Damage identification in a composite plate using prestack reverse-time migration technique

Migration technique, which is normally used in geophysical prospecting, is proposed to locate and image multiple delamination damages in a laminated composite plate. In this simulation study, an active diagnostic system with a linear array of actuators/sensors is used to excite/receive the lowest mode of flexural waves in the laminate. The wavefield scattered from the damages and sensor array data are synthesized using a two-dimensional explicit finite difference scheme to model wave propagation in the laminate based on the Mindlin plate theory. A prestack reverse-time migration technique is then adopted to interpret the synthetic sensor array data and to visualize the damages. The phase and group velocities of flexural waves in the composite plate are derived from the dispersion relations, and subsequently an excitation-time imaging condition specifically for migration of waves in the plate is introduced based on ray tracing and group velocity. Then the prestack reverse-time migration is performed using the same finite difference scheme to back-propagate the scattered energy to the damages. During the migration process, the laminate is imaged in terms of velocity of the transverse deformation. The locations and dimensions of the damages can be visually displayed. Simulated results demonstrate that multiple delamination damages can be successfully identified and the resulting image correlates well with the target damages.