Composite Materials and Their Applications

Matrix Materials

• Different types of matrix materials used in composites include polymer, metal, and ceramic matrices.
• Polymer matrix composite examples: carbon/epoxy, glass/epoxy, glass/polyester, Kevlar/epoxy
• Metal matrix composite examples: silicon carbide/aluminum, carbon fiber/aluminum
• Ceramic matrix composite examples: carbon/carbon, carbon/alumina

Polymer Matrix Composites

• Polymer matrix composites are more prevalent than other types due to compatibility considerations.
• Divided into thermoset and thermoplastic matrix composites.
• Thermoset matrix composites: carbon/epoxy, glass/epoxy, glass/polyester, Kevlar/epoxy.
• Thermoplastic matrix composites: carbon/PEEK, carbon/PPS, glass/nylon.
• Thermoset matrix composites are more common than thermoplastic matrix composites due to availability.

Viscosity of Thermoset and Thermoplastic Materials

• Material viscosity at different temperatures (in centipoise).
• 1 Pa-sec = 10 Poise = 1000 centi-Poise

Thermoset Resin

• Thermoset resins are characterized by crosslinking and network formation.
• Linked molecules form a rigid, non-melting structure.
• Partially linked networks are also possible.

Carbon Matrix Composites

• Carbon matrix composites are made from carbon fibers reinforced with phenolics.
• High-temperature applications include rocket nozzle liners, space shuttle nose cone tiles, aircraft brakes, race car/truck brakes.
• This material is known for its high energy adsorption (specific heat) compared to other materials.

Thermoplastic Matrix Composites

• No shelf life.
• Short processing cycle.
• Exhibit higher ductility than thermosets.
• Repairable and recyclable.
• Higher viscosity than thermosets, requiring high processing temperatures.
• Tapes are stiff and boardy.

Thermoplastic Resins

• Classified into industrial thermoplastics (up to 80°C) and high performance thermoplastics (up to 300°C).
• Industrial thermoplastics: Polyethylene (PE), Polyvinyl chloride (PVC), Polymethymethacrylate (PMMA), Polypropylene (PP), Polystyrene (PS), Acrylonitrile Butadiene Styrene (ABS).
• High performance thermoplastics: Poly-ether-ether-ketone (PEEK), Poly-ether-ketone-ketone (PEKK), Poly-ether- imide (PEI), Poly-phenylene sulfone (PPS), Poly sulfone.

Thermoplastic Matrix Fabrication

• Due to high viscosity, fabrication is challenging compared to liquid epoxy (106 centipoise vs. 1000 centipoise).
• Shear thinning phenomenon observed.
• Fabrication methods include comingled fibers and power impregnation.

Fillers in Composites

• Fillers are used to:
  • reduce cost
  • minimize shrinkage
  • enhance mechanical properties
  • improve flame resistance.
• They can also be used as colorants and pigments.

Metal Matrix Composites

• Metallic matrices, such as aluminum, titanium, magnesium, and copper.
• Reinforced with short fibers, particles, whiskers, or fibers.
• Applications include piston ring inserts, pistons, connecting rods.
• High temperature applications.
• Fabrication is challenging.

Ceramic Matrix Composites

• Ceramic matrices include oxides, carbides, borides, and nitrides.
• Reinforced with short fibers, particles, or whiskers.
• Made using chemical vapor deposition.
• High temperature applications.
• Fabrication is difficult.

Polymer Nanocomposites

• Polymer nanocomposites are created by incorporating nano-sized fillers into the polymer matrix.
• Incorporation of clay nanoparticles can enhance properties like strength, stiffness, and barrier properties.
• Clay nanoparticles can act as reinforcement agents, barrier materials, or flame retardants.
• Clay sheets act as barrier layers and suppress crack growth.

Clay Structure and Intercalation

• Clay sheets consist of layers of silica tetrahedra and alumina octahedra.
• Positive ions, like sodium or calcium, are present between these layers.
• Intercalation occurs when these positive ions are replaced with larger organic cations.

Dispersion Techniques for Nanocomposites

• High pressure mixing techniques are used to ensure uniform distribution of nanoparticles in the matrix.
• This method can increase interlayer spacing and enhance properties.
• Characterization techniques like X-ray diffraction (XRD) are used to evaluate nanocomposite structure.

Strain Energy Release Rate

• Nanoparticles can increase strain energy release rate (G1C) of composites, improving fracture toughness.
• The extent of improvement is directly related to clay loading.

Polyester Production

• Polyester resins can be produced using a reaction between maleic acid and ethylene glycol.
• The reaction yields a repeating unit of polyester and water.
• The amount of polyester formed can be calculated by considering the stoichiometric ratio of reactants.

Polyester Crosslinking

• Crosslinking of polyester resins usually involves incorporating styrene monomers into the polymer chain.
• These monomers create bonds between polyester molecules, improving the strength and stiffness of the material.
• The ratio of monomers determines the level of crosslinking and the resulting properties of the polyester composite.

Initiators in Polyester Production

• Initiators are used to accelerate the polymerization process in producing polyester resin.
• Different types of peroxides are commonly used as initiators:
• Hydrogen peroxide
• Hydroperoxides
• Dialkyl peroxides
• Diacyl peroxides
• Peroxyesters
• Peroxy Acids
• Peroxy Ketals
• Peroxy Dicarbonates