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High Temperature Composites

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  1. High Temperature Composites Rutgers University Federal Aviation Administration Advanced Materials Flammability Atlantic City, NJ October 24, 2001

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

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

  4. 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

  5. Hybrids: Fiber Characteristics • Glass – Economical, larger fiber diameter • Carbon – Higher modulus and strength, durability

  6. 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

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

  8. Test Setup • Simply supported • 3-point bending (ASTM D790) • Loading rate = 2.5 mm / min

  9. Mechanical Properties • Load – deflection response converted to stress and strain • Stress, • Strain,

  10. Assumptions for Analysis • Homogeneous • Elastic • Uncracked section • Perfect bond between glass and carbon layers

  11. Glass / Carbon Hybrid Results • Density • Failure pattern • Peak stress (strength) • Strain at peak load (ductility)

  12. 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

  13. 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

  14. 3k Unidirectional Carbon

  15. Samples with 2 Carbon Layers

  16. Varying Sample Thickness

  17. 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

  18. Thickness vs. Maximum Stress • 6 Glass + 1 carbon (uni): 347 MPa • 12 Glass + 2 carbon : 379 MPa • 18 Glass + 3 carbon : 362 MPa

  19. Maximum Strains • Matrix (tension): 0.0007 • Matrix (compression): 0.005 • All Glass (tension): 0.003

  20. 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

  21. Thickness vs. Maximum Strain • 6 Glass + 1 carbon (uni): 0.012 • 12 Glass + 2 carbon : 0.011 • 18 Glass + 3 carbon : 0.011

  22. 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.

  23. 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

  24. 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.

  25. Strain Capacity of Polysialates Cantilever Beam Method

  26. Variables Investigated • Silica / Alumina ratio • Discrete carbon fiber content • Effect of ceramic micro-fibers

  27. Influence of Carbon Fiber Content on Cracking Strain

  28. Effect of Microfibers Without Ceramic Microfibers With Ceramic Mircofibers

  29. Durability • Wet-Dry • Flexure • [±45°] In-Plane Shear • Thermo-mechanical • Exposure Temperatures (200, 400, 500, 600°C)

  30. Wet – Dry Durability

  31. 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

  32. Stress vs. Strain Relationships of Bi-directional Composites in Tension

  33. Tensile Strength of Bi-directional Composites

  34. Flexural Strength of Unidirectional Composites

  35. Flexural Stress-Strain Relationships of Unidirectional Composites

  36. Flexural Strength of Bi-directional Composites

  37. 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

  38. Typical Section of Sandwich Slab (Panel) Lightweight ceramic core • Carbon facings on both tension and compression sides

  39. Flexural Strength of Slabs With Different Reinforcement

  40. Load vs. Deflection for Slabs

  41. Commercially available plates + Inorganic matrix layer • Glass plates • Carbon plates • Fatigue • Sandwich panels Future Research