- Email: [email protected]
Effect of Impact Tensile Load on Strength of CFRP Bonded Steel Plate Joints
Available online at www.sciencedirect.com A Available onlin ne at www.sciencedirect.com
Proceedia Engineeering
Procedia Engineering Engiineering 14 000–000 00(2011) (201 1)1312–1317 www w.elsevier.com/loocate/procedia
The Twellfth East Assia-Pacific Conference C on Structurral Engineerring and Coonstruction
Effectt of Impaact Tenssile Loadd on Streength of CFRP B Bonded Steel Plaate Jointts H. A. AL--ZUBAIDY Y1, X. L. Z ZHAO1,a, an nd R. AL-M MAHAIDII2 2
1 Department off Civil Engineerin ing, Monash Univversity, Australia Faculty of Enngineering and In ndustrial Sciencess, Swinburne Uniiversity of Techno ology, Australia
Abstract
This paper reports an exxperimental in nvestigation iinto the effecct of impact tensile loads on the bond d l and faiilure modes oof double strap p joints. Unid directional norrmal moduluss strength, efffective bond length carbon fibree reinforced poolymer (CFRP P) sheet with oone and three layers (plies) and Araldite 420 adhesivee are used in this investigaation. Dynamiic results werre compared with w those sub bjected to staatic tension to o pact loading has h significantt influence on n highlight thee influence off loading rate. It was foundd that the imp joint strengtth but little inffluence on efffective bond leength. © 2011 Published by Elseevier Ltd. Keywords: Imppact load, Adhesivve bonded joints, Carbon Fibre Reeinforced Polymeer, Bond strength
1.
Introdu uction
Carbon F Fibre Reinforced Polymerr (CFRP) haas great poteential in stren ngthening steeel structuress (Hollaway aand Cadei 20002, Zhao and d Zhang 2007)). The bond between b CFRP and steel iss a key issue.. Extensive reesearch has beeen conducted d on bond behhaviour under static load (X Xia and Teng 2005, Fawziaa et al. 2009)). The effect of fatigue lo oading on thhe bond stren ngth was stud died by Liu eet al. (2010).. Adhesively bonded steel joints j are also o likely to be subjected to impact i loads. However therre is a lack off mpact load will affect the bbond between n CFRP and steel. s The effeect of loading g knowledge oon how the im rate on strenngth of adhesively bonded single lap joiints of steel-ssteel was exam mined by som me researcherss (Goglio andd Rossetto 20008, Beevers an nd Eillis 19844). Yokohama and Shimizu (1998) and R Raykhere et al.. o adhesively bbonded jointss (2010) usedd a pin and collar specimens to determinee dynamic shear strength of a
Corresponding author & Presenter. [email protected]
1877–7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.165
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
2
such as aluminium-aluminium and aluminium-GFRP joints. They found a shear strength enhancement of epoxy between CFRP and metal under dynamic loading. This paper reports an experimental investigation into the effect of impact tensile loads on the bond strength, effective bond length and failure modes of double strap joints. Dynamic results were compared with those subjected to static tension to highlight the influence of loading rate. 2.
Specimens details, experimental setup and test procedures
A total of 24 steel/CFRP double strap joints adhesively bonded using epoxy and grouped into 4 series, were prepared and tested under static and impact tensile loads. The configurations of these specimens and the manufactured impact tensile apparatus that was constructed and used for dynamic tests are shown in Figure 1 and Figure 2.
L2
L1
Steel Plate
Adhesive layer
5mm
CFRP ply 210mm
210mm
Figure 1: Schematic view of double strap specimen (not to scale)
1 Impact Position 2 Top Plate 3 Guide Pins 4 Linear Motion Guide 5 Grips 6 Load Cell 7 Specimen 8 Bottom Plate 9 Rubber
Figure 2: Fabricated impact tensile rig
1
2
3 6 7
9
5 8
4
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
3
Each joint was manufactured by bonding two mild steel plates from grade A36 steel with dimensions of (210mm length, 50mm width and 5mm thickness) using normal modulus CFRP sheet and Araldite 420 adhesive. The nominal modulus of elasticity and ultimate tensile strength of CFRP sheet and Araldite 420 adhesive are 240GPa, 3800MPa, 1.9GPa and 32MPa, respectively. Surfaces of steel plates were cleaned with acetone and sandblasted to remove rust, paints, oil, grease and primer along the bond length. The adhesive was then uniformly applied using a brush. This was followed by the application of the first ply with the use of a roller to saturate CFRP sheet with resin and to squeeze out the air bubbles and the excessive adhesive. The same procedure was used for the other CFRP layers (plies). Finally, the specimens were cured for at least 7 days before test according to the manufacturer’s recommendation. The bond length of CFRP L1 varied between 10mm and 60mm, which is shorter than L2 as shown in Table 1 in order to ensure that the failure occurred on the short end only. A Kistler piezoelectric load cell was installed above the specimen to measure applied load. A computer with necessary software is used for data acquisition. Load cell data readings were recorded at a sampling rate of 300 KHz. Digital video camera was used to record the tests at 1900 frames/second such that failure modes could be examined in details. 3.
Test results
Experimental static (2mm/min) and impact (3.35m/sec) tensile test results of double strap joints are summarised in Table 1. The first letter S in specimen label denotes specimen, the first numbers 10, 20,...etc. refer to the bond length L1 that is exhibited in Figure 1 and the second number represents the number of CFRP layers. F1 and F2 are the ultimate static and dynamic strength for specimens with 1 layer CFRP, whereas F3 and F4 are those for specimens with 3 layers of CFRP, respectively. Table 1: Experimental results of CFRP sheet/ steel plate joints (1 & 3 plies)
Specimen Label
4.
L1 [mm]
L2 [mm]
F1 [kN]
F2 [kN]
F3 [kN]
F4 [kN]
F2/F1
F4/F3
F3/F1
F4/F2
S10-1
S10-3
10
80
19.83
45.66
29.61
84.25
2.76
2.85
1.49
1.85
S20-1
S20-3
20
80
35.60
74.78
51.21 109.46
2.10
2.14
1.44
1.46
S30-1
S30-3
30
80
46.16
65.50
66.89 127.89
1.42
1.91
1.45
1.95
S40-1
S40-3
40
80
46.39
62.19
80.37 136.99
1.34
1.71
1.73
2.20
S50-1
S50-3
50
80
46.97
60.86
101.67 159.56
1.30
1.57
2.16
2.62
S60-1
S60-3
60
80
44.65
49.68
104.06 147.44
1.11
1.42
2.33
2.97
Effect of impact loads on bond strength
The values of bond strength ratio F2/F1 and F4/F3 in Table 1 illustrate the effect of impact loads on the strength of double lap joints with different bond lengths. At impact speed of 3.35m/sec which is about 100,000 times that of static load, the bond strength of joints is significantly increased with dynamic loads especially when the bond length is below the effective bond length (about 30mm for 1 layer of CFRP and 50mm for 3 layers of CFRP). The smaller the bond length is, the greater the increase becomes. The ratio F4/F3 is larger than F2/F1 indicating that more increase was obtained for specimens with 3 layers of CFRP.
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Proceedia Engineering g 00 (2011) 000–0 000
The reason for the increaase in bond sttrength is maiinly due to th he shear strength enhancem ment of epoxy y between CFRP and steel under u impact loading, a pheenomenon rep ported in Yokohama and Shhimizu (1998)) and Raykheere et al. (2010), as discusssed later in thhe paper. Wheen the numberr of CFRP layyers increasess from 1 to 3,, there is an inncrease in bon nd strength. Suuch an increase under staticc load can be expressed by y f impact load ding the ratio is F4/F2. It caan be seen fro om Table 1 tha hat the ratio off the ratio F3//F1, whereas for F4/F2 is generally larger than t F3/F1, i.ee. more increaase in bond strrength is achieved under im mpact loading g RP layers increeases. when the nuumber of CFR 5.
Effect oof impact loads on effectiv ve bond lengtth
The jointt strength variiation with thee bond lengthh is plotted in Figure 3 for specimens unnder static and d impact loadding. For bothh types of speecimens (1 annd 3 layers off CFRP), Figure 3 explicittly shows thee phenomenonn of effectivee bond length, i.e. beyond which no exttra bond stren ngth can be oobtained. It iss somewhat suubjective to define d the effeective length ffrom test dataa. The effectiv ve bond lengthh under staticc load is abouut 30mm for l layer CFRP and a 50mm forr 3 layers of CFRP. C The sam me effective bbond length iss observed in Figure 3 for the case of im mpact loadingg. It seems thaat the impact load has littlee influence on n the effectivee bond length.
Figure 3: Ultim mate load versus bond b length
6.
Effect oof impact loads on failure mode
Six failurre modes for CFRP bonded d steel joints w were classifieed by Zhao an nd Zhang (20007), including g (a) Steel annd adhesive interface i failu ure; (b) Coheesive failure (adhesive ( layer failure); (cc) CFRP and d Adhesive innterface failurre; (d) CFRP P delaminationn (separation of some carrbon fibres frrom the resin n matrix); (e) CFRP rupturee; (f) Steel yieelding, as show wn in Figure 4. 4
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Proceedia Engineering g 00 (2011) 000–0 000
(e) FRP rupture (d) FRP d elamination n F FRP
Adhessive
(c) FRP F and ad dhesive inte erface debo onding (b) Adhesive A la ayer failure (a) Steel and adhesive a interface deb bonding
Stteel (f) Steel yeilding y
Figure 4: Failurre modes for CFR RP bonded steel joints (adapted froom Zhao and Zhaang (2007))
For speciimens with onne layer of CF FRP, failure m mode (c) occu urs when the bond b length iss less than thee effective bonnd length. The shear streng gth of the adheesive plays an n important rolle in this failuure mode. Thee failure modee under impacct load changees to failure m mode (d) which h is CFRP dellamination. Thhis is becausee of the shearr strength enhhancement of epoxy underr impact load as reported in Yokohama and Shimizu u (1998) and R Raykhere et al. a (2010). Wh hen the bond leength exceedss the effectivee bond length of 30mm, thee failure mode (e) occurs under u static lo oading whereeas the failuree modes (e) an nd (d) occur under impactt o the propertty of CFRP raather than thatt of adhesivess. This is why y loading. Theese failure moodes depend on the increasee in ultimate looad becomes less significaant. Some typiical failure modes m under im mpact loading g are shown inn Figure 5.
Figure 5: Typiccal failure modes under impact loaading
For speciimens with thhree layers of CFRP, the maain failure mo ode is (c) com mbined with m mode (d) when n the bond lenngth is less than the effectiv ve bond lengtth. For the sam me reason desscribed above,, an increased d ultimate loadd was observeed. When the bond length eexceeds the efffective bond length l of 30m mm, the failuree mode (c) dooes not occur any a more, lead ding to less inncrease in ultim mate load capaacity.
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
6
7.
Conclusions
This paper presented an experimental investigation into the effect of impact tensile loads on the bond strength, effective bond length and failure modes of double strap joints. It was found that the bond strength of joints significantly increases under dynamic loads especially when the bond length is below the effective bond length. A higher level of increase was obtained for specimens with 3 layers of CFRP. The impact load has little influence on the effective bond length. The failure mode changed under impact loading due to the shear strength enhancement of epoxy between CFRP and steel under impact loading, leading to increased bond strength. Acknowledgment The project was sponsored by the Australian Research Council. The first author is sponsored by an Iraqi Government Scholarship. The authors wish to thank the technical staff in the Civil Engineering laboratory at Monash University for their assistance. References [1]
Beevers, A and Eillis, MD. Impact behaviour of bonded mild steel lap joints. International Journal of Adhesion and Adhesive, 4(1); 1984, pp. 13-16.
[2]
Fawzia, S., Zhao, XL and Al-Mahaidi, R. Bond–slip models for double strap joints strengthened by CFRP. Composite Structures. 92(9); 2009, pp. 2137-2145.
[3]
Goglio, L and Rossetto, M.. Impact rupture of structural adhesive joints under different stress combinations. International Journal of Impact Engineering, 35(7); 2008, pp. 635-643.
[4]
Hollaway LC and Cadei J. Progress in the technique of upgrading metallic structures with advanced polymer composites. Progress in Structural Engineering & Materials. 4(2); 2002, pp. 131-148.
[5]
Liu, HB, Zhao, XL and Al-Mahaidi, R. Effect of fatigue loading on bond strength between CFRP sheets and steel plates. International Journal of Structural Stability and Dynamics. 10(1); 2010, pp. 1-20.
[6]
Raykhere, SL, Kumar, P, Singh, RK and Parameswaran, V. Dynamic shear strength of adhesive joints made of metallic and composite adherents. Materials & Design, 31(4); 2010, pp. 2102-2109.
[7]
Xia, S and Teng, JG. Behaviour of FRP-to-steel bonded joints. Proceedings of the International Symposium on Bond Behaviour of FRP in Structures, Hong Kong; 2005, pp. 419-426.
[8]
Yokoyama, T and Shimizu, H. Evaluation of impact shear strength of adhesive joints with the Siplit Hopkinson Bar. JSME International Journal Serise 1, 41(4); 1998, pp. 503-509.
[9]
Zhao, XL and Zhang L. State-of-the-art review on FRP strengthened steel structures. Engineering Structures. 29(8); 2007, pp. 1808-1823.
1317
Proceedia Engineeering
Procedia Engineering Engiineering 14 000–000 00(2011) (201 1)1312–1317 www w.elsevier.com/loocate/procedia
The Twellfth East Assia-Pacific Conference C on Structurral Engineerring and Coonstruction
Effectt of Impaact Tenssile Loadd on Streength of CFRP B Bonded Steel Plaate Jointts H. A. AL--ZUBAIDY Y1, X. L. Z ZHAO1,a, an nd R. AL-M MAHAIDII2 2
1 Department off Civil Engineerin ing, Monash Univversity, Australia Faculty of Enngineering and In ndustrial Sciencess, Swinburne Uniiversity of Techno ology, Australia
Abstract
This paper reports an exxperimental in nvestigation iinto the effecct of impact tensile loads on the bond d l and faiilure modes oof double strap p joints. Unid directional norrmal moduluss strength, efffective bond length carbon fibree reinforced poolymer (CFRP P) sheet with oone and three layers (plies) and Araldite 420 adhesivee are used in this investigaation. Dynamiic results werre compared with w those sub bjected to staatic tension to o pact loading has h significantt influence on n highlight thee influence off loading rate. It was foundd that the imp joint strengtth but little inffluence on efffective bond leength. © 2011 Published by Elseevier Ltd. Keywords: Imppact load, Adhesivve bonded joints, Carbon Fibre Reeinforced Polymeer, Bond strength
1.
Introdu uction
Carbon F Fibre Reinforced Polymerr (CFRP) haas great poteential in stren ngthening steeel structuress (Hollaway aand Cadei 20002, Zhao and d Zhang 2007)). The bond between b CFRP and steel iss a key issue.. Extensive reesearch has beeen conducted d on bond behhaviour under static load (X Xia and Teng 2005, Fawziaa et al. 2009)). The effect of fatigue lo oading on thhe bond stren ngth was stud died by Liu eet al. (2010).. Adhesively bonded steel joints j are also o likely to be subjected to impact i loads. However therre is a lack off mpact load will affect the bbond between n CFRP and steel. s The effeect of loading g knowledge oon how the im rate on strenngth of adhesively bonded single lap joiints of steel-ssteel was exam mined by som me researcherss (Goglio andd Rossetto 20008, Beevers an nd Eillis 19844). Yokohama and Shimizu (1998) and R Raykhere et al.. o adhesively bbonded jointss (2010) usedd a pin and collar specimens to determinee dynamic shear strength of a
Corresponding author & Presenter. [email protected]
1877–7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.165
1313
H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
2
such as aluminium-aluminium and aluminium-GFRP joints. They found a shear strength enhancement of epoxy between CFRP and metal under dynamic loading. This paper reports an experimental investigation into the effect of impact tensile loads on the bond strength, effective bond length and failure modes of double strap joints. Dynamic results were compared with those subjected to static tension to highlight the influence of loading rate. 2.
Specimens details, experimental setup and test procedures
A total of 24 steel/CFRP double strap joints adhesively bonded using epoxy and grouped into 4 series, were prepared and tested under static and impact tensile loads. The configurations of these specimens and the manufactured impact tensile apparatus that was constructed and used for dynamic tests are shown in Figure 1 and Figure 2.
L2
L1
Steel Plate
Adhesive layer
5mm
CFRP ply 210mm
210mm
Figure 1: Schematic view of double strap specimen (not to scale)
1 Impact Position 2 Top Plate 3 Guide Pins 4 Linear Motion Guide 5 Grips 6 Load Cell 7 Specimen 8 Bottom Plate 9 Rubber
Figure 2: Fabricated impact tensile rig
1
2
3 6 7
9
5 8
4
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
3
Each joint was manufactured by bonding two mild steel plates from grade A36 steel with dimensions of (210mm length, 50mm width and 5mm thickness) using normal modulus CFRP sheet and Araldite 420 adhesive. The nominal modulus of elasticity and ultimate tensile strength of CFRP sheet and Araldite 420 adhesive are 240GPa, 3800MPa, 1.9GPa and 32MPa, respectively. Surfaces of steel plates were cleaned with acetone and sandblasted to remove rust, paints, oil, grease and primer along the bond length. The adhesive was then uniformly applied using a brush. This was followed by the application of the first ply with the use of a roller to saturate CFRP sheet with resin and to squeeze out the air bubbles and the excessive adhesive. The same procedure was used for the other CFRP layers (plies). Finally, the specimens were cured for at least 7 days before test according to the manufacturer’s recommendation. The bond length of CFRP L1 varied between 10mm and 60mm, which is shorter than L2 as shown in Table 1 in order to ensure that the failure occurred on the short end only. A Kistler piezoelectric load cell was installed above the specimen to measure applied load. A computer with necessary software is used for data acquisition. Load cell data readings were recorded at a sampling rate of 300 KHz. Digital video camera was used to record the tests at 1900 frames/second such that failure modes could be examined in details. 3.
Test results
Experimental static (2mm/min) and impact (3.35m/sec) tensile test results of double strap joints are summarised in Table 1. The first letter S in specimen label denotes specimen, the first numbers 10, 20,...etc. refer to the bond length L1 that is exhibited in Figure 1 and the second number represents the number of CFRP layers. F1 and F2 are the ultimate static and dynamic strength for specimens with 1 layer CFRP, whereas F3 and F4 are those for specimens with 3 layers of CFRP, respectively. Table 1: Experimental results of CFRP sheet/ steel plate joints (1 & 3 plies)
Specimen Label
4.
L1 [mm]
L2 [mm]
F1 [kN]
F2 [kN]
F3 [kN]
F4 [kN]
F2/F1
F4/F3
F3/F1
F4/F2
S10-1
S10-3
10
80
19.83
45.66
29.61
84.25
2.76
2.85
1.49
1.85
S20-1
S20-3
20
80
35.60
74.78
51.21 109.46
2.10
2.14
1.44
1.46
S30-1
S30-3
30
80
46.16
65.50
66.89 127.89
1.42
1.91
1.45
1.95
S40-1
S40-3
40
80
46.39
62.19
80.37 136.99
1.34
1.71
1.73
2.20
S50-1
S50-3
50
80
46.97
60.86
101.67 159.56
1.30
1.57
2.16
2.62
S60-1
S60-3
60
80
44.65
49.68
104.06 147.44
1.11
1.42
2.33
2.97
Effect of impact loads on bond strength
The values of bond strength ratio F2/F1 and F4/F3 in Table 1 illustrate the effect of impact loads on the strength of double lap joints with different bond lengths. At impact speed of 3.35m/sec which is about 100,000 times that of static load, the bond strength of joints is significantly increased with dynamic loads especially when the bond length is below the effective bond length (about 30mm for 1 layer of CFRP and 50mm for 3 layers of CFRP). The smaller the bond length is, the greater the increase becomes. The ratio F4/F3 is larger than F2/F1 indicating that more increase was obtained for specimens with 3 layers of CFRP.
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Proceedia Engineering g 00 (2011) 000–0 000
The reason for the increaase in bond sttrength is maiinly due to th he shear strength enhancem ment of epoxy y between CFRP and steel under u impact loading, a pheenomenon rep ported in Yokohama and Shhimizu (1998)) and Raykheere et al. (2010), as discusssed later in thhe paper. Wheen the numberr of CFRP layyers increasess from 1 to 3,, there is an inncrease in bon nd strength. Suuch an increase under staticc load can be expressed by y f impact load ding the ratio is F4/F2. It caan be seen fro om Table 1 tha hat the ratio off the ratio F3//F1, whereas for F4/F2 is generally larger than t F3/F1, i.ee. more increaase in bond strrength is achieved under im mpact loading g RP layers increeases. when the nuumber of CFR 5.
Effect oof impact loads on effectiv ve bond lengtth
The jointt strength variiation with thee bond lengthh is plotted in Figure 3 for specimens unnder static and d impact loadding. For bothh types of speecimens (1 annd 3 layers off CFRP), Figure 3 explicittly shows thee phenomenonn of effectivee bond length, i.e. beyond which no exttra bond stren ngth can be oobtained. It iss somewhat suubjective to define d the effeective length ffrom test dataa. The effectiv ve bond lengthh under staticc load is abouut 30mm for l layer CFRP and a 50mm forr 3 layers of CFRP. C The sam me effective bbond length iss observed in Figure 3 for the case of im mpact loadingg. It seems thaat the impact load has littlee influence on n the effectivee bond length.
Figure 3: Ultim mate load versus bond b length
6.
Effect oof impact loads on failure mode
Six failurre modes for CFRP bonded d steel joints w were classifieed by Zhao an nd Zhang (20007), including g (a) Steel annd adhesive interface i failu ure; (b) Coheesive failure (adhesive ( layer failure); (cc) CFRP and d Adhesive innterface failurre; (d) CFRP P delaminationn (separation of some carrbon fibres frrom the resin n matrix); (e) CFRP rupturee; (f) Steel yieelding, as show wn in Figure 4. 4
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H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Proceedia Engineering g 00 (2011) 000–0 000
(e) FRP rupture (d) FRP d elamination n F FRP
Adhessive
(c) FRP F and ad dhesive inte erface debo onding (b) Adhesive A la ayer failure (a) Steel and adhesive a interface deb bonding
Stteel (f) Steel yeilding y
Figure 4: Failurre modes for CFR RP bonded steel joints (adapted froom Zhao and Zhaang (2007))
For speciimens with onne layer of CF FRP, failure m mode (c) occu urs when the bond b length iss less than thee effective bonnd length. The shear streng gth of the adheesive plays an n important rolle in this failuure mode. Thee failure modee under impacct load changees to failure m mode (d) which h is CFRP dellamination. Thhis is becausee of the shearr strength enhhancement of epoxy underr impact load as reported in Yokohama and Shimizu u (1998) and R Raykhere et al. a (2010). Wh hen the bond leength exceedss the effectivee bond length of 30mm, thee failure mode (e) occurs under u static lo oading whereeas the failuree modes (e) an nd (d) occur under impactt o the propertty of CFRP raather than thatt of adhesivess. This is why y loading. Theese failure moodes depend on the increasee in ultimate looad becomes less significaant. Some typiical failure modes m under im mpact loading g are shown inn Figure 5.
Figure 5: Typiccal failure modes under impact loaading
For speciimens with thhree layers of CFRP, the maain failure mo ode is (c) com mbined with m mode (d) when n the bond lenngth is less than the effectiv ve bond lengtth. For the sam me reason desscribed above,, an increased d ultimate loadd was observeed. When the bond length eexceeds the efffective bond length l of 30m mm, the failuree mode (c) dooes not occur any a more, lead ding to less inncrease in ultim mate load capaacity.
5
H.A. AL-ZUBAIDY et al. / Procedia Engineering 14 (2011) 1312–1317 Author name / Procedia Engineering 00 (2011) 000–000
6
7.
Conclusions
This paper presented an experimental investigation into the effect of impact tensile loads on the bond strength, effective bond length and failure modes of double strap joints. It was found that the bond strength of joints significantly increases under dynamic loads especially when the bond length is below the effective bond length. A higher level of increase was obtained for specimens with 3 layers of CFRP. The impact load has little influence on the effective bond length. The failure mode changed under impact loading due to the shear strength enhancement of epoxy between CFRP and steel under impact loading, leading to increased bond strength. Acknowledgment The project was sponsored by the Australian Research Council. The first author is sponsored by an Iraqi Government Scholarship. The authors wish to thank the technical staff in the Civil Engineering laboratory at Monash University for their assistance. References [1]
Beevers, A and Eillis, MD. Impact behaviour of bonded mild steel lap joints. International Journal of Adhesion and Adhesive, 4(1); 1984, pp. 13-16.
[2]
Fawzia, S., Zhao, XL and Al-Mahaidi, R. Bond–slip models for double strap joints strengthened by CFRP. Composite Structures. 92(9); 2009, pp. 2137-2145.
[3]
Goglio, L and Rossetto, M.. Impact rupture of structural adhesive joints under different stress combinations. International Journal of Impact Engineering, 35(7); 2008, pp. 635-643.
[4]
Hollaway LC and Cadei J. Progress in the technique of upgrading metallic structures with advanced polymer composites. Progress in Structural Engineering & Materials. 4(2); 2002, pp. 131-148.
[5]
Liu, HB, Zhao, XL and Al-Mahaidi, R. Effect of fatigue loading on bond strength between CFRP sheets and steel plates. International Journal of Structural Stability and Dynamics. 10(1); 2010, pp. 1-20.
[6]
Raykhere, SL, Kumar, P, Singh, RK and Parameswaran, V. Dynamic shear strength of adhesive joints made of metallic and composite adherents. Materials & Design, 31(4); 2010, pp. 2102-2109.
[7]
Xia, S and Teng, JG. Behaviour of FRP-to-steel bonded joints. Proceedings of the International Symposium on Bond Behaviour of FRP in Structures, Hong Kong; 2005, pp. 419-426.
[8]
Yokoyama, T and Shimizu, H. Evaluation of impact shear strength of adhesive joints with the Siplit Hopkinson Bar. JSME International Journal Serise 1, 41(4); 1998, pp. 503-509.
[9]
Zhao, XL and Zhang L. State-of-the-art review on FRP strengthened steel structures. Engineering Structures. 29(8); 2007, pp. 1808-1823.
1317