Collaborative Research: Coupled Explicit Thermodynamics of Plasticity - An Innovative Model for Twinning Crystals

大多数金属材料本质上是多晶的，以单晶为基本构件的聚集体复合材料。金属材料通常由于原子键的扭曲而产生弹性变形，或者由于原子键的重排而产生塑性变形。塑性变形是通过位错运动和变形孪晶机制发生的。位错是受外加应力影响而移动的原子大小的特征，已经得到了比较充分的研究，并被许多先进的理论所描述。变形孪晶是单晶大小的特征，变形理论不能很好地理解或表示。该奖项支持变形孪晶的基础研究和克服这种塑性机制建模的局限性。新的知识和计算能力将广泛应用于先进制造、结构生存能力和运输。此外，该项目将支持在计算微观力学、材料科学和晶体塑性领域的研究生和本科生的教育。该奖项的合作性质也将为学生提供跨两个校区参与的机会。金属材料的塑性是由位错滑移和变形孪晶共同介导的。由于变形孪晶不能用体积平均值来表示，两种机制的特征长度差异限制了多晶塑性有限元模拟。这个项目的目标是开发一个基于嵌入式弱不连续技术的变形双胞胎显式表示的计算框架。嵌入的弱不连续是由单晶理论驱动的，单晶理论在一致的热力学和物理基础下解释了孪核、扩展和生长。位错滑移也将用热激活理论来表示，并允许滑移发生在孪晶和非孪晶区域。在孪晶生长阶段，位错与孪晶边界的相互作用也将被模拟。本项目将重点研究高纯钛的模型材料。验证实验将在大颗粒样品上进行，以便进行详细的表征。这些变形实验将在不同的初始温度下进行，并在变形过程中测量样品温度，以评估模型对Taylor-Quinney因子的预测。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Most metallic materials are polycrystalline in nature and behave as aggregate composites of single crystals as the basic building block. Metallic materials generally deform elastically by atomic bond distortion or plastically by atomic bond rearrangement. Plastic deformation takes place by the mechanisms of dislocation motion and deformation twinning. Dislocations are atom sized features which move by applied stress and have been relatively well studied and are described by many advanced theories. Deformation twins are single crystal sized features and are not well understood or represented by theories of deformation. This award supports fundamental study of deformation twinning and overcoming limitations to modeling of this plasticity mechanism. The new knowledge and computational capability will have a broad range of applications to advanced manufacturing, structure survivability, and transportation. In addition, the project will support the education of graduate and undergraduate students in the areas of computational micromechanics, materials science, and crystal plasticity. The collaborative nature of the award will also afford the students the opportunity to engage across the two campuses.Plasticity in metallic materials is mediated by both dislocation slip and deformation twinning. The disparity in characteristic length between the two mechanisms is a limitation to crystal plasticity finite element simulation of polycrystals as deformation twins cannot be represented by volume average. The objective of this project is to develop a computational framework for the explicit representation of deformation twins based upon an embedded weak discontinuity technique. The embedded weak discontinuity is driven by single crystal theory which accounts for twin nucleation, propagation, and growth within a consistent thermodynamic and physical basis. Dislocation slip will also be represented with a thermally activated based theory and will allow slip to occur in both twinned and untwinned regions. The interaction of dislocations with the twin boundaries will also be modelled during the twin growth phase. This project will focus upon the model material of high-purity titanium. Validation experiments will be conducted on large grain samples to allow for detailed characterization. These deformation experiments will be conducted at different initial temperatures and sample temperatures will be measured during deformation to evaluate the model prediction of the Taylor-Quinney factor.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.