Crack path instabilities in DCDC experiments in the low speed regime

TL;DR

This study reveals for the first time that crack path instabilities occur in low-speed fracture of glassy materials, characterized by out-of-plane oscillations with micrometer wavelengths and nanometer amplitudes, influenced by internal heterogeneity scales.

Contribution

It provides the first experimental evidence of crack path instabilities in the low-speed regime under uniaxial loading in glassy materials, linking instability features to heterogeneity length scales.

Findings

Out-of-plane crack front oscillations observed

Wavelengths in the micrometer range, amplitudes in nanometers

Instabilities occur when heterogeneity scale is below a few nanometers

Abstract

We studied the low speed fracture regime (0.1mm/s - 1nm/s) in different glassy materials (soda-lime glass, glass-ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on DCDC (double cleavage drilled compression) specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force (AFM) microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. (Phys. Rev. Letters (1996) 76} p1497).