We propose a linear stability analysis of a straight crack subjected to uniaxial loading. We argue that, under quasistatic extension conditions, the crack propagation follows a straight path until the creation of a “physical” shear stress at its tip. This instability leads to a deviation of the fracture from the direction perpendicular to the applied loading. We compare our tip criterion instability with both experimental results and previous theoretical models.

• Received 8 August 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.1497