The significance of crack closure under high temperature fatigue crack growth with hold periods

A finite element model has been developed that simulates crack growth under time dependent loading conditions. The model accounts for the hold time and frequency effect under high temperature fatigue crack growth. Time dependent deformation due to creep modifies the crack tip stress-strain fields and crack tip displacements. As the creep strain rates increase, the crack opening displacement and effective stress range over which the crack is open increases. The effective stress range is strongly dependent on the creep constitutive relations and increases with hold period at maximum stress. The increase in effective stress range depends on the level of applied stresses relative to yield strength and is influenced by the sensitivity of creep strain rates on stress. The implications of crack closure results in describing high temperature fatigue crack growth rate data is outlined.