Effect of gap-filling compensation on mechanical properties of carbon fiber/epoxy composite-aluminum assembly structure
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摘要: 碳纤维/环氧树脂复合材料和铝合金作为主要的航空材料,在飞机结构中存在着大量装配关系,但受成型工艺方法的限制,两种材料在制造和装配偏差的情况下,构件配合面间会产生装配间隙,当间隙超过一定大小时,需要采取填隙补偿措施。本研究基于实际结构抽象出碳纤维/环氧树脂复合材料-铝合金装配模型,使用装配试验台模拟施加螺栓预紧力,通过应变片实验比较强迫装配及垫片补偿情况下试件局部表面的应变分布,结合三维数字图像相关(3D-DIC)实验测得的试件表面应变场分析变形规律;通过有限元进行层间应力分析,提取内聚力单元各应力分量和损伤情况,研究填隙补偿对碳纤维/环氧树脂复合材料层间应力和局部损伤的影响。结合实验和仿真分析结果表明:强迫装配时,碳纤维/环氧树脂复合材料-铝合金试件主要受弯曲变形和螺栓头挤压的影响,且随着装配间隙的增大,各应变值均增大;垫片补偿在改善弯曲变形引起的应变状态的同时,也使中间贴合部位的螺栓头挤压区应变增大,但总体而言,垫片的引入使碳纤维/环氧树脂复合材料-铝合金试件表面应变分布趋于均匀,降低了碳纤维/环氧树脂复合材料损伤情况,且液体垫片补偿效果略好于可剥垫片。Abstract: As main aviation materials, there are a lot of assembly relationships between carbon fiber/epoxy composites and aluminum in aircraft structures. However, due to limitation of the composite forming process, assembly gaps will be created between the mating surfaces in the case of manufacturing and assembly deviations. When the gap exceeds a certain size, gap-filling compensation is necessary. Based on the actual structure, the carbon fiber/epoxy composite-aluminum assembly model was abstracted, the assembly test bench was used to simulate the pre-tightening force of the bolt, and the strain gauge and 3D digital image correlation(3D-DIC) experiment were used to compare the strain on the surface under the condition of forced assembly and gap-filling compensation in older to analyze the deformation rule of the component. The interlaminar stress analysis was carried out by finite element method, and the effects of gap-filling compensation on the interlaminar stress and local damage of the carbon fiber/epoxy composite-aluminum assembly structure were studied by extracting the stress components and damage of the cohesive element. The results of experimental and simulation analysis show that with the assembly gap increasing, the strain values increase; Gap-filling compensation improves the strain state caused by the bending deformation, while the strain of the bolt head extrusion zone is also increased. In general, gap-filling compensation makes the strain distribution more uniform and reduces damage of the carbon fiber/epoxy composite, and the liquid shim effect is slightly better than the peelable shim.
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表 1 碳纤维/环氧树脂复合材料和可剥垫片的性能参数[13, 29]
Table 1. Performance parameters of carbon fiber/epoxy composite and peelable shim[13, 29]
Material E11/GPa E22/GPa E33/GPa G12/GPa G13/GPa G23/GPa ν12 ν13 ν23 Carbon fiber/epoxy composite 156.0 8.35 8.35 4.20 4.20 2.52 0.33 0.33 0.55 Peelable shim 20.1 20.10 8.10 3.30 3.30 3.30 0.18 0.18 0.18 Notes: E11, E22, E33—Young’s modulus; G12, G13, G23—Shear modulus; ν12, ν13, ν23—Poisson’s ratio. 表 2 内聚力单元属性
Table 2. Properties of cohesive element
Kn/(105 N·mm−3) Ks=Kt/(105 N·mm−3) Gn/(N·mm−1) Gs =Gt/(N·mm−1) tn/MPa ts=tt/MPa 1 1 0.352 1.45 60 80 Notes: Kn—Normal modulus; Ks, Kt—Tangential modulus; Gn,Gs,Gt—Fracture energy of mode Ⅰ, Ⅱ, Ⅲ, respectively; tn—Normal strength; ts, tt—Tangential strength. 表 3 碳纤维/环氧树脂复合材料-铝合金无装配间隙时各测点实验应变片测量值
Table 3. Measurement of experimental strain gauges at each measuring point of carbon fiber/epoxy composite-aluminum without assembly gap
Measuring point 1 2 3 4 Carbon fiber/
epoxy composite−436.8 601.8 393.7 −337.4 Aluminum −181.5 142.5 245.1 −248.9 表 4 碳纤维/环氧树脂复合材料-铝合金无间隙时测点1和3应变片与3D-DIC测量值对比
Table 4. Strain comparison of measured values of strain gauges and 3D-DIC at points 1 and 3 of carbon fiber/epoxy composite-aluminum under no-gap conditions
Measuring method Strain gauge 3D-DIC Measuring point 1 3 exx eyy Carbon fiber/
epoxy composite−436.8 393.7 −444.5 399.3 Aluminum −181.5 245.1 −180.9 229.4 表 5 碳纤维/环氧树脂复合材料-铝合金在0.2 mm和2.0 mm装配间隙下各测点应变片测量值
Table 5. Measurements of strain gauges at each points of carbon fiber/epoxy composite-aluminum with gaps of 0.2 mm and 2.0 mm
Measuring point Gap/mm Strain of aluminum/10–6 Strain of composite/10–6 Forced assembly Liquid shim Peelable shim Forced assembly Liquid shim Peelable shim 1 0.2 −500.4 −200.9 −365.5 −733.1 −681.3 −729.8 2.0 −5 059.6 −1 469.5 −1 300.9 −7 140.8 −1 974.1 −2 389.5 2 0.2 −200.9 126.4 229.4 281.8 613.9 723.8 2.0 −2 370.4 444.5 337.4 −1 842.9 903.5 1 914.2 3 0.2 304.1 293.4 377.4 419.5 569.3 748.1 2.0 975.9 811.9 525.3 1 744.7 1 363.9 1 999.8 4 0.2 −236.9 −273.8 −326.4 −598.6 −451.5 −612.4 2.0 −845.9 −495.1 −1 233.7 −2 535.9 −1 276.1 −3 473.1 -
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