High temperature crack growth behavior of 304 stainless steel under creep and fatigue loading

Abstract

The crack growth behavior in a 304 stainless steel has been investigated at 538 degrees C in air environment. Compact tension specimens were subjected to fatigue, creep and creep-fatigue loading. The combined effects on crack growth rates of load level and hold time have been examined. Stress intensity factors are found to correlate crack growth rates reasonably well for fatigue crack growth. Creep crack growth rates are found to correlate with stress intensity factor and C*(t). Crack growth rates under hold time cycles are successfully correlated with C*(t)avg under various load levels and hold times. Crack growth under creep-fatigue loading has been simulated by elastic-plastic-steady state creep finite element analyses. The results of analysis show that fatigue loading interrupts stress relaxation around the crack tip during hold time and causes stress reinstatement, thereby giving rise to accelerated crack growth compared with crack growth under static loading. Analysis of hold time crack growth based on the cyclic stress-strain response yields crack closure during unloading, and creep deformation during hold time tends to lower the closure load.