引言结构和机器的零件通常都是承受着三向应力的,但对处在这种复杂应力状态下的工程材料的性能却是知道得很少。为了提供一种能预测在复杂应力作用下的变形体性能的方法,曾根据承受简单应力作用下的材料的性能导出了弹性和塑性理论,并曾用一些二向应力试验的结果不断地加以修正。同样的途径也曾用于蠕滑和疲劳的机械性质。然而,就这一点点可用的知识,也已在许多情况下发现了在三向应力作用下的金属性能可能不同于分析理论的预测。例如,实验观察的结果指出,和现代的塑性理论的假说相反,金属塑性流动的性质肯定地受静水压分量大小的影响。此外又发现钢的疲劳强度由于静水拉伸(三向等拉)的作用 INTRODUCTION Structures and machine parts are usually subjected to three-dimensional stress, but little is known about the performance of engineering materials in such a complex state of stress. In order to provide a method that can predict the behavior of deformable bodies under complex stresses, the theory of elasticity and plasticity has been derived from the properties of the material subjected to simple stresses and has been constantly modified with the results of some of the two-direction stress tests . The same approach has also been used for the mechanical properties of creeping and fatigue. However, with this little knowledge available, it has also been found in many cases that the properties of metals under three-direction stress may be different from the predictions of analytical theory. For example, experimental observations indicate that, contrary to modern hypotheses of plastic theory, the nature of metal-plastic flow is positively influenced by the magnitude of the hydrostatic pressure component. In addition, it was found that the fatigue strength of steel due to the hydrostatic stretching (three to pull) role