Fatigue and leakage-type damage detection in metallic plates and pipelines using piezoelectric patch acoustic sensors

Piezoelectric sensors are used to convert mechanical energy into electrical energy, and vice versa and, therefore, can effectively be used for dual applications as actuator or sensor. Though Piezoelectric patch sensors (piezos) have been commonly used for active sensing, application of piezos for passive sensing, such as capturing the acoustic emission (AE) signals, needs more in-depth investigations. The aim of the present study is to examine the suitability of using piezo sensors as passive sensors for effectively capturing the acoustic signals and AE based damage detection. Experimental investigations are carried out on (i) a thin metal plate subjected to monotonic and cyclic loading, and (ii) metal pipelines of two different lengths carrying pressurised water subjected to simulated leakage conditions. In both the cases, series of piezos and commercially available standard AE sensors are used side by side for comparative evaluation of the captured responses during the progress of damage/leakage. Different AE features i.e., amplitude, counts, energy, signal strength and average frequency are obtained from the captured signals for damage detection. It is observed that with the proper amplification and acceptable signal strength, piezo sensors are capable of capturing all the significant AE features, similar to the conventional AE sensors and are able to detect damage in metal plate and leakage in case of a pipe. The experimental results establish the feasibility of using piezos for passive AE sensing, besides its well documented efficacies for active actuation-sensing.