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Influence of the casting microstructure on damage mechanisms in Al-Si alloys by using 2D and 3D in-situ analysis

type de publication      thèse de doctorat
date de publication 23-01-2015
auteur(s) Wang Long
jury E. Charkaluk, N. Limodin, A. El Bartali, K.H. Lang, Y. Nadot, T. Beck, J.Y. Buffière, J. Rethoré, F. Szmytka
école Ecole Centrale de Lille
  
résumé An experimental protocol was developed in this thesis in order to study the influence of casting microstructure on the fatigue behavior in Lost Foam Casting Al-Si alloys in tension and in Low Cycle Fatigue at room temperature. First of all, the microstructures of studied alloys were thoroughly characterized both in 2D and in 3D. The most suitable and representative specimens and Region of Interest (ROIs) where the in-situ monitoring was performed were selected through a preliminary characterization using X-ray tomography, which is also necessary to understand damage mechanisms after failure. In-situ observations performed on surface using Questar long distance microscope and in volume using X-ray tomography allow following cracks initiations and their propagations and thus allow identifying the relation between damage mechanisms and casting microstructure. 2D/3D displacement and strain fields measured using Digital Image Correlation and Digital Volume Correlation allows analyzing the relation between measured fields and damage mechanisms. Postmortem analysis and FEM simulation gave more information for the damage mechanisms. Large pores favor crack initiation as they strongly increase local stress level. Hard inclusions (Si phase, iron intermetallics and copper containing phases) also play an important role in crack initiation and propagation due to strain localizations at these inclusions.
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