Thermosonic inspection of a welded SUS plate

The technique of bringing a sample to vibration in the near ultrasound regime (20 kHz and above) and to look at the thermal signal of the surface with an infrared camera has been used for several years as a nondestructive evaluation tool to detect defects such as cracks within materials. The basic idea of this technique is to excite the part with a short (similar to 280 ms duration) pulse of ultrasonic power (similar to 2 kW, similar to 20 kHz). The relative motion of defect faces causes the ultrasound energy to dissipate locally at the defect. In turn, this energy acts as a localized heat source (hot spot). The resulting surface temperature change in the vicinity of the defect is imaged by means of a thermal infrared camera. The sequence of images, taken before, during, and after the application of the ultrasonic pulse, reveals the presence of the defect. In this paper we show results of our investigations regarding the hot spot generation at defects in the welded thin SUS plate.