 441-455Article in journal (Other academic)
  • 14.
    Strömberg, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Mechanics.
    JAS39 VU/EBS MLG CDR Package S.O.R. 1471999Other (Other (popular science, discussion, etc.))
  • 15.
    Strömberg, Niclas
    et al.
    Jönköping University.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Minimization of Compliance of a Linear Elastic Structure with Contact Constraints by using Sequential Linear Programming and Newton's method2008In: Proceedings of the 7th International ASMO-UK/ISSMO International Conference on Engineering Design Optimization, 2008, p. 379-386Conference paper (Refereed)
  • 16.
    Strömberg, Niklas
    et al.
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Topology Optimization of Structures with Contact Constraints by using  a Smooth Formulation and Nested Approach2009In: 8th World Congress on Structural and Multidisciplinary Optimization June 1-5 2009, Lisbon, Portugal, Lissabon, Portugal, 2009Conference paper (Refereed)
1 - 16 of 16
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