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，表现为作为基本构件的单晶的集合体复合材料。金属材料通常因原子键扭曲而发生弹性变形，或因原子键重排而发生塑性变形。塑性变形通过位错运动和形变孪生机制发生。位错是原子大小的特征，它在外加应力的作用下运动，已经得到了较好的研究，并被许多先进的理论所描述。形变孪晶是单晶大小的特征，不能很好地理解或用形变理论来表示。该奖项支持变形孪生的基础研究，并克服了对这种塑性机制建模的限制。新的知识和计算能力将在先进制造、结构生存能力和交通运输方面有广泛的应用。此外，该项目将支持研究生和本科生在计算微观力学、材料科学和晶体塑性领域的教育。该奖项的协作性也将为学生提供跨越两个校区的机会。金属材料的塑性是由位错滑移和变形孪生所调节的。这两种机制之间特征长度的差异是晶体塑性有限元模拟的一个限制，因为变形孪晶不能用体积平均来表示。这个项目的目标是开发一个基于嵌入的弱不连续技术的形变孪晶的显式表示的计算框架。嵌入的弱不连续性是由单晶理论驱动的，该理论解释了孪晶的形核、传播和生长在一致的热力学和物理基础上。位错滑移也将用基于热激活的理论来表示，并将允许在孪晶和非孪晶区域发生滑移。在孪晶生长阶段，位错与孪晶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本上进行，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，变形过程中将测量样本温度，以评估泰勒-昆尼因子的模型预测。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.