Research on the defect detection of carbon fiber reinforced polymer based on pulse laser ultrasound

Abstract

The accumulation of micro damage such as matrix crack and fiber fracture in carbon fiber reinforced polymer (CFRP) under cyclic loading will seriously affect the mechanical properties of CFRP. The size of micro damage is small and the location is scattered, so it is difficult to identify accurately by traditional nondestructive testing methods. Laser ultrasonic testing technology has the advantages of non-contact, fast detection speed and wide measurement range, especially combining the advantages of long-distance excitation and large angle incidence of laser, it has great potential in the damage detection of large-scale and curved structure materials. In this paper, based on the laser thermos-elastic effect, the generation process and propagation characteristics of ultrasonic wave in CFRP are systematically studied on the basis of analyzing the distribution of temperature, stress and displacement fields after laser acting on CFRP. By analyzing and comparing the ultrasonic echo signals of different defects characteristics in CFRP, the defect depth and length are calculated based on the time when the longitudinal wave scattering wave (Lr) reaches the detector. The calculation results show that the errors of this method are about 7 % and 5 % for the detection of the depth and length of the CFRP.