An improved finite difference scheme has been used to simulate the propagation of a plane P-impulse in an elastic half space with a slot normal to its surface. Various angles of incidence and dimensions of slot are considered. The numerical results are presented in several visualizations; each emphasized a different type of wave and all representations help in understanding the scattered and diffracted wave pattern. Experiments were carried out using 0.5–6MHz ultrasonic pulses on a duralumin semidisc with a surface-breaking slot and the results are compared with those given by the numerical models.

The scattered wavefield includes compressional and Rayleigh pulses whose amplitude increases at the front of the slot and decreases behind it, as the angle of incidence is reduced. A diffracted compressional pulse is generated with a semicircular wavefront centred at the mid-point of the bottom of the slot. Also, two elliptical eddies are excited at the lower corners. These ellipses propagate into the medium and eventually spread out to form arc-shaped shear pulses.

In the shadow zone, behind the slot, the two components of displacement show independent behaviour. The horizontal component decreases either with decreasing angle of incidence or as the slot is made deeper. For acute angles, a reduction of displacement amplitude of about 50 per cent is obtained when the depth of the slot is made a half pulse width. On the other hand there is no diminution of the vertical displacement behind the slot, and, near the upper right corner, it is even amplified.