Yielding and mechanical failure in (amorphous) solids

Recently, a Monte Carlo simulation study [1] has shown that yielding in crystalline solids is associated with an underlying quasi-static first-order phase transition. As a consequence, in the limit of a deformation with sufficiently low strain rate, the rigid response of a crystal due to a shape change of its boundaries corresponds to a metastable state that transforms to a stable state where internal stresses are eliminated, maintaining the crystalline order. A nucleation theory based on these findings predicts the yield point as a function of strain rate and shows agreement with data from experiment and molecular dynamics (MD) simulations over 15 orders of magnitude [2]. In the case of amorphous solids (glasses), a MD simulation study, using an athermal quasi-static (aqs) deformation protocol [3], have found a sharp stress drop in the stress-strain relation that marks the transition from an elastic response of the glass to plastic flow. In Ref. [3], this stress drop has been interpreted as a non equilibrium first-order transition, leading to the occurrence of shear localization, i.e. shear banding, after the drop. Using MD simulations of glassforming model systems under shear, we study the conditions for the occurrence of shear bands at finite temperatures [4] and discuss the response of glasses to an external shear in the limit of zero strain rate. We argue that there is no quasi-static first-order transition as in the case of crystalline solids.

[1] P. Nath et al., Proc. Natl. Acad. Sci. USA 115, E4322 (2018).
[2] V. S. Reddy et al., Phys. Rev. Lett. 124, 025503 (2020).
[3] M. Ozawa et al., Proc. Natl. Acad. Sci. USA 115, 6656 (2018).
[4] M. Golkia et al., Phys. Rev. E 102, 023002 (2020).