Structural Health Monitoring of Shear Waves in Aluminum Plates

In this research, the acoustic emissions from simulated crack growth and incremental crack growth in a cyclically loaded aluminum panel were detected by acoustic emission sensors. One of these sensors was comprised of an array of thin strips of piezoelectric material bonded to the specimen and electrically connected. The geometry of these sensor strip arrays and their orientation to the fracture site enabled the sensors to capture the shear component of the acoustic emission waveform. Cyclical loading was used to grow the crack, allowing sensor performance to be assessed in comparison to bonded and resonant sensors. The detection of the shear wave is of particular interest as the shear component of fretting events is often small, providing a possible means of discriminating between critical events (crack propagation) and sources of minimal concern (fretting). Shear modes were detected in the acoustic emissions from both the simulated crack growth and the crack growth due to cyclical loading.