Non-contact detection of delamination in layered anisotropic composite materials with ultrasonic waves generated and detected by lasers

This paper presents the non-contact detection of internal delamination in layered anisotropic composite material with ultrasonic waves generated by a pulse laser and received by a two-wave mixing laser interferometer. Three-dimensional finite element method is used to simulate the propagation of laser generated ultrasonic waves in carbon fiber reinforced plastics and the interaction with internal delamination. A composite laminate with simulated internal delamination is made as specimen, and a laser ultrasonic system for experiments is set up. The reflection and attenuation characteristics of laser ultrasonic induced by the internal delamination are analyzed theoretically and experimentally. The effects of measuring position and wave frequency on the detection of internal delamination are discussed, and suitable choices of the parameters of laser ultrasonic are suggested. The C-scan images of the composite specimen are obtained using the laser ultrasonic system. The results show that it is possible to decrease the influences of the layered anisotropic feature of composite materials on the detection of internal delamination by controlling the laser parameters.