Numerical investigations into Nonlinear Vibro-ultrasonics and Surface Vibration Comparison method for detection of defects in a composite laminate

This paper begins with a numerical study based on earlier experiments of nonlinear vibro-ultrasonic behaviour of a composite laminate with a delamination defect upon sinusoidal linear sweep signal excitation . A methodology to model laminates with cross-ply layup is presented which can be extended to any layup if desired. In comparison to experiments where it is challenging to visualize the fine details of vibrations, simulations make it easier to visualize and helps in optimizing the defect probing methods. The paper goes on to discuss with the help of numerical results that a separation gap between the delamination surfaces occurs to be a common cause for the failure of nonlinear vibro-ultrasonic methods to detect delamination defects. This constraint can often be overcome with application of higher excitation amplitudes as has been demonstrated in several experimental works. However in this study, a new approach named Surface vibration comparison method (SVCM) to probe delamination defects in the absence of contact acoustic nonlinearity is proposed as a proof-of-concept. The technique is then evaluated for detection of weak kissing bond defects in composite beam specimens. Both the experimental and simulation results show potential of the method as damage detection technique in thin composite structures.