FATIGUE DAMAGE IN 2-STEP LOADING OF 316L STEEL .1. EVOLUTION OF PERSISTENT SLIP BANDS

An experimental study of the surface evolution during controlled plast ic strain amplitude single-step and two-step loading tests reveals the important damage mechanisms for 316L stainless steel. In the first st age, the cyclic plastic strain is concentrated into persistent slip ba nds (PSBs) and a surface relief is formed consisting of extrusions and intrusions. The frequency of occurrence and the total density of PSBs has been assessed using systematic observations in a scanning electro n microscope. The relative volume occupied by PSBs determines the fati gue damage in this stage. Two-step loading has only a small effect on the PSB damage evolution and nearly equal saturated values (correspond ing to the applied plastic strain amplitude) were achieved in the sing le-step and the two-step loading investigations.