碳纤维复合材料的激光超声测厚技术影响因素

Influencing factors of laser ultrasonic thickness measurement technology for carbon fiber composite materials

碳纤维复合材料具有显著的高比强度和高比模量,已成为飞行器结构材料的首选。碳纤维复合材料厚度的均匀性会严重影响飞行器的正常工作。本文采用激光超声脉冲反射法对碳纤维复合材料的厚度进行测量,实现复合材料的非接触式测量,并分别研究了不同透镜、不同直径的光斑和不同功率的光源对测厚信号的影响。检测结果表明:在控制相同能量的激光脉冲激励下,使用直径小的光斑能激发振幅较高的超声回波信号;使用凸透镜聚焦产生的超声信号幅值高于柱面透镜聚焦产生的超声信号幅值,且测量碳纤维复合材料厚度的相对误差小于5.3%;在无外加光的暗室下进行测量实验,背景噪声对底面反射回波信号干扰小。

Carbon fiber composites have remarkable high specific strength and high specific modulus, and have become the first choice of aircraft structural materials. The uniformity of carbon fiber composite thickness will seriously affect the normal operation of aircraft. In this paper, the thickness of carbon fiber composite material is measured by laser ultrasonic pulse reflection method, and the non-contact measurement of composite material is realized. The effects of different lenses, different diameters of light spots and different power light sources on the thickness measurement signal are studied respectively. The test results show that the ultrasonic echo signal with higher amplitude can be excited by using small diameter spot under the excitation of laser pulse with the same energy. The amplitude of ultrasonic signal generated by focusing with convex lens is higher than that generated by focusing with cylindrical lens, and the relative error of measuring the thickness of carbon fiber composite material is less than 5.3%. The measurement experiment is carried out in a dark room without external light, and the background noise has little interference on the echo signal reflected from the bottom surface.