Wrinkles in fiber-reinforced resin composites: Micro-stress non-destructive testing
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摘要: 纤维增强树脂复合材料在制造和服役过程中会不可避免地产生各类缺陷,且缺陷种类多、特征尺寸分散,检测难度大。缺陷检测的最终目的是对含缺陷构件的机械力学性能给出适应性评价,为此提出了一种特别适合于纤维增强树脂复合材料的集缺陷检测和性能评价为一体的微应力无损检测方法。该方法对构件施加一定的载荷使其处于微应力状态,结合全场位移的光学测量技术,捕捉缺陷导致的异常响应,以褶皱缺陷为例给出了具体的实施过程。首先基于褶皱缺陷特征响应的预测结果设计了特定的检测方案,并基于光栅投影测量技术创新性地提出了一种测量离面位移的新方法。试验结果表明,在轴向微应力加载下,利用提出的光栅投影测量方法可以探测到褶皱缺陷导致的离面位移畸变,畸变的位置和大小反映了缺陷的位置和严重程度。同时由于使用了光-力学的综合检测方法,可以跨越对缺陷具体形貌尺寸的探查,直接获得含缺陷构件在给定工况下的力学行为响应,为构件适应性评价提供参考依据。
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关键词:
- 纤维增强树脂复合材料 /
- 褶皱缺陷 /
- 特征响应 /
- 光栅投影 /
- 无损检测
Abstract: Various defects with dispersive feature sizes can be accumulated inevitably in fiber-reinforced resin composites during their manufacturing and service processes, which are also difficult to be detected. The final objective of defects testing is to obtain the accuracy assessment of performance of defective structures. A micro-stress non-destructive defect detection and evaluation method is proposed for fiber-reinforced resin composites, which is especially suitable for composites measurement. Combing with the optical measurement technology for full-field displacement, the abnormal responses which caused by the defects of the structure under low stress level is able to be captured. The wrinkle defect detection is taken as an example to show the measurement processes. First, a specific detection scheme is designed based on the theoretical prediction of characteristic responses of wrinkles. Then, a new method of full-field displacement measurement is innovatively proposed based on the grating projection technology. Results show that under the axial tensile loading, the distorted out-of-plane displacements caused by wrinkles can be detected by the improved grating projection technology. The distorted displacements revealed the spatial distribution and severity of defects, and the influence on structural performance degradation can be evaluated based on the degree of displacement distortion. Further, by applying the optical-mechanical detection method, the mechanical responses of the defective component under a given working condition can be obtained directly, which can provide a reference for the adaptability evaluation of the component. -
图 2 纤维增强树脂复合材料中含均匀型褶皱的RVE等效刚度计算模型
Figure 2. Calculation model of equivalent stiffness of RVE with uniform wrinkle in fiber-reinforced resin composites
Cij—Ply stiffness matrix; C*—Equivalent stiffness matrix of wrinkle-free laminates; C**—Equivalent stiffness matrix of laminates with uniform wrinkle; θk—Orientation angle of kth ply; φ—Out-of-plane misalignment
表 1 碳纤维(CF)/环氧树脂(EP)复合材料弹性参数
Table 1. Elastic parameters of carbon fiber (CF)/epoxy (EP) composites
E11 /GPa (E22 /E33) /GPa G23 /GPa G31 /GPa G12 /GPa ν21 ν32 ν31 133.3 9.09 3.16 7.24 7.23 0.261 0.436 0.261 Notes: E11, E22, E33—Elastic modulus (direction 11, 22, 33); G12, G23, G31—Shear modulus (direction 12, 23, 31); v21, v32, v31—Poisson’s ratio (direction 21, 32, 31). 表 2 CF/EP复材层合板中褶皱缺陷对不同载荷的响应敏感性
Table 2. Response sensitivity of wrinkle defects to different loading modes in CF/EP composite laminates
Loading mode Uniaxial tensile Bending Shearing Response sensitivity In-plane displacement u v Out-of-plane displacement w Note: *Sensitivity: > > . 表 3 CF/EP复材层合板中层间弱粘结缺陷对不同载荷的响应敏感性[30]
Table 3. Response sensitivity of weak bonding defects to different loading modes in CF/EP composite laminates
Loading mode Uniaxial tensile Bending Shearing Response sensitivity In-plane displacement u v Out-of-plane displacement w 表 4 CF/EP试样中的缺陷参数
Table 4. Defect parameters of the CF/EP specimens
Specimen number Layup sequences Wrinkle parameters Wavelength/mm Amplitude/mm Wrinkle ratio I [0/90/0/90]s 6.0 1.2 0.200 II [0/90/0/90]s 12.0 0.8 0.067 表 5 CF/EP试样离面位移实测结果与有限元结果比较
Table 5. Comparison of out-of-plane displacement of CF/EP specimens between measurement results and finite element results
Specimen number Load/N Measurement results/cm Finite element results/cm Error I 200 0.01078 0.0089 17.7% 500 0.01806 0.0154 14.7% 800 0.02093 0.0193 7.8% 1 000 0.02359 0.0212 10.1% 1 200 0.02508 0.0228 10.0% Ⅱ 200 0.00218 0.0027 20.1% 500 0.00918 0.0101 8.6% 1 200 0.01361 0.0115 18.3% -
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