Review of fatigue crack growth under non-proportional mixed-mode loading

Abstract

Cyclic non-proportional loading is common experimental practise for investigations of large structures like vehicles. Numerical analysis of local nonproportional loading conditions is also a well established field of research and application. However, theoretical and practical support is rare for evaluating the growth of fatigue cracks under non-proportional cyclic loading conditions. At least seven influence factors-most of them not yet throroughly understood-are listed and discussed in the paper: the mode-mixity, the material's influence including its anisotropy if existant, the degree of cyclic plastic deformation and its direction ahead of the crack tip, the crack closure phenomenon, the related mean stress effect, the component's geometry in general and especially the variable mode-mixity along a crack front. Two crack propagation mechanisms must be considered: The tensile stress dominated, mode II minimising mechanism and the shear stess dominated mechanism. Transition mode-mixities are observed. Some successful explanations of experimental findings have been published, however, a generally accepted and validated formulation of a crack driving force parameter is out of sight.

Multi-challenge aspects in fatigue due to the combined occurrence of multiaxiality, variable amplitude loading, and size effects

“…Little is known concerning mixed mode hypotheses for non-proportional fatigue [24]. Generally, the hypothesis has to specify the crack advance direction and the increment.…”

Fatigue Analysis of the Piston Rod in a Kaplan Turbine Based on Crack Propagation under Unsteady Hydraulic Loads

“…For most cases in practice, the crack is cyclically loaded in a way such that at the crack front nonproportional mixed-mode situations will occur. Since these fatigue load conditions are a combination of various load sequences originated from different sources [10]. Here, a mixed mode stress intensity factor ∆ MM range was introduced replacing the conventional ∆ in Paris crack growth rate equation:…”

Fatigue crack growth of aluminium alloy 7075-T651 under non-proportional mixed mode I and II loads

“…At present, experimental FCG investigations are predominantly undertaken for mode I or proportional mixed mode loads. Only a few studies [1][2][3][4][5][6][7][8] focus on non-proportional mixed mode loads. Limited results on A106-93 mild steel [3] reveal that a long and stable shear mode FCG -which is significantly different from the commonly understood open mode FCG -could be produced by non-proportional loads.…”