Adhesive Behavior in Aircraft Applications Adhesive Behavior in - - PowerPoint PPT Presentation

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RESEARCH / DESIGN / TESTING / CERTIFICATION Adhesive Behavior in Aircraft Applications Adhesive Behavior in Aircraft Applications N y N x John Tomblin Waruna Seneviratne N xy Paulo Escobar N xy Yoon-Khian Yap N xy Pierre Harter N xy National

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SLIDE 1

John Tomblin Waruna Seneviratne Paulo Escobar Yoon-Khian Yap Pierre Harter

National Institute for Aviation Research

Wichita State University

Nx Nx Ny Ny Nxy Nxy Nxy Nxy

FAA Workshop on Key Characteristics for Advanced Material Control September 16 – 18, 2003

RESEARCH / DESIGN / TESTING / CERTIFICATION

Adhesive Behavior in Aircraft Applications Adhesive Behavior in Aircraft Applications

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SLIDE 2

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Program Overview

  • Coupon Level Testing

– Investigation of Thick Bondline Adhesive Joints

  • Adhesive test methods
  • Bondline thickness effects
  • Environmental effects

[FAA Report: DOT/FAA/AR-01/33]

– Characteristic Shear Responses of Structural Adhesives

[FAA Report: DOT/FAA/AR-02/97]

– Fatigue & Stress Relaxation of Adhesive Joints

[FAA Report: Submitted to FAA]

  • Subcomponent Testing & Analysis

– Box Beam Torsion Lap Shear Test – Shear Loaded Bonded Joint (SLBJ) Theory [Purdue University]

[FAA Report: DOT/FAA/AR-03/21]

Available electronically at http://actlibrary.tc.faa.gov

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SLIDE 3

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Research Effort

Industry Partners

Funded by

FAA

Partnered with

Purdue University

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SLIDE 4

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Motivation

  • Number of certification programs

involve a large range of adhesive bonding applications

  • Migration from secondary to

primary structure

  • Limited guidance material existed
  • Limited experimental analytical

models that can be effectively used in design

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SLIDE 5

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Motivation (contd..)

  • Traditional bondline thicknesses

used : less than 0.010”

  • Current bondline thicknesses : up

to 0.140”

  • Generate data regarding the

effects of thick bondlines

  • Long term durability of adhesive

joint (fatigue/creep) needs to be addressed with respect to thick bondline joints

A A

Section A-A Closeout Bonded to Spar Caps Pinned Joints Through Spar Web Wing Skin Bonded Directly to Spar Caps Bending and Torsion Loads

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SLIDE 6

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Adhesive Test Methods

0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0 7000.0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Average bondline thickness (in) Apparent Shear Strength (psi)

ASTM D1002 ASTM D3165 ASTM D5656 Adhesive/Cohesive Adhesive Adhesive Adhesive/Cohesive

  • ASTM D1002 & D3165 for joint characterization
  • ASTM D5656 for adhesive characterization
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SLIDE 7

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

ASTM D5656 Test Method

  • Thick adherend

– Adhesive characterization rather than Joint characterization – Elastic Limit & Plastic Strain – Design & Analysis – Reduced peel stresses

  • Correction for metal

deformation

  • Four-Pin Configuration

– Reduces errors due to rotation and slippage – Reduced scatter in data

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SLIDE 8

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Failure Modes

ASTM D5656

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SLIDE 9

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Bondline Thickness Effects

  • Increasing bondline thickness resulted in reduced

plastic strain and lower yield stress

PTM&W ES6292

Bondline Thickness

500 1000 1500 2000 2500 3000 3500 4000 4500 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Shear Strain Shear Stress

t = 0.013 in t = 0.043 in t = 0.083 in t = 0.123 in

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SLIDE 10

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Environmental Effects

  • Yield stress and stiffness decreased with increasing

temperature and humidity

  • Environmental condition affects failure mode

MGS A100/B100

1000 2000 3000 4000 5000 6000 7000 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Shear Strain

Shear Stress (psi)

CTD RTD ETD 160° ETW 160° ETD 200° ETW 200° Bondline Thickness = 0.013" nom. Tg (dry) = 175°F Tg (wet) = 135°F

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SLIDE 11

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Characteristic Shear Responses of Structural Adhesives

  • 18 Adhesive Types

– 6 Film Adhesives – 12 Paste Adhesives

  • ASTM D5656 [4 pin holes]
  • Three Environmental

Conditions

– Room Temp. ambient [RTD] – Elevated Temp. (180°F) dry [ETD] – Elevated Temp. (180°F) wet [ETW]

  • 145 °F and 85% relative humidity for 1000 hrs
  • Bondline Thickness

– Film Adhesives: 0.01” – 0.03” – Paste Adhesives: 0.03” – 0.05”

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SLIDE 12

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Adhesive Types Investigated

Film Adhesives (6)

– AF 126 – EA 9628 – EA 9695 – EA 9696 – FM 300 – FM 73

Paste Adhesives (12)

– EA 9309.3 NA – EA 9346.5 – EA 9359.3 – EA 9360 – EA 9392 – EA 9394 – EA 9396 – MGS L418 – PTM&W ES 6292 – 3M DP-460 EG – 3M DP-460 NS – 3M DP-820

Adhesives & Aluminum sub-panels (Phosphoric Anodized) were provided by Cessna Aircraft, Wichita, KS

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SLIDE 13

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Apparent Shear Strength Comparison

1 2 3 4 5 6 7 A F 1 2 6 A F 1 2 6 E A 9 6 2 8 E A 9 6 2 8 E A 9 6 9 5 E A 9 6 9 5 E A 9 6 9 6 F M 3 F M 3 F M 7 3 F M 7 3 Film Adhesive Shear Strength (ksi) RTD ETD ETW 1 2 3 4 5 6 7 E A 9 3 9 . 3 N A E A 9 3 4 6 . 5 E A 9 3 5 9 . 3 E A 9 3 5 9 . 3 E A 9 3 6 E A 9 3 6 E A 9 3 6 E A 9 3 9 2 E A 9 3 9 2 E A 9 3 9 4 E A 9 3 9 6 M G S L 4 1 8 P T M & W E S 6 2 9 2 3 M D P

  • 4

6 E G 3 M D P

  • 4

6 N S 3 M D P

  • 8

2 Paste Adhesive Shear Strength (ksi) RTD ETD ETW

Film Adhesive Paste Adhesive

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SLIDE 14

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Shear Modulus Comparison

0.00 0.03 0.05 0.08 0.10 0.13 0.15 0.18 0.20 A F 1 2 6 A F 1 2 6 E A 9 6 2 8 E A 9 6 2 8 E A 9 6 9 5 E A 9 6 9 5 E A 9 6 9 6 F M 3 F M 3 F M 7 3 F M 7 3 Film Adhesive Shear Modulus (Msi) RTD ETD ETW 0.00 0.03 0.05 0.08 0.10 0.13 0.15 0.18 0.20 E A 9 3 9 . 3 N A E A 9 3 4 6 . 5 E A 9 3 5 9 . 3 E A 9 3 5 9 . 3 E A 9 3 6 E A 9 3 6 E A 9 3 6 E A 9 3 9 2 E A 9 3 9 2 E A 9 3 9 4 E A 9 3 9 6 M G S L 4 1 8 P T M & W E S 6 2 9 2 3 M D P

  • 4

6 E G 3 M D P

  • 4

6 N S 3 M D P

  • 8

2 Paste Adhesive Shear Modulus (Msi) RTD ETD ETW

Film Adhesive Paste Adhesive FAA Final Report: DOT/FAA/AR FAA Final Report: DOT/FAA/AR-

  • 02/97

02/97

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SLIDE 15

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Fatigue of Thick Bondline Adhesive Joints

Modified ASTM D3166-99 [Aluminum Adherend of 0.375”]

  • Three Adhesives

– PTM&W [0.060” & 0.160”] – Loctite [0.032”] – EA9696 [0.02”]

  • Three Stress Levels

– 103, 104 and 105 cycles

  • Three Frequencies

– F=2 Hz, 5 Hz and 10 Hz

  • Three Environmental

Conditions

– RTD, RTW – CTD (-40°F)

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SLIDE 16

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Stress Level Determination

Based on the initial SN Curve

y=-3.227*ln(x)+100.96 100000Cy SL1≈65% UL ≈183% LL 10000Cy SL2≈72% UL ≈202% LL 1000Cy SL3≈78% UL ≈220% LL Note: For RTW and CTD, %UL are different

10 20 30 40 50 60 70 80 90 100 200000 400000 600000 800000 1000000 1200000

Number of Cycles % of Ultimate

Loctite (RTD)

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SLIDE 17

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Loctite Stress Levels

Fatigue life in a range below knee point and above linear limit point.

Loctite RTD

10 0 0 2 0 0 0 3 0 0 0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 S h e a r S t ra in (in /in )

2 3 0 6 p s i 2 117 p s i 19 18 p s i

Lin e a r Lim it Lo a d 3 9 3 lb s (1 04 8 p si)

Loctite CTD

10 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 S h e a r S t ra in (in /in )

Lin e ar Lim it Load 576 lb s (1536 p s i) 3379 p s i 3102 p s i 2810 p s i

Loctite RTW

5 0 0 10 0 0 15 0 0 2 0 0 0 2 5 0 0 3 0 0 0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 S h e a r S t ra in (in /in )

Lin e ar Lim it Load 225 lb s (600 p s i) 1324 p s i 1215 p s i 1101 p s i

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SLIDE 18

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Fatigue Behavior of Adhesives

2 Hz 5 Hz 10 Hz

40 45 50 55 60 65 70 75 80 85 90 95 100 100 1000 10000 100000 1000000 10000000 Number of Cycles % of Ultimate RTD RTW CTD SL1 SL1 SL1 SL2 SL2 SL2 SL3 SL3 SL3 40 45 50 55 60 65 70 75 80 85 90 95 100 100 1000 10000 100000 1000000 10000000 Number of Cycles % of Ultimate RTD RTW CTD SL1 SL1 SL1 SL2 SL2 SL2 SL3 SL3 SL3 40 45 50 55 60 65 70 75 80 85 90 95 100 100 1000 10000 100000 1000000 10000000 Number of Cycles % of Ultimate RTD RTW CTD SL1 SL1 SL1 SL2 SL2 SL2 SL3 SL3 SL3

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SLIDE 19

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Stress Relaxation of Adhesive Joints

  • Applied stress gradually decreases to a stable value over time
  • Elastic strain that appears during initial rapid loading is slowly

replaced by creep strain, with the total of the two being constant

  • Steady-state creep and linear viscoelastic material behavior

t σ Ge ε’ G1 ε’ σ0 Δσ

G2

η2 σ

G1

ε

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SLIDE 20

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Modified ALCOA Stressing Fixture

σ(t) = μ • 2 δ (t)

Calibration for each environmental condition Test Results Format

δ P Load Cell δ P Load Cell

δ (t)

σ (t)

μ δ (t)

σ (t)

μ Time

σ

Time

σ

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SLIDE 21

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Stress Level Determination

S h e a r S t r e s s Shear Strain

25% YS 15% YS 10% YS

Test Temperatures

150°F 180°F 210°F Yield Stress

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SLIDE 22

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Creep Deformation

  • Loctite

– 25% YS – 180 °F – 167 hours

~ 18°

[50X magnification]

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SLIDE 23

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Loctite Stress Relaxation Results

50 100 150 200 250 300 350 400 450 10000 20000 30000 40000 50000

Time (sec) Stress (psi) 10% YS 15% YS 25% YS

50 100 150 200 250 10000 20000 30000 40000 50000

Time (sec) Stress (psi) 25% YS 10% YS 15% YS

20 40 60 80 100 120 10000 20000 30000 40000 50000

Time (sec) Stress (psi) 10% YS 15% YS 25% YS

150 °F 180 °F 210 °F

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SLIDE 24

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Box Beam Lap Shear Torsion Test

Load Loading Plate Side Plate (Inboard) 2½ Cylindrical Shaft Fixed-end block Side Plate (Outboard) Pivot-end Base Fixed-end Base

Joint Failure Prediction Shear Loaded Bonded Joint (SLBJ) Theory non-linear constitute behavior

  • f adhesive

Box Beam Lap Shear Torsion Testing Validation Design Guidelines & Certification

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SLIDE 25

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Adhesive Lap Joint Specimen

Flat Joint

PTM&W EA9360 Loctite

Joggle Joint

PTM&W EA9360 Gage width ~ 0.5” Gage section ~ 17.25”

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SLIDE 26

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Materials

  • Adhesives

– PTM&W ES6292 [t = 0.05” ~ 0.20”] – EA 9360 [t = 0.10”] – Loctite (CESSNA Proprietary) [t = 0.05”]

  • Adherend

– NEWPORT E-Glass Fabric 7781 / NB321 – NEWPORT NB321/3K70P Carbon Cloth

  • Fiberglass/Carbon Layup Schedule – [04/45/-45/04]

– Aluminum 2024-T3 Clad

  • Phosphorus Anodized & Bond Primed

[CESSNA Aircraft, Wichita, Kansas]

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SLIDE 27

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Maximum Shear Flow (Comparison)

Constitutive behavior for 0.20 was not available 500 1000 1500 2000 2500 0.00 0.05 0.10 0.15 0.20 0.25 Bondline Thickness (in)

  • Max. Shear Flow (lbf/in)

q-Experimental q-SLBJ ES6292 - Newport 7781FG

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SLIDE 28

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Conclusions

Environmental Effects

  • Adhesives become weak and ductile at high temperatures

and brittle at low temperatures.

  • Yield stress and modulus of all adhesives decrease with

increasing temperature and humidity

  • The

plastic behavior

  • f

adhesives at elevated temperatures caused significant shear deformation

  • Mechanical properties of adhesives can be substantially

degraded by the absorption of moisture

  • Environmental condition affects the failure mode as well

as the mechanical properties

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SLIDE 29

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Conclusions (Contd..)

Fatigue

  • ‘High stress’ fatigue life of adhesive exists in a range

below Knee point and above linear limit point

  • Failure modes indicate that moisture affects adhesive

bulk instead of the adhesive-adherend interface (RTW cohesive failures)

  • Observation – lower void in bondline = longer fatigue

life

  • Film adhesive indicates better resistance to moisture (less

voids?) Stress Relaxation

  • Stress relaxation was increased as the stress level and

temperature was increased

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SLIDE 30

NATIONAL INSTITUTE FOR AVIATION RESEARCH

Wichita State University

Conclusions (Contd…)

Box Beam Lap Shear Torsion

  • Load carrying capabilities of adhesive joints decreases as

bondline thickness increases

  • Purdue Analysis predictions (SLBJ Theory) comparable

with box beam test results

  • Increasing bondline thickness affects the failure mode of

bonded joints

  • Accumulation of large plastic strains in thin bondlines

resulted in high adherend interlaminar strains and caused substrate (first-ply) failure

  • Unstable damage development of thick bondlines (lower

plastic strain development) resulted in adhesive cracking in multiple locations with a cohesive type failure and lower failure strengths