Laser ultrasonic testing technology for carbon fiber reinforced resin braided composites based on air-coupled transducer
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摘要: 激光超声技术具有无需耦合剂、快速及高分辨等特点,适用于各向异性碳纤维增强树脂编织复合材料的缺陷检测。运用有限元法分析了激励位置和编织结构对激光点源激发超声波信号的影响,获得了弹性波在材料内部的传播规律以及能量分布特征,并采用1 MHz空气耦合换能器搭建了一套小型化、低成本的非接触激光超声C扫描成像系统,开展了斜纹和缎纹碳纤维增强树脂编织复合材料的近表微结构和内部缺陷检测实验。结果表明,基于空气耦合换能器的激光超声成像可以高精度地再现碳纤维增强树脂编织复合材料的近表树脂囊、碳纤维束形状、取向、尺寸及其内部缺陷等空间分布特征,有望为航空复合材料提供一种原位的微结构表征和缺陷检测方法。Abstract: Due to its non-contact, no coupling agent, fast and high resolution nature, laser ultrasonic technology has great potential in the detection of defects of anisotropic carbon fiber braided composites. In this paper, the finite element method was used to analyze the effect of the excitation position and braided structure on the ultrasonic signal excited by the laser point source, also the propagation law and energy distribution characteristics of the elastic wave inside the material were obtained. A non-contact laser ultrasonic C-scan imaging system was built based on a 1 MHz air-coupled transducer, and the experiments of near-surface micro structure and internal defect detection in plain and satin carbon fiber braided composites were carried out. The experimental results have shown that the spatial distribution characteristics of the near-surface resin capsule, carbon fiber bundle shape, orientation, size and internal defects and so on in the carbon fiber braided composites can be observed with high resolution by employing the laser air-coupled ultrasonic imaging technique. It provides an effective method of the micro structure characterization and defect detection for the aerospace composites.
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Key words:
- braided composites /
- laser ultrasound /
- air-coupled transducer /
- non-destructive testing /
- defect
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图 3 碳纤维增强树脂编织复合材料有限元仿真结果:(a)载荷施加位置示意图;(b)激励在纬向丝束处;(c)激励在弯曲丝束处;(d)激励在经向丝束处;(e)单向层压复合材料
Figure 3. Finite element simulation results of carbon fiber reinforced polymer braided composites: (a) Schematic diagram of load application position; (b) Excitation at the weft tow; (c) Excitation at the bending tow; (d) Excitation at the warp tow; (e) Unidirectional laminated composites
图 5 碳纤维增强树脂编织复合材料微结构C扫描成像: (a)斜纹; (b)近表纹理; (c)沿(b)和(d)中虚线分布的信号强度; (d)表面光反射率测量
Figure 5. Micro structure C-scan imaging of carbon fiber reinforced polymer braided composites: (a) Plain weave; (b) Near surface veins; (c) Signal intensity distributed along the dotted line in (b) and (c); (d) Surface light reflectance measurement
图 6 碳纤维增强树脂编织复合材料模拟缺陷C扫描成像: (a)模拟缺陷; (b)背部3 mm直径盲孔C扫描成像;(c)沿(b)中虚线分布的信号强度; (d)基于声程的C扫描成像
Figure 6. Simulated defect sample C-scan imaging (a) Simulated defects (b) Backside 3 mm diameter blind hole C-scan imaging (c) Signal intensity distributed along the dotted line in (b) (d) Sound path-based C-scan imaging
图 7 缎纹碳纤维增强树脂编织复合材料分层样品C扫描成像: (a)复合材料;(b) 20 MHz相控阵C扫描成像;(c) 激光空气耦合超声C扫描成像;(d)表面纹理
Figure 7. Delamination sample C-scan imaging of satin braided carbon fiber reinforced polymer composites: (a) Satin braided carbon fiber composites; (b) 20 MHz phased array C-scan imaging; (c) Laser air-coupled ultrasound C-scan imaging; (d) Near surface veins
表 1 碳纤维增强体与环氧树脂基体材料的机械和热学特性
Table 1. Mechanical and thermal properties of carbon fiber reinforcement and epoxy matrix
Material Carbon fiber Epoxy ρ/(kg·m−3) 1550 1200 E1/GPa 150 3.5 E2=E3/GPa 10 − G12=G13/GPa 4.9 − G23/GPa 3.2 − ν12=ν13 0.33 0.35 ν23 0.44 − C/(J·kg−1·K−1) 981 981 λ1/(W·m−1K−1) 60 0.2 λ2=λ3/(W·m−1K−1) 4 − α1/K−1 1×10−7 2×10−5 α2=α3/K−1 2.5×10−7 − Notes: ρ is the density; E is the Young’s modulus; G is the shear modulus; ν is the Poisson's ratio; C is the specific heat capacity; λ is the coefficient of thermal conductivity; α is the coefficient of thermal expansion. -
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