Structural health monitoring of anisotropic layered composite plates using guided ultrasonic Lamb wave data

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 the possibility of SHM using algebraic reconstruction techniques (ART) for tomographic imaging with Lamb wave data measured in realistic materials. Commercially available narrow bandwidth PZT crystals with the center firequency at 1.0 MHz were used as sensors on 5 mm thick 300 x 300 mm layered quasi-isotropic and cross-ply composite plates with and without defects. Defects (through holes) were synthetic and have been chosen to simulate high velocity impact damage in composite plates. The problem of Lamb wave mode identification to implement ART in anisotropic composite materials has been circumvented through the identification and use of a fairly general new wave energy-based reconstruction parameter. 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.