EXPERIMENTAL CHARACTERISATION OF THE EFFECT OF CRYSTALLOGRAPHY ON THE THREE DIMENSIONAL NUCLEATION AND GROWTH OF FATIGUE CRACKS IN METALS

摘要

This paper presents results on the experimental characterisation of the influence of crystallography on fatigue crack nucleation and growth in the interior of metallic materials. Synchrotron X ray tomography has been used to study fatigue mechanisms leading to crack initiation and growth inside various aluminium alloys. Classical surface observations have been complemented by three dimensional (3D) post mortem and in situ characterization. Thanks to a Gallium infiltration technique it is possible to obtain 3D images of grains in the interior of the material, allowing to study the interaction of the fatigue cracks with the local microstructure on the crack front. Experimental data on the configuration of the front of a crack as it enters new grains have been obtained: deflections of the crack plane seems to delay the crack front propagation. Quantitative data can be extracted from the reconstructed images of the propagating crack such as the crack growth rate at different positions along the crack front. It is also shown that the influence of grains on the crack path can be strongly dependent of the local stress state.