Influences of wave form and compressive loads on the crack propagation behavior of sintered Si3N4 under cyclic loads.

In order to know the influences of load wave form and compressive loads on the crack propagation behavior of sintered Si3N4 under cyclic loads, the crack propagation rate was measured using compact tension specimens at room temperature. The main results obtained are as follows.(1) The influences of stress ratio and test frequency to the crack propagation behavior under sine wave form cyclic loads were equal to those under square wave form cyclic loads. (2) In the range of large KImax, the crack propagated nearly time dependently. In the range of small KImax, the crack propagated cycle dependently. (3) Crack closure phenomenon was observed using the unloading elastic compliance method. (4) The effective stress intensity factor range ΔKeff, together with KImax, can be a reasonable parameter to describe the crack propagation rate. (5) The compressive load crushed the debris, lowered the crack opening load and resulted in a large ΔKeff which promote the increase of the crack propagation rate.