A Fundamental Study of Localized Plastic Instabilities

局部塑性不稳定性的基础研究

• 批准号: 9021671
• 负责人: Sia Nemat-Nasser
• 金额: $ 56.56万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1991
• 资助国家: 美国
• 起止时间: 1991-07-01 至 1995-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9021671&HistoricalAwards=false
• 关键词: Fundamental; Study; Localized; Plastic; Instabilities

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.

本研究旨在对剪切带的形成和传播有一个基本的认识。所要研究的材料钛和铝合金在航空航天工业中具有重要意义，它们在塑性变形过程中会发生剪切局部化，这是一个重要的实际问题。对剪切带形成现象进行了系统、完整的实验和理论研究。这将导致剪切失稳的预测和控制，并建立其对广泛类别材料的强度和破坏模式的影响。将进行动态实验，以便在受控条件下产生剪切带。霍普金森杆实验技术将用于帽状和双缺口试件。霍普金森棒中的脉冲幅度和形状将会改变，以控制剪切带传播的程度。随后将进行包括光学显微镜、扫描显微镜和透射电子显微镜在内的微观结构表征。还将系统地研究受控高应变率变形阶段之后和宏观剪切局部化开始之前的微观组织，以确定哪些内部缺陷可以导致局部化的开始，并表征组织的演变。将检查剪切带尖端的微观结构，以确定剪切带延伸之前该区域的结构变化。