The near crack line analysis method is used to investigate a center crack loaded by two pairs of point tensile forces in an infinite plate in an elastic-perfectly plastic solid, and the analytical solutions are obtained in this paper. These solutions include: the elastic-plastic stress field near the crack line, the law that the length of the plastic zone along the crack line is varied with an external loads and the bearing capacity of an infinite plate with a center crack. The results of this paper are sufficiently precise near the crack line because the assumptions of the small scale yielding theory have not been used and no other assumptions have been taken.

Stress redistribution induced by excavation results in the tensile zone in parts of the surrounding rock mass. It is significant to analyze the localization of deformation and damage, and to study the complete stress-strain relation for mesoscopic heterogeneous rock under dynamic uniaxial tensile loading. On the basis of micromechanics, the complete stress-strain relation including linear elasticity, nonlinear hardening, rapid stress drop and strain softening is obtained. The behaviors of rapid stress drop and strain softening are due to localization of deformation and damage. The constitutive model, which analyze localization of deformation and damage, is distinct from the conventional model. Theoretical predictions have shown to consistent with the experimental results.

It is of important significance to study the coalescence mechanism of splitting failure of crack-weakened rock masses under compressive loads. In this paper, a simplified mechanism of crack propagation, in which the crack grows along the direction of maximum principal compressive stress, is proposed. Thus, only mode I is taken into account in the formulation and solution. On the basis of the near crack line analysis method, the elastic-plastic stress field near the crack line is analyzed, and the law that the length of the plastic zone along the crack line is varied with an external loads have been established by the matching condition of the elastic-plastic fields on the boundary, the coalescence stress and the strength properties of rock masses have been determined. The solution is a function of the geometry of the crack array. The results show that the crack coalescence depends on the crack interface friction coefficient, the sliding crack spacing, orientation of the cracks, and the crack half-length. The conclusions are of important significance for rock mass engineering.

Many experimental results show that a wide class of ductile materials obey often nonlinear behavior. thus it is im portant to propose a nonlinear criterion describing nonlinear behavior of ductile m ateria1. A new non-linear yield criterion was proposed which gives a series of new failure criteria, establishes a relationship among var-ious failure criteria, and encom passes previous yield criteria as special cases or approximations. The criterion is ca-pable of being expressed in a sim ple m athem atical expression and through a particular physical concept, it also agree with some experimental data. It may therefore serve as a possible admissible isotropic yield criterion.

研究了中低围压条件下细观非均匀性岩石的变形局部化问题和全过程应力应变关系。研究表明，全过程应力应变关系包括线弹性阶段、非线性强化阶段和应变软化阶段。分析了产生应变软化的主要原因是损伤和变形局部化，将损伤和变形局部化引入本构模型是和以往本构模型的重要区别。通过和实验对比分析验证了模型的正确性和有效性。