Thèse de doctorat en Sciences pour l'ingénieur. Sciences et génie des matériaux
Sous la direction de Sandrine Thuillier.
Soutenue en 2013
à Lorient , dans le cadre de École doctorale Santé, information-communication et mathématiques, matière (Brest, Finistère) , en partenariat avec Université européenne de Bretagne (autre partenaire) .
Caractérisation expérimentale et prédiction numérique de la rupture des tôles métalliques en pliage
The study is performed to identify an effective tool for prediction of bendability of sheet metal alloys. Previous studies indicate that the forming limit diagram is not the right tool to use in prediction of rupture of sheet metal alloys in bending on small radii and it demands the taking into account of rupture. The materials used to perform this study are DP980 steel sheets and AA6016-T4 aluminum alloy sheets. In the first step mechanical experiments i. E. Tensile tests of rect- angular and notched samples, bulge, shear and bending tests were performed to characterize the material behavior and evaluate strains just before rupture. For the aluminum alloy sheets, effect of aging is an important factor and has been taken into account and hence two series of mechanical tests have been performed after two and six months of preparation of the sheets. For the strain measure- ments during the tests, digital image correlation (DIC) system was used and the rupture after the tests was analyzed using scanning electron microscope. The rupture limit in bending corresponds to the first crack appearance in the samples and not to the splitting of samples into two parts. However, in case of AA6016- T4 alloy sheets, no rupture in bending was found for both series of tests under present experimental conditions, which shows the higher ductility of the material. In the next step, numerical simulation of the mechanical tests were performed us- ing elasto-plastic material model in order to compare the macroscopic load and local strains. Four macroscopic rupture criteria, i. E. Latham-Cockcroft, Brozzo, Ayada and Rice-Tracey, were used in the numerical simulations with the finite element code ABAQUS. Critical values of these macroscopic rupture criteria were identified using tensile test simulation and were used in simulation of bending and other tests. The evolution of equivalent strain at rupture is plotted versus the triaxiality ratio obtained from numerical simulations for the different tests from the database, as well as the rupture diagram in the principal strain space.
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