Taking into account the non-proportional loading effect on high cycle fatigue life predictions obtained by invariant-based approaches

Abstract

Industrial structures are often subjected to multiaxial fatigue loadings. If the multiple stress signals are not synced the loading is said to be non-proportional. Most of the multiaxial fatigue criteria give highly inaccurate lifetime predictions when used in the case of such loadings. The scalar equivalent stress defined by the criteria does not take into account the non-proportional nature of the multiaxial loading and leads to non-conservative predictions. Moreover a multiaxial fatigue criterion can only be applied on a stress cycle which has no clear definition when multiple unsynced signals are to be considered. This study addresses these issues by proposing a correction of an invariant based multiaxial fatigue criterion through the definition of a non-proportional degree indicator. A definition of multiaxial cycle is also given based on the Wang-Brown method. Finally a complete chain of invariant based lifetime prediction for non-proportional multiaxial fatigue is validated.

A modification of Matake criterion for considering the effect of mean shear stress under high cycle fatigue loading

“…At present, there are three major approaches to estimating the multiaxial HCF life, that is, the stress invariant methods, 3,4 mesoscopic scale method, 5,6 and critical plane-based method. [7][8][9][10][11][12][13][14][15] Among these methods, the critical plane-based method is considered as the very effective since the critical plane criterion is based on the physical observation of the fatigue failure.…”