School of Mechanical and Materials Engineering Project Motivation - - PowerPoint PPT Presentation
School of Mechanical and Materials Engineering Project Motivation - - PowerPoint PPT Presentation
The Effect of Surface Treatment on the Degradation of Composite Adhesives Lloyd Smith and Prashanti Pothakamuri School of Mechanical and Materials Engineering Project Motivation Higher efficiencies in commercial aircraft are being
SLIDE 1
SLIDE 2
Project Motivation
- Higher efficiencies in commercial aircraft are being
realized through composite materials
- Bonded joints contribute to the weight savings
afforded by advanced materials
- The resistance of adhesives to long-term
degradation is not understood as well as their adherends
- Stress can accelerate degradation and is often not
considered in degradation studies
SLIDE 3
Environmental Exposure Facility
- Aggressive
environments
- Temperature
- Stress
Creep or cyclic
- Time
SLIDE 4
Environmental Exposure Facility
SLIDE 5
Project Goals
Surface treatment effects
- Strength
- Fracture toughness
- Durability
Accelerated test methods
- Wedge crack
Model degradation
- Geometry
- Temperature
SLIDE 6
Characterization
- Mode I fracture toughness
Double cantilever beam
- Creep load (s)
Wide area lap shear
- Cyclic load (s) (low frequency, < 1 hz)
Wide area lap shear
- Accelerated testing
Wedge crack coupons Compliant adherends
- Degradation modeling
Weight change
SLIDE 7
Materials
- Low cost prepreg adherends
777 or 7e7
- Co-bonded adhesive films
Metal bond 1515-3 or AF555
- Surface treatments
No prep (60001 peel ply) Grit blast Plasma etch
SLIDE 8
Simulated Environmental Exposure
- 140F water immersion
- Up to 10k hour durations
- Post mortem surface characterization to be
performed at University of Washington
SLIDE 9
Fickian and Non-Fickian Weight Change
SLIDE 10
( )
∫
⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ − − =
t
- d
d dC t k z t C ) ( exp ) , ( τ τ τ
( )
∫
⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ − − =
t
- d
d dC t k z t C ) ( exp ) , ( τ τ τ
( )
∫
⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ − − =
t
- d
d dC t k z t C ) ( exp ) , ( τ τ τ
( )
∫
⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ − − =
t
- d
d dC t k z t C ) ( exp ) , ( τ τ τ
Modeling Degradation
2 2
z c D t c ∂ ∂ ⋅ = ∂ ∂
[ ] [ ]
C k dt C d = −
( )
∫
⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ − − =
t
- d
d dC t k z t C ) ( exp ) , ( τ τ τ
∫
⋅ =
h
dz z t C h t C ) , ( 1 ) (
SLIDE 11
Comparison of predicted and measured moisture concentration
0.01 0.02 0.03 0.04 0.05 0.06 20 40 60 80 100 120 140 time (sec)0.5 Concentration (%)
Experimental Concentration Model Concentration
SLIDE 12
Proposed First Year Work
- Long term durability
Consider current bond preparation practices 140F water immersion Residual fracture toughness after sustained environmental exposure (DCB) Residual strength and modulus after sustained creep and cyclic loading (WLS)
- Accelerated testing
Wedge crack coupons Adherend compliance proportional to fracture toughness Compare crack growth as a function of bond quality
SLIDE 13
Proposed First Year Work
- Modeling degradation