Numerical models of shear fracture propagation

Two-dimensional numerical models using the displacement discontinuity method and the PATH algorithm show that shear fractures can propagate in three different patterns, depending on the lateral normal stress (LNS). Under 0 or very small LNS they propagate by open wing cracks, as shown in many previous results. Under increasing LNS, the extension consists first of a short wing crack followed by a succession of small closed and open segments forming a stair-step pattern. As the LNS increases, the length of the closed segments increases, thus changing the general orientation of the extension. Under sufficiently high LNS the transition is complete, and propagation takes place as a closed shear fracture. These results provide a remarkable confirmation of the theoretical predictions made by Cherepanov [J. Appl. Math. Mech. (English transl. of Prikl. Mate. Mekh.) 30 (1966) 96]. They also explain the difference between the fracture parameters in tension and in shear.