Mechanical characterization of mode I fracture at the interface of CFRP single-sided patch repair of damaged aerospace titanium alloy components
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摘要: 针对航空钛合金损伤贴补修复结构在I型受载条件下的力学响应与断裂特性,本文采用共固化成型方法设计了碳纤维增强树脂基预浸料(Carbon Fiber Reinforced Polymer, CFRP)单面贴补钛合金构件的修复试样,通过双悬臂梁试验,系统的研究了补片厚度、铺层方向以及表面处理方法三个典型因素对修复界面I型断裂力学特性的影响规律,以峰值载荷和层间断裂韧性为指标评估整体修复效果。结合试样在宏观和微观尺度下的失效模式与断面形貌分析,揭示了钛合金/CFRP贴补修复试样I型静态分层扩展的破坏机制。研究结果表明,随着补片厚度的增加,试样弯曲刚度和纤维桥联规模呈上升趋势,修复界面的I型断裂性能明显提高,失效模式均表现为胶膜粘附失效与内聚破坏到CFRP界面破坏的演化过程;在复合铺层试样中,补片底部的0°铺层表现出最强的分层路径约束作用,而45°铺层能够诱发裂纹的层间迁移以提高增韧效果,二维编织型补片则具有最佳的修复效果;胶膜内聚破坏为表面处理试样的主要失效模式,其中硫酸阳极化的增韧效果最为显著,断裂韧性较石英喷砂和400#砂纸打磨分别提高3.8%和1.9%,相比无处理试样则提高了19.2%。该结论为I型受载条件下钛合金损伤复合材料贴补修复工艺的优化设计与应用实践提供参考。Abstract: To investigate the mechanical response and fracture characteristics of adhesively bonded titanium alloy structures under mode I loading conditions, this study employed a co-curing method to fabricate repair specimens with single-sided carbon fiber reinforced polymer (CFRP) patches bonded to titanium alloy substrates. The effects of patch thickness, ply orientation, and surface treatment on mode I interfacial fracture mechanics were systematically examined using double cantilever beam (DCB) tests. Peak load and interlaminar fracture toughness were utilized as quantitative metrics to evaluate the overall repair performance. Furthermore, failure modes and fracture surface morphologies at both macroscopic and microscopic scales were analyzed to elucidate the underlying failure mechanisms of mode I static delamination in the titanium alloy/CFRP repaired specimens. The results reveal that increasing the thickness of the patch leads to a rising trend in both the bending stiffness of the specimen and the extent of fiber bridging. The mode I fracture performance of the repair interface improves significantly, with failure modes consistently evolving from adhesive failure of the glue film and cohesive damage to failure at the CRFP interface. For multidirectional laminates, the 0° ply at the bottom of the patch exhibits the strongest constraint on delamination paths, while the 45° ply effectively induces inter-ply crack migration, enhancing the toughening effect. Notably, the two-dimensional woven patch demonstrates the best repair performance. For surface-treated specimens, cohesive failure of the adhesive film is the predominant failure mode. Specifically, sulfuric acid anodization provides the most significant toughening effect, increasing fracture toughness by 3.8% and 1.9% compared to quartz sandblasting and 400# sandpaper abrasion, respectively, and by 19.2% compared to untreated specimens. These conclusions provide references for the optimized design and practical application of damage repair processes under mode I loading conditions for titanium alloy components.
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Key words:
- composite materials /
- patch repair /
- mode I fracture /
- fracture toughness /
- aviation metal /
- double cantilever beam
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图 13 不同铺层方向修复试样分层断面的微观形貌:(a) [±45]2 s;(b) [0/90]2 s;(c) [90/0]2 s;(d) [0/±45/90]s;(e) [±45/02]s;(f) [(0/90)w]8
Figure 13. Microscopic morphology of delamination sections of repaired specimens with different layup orientations: (a) [±45]2 s; (b) [0/90]2 s; (c) [90/0]2 s;(d) [0/±45/90]s; (e) [±45/02]s; (f) [(0/90)w]8
图 17 经处理后的钛合金表面微观形貌:(a)无处理;(b)400#砂纸打磨;(c)硫酸阳极化;(d)石英喷砂;及修复试样粘接界面:(e)无处理;(f)400#砂纸打磨;(g)硫酸阳极化;(h)石英喷砂
Figure 17. Microstructure of the Ti-alloy substrate surfaces treated by: (a) Untreated; (b) Sandpapering-400#; (c) Sulphuric acid anodizing; (d) Quartz-blasting; and bonding interfaces in repaired specimens: (e) Untreated; (f) Sandpapering-400#; (g) Sulphuric acid anodizing; (h) Quartz-blasting
表 1 钛合金/CFRP单面贴补修复试样几何参数
Table 1. Geometric parameters of titanium alloy-CFRP single-sided patch repaired specimen
Parameter Description Value / mm l0 Hinge additional length 17 a0 Length of initial crack 50 L Total length 150 b Specimen width 25 t Ti-alloy thickness 1.5 t0 Thickness of adhesive film 0.12 表 2 结构胶膜、单向及平纹编织CFRP力学性能参数
Table 2. Mechanical properties of adhesive film unidirectional (UD) and plain weave (PW) CFRP
Adhesive
SY-24 CUD
Laminate
(T700/725)PW
Laminate
(T700/725)Property Value Property Value Property Value E/MPa 5750 E1/GPa 119 E1/GPa 66.28 G/MPa 1920 E2/GPa 9 E2/GPa 61.8 σ/MPa 451.6 E3/GPa 9 E3/GPa 10 τ/MPa 36.5 ν12, ν13 0.309 ν12 0.057 GC n /(N·mm−1) 0.48 ν23 0.35 ν13, ν23 0.25 GC s /(N·mm−1) 0.64 G12, G13 /GPa 4 G12/GPa 4.52 GC t /(N·mm−1) 0.64 G23/GPa 3.33 G13, G23 /GPa 4 Notes: E, G – Elastic modulus in tension and shear; σ, τ – Failure strengths in tension and shear; GC n– Toughness in tension; GC s, GC t– Toughness in shear; Eii (i =1, 2, 3) – Young’s modulus (i direction); Gij (i, j =1, 2, 3) – Shear modulus (i-j plane); vij (i, j=1, 2, 3) – Poisson’s ratio (i-j plane). 表 3 钛合金/CFRP单面贴补修复试样影响因素及参数设置
Table 3. Influencing factors and parameter setting of titanium alloy-CFRP single-sided patch repaired specimen
Repair factors Symbol Factor settings Patch thickness/mm TP 1.14, 1.52, 1.90, 2.28, 2.66 Lay-up direction/(°) θP [0]8, [±45]2 s, [0/90]2 s, [90/0]2 s, [(0/90)w]8, [0/±45/90]s, [±45/02]s Surface treatment RT Sandpapering, Quartz-blasting, Sulphuric acid anodizing, Untreated -
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