Print Entire Section
Must have Adobe Acrobat Reader

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.

<