Robot assistant laser ultrasonic test system and its parameter matching method

In order to solve the problem of non-contact and high precision non-destructive test of aircraft composite material structures, a laser ultrasonic test system based on articulated robot and optoacoustic parameter matching method is proposed. The model of layered anisotropic composite material is built with finite element method, and the characteristics of the asymmetric distribution and beam tilt and distortion of laser ultrasonic induced by the layered anisotropic property of the material are calculated and analyzed. The optoacoustic parameter matching method using laser ultrasonic to characterize the delamination is obtained based on the numerical simulation and experiment results. In the system design, an Nd:YAG pulse laser with 1064 nm wavelength is used to generate the ultrasonic signal, and the ultrasonic signal is detected by a two wave mixing laser interference system based on photorefractive effect. The exciting and detecting lasers are transmitted by the optical fibers and projected on the surface of the target under test. A precise six-axis articulated robot is adopted as the C-scan device. The laboratory prototype of the system was built, the C-scan test of the carbon fiber reinforced plastic (CFRP) specimen was realized, and the shape, size and distribution characteristics of the simulated defects in the specimen was obtained. Thus the effectiveness of the test system and parameter matching method is verified. The research results prove that the developed robot assistant laser ultrasonic test system can realize the detection and imaging of the internal delamination with diameter larger than 1 mm in the CFRP composite specimen, and has application prospect in the nondestructive test of aircraft composite material structures.