Numerical simulation of fatigue crack propagation in real polycrystals imaged by X ray tomography

Abstract : The short fatigue crack propagation in polycrystal materials depends strongly on microstructure. Although numerous studies of characterisation and of simulation, the prediction of the short fatigue crack propagation remains a challenge.In order to understand the mechanisms of short fatigue crack propagation, an in-situ characterisation by X-ray tomography was carried out at ESRF, using two techniques of tomography. Diffraction Contrast Tomography (DCT) that is a non-destructive method can be used to obtain 3D morphology and grain orientations in an undeformed state of polycrystal materials. Couple with Phase Contrast Tomography (PCT), it allows to characterise the short fatigue crack propagation at different loading stages. Access to this information, it is possible to simulate the short fatigue crack propagation using a 3D reel microstructural mesh reconstructed from the tomographic images.In this work, the elastic anisotropic behaviour in a 3D microstructural mesh is performed. The elastic strain tensors averaged in grains are also compared to the experimental measurements. Then, a new numerical approach is proposed to simulate crack propagation. From a crystal plasticity FE simulation, the crack growth direction is determined by a post processing. Next, the crack is propagated through remeshing. This approach is firstly applied to the single crystals, then to the polycrystal mesh reconstructed from the tomographic images. The grain boundary effects and the crack growth rate are also analysed. By comparing between simulation and experimental crack, the damage indicator is discussed at the end.
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Submitted on : Wednesday, May 25, 2016 - 12:03:08 PM
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Jia Li. Numerical simulation of fatigue crack propagation in real polycrystals imaged by X ray tomography. Material chemistry. Ecole Nationale Supérieure des Mines de Paris, 2015. English. ⟨NNT : 2015ENMP0079⟩. ⟨tel-01321257⟩

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