Elastics Wave Conversion From Fractures With Oriented Voids

Natural and induced processes can produce oriented mechanical discontinuities. Compressional to shear (P-to-S) wave conversions propagated at normal incidence to a fracture (Nakagawa et al., 2000) occur as a fracture undergoes shear stress because of coupling fracture compliances. In this study, experiments and computer simulations were performed to demonstrate the link among cross-coupling stiffness, micro-crack orientation and energy partitioning into P, S, and P-S/S-P wave. 3D printed samples with linear arrays of micro-cracks oriented at 0°, ±15°, ±30°, ±45°, ±60°, ±75°, and 90° were fabricated to provide understanding of crosscoupling stiffness. Wave amplitudes were compared with 2D simulations of compressional and shear stress waves based on a Discontinuous Galerkin method. For normal incidence, wave conversions were observed for micro-crack inclinations greater than 0° and less than 90°. In addition, cracks oriented at negative and positive angles have 180°-reversed phase difference in P-to-S and S-to-P wave conversions. This finding supports a wide range of potential application for monitoring and determining the presence and inclination angle of mechanical discontinuities.