A Study on Fatigue Crack Propagation Behavior of Silicon Nitride Ceramics Using a Fracture Mechanics Fatigue Test

摘要

Fatigue crack propagation tests of silicon nitride were conducted under constant K_max and constant stress ratio R using double eccentric pulsating compressive loading at room temperature. The crack propagation rate da/dN could be expressed as a function of K(~a)_max·ΔK~(1-a). However, scatter due to bridging friction was observed in the diagram of da/dN versus K(~a)_max·ΔK~(1-a). The plotting of da/dN against ΔK_eff reduced the influence of bridging friction on the expression of crack propagation. Also, the plotting revealed that the crack propagtion under high K_max is caused by static fatigue and the propagation under lower K_max is by pure fatigue. From these observation, it is suggested that ΔK_eff defined as the range of stress intensity factor during crack opening is close to the range of stress intensity factor at crack tip K_tip.