Study of fatigue and high strain rate behaviour of materials

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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.