Vibration-Based Nondestructive Evaluation of Thermal Stress-Induced Damage in Thin Composite Laminates

A feasibility investigation on vibration-based nondestructive evaluation of thermal stress-induced micro-failure in the free edge region of thin composite laminates(1mm thick) has been carried out. The failure occurrence and damage zone, which were predicted by the three-dimensional finite-element thermal stress analysis, were observed using the ultrasonic C-scan and optical microscopy. Analysis of the vibration spectrum measured from the laminate beam specimens by the vibration sweep test exhibited that the obvious decrease in resonance frequency and some considerable increase in damping factor were associated with the micro-failure formation. The vibration technique utilizing short beam and high resonant frequency was found to be very sensitive to the thermal stress-induced damage in the thin laminates