Crack Propagation Behavior of Sintered Silicon Nitride under Cyclic Loads : Influence of Difference in Material

Abstract

The crack propagation behavior under cyclic load was investigated on two types of sintered Si₃N₄. The main results obtained are as follows. (1) The crack propagation rate was accelerated by cycling the load. As the stress ratio decreased or the test frequency increased, the crack propagation rate increased. (2) If the fracture toughness of a specimen was high, the crack propagation rate was low as compared with that of another specimen with low fracture toughness. (3) Debris of the fractured grains and wear mark were left on the fracture surface under the cyclic loads. (4) By measuring the crack opening displacement, crack closure was observed. The size of the debris (∼1μm) on a fracture surface under cyclic load was nearly equal to the crack opening displacement at no load. It was concluded that the crack closure of sintered Si₃N₄ was induced by debris between the crack surface.