Roughness of oxide glass subcritical fracture surfaces

TL;DR

This study introduces a novel experimental setup to precisely measure nanometric roughness of oxide glass fracture surfaces under controlled conditions, revealing how roughness varies with stress intensity and material heterogeneity.

Contribution

It presents a new method combining stable sub-critical crack propagation with AFM analysis, and develops a synthetic model linking heterogeneity, crack tip stresses, and surface roughness.

Findings

Roughness amplitude decreases with increasing stress intensity factor.

Roughness is insensitive to humidity levels.

Roughness increases with glass heterogeneity.

Abstract

An original setup combining a very stable loading stage, an atomic force microscope and an environmental chamber, allows to obtain very stable sub-critical fracture propagation in oxide glasses under controlled environment, and subsequently to finely characterize the nanometric roughness properties of the crack surfaces. The analysis of the surface roughness is conducted both in terms of the classical root mean square roughness to compare with the literature, and in terms of more physically adequate indicators related to the self-affine nature of the fracture surfaces. Due to the comparable nanometric scale of the surface roughness, the AFM tip size and the instrumental noise, a special care is devoted to the statistical evaluation of the metrologic properties. The 2 roughness amplitude of several oxide glasses was shown to decrease as a function of the stress intensity factor, to be quite insensitive to the relative humidity and to increase with the degree of heterogeneity of the glass. The results are discussed in terms of several modeling arguments concerning the coupling between crack propagation, material's heterogeneity, crack tip plastic deformation and water diffusion at the crack tip. A synthetic new model is presented combining the predictions of a model by Wiederhorn et al. [1] on the effect of the material's heterogeneity on the crack tip stresses with the self-affine nature of the fracture surfaces.