Detection of laminar damage in composite beams using nonlinear ultrasonic modulation techniques

This paper presents the findings of a simulation study of nonlinear ultrasonic modulation in composite laminate beams with delamination damage. Nonlinear modulation of a low-frequency pumping wave and a high-frequency probing wave due to structural damage results in the generation of higher-order harmonics and sideband frequency components. The influence of different system parameters on the magnitude of nonlinear modulations was investigated numerically using 3D explicit finite element analysis. These parameters were the size of the damage relative to the wavelengths of the low-frequency and high-frequency waves; the magnitudes of the low-frequency and high-frequency excitation waves; and the location of the damage relative to the mode shape of the low-frequency pumping wave. The results show that these system characteristics have a strong influence on the magnitude of generated sideband frequencies, and that the development of strategies to optimise the nonlinear interaction of stress waves with localised damage are essential to maximise detectability and damage characterisation in composite structures.