率相关非比例循环塑性内时本构模型

将材料响应的总应力表示为平衡态应力和非平衡成过应力的和，分别定义描述率无关和率相关变形过程的内时，在平衡态响应的描写中，假定反映非比例加载效应的附加等等向强化和异向强化函数与沿应力迹法向的塑性应变分量的累积量相关，并在其中考虑加载路径几何性质变化的影响，建立一组率相关非比例循环塑性内时本构方程，对ＸＣｒＮｉ１８．９不锈钢在不同加载率下的单轴比例和多轴非比例响应进行预测，与Ｈａｕｐｔ和Ｌｉｏｎ的实验     

An endochronic constitutive model for rate-dependent and nonproportional cyclic plasticity

The total stress response of material is decomposed into a sum of an equilibrium stress response and a non-equilibrium overstress response. Correspondingly, the rate-independent intrinsic time and the rate-dependent intrinsic time are defined respectively. Additional hardening functions for describing the isotropic and anisotropic nonproportional effects are assumed to be related to the accumulation of plastic strain component along the normal of equilibrium stress trajectory, in which the effects of geometry of the loading path are included. An endochronic constitutive model for rate-dependent, nonproportional cyclic plasticity is formulated and applied to simulate the stress responses of stainless steel XCrNi18.9 for some typical loading programs at different loading rates. A comparison between predicted results and experimental ones by Haupt and Lion shows that the former are in agrreement with the latter.     

裂纹动态起始问题的研究进展

力图就前人提出的冲击载荷下裂纹的起始判据进行较全面的综述．这些较著名的判据有：（１）动态应力强度因子判据；（２）动态Ｊ积分判据；（３）最小作用量判据；（４）极小作用时间判据等．简要介绍了近年来有关裂纹在冲击载荷（特别是短脉冲）下动态起始的一些重要实验和实验中所发现的一些重要结论．实验公认，一般对于小范围屈服而言，材料的动态断裂韧性随加载（应变）率的提高而减小，此时材料的断裂形式为解理型；而对于大范围屈服则韧性随加载率的提高而增大，此时材料的断裂形式为纤维型．特别指出，Ｂｒｏｗｎ大学的平板撞击实验表明，裂纹在起始时，观察到一个不再满足二分之一阶奇异性的“尖峰”，按Ｃｌｉｆｔｏｎ和Ｆｒｅｕｎｄ等人所给出的模型，在裂纹起始断裂瞬间，在裂纹顶端会突然形成一个小洞，该洞的半径作为一个参数等于二相粒子的间距．