Study of fatigue and high strain rate behaviour of materials

及早发现结构和部件的损坏和故障有助于防止灾难性故障和可能的生命财产损失。损坏可能是由于撞击或疲劳造成的。申请人研究了有关材料因冲击或疲劳造成的定量评估和破坏机制，范围从纯金属到工业和航空航天合金，以及最近的陶瓷和金属基复合材料。损伤可以通过塑性变形、断裂和疲劳裂纹的萌生和扩展来发生。它也可以发生在高应变率下的冲击，其中局部变形是由于形成绝热剪切带(ASB)。申请人开发了一个高应变率实验室，并检查了高强度合金和先进陶瓷。申请人建议开展以下研究：(1)关于高应变率冲击或低周疲劳过程中变形机制特征的基础研究。这些研究将使用先进的技术，包括分析扫描和透射电子显微镜、原子力显微镜和场离子束。建议与牛津大学和马里兰大学进行合作研究。(2)面心立方金属ASB和疲劳永久滑移带萌生的基础实验研究。(3)建立了ASB在应变硬化和热软化过程中的弹塑性演化模型，并用该模型预测了材料在高应变率下的性能。防止破坏将为加拿大经济节省大量资金，并可能挽救生命(如在军事应用中)。此外，这项研究还将培养材料科学、建模、模拟和电子显微镜领域的高素质人才。

Early detection of damage and failure of structures and components helps prevent catastrophic failure and possible loss of life and propery. Damage may occur either by impact or by fatigue. The applicant has studied quantitative evaluation and mechanisms of damage of materials of interest due to impact or fatigue, ranging from pure metals to industrial and aerospace alloys as well as, more recently, ceramics and metal matrix composites. Damage could occur by plastic deformation, fracture and fatigue crack initiation and propagation. It can also occur because of impact at high strain rates where localized deformation is due to formation of adiabatic shear bands (ASBs). The applicant has developed a high strain rate laboratory and has examined high strength alloys as well as advanced ceramics. The applicant proposes to perform the following research: (1) Fundamental studies on characterization of the mechanisms of deformation during either impact at high strain rates or in low-cycle fatigue. Advanced techniques including analytical scanning and transmission electron microscopy, atomic force microscopy and field ion beam will be used for these studies. Collaborative studies with Oxford University and the University of Maryland are proposed. (2) Fundamental experimental studies on initiation of ASB's in FCC metals and of permanent slip bands in fatigue. (3) Development of elastic-plastic models for evolution of ASB's as a result of strain hardening and thermal softening and use this model to predict the performance of materials at high strain rates. Preventing damage will result in large savings for the Canadian economy as well as possibly saving lives (as in military applications). Also, this research will train highly qualified personnel in the fields of materials science, modelling, and simulation and electron microscopy.