Influence of Multiaxial Far Field Loadings on the Fatigue Crack-Growth Behaviour by Using Corner-Crack and Cruciform Specimen

By means of fracture mechanics evaluation concepts, the most accurate possible estimation of the crack growth behaviour of complex and highly loaded structures is to be aimed for a more efficient use of components, a more precise planning of inspection intervals and for the realization of advanced design approaches. Standard fracture mechanics specimen used in materials testing are globally subjected to purely uniaxial loading. In contrast, the technical components usually experience multi-axial stresses due to the external loads and to their complex geometry. The influence of multi-axial far-field loads on the crack propagation rate and the crack closure behaviour is unclear and controversially discussed in literature. In this context, the crack propagation behaviour of uniaxially loaded corner-crack specimens and multiaxially loaded cruciform specimens is systematically studied in this investigation. Here, the multiaxiality condition is characterized by the so-called T-stress and systematically varied within the tests. The results so far show no significant influence of the far-field multiaxiality or the T-stress on the crack propagation behaviour. However, the evaluation of the crack closure behaviour indicates that an engineering approach for thin-walled structures leads to a non-conservative estimation.