APPLICATION OF TRANSIENT ELASTIC-WAVES TO THE NONDESTRUCTIVE EVALUATION OF PLATE STRUCTURE WITH CAVITY OR INCLUSION

This paper utilized the heterogeneous finite difference formulation to study the propagation of transient elastic waves in media with intern al interfaces due to a steel ball impact. The media considered in this paper include a parallel layered half-plane, a dipping layered half-p lane, and a plate with a hole or circular inclusion. Transient elastic waves generated by dropping a steel ball on the layered (both paralle l and dipping) plates are recorded to check the validity of the result s simulated from the present numerical scheme. In order to detect a vo id or inclusion in a plate structure, the near-offset seismogram and p oint-source/array-receiver (PS/AR) seismogram are simulated numericall y. The simulated results of the near-offset seismogram suggested that the bottom-reflected P wave can be utilized to estimate the diameter o f a circular inclusion. The unique features in the PS/AR seismogram su ggested that the PS/AR seismogram can be utilized to identify a void o r inclusion in plate structures. In combination with recent laser ultr asound developments, the present study can also serve as a basis for t he detection of fine voids or inclusions in materials.