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

研究了材料在动载荷作用下的失稳和流动局部化行为。为了考虑材料的应变率和温度敏感性，本文建立了J2变形理论的热弹粘塑性本构方程和单晶滑移本构方程。本文提出了一种有效的有限元刚度矩阵计算方法，使我们能够在实际可接受的计算时间内分析复杂的二维和三维流动局部化过程.通过对块体平面应变和三维拉压热耦合流动局部化过程的计算机模拟，阐明了变形率、材料应变率敏感性、热导率和块体尺寸对不稳定性和流动局部化的影响。此外，还研究了板料在冲压成形过程中失稳的发生和起皱的扩展、复合材料圆柱体的断裂极限、空隙材料的断裂过程和缺口体的韧性断裂过程，阐明了变形过程的特点。

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.