Temperature and Damage-Affected Lamb Wave Signals in a Composite Sandwich Plate

The difference between damage-affected signals and temperature-affected signals is investigated. Temperature effects were examined by measurements in a climatic chamber. Sensors were mounted on the skin of a CFRP sandwich structure which was exposed to temperatures from −50 to +50 °C with the step of 10 ℃. Both A0 and S0 modes were analyzed in the frequency range of 50–300 kHz. Time of flight delays indicating a velocity decrease with increasing temperature were confirmed for the corresponding modes. However, with decreasing temperature, frequency shifts towards higher frequencies were observed, which caused difficulties for dispersion curve determination. Damage–type signals were demonstrated by impact-induced damage. Time of flight change was examined in relation to the temperature and damage. Temperature affected time delay/time advance increased with the signal length while damage influenced only some part of the signal. These findings enabled to distinguish the cause of the time of arrival change. Therefore, false alarms regarding damage detection are likely to be reduced.