Investigation and Prediction of Onset of Plastic Instabilities and Flow local izations under Dynamic Loading Condition

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Instabilities and flow localization behaviors of materials subjected to dynamic loading have been investigated. In order to account for the material strain rate and temperature sensitivities,the constitutive equations of thermo elasto-viscoplastic version of J2 deformation theory and that derived from slip of single cristal are newly developed. An effective computational strategy has been proposed in the evaluation of stiffness matrices of finite element equation and this enables us to analyze complicate 2 and 3 dimensional flow localization processes with practically acceptable computing time.The computer simulation of thermo coupled flow localization of plane strain and three dimensional tension and compression of blocks clarified the effect of deformation rate, material strain rate sensitivity, thermal conductivity, and size of blocks on the onset of instability and flow localization. Furthermore, the onset of instabilities and growth of wrinkles of sheet metal during the press forming processes, fracture limit of composite cylinders , fracturing processes of voidematerials, and ductile fracturing processes of notched bodies are also investigated and the characteristics of deformation processes were clarified.