Nondestructive control of weldings using the mirage detection

Small defects in edge-to-edge weldings of thin pieces of stainless steel have been detected by the mirage effect. A simple 1D theoretical model shows the physical parameters influencing the experimental results. Using the phase of both the transverse and normal deviations at various frequencies allows for the separation of optical and thermal effects, of surface and subsurface defects, and for the determination of the depths and widths of the subsurface defects.