EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The talk brings together two areas of research: the mechanical behavior of nano-structured materials with a grain-size gradient and the plastic instability in metal alloys, known as the Portevin-Le Chatelier (PLC) effect. The treatment of the surface by hyper-deformation processes locally increasing the dislocation density and/or forming a fine-grained layer has proven its effectiveness in the development of metallic materials with high mechanical properties. However, the influence of gradient microstructure on the PLC instability is very little studied, probably due to the complex multi-scale nature of the instability phenomenon. Moreover, most works aim at establishing the relationships between the microstructure and the macroscopic behavior of the material and remain within the framework of the continuous plasticity approach, i.e., are based on the hypothesis of a homogeneous plastic flow, where random fluctuations of the distribution and mobility of dislocations compensate each other statistically. However, the interaction between dislocations results in their self-organization and generates collective effects characterized by mesoscopic-scale internal lengths, which bring into play an intrinsically heterogeneous and intermittent plastic flow. Considering these aspects is crucial when the size of the grains is comparable to the intrinsic lengths controlled by the collective processes.
The talk will present first results of experimental and numerical study of the effect of SMAT (Surface Mechanical Attrition Treatment) on both the mechanical properties and spatiotemporal complexity associated with the unstable plastic flow of an AlMg alloy. The influence of SMAT on the correlations of deformation processes will be revealed through statistical analysis of stress serrations, acoustic emission, and local strain-rate fields provided by the digital image correlation technique. Modeling of the PLC effect will be implemented based on an elasto-visco-plastic model regularized by virtue of the second strain gradient approach.