Papers by Author: Herve Louche

Abstract: The tension behaviour of initially austenitic NiTi thin wall tubes was investigated using measurements of temperature and strain fields simultaneously. The first specimen was totally superelastic but the unloading was performed before the end of the loading stress plateau. The second specimen loading was performed beyond the stress plateau to allow analyzing the unloading, but was not superelastic and at a faster strain rate. Both tests show homogeneous behaviour at the beginning of the loading. Strong localisations, taking the shape of helical bands, are observed during the loading and unloading stress plateaus. To obtain quantitative energy information, allowing a better recognition of the deformation mechanisms, an estimation of the local heat sources based on image processing of the temperature fields is presented. Two methods of heat sources estimation allowing analysis of deformation mechanisms are proposed in the present paper: first during the homogeneous, then during localized stages.

Abstract: In this paper, we present a fundamental model of FCC single crystal behaviour at room temperature: this model includes kinematic work hardening derived from the elementary description of the collective dislocations density evolution during cyclic loading. This kinematic work hardening is then coupled with the isotropic work hardening mechanism. Using this original model, a simulation of a tensile test on a single crystal sample is carried out in the case of an initial crystal orientation that promotes single glide even at rather large strains. The evolution of resolved shear stresses on the primary and secondary slip systems are interpreted by means of the interaction between the evolution of isotropic and kinematic work hardening variables. The evolution of the model state-variables including applied resolved shear strain, dislocation densities, and critical shear stresses are represented as functions of the evolution of crystalline orientation during plastic deformation.

Abstract: This paper presents a method to estimate the stored energy during the tensile deformation of an aluminum multicrystal and polycrystal sheet sample. The method is based on thermo mechanical macroscopic fields analysis, like strains and temperature, obtained by a visible and an infrared cameras. Preliminary experimental results are presented. On an Al multicrystal sheet, heterogeneous thermo mechanical fields associated to the localized movement of dislocations at a microscopic scale are presented. Furthermore, the energetic balance established during the tensile deformation of an Al polycristal show a decreasing ratio of stored energy on anelastic energy and a non constant fraction of total work converted into heat.