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Prof. Bi Zhang
Abstract: Material embrittlement is often encountered in machining, heat treatment, hydrogen and low-temperature conditions among which machining is strain-rate related. It can be a result of an enhanced strength and hardness, and a reduced fracture toughness of a material. Strain-rate evoked embrittlement can occur in a material subjected to high strain-rate loading (e.g., high-speed machining and projectile penetration). Loading to a material at a high strain rate (> 103 s-1) leads to material embrittlement which in turn contributes to the “skin effect” of material damage. This presentation is concerned with the strain-rate evoked material embrittlement and the “skin effect” of damage distribution in a material under high strain-rate loading. Empirical and physical models are compared for the assessment of the material embrittlement and damage. Strain-rate sensitivity is used to characterize material embrittlement and the concept of pseudo embrittlement is proposed for understanding material responses to extremely high strain rates. Material embrittlement and “skin effect” of damage are discussed in terms of dislocation kinetics and crack initiation and propagation. It provides guidance to predicting the material deformation and damage at a high strain-rate for applications ranging from the armor protection, quarrying, petroleum drilling, and high-speed machining of engineering materials (e.g., ceramics and SiC reinforced aluminum alloys).



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