Origin of the Microbranching Instability in Rapid Cracks

 

Tamar Goldman Boué, Gil Cohen, and Jay Fineberg

The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

(Received 24 November 2014; published 2 February 2015)

 

The origin of the microbranching instability is a long-standing unresolved issue in the fracture of brittle

amorphous materials. We investigate the onset of this instability by measuring the real-time dynamics and

symmetries of the strain fields produced by rapid tensile cracks in brittle gels. We find that once a simple

tensile crack is subjected to shear perturbations, cracks undergo the microbranching instability above a

finite velocity-dependent threshold. We further reveal a distinct relation between the microbranching and

the oscillatory instabilities of rapid cracks.