Modelling of crack surface interference under cyclic shear loads

Abstract

Crack surface interference under cyclic shear loads is studied by an analytical method. The proposed model simulates the effects arising from both the residual stresses and the asperity interactions. A closed‐form and a discrete approach are presented in obtaining the crack surface interference solutions. Backlashes of shear displacements, peeling or group sliding behaviours and induced cyclic mode I stress intensities are predicted under three configurations of residual stress distributions. The effects of a static mode I load, the facet angle and the frictional angle are also analysed. The predicted relationship between the effective shear mode stress intensity range and the R‐ratio is discussed together with the experimentally observed ‘contrasting’ R effects.

Influence of the loading path on fatigue crack growth under mixed-mode loading

“…3b). The computed effective loading path is rather similar to that obtained with an analytical model-assuming rigid asperities-by Yu and Abel (1999). K effective II / K nominal II was found to be independent of K nominal II in the range simulated, but decreasing with R, when the latter is positive, as shown on Fig.…”

“…Mode I reduces crack faces contact and friction and thus tends to increase K effective II (Yu and Abel 1999), whereas static or intermittent mode II produces a relative shift of the crack faces thus increasing asperity-induced closure and reducing K effective I (Stanzl et al 1989;Dahlin and Olsson 2003). But, on the other hand, pure mode II loading on a rough crack generates a cyclic mode I, because gliding asperities wedge the crack open.…”

“…But, on the other hand, pure mode II loading on a rough crack generates a cyclic mode I, because gliding asperities wedge the crack open. Several analytical models (Tong et al 1995;Yu and Abel 1999;Bian et al 2006) were developed to describe the latter effect, but the assumption of rigid asperities leads to overestimate the induced K I and to underestimate K effective II . Elastic-plastic finite element simulations taking into account the contact and friction of crack face asperities can be used to overcome this limitation, as shown below.…”

Mixed‐mode crack surface interference under cyclic shear loads

“…While the mode II CSI‐induced strains can explain the shear attenuation described in an experimental study, 8 the existence of cyclic mode I CSI‐induced strains may provide evidence for the cyclic wedge‐opening behaviour which so far has only been revealed in modelling analyses 9 ,. 10 It can be imagined that when the remote tensile stresses remain steady, the cyclic variations of mode I CSI forces will lead to cyclic opening at crack surfaces. Nevertheless, this cyclic opening is CSI forces‐promoted so that the facing crack surfaces must keep in contact during the opening displacement.…”

“…The term ‘shear attenuation’, however, may not provide a complete description of the crack surface interference. Modelling analyses 9 , 10 predicted that as a companion of the shear attenuation, cyclic mode I stress intensities could also be induced if sliding movements between crack surfaces were promoted along the inclined asperity facets. This prediction indicates that the nature of the crack surface interference is of a mixed‐mode type although the cyclic portions of the applied loads are merely in shear mode.…”