PREDICTION OF FATIGUE LIFE OF COMPOSITE LAMINATES USING LASER ULTRASONIC METHOD

Composite laminates suffer from fatigue damages under cyclic loads and can display quite notable property degradation during the process. Stiffness degradation is one of the most utilized to characterize fatigue damages. However, stiffness measurement in real applications remains a challenge. Since the stiffness degradation also directly affects the velocity of the ultrasonic wave that propagates inside the structure, it is reasonable to use the wave velocity to assess the damage levels and further predict the residual life. In a multi-layer laminate, dispersive matrix cracks, delamination and fibre breakage are usually considered to be the main causes of decrease in stiffness. In this paper, a stiffness/velocity degradation model based on the three damage mechanisms is proposed to characterize the fatigue damages in GFRP composite laminates using Lamb wave velocity measured with laser ultrasonic method. Life predictions were also made with a residual velocity criterion, multiple prediction points were chosen to evaluate the model's ability of early stage life prediction. The prediction results were compare to experimental data where overall good agreement was obtained.