Low self-affine exponents of fracture surfaces of glass ceramics

TL;DR

This study experimentally shows that fracture surfaces of glass ceramics are self-affine with a low exponent of 0.40, which is consistent across various porosities and microstructural parameters, differing from the typical universal value.

Contribution

It provides the first detailed measurement of low self-affine exponents in glass ceramics and links the fracture surface roughness to microstructural features and fracture modes.

Findings

Fracture surface exponent zeta ≈ 0.40, lower than the universal 0.8.

Roughness amplitude increases linearly with porosity.

Exponent zeta is unaffected by porosity, bead size, or crack velocity.

Abstract

The geometry of post mortem rough fracture surfaces of porous glass ceramics made of sintered glass beads is shown experimentally to be self-affine with an exponent zeta=0.40 (0.04) remarkably lower than the 'universal' value zeta=0.8 frequently measured for many materials. This low value of zeta is similar to that found for sandstone samples of similar micro structure and is also practically independent on the porosity phi in the range investigated (3% < phi < 26%) as well as on the bead diameter d and of the crack growth velocity. In contrast, the roughness amplitude normalized by d increases linearly with phi while it is still independent, within experimental error, of d and of the crack propagation velocity. An interpretation of this variation is suggested in terms of a transition from transgranular to intergranular fracture propagation with no influence, however, on the exponent zeta.