Notch Fracture Toughness of Glasses: Dependence on Rate, Age, and Geometry

Abstract

Understanding the fracture toughness (resistance) of glasses is a fundamental problem of prime theoretical and practical importance. Here we theoretically study its dependence on the loading rate, the age (history) of the glass and the notch radius ρ. Reduced-dimensionality analysis suggests that the notch fracture toughness results from a competition between the initial, age-and historydependent, plastic relaxation timescale τ pl 0 and an effective loading timescale τ ext (KI , ρ), whereKI is the tensile stress-intensity-factor rate. The toughness is predicted to scale with √ ρ independentlypl 0 for ξ 1, to scale as T √ ρ log(ξ) for ξ 1 (related to thermal activation, where T is the temperature) and to feature a non-monotonic behavior in the crossover region ξ ∼ O(1) (related to plastic yielding dynamics). These predictions are verified using novel 2D computations, providing a unified picture of the notch fracture toughness of glasses. The theory highlights the importance of timescales competition and far from steady-state elasto-viscoplastic dynamics for understanding the toughness, and shows that the latter varies quite significantly with the glass age (history) and applied loading rate. Experimental support for bulk metallic glasses is presented.

Pinching a glass reveals key properties of its soft spots

“…3, when interpreted in terms of STZs, is a cornerstone of the nonequilibrium thermodynamic STZ theory of the glassy deformation (46)(47)(48), where Tp is treated as a thermodynamic temperature that characterizes configurational degrees of freedom and that differs from the bath temperature. The strong depletion of STZs with decreasing Tp, as predicted by the Boltzmann-like relation, was shown to give rise to a ductile-to-brittle transition in the fracture toughness of glasses (58,59). This prediction was recently supported by experiments on the toughness of bulk metallic glasses, where Tp was carefully controlled and varied (60).…”

“…The strong depletion of QLMs upon deeper supercooling has dramatic consequences for the properties of the resulting glassy states. For example, brittle failure (56,57) and reduced fracture toughness (58)(59)(60) are claimed to be a consequence of this depletion. It is interesting to note that the range of variability observed in Fig.…”

Random critical point separates brittle and ductile yielding transitions in amorphous materials

“…This widespread mesoscopic approach successfully reproduces the key phenomenology of deformation and flow in amorphous materials. Our main focus is on the role of the initial preparation, which has received much less attention (see however (28)(29)(30)(31)).…”

Parallel three-dimensional simulations of quasi-static elastoplastic solids

“…The initial conditions in Eqs. 44 Fig. 13(d), the disk has expanded and has developed a pointed front in the y direction.…”