The relationship between striation spacing, macroscopic crack growth rate, and the low-cycle fatigue life of a Type 316 stainless steel at 625°C

Abstract

The fracture surfaces of smooth and notched Type 316 stainless steel specimens tested under essentially low-cycle fatigue conditions in air at 625°C and a cyclic frequency of one per minute have been examined under a scanning electron microscope. Observations from notched specimens indicate that for plastic strain ranges above the smooth specimen fatigue limit, macroscopic crack growth per cycle and striation spacing are in good agreement. Below this strain level, striation spacing exceeds macroscopic growth rate. Smooth specimen failure occurs by the initiation and propagation of one or more surface cracks. Striation spacing data from these specimens imply that low-cycle fatigue is dominated by the crack propagation process.