基于CPRVE模型的304不锈钢极薄箔材参数标定

基于晶体塑性有限元方法 (CPFEM)结合形状因子与临界距离控制生成的三维晶体塑性代表体积单元(CPRVE)模型,模拟了304不锈钢极薄箔材的单轴拉伸过程。将代表性体积单元(RVE)模型的单轴拉伸结果与拉伸实验结果进行匹配,标定了304不锈钢极薄箔材的晶体塑性参数,分析了晶粒个数和晶粒内单元数对RVE模型的影响。结果表明,包含512个随机取向的晶粒,每个晶粒内约有125个单元的RVE模型可以准确地体现304不锈钢极薄箔材的宏观力学性能。使用标定的晶体塑性参数模拟单轴拉伸应变为0. 54时的织构演化,模拟结果与EBSD测得的织构演化结果相吻合,证明了标定的晶体塑性参数的准确性。     

耦合孪生的TWIP钢多晶体塑性变形行为研究

基于已建立的单晶体塑性模型,建立了耦合孪生的孪生诱发塑性(TWIP)钢多晶体塑性模型,该模型采用有限元多晶均匀化处理相邻晶粒间的几何协调和应力平衡条件,获得了单晶体与多晶体状态变量的关系,开发了基于ABAQUS/UMAT的计算程序.采用EBSD研究了TWIP钢拉伸应变分别为0.27和0.6时的织构变化,并对模型进行了应力应变及织构演化的验证.用该本构模型分别建立了拉伸、压缩和扭转3种简单加载条件下的有限元模型,分析了不同变形条件下的宏观力学响应及织构演化规律.结果表明:拉伸变形过程中,应变硬化现象和织构密度水平随应变增加而增强;在压缩过程中,织构类型随应变增加而发生变化,但是织构密度水平基本不变;而在扭转过程中,当扭转应变较小时,基本无织构形成,随着应变增加,织构逐渐显现出来,这是因为变形较小时,圆柱沿径向方向内部变形量较小,故织构不明显.     

基于晶体塑性有限元方法的不同变形状态下织构演化预测(英文)

提出一种以线性方程组为控制方程的显式晶体塑性模型。该模型可用高斯全主元消去法直接求解,无需任何迭代。提出基于晶体学坐标系的求解流程以减少由于变形中晶粒旋转而额外增加的计算量。建立晶体塑性有限元模型,并将预测结果与试验结果进行对比,验证该模型在织构演化预测方面的可靠性。该模型被用于预测不同变形状态下的织构演化,而这些不同的变形状态是通过调整Z和Y方向上的加载速度比(k)实现的。实验结果表明:该模型在织构演化预测方面是可靠的(在压缩、拉伸、简单剪切和平面应变压缩过程中的预测结果与试验吻合良好)和高效的(比隐式模型快 100 多倍);随着k值的增大,强织构由与法向(ND)成±35°角向{111}面上的丝织构转变,且织构强度增大;当应变速率在 0.1~100s 1之间增大时,织构强度迅速降低,而当应变速率在 100~7×104s 1之间增大时,织构强度缓慢减小,这表明该模型在模拟超高应变速率变形时也是数值稳定的。     

基于耦合有限元的晶体塑性力学模型的FCC,BCC和HCP晶体织构演化的模拟

介绍单晶体模型的2种实现方法,并通过对有限元软件ABAQUS/Explicit的用户材料接口VUMAT做二次开发,实现2种单晶体模型构架和显式有限元方法的耦合。采取实体单元来存储材料信息,每个单元代表一个晶粒,在每个增量步中读取并更新晶粒取向。采用切线系数法来计算每个增量步中不同变形系统的塑性应变增量,通过硬化模型来描述硬化响应。利用编制的2种用户子程序模拟铜（FCC）单向拉伸过程、IF铁（BCC）冷轧过程和AZ31 镁合金（HCP）单向压缩过程中的织构演化,模拟结果和试验结果吻合较好。     

基于多晶体塑性与唯象学本构模型的纯铝与单晶铝的有限变形分析与对比

多晶体塑性模型能够反映材料的微观结构和各种力学响应,但是模型复杂,本构积分计算量大,而唯象学弹塑性本构模型相对简单,但是基于变形率张量弹塑性加法分解的唯象学弹塑性本构模型又不能反映材料的微结构发展演化,在大变形时会产生差别。分别采用以上2种本构模型对纯铝和单晶铝的有限变形单向拉伸过程进行了计算分析,比较了2种模型在不同变形量下计算结果的差别。结果表明,纯铝唯象学弹塑性本构模型在真应变超过25.5%时,应力应变曲线开始出现差别,且随应变的增加而增大。多晶体塑性模型能够从变形、织构和残余应力等方面反映纯铝和单晶铝大变形产生的各向异性。     

拉拔过程中珠光体钢丝心部的织构演化规律及其对力学性能的影响

采用电子背散射衍射(EBSD)技术研究了拉拔过程中珠光体钢丝心部织构演变规律.结果表明,经过多道次干拉和淬火处理的钢丝存在强度较小的110丝织构,经过湿拉拔后,110丝织构强度明显增加.应用黏塑性自洽模型(VPSC),建立了拉拔过程中钢丝心部织构计算模型,预测了织构的演化规律,并用虚拟的单向拉伸实验研究了初始织构对力学行为的影响.预测结果与EBSD测试结果相符,随着拉拔应变的增加,晶粒的110取向逐渐转向拉拔方向.在拉拔方向上的反极图中,存在113和012连线上稳定的取向,靠近001和111连线上的取向先转向到稳定取向再转向110取向,其它取向直接转向110取向.随着拉拔应变增加110丝织构的体积分数逐渐增加,增加速率逐渐减小.随着初始110丝织构体积分数的增加钢丝心部的屈服应力逐渐增加.     

单晶纯钛的细观力学性能模拟

采用晶体塑性理论和有限元方法,建立描述密排六方结构(hcp)金属力学行为的细观数值本构模型,利用该模型对单晶纯钛在高温下的单向拉伸试验进行模拟。模拟结果和实验现象相吻合,显示了该模型的有效性。计算结果同时揭示了单晶纯钛变形过程中各个滑移系所起的作用,并对滑移系的运动和晶格转动等细观演化规律进行了分析。     

单向拉伸试验研究AZ31B镁合金板材的电塑性效应

通过单向拉伸试验研究镁合金 AZ31B 的电塑性效应。为了显示脉冲电流的非热效应,在相同温度下开展两类试验：环境箱中的单向拉伸试验和脉冲电流辅助的单向拉伸试验。此外,对脉冲电流在材料变形过程中引起的温度场进行数值模拟。结果表明,沿材料截面方向温度分布均匀。通过对比两类单向拉伸试验的真应力?真应变曲线,证实了脉冲电流非热效应的存在。通过光学显微镜研究脉冲电流对材料微观组织演化的影响,结果表明：脉冲电流引起的动态再结晶对流动应力的下降起重要作用。最后,提出一个考虑电塑性响应的 AZ31B 流动应力模型,并通过实验进行验证。结果表明：模型预测结果和实验结果吻合较好。     

单向拉伸试验研究AZ31B镁合金板材的电塑性效应（英文）

通过单向拉伸试验研究镁合金AZ31B的电塑性效应。为了显示脉冲电流的非热效应,在相同温度下开展两类试验:环境箱中的单向拉伸试验和脉冲电流辅助的单向拉伸试验。此外,对脉冲电流在材料变形过程中引起的温度场进行数值模拟。结果表明,沿材料截面方向温度分布均匀。通过对比两类单向拉伸试验的真应力-真应变曲线,证实了脉冲电流非热效应的存在。通过光学显微镜研究脉冲电流对材料微观组织演化的影响,结果表明:脉冲电流引起的动态再结晶对流动应力的下降起重要作用。最后,提出一个考虑电塑性响应的AZ31B流动应力模型,并通过实验进行验证。结果表明:模型预测结果和实验结果吻合较好。     

拉伸取向控制对AZ31镁合金孪生和织构演化的影响

以室温单轴拉伸实验与晶体塑性有限元相结合的方法,通过拉伸取向控制,研究了AZ31镁合金拉伸变形过程中孪生行为、织构演化规律、塑性各向异性之间的关系。基于率相关晶体塑性本构理论,建立了滑移和孪生机制耦合的具有不同取向的晶体塑性本构模型,引入孪晶体积分数研究孪生对AZ31镁合金塑性变形过程中织构演变和力学性能的影响。结果表明,2种不同取向的样品在塑性变形过程中呈现出明显不同的织构演变规律,表现出明显的各向异性。轴向拉伸时孪生被抑制,孪晶激活体积分数低,径向拉伸时孪晶极易产生,孪晶激活体积分数高。轴向试样在整个塑性变形过程中{0001}极图偏移较小,径向试样因大量拉伸孪晶的开启,使得{0001}棱柱面织构的极密度逐渐向RD的正反方向发生明显偏移。     

MICROSCOPIC ANALYSIS OF POLYCRYSTALLINE MATERIAL AT HIGH TEMPERATURE

The microscopic analyses of polycrystalline material at high temperature were carried out. The crystal plasticity model proposed by Asaro and Needleman was applied to a polycrystal model in the finite element simulation and the crystal slip system was randomly provided for each crystal. The grain boundary sliding, which was characteristic at high temperature, was also taken into account. It was shown that the inhomogencous deformation develops over the polycrystal and that the strain concentration appears around the triple point of crystal grain boundary.     

Computation of deformation-induced textures in electrodeposited nickel coating

The deformation-induced textures in electrodeposited nickel coating were numerically studied. The finite element method （FEM） for polycrystalline was developed based on Taylor model. Then the deformation-induced textures in electrodeposited nickel coating with initial random and lamellar texture were simulated under tensile load. It is found that the initial textures significantly influence the deformation-induced textures. For nickel coating with the initial random textures, when （he tensile strain is about 40%, there are some lamellar textures. For nickel coating with the initial lamellar textures, the lamellar texture is more intensity with the increase of the tensile strain. With the increase of the tensile strain in the coating, there are more pronounced element distortion and a more inhomogeneous deformation. Due to the different crystal orientations, the grain-scale roughness is observed. With increasing tensile strain in the coating, the surface grain-scale roughness increases on the flee surface. The surface roughness of the coating with initial random texture is lower than that with the initial lamellar texture.     

Simulation of polycrystalline aluminum tensile test with crystal plasticity finite element method

The crystal plasticity was implemented in the finite element method（FEM） software ABAQUS through the user subroutine UMAT. By means of discretizing the space at the grain level with the Voronoi diagram method, a polycrystal model was built and used in the FEM analysis. The initial orientation of each grain was generated based on the orientation distribution function（ODF）. The developed model was successfully applied in simulation of polycrystalline aluminium samples deformed by the tensile tests. The theoretical strain--stress relation was in good agreement with the experimental result. The simulation results show that the grain size has significant effect on the deformation behavior. The initial plastic deformation usually occurs at grain boundaries, and multiple slip often results in an enhanced local hardening at grain boundaries.     

应力状态对纯钛织构演化机制影响研究

采用拉伸、压缩的试验方法,结合Schmid因子计算和晶体塑性模拟计算研究了TA2纯钛在不同应力（拉应力、压应力）状态下织构的演化机制。结果表明：在拉伸变形过程中,较大的应变量也难以使织构发生显著变化,相对而言,压缩变形过程中织构变化较为显著。在不同应变路径下,变形初期启动的变形方式有一定的差异。在不同应变量下,随着变形程度的增加,发生基面滑移或锥面滑移或■拉伸孪生的晶粒数变多是导致形成不同织构的主要原因。     

Non-crystallographic shear banding in crystal plasticity FEM simulations: Example of texture evolution in α-brass

We present crystal plasticity finite element simulations of the texture evolution in α-brass polycrystals under plane strain compression. The novelty is a non-crystallographic shear band mechanism [Anand L, Su C. J Mech Phys Solids 2005;53:1362] that is incorporated into the constitutive model in addition to dislocation and twinning. Non-crystallographic deformation associated with shear banding leads to weaker copper and S texture components and to a stronger brass texture compared to simulations enabling slip and twinning only. The lattice rotation rates are reduced when shear banding occurs. This effect leads to a weaker copper component. Also, the initiation of shear banding promotes brass-type components. In summary the occurrence of non-crystallographic deformation through shear bands shifts face-centered-cubic deformation textures from the copper type to the brass type.     

Variational self-consistent estimates for texture evolution in viscoplastic polycrystals

The variational self-consistent (V-SC) method is presented for simulating texture evolution in viscoplastic polycrystals undergoing large deformation. The theory is based on a recent non-linear homogenization procedure which makes use of estimates of the self-consistent type for the instantaneous response of a suitably chosen “linear comparison polycrystal” to generate corresponding estimates for the non-linear viscoplastic polycrystal. Making use of consistent estimates for the average strain rate and spin in the grains of the polycrystal, and of standard kinematical arguments, evolution equations are derived for the crystallographic and morphological textures. Applications to titanium polycrystals under uniaxial tension, compression and plane-strain compression performed at 750 °C are presented. The texture predictions and macroscopic stress–strain responses are compared with those given by earlier models, and with finite element (FEM) simulations and experimental measurements taken from the literature. Better overall agreement with FEM simulations is obtained for the V-SC estimate than for the other models. However, the comparison with the experimental results is not as good, especially for plane-strain compression, where additional effects due to friction cannot be ruled out.     

On the dependence of in-grain subdivision and deformation texture of aluminum on grain interaction

We present plane strain simulations about the dependence of orientational in-grain subdivision and crystallographic deformation textures in aluminum polycrystals on grain interaction. The predictions are compared to experiments. For the simulations we use a crystal plasticity finite element and different polycrystal homogenization models. One set of finite element simulations is conducted by statistically varying the arrangement of the grains in a polycrystal. Each grain contains 8 integration points and has different neighbor grains in each simulation. The reorientation paths of the 8 integration points in each grain are sampled for the different polycrystal arrangements. For quantifying the influence of the grain neighborhood on subdivision and texture we use a mean orientation concept for the calculation of the orientation spread among the 8 originally identical in-grain orientation points after plastic straining. The results are compared to Taylor–Bishop–Hill-type and Sachs-type models which consider grain interaction on a statistical basis. The study reveals five important points about grain interaction. First, the consideration of local grain neighborhood has a significant influence on the reorientation of a grain (up to 20% in terms of its end orientation and its orientation density), but its own initial orientation is more important for its reorientation behavior than its grain neighborhood. Second, the sharpness of the deformation texture is affected by grain interaction leading to an overall weaker texture when compared to results obtained without interaction. Third, the in-grain subdivision of formerly homogeneous grains occurring during straining is strongly dependent on their initial orientation. For instance some crystals build up in-grain orientation changes of more than 20° after 95% straining while others do practically not subdivide. Fourth, the dependence of in-grain subdivision on the neighbor grains is different for crystals with different initial orientation (cube or rotated Goss grains reveal strong subdivision). Fifth, the upper bound for the variation of texture due to changes in grain neighborhood amounts at most to 5% in terms of the positions of the main texture components. In terms of the overall orientation density all predictions (using different neighborhood configurations) remain within a narrow tube with an orientation scatter of 10% (β-fiber) to 20% (Brass component, α-fiber)) when the neighborhood changes.