Oscillations in Rapid Fracture

TL;DR

This paper investigates a new oscillatory instability in brittle gels during rapid tensile fracture, occurring at a critical velocity, and suggests an intrinsic scale unrelated to traditional fracture mechanics.

Contribution

It identifies a novel dynamic oscillatory instability at high crack speeds and proposes the existence of an intrinsic scale beyond LEFM predictions.

Findings

Oscillations occur at a critical velocity Vc = 0.87 Cs.

Wavelength of oscillations is independent of sample size.

Suppression of micro-branching allows higher crack speeds.

Abstract

Experiments of pure tensile fracture in brittle gels reveal a new dynamic oscillatory instability whose onset occurs at a critical velocity, Vc = 0.87 Cs, where Cs is the shear wave speed. Until Vc crack dynamics are well described by linear elastic fracture mechanics (LEFM). These extreme speeds are obtained by suppression of the micro-branching instability, which occurs when sample thicknesses are made comparable to the minimum micro-branch width. The wavelength of these sinusoidal oscillations is independent of the sample dimensions, thereby suggesting that a new intrinsic scale exists that is unrelated to LEFM.