Application of Fracture Mechanics to Micro and/or Macro Tribology Problem

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(1) Relationship between the temperature distribution and fatigue damage on a contact surface is investigated by an infrared thermography temperature measuring system. Although the sum of principal stresses, i.e.the first invariant of stress, on the contact surface is obtained using a thermography stress analyzer, it has not been thought that stress components can be resolved from the first invariant of stress. The head investigator theoretically constructs the basic conditions for the resolution of stress components and develops the technique to obtain the stress field in almost all practical cases where the first invariant of stress can be measured by a thermography stress analyzer.(2) Under heavy repeated rolling and/or sliding contact load, fatigue cracks grow in Mode II to a large extent. However, since it is very difficult to reproduce Mode II fatigue crack growth in a laboratory test, the threshold stress intensity factor range for Mode II of hard steels such as bearing steels, gear steels and roll steels has not been obtained. In this research, the new method to measure the threshold stress intensity factor range for Mode II of even hard steels in developed and ranges of bearing steels, gear steels and roll steels are measured. Consequently, it is made clear that the threshold stress intensity factor range for Mode II is larger than that for Mode I.(3) In order to elucidate the mechanism of contact fatigue in ceramics, which are expected to be used in severe conditions such as vacuum and/or high temperature, a fatigue test system of a ball-on-plate sliding contact is developed. The crack propagation from a preindentation of a Si_3N_4 plate is carefully observed and the crack growth behavior is analyzed by calculating the stress field under a ball-on-plate sliding contact.