Delamination detection in square composite tubes using higher harmonic generation of longitudinal guided waves

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This paper presents the first study on delamination detection in square composite tubes using higher harmonic generation technique. The semi-analytical finite element (SAFE) method is used to analyze the dispersion characteristics of multilayered square composite tubes. A convention displacement field description is provided. Based on the obtained mode shapes of guided waves, a longitudinal guided wave mode with dominated out-of-plane displacement component is selected for delamination detection. Three-dimensional (3D) finite element (FE) models are then developed to simulate guided wave propagation in the square composite tube without and with delamination. With appropriate loads applied on the FE model, a pure longitudinal guided wave mode can be well excited in the simulation. More importantly, higher harmonics including second and third harmonics can be effectively generated due to this longitudinal guided wave mode interacting with the delamination. Numerical results also indicate the nonlinear acoustic parameter can be employed to identify the side of tube wall where the delamination occurs. Subsequently, ultrasonic measurements are conducted on square composite tube without and with delamination to validate the numerical results. It is found that the experimental results agree well with the numerical ones. Finally, parametric studies further investigate the ability of the nonlinear acoustic parameters to identify and locate the delamination. The proposed higher harmonic generation technique shows great potential for detecting early-stage delamination in square composite tubes in practice.