Elastic-Plastic Fracture Mechanics Study of Tribology Problems.

采用体积力法（BFM）和有限元法（FEM）相结合的方法（BFM+FEM），分析了滚动-滑动循环接触载荷作用下次表层的弹塑性行为。数值计算得到的前向流动量与中碳钢的实验测量值之间的比较表明，在循环接触载荷下的材料服从各向同性硬化规则（IHR）和运动硬化规则（KHR）的中间作用。为了研究润滑滚动-滑动接触表面裂纹、凹坑和层裂的扩展机理，开发了曲面和交叉面裂纹的计算程序。在数值分析中，考虑了表面粗糙度引起的非赫兹载荷。考虑裂纹起裂和扩展分析的结果，结果表明，在润滑轧制条件下，裂纹扩展条件比裂纹萌生条件对凹坑的形成更为重要。指出了Ⅱ型裂纹扩展在裂纹扩展早期阶段的重要性，提出了一种新的测量剪切型疲劳裂纹扩展门槛应力强度因子范围Δ Ktau_的实验方法<th>。

The elastic-plastic behavior of the subsurface layer under cyclic rolling-sliding contact loading is analyzed by the combination method (BFM+FEM) of the body force method(BFM) and the finite element method(FEM). Comparison between the amount of forward flow obtained numerically and the experimental measurements on a medium carbon steel shows that the material under the cyclic contact loading obeys the intermediate role of the isotropic hardening rule(IHR) and the kinematic hardening rule(KHR). The residual stresses and incremental cyclic plastic strains are also analyzed to investigate the easiness of crack initiation for driver and follower surface.In order to study the growth mechanism of surface crack ; pits and spall, on lubricated rolling-sliding contact surface, comouting programs for the analysis of cracks with curved and crossed planes were developed. In the numerical analysis, the Non-Hertzian loadings caused by surface roughness were considered. The effects of the contact of crack surfaces and friction between crack surfaces under compressive loading were also investigated.Considering the results of the crack initiation and growth analysis, it is concluded that the crack propagation condition is more crucial than the crack initiation condition as the cause of a pit formation under lubricated rolling-sliding contact loading.The importance of the mode II type crack growth in the early stage of crack propagation was pointed out and a new experimental method to measure the threshold stress intensity factor range for shear mode fatigue crack growth DELTAKtau_<th> was proposed.