The increasing need of structures having multiple functions orientates designers to combine materials in order to obtain, according to coupling scales, multi-materials structures. The lifetime of these structures represents the essential decisive element for study offices and manufacturers. The results of this work should add to the set of functional charges and constraints of resistance, the improvement of the lifetime as an objective to optimize a multi-material. In this study, we propose a numerical analysis by the finite elements method of the thermo mechanical behavior of these materials and their damage under thermal cyclic solicitations. The sample is a two-dimensional plate constituted of two different isotropic layers (steel, aluminum) submitted to variable thermal conditions (heat flux condition on one side and convection exchange condition on the opposite side). The sample is supposed to be fixed in one direction and free in the other. The damage model is based on the works of Lemaiˆtre and Chaboche [8]. Numerical results are presented for different forms of heat flux cycling (triangular, square and sinusoidal excitations) with a comparison of the multi-material damage for each excitation. The study is concluded by an empirical optimizing of the thickness of materials according to the total lifetime caused by thermo-mechanical effect.

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