Effect of drilling delamination on compressive mechanical behaviour of open-hole laminates
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摘要: 钻孔分层损伤对复合材料层合孔板的承载能力和失效模式有着显著的影响。通过实验和仿真相结合的方式,开展单一预制分层缺陷下、双分层缺陷同侧耦合及双分层缺陷异侧耦合作用下复合材料层合孔板的压缩承载能力及失效模式的研究。通过预埋聚四氟乙烯薄膜,制备了含单一圆形预制分层缺陷的碳纤维增强树脂复合材料开孔板试件,采用浸没式超声C扫和数字图像DIC技术分别对复合材料层合板损伤和法向变形进行检测,研究含不同尺寸预制分层开孔层合板在压缩载荷下的分层扩展及失效变形特征,进而揭示分层缺陷大小对其承载能力的影响机制。构建基于内聚力单元方法的含孔复合材料层合板数值模型,对比实验修正模型,探索了单一预制分层缺陷下碳纤维增强树脂复合材料开孔板的损伤扩展机制,并在此模型基础上开展双分层缺陷耦合作用下复合材料开孔板在压缩载荷作用下的屈曲变形、分层扩展和承载能力的数值预测和分析。实验结果表明:含单一圆形预制分层缺陷的碳纤维增强环氧树脂复合材料开孔层合板试件呈现出初始受压、局部屈曲、整体屈曲后破坏的失效模式,预制分层缺陷对复合材料孔板压缩力学性能有显著影响,随着缺陷的增大压缩承载能力逐渐下降。双分层缺陷耦合作用数值分析表明:双分层缺陷进一步降低了复合材料孔板压缩承载能力,同侧非对称耦合分层缺陷结构的失效模式与单一缺陷结构基本一致,而异侧非对称耦合分层缺陷结构出现了双裂纹扩展,该裂纹扩展模式进一步削弱了孔板的压缩承载能力。Abstract: The delamination damage has significant influence on the bearing capacity and failure mode of open-hole laminates. By combining experiment and simulation, the compression bearing capacity and failure mode of composite open-hole laminates with single prefabricated laminated defects, two laminated coupling defects on the same side and double laminated coupling defects on the different side were studied. Through the embedded polytetrafluoroethylene (PTFE) membrane, the open-hole laminate containing single prefabricated delamination defects was prepared. By means of immersion ultrasonic C scan and digital image DIC technique, the damage evolution and normal deformation were characterized and monitored. The delamination propagation behavior and failure deformation characteristics of laminates with various defect sizes under compression loading were studied, and the influence mechanism of the size of the delamination defects on the bearing capacity of the laminates was revealed. A numerical model of open-hole laminate was established based on the cohesion element method. The damage propagation mechanism of open-hoe laminate with single prefabricated laminated defects was explored. Based on the optimized model, the numerical prediction and analysis of the buckling deformation, delamination expansion and bearing capacity of the open-hole laminate with two delaminated coupling defects were carried out. The experimental results show that the specimen with single delamination defect presents the initial compression, local buckling and overall buckling. The delamination size has significant impact on the compressive capability, which decreases with the increasing of delamination size. The numerical results of two delaminated defects show the second delaminated defect further reduces the compressive bearing capacity. The failure model of laminate with two coupling defects on the same sides is similar with that of laminates with single prefabricated defect; while, double-crack propagation occurs in the asymmetrical coupled laminated structure on the opposite side, which further weakens the compression bearing capacity of open-hole laminates.
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Key words:
- composite /
- drilling-induced delamination /
- compressive buckling /
- cohesive element /
- damage evolution
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图 2 单一预制分层缺陷的CF/EP开孔层合板模型示意图
Figure 2. Schematic diagram of CF/EP open-hole laminates with a single prefabricated lamination defect
L0—Total length of laminate; L1—Length of clamping end; b—Width of laminate; D—Diameter of prefabricated defect; d—Diameter of open-hole; t—Thickness of laminates; PTFE—Polytetrafluoroethylene
图 6 双线性内聚力单元损伤模型示意图
Figure 6. Diagram of bilinear cohesive damage model
Ti—Traction force of laminates during type i fracture; Kp—Penalty stiffness; δi—Displacement response under type i traction; δi0—Crack opening displacement corresponding to the maximum stress; σmax—Maximum normal stress value; τmax—Maximum tangential stress
表 1 CF/EP开孔层合板详细尺寸
Table 1. Detailed dimensions of CF/EP open-hole laminates
Type L0/mm L1/mm b/mm D/mm d/mm t/mm I-0 135 30 35 − 6 2.6 D-10 135 30 35 10 6 2.6 D-15 135 30 35 15 6 2.6 D-20 135 30 35 20 6 2.6 Notes: I—Defect-free porous composite plate; The number after the letter D is the diameter of the damaged area. 表 2 CF/EP预浸料材料属性及参数
Table 2. Material properties and parameters of CF/EP prepreg
Parameter Value E11/MPa 144700 E22/MPa 9650 E33/MPa 9650 G12/MPa 5800 G13/MPa 5800 G23/MPa 4800 ν12 0.3 ν13 0.3 ν23 0.45 Notes: E—Elastic modulus; ν—Poisson's ratio; G—Shear modulus; 1—Direction of fiber; 2—Direction of matrix; 3—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. 表 3 双缺陷耦合作用下CF/EP开孔层合板压缩屈曲数值模拟结果(D-20-FEA-T)
Table 3. Numerical simulation results of compression buckling of CF/EP open-hole laminates under the coupling action of double defects (D-20-FEA-T)
State 1 2 3 4 Sublaminate 1 Sublaminate 2 表 4 双缺陷耦合作用下CF/EP开孔层合板压缩屈曲数值模拟结果(D-20-FEA-Y)
Table 4. Numerical simulation results of compression buckling of CF/EP open-hole laminates under the coupling action of double defects (D-20-FEA-Y)
State 1 2 3 4 5 Sublaminate 1 Sublaminate 3 -
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