Title: Dynamic defect generation in metals

Abstract: High-speed dislocations have long been recognised as the predominant factor influencing the plastic response of crystalline materials subjected to high strain rates, thereby governing deformation and failure across various dynamic mechanical processes, including earthquakes, crashworthiness and foreign object damage, machining, laser shock peening, punching, and drilling. Despite decades of investigation, the precise role of high-speed dislocations in the material's response remains elusive. Chief among these unresolved issues is the absence of a unified theory of dislocation mobility, which is hindered by the current lack of empirical evidence. In this talk, I will add to the many ambiguities in this field by arguing that, in certain instances, high-speed dislocations themselves act as sources of additional dislocations or twins. I will present several molecular dynamics (MD) simulations of various metals that exhibit this phenomenon and attempt to elucidate the effect using harmonic lattice models. These models suggest that the observed behaviour may be interpreted as a fundamental resonance between the crystalline lattice and the moving dislocation. This resonance is resolved by the lattice through the generation of new defects via dislocation-mediated reactions which thermodynamic calculations alone would typically preclude. I will delineate the nature of these reactions and argue that, in many instances, these resonances can be predicted a priori by studying the material’s phonon spectrum. The presence of these instabilities appears to provide a rationale for shear banding, which is the fundamental deformation and failure mechanism behind e.g. machining or punching, and where ultra-fast defect generation promoting plastic hardening is accompanied by equally fast thermal softening.

Bio: Beñat Gurrutxaga-Lerma is lecturer in materials modelling in the School of Metallurgy and Materials at the University of Birmingham, where he works on defect micromechanics and multiscale modelling of crystalline materials. Prior to that, he was a Junior Research Fellow at Trinity College Cambridge, having completed his PhD on Dynamic Dislocation Dynamics at Imperial College London in one of the earliest iterations of a CDT.

NOTE CHANGE OF ROOM TO RAMPHAL R0.14

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