In-situ remaining fatigue life prognosis for unidirectional polymer composite laminates based on modal frequency attenuation

To address the challenge of in-situ fatigue damage prognosis in polymer matrix composite (PMC) laminates under cyclic loading, the acoustic emission technique offers high precision but is expensive, while the static strain–displacement method is economical but lacks sufficient accuracy. This study provides an in-situ fatigue life prognostic framework for unidirectional PMC laminates based on modal frequency attenuation. This approach evaluates stiffness degradation by measuring modal frequencies via impact hammer testing, eliminating the need for disassembly. It offers a cost-effective alternative to acoustic emission while surpassing the accuracy of strain–displacement method. This framework establishes three critical mapping relationships: (1) between remaining life and stiffness degradation, (2) between stiffness degradation and frequency attenuation, and (3) between frequency attenuation and failure characteristics (damage location and area). A demonstration using GFRP laminates under tension–tension cyclic loading shows that all predicted fatigue life values fall within a threefold error band of the experimental fatigue life. The proposed method provides a convenient, accurate, cost-effective, and rapid solution with significant engineering value.