Figure 14.

(a) Schematic of the Lamb problem (i.e. the motion of a half-space induced by a concentrated force). (b) Typical displacement field in the TE given by FEA. The frequency of the vibrator is 50 Hz and the loading process lasts 20 ms. (c) The axial displacements of the points on the axis at different depths (5 ∼ 25 mm). The displacements are normalized by the displacement at the depth of 5 mm. Based on the arrival times of the displacement peaks, the velocity of the transient wave can be determined. (Online version in colour.)