Micromechanisms of fatigue crack growth retardation following overloads

Abstract

New mechanistic interpretations to rationalize fatigue crack growth retardation due to load excursions are presented. It is reasoned that crack closure arising from residual tensile displacements is not the primary mechanism for growth attenuation following a peak tensile overload.A new mechanism for retardation is discussed in terms of a "micro-roughness" model. Quantitative analyses are provided to estimate the extent of reducti ons ineffective dri vi ng force in the reta rded growth regi on due to possible crack branching, residual compressive stresses and fracture face micro-roughness. It is argued that the retarded crack advance is effectiveLy governed by the micromechamisms of Stage I growth although nominaLLy Stage II conditions exist in the post-overload zone.The impl i cations of the present arguments are shown to be consi stent wi th a number of typi cal post-overload phenomena cited in the 1 iterature .= crack length = total retarded crack growth distance = delay distance (retarded crack advance up to the lowest growth ra te ) = baseline crack propagation rate = retarded crack propagation rate = average asperity height = height of the specimen = effective stress intensity factor for branched crack = Mode I stress intensity factor for branched crack = Mode I stress intensity factor for main crack = Mode II stress intensi ty factor for branched crack = Mode II stress intensity factor for main crack = closure stress intensity factor = closure stress intensity factor accounting for asperity contact = baseline maximum stress intensity factor -overload maximum stress intensity factor = baseline minimum stress intensity factor = stress intensity factor due to residual stress field = value of KIR during baseline (pre-overload) crack growth = value of KIRfollowing an overload = number of cyl ces for retarded crack growth

Fatigue crack shielding and deflection in plain bearings under large-scale yielding

“…These results are consistent with those previously published [2,6,7,28,29], which mostly used the J integral as CDF parameter. Elasto-plastic stress analyses of bearings in operation have predicted LSY [30,31]; CTOD could thus prove to be a reliable indicator of crack growth under such conditions.…”

Determination of crack growth for 6082-T6 aluminium subjected to periodic single and block overloads and underloads using a two dimensional finite element model

“…There is though some debate about which interactions cause crack retardation and acceleration and several hypotheses have been proposed as a source of these phenomena. There have been several reviews about load interactions on fatigue crack growth (4)(5)(6)(7)(8)(9)(10) which suggest that the principal reasons are: crack closure (plasticity, roughness and oxide), residual stresses, crack tip blunting, crack tip sharpening, crack tip branching, strain hardening, crack deflexion, and change in rate of damage accumulation in the reversed plastic zone ahead of the crack tip. All these interaction mechanisms depend on stress/strain conditions, material quality, load type, environment and other specific conditions that depend on the application.…”

Finite element modeling of fatigue crack bifurcation

“…Much effort has been given to the case of symmetrically bifurcated (forked) cracks [1]. Although many branches can be developed along the main crack path, it is experimentally observed that only the fastest branch continues to grow, while all others are brought to a stop due to the shielding caused by this fastest branch.…”