Resonances and Crack Roughness Effects in Surface Breaking Cracks

This study deals with two different aspects of scattering from the cracks. The first one is the measurement of crack resonances by local probes and the second is the effect of the roughness of the crack forces on the scattering data. Unlike the scattering measurement reported elsewhere, these measurements of crack resonances are to be performed by local probes. Two different types of probes are described and their problems are discussed. The effect of crack roughness on the scattering data is investigated via the reciprocity relation. The crack roughness is analyzed using perturbation theory and the equivalent boundary condition concept developed by Brekhovskikh is used to express the fields in the presence of the roughness. The effect of roughness on the scattering data is then discussed in qualitative terms. INTRODUCTION In our last year's report (1], we proposed a model to explain the crack resonance phenomena, which regards the resonances as standing waves due to the modes that propagate on crack surfaces along the length and depth directions. For these resonances, we gave the following formulas which agreed well with the available experimental data available at that time [2,3]: VL (M + (1) "" 2L