マイクロピッチングの発生機構に関する考察

抄録

In earlier report, the authors carried out surface durability test with carburized steel roller and carburized steel roller with shot peened by two different methods. After examination, some micropitting were observed on contact surface. In this study, we clarified the generation mechanism of micropitting by measuring the geometry of micropitting in detail. The object of the geometry measurement is width and maximum depth of micropitting, and an angle that contact surface and crack formed. According to measurement result, the maximum depth of micropitting was considerably shallower than the maximum shearing stress depth that predicted by cylinder to cylinder contact of test rollers. Further, a strong correlation between the maximum depth of micropitting and the damage width along tool mark was confirmed. Also, the damage width that vertical direction to tool marks was depending on tool mark width which increases along with the contact load. It is thought that micropitting was caused by asperity contact of contact surface after running-in process. Shapes in the radius of curvature of contact asperity were estimated by measurements of micropitting width and depth. The stress analysis was carried out for obtained asperity shape, and stress direction was calculated. Then, the stress that caused micropitting was determined by comparing stress direction and crack propagation angle. As a result, micropitting was caused by maximum shearing stress that increases with high friction coefficient.