Diagnostics of residual stress in metals with wideband surface acoustic pulses

A method for diagnostics of biaxial residual stress in metals with the use of short pulses of surface acoustic waves (SAWs) is discussed. Laser thermoelastic excitation of SAW pulses with a length of about 30 ns and piezoelectric detection by a specially designed wedgelike receiver with a high time resolution are used. Relative variations in the phase and group SAW velocities due to the presence of a weld are measured experimentally in two mutually perpendicular directions. The frequency range of measurements was 5–25 MHz, which corresponds to a depth of SAW penetration of about 120–600 μm. Measurements were conducted on samples made of 12X18H10T stainless steel with planar dimensions of 105 × 76 mm and thickness h = 8 mm, which were welded along the axis by an electron beam. The weld width was 5–7 mm. After the measurements, the samples were investigated by the fracture method based on the technique of a complete relief. The results of measurements are compared with the data obtained by fracture tests. The potential of the studied method is analyzed, and the measurement errors are estimated.