Effect of single initial overload and mean load on the low-cycle fatigue life of normalized 300 M alloy steel Cheek

In this work the effect of single overload and the resulting residual stress on the low-cycle fatigue life of 300 M alloy steel was experimentally investigated. Notched fatigue specimens were designed to localize the residual stress/strain and provide a known location for fatigue damage initiation. A common design assumption, whereby a residual stress is approximated as a mean stress was tested through comparing the fatigue life of specimens with residual stresses to the fatigue life of specimens with the same level of stress, except applied as a mean stress during testing. The residual stress was determined numerically through examining a finite element model of the test coupon. ABAQUS 2017x was used to generate the model and numerically solve the analysis. All simulations and tests were examined under quasi-static loading conditions. It was found that the residual stress generated by a single initial overload (tensile and compressive) had minimal effect on the low-cycle fatigue life of 300 M steel. The initial overload appeared to increase the life slightly. Moreover, it was shown that approximating the residual stress as a mean stress for calculating the expected life of a component is highly conservative with tensile residual stresses and highly non-conservative with compressive residual stresses when dealing with low-cycle fatigue.