Papers by Keyword: Crystal Plasticity

Abstract: Kink-strengthening for mille-feuille structures has attracted many attentions in recent years. This study aims at identifying the kink formation/strengthening mechanisms via numerical reproductions of emerging kink-like morphologies based on FTMP (Field Theory of Multiscale Plasticity)-incorporated FE simulations, considering the Rank1 connection, where the incompatibility-based relevant underlying microscopic degrees of freedom for kinking are introduced. The targeted phenomena here include an experimentally-observed unique feature recently reported based on the combined ND–AE (neutron diffraction - acoustic emission) technique, i.e., scale-free-like energy release before (precursor) and during kink formations. This study uses a Mg single crystal model with alternatingly aligned soft and hard layers in parallel to the basal plane under c-axis plane-strain compression, where the soft/hard regions are controlled by the values of the hardening ratio. Also, we assume that the kink mode is only active, while the basal, prismatic and pyramidal slip and the twin systems are not operative associated with the layered structure. From the simulated results, we confirm kink-like morphologies and the attendant significant misorientation in the basal plane angles. Also, the simulated results are demonstrated to exhibit power-law type distributions in the strain energy fluctuation from the early stage of deformation even before the massive emergence of kink-like regions, which are analogous to the above-mentioned ND–AE observations.

Abstract: High strength can be achieved by severe plastic deformation but at the cost of ductility. A novel strategy, which named multiple surface rolling was applied on a homogeneous annealed pure copper to break the strength and ductility trade-off. A combination of high strength and acceptable ductility was achieved in copper strips after submitted to multiple surface rolling. The detail microstructure evolution rolled samples were characterized by EBSD observation and compared with the initially annealed ones. The average grain size does not show significant deviation in both initially annealed and multiple surfaces rolled copper. Detailed observations show a heterogeneous distribution of low angle grain boundaries through thickness direction. The low angle grain boundaries and misorientations revealed the potential strengthening mechanisms in the material. Both microstructural characterization and numerical simulations indicate that multiple surface rolling contributes to strain hardening at the sample surface, while the interior layer was undergoing elastic deformation or partial plastic deformation. This heterogeneous deformation renders copper sheet with a combination of high strength and ductility.

Abstract: Crystal plasticity deformation of aluminium plays an important role on the investigation of macro deformation. In this paper, to discuss the effect ot crystal plasticity on the aluminium material behavior, crystal plasticity theory and macro finite element was combined together. The basic theory of crystal plasticity and finite element was introduce and the simulation result of aluminium was given. The stress and strain distribution was discussed and the efficient of the method was shown. It is shown that the orientation of the material and other micro character of the materials all influence the plasticity behavior of the material greatly.

Abstract: In the plastic deformation of hexagonal metals, deformation twinning plays an important role as well as slip deformation. Therefore, a modelling of deformation twinning is essential in the crystal plasticity modeling. In this study, a model considering the volume fraction of deformation twinning is presented in the framework of crystal plasticity, and it is combined with a finite element-based homogenization scheme to represent the polycrystalline behavior. The presented model is adopted to a sheet necking formulation. Plastic flow behaviors under several strain paths are evaluated using the present framework, and the effect of volume fraction of deformation twinning on the formability of hexagonal metal is discussed.

Abstract: TRIP steel shows excellent mechanical properties such as greatly high strength, ductility and toughness by means of the appropriate combination of the strain-induced martensitic transformation (SIMT) behavior and the deformation behavior of each phase at crystal scale. In the past, the effect of grain size in the austenite on the deformation behavior of TRIP steel is investigated by introducing the grain size into a generalized model for the kinetics of SIMT. In order to validate the size-dependent kinetics modelling, it is necessary to simulate the deformation and SIMT behavior of the polycrystalline for the different grain size at the crystal scale. This study focuses on an investigation of SIMT behavior in polycrystalline TRIP steel by finite element simulation. The constitutive formula for monocrystalline TRIP steel including transformation strain in each variant system derived on the basis of the continuum crystal plasticity theory is applied. For the polycrystalline model, Voronoi tessellation is employed. The deformation behavior with a patterning process of martensitic phase in two different numbers of grains with initial crystal orientations for describing the deformation-related length scale is simulated under plane strain condition with two planar slip systems by a cellular automata approach.

Abstract: The typical textures developed in aluminium alloys for deep drawing applications are less favourable as those in competing steel sheet material. The {111} fibre texture in steel, associated to high r-values, is favourable to this purpose, but the typical textures of the aluminium materials, the {001}<100> "cube" texture component and the β-fibre component, are not. Asymmetric rolling (ASR) as part of the production process generates a shear component at the expense of the unfavourable components. Modelling was tried out as a possible tool to fine-tune the process parameters. A multiscale FEM model (with a built-in polycrystal deformation model to predict the texture) was used to this purpose. The effect of the shear component on the resulting texture is discussed in function of the values of the process variables, as well as its effect on the resulting plastic anisotropy parameters (r and q values).

Abstract: The effect of the activated slip systems on the temperature dependence of yield stress was investigated in α-Ti by using crystal plasticity finite element method. A model for finite element analysis (FEA) was constructed based on experimental results. The displacement in FEA was applied up to the nominal strain of 4% which is the same strain as the experimental one. Stress-strain curves were obtained, which corresponds to experimental data taken every 50 K between 73 K and 673 K. The used material constants which are temperature dependent were elastic constants, and lattice friction stresses. The lattice friction stresses of basal slip systems were set to be higher than that of pyramidal slip systems at 73 K. Then, the lattice friction stresses were set to be closer as the temperature increases. It was found that the activation of slip systems is strong temperature dependent, and that the yield stress depends on the number of active slip systems.

Abstract: In this study, yield surfaces of austenitic stainless steel produced by a cold-rolling process are measured using uniaxial and biaxial tensile tests. Using results obtained by electron backscatter diffraction, information on crystal orientation is introduced into a computational model for a multiscale crystal plasticity simulation. Finite element simulations for polycrystal of fine-grained austenitic stainless steel under biaxial tension are performed in order to predict yield surfaces of fine-grained austenitic stainless steel. Validity of predicted yield surfaces is evaluated by comparison between yield surfaces obtained by numerical simulations and experimental tensile tests.

Abstract: This paper presents the results of the numerical multi-axial material tests for predicting elastoplastic deformation behavior of aluminum alloy sheets under equi-biaxial tension and in-plane tension-compression stress states. In this study, we have performed the numerical biaxial tensile and tension-compression tests of a 5000-series aluminum alloy sheet using the crystal plasticity finite element method based on the mathematical homogenization method which has been developed by the previous studies. We found that the true stress-logarithmic plastic strain (SS) curves calculated by the numerical biaxial tensile test slightly deviate from those measured by the biaxial tensile tests using a cruciform specimen. On the other hand, the results of the numerical tension-compression test demonstrated that the predicted SS curves shows a reasonable agreement with those obtained by the experiment using the biaxial stress-testing machine with comb-shaped dies.

Abstract: In this paper, strain gradient plasticity theory is extended to include the corner-like effect that is inherent in crystal plasticity. The predictive feature of the extended theory is examined via finite element analysis of a constrained simple shear problem and a plane-strain tension problem involving plastic flow localization. Numerical issues with respect to finite element formulations are also discussed.