Influence of embossed wrinkle and its grinding on the compressive failure behavior of laminates
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摘要:
外突褶皱是复合材料结构的常见制造缺陷，评估打磨处理对含外突褶皱复合材料结构承载行为的影响，是开展复合材料制造质量评定与制定装配策略的重要依据，但目前相关研究报道缺失。本文采用实验与数值模拟相结合的方法研究了外突褶皱及打磨处理对层合板压缩失效行为的影响。实验方面，采用横条法引入褶皱缺陷，制备含外突褶皱层合板并通过打磨手段处理外突褶皱。借助数字图像DIC技术监测加载过程表面应变分布，采用电子显微相机捕捉损伤过程，分析试样的压缩承载行为和破坏模式。数值模拟方面，表征被测试样的褶皱铺层起伏形态，采用Hashin失效准则与内聚力方法构建高保真度含褶皱层合板层内/层间失效分析有限元模型，探讨含外突褶皱以及打磨褶皱层合板的应力分布特征及失效机制并分析外突褶皱高度对层合板压缩强度影响。结果表明，外突褶皱降低层合板压缩承载能力，而打磨处理会进一步降低层合板的承载能力与刚度。本文所建立的数值模型与实验结果吻合较好。对于外突褶皱层合板，层合板向褶皱凸起一侧屈曲，褶皱上方发生分层损伤并向端部扩展，纤维损伤从褶皱下侧铺层波谷处向其他层扩展；对于打磨褶皱层合板，主层板向褶皱凸起的相反方向屈曲，首先在打磨断层处发生面外拱起分层损伤，随后褶皱上方纤维层发生拱起断裂，纤维损伤向其他层扩展。随外突褶皱高度的增加，含褶皱层合板以及打磨褶皱层合板的压缩失效载荷均显著降低。以上研究可为含外突褶皱复合材料结构的处置方案评估提供参考。 打磨褶皱层合板(GMW)表面压缩应变 ${\varepsilon _{yy}}$ 变化(a) GMW实验与数值位移载荷曲线 (b) GMW模型纤维压缩损伤扩展过程 Abstract: Evaluation of the grinding impact on the bearing capacity of laminates with embossed wrinkle is essential for the manufacturing quality assessment and the determination of assembly strategies for composites. In this study, both the experimental and numerical investigations were carried out to understand the impact of embossed wrinkle and its grinding treatment on the compressive failure behavior of laminates. In experimental study, Digital Imaging Correlation (DIC) technology was applied to monitor the distribution of surficial strain and industrial digital camera with electron microscope was used to record the damage process. The bearing behavior and fracture mode of the laminates were analyzed. In numerical study, high-fidelity finite element models were created to predict the intra/inter-laminar failure by combining the Hashin failure criterion and cohesive element method. The features of stress distribution and failure mechanism of the laminates with embossed wrinkle and the one grinded were investigated, the influence of wrinkle height on compressive strength were also explored. The results show that the embossed wrinkle plays a significantly negative impact on the compressive loading capacity of laminates, and the loading capacity would be decreased further by the grinding operation, as well as the stiffness. The numerical prediction fits well with the test data. For the embossed wrinkle samples, the laminate buckles along the convex direction of wrinkled layers. Delamination occurs above the wrinkled area and extends to the loading ends. The fiber breakage extends from the trough of wave layer under the wrinkled area to the other layers. For the grinded samples, the laminate buckles opposite the wrinkle convex direction. First, the discontinuous layer hunches-up and delamination occurs. Afterwards, the upside continuous layer at wrinkle area hunches-up and breaks, the fiber damage spreads around. With the increase of wrinkle height, the compressive failure loads of wrinkled laminates and the grinding samples both significantly decrease. This work provides a reference for the assessment of the treatment scheme for composite structures with embossed wrinkle defects.-
Key words:
- composite laminates /
- wrinkle defect /
- compressive strength /
- numerical analysis /
- grinding operation
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图 3 横条法制备含褶皱试样示意图
Figure 3. Wrinkled specimen manufacture using the strip-insertion method
图 6 T300级碳纤维/环氧树脂正交层合板压缩位移-载荷曲线
Figure 6. Compressive displacement-load curves of T300 carbon fiber/epoxy orthogonal laminates
图 7 压缩过程中试样表面εxx应变分布的演变过程：(a) NW；(b) MW；(c) GMW
Figure 7. Variation of surface strain εxx distribution during compression: (a) NW; (b) MW; (c) GMW
图 8 试样压缩破坏过程：(a) NW；(b) MW；(c) GMW
Figure 8. Damage process of samples: (a) NW; (b) MW; (c) GMW
图 10 不同褶皱大小层合板模型的局部网格信息
Figure 10. Local mesh information of the different wrinkled laminate models
图 12 试样实验及数值模拟的压缩失效载荷
Figure 12. Experimental and numerical results of compressive failure load
图 13 NW模型纤维压缩损伤演化与应力分布
Figure 13. Fiber compressive damage progression and stress distribution of NW model
图 14 MW模型分层损伤起始与扩展
Figure 14. Delamination damage initiation and progression of MW model
图 15 MW模型纤维损伤起始与扩展
Figure 15. Fiber and matrix damage initiation and progression of MW model
图 16 MW模型内聚力单元S33应力分布
Figure 16. Variation of stress distribution S33 of cohesive element in MW model
图 17 MW模型S11应力分布以及面法向位移
Figure 17. Variation of stress distribution S11 and out-of-plane displacement in MW model
图 18 GMW试样试验和仿真载荷-位移曲线
Figure 18. Experimental and numerical load-displacement curves of GMW sample
图 19 GMW模型分层损伤起始与扩展
Figure 19. Delamination damage initiation and progression of GMW model
图 20 GMW模型纤维压缩损伤起始与扩展
Figure 20. Fiber compressive damage initiation and progression of GMW model
图 21 GMW模型内聚力单元S13应力变化
Figure 21. Variation of stress S13 of GMW model cohesive element
表 1 显微图片测量褶皱参数
Table 1. Wrinkling parameters measured by microscopic images
h1/mm h2/mm h3/mm h4/mm λ1/mm λ2/mm λ3/mm 0.50 1.02 1.40 0.10 13.8 14.8 16.8 Notes: h1−Wrinkle height of the 15th layer; h2−Wrinkle height of the 17th layer; h3−Wrinkle height of the 20th layer; h4 −Wrinkle height of the 14th layer; λ1−Wavelength of the 11th layer to the17th layer; λ2−Wavelength of the 17th layer to the19th layer; λ3−Wavelength of the 20th layer. 
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表 2 T300级碳纤维/环氧树脂正交层合板失效载荷与表观刚度
Table 2. Failure load and apparent stiffness of T300 carbon fiber/epoxy orthogonal laminates
Label F/(kN·mm−1) CV/% K/(kN·mm−2) CV/% NW 2.28 1.79 5.9 3.05 MW 1.73 4.11 5.7 1.35 GMW 1.45 1.03 4.6 2.28 Notes: F−Failure load per unit width modulus; CV−Coefficient of variation; K−Slope of F vs. displacement.
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表 3 复合材料单向板材料参数
Table 3. Material Properties of unidirectional laminate
Parameter Value Parameter Value E11/GPa 130.9 XT/MPa 1911.5 E22/GPa 7.906 XC/MPa 1100 E33/GPa 7.906 YT/MPa 38.5 μ12 0.35 YC/MPa 142.7 μ13 0.35 S/MPa 90.9 μ23 0.40 Gft/(mJ·mm−2) 133 G12/MPa 3145 Gft/(mJ·mm−2) 30 G13/MPa 3145 Gmt/(mJ·mm−2) 0.352 G23/MPa 2824 Gmc/(mJ·mm−2) 1.54 Notes: E−Elastic modulus; μ−Poisson’s ratio; G−Shear modulus; 1−The direction of fiber; 2−The direction of matrix; 3−The thickness direction of layer; XT−Longitudinal tensile strength; XC−Longitudinal compressive strength; YT−Transverse tensile strength; YC−Transverse compressive strength; S−In-plane shear strength; Gft, Gfc, Gmt, Gmc−Critical value of strain energy release rate.
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表 4 不同大小褶皱缺陷参数
Table 4. Wrinkles defect parameter of different levels
Label SW MW LW h1/mm 0.31 0.56 0.92 h2/mm 0.70 0.97 1.37 h3/mm 1.05 1.35 1.75 h4/mm 0.11 0.07 0.09 λ1/mm 10.6 13.8 14.8 λ2/mm 13.2 14.8 15.8 λ3/mm 13.8 16.8 16.8
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表 5 层合板层间性能
Table 5. Interlaminar properties of laminates
${K_{\text{I}}} = {K_{{\text{II}}}}$/
(N·mm−3)$\sigma _{\text{I}}^{{\text{max}}}$/
MPa$\sigma _{ {\text{II} } }^{ {\text{max} } }$/
MPa${G_{{\text{IC}}}}$/
(N·mm−1)${G_{{\text{IC}}}}$/
(N·mm−1)α 106 28 55 0.102 0.277 1.8 Notes: KI, KII—Mode I/II interfacial stiffness; $\sigma _{\text{I}}^{{\text{max}}}$, $\sigma _{{\text{II}}}^{{\text{max}}}$—Mode I/II interfacial strength; GIC, GIIC—Mode I/II critical strain energy release rate; α—Empirical parameter of Power law.
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