Papers by Author: Emilie Ferrié

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Authors: Emilie Ferrié, Jean Yves Buffière, Wolfgang Ludwig
Abstract: In-situ fatigue tests monitored by Synchrotron Radiation X-ray microtomography were carried out in order to visualize the three dimensional (3D) shape and evolution of short cracks in the bulk of a cast Al alloy. After the in-situ fatigue test the sample has been infiltrated with liquid Gallium (Ga) in order to visualize the grain structure of the material. Irregularities of the crack advance along the crack front can clearly be correlated to the grain structure of the material.
Authors: Jean Yves Buffière, Emilie Ferrié, Wolfgang Ludwig, Anthony Gravouil
Abstract: This paper reports recent results on the characterisation and modelling of the three dimensional (3D) propagation of small fatigue cracks using high resolution synchrotron X ray micro-tomography. Three dimensional images of the growth of small fatigue cracks initiated in two Al alloys on natural or artificial defects are shown. Because of the small size of the investigated samples (millimetric size), fatigue cracks grown in conventional Al alloys with a grain size around 100 micrometers can be considered as microstructurally short cracks. A strong interaction of these cracks with the grain boundaries in the bulk of the material is shown, resulting in a tortuous crack path. In ultra fine grain alloys, the crack shapes tend to be more regular and the observed cracks tend to grow like ”microstructurally long cracks” despite having a small physical size. Finite Element meshes of the cracks can be generated from the reconstructed tomographic 3D images. Local values of the stress intensity factor K along the experimental crack fronts are computed using the Extended Finite Element method and correlated with the crack growth rate.
Authors: Emilie Ferrié, Maxime Sauzay
Abstract: In the work presented here an elastic-plastic crystalline finite element method is used to simulate the cyclic behavior of 316L austenitic stainless steel single crystals and polycrystal. The evolution of the back stress on each slip system is described using a non linear kinematics hardening law to account for the hardening induced by long range dislocation interactions. As the contribution of short range interactions is assumed to be negligible, the value of the friction stress is kept constant. Three dimensional finite element calculations are performed to simulate the cyclic stress strain curves in the case of a single crystal oriented for multiple slips, as well as for the case of the polycristal. Simulations are compared to experimental data. They seem to be satisfactory for low strain values (εp\2 <10-3) whereas, for εp\2 >10-3, they underestimate the hardening observed experimentally.
Authors: Emilie Ferrié, Jean Yves Buffière, Wolfgang Ludwig, Anthony Gravouil
Abstract: In this paper we will present how it is possible to couple a 3D experimental technique with a 3D numerical method in order to calculate the stress intensity factors along the crack front taking into account the real shape of the crack. This approach is used to characterize microstructurally short fatigue cracks that exhibit a rather complicated 3D shape. The values of the stress intensity factors are calculated along the crack front at different stages of crack propagation and it can be seen that the crack shape irregularities introduce rather important fluctuations of the values of KI, KII and KIII along the crack front. The values of KI obtained taking into account the real shape of the crack are significantly different from the ones calculated using an approach based on a shape assumption
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