Fatigue Crack Growth in Self-Reinforced Silicon Nitride Based Materials

摘要

Fatigue crack growth has been studied in two self reinforced silicon nitride based materials (Sm- SiAlON and GPS Si_3N_4) using indentation flexure method in four-point bending mode at room temperature under static and cyclic conditions. The method is simple, cost-effective, material and time saving and produces stable crack growth. However, the analysis requires the estimation of the residual stress intensity factors produced by the indentations and assumptions about the shape of the indentation flaws to calculate the applied stress intensity factors. It was found that crack growth resistance was lower under cyclic loading. This degradation was particularly dramatic in the case of the Si_3N_4 - the material with higher fracture toughness, which exhibits strong toughening produced by contact shielding. Crack growth parameters were calculated assuming a Paris' power law dependence. The crack growth mechanisms were identified using scanning electron microscope and have been correlated to the results of the fatigue tests.