Effect of high-amplitude loading on accumulated fatigue damage under variable-amplitude loading in 316 stainless steel

To investigate whether high-amplitude stress and cycle ratios affect cumulative fatigue damage below the fatigue limit in 316 stainless steel, fatigue tests were carried out under incorporating high- (fixed at 277 MPa) and low-amplitude stress in which high stress level was set higher than previous applied (fixed at 260 MPa) and low stresses were below the fatigue limit with varying cycle ratios. Cumulative fatigue damage values for various cycle ratios calculated via previously proposed approach are inaccurate, it indicates that both high-amplitude stress and cycle ratios affect cumulative fatigue damage below the fatigue limit. In additional, saturation cycles of low-amplitude stress in one test block which can contribute to fatigue damage effectively is less than previous value. Thus, a rational evaluative approach for predicting cumulative fatigue damage below the fatigue limit has been developed on the basis of incorporating high- and low-amplitude stress tests outcomes, whose accuracy has been proved by repeated four-step and random-amplitude stress tests.