Experimental investigation on the proper fatigue parameter of cyclically non-stabilized materials

Low-cycle fatigue tests were carried out in air in a wide temperature range from room temperature to 650°C to investigate the role of temperature on the low-cycle fatigue behavior of two types of stainless steels, cold-worked (CW) 316L austenitic stainless steel and 429 EM ferritic stainless steel. CW 316L stainless steel underwent additional hardening at room temperature and in 250-600°C: plasticity-induced martensite transformation at room temperature and dynamic strain aging in 250-600°C. As for 429 EM stainless steel, it underwent remarkable hardening in 200-400°C due to dynamic strain aging, resulting in a continuous increase in cyclic peak stress until failure. Three fatigue parameters, such as stress amplitude, plastic strain amplitude and plastic strain energy density, were evaluated. The results revealed that plastic strain energy density is nearly invariant through a whole life and, thus, recommended as a proper fatigue parameter for cyclically non-stabilized materials.