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

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

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

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

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

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

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

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

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

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

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

Density All glass: 2.36 g/cm 3 All carbon: 1.9 to 2.0 g/cm 3 for 3 types Increase in carbon layers provide consistent decrease in density

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

3k Unidirectional Carbon

Samples with 2 Carbon Layers

Varying Sample Thickness

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

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

Maximum Strains Matrix (tension): Matrix (compression): All Glass (tension): 0.003

Maximum Strain: 3k Uni Carbon Pure Glass: Glass + 1 Layer: Glass + 2 Layers: Glass + 3 Layers: k Uni Carbon: 0.005

Thickness vs. Maximum Strain 6 Glass + 1 carbon (uni): Glass + 2 carbon : Glass + 3 carbon : 0.011

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.

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

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.

Strain Capacity of Polysialates Cantilever Beam Method

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

Influence of Carbon Fiber Content on Cracking Strain

Effect of Microfibers Without Ceramic Microfibers With Ceramic Mircofibers

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

Wet – Dry Durability

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

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

Tensile Strength of Bi-directional Composites

Flexural Strength of Unidirectional Composites

Flexural Stress-Strain Relationships of Unidirectional Composites

Flexural Strength of Bi-directional Composites

Lightweight Sandwich Panels Core features: - Inorganic matrix + ceramic spheres - Density: 0.6 to 0.7 g/cm 3 - Compressive strength: 5.12 MPa Carbon fabric laminated onto facings

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

Flexural Strength of Slabs With Different Reinforcement

Load vs. Deflection for Slabs

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