STUDY ON MECHANISM OF MICROSCOPIC FAILURE OF ROUGH SURFACE UNDER REPETITIVE CONTACT STRESS

首先，作为理论研究，本文提出了一种计算具有表面粗糙度的宏观二维几何体中粗糙面接触附近的三维应力场的方法。将该方法应用于用体力法计算韧性表面滚动接触裂纹的应力强度因子时，考虑了裂纹面间存在粘结和滑移的条件，使裂纹面间的摩擦阻力保持不变。和。结果表明，裂纹面间的摩擦通过裂纹面的粘结降低了应力强度因子，而渗油引起的摩擦力的减小加速了裂纹的扩展。考虑表面粗糙度的应力强度因子为微裂纹扩展提供了一个足够大的数值，解释了低速移动表面容易产生点蚀，而高速移动表面不容易产生点蚀的事实。在实验研究中，进行了重复压缩试验、双辊试验、微动试验。在重复压缩试验中，滚子表面经过小角度旋转后被重复压缩到平坦的表面，同时表面被分离。在与滚动接触点蚀极限相当的载荷条件下，在10万次循环内观察到平板表面的大量裂纹。通过对滚动-滑动接触过程中点蚀裂纹的连续观察，阐明了点蚀初始裂纹是在与配合辊粗糙度铺设方向相对应的方向上出现的。在所有这些实验中，都观察到了粗糙接触区的大小与失效规模之间的明显关系。这些研究人员希望进一步研究，以便理论研究的预测将得到实验的证实。

At first as a theoretical study, a method of calculation of 3-dimensional stress fields near the asperity contacts which whould be caused in macroscopically 2-dimensional geometry bodies having surface roughness, was developed in this study. This method was applied to calculate stress intensity factors of cracks by body force method in rolling contacts of tough surfaces, taking into consideration of existence of sticking and slipping conditions for the sake of frictional resistance between crack-faces when compressional forces remain. And. it was shown that the friction between crack-faces decrease stress intensity factors by the sticking of crack-faces and a decrease in friction by oil-penetration into the crack accelerates the propagation of crack. The stress intensity factor, which was calculated taking into consideration of surface roughness, becomes a enough value for the propagation of micro-crack and explains the fact that pittings apt to be caused on the surface moving with lower speed, but not to be caused on the surface moving with higher speed. In expermental studies, repetitive compression tests, two-roller tests, fretting tests were conducted. In repetitive compression tests, a roller surface was repetitively compressed to a flat surface after a small angle rotation while surfaces was separated. and numerous cracks in the flat surface were observed within a hundred thousand cycles, under a comparable load condition with pittings limits in rolling contact. By a successive observation of pitting cracks in rolling-sliding contact, it was elucidated that initial cracks of pitting made their appearance in the direction corresponding to the roughness lay direction of mating roller. A clear relationship between the largeness of asperity contact regions and the scale of failure was observed in all those experiments. These investigators wish to study further so that predictions by theoretical study will be confirmed by experiments.