Hélène Welemane

Residual Stresses in Ceramic Metal Assembly after Brazing Process

The framework of this study is the thermo-mechanical analysis of the brazing process of ceramic metal assemblies. The thermal expansion gradient between ceramic and metallic materials leads to the development of residual stresses during the cooling phase of the brazing process which induce consequently an important reduction of the strength of these composite structures. In the present work, numerical simulations are performed in order first to predict the residual stresses distribution after the brazing process and in a second step, to study their influence on the tensile strength of metallized ceramic seals. Results obtained are compared with experimental tests.

Thermo-mechanical behaviour of ceramic metal brazed assemblies

This study investigates the effects of residual stresses developed during brazing on the performance of brazed ceramic metal joints. The thermal expansion gradient between ceramic and metallic materials leads to the development of such stresses during the cooling phase of the brazing process, which consequently reduce the strength of these composite structures. Here, the objective is to compare the failure behaviour of various assemblies observed during experimental tests and obtained through numerical simulations. In order to get a representation consistent with the physical mechanisms involved, these simulations must account for the brazing phase giving rise to residual stresses before applying in use solicitations to brazed joints. This paper focuses on the tensile strength of ceramic metal joints, for which two brittle failure modes (within the ceramic or at the interface) are observed during the experimental tests.

Thermographic investigation of heat source in transversely isotropic composites

This paper deals with the estimation of heat sources from infrared thermographic measures on anisotropic CFRP n(Carbon-Fibre Reinforced Composites). Such procedure combines the data processing of the thermal signal, especially as spatial and temporal derivation quantities involved in the heat equation are notably affected by the measurement noise, and the determination of thermo-physical properties of the material, especially to account for the anisotropic conductivity behavior of the material. A comparative analysis of different filtering techniques is done to define a filtering method able to decrease the noise while keeping the useful features of the signal. Then, we use a homogenization scheme based on single-inhomogeneity solutions of Eshelby to derive the transversely isotropic thermal conductivity tensor.