CFRP-铝合金单搭接胶接接头疲劳寿命和失效模式

邹田春; 巨乐章; 符记; 刘志浩; 李晔

doi:10.13801/j.cnki.fhclxb.20211126.002

CFRP-铝合金单搭接胶接接头疲劳寿命和失效模式

doi: 10.13801/j.cnki.fhclxb.20211126.002

邹田春^1, ,,
巨乐章^1,,
符记¹,
刘志浩¹,
李晔²

1.
中国民航大学　安全科学与工程学院，天津 300300
2.
中国民航大学　航空工程学院，天津 300300

详细信息

通讯作者:
邹田春，博士，副教授，硕士生导师，研究方向为复合材料胶接　 E-mail: Zoutianchun@126.com

中图分类号: TB332
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出版历程
- 收稿日期: 2021-09-23
- 修回日期: 2021-11-17
- 录用日期: 2021-11-22
- 网络出版日期: 2021-11-29
- 刊出日期: 2022-12-01

Fatigue life and failure mode of CFRP-aluminum alloy single-lap adhesive joints

ZOU Tianchun^{1
, ,},
JU Yuezhang^1
,,
FU Ji¹,
LIU Zhihao¹,
LI Ye²

1.
College of Safety Science and Engineering, Civil Aviation University of China, Tianjin 300300, China
2.
College of Aeronautical Engineering, Civil Aviation University of China, Tianjin 300300, China

摘要

摘要: 在室温下制备碳纤维增强树脂复合材料(CFRP)-铝合金单搭接胶接试样。利用电子万能试验机和电液伺服疲劳试验机进行准静态拉伸和拉-拉疲劳试验，基于疲劳试验结果和双参数威布尔分布方法，采用多种函数模型对接头应力-寿命(S-N)曲线进行拟合。同时，利用三维数字图像相关技术(3D digital image correlation，3D-DIC)和SEM等设备，获得接头应变分布云图和失效形貌，揭示CFRP-铝合金胶接接头在循环载荷下的破坏机制。结果表明，幂函数对CFRP-铝合金单搭接胶接接头S-N曲线拟合度最高，相关系数R²为0.987，且接头疲劳寿命随着载荷水平的降低逐渐提高，变异系数逐渐增大。载荷水平为25%和35%失效载荷时，CFRP-铝合金单搭接接头破坏模式主要为胶层内聚破坏和铝合金-胶层界面破坏，且随着载荷水平的升高内聚破坏面积逐渐增加，载荷水平达到75%失效载荷时，CFRP-铝合金单搭接接头只发生胶层内聚破坏。在载荷水平为25%失效载荷下，接头由于内部温度上升主要发生韧性断裂，且随载荷水平上升至75%失效载荷时，接头由于受到较大拉应力逐渐向脆性断裂转变。
- 复合材料 /
- 异质材料胶接 /
- 疲劳寿命 /
- 应变分布 /
- 失效形貌
Abstract: Carbon fiber reinforced polymer (CFRP)-Al single-lap adhesive joints were made at room temperature. Firstly, a universal testing machine as well as an electro-hydraulic servo fatigue testing machine were used for quasi-static tensile tests and tensile-tension fatigue tests, respectively. Based upon the fatigue test results and two-parameter Weibull distribution methods, multiple function models were applied to fit the stress-life (S-N) curves of joints. Meanwhile, 3D digital image correlation (3D-DIC) and SEM were used respectively to obtain the strain field distribution and failure morphology of joints, revealing the failure mechanism of joints under cyclic load. According to the test results, the power function has the highest fitting degree for the S-N curves of the joints, with the correlation coefficient R² of 0.987. Besides, with the load level decreasing, the fatigue life and the coefficient of variation of the joints gradually increase. When the load levels are 25% and 35% of the failure load, the failure modes of joints are mainly cohesive failure and interface failure. And the cohesive failure area increases correspondingly with the increase of the load level. Even when the load level is up to 75% of the failure load, only cohesive failure occurs. Moreover, when the load level is 25% of the failure load, ductile fracture occurs due to the increase of the internal temperature of the joints. And when the load level rises to 75% of the failure load, the joints gradually change to brittle fracture as a result of large tensile stress.
- composites /
- bonding of dissimilar materials /
- fatigue life /
- strain field distribution /
- failure morphology

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图 1 CFRP-铝合金单搭接接头

Figure 1. Single-lap joint of CFRP-Al

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图 2 胶厚控制方法示意图

Figure 2. Schematic diagram of adhesive layer thickness control

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图 3 试验设备：(a) 电子万能试验机；(b) 电液伺服疲劳试验机

Figure 3. Testing equipment: (a) Universal testing machine; (b) Electro-hydraulic servo fatigue testing machine

SLJ—Single lap joint; CCD—Charge coupled

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图 4 不同载荷水平下CFRP-铝合金单搭接胶接接头的Weibull概率图

Figure 4. Weibull probability plots of CFRP-aluminum alloy single-lap adhesive joints under different load levels

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图 5 不同载荷水平下CFRP-铝合金单搭接胶接接头平均疲劳寿命与变异系数关系

Figure 5. Relationship between T_MTTF and C_V of CFRP-aluminum alloy single-lap adhesive joints under different load levels

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图 6 CFRP-铝合金单搭接胶接接应力-寿命(S-N)曲线

Figure 6. Stress-life (S-N) curves of CFRP-aluminum alloy single-lap adhesive joints

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图 7 不同载荷水平下CFRP-铝合金单搭接胶接接头典型滞回环

Figure 7. Typical hysteresis loops of CFRP-aluminum alloy single-lap adhesive joints under different load levels

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图 8 不同载荷水平下CFRP-铝合金单搭接胶接接头侧面x方向应变场：(a) 25%；(b) 35%；(c) 55%；(d) 75%

Figure 8. Strain field in side x direction of CFRP-aluminum alloy single-lap adhesive joints under different load levels: (a) 25%; (b) 35%; (c) 55%; (d) 75%

ε_xx—Strain field in side x direction

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图 9 准静态拉伸载荷下CFRP-铝合金单搭接胶接接头的破坏模式

Figure 9. Destruction mode of CFRP-aluminum alloy single-lap adhesive joints under quasi-static tensile loading

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图 11 不同载荷水平下CFRP-铝合金单搭接胶接接头微观失效形貌：((a)、(b)) 35%；((c)、(d)) 75%

Figure 11. Micro failure morphologies of CFRP-aluminum alloy single-lap adhesive joints under different load levels: ((a), (b)) 35%; ((c), (d)) 75%

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图 10 不同载荷水平下CFRP-铝合金单搭接胶接接头的破坏模式：(a) 25%；(b)35%；(c)55%；(d)75%

Figure 10. Destruction modes of CFRP-aluminum alloy single-lap adhesive joints under different load levels: (a) 25%; (b) 35%; (c) 55%; (d) 75%

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表 1 碳纤维增强树脂复合材料(CFRP)层合板材料性能

Table 1. Material properties of carbon fiber reinforced polymer (CFRP) laminates

Property	Value
E₁₁/MPa	121000
E₂₂/MPa	8600
E₃₃/MPa	8600
G₁₂/MPa	3450
G₁₃/MPa	2850
G₂₃/MPa	2850
$\nu$	0.301
ρ/(kg·m⁻³)	1467
Notes: E—Young’s modulus; $ i $ ($ i $=1, 2, 3)—Direction; G—Shear modulus; $\nu $—Poisson’s ratio; ρ—Density.

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表 2 Al7075材料性能

Table 2. Material properties of Al7075

Property	Value
E/MPa	71700
$\nu$	0.32
ρ/(kg·m⁻³)	3000

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表 3 不同载荷水平下CFRP-铝合金单搭接胶接接头的疲劳寿命

Table 3. Fatigue life of CFRP-aluminum alloy single-lap adhesive joints under different load levels

Load level	Fatigue life	$\ln \ln \dfrac{1}{{R\left( t \right)}}$	$\ln t $
100% (5.93 kN)	1	−	−
75% (4.45 kN)	474	−1.753	6.161
	638	−0.717	6.458
	1026	−0.050	6.933
	1248	0.609	7.129
55% (3.26 kN)	2442	−1.753	7.801
	3283	−0.717	8.097
	5235	−0.050	8.563
	7562	0.609	8.931
35% (2.08 kN)	33364	−1.753	10.415
	68903	−0.717	11.140
	103672	−0.050	11.549
	135573	0.609	11.817
25% (1.48 kN)	99998	−1.753	11.513
	179375	−0.717	12.097
	252329	−0.050	12.620
	457897	0.609	13.034
15% (0.89 kN)	5301850	−	−
Notes: lnln[1/R(t)]—Result of taking the logarithm of reliability, and the calculation formula is shown in formula (4)-(5); lnt—Result of taking the logarithm of mean time to fatigue, and the calculation formula is shown in formula (6).

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表 4 不同载荷水平下CFRP-铝合金单搭接胶接接头的Weibull参数

Table 4. Weibull parameters under different load levels

Load level	α	β	T_MTTF	C_V
75%	2.25	975.56	864	0.47
55%	1.98	5372.48	4763	0.53
35%	1.64	100859.46	90269	0.62
25%	1.53	305218.04	275001	0.67
Notes: α—Shape parameter; β—Scale parameter; T_MTTF—Mean time to fatigue of the joints; C_V—Coefficient of variation of the joints.

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