GUIDED WAVE BASED NONDESTRUCTIVE TESTING: A REFERENCE-FREE PATTERN RECOGNITION APPROACH

A new methodology of guided wave based nondestructive testing (NDT) is developed to detect crack/corrosion damage in metallic structures without using prior baseline data. In conventional guided wave based techniques, damage is often identified by comparing the "current" data obtained from a potentially damaged condition of a structure with the "past" baseline data collected from the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. To develop a more robust damage diagnosis technique, a new concept of NDT is conceived so that defects such as crack and/or corrosion can be detected without direct comparison with previously obtained baseline data. The proposed NDT technique utilizes the polarization characteristics of the piezoelectric wafer transducers attached on the both sides of the thin metallic structure. Crack/corrosion formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the defects by extracting this mode conversion from the measured Lamb waves even at the presence of changing operational and environmental conditions. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to crack/corrosion detection.