High Temperature Fretting Fatigue Properties of Silicon Nitride

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(1) A fretting fatigue test machine for ceramic materials was designed and fabricated to investigate the fretting fatigue properties of ceramic materials. Fretting occurred at the contact surface between the rectangular specimen which was maintained under static fatigue conditions and the cylindrical contact piece. The major factors which affect the fretting fatigue properties such as relative slip amplitude and contact load can be controlled and their values can be measured in the test machine.(2) Fretting significantly reduced static fatigue strength of silicon nitride. Fretting damage was observed on the contact surface under small relative slip amplitude which never produced fretting damage in the case of metallic materials. Since fretting cracks are initiated at a very carly stage of fatigue life, crack propagation life is dominant in fretting fatigue life.(3) Fretting fatigue strength of silicon nitride was not necessarily decreased with increasing the contact load(contact pressure), which is in contrast with the case of metallic materials. This contray behavior in ceramics is resulted from that the relative slip ampilitude between specimen and contact pad increases with decreasing the contact load.(4) Fretting fatigue strengh of silicon nitride is affected not only by frictional force but also by the condition of partial slip in the contact region, that is fretting wear behavior.(5) Fretting fatigue tests under static and cyclic loading conditions showed that the effect of cyclic loading on fretting fatigue strngth of silicon nitride was almost negligible, and fretting fatigue stenghts under two test conditions were indentical.