Pulsed Thermography and Ultrasonic Non-Destructive Evaluation of Corrugated Metallic Thermal Protection System (MTPS) Panel

Abstract

Space vehicles that re-enter earth’s atmosphere require thermal protection system (TPS) to safeguard them from intense aerodynamic heating. Depending on the type of re-entry (lifting/ballistic), trajectory, duration of flight in atmospheric regime etc., the heat flux may vary from 40kW/m2to 180kW/m2. In our studies on metallic TPS (MTPS), corrugated core is joined to either side of the skins by brazing. The brazed joint is evaluated using both pulsed thermography (PT) and ultrasonic testing. PT images show clear visualization of joint and defects. Also it is faster and easier. Ultrasonic testing is done using pitch-catch and pulse-echo techniques, which shows many limitations. In literature, it is reported that for brazed joints using ultrasonic testing, defect location can be identified by faster decay pattern of multiple echoes (compared to that of good location). In case of PM 2000 panel, reversal of the patterns is observed. This new phenomenon is verified with the support of PT. It is also found that for inconel panel, the decay patterns are as reported in literature.