Microbranching in mode-I fracture using large-scale simulations of amorphous and perturbed-lattice models

We study the high-velocity regime mode-I fracture instability wherein small microbranches start to appear near the main crack, using large-scale simulations. Some of the features of those microbranches have been reproduced qualitatively in smaller-scale studies [using O(104) atoms] on both a model of an amorphous material (via the continuous random network model) and using perturbed-lattice models. In this study, larger-scale simulations [O(106) atoms] were performed using multithreading computing on a GPU device, in order to achieve more physically realistic results. First, we find that the microbranching pattern appears to be converging with the lattice width. Second, the simulations reproduce the growth of the size of a microbranch as a function of the crack velocity, as well as the increase of the amplitude of the derivative of the electrical-resistance root-mean square with respect to the time as a function of the crack velocity. In addition, the simulations yield the correct branching angle of the microbranches, and the power law exponent governing the shape of the microbranches seems to be lower than unity, so that the side cracks turn over in the direction of propagation of the main crack as seen in experiment.