Composite Materials: Types and Classifications

• Composite materials consist of two or more physically distinct phases, combining to produce unique aggregate properties different from their original components.
• They are heterogeneous on a microscopic scale but statistically homogeneous on a macroscopic scale.
• Components are combined macroscopically but are insoluble with reinforcement and a matrix.

Common Examples

• Cement/concrete is reinforced with steel rebars.
• Epoxy is reinforced with graphite fibers.
• Plastic molding compounds contain fillers.
• Rubber is mixed with carbon blacks.

Classification Based on Matrix Type

• Polymer matrices: Include thermosets like epoxy and polyester, and thermoplastics like polystyrene and nylons.
• Metal matrices: Include alloys like steels and aluminums.
• Ceramic matrices: Include glass, ceramics (semiconductors, cermets), and cements.
• Use of carbon and graphite based matrices

Classification Based on Reinforcement Geometry

• Particle-reinforced composites
• Fiber-reinforced composites: continuous (aligned) and discontinuous (short).
• Structural composites: laminates and sandwich panels

Reinforcement

• Reinforcement is the action or process of strengthening a material.
• Reinforcing phase as it enhances the mechanical properties of the matrix.
• Reinforcement is typically harder, stronger, and stiffer than the matrix material.
• The geometry of the reinforcing phase is a major parameter determining the effectiveness of the reinforcement.
• Geometry: In composite materials refers to the shape and arrangement of reinforcement within the matrix
• Dispersed phase determines if it is particulate, fiber reinforced or structural composite

Particulate-Reinforced Composites

• Particulate reinforcements have dimensions approximately equal in all directions.
• The shape of reinforcing particles can be spherical, cubic, platelets, or irregular.
• Particulate reinforcement arrangement can be random or with a preferred orientation.
• Solid particulates of metal oxides or carbides of varying sizes are dispersed in metal, metal alloy, ceramic or polymer liquid matrix.
• Particle-reinforced composites are classified into large-particulate and dispersion-strengthened composites

Large-Particulate Composites

• Large particle composites can be used with metals, polymers, and ceramics.
• Particle size ranges from 1-50 µm.
• Particle concentration ranges from 15-40% by volume.
• The particulate phase is harder and stiffer than the matrix.
• Particles provide strength to the composite by restraining movement of the matrix.
• Concrete is composed of cement matrix and particulates of sand and gravel.
• Automobile tires incorporate carbon black particles dispersed in a rubber matrix
• Ceramic-metal composites are known as cermets.
• Al2O3 dispersed in Cr matrix cermets have good strength and thermal shock resistance.
• Tungsten carbide(WC) dispersed in Co matrix is in Valves, Spray nozzles and machine parts that require high surface hardness.

Dispersion-Strengthened Composites

• Uniformly dispersed fine, hard particles (less than 0.1 µm) are used as reinforcement.
• The volume fraction of reinforcement ranges from 5-15%.
• Reinforcement particles are stronger than the metal matrix and can be metallic, inter-metallic or nonmetallic.
• The matrix is the load-bearing phase.
• Examples include thoria dispersed-nickel, Cu-Al2O3, and Cu-Zn-Al2O3

Fiber-Reinforced Composites

• Fibers are the main components in a fiber-reinforced composite material.
• Fibers occupy the largest volume fraction in a composite laminate.
• Fibers share the major portion of the load acting on a composite structure.
• They consist of continuous and discontinuous fibers

Factors Affecting Properties of Fibrous Composites

• Length, volume fraction, shape and size, distribution, and orientation are all important.
• Properties of the fibers and matrix materials
• Fiber concentration
• Fiber orientation relative to loading direction

Orientation of Fibers

• Orientation of the fiber in the matrix is strength indication.
• One-dimensional orientation provides maximum strength and stiffness in the fiber direction.
• Planar orientation uses two-dimensional woven fabric.
• Random or three-dimensional orientation tends to create isotropic properties.

Fiber Influence on Composite Characteristics

• Density
• Tensile strength and modulus
• Compressive strength and modulus
• Fatigue strength and failure mechanisms
• Electrical and thermal conductivities
• Cost

Properties of Fibers

• Small diameter needed for high-performance, since a lower size lowers the chances of imperfections in the material.
• High aspect ratio (length to diameter, l/d) allows a large load fraction to transfer through matrix to fiber.
• An aspect ratio should be around 200 for load transfer.
• High flexibility facilitates various composite manufacturing techniques.

Flexibility

• The smaller the size the better will be the flexibility
• Flexibility = 1/MR = 64/Eπd^4
• Where M is bending moment, I is moment of inertia, E is Young's modulus, R is radius of curvature, and d is diameter

Natural Vs. Synthetic Fibers

• Synthetic: Rayon, Nylon, Acetate, Acrylic, Spandex, Polyester
• Natural: Silk, Cotton, Wool, Mohair, Cashmere

Classification of Natural Fibers

• Vegetable/cellulose, animal/protein, and mineral.
• Cotton, rayon, and cellulose acetate are cellulose fibers

Synthetic Fibers

• Can't be biodegraded, so represents a threat to environemnt.
• Synthetic man-made fibers: Boron fiber, Carbon fiber, Ceramic fiber , Glass fiber, Graphite fiber, Kevlar fiber, Silica fiber

Categorization Of Fibers

• Fibers are divided into Filaments, Wires, and Rods

Performance of Fibers

• Grouped into high, medium, and low
• High-performance: boron, carbon, and Kevlar fibers.
• Medium performance: glass fibers.
• Low performance: natural fibers.

Glass Fibers

• Common for Polymer Matrix Composites(PMC's).
• They come in two forms: Continuous and discontinuous.
• Drawn from molten mixture: quartz sand, limestone, dolomite, paraffin, soda, and boric acid.
• Diameters are 5 to 20 um, and finer fiber is better performance.

Composition of Glass Fibers

• SiO2 is a main portion.
• Silicate glass fibers are: E-glass and S-glass

Types of Commercially Available Glass Fibers

• A-glass: contains high alkali metal oxides.
• C-glass: resists chemical attack and corrosion; used in chemical applications due to its high chemical resistance.
• D-glass: high dielectric property and good dielectric properties.
• E-glass: is non-alkali, with high electric insulation, high strength, high resistivity; is used in the FRP industry with low cost. A form of Ca-Al-B-Si glass fiber with 0.8wt% of alkali content, and high conductivity resistance.
• S-glass: high-strength with 35% tensile strength vs E-glass. Also has stability and resistance under extreme temperatures and corrosive environments, and are used for aircrafts and missiles.

M-Glass Fibers

• High-modulus glass fibers, higher modulus than common glass fibers.
• AR-glass fibers: alkali resistant and contain 16 wt% ZrO2
• Used to reinforce cement matrix.
• Compared to regular cement, AR-glass has about 2-3 times strength, about 3-4 times bending strength, and about 15-20 times toughness

Special Glass Fibers

• There are Hollow Glass Fibers
• Also Radiation-Resistant Insulating Fibers
• Hollow glass: feature lightness, high stiffness, low dielectric constants and low thermal conductivity.
• Main indexes are hollow percentage and degree. Hollow percentage is ratio of hollow filaments to total filaments. Hollow degree is the ratio inner diameter to outer diameter. Made from E-glass to to make aviation and structures
• Radiation-Resistant: Low thermal neutron capture, high insulation resistance, mechanical properties, and water resistance. Used in high irradiation and temps. Made of SiO2, Al2O3, CaO and MgO to make cables and radiation resitance nuclear reactors

Advantages of Glass Fibers

• Good chemical stability
• Good heat resitance
• High tensile strength
• High electrical resistence
• Low tensile strain
• Low insulation
• A low coefficient of thermal expansion

Disadvantages of Glass Fibers

• Low density (among the commercial fibers)
• Poor adhesion to specific polymer matrix materials
• Low fatigue resistance
• High hardness and Poor adhesion in humid environments

Carbon Fibers

• Composed of carbon atoms bonded together.
• Carbon exists in: graphite, diamond, and fullerenes.
• Carbon atoms are in the graphite structure
• Structure: layer is packed with strongly bonded with weak van der Waals forces.
• Graphite is anisotropic, thus it has one set of mechanical properties

Modulus Value in Graphite

• Layer Plane is 1000 GPa
• Along C-axis is 35 GPA
• Exists in fiber carbon

Allotropes

• Diamond: Cubic Structure with 3 directions covalent bonding

Fullerenes

• Made of 60-70
• Used as reinforcement

Attributes of Carbon Fibers

• Light weight
• 5x stronger steel
• 2/3 wight
• twisted to wovens
• Strands can be twisted together, like yarn-can be woven like cloth extremely light weight.

Carbon Fiber Classifications

• High-tenacity type (HT)
• Ultra-high-tenacity type (UHT)
• High-modulus type (HM)
• Ultra-high-modulus type (UHM)

Carbon Production

• Production based on type of carbon precursor used: Polyacrylonitrile (PAN), Pitch, Rayon

Four Production Stage for Carbon FIbers

• Fiberization for precursor
• Stabilization prevents from melting
• Carbonization thermal removes carbon elements Graphitization improves property

Properties of Carbon Fiber

• High tensile
• Low Thermal Expansion
• Good electronic Conductor
• High Resistance

Advanatages of Carbon Fibers

• Long life cycle
• lower density
• insensitive

Disdvanatges of Carbon Fibers

• High electric conductivity/Low strain
• Impact resistence and "shorting"

Organic Fibers

• Synthetic from polymers.
• A chain holds to give properties
• This improves by stretching Align the moluce

Aramid Fibers

• Can also call aromatic polyamide.
• Have 85% amide link attach rings

Kevlar Fibers

• Trade name Dupont's and PPD
• Reacts to mole HCl

General Properties of Fibers

• Hight tensile
• Good modulus

Advantages of Fibers

• Resitance and high thermal shrinkage

Disadvantages of Kevlar

• Difficult
• Used in jackets

Ceramic Fibers

• Made from metal, metallic materials
• Commercial with oxide and non- oxide

Ceramic Fiber properties

• High temp
• Thermal pyrosis

Boron Fibers

• Important for composites
• Depost b w/c.

General

• Fiber selection and costs and direction properties

Fiber Selection

• Fiber interfaces
• Three for composites, matrix, interface
• Needs an surface, energy, area, and bond

Test

• Flex test and test
• flex test.