Research of Effects of Temperature Change and Thermal Cycles on Lamb Waves in the Thermal Protection Structure

Abstract

Thermal protection structure (TPS) is one of the most critical parts of reusable aircraft, which represents the greatest risk factor for any mission. Structural health monitoring (SHM) has become a promising candidate for completing the task of monitoring the TPS. Lamb waves are widely applied in SHM benefiting from the high sensitivity to damage and wide propagation range. When there is damage in the structure, Lamb waves scatter and refract during propagation, and the information is transmitted to adjacent piezoelectric transducers (PZT). Therefore, damage detection is usually carried out by comparing Lamb wave signals in the health state and damage state. However, Lamb waves suffer from robustness limitations of temperature, which produces almost the same changes as damage. Therefore, the influence of PZT-induced Lamb wave propagation in the TPS exposed to temperature change and thermal cycles is illustrated in this study. The changes of characteristics in PZT sensors and Lamb wave signals of the structure in the temperature range of 20 °C~150°C and 15 thermal cycles at 150°C are studied. Experiments show that high temperature has a significant impact on Lamb wave signals, mainly reflected in the changes of signal amplitude and phase. The thermal cycles mainly change the amplitude of Lamb wave signals, and the degree is less than that of high temperature.