Journal of Jilin University(Engineering and Technology Edition) ›› 2021, Vol. 51 ›› Issue (1): 139-146.doi: 10.13229/j.cnki.jdxbgxb20191063

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Residual strength prediction of adhesive CFRP-aluminum alloy adhesively bonded joint based on FTIR analysis

Wen-long MU1,2(),Jing-xin NA1(),Wei TAN1,Guang-bin WANG1,Hao SHEN1,Jian-ze LUAN1   

  1. 1.State Key Laboratory of Automotive Simulation and Control，Jilin University，Changchun 130022，China
    2.College of Mechnical and Electrical Engineering，Henan Agricultural University，Zhengzhou 450002，China
  • Received:2019-09-27 Online:2021-01-01 Published:2021-01-20
  • Contact: Jing-xin NA E-mail:muwl1992@hotmail.com;najingxin@jlu.edu.cn

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Abstract:

The aging behavior and mechanism of adhesively bonded joints of CFRP- aluminum alloy exposured to hygrothermal environment were studied in this paper. First， the joints were aged at 80℃ with 95% relative humidity （RH） for different durations and then the quasi-static tensile and shear tests were performed. Second， the residual strength and failure mode of the joint were analyzed. Third， combined with the Fourier transform infrared spectroscopy （FTIR） results of adhesive， the aging mechanism of adhesive joints was revealed. The results indicate that the strength of joint decreases significantly due to hygrothermal aging， which approximates the exponential function. The failure modes of unaged and aged joints all presented cohesive failure primarily. However， with the increase in aging duration the adhesive-substrate interface was damaged， and the surfaces of aged joints became relatively rough due to the plasticizing of the adhesive. The hydrolysis reaction occurred in the adhesive due to hygrothermal aging， resulting in chain scission. The post curing of adhesive was also observed at the initial stage of aging. Adhesive degradation is the primary cause of the decrease in the strength of the joint. Finally a residual strength prediction method was established， which can be used to predict residual strength of hygrothermally aged joints by testing the chemical characteristics of adhesive.

Key words: carbon fiber reinforced polymer composites（CFRP）, adhesively bonded joint, hygrothermal aging, fourier transform infrared spectroscopy analysis, residual strength prediction

CLC Number: 

  • U463.82

Table 1

Mechanical properties of CFRP"

Ex/GPaEy/GPaVxyGxy/GPaGxz/GPaGyz/GPa
单向125±1210±20.077±0.62±0.52±0.3
斜纹55±555±50.134±0.52±0.32±0.3

Fig.1

Geometries and dimensions of adhesive joints"

Fig.2

Model of adhesive fixture"

Fig.3

Quasi-static testing of joints"

Fig.4

Residual strength loads of joints as a function of exposure time"

Fig.5

Representative fracture surfaces of butt joints before and after hygrothermal aging"

Fig.6

Representative fracture surfaces of shear joints before and after hygrothermal aging"

Fig.7

Representative SEM photos of fracture surfaces -×100"

Fig.8

Normalized FTIR spectrum of adhesive Araldite? 2015 with different aging times"

Table 2

Typical functional groups and corresponding wave numbers in FTIR spectra of Araldite? 2015"

波数/cm-1官能团
3325-OH、-NH伸缩振动
2923、2850烷基 (-CH3、-CH2) 伸缩振动
1736酯基 (-(C=O)-O)
1648羰基 (C=O)
1508p-二取代苯环的半圆伸缩振动
1452脂族基的C–H弯曲振动
1053醚类C-O-C反式伸缩振动
914p-亚苯基

Fig.9

Changes in absorbance intensities of functional groups as functions of the hygrothermal exposure time"

Fig.10

Pearson correlation coefficients between absorbance intensities functional groups and residual strength"

Table 3

Residual strength prediction accuracy"

波数/cm-1接头类型
对接剪切
332594.0394.19
173699.7199.70
164895.8996.03
91498.5998.67

Fig.11

Relative error of residual strength prediction"

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[1] NA Jing-xin,MU Wen-long,FAN Yi-sa,TAN Wei,YANG Jia-zhou. Effect of hygrothermal aging on steel-aluminum adhesive joints for automotive applications [J]. Journal of Jilin University(Engineering and Technology Edition), 2018, 48(6): 1653-1660.
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