The acoustical wave propagator technique is applied to study the time-domain dynamic stress concentration in a two-dimensional flexible plate with a sharp change of section. As a wave packet approaches the plate discontinuity where the sharp change of thickness is introduced, the spatial interference patterns in the displacement of the plate and internal stresses vary with time. The constructive interference of stresses is referred to as time-domain stress concentration. The superposition of wave fronts of incident and reflected wave packets is used to explain the spatial distribution of the interference patterns. The increase of dynamic stress near the vicinity of the discontinuity boundary of the plate is studied as a function of time and the thickness ratio of the plates. (C) 2004 Acoustical Society of America.