Plate waves structural health monitoring of composite structures

Layered composite plate-like structures are finding an increasing range of applications in the aerospace industry. Structural Health Monitoring (SHM) of such structures is seen as a paradigm that will embrace efficient non-destructive testing/evaluation techniques. The present study demonstrates two techniques that have the potential for the SHM of multi-layered composite structures. The first technique is based on multi-transmitter-multi-receiver (MTMR) technique with tomographic methods used for data reconstruction. In the MTMR, the possibility of SHM using algebraic reconstruction techniques (ART) for tomographic imaging with Lamb wave data measured in realistic materials is examined. Commercially available narrow bandwidth PZT crystals were used as sensors on multi-layered quasi-isotropic and cross-ply composite plates with and without defects. Defects (through holes and low velocity impact delaminations) were synthetic and have been chosen to simulate impact damage in composite plates. To achieve reasonable image quality, conventional cross-hole configuration is replaced by a new modified cross-hole configuration that also optimizes the number of sensors. The second technique is a single-transmitter-multi-receiver (STMR) technique that is more compact and uses reconstruction techniques that are analogus to synthetic aperture techniques. Here, the phase shifting is performed on the individual signals based on the guided wave dispersion relationships. The reconstruction algorithm uses summation of the phase shifted signals to image the location of defects, portions of the plate edges, and any reflectors from inherent structural features of the component.