Propagation Path and Fatigue Life Predictions of Branched Cracks Under Plane Strain Conditions

Fatigue cracks can significantly deviate from their Mode I growth direction due to the influence of overloads, multi-axial stresses, micro structural inhomogeneities such as grain boundaries and interfaces, or environmental effects, generating crack kinking or branching (Lankford and Davidson [

1

]). The stress intensity factors (SIF) associated to branched fatigue cracks can be considerably smaller than that of a straight crack with the same projected length, causing crack growth retardation or even arrest, as discussed by Suresh [

2

]. This mechanism can quantitatively explain retardation effects even when plasticity induced crack closure cannot be applied, e.g. in high R-ratio fatigue problems under plane strain conditions. Analytical solutions have been obtained for the SIF of some branched cracks, however numerical methods such as the ones presented in Miranda

et al

. [

3

] are the only means to predict the subsequent curved propagation behaviour.