Finite Disorder Critical Point in Brittle-to-Ductile Transition in Amorphous Solids with Aspherical Impurities

Enhancing the mechanical properties of amorphous solids is crucial for material design, with microalloying being a common but not well-understood method. Using extensive molecular dynamics simulations, we investigate the effect of impurity particles on the yielding transition of amorphous solids in the context of brittle-ductile transition with microalloying. Spherical impurities larger than the constitutive particles enhance the systems mechanical stability, leading to a higher yield strain and increased brittleness. Much more potent effects are observed for rod-shaped impurities of the same size as the spherical impurities, with an aspect ratio slightly larger than one, which primarily introduce rotational degrees of freedom into the system. However, as the aspect ratio increases, their rotational degrees of freedom decrease, causing a more brittle yielding with more localized shear band formation. It is remarkable to see how freezing the rotational degrees of freedom can create extremely brittle, yet remarkably stable amorphous solids. Enhancing brittleness through higher concentrations of aspherical impurities presents an intriguing opportunity to explore the ductile-to-brittle transition, which is easily accessible in experiments, particularly in colloidal experiments. Our thorough finite-size scaling analysis has revealed a compelling suggestion of a finite-disorder critical point: a boundary between ductile and brittle behaviors.