Study of fatigue and high strain rate behaviour of materials

早期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和财产损失。损坏可能是由于冲击或疲劳造成的。申请人研究了由于冲击或疲劳引起的材料损伤的定量评估和机制，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。塑性变形、断裂和疲劳裂纹的萌生和扩展可引起损伤。它也可能发生，因为在高应变率下的冲击，局部变形是由于绝热剪切带（asb）的形成。申请人开发了一个高应变率实验室，并研究了高强度合金和先进陶瓷。申请人拟进行以下研究：(1)对高应变率或低周疲劳冲击时变形机制的特征进行基础研究。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合作研究。(2) FCC金属中ASB的起始和永久滑移带疲劳的基础实验研究。(3)建立ASB在应变硬化和热软化过程中演化的弹塑性模型，并利用该模型预测材料在高应变速率下的性能。防止损害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）。同时，本研究将培养材料科学、建模与仿真、电子显微镜等领域的高素质人才。

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.