Meso-Scale Plasticity and Deformation Processing

henry T. Y. Yang，加州大学圣巴巴拉分校，CASrinivasan Chandrasekar，普渡大学西拉菲特分校，INA最近“发现”了一种对中尺度（0.1-10 mm）塑性变形具有重要影响的现象，即应变梯度塑性，它指的是应变梯度对材料流动行为的集体影响。应变梯度塑性的发现源于测量，当与非均匀塑性变形相关的特征长度尺度较小时，材料在力学响应中表现出强烈的尺寸效应。探索了两种新的方法来估计存在应变梯度的金属和合金的流动应力-应变曲线。第一种方法是模拟和测量细观尺度压痕，研究硬度随压头尖角的变化。这种方法的一个独特的方面是使用锥形压头与不同的顶角施加一个广泛的，但控制，应变和应变梯度的范围在一个固体。第二种技术涉及准静态、中尺度加工中材料响应的研究，其中应变梯度甚至比压痕更强烈。在这里，细观加工是估计本构应力-应变曲线的工具。该研究旨在为中尺度塑性现象提供基本见解；开发和验证与变形处理相关的中尺度流动应力数据的估计技术；并生成详细的应力应变数据，用于材料加工操作的多尺度建模。这些应有助于发展可持续的材料加工系统，使其在生产高质量产品的同时能高效率地运作。

Meso-Scale Plasticity and Deformation ProcessingHenry T. Y. Yang, University of California, Santa Barbara, CASrinivasan Chandrasekar, Purdue University, West Lafayette, INA recently 'discovered' phenomenon with important consequences for plastic deformation at the meso-scale (0.1-10 mm) is strain gradient plasticity, which refers to the collective effects of strain gradient on flow behavior of materials. The discovery of strain gradient plasticity has its origins in measurements, which show that materials display strong size effects in their mechanical response when the characteristic length scale associated with non-uniform plastic deformation is small. Two novel techniques are explored for estimating the flow stress-strain curves of metals and alloys in the presence of strain gradients. The first of these involves simulation and measurement of meso-scale indentation to study the variation of hardness with indenter apical angle. A unique aspect of this approach is the use of cone indenters with different apical angles to impose a wide, but controlled, range of strains and strain gradients in a solid. The second technique involves a study of material response in quasi-static, meso-scale machining where strain gradients are even more intense than in indentation. Here, meso-scale machining is a vehicle for estimating the constitutive stress-strain curve. The research is intended to provide fundamental insights into meso-scale plasticity phenomena; develop and validate techniques for estimating meso-scale flow stress data of relevance to deformation processing; and generate detailed stress-strain data for multi-scale modeling of materials processing operations. These should facilitate the development of sustainable materials processing systems that operate at a high level of efficiency, while creating products of enhanced quality.