Deformation Processing: Crystallographic Texture Evolution and Shear Band Formation

可加工性通常被定义为在特定的变形加工操作中可以达到的变形程度而不会失效。失效可能是与开裂或断裂有关的基本材料现象，但也可能是任何其他不希望出现的情况，例如缺少模具填充或表面光洁度差。影响材料可加工性的主要因素有：(1)应力、温度、应变、应变率、摩擦和传热边界条件等外部过程变量及其演变；(2)内部微观组织变量，如孔隙率、晶体织构、变形局部化及其演化，最终导致韧性破坏。虽然在变形处理过程中，人们已经对预测与孔隙度增长有关的缺陷的能力给予了相当大的关注，但在宏观数学模型中纳入其他重要微观结构特征的演变方面仍有许多工作要做。具体来说，需要考虑晶体织构和变形局部化和破坏的影响。本项目旨在开发准确的各向异性热弹粘塑性本构方程和计算程序，用于模拟和模拟面心立方和六边形封闭填充合金中由于晶体滑移和孪晶引起的非弹性变形。计算能力将有助于模拟由于晶体织构的演变而引起的各向异性的发展，以及在低和高同源温度下大变形时与局部剪切带相关的材料加工缺陷的发展。该数学模型对各种冷热变形加工操作的设计和分析是有用的。这样的模型将允许更快和更准确地设计工具和程序，形成金属零件。

Workability is often defined as the degree of deformation that can be achieved in a particular deformation processing operation without failure. Failure may be the basic material related phenomena of cracking or fracture, but it could also be any other undesirable condition, for example lack of die fill or poor surface finish. The major factors which influence the workability of a material are: (1) the external process variables of stress, temperature, strain, strain rate, frictional and heat transfer boundary conditions, and their evolution; and (2) the internal microstructural variables, for example porosity, crystallographic texture, deformation localization and their evolution culminating in ductile failure. While considerable attention has been paid to developing a capability for predicting defects associated with the growth of porosity in deformation processing operations, much remains to be done with regard to incorporating the evolution of other important microstructural features in macroscopic mathematical models. Specifically there is need for incorporating the effects due to crystallographic texture and deformation localization and failure. This project is to develop accurate anisotropic thermo- elastic-viscoplastic constitutive equations and computational procedures for modeling and simulation of inelastic deformations due to both crystallographic slip and twinning in face-centered cubic and hexagonal-closed packed alloys. The computational capability will be useful in simulating the development of anisotropy due to the evolution of crystallographic texture, and the development of material processing defects associated with localized shear bands at large deformations at both low and high homologous temperatures. The mathematical models should be useful in the design and analysis of a variety of cold and hot deformation processing operations. Such models will allow the faster and more accurate design of tools and procedures for forming metal parts.