Papers by Keyword: Crystal Plasticity

Abstract: Experimental and numerical investigations of the ridging in ferritic stainless steels were presented in this paper. Two kinds of ferritic stainless steels exhibiting different levels of ridging were selected as model materials. The measured roughness of the uniaxially elongated specimens up to 15% in rolling direction (RD) was compared to the prediction using a rate-dependent crystal plasticity FEM (CPFEM). Initial textures of the two materials on 5 equi-spaced sequential RD planes were obtained by EBSD measurement. The initial textures were utilized as input data for the constitutive parameters of the crystal plasticity. Measured respective single planar textures were collected all together so that the 5-layer textures complete 3-dimensional structure and they were mapped onto the FE mesh. Ridging profiles predicted by the CPFEM using both every single layer texture and multilayer texture were compared to the experimental results. Predicted ridging profile of a material exhibiting weak ridging by using 5-layer EBSD mapping was in good agreement with the experimental result. On the other hand, prediction by using only single layer texture was efficient to estimate the ridging in a material exhibiting severe ridging due to the elongated cluster of analogous orientations along RD.

Abstract: The paper considers physical approach to the description of inelastic deformation of two-phase polycrystalline materials – duplex steels. Such approach is based on the introduction the key mechanisms of inelastic deformation in explicit way. The main mechanism of plastic deformation is slipping of edge dislocations. The structure of duplex steel consists of austenite and ferrite phases. At high temperatures ferrite reveals dynamic recovery (DRV) and austenite ability to undergo dynamic recrystallization (DRX). The way to describe DRV and DRX processes within the multilevel approach of elastoviscoplastic modeling is proposed. Obtained results of numerical experiments of uniaxial compression deformation at different temperatures have good qualitative agreement with experimental data.

Abstract: This paper is devoted to one of the crystal plasticity physical theories for description of the crystalline solid behavior under high strains. The boundary value problem is formulated to consider uniaxial compression of aluminum single crystal. The numerical experiment data were obtained during the solving of this problem, which analysis shows good accordance with the full-scale experiment.

Abstract: The paper deals with three-level model of polycrystal inelasticity based on crystal plasticity. This model allows to regard the most important inelastic deformation mechanisms of polycrystals including grain boundary sliding. The inflow of intragranular dislocations, changing of the boundary structure under realization of grain boundary sliding and diffusion processes are taken into account in equations for grain boundary sliding. Consistency conditions of constitutive relations at the different scale levels are used in constructing model. The results of computational experiments under uniaxial tension of a representative volume are obtained with developed model. The results show that grain boundary sliding is important and must be taking into account.

Abstract: The problems related to the construction of multi-level mathematical models of inelastic deformation of crystalline materials based on crystal plasticity are considered. The example of the two-level model for description the severe plastic deformation of fcc polycrystals is discussed. The issues relating to the description of hardening and rotations of crystal lattices of the grains are discussed. The focus is on the formation of residual mesostresses in individual grains in the case of polycrystalline stress relief with a representative volume in general.

Abstract: A three-dimensional compression analysis is performed by finite element method using a dislocation-based crystal plasticity model to clarify the formation mechanism of kink band in a polycrystalline Mg alloy with a long-period stacking ordered structure (LPSO) phase. The crystalline structure of LPSO phase is regarded as a HCP for simplicity, however, any deformation twinning is not taken into account. In addition, the activities of non-basal systems are considerably limited in the LPSO phase setting the values of their critical resolved shear stresses to large ones. We analyze a simple polycrystalline specimen composed of two α-Mg matrix phases and a LPSO phase both having a rectangular shape and twist grain boundaries are introduced into the interface. The obtained result shows that the kink band formation in the alloy is accomplished by the basal slips with different variants and the non-basal slips are activated on the grain boundary to maintain the continuity of deformation.

Abstract: Plastic deformation and dislocations accumulation in a steel alloy dispersed with vanadium carbide particles is numerically analyzed by a crystal plasticity finite element technique and work hardening characteristics are discussed. Increment of dislocation density that contributes to work hardening is calculated from the mean free path of dislocations. The mean free path is defined by the spacing of forest dislocations and the average spacing of dispersed particles. Obtained yield stress and work hardening characteristics was close to that of experimental result, except that the value of work hardening rate was higher than that of experimental one.

Abstract: A coupled model based on crystal plasticity and phase field theories that express both plastic anisotropy of HCP metals and expansion/shrinkage of twin-bands is proposed in the present study. In this model, the difference of the hardening rate in each slip system is expressed by changing their dislocation mobility as a numerical parameter defined in the crystal plasticity framework. The stress calculated via crystal plasticity analysis becomes to the driving force of multi-phase filed equations that express the evolution of twin bands of several variants, which include both the growth and shrinkage. Solving this equation set, the rate of twinning/detwinning and the mirror-transformed crystal basis in the twinned/detwinned phase are obtained and then, crystal plasticity analysis is carried out again. Using the present model, a uniaxial cyclic loading simulation along [0001] direction on the specimen including two variants of twin-bands is carried out by means of finite element method (FEM). The results show that the detwinning stress decreases with increase of the pre-tensioned strain. This is caused by a residual compression stress resulting from the twin shearing that occurs in the vicinity of two twin boundaries approaching each other.

Abstract: In this study, a framework to predict the onset of plastic flow localization is introduced. The Marciniak-Kuczyński type approach, which is a classical method to predict the strain localization, and a crystal plasticity model with a homogenization-based finite element method are combined, and forming limit strains that are defined as the onset of plastic flow localization for FCC polycrystals are computed. The forming limit strains with several kinds of textures are evaluated with the present approach, and the results are compared with those obtained by the Taylor model, which is a widely used conventional polycrystalline model. Within the present application, the present method and the classical Taylor model give similar forming limit strains for FCC polycrystal sheets. According to the present results, the use of the Taylor model in the sheet necking analysis might be justified, at least for FCC polycrystal sheets with various textures.

Abstract: In numerical models based on the crystal plasticity theory, various rules are implemented to describe hardening on the slip system level. The rules used are often variations of the Mecking-Kocks law, where the statistically stored dislocation density is the single internal variable. The dislocation density evolution equation consists of two terms representing accumulation and annihilation of dislocations. The accumulation term depends on a scalar parameter and an interaction matrix, which describes the contribution of all slip systems to the accumulation of the dislocations on a given slip system. Physically this matrix represents the relative strength of various dislocation locks which form when dislocations from different slip systems interact. The numerical values of the elements of the interaction matrix are rather hard to establish, but this has been done experimentally for different alloys and also based on numerical simulations. The obtained values, found in literature, are very different from each other. We use some new experimental data in an attempt to establish the influence of the numerical values of the elements of the interaction matrix on the hardening of a polycrystal.