Contribution à la compréhension et à la modélisation de l’effet de la plasticité sur le comportement magnéto-mécanique des matériaux ferromagnétiques

Mechanical loadings are known to significantly modify the magnetic behavior of materials. Among these stresses, plastic deformation probably leads to the most extreme variations which constitutes a challenge in terms of energy losses but also allows new developments in terms of non-destructive control tools. Traditionally, the magneto-plastic effect is attributed to crystal defects density and their interaction with magnetic domain walls. Plasticity also generates heterogeneous mechanical fields in materials, whose magneto-elastic effect can also explain the magnetic behavior variations. The purpose of this thesis is to provide new elements to resolve this controversy. To achieve this, we have, on the one hand, designed experiments to develop different mechanical loadings and plastic strain states (tension/compression/torsion) in a single-phase material (pure iron) and a two-phase material (ferrito-pearlitic steel); we were then able to observe and then measure the density of dislocations, and carry out magnetic and magnetostrictive measurements. Our observations indicate that the effects of residual stresses and associated magneto-elastic interactions dominate the behavior of steel in tension/compression. Structural defects, on the other hand, play a significant role in the behavior of pure iron subjected to the same stresses. Defects density completely dominate in a shear situation when the magnetic measurement and the torsion axes coincide. Two constitutive models based on magneto-elastic coupling have been used. They corroborate the experimental results.