A Fundamental Study of Localized Plastic Instabilities

研究的目的是对剪切带的产生和传播有一个基本的认识。将要研究的材料是钛和铝合金，它们在航空航天工业中具有重要意义；它们在塑性变形过程中发生剪切局部化，这是一个重要的实际问题。对剪切带形成现象进行系统、综合的实验和理论研究。这将导致剪切失稳的预测和控制，并建立其对强度和破坏模式的影响，广泛的一类材料。将进行动态实验，以便在受控条件下产生剪切带。帽形和双缺口试样均采用霍普金森杆实验技术。脉冲振幅和形状在霍普金森酒吧将改变，以控制剪切带传播的程度。接下来是显微结构表征，包括光学、扫描和透射电子显微镜。在受控的高应变速率变形阶段和宏观剪切局部化开始之前的微观结构，也将被系统地研究，以确定哪些内部缺陷可以导致局部化的开始，并表征微观结构的演变。为了确定剪切带延伸之前该区域的结构变化，将对剪切带尖端的微观结构进行检查。

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.