Experimental Investigations of 3D Fatigue Crack Propagation

ABSTRACT. In the present paper, some interesting questions concerning 3D fatigue crack propagation are discussed. The main focus is on experimental investigations of 3D fatigue crack propagation under Mode I loading conditions. Transparent specimens of PMMA are used, in order to be able to observe and to document accurate sequences of the real 3D crack front evolution profiles via in situ photographic measurement. Such well documented experimentally observed sequences of real crack front profiles are necessary to identify an appropriate crack propagation criterion via comparing the experimental observations with corresponding numerical simulations. The aim of this paper is to present a new 3D crack propagation criterion, based on simple 2D fatigue tests on CT specimens, which allows to predict the correct distribution of the incre-mental crack extension also for complicated loading conditions under which only parts of the crack front propagate. Another focus of the experimental investigations concerns the influence of the additional corner singularities in the case of surface breaking cracks. Results of both, numerical simulations of 3D fatigue crack propagation an cor-responding experimental investigations, are presented