methods to improve the strength of adhesive joints

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Methods to improve the strength of adhesive joints


Lucas F M da SilvaFaculdade de Engenharia da Universidade do Porto (FEUP)

Mazda, Hiroshima, Japan27 August 2008

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Contents

• Introduction• Labs• Professional activities• Group• International partners

• Simple rules for single lap joints• Mixed adhesive joints• Tapers and spew fillets• Substrates with grooves• Publications

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Introduction

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Introduction

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Labs

Fabrication

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LabsTests

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Labs

Simulation (finite element method)

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Labs

Simulation (analytical method)

Overlap, x [mm]

70 80 90 100 110

Shea

r str

ess

[MPa

]

0

2

4

6

8

10

12

14

16 Neves & da Silva analysisFinite Element Analysis (FEA)

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Professional activities

Member of the editorial board

Reviewer of:•The Journal of Adhesion•Journal of Adhesion Science and Technology•Composites Part A: Applied Science and Manufacturing•Composites Science and Technology

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Special Issues• LFM da Silva, A Öchsner (Guest Editors),

‘Special issue on adhesive bonding’, J Adhesion Sci Technol, in press, 2008.

• LFM da Silva, Andreas Öchsner (Guest Editors), ‘Special topic issue on structural adhesive joints’, Inter J Adhes Adhes, in press, 2008.

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Group

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GroupMarcelo de MouraJ ChousalMiguel Figueiredo

Master• Pedro Neves• Ricardo Lima• Ricardo Carbas

PhD• Filipe Chaves• Mariana Banea• Eduardo Marques

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International partners

• Bob Adams, University of Oxford (UK)• Dave Dillard, Virginia Tech (USA)• Andreas Öchsner, Universiti Teknologi

Malaysia (Malaysia)• Gary Critchlow (Loughborough University,

UK)

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Simple rules for single lap joints• Elastic adherends (e.g. high strength steel)• Brittle adhesives

Volkersen (1938)

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Simple rules for single lap joints• Elastic adherends (e.g. high strength steel)• Brittle adhesives

da Silva et al. (2008b)

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Simple rules for single lap joints• Elastic adherends (e.g. high strength steel)• Ductile adhesives

Hart-Smith (1973)

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Banea & da Silva (2008)

0

2

4

6

8

10

12

0 10 20 30 40 50 60

Overlap length (mm)

Failu

re L

oads

(kN

) AV138 Exp.

AV138 Eq. 2

Sikaflex 255 Eq. 1

Sikaflex 255 Exp.

AS1805 Eq. 1

AS1805 Exp.

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Simple rules for single lap joints

• Plastic adherends (e.g. low strength steel)

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max yF wtσ=

maxF wlτ=2

sup

sup

6 / e / 2 (G&R)

3 /

M wt M kFt

kF wt

σσ

= =

=

Adherend yielding

•For low loads and short overlaps, k = 1•For joints which are long compared to the adherend thickness (l/t = 20), k = 0

max y / 4F wtσ=

t /F wtσ =

max sup t

max y

(1 3 ) /

/(1 3 )

F k wt

F wt k

σ σ σσ

= + = +

= +

Adams et al. (1997)


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Simple rules for single lap joints• Plastic adherends (e.g. low strength steel)

Steel yielding

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12 14

Displacement (mm)

Load

(kN

)

Test nº 4

Test nº 7

Adherend yielding (Eq.7)

Carbas et al. (2008)

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Simple rules for single lap joints• Parametric study of adhesively bonded single lap joints by the

Taguchi method

Araldite®

AV138M / HV998

Araldite® 2015

Sikaflex-255 FC

Shear modulus G (MPa) 1559 ± 11 487 ± 77 1.351 ± 0.04

Shear yield strength �ya (MPa) 25.0 ± 0.55 17.9 ± 1.8 8.26 ± 0.30

Shear strength �r (MPa) 30.2 ± 0.40 17.9 ± 1.8 8.26 ± 0.30

Shear failure strain �f (%) 5.50 ± 0.44 43.9 ± 3.4 330 ± 27

Critical strain energy release rate in mode I GIc (N/m)

345.9 ± 47.8 525.7 ± 80.8 2901.1 ± 121.9


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Taguchi methodTest � ys l t s t a G Ic S T A V Error

nº. [MPa] [mm] [mm] [mm] [N/m] [sem.] [mm/min.] [kN] Mode [kN] Criterion [%]1 184 12.5 1 0.5 2868 P 0 1 2.36 DP/Coes 3.31 DP 40.32 184 12.5 2 1 516 A1 1 10 5.42 DP/Int 4.46 DP 17.73 184 12.5 3 2 356 A2 4 100 3.10 Ades4 184 25 1 0.5 516 A1 4 100 7.02 DP/Int 4.60 DP 34.55 184 25 2 1 356 A2 0 1 3.05 Ades6 184 25 3 2 2868 P 1 10 5.19 DP/Coes 6.90 DP 32.97 184 50 1 1 2868 A2 1 100 6.44 DP/Mist 4.60 DP 28.68 184 50 2 2 516 P 4 1 8.41 DP/Int 9.20 DP 9.49 184 50 3 0.5 356 A1 0 10 12.60 DP/Int 12.08 DP 4.1

10 1260 12.5 1 2 356 A1 1 1 1.81 Ades11 1260 12.5 2 0.5 2868 A2 4 10 3.84 Coes 2.58 CG 32.812 1260 12.5 3 1 516 P 0 100 6.97 Mist 5.60 CG 19.713 1260 25 1 1 356 P 4 10 5.24 Ades14 1260 25 2 2 2868 A1 0 100 4.48 Coes 5.16 CG 15.2

15 1260 25 3 0.5 516 A2 1 1 12.39 Coes 11.19 CG 9.716 1260 50 1 2 516 A2 0 10 6.12 Ades17 1260 50 2 0.5 356 P 1 100 13.67 Int 11.99 Volk 12.318 1260 50 3 1 2868 A1 4 1 11.40 Coes 10.33 CG 9.4

F L - Failure load Coes - Cohesive failureDP - Plastic deformation of the steel Int - Cohesive failure close to the interfaceCG - Global yielding of the adhesive Ades - Adhesive failureVolk - Model of Volkersen Mist - Mixed failure

F LExperim. F L

Predicted


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Taguchi method

0

2

4

6

8

10

12

0 250 500 750 1000 1250 1500Adherend yield strength (MPa)

Mea

ns o

f fai

lure

load

(kN

)

0

2

4

6

8

10

12

0 10 20 30 40 50 60Overlap (mm)

Mea

ns o

f fai

lure

load

(kN

)

Source Sum of squares Degrees of freedom Mean square F-value P-value % of contributionσ ys 35831282.2 1 35831280.0 320.6106 0.0001 3.8l 426166569.1 2 213083300.0 1906.6236 0.0001 45.5t s 171951105.5 2 85975550.0 769.2908 0.0001 18.4t a 176921151.3 2 88460580.0 791.5263 0.0001 18.9G Ic 51724615.9 2 25862310.0 231.4104 0.0001 5.5

S T 25921273.1 2 12960640.0 115.9690 0.0001 2.7A 29737429.3 2 14868710.0 133.0420 0.0001 3.2V 3208753.7 2 1604377.0 14.3556 0.0001 0.3σ ys * l 8145888.8 2 4072944.0 36.4438 0.0001 0.8Residual (error) 6035013.5 54 111759.5 0.8Total 935643082.2 100.0


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Taguchi method

0

2

4

6

8

10

12

0 0.5 1 1.5 2 2.5Adhesive thickness (mm)

Mea

ns o

f fai

lure

load

(kN

)

0

2

4

6

8

10

12

0 500 1000 1500 2000 2500 3000Critical strain energy release rate (N/m)

Mea

ns o

f fai

lure

load

(kN

)

0

2

4

6

8

10

12

A1 A2 PSurface treatment

Mea

ns o

f fai

lure

load

(kN

)

0

2

4

6

8

10

12

0 0.5 1 1.5 2 2.5 3 3.5Adherend thickness (mm)

Mea

ns o

f fai

lure

load

(kN

)


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Taguchi method

0

2

4

6

8

10

12

1 10 100Test speed (mm/min)

Mea

ns o

f fai

lure

load

(kN

)

0

2

4

6

8

10

12

0 1 4Ageing (weeks)

Mea

ns o

f fai

lure

load

(kN

)


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Simple rules for single lap joints• Development of a software for the design of adhesive joints

WebsiteWebsite

UserUser

Mathematical modelMathematical model

DataBaseDataBase

MAXIMAMAXIMA MAPLEMAPLECC

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�Single lap jointsLinear analyses

Volkersen Goland & Reissner

Non linear analysesHart-Smith

Plastic substratesAdams et al.

�SandwichBigwood & Crocombe (linear)

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�SandwichBigwood & Crocombe (linear)

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http://ni.fe.up.pt/~rteixeira/rjoints

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Mixed adhesive joints (temperature)

• Problem

TemperatureSt

reng

th

-55 to 200ºC

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• Solution

-55 22 100 200

Stre

ngth Supreme 10HT

Redux 326Redux 326 + Supreme 10HT

τ -55ºC

τ 200ºC

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Mixed adhesive joints (temperature)• Stress distribution

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Mixed adhesive joints (temperature)• Experiments

0

5

10

15

20

25

30

35

40

45

50

-100 -50 0 50 100 150 200 250

Temperature (ºC)

Failu

re lo

ad (k

N)

Redux 326

Supreme 10HT

MAJ1-1

MAJ3

da Silva & Adams (2007)

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Mixed adhesive joints (temperature)• Analytical model

Overlap, x [mm]

70 80 90 100 110Sh

ear s

tres

s [M

Pa]

0

2

4

6

8

10

12

14

16 Neves & da Silva analysisFinite Element Analysis (FEA)

das Neves et al. (2008a)

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Mixed adhesive joints (temperature)• Parametric study

Adhesives Young's modulus ratio, ELTA/EHTA

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

Max

imum

she

ar s

tres

s [M

Pa]

0123456789

10111213

HTA alone

LTA alone

MADJ

High Temperature

Low Temperature

Adhesives Young's modulus ratio, ELTA/EHTA

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

Max

imum

pee

l str

ess

[MPa

]

0123456789

101112 HTA alone

LTA aloneMADJ

High Temperature

Low Temperature

das Neves et al. (2008b)

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• Adhesive joints for aerospace applications

NASA/Associated Press

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• Adhesive joints for aerospace applications

•Cotronics Resbond 940 SS

�Max temperature: 1093ºC

�2 component

�Flexural strength: 17 MPa

�Stainless steel based

�Cure: 8 hours at 25ºC

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Mixed adhesive joints (temperature)• Adhesive joints for aerospace applications

Marques & da Silva (2008)

+ =

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Mixed adhesive joints (temperature)• Adhesive joints for aerospace applications

Marques & da Silva (2008)

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Mixed adhesive joints• Single lap joints da Silva & Lopes (2007)

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Mixed adhesive joints• Single lap joints

da Silva & Lopes (2007)

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Mixed adhesive joints


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Mixed adhesive joints• Single lap joints


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Adhesive(s) Volkersen Global yielding Volker. + global yield.*AV138 (brittle) 11.3 ± 0.26 16.6 31.32013 (ductile) 23.4 ± 1.32 15.0 26.32021 (ductile) 28.1 ± .60 16.8 23.0DP8005 (very ductile) 7.8 ± 0.90 9.0 6.6AV138 + 2013 20.5 ± 0.70 22.6AV138 + 2021 24.0 ± 0.84 21.3AV138 + DP8005 17.2 ± 0.15 14.7* Volkersen for adhesive AV138 and global yielding for the ductile adhesives

Failure loadPredictedExperimental

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Tapers and spew fillets• Composites

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Tapers and spew fillets• Composites Adams et al. (1986)

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Tapers and spew fillets• Composites (temperature)

da Silva and Adams (2007)

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Transverse stresses in composite for Supreme 10HT

17,6

2,2

8,09,6

19,7

10,8

0

5

10

15

20

25

30

Basic design Internal taper and adhesive fillet

Str

ess

(MP

a)

Load (10 kN) Temperature (-10ºC) Load + temperature


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05

101520253035404550

-55ºC 22ºC -55ºC 22ºC -55ºC 22ºC

Supreme10HT

AV119 Adams et al(1986)

Failu

re lo

ad (k

N)

Basic design

Taper and adhesive fillet


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0

5

10

15

20

25

30

35

40

45

Supreme 10HT AV119

Failu

re lo

ad (k

N)

Basic design, compositeinner adherend

Taper and adhesive fillet,composite inneradherend

Basic design, compositeouter adherend


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Tapers and spew fillets• Stress analysis and failure properties of adhesively

bonded patches

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bonded patches

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bonded patchesMarques & da Silva (2008)

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bonded patchesMarques & da Silva (2008)

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Substrates with grooves• Surface patterns

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Substrates with grooves• Brittle adhesive without etching

AV138

0

1

2

3

4

5

6

7

Smooth 90º (0.1) 90º (0.3)

Failu

re lo

ad (k

N)

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Substrates with grooves• Brittle adhesive without etching (fracture surface)

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Substrates with grooves• Joints with etching (brittle and ductile adhesives)

0

2

4

6

8

10

12

Smooth 45

º90

º

90º

90º

45º ´

45º

Failu

re lo

ad (k

N)

AV138

2015

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Substrates with grooves• Fracture surfaces of joints with etching (brittle and

ductile adhesives)

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Publications (selection)Papers ISI• da Silva LFM, Adams RD, Inter J Adhes Adhes 27: 216-226, 2007.• da Silva LFM, Adams RD, Inter J Adhes Adhes 27: 227-235, 2007.• da Silva LFM, Adams RD, Inter J Adhes Adhes, 27: 362-379, 2007.• da Silva� LFM, da Silva RAM, Chousal JAG, Pinto AMG, J Adhesion Sci Technol,

22: 15–29, 2008. • da Silva� LFM, Critchlow G W, Figueiredo M A V, J Adhesion Sci Technol, 2008,

in press.• da Silva LFM , das Neves PJC, Adams RD, Spelt JK, ‘Analytical models of

adhesively bonded joints – Part I: Literature survey’, Inter J Adhes Adhes, 2008, accepted for publication.

• da Silva LFM , das Neves PJC, Adams RD, Wang A, Spelt JK, ‘Analytical models of adhesively bonded joints – Part II: Comparative study’, Inter J AdhesAdhes, 2008, accepted for publication.

• das Neves PJC, da Silva LFM, Adams RD, ‘Analysis of mixed adhesive bonded joints – Part I: Theoretical formulation’, J Adhesion Sci Technol, 2008, in press.

• das Neves PJC, da Silva LFM, Adams RD, ‘Analysis of mixed adhesive bonded joints – Part II: Parametric study’, J Adhesion Sci Technol, 2008, in press.

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Publications (selection)

methods to improve the strength of adhesive joints

Documents