ICMM6

This volume contains selected papers presented at the 6th International Conference on Material Modeling (ICMM6), which took place June 26-28 2019 at the campus of Lund University, Sweden. By all meaningful measures, ICMM6 was a great success, attracting 161 participants from almost 30 countries (ranging from senior colleagues to graduate students)and featuring a technical program that well reflected the cutting-edge of materials modeling research. ICMM6 included thematic sessions on the following topics • linear elasticity and viscoelasticity • nonlinear elasticity • plasticity and viscoplasticity • experimental identification and material characterization • Cosserat, micromorphic and gradient materials • atomistic/continuum transition on the nanoscale • optimization and inverse problems in multiscale modeling • granular materials and particle systems • biomechanics and biomaterials • electronic materials • heterogeneous materials • coupled field problems • creep, damage and fatigue • numerical aspects of material modeling. The aim of the ICMM conferences is to bring together researchers from different fields of material modeling and material characterization, and to cover essentially all aspects of material modeling thus providing the opportunity for interactions between scientists working in different subareas of material mechanics who otherwise would not come into contact with each other

Simulation of discontinuous dynamic recrystallization in pure Cu using a probabilistic cellular automaton

A cellular automaton algorithm with probabilistic cell switches is employed in the simulation of dynamic discontinuous recrystallization. Recrystallization kinetics are formulated on a microlevel where, once nucleated, new grains grow under the driving pressure available from the competing processes of stored energy minimization and boundary energy reduction. Simulations of the microstructural changes in pure Cu under hot compression are performed where the influence of different thermal conditions are studied. The model is shown to capture both the microstructural evolution in terms of grain size and grain shape changes and also the macroscopic flow stress behavior of the material. The latter gives the expected transition from single- to multiple-peak serrated flow with increasing temperature. Further, the effects on macroscopic flow stress by varying the initial grain size is analyzed and the model is found to replicate the shift towards more serrated flow as the initial grain size is reduced. Conversely, the flow stress is stabilized by larger initial grain sizes. The extent of recrystallization as obtained from simulations are compared to classical JMAK theory and proper agreement with theory is established. In addition, by tracing the strain state during the simulations, a post-processing step is devised to obtain the macroscopic deformation of the cellular automaton domain, giving the expected deformation of the equiaxed recrystallized grains due to the macroscopic compression

Accelerating crystal plasticity simulations using GPU multiprocessors

Crystal plasticity models are often used to model the deformation behavior of polycrystalline materials. One major drawback with such models is that they are computationally very demanding. Adopting the common Taylor assumption requires calculation of the response of several hundreds of individual grains to obtain the stress in a single integration point in the overlying FEM structure. However, a large part of the operations can be executed in parallel to reduce the computation time. One emerging technology for running massively parallel computations without having to rely on the availability of large computer clusters is to port the parallel parts of the calculations to a graphical processing unit (GPU). GPUs are designed to handle vast numbers of floating point operations in parallel. In the present work, different strategies for the numerical implementation of crystal plasticity are investigated as well as a number of approaches to parallelization of the program execution. It is identified that a major concern is the limited amount of memory available on the GPU. However, significant reductions in computational time – up to 100 times speedup – are achieved in the present study, and possible also on a standard desktop computer equipped with a GPU

Thermo-mechanically coupled model of diffusionless phase transformation in austenitic steel

Abstract in UndeterminedA constitutive model of thermo-mechanically coupled finite strain plasticity considering martensitic phase transformation is presented. The model is formulated within a thermodynamic framework, giving a physically sound format where the thermodynamic mechanical and chemical forces that drive the phase transformation are conveniently identifiable. The phase fraction is treated through an internal variable approach and the first law of thermodynamics allows a consistent treatment of the internal heat generation due to dissipation of inelastic work. The model is calibrated against experimental data on a Ni-Cr steel of AISi304-type, allowing illustrative simulations to be performed. It becomes clear that the thermal effects considered in the present formulation have a significant impact on the material behavior. This is seen, not least, in the effects found on forming limit diagrams, also considered in the present paper

A constitutive model for the formation of martensite in austenitic steels under large strain plasticity

A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations is developed. The model takes basic thermodynamic relations as its starting point and the phase transition is treated through an internal variable (the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, along with the derivation of a consistent algorithmic tangent modulus. Simulations based on the presented model are shown to agree well with experimental findings. The proposed model provides a robust tool suitable for large-scale simulations of phase transformations in austenitic steels undergoingz extensive deformations, as is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process

Modeling of continuous dynamic recrystallization in commercial-purity aluminum

A constitutive model for polycrystalline metals is established within a micromechanical framework. The inelastic deformation is defined by the formation and annihilation of dislocations together with grain refinement due to continuous dynamic recrystallization. The recrystallization studied here occurs due to plastic deformation without the aid of elevated temperatures. The grain refinement also influences the evolution of the dislocation density since the recrystallization introduces a dynamic recovery as well as additional grain and subgrain boundaries, hindering the movement of dislocations through the material microstructure. In addition, motivated by experimental evidence, the rate dependence of the material is allowed to depend on the grain size. Introducing a varying grain size into the evolution of the dislocation density and in the rate dependence of the plastic deformation are believed to be important and novel features of the present model. The proposed constitutive model is implemented in a numerical scheme allowing calibration against experimental results, which is shown using commercial-purity aluminum as example material. The model is also employed in macroscale simulations of grain refinement in this material during extensive inelastic deformation. (C) 2009 Elsevier B.V. All rights reserved

Prediction of stored energy in polycrystalline materials during cyclic loading

AbstractThe effect of initial texture on the stored energy is investigated. Uniaxially loaded polycrystalline materials with initial textures based on the Goss component and the Brass component are analyzed. For reference purposes a single crystal and an initial isotropic crystal orientation distribution are also analyzed. Special attention is directed at the thermomechanical behavior of polycrystalline material during cyclic loading, the temperature evolution and change in stored energy are studied. Cyclic loading of Cook’s membrane is also considered. The simulations are done using a rate-dependent crystal plasticity model for large deformations formulated within a thermodynamic framework. It is shown that incorporation of the latent-hardening into the Helmholtz free energy function and use of evolution laws of appropriate form allows a thermodynamically consistent heat generation due to plastic work