School of Mechanical and Materials Engineering Project Motivation - - PowerPoint PPT Presentation

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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


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SLIDE 1

School of Mechanical and Materials Engineering

The Effect of Surface Treatment on the Degradation of Composite Adhesives Lloyd Smith and Prashanti Pothakamuri

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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

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SLIDE 3

Environmental Exposure Facility

  • Aggressive

environments

  • Temperature
  • Stress

Creep or cyclic

  • Time
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SLIDE 4

Environmental Exposure Facility

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SLIDE 5

Project Goals

Surface treatment effects

  • Strength
  • Fracture toughness
  • Durability

Accelerated test methods

  • Wedge crack

Model degradation

  • Geometry
  • Temperature
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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

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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

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SLIDE 8

Simulated Environmental Exposure

  • 140F water immersion
  • Up to 10k hour durations
  • Post mortem surface characterization to be

performed at University of Washington

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SLIDE 9

Fickian and Non-Fickian Weight Change

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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 ) (

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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

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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

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SLIDE 13

Proposed First Year Work

  • Modeling degradation

Expose polymer to aggressive solvent with measurable weight change (gain or loss) Characterize fundamental degradation parameters (D, cm, k) Consider temperature and geometry effects