Resonance effects for a crack near a free surface

Stress intensity factors are computed for a horizontal subsurface crack that is subjected to time harmonic excitation. The problem is analyzed by determining displacement potentials that satisfy reduced wave equations and specified boundary conditions. The formulation of the problem leads to a system of coupled integral equations for the dislocation densities. The numerical solution of the integral equations leads directly to the stress intensity factors. Curves are presented for the ratios of the elastodynamic and the corresponding elastostatic Mode-l and Mode-II stress intensity factors. At specific values of the frequency, a resonance effect is observed and a correlation with the natural frequencies calculated by a Timoshenko plate theory for the layer between the crack and the free surface is noted.