A Fundamental Study of Localized Plastic Instabilities

研究的目的是从根本上了解 剪切带的产生和扩展。 这些材料将 钛合金和铝合金的研究具有重要意义 在航空航天工业中;它们在过程中经历剪切局部化 塑性变形，这是一个重要的实际问题。 系统的、综合的实验和理论 剪切带形成现象的研究将是 贯彻 这将导致剪切的预测和控制 不稳定性及其对强度的影响 和一大类材料的失效模式。 动态 将进行实验，以产生剪切带 在受控条件下。 霍普金森杆实验 技术将用于帽形和双缺口 标本 霍普金森杆中的脉冲幅度和形状将是 改变以控制剪切带传播的程度。 这将 随后进行涉及光学， 扫描和透射电子显微镜。 微观结构 在受控的高应变速率变形阶段之后和在 宏观剪切局部化的开始，也将 系统地调查，以确定哪些内部 缺陷可能导致本地化的启动， 表征微观结构演化。 处的微观结构 将检查剪切带的尖端，以确定 剪切带伸展前该区的结构变化。

The research aims at developing a fundamental understanding of shear-band initiation and propagation. The materials that will be investigated, titanium and aluminum alloys, have great importance in the aerospace industry; they undergo shear localization during plastic deformation and this is an important practical problem. Systematic and integrated experimental and theoretical investigation of the phenomenon of shear-band formation will be carried out. This will lead to the prediction and control of shear instability and to the establishment of its effect on the strength and failure modes of a broad class of materials. Dynamic experiments will be performed, in order to generate shear bands under controlled conditions. The Hopkinson bar experimental technique will be used with both hat-shaped and double-notched specimens. Pulse amplitude and shape in the Hopkinson bar will be varied to control the extent of shear-band propagation. This will be followed by microstructural characterization involving optical, scanning, and transmission electron microscopy. The microstructure after controlled high-strain-rate deformation stages and prior to the onset of macroscopic shear localization, will also be systematically investigated in order to establish which internal defects can lead to the initiation of localization and to characterize the microstructural evolution. The microstructure at the tip of the shear band will be examined in order to establish the structural changes in this zone prior to shear band extension.