High Temperature Composites

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High Temperature Composites

• Rutgers University
• Federal Aviation Administration
• Advanced Materials Flammability
• Atlantic City, NJ
• October 24, 2001

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Research Team

• P. Balaguru
• J. Giancaspro
• C. Papakonstantinou
• R. Lyon (FAA)

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Introduction

• Polysialate (Geopolymer)
• Aluminosilicate
• Water-based, non-toxic, durable
• Resists temperatures up to 1000C
• Curing temperature 20, 80, 150C
• Protects carbon from oxidation

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Ongoing Research at Rutgers

• Mechanical properties of carbon and glass
  composites
• Hybrid composites carbon/glass and
  inorganic/organic
• Structural sandwich panels
• Comparison with other high temperature composites

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Hybrids Fiber Characteristics

• Glass Economical, larger fiber diameter
• Carbon Higher modulus and strength, durability

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Variables

• Eglass fiber core with carbon fiber skins
• Number of layers on tension side 1,2,3
• Type of carbon fabric 1k and 3k woven, 3k
  unidirectional
• Number of layers on the compression side 1,2,3
• Specimen thickness 6, 12, and 18 layers of
  glass fabrics

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Specimen Preparation

• Hand impregnation
• Room temperature (20C) curing
• 1 MPa of pressure for 24 hours
• Post curing for 3 weeks
• Room temp. curing reduces degradation of glass
  under alkali environment

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Test Setup

• Simply supported
• 3-point bending (ASTM D790)
• Loading rate 2.5 mm / min

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Mechanical Properties

• Load deflection response converted to stress
  and strain
• Stress,
• Strain,

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Assumptions for Analysis

• Homogeneous
• Elastic
• Uncracked section
• Perfect bond between glass and carbon layers

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Glass / Carbon Hybrid Results

• Density
• Failure pattern
• Peak stress (strength)
• Strain at peak load (ductility)

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Density

• All glass 2.36 g/cm3
• All carbon 1.9 to 2.0 g/cm3 for 3 types
• Increase in carbon layers provide consistent
  decrease in density

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Failure Pattern

• Glass brittle, no post-cracking strength
• Glass with 1 and 2 carbon layers failed in
  tension
• Glass with 3 carbon layers compression failure
• Glass with both tension and compression
  reinforcement compression failure

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3k Unidirectional Carbon
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Samples with 2 Carbon Layers
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Varying Sample Thickness
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Maximum Stress 3k Uni Carbon

• Pure Glass 103 MPa
• Glass 1 Layer 212 MPa
• Glass 2 Layers 379 MPa
• Glass 3 Layers 354 MPa
• 3k Unidirectional Carbon 466 MPa

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Thickness vs. Maximum Stress

• 6 Glass 1 carbon (uni) 347 MPa
• 12 Glass 2 carbon 379 MPa
• 18 Glass 3 carbon 362 MPa

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Maximum Strains

• Matrix (tension) 0.0007
• Matrix (compression) 0.005
• All Glass (tension) 0.003

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Maximum Strain 3k Uni Carbon

• Pure Glass 0.003
• Glass 1 Layer 0.007
• Glass 2 Layers 0.011
• Glass 3 Layers 0.009
• 3k Uni Carbon 0.005

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Thickness vs. Maximum Strain

• 6 Glass 1 carbon (uni) 0.012
• 12 Glass 2 carbon 0.011
• 18 Glass 3 carbon 0.011

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Conclusions Glass/Carbon Hybrids

• Eglass / carbon is a viable combination.
• For all types of carbon fabric, 2 layers on the
  tension side provides the highest strength.
• Placing carbon on both compression and tension
  faces does not significantly increase the
  strength.

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Conclusions Glass/Carbon Hybrids

• Eglass reinforced with 1, 2, or 3 carbon layers
  exhibited the highest strength when the fabric
  was 3k unidirectional
• Slightly lower strengths were achieved using 3k
  woven carbon fabric
• The lowest strengths were achieved using 1k woven
  carbon fabric

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Conclusions Glass/Carbon Hybrids

• The uncracked section modulus for Eglass
  reinforced with 1k or 3k woven on the tension
  side showed little change as the number of carbon
  layers increased.
• 3k unidirectional carbon on the tension side
  provided a modulus increase with an increasing
  number of layers.
• An increase in modulus also results for carbon on
  both compression and tension sides.

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Strain Capacity of Polysialates

• Cantilever Beam Method

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Variables Investigated

• Silica / Alumina ratio
• Discrete carbon fiber content
• Effect of ceramic micro-fibers

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Influence of Carbon Fiber Content on Cracking
Strain
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Effect of Microfibers
Without Ceramic Microfibers
With Ceramic Mircofibers
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Durability

• Wet-Dry
• Flexure
• 45 In-Plane Shear
• Thermo-mechanical
• Exposure Temperatures (200, 400, 500, 600C)

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Wet Dry Durability
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Comparison of Polysialate and Other Inorganic
Composites

• Relative performance of polysialate composites
• Processing requirements
• Mechanical properties
• Carbon/Carbon composites
• Ceramic matrix composites
• Carbon/Polysialate composites

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Stress vs. Strain Relationships of Bi-directional
Composites in Tension
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Tensile Strength of Bi-directional Composites
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Flexural Strength of Unidirectional Composites
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Flexural Stress-Strain Relationships of
Unidirectional Composites
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Flexural Strength of Bi-directional Composites
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Lightweight Sandwich Panels

• Core features
• - Inorganic matrix ceramic spheres
• - Density 0.6 to 0.7 g/cm3
• - Compressive strength 5.12 MPa
• Carbon fabric laminated onto facings

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Typical Section of Sandwich Slab (Panel)

• Lightweight ceramic core
• Carbon facings on both tension and compression
  sides

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Flexural Strength of Slabs With Different
Reinforcement
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Load vs. Deflection for Slabs
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Future Research

• Commercially available plates Inorganic
  matrix layer
• Glass plates
• Carbon plates
• Fatigue
• Sandwich panels