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Glossary of Terms
 

Abrasion 
The wearing away of materials by friction. Particles become detached by a combined cutting, shearing and tearing action.

Absorbed Moisture 
Moisture that has entered a solid by absorption and has physical properties not substantially different from ordinary water at the same temperature and pressure.

Accelerated Test 
A test procedure in which conditions are increased in magnitude to reduce the time required to obtain a result. To reproduce in a short time the deteriorating effect obtained under normal service conditions. 

Accelerator 
A material that acts synergistically with the prompter to speed up the chemical reaction between the catalyst and the resin. 

Acoustic Emission 
A measure of integrity of a material, as determined by sound emission when a material is under stress. Ideally, emissions can be correlated with defects and/or incipient failure.

Additive
A constituent component that may be added to the composite matrix to modify its properties and in general, enhance its performance.  Additives include catalysts, colorants, flame retardants and other ingredients that expand and improve the capabilities of the matrix. 

Adhesive
The method of joining two substrates using either paste, liquid or film.

Admixture
The addition and uniform dispersion of components before cure.

AFRP
Aramid fiber reinforced polymer.

Aging
The effect on materials of exposure to an environment for an interval of time.  The process of exposing materials to an environment for an interval of time.

Air Void
Air entrapment within and between the plies of reinforcement or within a bondline or encapsulated area; localized, non-interconnected, spherical in shape.

Alkalinity
The condition of having or containing hydroxyl (OH^-) ions; containing alkaline substances.

Ambient
The surrounding area; encompassing on all sides.  In composites, refers to environmental conditions such as temperature, humidity, pressure, etc.

Anisotropic
Not exhibiting the same physical properties in all directions.

Antioxidant
A substance that when added in small quantities to the resin, prevents its oxidative degradation and contributes to the maintenance of its properties.

Aramid
Used as a high-strength, high-modulus (stiffness) fiber.  It is a type of highly oriented organic material derived from polyamide, but incorporating aromatic ring structure.  

Arc Resistance
The length of time (in seconds) that an arc may cross a surface without rendering it conductive.

Aspect Ratio
Ratio of length to diameter.  For a composite, it refers to the specific ratio of the fiber or filler in the composite matrix.

B

B-Stage 
Intermediate stage in the polymerization reaction of thermosets, following which material will soften with heat and is plastic and fusible. The resin of an uncured prepreg or premix is usually in B-stage.

Barcol Hardness
A hardness value obtained by measuring the resistance to penetration of a sharp steel point under a spring load.  Measured on a scale of 0-100, the hardness value is used to measure the degree of cure of plastic.

Bearing Strength
The maximum bearing stress that can be sustained. Also, the bearing stress at that point on the stress-strain curve where the tangent is equal to the bearing stress divided by n% of the bearing hole diameter

Bearing Stress
The applied load in pounds sustained by a specimen divided by the bearing area.

Bias Fabric
Warp and fill fibers at an angle to the length of the fabric. 

Bidirectional Laminate
A reinforced plastic laminate with the fibers oriented in two directions in its plane. A cross laminate.

Binder
Chemical treatment applied to the random arrangement of glass fibers to give integrity to mats. Specific binders are utilized to promote chemical compatibility with the various laminating resins used.

Bond
The adhesion and grip of a material to other surfaces against which it is placed.

Bond Area
The nominal area of interface between two elements across which adhesion develops or may develop

Bond Strength
The measurement of the stress needed to separate two bonded surfaces calculated using the load/bond area.

Bond Stress
The force per unit area necessary to rupture a bond

Braid-Braiding
The weaving of fibers into a tubular shape to be used as a reinforcement instead of a flat reinforcement.

C

C-Stage
The final stage in the reaction of certain thermosetting resins in which the material is practically insoluble and infusible.

Carbon
An element common to all organic substances.  Graphite is one of the forms under which carbon occurs in nature (as is diamond)

Carbon-Carbon
A composite that consists of a carbon matrix and a carbon reinforcement

Carbon Fiber
Fiber produced by the prolysis of organic precursor fibers such as rayon, polyachrylonitrile (PAN) and pitch in an inert environment

Casting
The process of pouring the resin and fillers (and possibly fibers) into a mold.

Catalyst
A substance that initiates a chemical reaction and enables it to proceed under milder conditions than otherwise required and which does not, itself, alter or enter into the reaction. Also called an initiator.

Catenary
The property of or creating or maintaining equal tension in parallel fibers.

CFRP 
Carbon fiber reinforced plastic (includes graphite fiber reinforced plastic).

Chopped Strand Mat
A fiberglass reinforcement that utilizes continuous rovings that are cut into short strands, arranged in a random pattern and held together with a binder.

Coefficient of Thermal Expansion (CTE)
The change in length (or volume) per unit length (or volume) produced by one degree Celsius rise in temperature.

Cohesion
The propensity of a single substance to adhere to itself.  The internal attraction of molecular particles toward each other.  The force holding a single substance together.

Composite
A combination of one or more materials differing in form or composition on a macroscale. The constituents retain their identities; i.e. they do not dissolve or merge completely into one another, although they act in concert.  Normally, the components can be physically identified and exhibit an interface between one another (see FRP Composite).

Compound
An admixture of a polymer with other ingredients such as reinforcements, fillers, and additives.  A thermoset compound normally consists of the necessary ingredients for the finished product.

Compression Molding 
A composite manufacturing technique whereby thermoset composite materials are compressed between matched die molds using hydraulic pressure and heated until the materials are cured to its final form

Compressive Strength
The ability of a material or structure to resist a crushing or buckling force.  The maximum compressive load sustained by the material or structure divided by the original cross-sectional area of the material or structure.

Continuous Roving
Parallel filaments coated with sizing, drawn together into single or multiple strands and wound into a cylindrical package.

Core
The central member, usually foam or honeycomb, of a sandwich construction to which the faces of the sandwich are attached or bonded.  The central member of a plywood assembly.  A channel in a mold for circulation of heat transfer media.  A device on which prepreg is wound.

Corrosion Resistance 
The ability of a material to withstand contact with ambient natural factors or those of a particular artificially created atmosphere, without degradation or change in properties. 

Coupling Agent
Part of a surface treatment or finish which is designed to provide a stronger bonding link between the fiber surface and the laminating resin.

Crazing
The development of ultrafine cracks; the pattern of cracks that extend on or under the surface of a resin or plastic material.

Creel 
A device for holding the required number of roving balls (spools) or supply packages of reinforcement in desired position for unwinding onto the next processing step, that is, weaving, braiding, or filament winding.

Creep
The change in dimension of a material under sustained load over a period of time, not including the material's initial elastic deformation.  The time-dependent part of strain resulting from an applied load.

Crimp 
Waviness of a fiber, a measure of the difference between the length of the unstraightened and straightened fibers.

Cure
To irreversibly change the properties of a thermosetting resin by chemical reaction, that is, condensation, ring closure, or addition.  Cure may be accomplished by addition of curing (cross-linking) agents, with or without heat and pressure.

Curing Agent 
A catalytic or reactive agent that, when added to a resin, causes polymerization.  Also called hardener.

D
E

Debonding
The separation of bonded surfaces, usually unplanned.

Deformation
A change in dimension or shape due to stress.

Delamination
A separation of the layers of a material in laminate, either local or covering a wide area.  Can occur in the cure or during the life of a product.

Dieletric
The ability of a material of resist the flow of electricity.  Non-conductive.

Dieletric Strength
The property of an insulating material that enables it to withstand electric stress.  The average potential per unit thickness at which failure of the dielectric material occurs.  The higher the dielectric strength, the greater insulating properties of the material.

Dimensional Stability
Ability of a part to retain the precise shape to which it was molded, cast, or otherwise fabricated.

Ductility
The ability of a part to undergo large, permanent deformation without rupture.  The ability of a material to deform plastically before fracturing.

Durability
The ability of a material to resist weathering action, chemical attack, abrasion, and other conditions of service. Also, the capability of a structure or its components to maintain serviceability over a designed period of time in a specified environment.

E-Glass 
A family of glasses with a calcium alumina borosilicate composition and a maximum alkali content of 2.0%  A general-purpose fiber that is most often used in reinforced plastics, and is suitable for electrical laminates because of its high resistivity.

Elasticity
The ability of a material to recover to its original size and shape after the removal of a force causing deformation.

Elongation
The increase in length of a material

Elongation at Break
Elongation recorded at the moment of rupture of the specimen, often expressed as a percentage of the original length.

End
A strand of roving consisting of a given number of filaments gathered together.  The group of filaments is considered and end or strand before twisting, a yarn after twisting.

Epoxy 
A polymerizable thermoset polymer containing one or more epoxide groups and curable by reaction with amines. alcohols, phenols carboxylic acids, acid anhydrides, and mercaptans. 

Exotherm (Exothermic)
A compound in the formation of which heat is liberated, and in the reduction of which to its original components, heat is absorbed.  For composite terminology, it applies to the heat released during the curing of the composite.

Extenders
An inert material added to provide economical extension of resins without lessening of properties.

F

Fabric 
Arrangement of fibers held together in two dimensions.  A fabric may be woven, nonwoven, or stitched.  

Fabric, nonwoven 
Material formed from fibers or yams without interlacing.  This can be stitched. knit or bonded.  

Fabric, woven 
Material constructed of interlaced yams,  fibers, or filaments.  

Fatigue
The lessening or failure of mechanical properties after repeated applications of stress.

Fatigue Life
The number of cycles of deformation required to bring about failure of the test specimen under a given set of oscillating conditions (stresses and strains).

Fatigue Strength
The maximum cyclical stress a material can withstand for a given number of cycles before failure occurs. Also the residual strength after being subjected to fatigue.

Fiber 
General term for a filamentary material.  The single unit of substance that is broken into parts fit to form threads to be woven; a filament. Any material whose length is at least 100 times its diameter, typically 0.10 to 0.13 mm.  

Fiber Architecture
The design of the reinforcement; the arrangement of the fibers to achieve specific results.  Examples include braiding, fabrics (stitched and woven), rovings, mats, etc.

Fiber Content 
The amount of fiber present in a composite.  This is usually expressed as a percentage volume fraction or weight fraction of the composite.

Fiber Direction  
The orientation or alignment of the longitudinal axis of the fiber with respect to a stated reference axis.

Fiberglass Reinforcement
Major material used to reinforce plastic.  Available as a mat, roving, fabric, etc.

Fiber Pattern
Visible fibers on the surface of laminates or molding. The thread size and weave of glass cloth.

Fiber-Reinforced Plastic (FRP) 
A general term for a composite that is reinforced with cloth, mat, strands, or any other fiber form.

Filament 
Smallest unit of a fibrous material.  A fiber made by spinning or drawing into one long continuous entity.  

G
H

Gel Coat 
A quick setting resin applied to the surface of a mold and gelled before lay-up.  The gel coat becomes an integral part of the finished laminate, and is usually used to improve surface appearance and performance.

GFRP 
Glass fiber reinforced plastic.

Glass Fiber 
Fiber drawn from an inorganic product of fusion that has cooled without crystallizing.

Glass Fiber, types
Alkali resistant (AR-glass)
General Purpose (E-glass)
High Strength (S-glass)

Glass-Transition Temperature 
The midpoint of the temperature range over which an amorphous material changes from (or to) a brittle, vitreaous state to (or from) a plastic state.

Graphite Fiber
Fiber containing more than 99 percent elemental carbon made from a precursor by oxidation.

Grid 
Large cross-sectional area construction in two or three axial directions made up using continuous filaments.

Hand Lay-Up 
Fabrication method in which reinforcement layers, pre-impregnated or coated afterwards, are placed in a mold by hand, then cured to the formed shape.

Hardener 
Substance added to thermoset resin to cause curing reaction.

Heat Deflection Temperature
The temperature at which a plastic material has an arbitrary deflection when subjected to an arbitrary load and test condition; an indication of the glass transition temperature.

Honeycomb
Manufactured product of resin-impregnated sheet material formed into hexagonal-shaped cells.  Used as a core material in sandwich construction.

Hoop Stress
The circumferential stress in a material or cylindrical form subjected to internal or external pressure.

Hybrid 
A composite laminate consisting of laminae of two or more composite material systems.  A combination of two or more different fibers, such as carbon and glass or carbon and aramid, into a structure.

I-
L

Impact Strength
The ability of a material to withstand shock loading.

Impregnate 
In reinforced plastics, to saturate the reinforcement with a resin. A process of filling the interstices of a porous body with polymer compound.

Inhibitor 
A substance that retards a chemical reaction.  Also used in certain types of monomers and resins to prolong storage life.

Initiator 
Peroxides used as sources of free radicals.  They are used in free-radical polymerizations, for curing thermosetting resins, as cross-linking agents for elastomers and poly-ethylene, and for polymer modification.

Interface
The common boundary surface between two substances.  In a composite laminate, it is the contact area between the resin and the reinforcement.  On fibers, it is the contact area between the sizing or finish. 

Interlaminar
Term to describe an event that occurs between two or more adjacent laminae.  

Interlaminar Shear
Shearing force that produces a relative displacement between two laminae along their interface.

Isophthalic acid
A raw material that is added to polyester resins to increase their ability to withstand severe environmental/chemical factors and increase its heat deflection temperature.

Isopolyester
Resins that have been re-formulated with isophthalic acid and glycols of various types to enhace water, heat and corrosion resistance of the composite part.

Isotropic
Having uniform properties in like degree in all directions

Kevlar
See Aramid 

Laminate
Two or more layers of fiber bound together in a resin matrix usually through pressure and heat.

Lay-Up
The reinforcing material placed in position in the mold.  The process of placing the reinforcing material in position in the mold.  

M-
O

Mandrel 
The core tool around which resin-impregnated paper, fabric, or fiber is wound to form pipes, tubes, or structural shell shapes.  

Mat 
A fibrous material for reinforced plastic consisting of randomly oriented chopped filaments, short fibers (with or without a carrier fabric), or swirled filaments loosely held together with a binder.

Matrix
The essentially homogeneous resin or polymer material in which the fiber system of a composite is imbedded.  Both thermoplastic and thermoset resins may be used, as well as metals, ceramics, and glasses.

Mean Stress
The average of the maximum and minimum stress in one cycle of fluctuating loading (as in a fatigue test); tensile stress is considered positive and compressive strength, negative.

Mechanical Properties
The properties of a material such as compressive and tensile strengths and modulus that are associated with elastic and inelastic reaction when force is applied.  The relationship between stress and strain.

Microcracking
The cracks formed when exerted stress exceeds the strength of the matrix.

Mil
The unit of measurement for the diameter of glass strands 
(1 mil = 0.001 inch)

Modulus
The ratio of stress to strain. A high modulus indicates a stiff material.

Modulus of Elasticity
The ratio of normal stress to corresponding strain for tensile or compressive stresses below the proportional limit of the material.

Mold
The cavity on which composite materials are placed in order to fabricate the final part.                       

Monomer
A single molecule that can react with like or unlike molecules to form a polymer.  The smallest repeating structure of a polymer.

Nondestructive Evaluation (NDE) 
A process or procedure, such as ultrasonic or radiographic inspection, for determining the quality or characteristics of a material, part, or assembly, without permanently altering the subject or its properties.

Nomex
See Aramid

Nonwoven Roving (Fabric)
A textile structure produced by loosely compressed fibers (rovings) with or without a scrim cloth carrier.

Open Molding
The general term used to describe composites manufacture whereby resin and reinforcement are placed on an open mold.  See also hand lay up and spray-up.

Orthotropic
A material that has six different sets of moduli and Poisson's ratios.

Outgassing
The release of solvents and moisture from composite parts under a vacuum.

Oxidation
Combining or increasing the proportion of oxygen.

P

Pan
A carbon fiber made from polyacrylonitrile (pan) fiber.

Part Consolidation
The process of replacing assemblies of several parts and fasteners by designing and fabricating a single part.

Peel Ply
A layer of open-weave material, usually fiberglass, applied directly to the surface of a prepreg lay-up.

Permeability
The passage or diffusion rate of a gas, vapor, liquid or solid through a barrier without physically or chemically affecting it.

Phenolic
A thermosetting resin produced by the condensation of an aromatic alcohol particularly based on phenol (carbolic acid) and formaldehyde.

Pit
A small crater in the surface of plastic, usually of a width approximately the same as its depth.

Pitch
Carbon fiber made from a residual petroleum product.

Plain Weave 
A weaving pattern in which the warp and fill fibers alternate; that is, the repeat pattern is warp/fill/warp/fill, and so on.

Plastic 
A material that contains as a essential ingredient and organic polymer of large molecular weight, hardeners, fillers, reinforcements, and so forth; is solid in its finished state; and at some stage in its manufacture of its processing into finished articles, can be shaped by flow.

Plastic Deformation
Changes in dimensions of an object under load that is not recovered when the load is removed as opposed to elastic deformation.

Ply 
In general, fabrics or felts consisting of one or more layers (laminates, and so forth).  The layers that make up a stack.

Poisson's Ratio
The ratio of the change in lateral width per unit width to change in axial length per unit length caused by the axial stretching or stressing of a material.  The ratio of transverse strain to the corresponding axial strain below the proportional limit.

Polyester  
Resin produced by the polycondensation of dihydroxy derivatives and dibasic organic acids or anhydrides yielding resins that can be compounded with vinyl.

Polymer 
A high molecular weight organic compound, natural or synthetic, containing repeating units.

Polymerization
A chemical reaction in which the molecules of monomers are linked together to form large molecules whose molecular weight is a multiple of that of the original substances.  When two or more monomers are involves, the process is called copolymerization.

Porosity
The ratio, usually expressed as a percentage of the volume of voids in a material, to the total volume of a material, including the voids.

Post Cure
Additional elevated temperature cure, usually without pressure, to improve final properties and/or complete the cure or to decrease the percentage of volatiles in the molding.

Pot Life
The length of time that a catalized thermosetting resin retains a viscosity low enough to be used in processing.

Precursor 
For carbon or graphite fiber, the rayon, PAN or pitch fibers from which carbon and graphite fibers are derived.

Preform 
A preshaped fibrous reinforcement formed by distribution of chopped fibers or cloth by air, water flotation, or vacuum over the surface of a perforated screen to the approximate contour and thickness desired in the finished part.

Preform Binder
A resin applied to the chopped strands of a preform, usually during its formation, and cured so that the preform will retain its shape and can be handled.

Premix
A molding compound prepared prior to and apart from the molding operations and containing all components required for molding.

Prepreg 
Either ready-to-mold material in sheet form or ready-to-wind material in roving form, which may be cloth, mat, unidirectional fiber, or paper impregnated with resin and stored for use. Also semi-hardened construction made by soaking strands or roving with resin.

Promoter 
A chemical that reduces the activation energy required for a given initiator.

Pultrusion 
A continuous process for manufacturing composites that have a cross-sectional shape.  The process consists of pulling a fiber - reinforcing material through a resin impregnation bath and through a shaping die, where the resin is subsequently cured. 

Pyrolysis
The transformation (or decomposition) of a compound by the action of heat.  In respect to organic precursor fiber materials such as pan and pitch, the action of heat chemically changes them into carbon fiber in an inert atmosphere.

Q
R
S

Quality Assurance 
Actions taken by an owner or his representative to provide assurance that what is being done and what is being provided are in accordance with the applicable standards of good practice for the work.

Reinforcement 
Strong materials bonded to or into a matrix to improve mechanical properties.  Materials, ranging from short fibers through complex textile forms, that is combined with a resin to provide the composite with enhanced mechanical properties.

Release Agent
A substance used to prevent the unwanted bonding of the composite material to the mold/tooling. Assists in the removal of the part from the mold.

Repair Systems
To replace or correct deteriorated, damaged, or faulty materials, components or elements of a structure.  The materials and techniques used for repair.

Resin 
A natural or synthetic viscous liquid, solid or semisolid, organic material of indefinite and often high molecular weight having a tendency to flow under stress, usually has a softening or melting range, and usually fractures conchoidally.  Polymeric material that is rigid or semi-rigid at room temperature, usually with a melting-point or glass transition temperature above room temperature.

Resin Content 
The amount of resin in a laminate expressed as either a percentage of total weight or total volume.

Resin Transfer Molding (RTM) 
A process whereby catalyzed resin is transferred or injected into a closed mold in which the fiberglass reinforcement has been placed.

Rheology
The study of the flow of materials, particularly plastic flow of solids. The science of treating the deformation and flow of matter.

Rockwell Hardness
A value derived from the increase in depth of an impression as the load on an indenter is increased from a fixed minimum value to a higher value and then returned to the minimum value.

Roving 
A number of yarns, strands, tows, or ends collected into a parallel bundle with little or no twist.  

Shear
An action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their plane of contact.

Shear Reinforcement
Reinforcement designed to resist shear or diagonal tension stresses.

Shear Strength
The maximum shearing force a flexural member can support at a specific location as controlled by the combined effects of shear forces and bending moment.

Sheet Molding Compound (SMC)
A composite of fibers, a liquid thermosetting resin and other filler/additives that have been compounded together and processed into sheet form to facilitate handling in the molding operation.

Shrinkage
Decrease in either length or volume; a volume decrease caused by curing, drying and/or chemical changes.

Sizing 
Surface treatment or coating applied to filaments to improve the filament-to-resin bond and to impart processing and durability attributes.

Solvent 
A liquid in which another substance may be dissolved.

Spray-up 
Technique in which a spray gun is used as an applicator tool.  In reinforced plastics, for example, fibrous glass and resin can be simultaneously deposited in a mold.  

T-
V

Tensile Reinforcement
Reinforcement designed to carry tensile stresses.  Can be internal reinforcement of the product or external reinforcement such as a composite repair material placed on an existing structure.

Tensile Strength
Maximum unit stress that a material is capable of resisting under axial tensile loading; based on the cross-sectional area of the specimen before loading.

Textile
Fabric, usually woven.

Thermal Conductivity
The property of a particular body or assembly to transfer heat.

Thermal Contraction
Contraction caused by the decrease in temperature.

Thermal Expansion
Expansion caused by by an increase in temperature.

Thermoplastic 
Resin that is not cross linked.  Thermoplastic resin generally can be remelted and recycled.

Thermoset 
Resin that is formed by cross linking polymer chains.  A thermoset cannot be melted and recycled because the polymer chains form a three dimensional network.

Thixotropic (thixotropy)
Concerning materials that are gel-lie at rest but fluid when agitated.  

Tool (Tooling)
The mold onto which the composite material is placed to in order to fabricate the composite part.  The mold itself may or may not be made of composite materials, it may be one or two sided and may be open or closed.

Tow 
An untwisted bundle of continuous filaments.  Commonly used in referring to man-made fibers, particularly carbon and graphite, but also glass and aramid.  A tow designated as 140K has 140,000 filaments.

Tracer
A fiber, tow or yarn added to a prepreg for verifying fiber alignment and, in the case of woven materials, for distinguishing warp fibers. It is often time a particular color in order to distinguish it from the other reinforcement.

Twist
The spiral turns about its axis per unit of length in a yarn or other textile strand.

Unidirectional Laminate 
A reinforced plastic laminate in which substantially all of the fibers are oriented in the same direction.

V-RTM (VARTM) 
Acronym for vacuum resin transfer molding; a vacuum process to combine resin and reinforcement in an open mold.

Vacuum Bag Molding 
A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed over the lay-up on the mold and sealed at the edges.  A vacuum is applied between the sheet and the lay-up.

Veil  
An ultrathin mat similar to a surface mat, often composed of organic fibers as well as glass fibers.

Vent
A small hole or shallow channel in a mold that allows air or gas to exit as the molding material enters.

Vinyl Esters 
A class of thermosetting resins containing ester of acrylic and/or methacrylic acids, many of which have been made from epoxy resin.

Viscosity
The property of a body of material to resist a change to its shape: internal friction.

Voids
Pockets of entrapped gas that were cured into a laminate.  Void content should be less than 1% in a properly cured composite.

W-
Z

Warp
The yarn running lengthwise in a woven fabric.  A group of yarns in long lengths and approximately parallel.

Weave
The specific pattern which a fabric is formed from interlacing yarns.

Wet Lay-Up 
A method of making a reinforced product by applying the resin system as a liquid when the reinforcement is put in place.

Wet-Out
The condition of an impregnated roving or yarn in which substantially all voids between the sized strands and filaments are filled with resin.

Wetting Agent
A substance capable of lowering the surface tension of liquids facilitating the wetting of solids surfaces and permitting the penetration of liquids into the capillaries.

Woven Fabric
A material constructed by interlacing yarns, fibers or filaments to form specific fabric patterns.

Woven Roving
A heavy glass fiber fabric made by weaving roving.

Yarn
An assemblage of twisted filaments, fibers, or strands, either natural or manufactured, to form a continuous length that is suitable for use in weaving or interweaving into textile materials. 

Yield Point
The point at which permanent deformation of a stressed specimen begins to take place.

Yield Strength
The stress at the yield point.  The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain.

Young's Modulus
The ratio of normal stress to corresponding strain for tensile or compressive stresses less than the proportional limit of the material.

Zero Bleed
A procedure that prohibits the loss of resin during the cure of a laminate.

Glossary References

The Market Development Alliance would like to gratefully acknowledge the following publications that were used in the compilation of the Glossary of Terms.

	Advanced Composites World Reference Dictionary, J. Morena, Krieger Publishing Company, Malabar, FL, 1997
	First Source – A Comprehensive Buyer’s Guide to the World of Composites, Composites Institute of the Society of the Plastics Industry, Washington, D.C., 1998.
	Fundamentals of Composites Manufacturing: Materials, Methods, and Applications, B. Strong, Society of manufacturing Engineers, Dearborn, MI, 1989.
	Handbook of Composites, Edited by George Lubin, Van Nostrand Reinhold Co., New York, 1982.
	Introduction to Composites, 4th Edition, Composites Institute of the Society of the Plastics Industry, Washington, D.C., 1998.
	Source Book 2000, High Performance Composites, Ray Publishing, Wheat Ridge, CO, 2000.
	Yellow Pages 1999, Composites Technology, Ray Publishing, Wheat Ridge, CO, 1999.