Transcript Adhesive Behavior in Aircraft Applications
N xy N x N xy RESEARCH / DESIGN / TESTING / CERTIFICATION
Adhesive Behavior in Aircraft Applications
N y N y N xy N xy N x John Tomblin Waruna Seneviratne Paulo Escobar Yoon-Khian Yap Pierre Harter
National Institute for Aviation Research Wichita State University
FAA Workshop on Key Characteristics for Advanced Material Control September 16 – 18, 2003
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
Research Effort
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Funded by FAA
Industry Partners
Partnered with Purdue 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
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 Pinned Joints Through Spar Web NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Closeout Bonded to Spar Caps Section A-A Bending and Torsion Loads Wing Skin Bonded Directly to Spar Caps
7000.0
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Adhesive Test Methods
6000.0
5000.0
Adhesive/Cohesive 4000.0
Adhesive/Cohesive 3000.0
Adhesive Adhesive 2000.0
1000.0
ASTM D1002 ASTM D3165 ASTM D5656 0.0
0 0.02
0.12
0.14
0.04
0.06
0.08
0.1
Average bondline thickness (in)
• ASTM D1002 & D3165 for joint characterization • ASTM D5656 for adhesive characterization
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
Failure Modes
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
ASTM D5656
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Bondline Thickness Effects
4500 4000 3500 3000 2500 2000 1500 1000 500 0 0.00
0.05
0.10
0.15
PTM&W ES6292 Bondline Thickness 0.30
t = 0.013 in t = 0.043 in t = 0.083 in t = 0.123 in 0.35
0.40
0.45
0.20
0.25
Shear Strain
• Increasing bondline thickness resulted in reduced plastic strain and lower yield stress
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Environmental Effects
7000 6000 5000 4000 3000 2000 CTD RTD ETD 160° ETW 160° Bondline Thickness = 0.013" nom.
Tg (dry) = 175°F Tg (wet) = 135°F ETD 200° ETW 200° MGS A100/B100 1000 0 0 0.1
0.2
0.6
0.7
0.8
0.3
0.4
Shear Strain 0.5
• Yield stress and stiffness decreased with increasing temperature and humidity • Environmental condition affects failure mode
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”
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 Adhesives & Aluminum sub-panels (Phosphoric Anodized) were provided by Cessna Aircraft, Wichita, KS 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
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Apparent Shear Strength Comparison
5 4 7 6 RTD ETD ETW 3 2 1 0 A F 12 6 A F 12 6 EA 9 62 8 E A 96 28 EA 9 69 5 E A 96 95 EA 9 69 6 Film Adhesive FM 3 00 FM 3 00 FM 7 3 FM 7 3 Paste Adhesive Film Adhesive 7 4 3 6 5 RTD ETD ETW 2 1 0 E A 93 09 .3
N A E A 93 46 .5
E A 93 59 .3
E A 93 59 .3
E A 93 60 EA 9 36 0 E A 93 60 E A 93 92 EA 9 39 2 E A 93 94 E A 93 96 M G P S L4 TM 18 &W E S 62 3M 92 D P 46 0 3M E G D P 46 0 N S 3M D P -8 20 Paste Adhesive
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Shear Modulus Comparison
0.20
0.18
0.15
0.13
RTD ETD ETW 0.10
0.08
0.05
0.03
0.00
A F 12 6 A F 12 6 E A 96 28 E A 96 28 E A 96 95 E A 96 95 E A 96 96 Film Adhesive FM 3 00 FM 3 00 FM 7 3 FM 7 3 Film Adhesive Paste Adhesive
FAA Final Report: DOT/FAA/AR-02/97
0.20
0.18
0.15
0.13
RTD ETD ETW 0.10
0.08
0.05
0.03
0.00
E A 93 09 .3
N A E A 93 46 .5
EA 9 35 9.
3 E A 93 59 .3
E A 93 60 E A 93 60 E A 93 60 EA 9 39 2 EA 9 39 2 E A 93 94 E A 93 96 M G P S L4 TM 18 &W E S 62 3M 92 D P 46 0 3M E G D P 46 0 N S 3M D P -8 20
Paste Adhesive
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 – 10 3 , 10 4 and 10 5 cycles • Three Frequencies – F=2 H z , 5 H z and 10 H z • Three Environmental Conditions – RTD, RTW – CTD (-40°F)
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 40 30 20 10 0 0 100 90 80 70 60 50
Loctite (RTD)
200000 400000 600000 800000
Number of Cycles
1000000 1200000
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Loctite Stress Levels
Fatigue life in a range below knee point and above linear limit point.
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Fatigue Behavior of Adhesives
100 95 90 85 80 75 70 65 60 55 50 45 40 100 100 100 RTD RTW CTD 95 90 RTD RTW CTD 95 90 85 85 80
SL3 SL3
75
SL2 SL2
70
SL3 SL2 SL1
65
SL2
60
SL1
55
SL3
1000 50
SL2
45
SL1
10000 100000
Number of Cycles
1000000 10000000 40 100
SL3
1000
SL3 SL2 SL1 SL1 SL1
10000 100000
Number of Cycles
1000000 10000000 80 75 70 65 60 55 50 45 40 100
SL3 SL3 SL2 SL3 SL2 SL1 SL2 SL1
RTD RTW CTD
SL1
1000 10000 100000
Number of Cycles
1000000 10000000 2 Hz 5 Hz 10 Hz
s s 0
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Stress Relaxation of Adhesive Joints
s e G 1 e ’
G1
Ds G e e ’
G2 t
0 • 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 h
2
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Modified ALCOA Stressing Fixture
Calibration for each environmental condition s (
t)
s(
t
) = m 2 d (
t
) d (
t)
Test Results Format
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Stress Level Determination
Yield Stress
Test Temperatures
150°F 180°F 210°F
25% YS 15% YS 10% YS
Shear Strain
Creep Deformation
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
• Loctite – 25% YS – 180 °F – 167 hours ~18° [50X magnification]
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Loctite Stress Relaxation Results
450 400 350 300 250 200 150 100 50 0 0 10000 25% YS 20000 30000
Time (sec)
180 °F 15% YS 10% YS 250 40000 200 50000 150 100 50 0 0 10000 150 °F 20000 30000
Time (sec)
210 °F 25% YS 15% YS 10% YS 120 100 40000 80 50000 60 40 20 0 0 10000 20000 30000
Time (sec)
25% YS 15% YS 10% YS 40000 50000
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Box Beam Lap Shear Torsion Test
non-linear constitute behavior of adhesive
Shear Loaded Bonded Joint (SLBJ)
Theory
Box Beam Lap Shear Torsion Testing
Joint Failure Prediction
Validation Design Guidelines & Certification
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Adhesive Lap Joint Specimen
Gage width ~ 0.5” Gage section ~ 17.25” Flat Joint PTM&W EA9360 Loctite Joggle Joint PTM&W EA9360
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 – [0 4 /45/-45/0 4 ] – Aluminum 2024-T3 Clad • Phosphorus Anodized & Bond Primed [CESSNA Aircraft, Wichita, Kansas]
2500 2000 1500 1000 500 0 0.00
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Maximum Shear Flow
(Comparison)
ES6292 - Newport 7781FG q-Experimental q-SLBJ 0.05
0.10
0.15
Bondline Thickness (in) 0.20
0.25
Constitutive behavior for 0.20 was not available
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 of adhesives at temperatures caused significant shear deformation elevated • 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
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
Conclusions
(Contd..)
Fatigue
•
‘High stress’
fatigue life of adhesive exists in a range below life voids?)
Knee point
cohesive failures) and above
linear limit point
• Failure modes indicate that moisture affects adhesive bulk instead of the adhesive-adherend interface (RTW • Observation – lower void in bondline = longer fatigue • Film adhesive indicates better resistance to moisture (less
Stress Relaxation
• Stress relaxation was increased as the stress level and temperature was increased
Conclusions
(Contd…)
NATIONAL INSTITUTE FOR AVIATION RESEARCH
Wichita State University
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