Influence of acoustoelastic effect on the propagation of Lamb waves in CFRP laminates

The presence of initial stress/strain in structures can affect the accuracy and reliability of existing non-destructive testing (NDT) and structural health monitoring (SHM) techniques using ultrasonic waves, while the current understanding of the acoustoelastic effect in multi-layered carbon fibre-reinforced polymer (CFRP) composite structures is insufficient. This paper explores the acoustoelastic effect on the propagation of Lamb waves in composite laminates. Firstly, a quasi-one-dimensional (1D) finite element (FE) model was developed, incorporating a 14-constant hyperelastic constitutive model, to simulate the acoustoelastic effect on longitudinal bulk waves propagating in transversely isotropic materials. The results were compared with the corresponding theoretical results for validation purposes. Subsequently, the validated FE method was applied to a three-dimensional (3D) FE model to investigate the acoustoelastic effect on the propagation of Lamb waves in unidirectional, bidirectional and quasi-isotropic (QI) CFRP laminates. Both uniaxial and biaxial stress-induced acoustoelastic effects on the propagation of Lamb waves in composite laminates are investigated. Furthermore, a uniaxial tension experiment was conducted to investigate the feasibility of in-situ stress monitoring for composite laminates using Lamb waves. The results indicate that the acoustoelastic effect can be utilised for in-situ stress monitoring in composite laminates. The outcomes of this study provide fundamental knowledge for the application of Lamb waves in in-situ stress monitoring of composite structures.