Fatigue Damage Detection in Thin Composite Laminates Using Out-of-Plane Moire Interferometry

HE APPLICATION OF CYCLIC loads to a structural component generally proTduces local damage prior to catastrophic failure. In contrast to the behavior of metals, which propagate fatigue damage as unique surface cracks, fatigue damage in composites often initiates and propagates internally. A variety of nondestructive inspection methods are currently employed to detect this internal damage in laminates. Ultrasonic and x-ray techniques are commonly used in industrial applications. Thermographic, laser holographic and acoustic emission methods have demonstrated varying degrees of applicability in experimental programs. Unfortunately, these methods all require the use of sophisticated equipment and highly skilled operators. In addition, interpretation of the output from these devices is not always straightforward [1-8]. Propagation of delamination is the damage mechanism most responsible for the ultimate failure of laminates containing some angle plys [9-13]. This