Intersonic shear crack growth along weak planes

Abstract

Classical dynamic fracture theories predict the Rayleigh surface wave speed (c_R ) to be the limiting speed of propagation for mode-I cracks in constitutively homogeneous, isotropic, linear elastic materials subjected to remote loading. For mode-II cracks, propagating along prescribed straight line paths, the same theories, while excluding the possibility of crack growth in the speed regime between c_R and the shear wave speed, c_s , do not exclude intersonic (c_s <υ<c_l ) crack tip speeds. In the present study, we provide the first experimental evidence of intersonic crack growth in such constitutively homogeneous and isotropic solids, ever recorded in a laboratory setting. Intersonic shear dominated crack growth, featuring shear shock waves, was observed along weak planes in a brittle polyester resin under far-field asymmetric loading. The shear cracks initially propagate at speeds just above c_s and subsequently accelerate rapidly to the longitudinal wave speed (c_l) of the solid. At longer times, when steady state conditions are attained, they propagate at speeds slightly higher than √2–c_s . The experimental results compare well with existing asymptotic theories of intersonic crack growth, and the significance of the preferred speed of √2–c _ is discussed.