Separating plasticity-induced closure and residual stress contributions to fatigue crack retardation following an overload

摘要: Abstract The introduction of an overload or underload within a constant amplitude loading fatigue test leads to retardation acceleration the Fatigue Crack Growth Rate (FCGR). understanding causes these effects is essential in context variable loading, since principle any history can be represented as sequence overloads and underloads. In case overload, along with some other minor causes, residual stress changes at crack tip closure behind thought main factors that affect growth rate. Whilst this has been recognised accepted for many decades, controversy persists regarding relative significance presence two effects, consensus yet emerge. effect closure, when baseline ratio high enough, inhibited so cause becomes doubtless present ahead tip. paper we report our attempt deconvolve contributions on following overload. To accomplish task analyse results tests run load ratios, namely R=0.1 R=0.7. At R=0.7 not operative, confirmed by Digital Image Correlation analysis flanks close tip, post mortem fractographic surfaces. Therefore, compressive region created sole mechanism causing retardation. focus must placed entirely strain field around end, line profiles bisector elastic opening direction were collected several stages propagation past using situ Synchrotron X-ray Powder Diffraction (SXRPD) technique. By performing comparison between conditions (R=0.7 R=0.1), information was extracted role alone, then, subtracting sample, alone. enable analysis, propose introducing concept equivalent effective intensity factor range, ∆ K eq , eff proposed Walker. Afterwards, SIF range reduction ratio, β which represents “knock down” respect steady state assessed. It terms newly introduced parameters magnitude extent overload-induced rate plotted, fitted decomposed into respectively. concluded although all values R, its relatively short-lived, whilst dominant low R longer