Modeling the fracture toughness of metallic glasses through a multiscale approach
Bulk metallic glasses (BMGs) are promising materials that combine the strength of metal alloys with the elasticity of glassy polymers. Compared to their crystalline counterpart, the lack of dislocations and grain boundaries translates into better energy restitution, excellent wear, and corrosion resistance, making them promising candidates for sports goods to biomedical materials. Unfortunately, BMGs are notorious for exhibiting crack growth, fracture, and, ultimately, catastrophic failure, severely limiting their applications. Recently, experimental observation showed that BMGs could exhibit a mechanical transition revealed by a sharp drop in fracture toughness (ability to resist failure in the presence of a crack) as a function of a protocol (fictive) temperature that controls the glass stability. This transition strongly echoes with the ductile to brittle transition seen in recent numerical and theoretical works and is found to be linked to a sharp decrease in plastic defects (soft spots), which play a role similar to dislocations in crystals.
In this action, we propose investigating the toughening transition seen in BMGs through a novel multiscale numerical approach. This action aims to enable the parametrization of continuum models with the insight gained from microscopic simulations. In ToughMG, I will associate my experience in the detection and micromechanics of plastic defects at the microscopic level to the prominent expertise provided by Prof. Barrat and the host institution in modeling plasticity at the mesoscopic and macroscopic scale. The methodology developed will allow me to predict large scale plastic strain observed prior fracture as a function of the material's protocol history. This research plan can substantially advance our understanding of the connection between glassy structure and fracture mechanics of bulk metallic glasses and allows for better material design.