Introduction to Composites 151

additives

A substance added to a composite to modify its properties or improve its performance. Additives are most frequently used with polymer-matrix composite materials.

advanced composites

A high-performance material consisting of long reinforcement fibers and polymer, metal, ceramic, or carbon matrices. Advanced composites are more expensive than engineering composites.

aerospace

The industry that covers machines or vehicles of flight. Aerospace manufacturers generally require materials with very specific properties.

alumina

A ceramic compound of aluminum and oxygen in the form of a white powder or clear crystals. Alumina is sometimes used to create ceramic matrices for composites.

aluminum

A lightweight, non-magnetic, metallic element that is silver-white in color. Aluminum has low hardness levels.

anisotropic

Not having equal measurements in all directions. Anisotropic materials, such as whiskers and fibers, provide greater reinforcement than isotropic materials in composites.

aramid

A synthetic material, made from nylon, that is strong and flexible. Aramid is sometimes used to make fiber reinforcements for composite materials.

bind

To hold two or more materials together. Matrix and reinforcement materials bind together to create a composite part.

body panels

A component of the outer shell of an automobile. Body panels must be made of resilient materials like metal or fiberglass-reinforced plastic.

boron

A semi-metallic chemical element used in advanced composite reinforcements. Boron fibers are much stronger than carbon or glass fibers.

brake systems

A collection of mechanical components that uses friction to slow or stop motion. Brake systems must be able to resist wear, heat, and fracture.

brittle

Resistant to being drawn, stretched, or formed. Brittle materials can fracture when subjected to mechanical forces.

carbon

A common nonmetallic element that is very strong and heat resistant. Carbon can be used to make composite matrices and/or reinforcements.

carbon fiber

A material made from slender, thread-like strands of carbon, a strong nonmetallic element. Carbon fiber is a rigid material with good tensile strength, chemical resistance, and temperature tolerance.

carbon fiber-reinforced plastics

CFRPs. An advanced composite material made with a polymer matrix and a carbon fiber reinforcement. Carbon fiber-reinforced plastics are popular because their properties include high strength, stiffness, and light weight.

carbon-reinforced carbon composites

A material consisting of a matrix material and reinforcement fibers, both of which are made up of the nonmetallic element carbon. Carbon-reinforced carbon composites are both strong and resistant to heat.

cast iron

A metal consisting of iron, more than 2% carbon, 1 to 3% silicon, and trace amounts of other elements. Cast irons are brittle metals that offer heat resistance and compressive strength.

catastrophic failure

The sudden and complete breakdown of a tool or part. Catastrophic failure renders the tool or part unusable.

ceramic-matrix composites

CMCs. A stiff, lightweight composite material that can withstand extremely high temperatures. Ceramic-matrix composites are highly specialized advanced composites and are often used for aerospace applications.

ceramics

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics include traditional materials such as brick and clay, as well as advanced ceramics used as abrasives and cutting tools.

c-glass

A type of glass fiber that provides greater resistance to chemicals. C-glass is used as composite reinforcements less frequently than E-glass or S-glass.

chemical properties

A property that describes a material's ability to withstand deterioration by solvents, chemicals, or water on the chemical level. An example of a chemical property is a material's ability to resist corrosion.

chemicals

Any substance or mixture of substances. Chemicals may be in the form of solids, liquids, or gases, and may consist of one element, such as hydrogen, or a combination of elements, such as water.

chopped fibers

A discontinuous piece of fiber that has been cut to a length of 1 to 3 inches (2.5 to 7.6 cm). Chopped fibers do not provide as much reinforcement as continuous fibers do.

CMC

Ceramic-matrix composite. A stiff, lightweight composite material that can withstand extremely high temperatures. CMCs are highly specialized advanced composites and are often used for aerospace applications.

coefficient of thermal expansion

The change in density that occurs as a material changes in temperature. Metal-matrix composites have better coefficients of thermal expansion than unreinforced metals.

composites

A material composed of two or more unlike materials that are bonded together without losing their individual properties or characteristics. Composites consist of a matrix material and a reinforcement material.

compressive strength

The ability of a material to resist forces that attempt to squeeze or crush it. Compressive strength improves in a metal-matrix composite that uses boron continuous fiber reinforcements.

continuous fibers

A fiber that covers an entire dimension of a part without a break or interruption. Continuous fibers provide greater reinforcement than chopped fibers.

copper

A reddish, nonferrous metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper is often used to make electrical wiring.

corrosion

The deterioration of a material as a result of chemical reactions between it and the environment. Corrosion is irreversible and degenerative.

corrosion resistant

The ability of a material to resist chemical destruction from an environment. Corrosion-resistant materials are needed for high-temperature applications because heat increases corrosion.

creep

The deformation of a material that occurs over time due to the presence of a constant load. Creep can affect composites made from polymers.

cross-linking

The development of primary bonds between polymer molecules. Cross-linking is a chemical reaction that occurs in a thermoset during processing.

cure

To cause a material to bond and solidify by permanently cross-linking its molecules. Thermoset matrices must cure during the production process to form a rigid structure.

density

The amount of mass within a specific volume of a substance. Objects with greater density increase in mass and weight.

ductility

A material's ability to be drawn, stretched, or formed without breaking. Ductility generally increases as hardness decreases.

e-glass

A type of glass fiber with good general properties used as reinforcements in polymer-matrix composites. E-glass is less expensive and, therefore, used more commonly than S-glass and C-glass.

electrical conductivity

A material's ability to act as a medium for conveying electricity. Electrical conductivity depends on the material's structure.

electricity

A form of energy created by the movement of electrons. Electricity can be carried by conductors.

engineering composites

A material generally consisting of particles, whiskers, or chopped fiber reinforcements and a polymer matrix with lower mechanical properties. Engineering composites can provide more strength than some unreinforced materials, but they are not as strong as advanced composites.

exhaust nozzles

The part of a jet or rocket engine that directs air out of the combustion chamber. Exhaust nozzles must be able to retain their shape and structural integrity under high temperature and high pressure.

fabric

A sheet of material created by weaving fibers together. Fabric reinforcement is stronger than mat reinforcement because it is woven together.

fabrication

A general category of processes that produces parts by adding or removing material. Fabrication includes welding and assembly processes.

ferrous

A metal in which iron is the main ingredient. Ferrous metals include steels and cast iron.

fiberglass

A lightweight and strong material composed of fine glass fibers. Fiberglass is used as a reinforcement in many composites.

fiberglass-reinforced plastic

FRP. A composite made from a thermoset resin, typically polyester, combined with long, thin glass reinforcing fibers. Fiberglass-reinforced plastic's strength depends on the reinforcing fibers.

fibers

A thin strand of composite reinforcing material that is longer than 0.005 inches (0.13 mm). Fibers provide greater reinforcement than whiskers or particles.

fillers

An inert substance added to a composite to take up space and reduce material shrinkage. Fillers can also reduce material weight and/or cost.

forces

An influence, like a push or a pull, that produces a change in an object's motion or state of rest. Forces have specific directions and magnitudes.

fracture resistance

An object's ability to withstand breaking into two or more pieces as a result of stress. Fracture resistance is a kind of toughness.

fracture toughness

A material's ability to absorb energy without breaking or chipping. Polymer-matrix composite parts exhibit higher levels of fracture toughness than parts made from unreinforced polymers.

gold

A soft, yellow metal that is highly ductile and electrically conductive. Gold is sometimes used as a conductor in electronic devices.

graphite

A soft, black carbon-based material that can be used as a lubricant. Graphite can be placed on the surface of a workpiece or incorporated into the tool itself.

grinding wheels

A circular-shaped tool that is made by bonding and forming abrasive grit. Grinding wheels must be harder than the materials they are intended to grind.

hardness

A material's ability to resist indentation or scratching. An increase in hardness generally leads to a decrease in toughness, or ability to withstand fracture.

heat resistant

Able to withstand high temperatures. Heat-resistant materials will not deform or lose their shape when exposed to heat.

heat shields

The panel that protects other components from being damaged by thermal energy. Heat shields are often made from ceramic-matrix composites or carbon-reinforced carbon composites.

hexagonal

Having a six-sided structure. Hexagonal molecular structures, like that of carbon fibers, can be very strong.

high-performance automobiles

A vehicle that has been designed for competition or other demanding specifications. High-performance automobiles often require higher acceleration, braking, temperature, and other performance specifications compared to standard automobiles.

hulls

The body or outer shell of a boat. Hulls are often made of lightweight and strong materials, like fiberglass-reinforced plastics.

hybrid

A mixture of two separate materials or components into a single product. Hybrid originally referred to two genetic strains that were cross-bred or grafted together.

inert

Chemically inactive or having a limited ability to form chemical reactions. Inert materials are used in applications where more reactive materials would cause undesirable reactions.

insulators

A material or element that has little electrical conductivity and high resistance to electrical charges. Most insulators are plastics and ceramics.

iron

A naturally abundant and commonly used metal. Iron is the main ingredient in steel.

isotropic

Having equal measurements in all directions. Isotropic materials, such as particles, provide less reinforcement strength than anisotropic materials in composites.

loads

The overall force applied to an object by external objects. Loads applied to composite materials transfer from the matrix to the reinforcement material.

machine

To remove material from a workpiece to form an object. Traditional machining methods, such as milling, turning, and drilling, remove metal using cutting tools.

magnetic fields

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

magnetism

An attraction between materials having opposite electrical charges. Magnetism most often occurs between metals.

manufacturing materials

A naturally occurring or synthetic material that is used in manufacturing applications. Manufacturing materials are selected for their properties that make them suitable for a given application.

mat

A sheet of material covered with fiber reinforcements. Mats can have either chopped or continuous fiber reinforcements glued to their surfaces.

matrix

A material that binds together the reinforcing fibers of a composite and hardens to give the part shape and protect the fibers from damage. Matrices are usually viscous materials that can be a variety of polymers, metals, or ceramics.

mechanical properties

A characteristic that describes how a material reacts when subjected to a force that attempts to stretch, compress, bend, dent, scratch, or break it. Mechanical properties include strength, toughness, ductility, and hardness.

metal-matrix composites

MMCs. A composite made from a metallic matrix and usually metal, ceramic, boron, or carbon reinforcements. Metal-matrix composites are often very strong, stiff, and heat resistant.

metals

A naturally occurring material that is desirable when strength, hardness, ductility, or thermal or electrical conductivity is needed. Metals include iron, steel, aluminum, and copper.

microballoons

A small, hollow sphere of composite reinforcement material. Microballoons, or microspheres, can enhance a composite part's strength and reduce its weight.

microspheres

A small, hollow sphere of composite reinforcement material. Microspheres, or microballoons, can enhance a composite part's strength and reduce its weight.

MMCs

Metal-matrix composites. A composite made from a metallic matrix and usually metal, ceramic, boron, or carbon reinforcements. MMCs are often very strong, stiff, and heat resistant.

mold

A hollow cavity that holds heated liquid material and imparts its shape on the material as it cools. Molds are often used during processing of thermoplastic polymer-matrix composites.

molecules

The smallest unit into which a material can be divided without changing its properties. Molecules consist of groups of atoms held together by strong primary bonds.

mullite

A ceramic compound consisting of alumina and silicon dioxide. Mullite can be used to form ceramic matrices for composites.

nickel

A silvery metal that is both tough and corrosion resistant. Nickel can be used as a coating to make carbon fiber electrically conductive.

nonferrous

A metal that does not contain a significant amount of iron. Nonferrous metals include aluminum and copper.

nose cones

The cap at the front end of an air, space, or other vehicle. Nose cones for air and space vehicles must be very strong and resistant to heat because of the environments in which they operate.

nylon

A type of thermoplastic polymer that is strong and flexible. Nylon can be used to make matrices for traditional composites.

oxidation

A chemical reaction involving the addition of oxygen, the removal of hydrogen, or the removal of electrons from a material. Oxidation weakens and degrades a material.

oxidize

A process in which a substance combines and chemically reacts with oxygen. Carbon-reinforced carbon composites can oxidize when exposed to flame even though they can resist high-heat environments.

particles

A small piece of material with a shape that is isotropic, or equal in all directions. Particles can be used in composites to provide small amounts of reinforcement or as fillers.

pellets

A very small, round ball of material. Pellets of polymer material can be melted down and used as composite matrix material.

physical property

A characteristic that describes a material's volumetric, thermal, electrical, and magnetic characteristics. Physical properties are a collection of characteristics that describe how a material responds to forces other than mechanical forces.

pitch

A dark, resinous substance produced by distilling petroleum or tar. Pitch can be used to create carbon fibers or carbon matrices for composites.

plastics

A lightweight material that generally has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Plastics, or polymers, are some of the most common manufacturing materials.

pliable

To be flexible and easily bent. Pliable materials are easily shaped.

PMC

Polymer-matrix composite. A composite made from a thermoset or thermoplastic matrix and reinforcement materials. PMCs are not as strong or heat resistant as metal-matrix and ceramic-matrix composites.

polyacrylonitrile

PAN. A type of thermoplastic polymer resin. Polyacrylonitrile can undergo a costly and time-consuming process to create a carbon for use as composite matrices or reinforcements.

polymer-matrix composites

PMCs. A composite made from a thermoset or thermoplastic matrix and reinforcement materials. Polymer-matrix composites are not as strong or heat resistant as metal-matrix and ceramic-matrix composites.

polymers

A lightweight material that generally has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Polymers, or plastics, are some of the most common manufacturing materials.

porous

Having many openings or voids. Porous materials are not as strong as non-porous materials.

power plants

A facility that uses combustion or another force to generate electricity. Power plants have demanding requirements because they must operate continually at high temperatures and achieve high efficiency as well.

processing

The steps that manufacturers take to create parts out of raw materials. Processing of composites usually involves wetting the reinforcement with the matrix material.

properties

A defining characteristic of a material. Properties are often divided between mechanical properties, which describe how a material responds to external forces, and physical properties, which describe basic qualities of the material.

puncture resistance

A material's ability to prevent an external object from creating a hole in it. Puncture resistance can be improved by using aramid or another reinforcement with high toughness.

radiation

Energy emitted in the form of particles or waves. Radiation exposure in an application will make it necessary to select a material that is relatively resistant to radiation.

reinforcement

The part of the composite that provides strength, stiffness, and the ability to carry a load. Reinforcement materials can be in the form of whiskers, particles, or fibers.

residual stress

Internal pressure or tension that remains in an object or substance after the original load or force has been removed. Residual stress can cause deformation, warping, or failure.

resins

A raw polymer, usually in the form of liquid, beads, or pellets, that is not yet molded into its final shape. Polymer resins can be used as composite matrices.

rigid

Resistant to bending. Rigid materials are stiff and inflexible and useful in applications where a part must hold its shape.

rust

A reddish-brown substance caused by a metal's reaction with moisture and oxygen. Rust is a type of corrosion that results from exposure to various chemicals in an environment.

self-cleaning

Containing compounds that repel water, dirt, grease, and other contaminants, reducing the amount of cleaning required. Self-cleaning materials can reduce maintenance costs and increase product life.

self-healing

Containing low-melting-point fillers that will automatically patch damaged areas on the surface of the part. Self-healing materials can reduce maintenance costs and increase product life.

self-lubricating

Containing dry lubricants or other additives that reduce friction between surfaces that move against each other. Self-lubricating materials can reduce maintenance costs and increase product life.

s-glass

A type of glass fiber that is strong and able to withstand high temperatures. S-glass can be used as a reinforcement in several polymer-matrix composites.

silicon carbide

A colorless ceramic compound of silicon and carbon. Silicon carbide is sometimes used to form ceramic matrices for composites.

sintering

Pressing and heating powdered materials close to their melting point to create a solid shape. Sintering is used in processing metal- and ceramic-matrix composites.

specifications

A description of the essential physical and technical properties of a finished part. Specifications outline important information including finished part dimensions and how the part must respond to forces acting upon it.

spheres

A perfectly round three-dimensional shape. Spheres are very strong shapes because force directed at a single point on a sphere is easily deflected to other points on the outside of the sphere.

stainless steel

A type of steel that contains large percentages of chromium, as well as nickel, manganese, and/or nitrogen. Stainless steel has very high hardness and corrosion resistance.

steel

A ferrous metal consisting of iron and carbon, usually with small amounts of manganese, phosphorus, sulphur, and silicon. Steels are the most common metals used in manufacturing.

stitching

Running an additional fiber or fibers through the reinforcement material. Stitching can provide extra reinforcement to a composite part.

strength

A material's ability to resist forces that attempt to break or deform it. Strength is an important mechanical property.

stress

The intensity or concentration of a deforming force applied to a material. Stress can cause materials with low levels of toughness to fail or break.

structural applications

A use of a material that pertains to the material supporting itself or another material. Structural applications require some measure of rigidity in a material.

structural strength

The measure of a material's ability to support itself or other materials without breaking or deforming. Structural strength is important to a material's mechanical properties.

tensile

Relating to a material being pulled apart or stretched. Tensile properties determine how much a material will deform, bend, or stretch before breaking.

tensile strength

A material's ability to resist forces that attempt to pull it apart or stretch it. Materials with high tensile strength tend to deform, bend, or stretch before breaking.

thermal conductivity

A physical property that indicates how well heat energy transfers through a material. High thermal conductivity properties are present in steel alloys, copper, and aluminum.

thermal degradation

Deterioration of a material due to overexposure to heat or sun. Thermal degradation can diminish a material's mechanical properties.

thermal energy

A form of power resulting from the motion of particles. Thermal energy is transferred as heat.

thermal expansion

The tendency of a material to increase in size as it increases in temperature.  Every material has its own unique rate at which it expands when subjected to increases in temperature.

thermal shock

A potentially catastrophic stress in a material from sudden extreme changes in temperature. Thermal-shock resistance must be considered when designing engine components and other high-temperature components.

thermoplastic

A type of polymer that can be repeatedly heated, shaped, and cooled. Thermoplastic molecules are not cross-linked.

thermoset

A type of polymer that is permanently hardened by heating. Thermosets have covalent bonds and cross-linked molecule chains.

toughness

A material's ability to absorb energy without breaking or fracturing. Toughness is a key property that determines a material's ability to withstand a sudden stress.

transverse stiffness

The ability to maintain shape without deforming in the direction perpendicular to the primary or long axis of the piece. Transverse stiffness is important when a part will be exposed to force in multiple directions.

transverse strength

A part's resistance to being pushed together or pulled apart along the axis perpendicular to the primary or long axis of a piece. Transverse strength is important when a part will be exposed to force in multiple directions.

tungsten carbide

A ceramic compound consisting of tungsten and carbon that offers excellent hardness and wear resistance. Tungsten carbide can be used as reinforcement material in metal-matrix composites.

turbine blades

A flat component attached to the rotary axis of a turbine to direct air, steam, or gas flow. Turbine blades for aerospace applications can be made using ceramic-matrix composites.

unsaturated polyesters

A lightweight and strong thermoset that is commonly used in composites. Unsaturated polyester, also known as thermoset polyester, is a low-cost material.

vibration

Rapid, repetitive back-and-forth movement in a machine part or other component. Excessive vibration can cause premature component or machine failure.

viscous

Having a high resistance to flow. Viscous fluids tend to be sticky or syrupy.

wet out

The process of saturating the reinforcement material of a composite with the matrix material. Wet out must be done thoroughly to give the composite part its full strength.

whiskers

A thin strand of composite reinforcement that is less than 0.005 in. (0.13 mm) long. Whiskers are shorter than fibers but longer than particles.