COMPOSITES GLOSSARY
    A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z


[ A ]

Ablative Material

A material which absorbs heat (while part of it is being consumed by heat) through a decomposition process (pyrolysis) taking place near the surface exposed to the heat.



A material mixed with a catalyed resin to speed up the chemical reaction between the catalyst and resin; used in polymerising resins.



A ketone group solvent that is used to dissolve polyester resins. Used to a large extent for clean up of tools in fiberglass operations.


Addition Reaction

A polymerisation reaction in which no by-products are formed.



Any substance added to another, usually to improve properties.



A body held to another body by an adhesive.


Adhesion, mechanical

Adhesion between surfaces in which the adhesive holds the parts together by interlocking action.


Adhesive Failure

A rupture of adhesive bond that appears to be a separation at the adhesive/adherend interface.


Adhesive Film

A polymer resin adhesive, usually thermosetting, in the form of a thin dry film of resin, used under heat and pressure as an interleaf in the production of laminated material or for bonding to core materials.



The process or the effect on materials of exposure to an environment for an interval of time.


Air-bubble void

Non-interconnected air entrapment within and between the plies of reinforcement.


Air Locks

Surface depressions on a moulded part, caused by trapped air between the mould surface and the plastic.



A visible cosmetic defect in the exposed gel coat which looks like wrinkled or alligator skin.



The surrounding environmental conditions, e.g., pressure or temperature.



Describes polymers that have no order to their molecules, thus no crystalline component.



Exhibiting different properties in response to stresses applied along axis in different directions.


Anistropic Laminate

One in which the strength properties are different in different directions.


Antimony Trioxide

Fire retardant additive for use with resins.



Aromatic polyamide fibers characterized by excellent high temperature, flame-resistance, and electrical properties. Aramid fibers are used to achieve high strength, high modulus reinforcement in plastic composites. More usually found as polyaramid - a synthetic fiber (trade name Kevlar or Twaron).


Area Weight

The weight of fibre per unit area (width times length) of tape or fabric.


Ash Content

The solid residue remaining after a reinforcing substance has been incinerated or strongly heated.


Aspect Ratio

The ratio of length to diameter of a fibre.


A Stage

An early stage in the polymerisation reaction of certain thermosetting resins (especially phenolic) in which the material, after application to the reinforcement, is still soluble in certain liquids and is fusible; sometimes referred to as resole. (See also B stage, C stage.)



A closed pressure vessel used for curing laminates under pressure and heat.


Autoclave Moulding

After lay-up, the entire assembly is placed in an autoclave. The additional pressure achieves higher fibre to resin ratios and improved removal of air.


Axial Winding

In filament-wound reinforced plastics, a winding with the filaments parallel to the axis.

                                                                                                                      [Back to Top]


[ B ]                                                                                                          



Back Pressure

Resistance of a material, because of its viscosity, to continued flow when a mould is closing.


Bag Molding

A technique in which the consolidation of the material in the mould is affected by the application of fluid pressure through a flexible membrane.


Balanced Design

In filament-wound reinforced plastics, a winding pattern so designed that the stresses in all filaments are equal.


Balanced Laminate

All laminate plies, except those at 0░/90░, are placed in plus/minus pairs (not necessarily adjacent) symmetrically about the lay-up centreline. This minimises distortion on demoulding.


Balanced Twist

An arrangement of twist in a plied yarn or cord which will not cause twisting on itself when the yarn of cord is held in the form of an open loop.


Barcol Hardness

A hardness value obtained by measuring the resistance to penetration of a sharp steel point under a spring load. The instrument, the Barcol Impressor, gives a direct reading on a scale of 0 to 100. The hardness value is often used as a measure of the degree of cure of a plastic.


Bare Glass

Glass (yarns, roving or fabrics) from which the sizing or finish has been removed or before it has been applied.


Barrier Cream

A cream used to protect the skin from contact with resins.



The reinforcing material (glass fibre, paper, cotton, asbestos, etc.) which is impregnated with resin in the forming of laminates.


Bearing Stress

The applied load divided by the bearing area. (Maximum bearing stress is the maximum load sustained by the specimen during the test divided by the original bearing area.)


Benzoyl Peroxide (BPO)

An initiator for curing polyester resin. BPO is used with aniline accelerators or where heat is used to cure the resin.


Bias Fabric

A fabric in which warp and weft fibre are at an angle (usually ▒45░) to the length.


Biaxial Load

A loading condition in which a laminate is stressed in at least two different directions in the plan of the laminate.


Biaxial Winding

In filament winding, a type of winding in which the helical band is laid in sequence, side by side, with no crossover of fibres.


Bidirectional Laminate

A reinforced plastic laminate with the fibres oriented in two directions (usually, but not necessarily, 0/90░) in the plane of the laminate. (See also Unidirectional Laminate.)



The agent applied to glass mat or preforms to bond the fibres before laminating or moulding.



A type of polyimide resin that cures by an addition reaction, avoiding formation of volatiles, and has temperature capabilities between those of epoxy and polyimide.


Bleeder Cloth

A layer of woven or non-woven material, not a part of the composite, that allows excess gas and resin to escape during cure.



The excess liquid resin that migrates to the surface of a laminate in any pressure moulding process.



Undesirable rounded elevation of the surface of a plastic with boundaries that are more or less sharply defined, resembling in shape a blister on the human skin.


Block Copolymer

An essentially linear copolymer in which there are repeated sequences of polymer segments of different chemical structure some of which may be crystalline in nature, others of which may be amorphous.


Bond Strength

The amount of adhesion between bonded surfaces; a measure of the stress required to separate a layer of material from the base to which it is bonded. (See also Peel Strength.)


Boron Fibre

A fibre usually of a tungsten-filament core with elemental boron vapor deposited on it to impart strength and stiffness.



A process for assembling fibres into a tubular shape.



A usually non-woven material that does not come in contact with the resin but serves as a continuous vacuum path over a part in production.



A region of a contoured part which has cured without being properly compacted against the mould.


B Stage

An intermediate stage in the reaction of certain thermosetting resins. The resin in an uncured prepreg or premix is usually in this stage. (See also A Stage, C Stage.)



A spherical internal void; globule of air or other gas trapped in a plastic.



Crimping of fibres in a composite material, often occurring in glass-reinforced thermoset due to resin shrinkage during cure.


Bulk Density

The density of a moulding material in loose form (granular, nodular. etc.), expressed as a ratio of weight to volume.


Burst Strength

Hydraulic pressure required to burst a vessel of given thickness; commonly used in testing filament-wound composite structures.

                                                                                                                     [Back to Top]

[ C ]



Computer-aided design.



Computer-aided manufacturing.



A composite of carbon fibre in a carbon matrix.


Carbon Fibre

An important reinforcing fibre known for its light weight, high strength, and high stiffness that is produced by pyrolysis of an organic precursor fibre in an inert atmosphere at temperatures above 1800░F (982░C). The material may also be graphitised by heat treating above 3000░F (1649░C).



The process of pouring a mixture of resin, fillers and/or fibers into a mold as opposed to building up layers through lamination. This technique produces different physical properties from laminating.



A substance which changes the rate of a chemical reaction without itself undergoing permanent change in its composition; a substance which markedly speeds up the cure of a compound when added in small quantity compared with the amounts of primary reactants.



A measure of the difference in length of the strands in a specified length of roving as a result of unequal tension; the tendency of some strands in a taut horizontal roving to sag lower than the others.



An elastic material used to protect joints or connections from external elements, particularly moisture.


Caul Plate

A sheet the size of the platens used in hot pressing, or other pressure moulding processes.



The space between a male and female mold set in which the part is formed. Sometimes used to refer to a female mold.



A unit of measure used to describe the viscosity of a liquid. Viscosity is measured with a Brookfield Viscometer for most polyester resin applications.


Centrifugal Casting

A high production technique for cylindrical composites, such as pipe, in which chopped fibre and resin is positioned inside a hollow mandrel designed to be heated and rotated as resin is added and cured.


Ceramic Matrix Composites

Materials consisting of a ceramic or carbon fibre surrounded by a ceramic matrix, usually silicon carbide.



A surface phenomenon indicating degradation of a cosmetic surface. Chalking is a powdery film which appears lighter than the original color.



The measurement or weight of material (liquid, preformed, or powder) used to load a mould at one time or during one cycle.


Chemical Vapor Deposition (CVD)

A process in which desired reinforcement material is deposited from vapor phase onto a continuous core; boron on tungsten, for example.



(1) To cool a mould by circulating water through it. (2) To cool a moulding with an air blast or by immersing it in water.


Chopped Strand Mat

A fiberglass reinforcement consisting of short strands of fiber arranged in a random pattern and held together with a binder. Mat is generally used in rolls consisting of 3/4 oz/ft2 material to 2 oz/ft2 material.



In filament winding (1) one complete traverse of the fibre-feed mechanism of a winding machine; (2) one complete traverse of a winding band from one arbitrary point along the winding path to another point on a plane through the starting point and perpendicular to the axis.


Circumferential (“circ”) Winding

In filament-wound reinforced plastics a winding with the filaments essentially perpendicular to the axis.


Clamping Pressure

In injection moulding and transfer moulding the pressure applied to the mould to keep it closed, in opposition to the fluid pressure of the compressed moulding material.



A fiberglass reinforcement made by weaving strands of glass fiber yarns. Cloth is available in various weights measured in ounces per square yard or Kg/m2.



Simultaneous bonding and curing of components, or dissimilar materials.


Coefficient of Elasticity

The reciprocal of Young’s modulus in a tension test.


Coefficient of Expansion

The fractional change in dimension of a material for a unit change in temperature. Also called coefficient of thermal expansion.


Coefficient of Friction

A measure of the resistance to sliding of one surface in contact with another surface.


Coefficient of Thermal Expansion

The change in length per unit length produced by a unit rise in temperature.



(1) The propensity of a single substance to adhere to itself. (2) The internal attraction of molecular particles toward each other. (3) The force holding a single substance together.


Cohesive Failure

Failure of a bonded joint within the adhesive itself.


Cold-setting Adhesive

A synthetic resin adhesive capable of hardening at normal room temperature in the presence of a hardener.


Color Stability

The ability of a surface coating or pigment to resist degradation due to environmental exposure.


Co-mingled Yarn

A hybrid yarn made with two types of materials intermingled in a single yarn, for example, thermoplastic filaments intermingled with carbon filaments to form a single yarn.



A homogeneous material created by synthetic assembly of two or more materials (selected filler or reinforcing elements and compatible matrix binder) to obtain specific characteristics and properties. Composites are subdivided into the following classes on the basis of the form of the structural constituents; fibrous: the dispersed phase consists of fibers; flake: the dispersed phase consists of flat flakes; laminar: composed of layers of laminate constituents; particulate: dispersed phase consists of small particles; skeletal: composed of a continuous skeletal matrix filled by a second material.


Compression Molding

A technique for molding thermoset plastics in which a part is shaped by placing the fibre and resin into an open mould cavity, closing the mould, and applying heat and pressure until the material has cured or achieved its final form.


Compression Molding Pressure

The pressure applied to the moulding material in the mould.


Compressive Modulus Ec

Ratio of compressive stress to compressive strain below the proportional limit. Theoretically equal to Young’s modulus determined from tensile experiments.


Compressive Strength

(1) The ability of a material to resist a force that tends to crush. (2) The crushing load at the failure of a specimen divided by the original sectional area of the specimen.


Compressive Stress

The compressive load per unit area of original cross section carried by the specimen during the compression test.


Condensation Reaction

A polymerisation reaction in which simple by-products (for example, water) are formed.



Where two panels are attached to each other or a panel is attached to the building.



A processing step that compresses fibre and matrix to reduce voids and achieve a desired density.


Contact Molding

A process for molding reinforced plastics in which reinforcement and resin are placed on an open mould, cure is at room temperature using a catalyst-promoter system or by heat in an oven, and no additional pressure is used.


Continuous Filament

An individual flexible fibre of glass of small diameter and great or indefinite length.


Continuous-filament Yarn

Yarn formed by twisting two or more continuous filaments into a single continuous strand.


Continuous Laminating

An automated process for forming panels and sheeting in which fabric or mat is passed through a resin bath, brought together between covering sheets, and passed through a heating zone for cure. Squeeze rolls control thickness and resin content as the various plies are brought together.


Continuous Roving

Parallel filaments coated with sizing, gathered together into single or multiple strands, and wound into a cylindrical package. It may be used to provide continuous reinforcement in woven roving, filament winding, pultrusion, prepregs, or high strength moulding compounds, or it may be used chopped.


Cooling Fixture

A fixture used to maintain the shape or dimensional accuracy of a moulding after it is removed from the mould and until the material is cool enough to hold its shape.



(1) The central member of a sandwich construction to which the faces of the sandwich are attached. (2) A channel in a mould for circulation of heat-transfer media.



(1) For fabric the number of warp and weft yarns per cm in woven cloth. (2) For yarn the size based on relation of length and weight. Basic unit is a tex which is the weight in grammes of 1000 linear metres of the fibre.


Coupling Agent

Any chemical substance designed to react with both the reinforcement and matrix phases of a composite material to form or promote a stronger bond at the interface; a bonding link.


Cowoven Fabric

A reinforcement fabric woven with two different types of fibres in individual yarns, for example, thermoplastic fibres woven side by side with carbon fibres.



Fine cracks which may extend in a network on or under the surface of a plastic material.



A device for holding the required number of fibre bobbins in the desired position for unwinding.



The change in dimension of a plastic under load over a period of time not including the initial instantaneous elastic deformation; at room temperature it is called cold flow.



The waviness of a fibre, particularly in a woven fabric.


Critical Length

The minimum length of a fibre necessary for matrix shear loading to develop fibre ultimate strength by a matrix.


Critical Strain

The strain at the yield point.


Crosswise Direction

Refers to cutting specimens and to application of load. For rods and tubes, crosswise is the direction perpendicular to the long axis. For other shapes or materials that are stronger in one direction than in another, crosswise is the direction that is weaker. For materials that are equally strong in both direction, crosswise is an arbitrarily designed direction at right angles to the length.



The quality of having a molecular structure with atoms arranged in an orderly, three-dimensional pattern.


C Stage

The final stage in the reaction of certain thermosetting resins in which the material is relatively insoluble and infusible. The resin in a fully cured thermoset moulding is in this stage. (See also A Stage, B Stage.)



To change the properties of a resin by chemical reaction, which may be condensation or addition; usually accomplished by the action of heat or catalyst, or both, and with or without pressure.


Curing Agent

Hardener, a catalytic or reactive agent added to a resin to cause polymerisation. Curing agents participate in the polymerisation process. They may be latent - curable only at elevated temperatures - or they may be activated at room temperature (25░C).


Curing Temperature

Temperature at which a cast, moulded, or extruded product, a resin impregnated reinforcement, an adhesive, etc., is subjected to curing.


Curing Time

The length of time a part is subjected to heat or pressure, or both, to cure the resin. (Further cure may take place after removal of the assembly from the conditions of heat or pressure.)



The complete, repeating sequence of operations in a process or part of a process. In moulding, the cycle time is the elapsed time between a certain point in one cycle and the same point in the next.

                                                                                                                     [Back to Top]

[ D ]


D Glass

A high-boron-content glass made especially for laminates requiring precisely controlled dielectric constant.


Damage Tolerance

A measure of the ability of structures to retain load carrying capability after exposure to sudden loads (for example, ballistic impact).


Damping (Mechanical)

Mechanical damping gives the amount of energy dissipated as heat during the deformation of a material. Perfectly elastic materials have no mechanical damping. Damping also diminishes the intensity of vibrations.



The distance in the open position between the moving and fixed tables (platens) of a hydraulic press. For a multidaylight press, daylight is the distance between adjacent platens.



An unplanned nonadhered or unbonded region in an assembly.


Deflection Temperature Under Load

The temperature at which a simple beam has deflected a given amount under load (formerly called heat-distortion temperature).


Deformation Under Load

The dimensional change of a material under load for a specific time following the instantaneous elastic deformation caused by the initial application of the load; also called cold flow or creep.



To split a laminated plastic material along the plane of its layers. (See also Laminate.)



Physical separation or loss of bond between laminate plies.



A yarn and filament numbering system in which the yarn number is equal numerically to the weight in grams of 30,000 ft (9144 m) (used for continuous filaments). The lower the denier the finer the yarn.



A comparison of weight per volume, measured in pounds per cubic foot.


Design Allowable

A limiting value for a material property that can be used to design a structural or mechanical system to a specified level of success with 95% statistical confidence. B-basis allowable: material property exceeds the design allowable 90 times out of 100. A-basis allowable: material property exceeds the design allowable 99 times out of 100.



A nonconductor of electricity.


Dielectric Constant

(1) The ratio of the capacity of a capacitor having a dielectric material between the plates to that of the same capacitor when the dielectric is replaced by a vacuum. (2) A measure of the electrical charge stored per unit volume at unit potential.


Dielectric Strength

The value of a material as an electrical insulator or the resistance to the flow of electric current.


Dimensional Stability

Ability of a plastic part to retain the precise shape to which it was moulded, cast, or otherwise fabricated.


Displacement Angle

In filament winding the distance of advance of the winding ribbon on the equator after one complete circuit.



A change in shape form that which is intended.


Doctor Roll

A device for regulating the amount of liquid material on the rollers of a spreader; also called doctor bar or doctor blade.



In filament winding the planar reinforcement applied to a local area between windings to provide extra strength in an area where a cutout is to be made, e.g. port openings.



In filament winding the portion of a cylindrical container that forms the integral ends of the container.



Localised area of extra layers of reinforcement, usually to provide stiffness or strength for fastening or other abrupt load transfers.



The taper or slope of the vertical surfaces of a mould designed to facilitate removal of moulded parts.


Draft Angle

The angle between the tangent to the surface at that point and the direction of ejection.



The ability of preimpregnated broad goods or dry fabrics to conform to an irregular 3-D shape; textile conformity.


Dry Winding

Filament winding using preimpregnated roving, as differentiated from wet winding. (See also Wet Winding.)


Dry Lay-up

Construction of a laminate by layering preimpregnated reinforcement in a female or male mould, usually followed by bag moulding or autoclave moulding.



Differential scanning calorimeter. Instrumentation for measuring chemical reactions by observing exothermic or endothermic (heat output or heat input) reactions of materials - usually over a programmed temperature cycle.



(1) A pause in the application of pressure to a mould, made just before the mould is completely closed, to allow gas to escape from the moulding material. (2) In filament winding the time the traverse mechanism is stationary while the mandrel continues to rotate to the appropriate point for the traverse to begin a new pass. (3) A pause in the temperature rise of a cure cycle, where the part being cured is held at a constant temperature for a period.

                                                                                                                     [Back to Top]

[ E ]



Refers to the application of load. The load is applied edgewise when it is applied to the edge of the original sheet or specimen.


E Glass

A borosilicate glass; the type most used for glass fibres for reinforced plastics; suitable for electrical laminates because of its high resistivity. (Also called electric glass.)



Removal of a moulding from the mould impression by mechanical means, by hand, or by using compressed air.


Elastic Deformation

The part of the total strain in a stressed body which disappears upon removal of the stress.



The property of plastics materials by virtue of which they tend to recover their original size and shape after deformation.


Elastic Limit

The greatest stress which a material is capable of sustaining without permanent strain remaining upon the complete release of the stress. A material is said to have passed its elastic limit when the load is sufficient to initiate plastic (nonrecoverable) deformation.


Elastic Recovery

The fraction of a given deformation that behaves elastically.


Elastic recovery = elastic extension

total extension


Electroformed Moulds

A mould made by electroplating metal on the face of a mould.



Deformation caused by stretching; the fractional increase in length of a material stressed in tension. (When expressed as percentage of the original gauge length, it is called percentage elongation.)



A strand of roving consisting of a given number of filaments gathered together (the group of filaments is considered an end or strand before twisting and a yarn after twist has been applied): an individual warp yarn, thread, fibre, or roving.



Completely surrounding an object with resin or a fiber resin composite.



A polymer resin characterized by epoxide molecule groups.


Even Tension

The process whereby each end of roving is kept in the same degree of tension as the other ends.



The liberation or evolution of heat during curing of a plastic product.

                                                                                                                    [Back to Top]

[ F ]



A material constructed of interlaced yarns, fibres, or filaments, usually planar.


Fabric, nonwoven

A material formed from fibres or yarns without interlacing.


Fabric, woven

A material constructed of interlaced yarns, fibres, or filaments.


Fabricating, fabrication

The manufacture of plastic products from moulded parts, rods, tubes, sheeting, extrusions, or other form by appropriate operations such as punching, cutting, drilling, and tapping. Fabrication includes fastening plastic parts together or to other parts by mechanical devices, adhesives, heat sealing, or other means.



The failure or decay of mechanical properties after repeated applications of stress. (Fatigue tests give information on the ability of a material to resist the development of cracks, which eventually bring about failure as a result of a large number of cycles.)


Fatigue Life

The number of cycles of deformation required to bring about failure of the test specimen under a given set of oscillating conditions (pressure/load).


Fatigue Limit

The stress below which a material can be stressed cyclically for an infinite number of times without failure.


Fatigue Strength

(1) The maximum cyclic stress a material can withstand for a given number of cycles before failure occurs. (2) The residual strength after being subjected to fatigue.



A fibrous material made from interlocked fibres by mechanical or chemical action, moisture, or heat; made from asbestos, cotton, glass, etc.


Female Mold

A concave mold used to precisely define the convex surface of a molded part.


Fibre-composite Material

A material consisting of two or more discrete physical phases, in which a fibrous phase is dispersed in a continuous matrix phase. The fibrous phase may be macro-, micro-, or submicroscopic, but must retain its physical identity so that it can be removed from the matrix intact.


Fibre Glass

An individual filament made by extruding fibres from molten glass.


Fibre Diameter

The measurement of the diameter of individual filaments.


Fibre-matrix Interface

The region separating the fibre and matrix phases, which differs from them chemically, physically, and mechanically. In most composite materials, the interface has a finite thickness (nanometers to thousands of nanometers) because of diffusion or chemical reactions between the fibre and matrix. Thus, the interface can be more properly described by the terms interphase or interfacial zone.


Fibre Pattern

(1) Visible fibres on the surface of laminates or mouldings. (2) The thread size and weave of fabrics.


Fibre Placement

A continuous process for fabricating composite shapes with complex contours and/or cutouts by means of a device that lays preimpregnated fibres (in tow form) onto a non-uniform mandrel or tool. It differs from filament winding (below) in several ways: there is no limit on fibre angles; compaction takes place online via heat, pressure, or both; and fibres can be added and dropped as necessary. The process produces more complex shapes and permits a faster putdown rate than filament winding.



Any fibre whose aspect ratio (length to effective diameter) is for all practical purposes infinity, i.e. a continuous fibre.


Filament Winding

A process for fabricating a composite structure in which continuous reinforcements (filament, wire, yarn, tape, or other) impregnated with a matrix material either previously or during the winding are placed over a rotating removable form or mandrel in a prescribed way to meet certain stress conditions. When the right number of layers has been applied, the wound form is cured and the mandrel removed.



(Also known as weft). Yarn oriented at right angles to the warp in a woven fabric.



A relatively inert material added to a plastic mixture to reduce cost, modify mechanical properties, serve as a base for colour effects, or improve the surface texture.



A radiused joint of adhesive between two surfaces being bonded.


Filling Yarn

The transverse threads or fibres in a woven fabric, i.e. fibres running perpendicular to the warp; also called weft.


Film Adhesive

A synthetic resin adhesive in the form of a thin dry film of resin with or without a carrier.



A material applied to the surface of fibres in a fabric used to reinforce plastics, and intended to improve the physical properties of the reinforced plastics over those obtained using reinforcement without finish. Not to be confused with "size" (q.v.).


Fish Eye

The effect of surface contamination which causes a circular separation of a paint or gel coat.


Flame Resistance

Ability of a material to not support flame once source of heat is removed.


Flame Retardants

Chemicals used to reduce or eliminate the tendency of a resin to burn.


Flame-retarded Resin

A resin compounded with certain chemicals to reduce or eliminate its tendency to burn.



A measure of the extent to which a material will support combustion.



An extension around the perimeter of a mold or part for the purpose of demolding, stiffening or connecting two components.


Flash Point

The lowest temperature at which a substance gives off enough vapors to form a flammable mixture.



Refers to cutting specimens and the application of load. The load is applied flatwise when it is applied perpendicular to the flat face of the original sheet or specimen.


Flexural Modulus

The ratio, within the elastic limit, of the applied stress on a test specimen in flexure to the corresponding strain in the outermost fibres of the specimen.


Flexural Rigidity

(1) For fibres this is a measure of the rigidity of individual strands or fibres; the force couple required to bend a specimen to unit radius of curvature. (2) For plates the measure of rigidity is D = El. where E is the modulus of elasticity and I is the moment of inertia.


Flexural Strength

(1) The resistance of a material to breakage by bending stresses. (2) The strength of a material in bending expressed as the tensile stress of the outermost fibres of a bent test sample at the instant of failure. For plastics this value is usually higher than the straight tensile strength. (3) The unit resistance to the maximum load before failure by bending.



The movement of resin under pressure, allowing it to fill all parts of a mould.



A lightweight, cellular plastic material containing gas-filled voids. Typical foams include urethane, PVC and polyester.


Foamed Plastics

Resins in sponge form; may be flexible or rigid; cells may be closed or interconnected.



The process of creating a foam by the combination of two liquid polymers. See In-Situ.


Fracture Toughness

A measure of the damage tolerance of a material containing initial flaws or cracks.



Fibrous reinforced plastic, any type of plastic-reinforced cloth, mat, strands, or any other form of fibrous material.



Fibre Volume Fraction. The ratio of the volume of fibre in a laminate to the total volume of fibre and resin.



Fibre Weight Fraction. The ratio of the weight of fibre in a laminate to the total weight of fibre and resin.

                                                                                                                     [Back to Top]

[ G ]


Gauge Length

Length over which deformation is measured.



In filament winding the space between successive windings, which are usually intended to lie next to each other.



The initial jellylike solid phase that develops during the formation of a cured resin from a liquid.



The formation of a gel.


Gel Time

For thermosetting resins the time between introduction of a catalyst or hardener into a resin and gel formation.



A filled resin applied to the surface of a mould before Iay-up. (The gelcoat becomes an integral part of the finished laminate and is usually used to improve surface appearance, etc.)


Glass Filament

A form of glass that has been drawn to a small diameter and extreme length. Most filaments are less than 0.005 (130 microns) in diameter.


Glass Finish

A material applied to the surface of a glass reinforcement to improve its effect upon the physical properties of the reinforced plastic.


Glass Flake

Thin, irregularly shaped flakes of glass typically made by shattering a continuous thin-walled tube of glass.


Glass Transition

The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle state. The glass transition generally occurs over a relatively narrow temperature region and is similar to the solidification of a liquid to a glassy state; it is not a phase transition. The glass transition temperature is the approximate midpoint of the temperature range over which glass transition takes place. See extra notes in Formulated Products Article.


Glass-transition Temperature Tg

The approximate temperature at which increased molecular mobility results in significant changes in properties of a cured resin. The measured value of Tg can vary, depending on the test method.


Good Side

The side of a molding in contact with a mold surface.



Resin which has not completely cured and is still rather soft and rubbery.



Fabric before finishing; yarn or fibre before bleaching or dyeing. Also called grey goods, greige goods, greige grey.



Glass reinforced plastics. Generally based on polyester resin. See FIBERGLASS, FRP

                                                                                                                    [Back to Top]

[ H ]



The softness of a piece of fabric, as determined by the touch (individual judgement).


Hand Lay-up

The process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mould by hand, then cured to the formed shape.



A substance or mixture added to a plastic composition to promote or control the curing action by taking part in it.



The resistance to surface indentation, usually measured by the depth of penetration (or arbitrary units related to depth of penetration) of a blunt point under a given load using a particular instrument according to a prescribed procedure. (e.g. Barcol hardness, Rockwell hardness number.)


Heat-distortion Temperature

Temperature at which a test bar deflects a certain amount under specified temperature and a stated load.


Heat Resistance

The property or ability of plastics and elastomers to resist the deteriorating effects of elevated temperatures.


Het-acid Resin

Polyester resin with exceptional fire qualities.



High-modulus. Often applied to carbon fibres having a tensile modulus >350 GPa.



Manufactured product of resin-impregnated sheet material (paper, glass fabric, etc.) or sheetmetal formed into hexagonal-shaped cells; used as a core material in sandwich construction.


Hoop Stress

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


Hybrid Fabric

Two or more reinforcing fibres in a fabric, such as aramid and glass, or carbon and aramid.


Hydraulic Press

A press in which the moulding force is created by the pressure exerted on a fluid.



Capable of absorbing water.



Capable of repelling water.



Capable of absorbing and retaining atmospheric moisture.

                                                                                                                     [Back to Top]

[ I ]



lntermediate-modulus often applied to carbon fibres having a tensile modulus of approximately 300 GPa.


Impact Strength

The ability of a material to withstand shock loading; the work done in fracturing a test specimen in a specified manner under shock loading.



In reinforced plastics, to saturate the reinforcement with a resin.


Impregnated Fabric

A fabric impregnated with a synthetic resin. (See also Prepreg.)


Inert Filler

A material added to a plastic to alter its properties through physical rather than chemical means.



A substance which retards a chemical reaction; used in certain types of monomers and resins to prolong storage life.


lnjection Molding

A technique developed for processing thermoplastics which are heated and forced under pressure into closed moulds and cooled.



In the position which it will finally occupy, e.g. molding or forming foam.



A make of mechanical testing instrument used to determine the tensile and compressive properties of materials.


Insulating Resistance

The electric resistance between two conductors or systems of conductors separated only by insulating material.



The junction point or surface between two different media; on fibres, the contact area between the fibre and sizing or finish; in a laminate, the contact area between the reinforcement and the laminating resin.



Existing or occurring between two or more adjacent laminae.


Interlaminar Shear

The shearing force tending to produce displacement between two laminae along the plane of their interface; usually the weakest element of a composite.


Interlaminar Shear Strength

The maximum shear stress existing between layers of a laminated material.


Internal Stress

Stress created within a laminate due to different rates of contraction or expansion of the fibres and resin system.



A fire-retardant technology which causes an otherwise flammable material to foam, forming an insulating barrier when exposed to heat.



A polyester resin based on isophthalic acid, generally higher in properties than a general purpose or orthothatic polyester resin.



The description of equal strength properties in all orientation. Isoptropic composites are usually achieved by random fiber orientation.


Isotropic Laminates

One in which the strength properties are equal in all directions.


Izod Impact Test

A destructive test designed to determine the resistance of a plastic to the impact of a suddenly applied force.

                                                                                                                    [Back to Top]

[ J ]



A visual effect of glass fiber turning white in a cured laminate. This usually does not effect the strength of a laminate, but could be an indication of materials incompatibility.



Any fixture for holding parts in position, while joining them together or to maintain their shape.



A line or distinction formed when two panels are connected. Also referred to as a seam.

                                                                                                                    [Back to Top]

[ K ]


                                                                                                                    [Back to Top]

[ L ]



The product of lamination. A composite consisting of a layer or layers of thermoset polymer and fiber reinforcement.



To place into a mold a series of layers of polymer and reinforcement. The process of applying FRP materials to a mold. To lay up.



Applying layers of glass and resin to a mold. Also used to describe a single ply of laminate.



A single ply of lay up or laminate.


Lay Up

The act of building up successive layers of polymer and reinforcement. Layers of catalyzed resin and fiberglass or other reinforcements are applied to a mold in order to make a part.


Low-pressure Laminates

Laminated, molded and cured using pressures from 400 psi down to and including the pressure obtained by the mere contact of the plies.

                                                                                                                     [Back to Top]

[ M ]


Male Mold

A convex mold where the concave surface of the part is precisely defined by the mold surface.


Master (plug)

A full scale representation of the intended part, usually retained as a reference and the part from which production molds are made.



See Chopped Strand Mat.


Matched Die Molding

Technique for producing long runs of identical parts with two finished sides.


Matched Molds

Two or more tools arranged in a set as a male and female mold. Normally used in a press.



The liquid component of a composite or laminate.


MEK Peroxide (MEKP)

An initiator often referred to as catalyst and used to initiate polymerization of a resin. Methyl Ethyl Ketone Peroxide.


MEK Solvent

Methyl Ethyl Ketone; a colorless, flammable liquid sometimes used in clean up procedures.



Microscopic bubbles of glass, ceramic or phenolic, used as filler or to create syntactic foam or putty mixtures.


MIL (MIL Thickness)

The unit used in measuring film thickness.

One mil equals one thousandth of an inch (l mil = .001 ").


Milled Fibers

Glass fiber processed by a hammer mill into lengths of 1/32" to 1/8". Commonly used as a reinforcement in polyester putty.


Modulus of Elasticity

An engineering term used to describe a material's ability to bend without losing its ability to return to its original physical properties.



The tool used to fabricate the desired part shape. Also used to describe the process of making a part in a mold.



The process of using a mold to form a part.


Mold Release

A wax or polymer compound that is applied to the mold surface which acts as a barrier between the mold and the part, thus preventing the part from bonding to the mold.



One of the constituents of polyester resin.

                                                                                                                    [Back to Top]

[ N ]



In reinforced plastics placing plies of fabric so that the yarns of one ply lie in the valleys between the yarns of the adjacent ply (nested cloth).


NDI (Non Destructive Inspection)

A process or procedure for determining material or part characteristics without permanently altering the test subject. Nondestructive testing (NDT) is broadly considered synonymous with NDI.


Nonwoven Fabric

Fabric produced by loosely bonding together yarns, rovings, etc.


Notch Sensitivity

Extent to which the sensitivity of a material to fracture is increased by the presence of a surface inhomogeneity such as a notch, a sudden change in section, a crack, or a scratch. Low notch sensitivity is usually associated with ductile materials and high notch sensitivity with brittle materials.



A phenolic-aldehyde resin which remains permanently thermoplastic unless a source of methylene groups is added; a linear thermoplastic B-staged resin.


NPG Gel Coat

Neopentyl glycol gel coat has enhanced weatherability compared to non-NPG gel coat.

                                                                                                                    [Back to Top]

[ O ]

Offset Yield Strength

The stress at which the strain exceeds by a specific amount (the offset) an extension of the initial proportional portion of the stress-strain curve.


Orange Peel

An uneven surface of a coating resembling that of orange peel.



Designating or composed of matter originating in plant or animal life or composed of chemicals of hydrocarbon origin, natural or synthetic.


Orthophthalic or Ortho Resin

A polyester resin based on orthophthalic acid, also known as a general purpose resin (GP).



Having three mutually perpendicular planes of elastic symmetry.



The period of time a prepreg material remains in a handleable form and with properties intact outside of the specified storage environment; for example, out of the freezer in the case of thermoset prepregs.



A simple adhesive joint, in which the surface of one adherend extends past the leading edge of another.

                                                                                                                    [Back to Top]

[ P ]



Polyacrylonitrile. The precursor for most carbon fibres.



Laminated so that all the layers of material are oriented approximately parallel with respect to the grain or strongest direction in tension.


Parting Agent

See Mold Release and PVA


Parting Line

The location on a molded product between different segments of the mold used to produce the product.



The initial model for making fiberglass molds. See Plug.


Peel Ply

A tightly woven polyester or nylon fabric which is applied to the outside layer of a laminate. This is removed or sacrificed to achieve improved bonding of additional plies and leaves a clean, resin-rich surface ready for bonding.


Peel Strength

Bond strength, obtained by peeling apart layers. (See also Bond Strength.)


Permanent Set

The deformation remaining after a specimen has been stressed in tension a prescribed amount for a definite period and released for a definite period.


Phenolic, Phenolic Resin

A synthetic resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. (See also A stage, B stage, C stage, Novolac.) Phenolics have particularly good fire-resistance properties.



An individual filling yarn, running the width of a woven fabric at right angles to the warp, also called fill, woof, weft.



A colorant added to gel coat or resin.


Pigment Separation

Occurs when the pigment is not thoroughly mixed into the gel coat during formulation or the gel coat is improperly mixed prior to use. It is characterized by a non homogeneous surface color.



A tiny hole in the surface of, or through a coating material.



Small regular or irregular crater in the surface of a moulding, usually with width about the same order of magnitude as the depth.



A residual petroleum product used in the manufacture of certain carbon fibres.


Planar Helix Winding

A winding in which the filament path on each dome lies on a plane which intersects the dome while a helical path over the cylindrical section is connected to the dome paths.


Planar Winding

A winding in which the filament path lies on a plane intersecting the winding surface.



A material that contains, as an essential ingredient, an organic substance of high molecular weight, is solid in its finished state and, at some stage in its manufacture or processing into finished articles, can be shaped by flow; made of plastic. A rigid plastic is one with a stiffness or apparent modulus of elasticity greater than 690 MPa at 23░C. A semirigid plastic has a stiffness or apparent modulus of elasticity between 69 and 690 MPa at 23░C.


Plastic Deformation

Change in dimensions of an object under load that is not recovered when the load is removed; opposite of elastic deformation. See also Elastic Recovery.



The mounting plates of a press, to which the entire mould assembly is bolted.


Plied Yarn

A yarn formed by twisting together two or more single yarns in one operation.



A composite industry term for a pattern or model.



One of the layers that make up a stack or laminate.



A type of Polyimide resin.


Poisson's Ratio n

A constant relating to change in cross-sectional area to change in length when a material is stretched; n = 1/2 for rubbery materials, 1/4 to 1/2 for crystals and glasses.


Polyacrylonitrile (PAN)

A product used as a base material in the manufacture of certain carbon fibres.



A polymer in which the structural units are linked by amide or thioamide groupings; many polyamides are fibre-forming.



Thermosetting resins produced by dissolving unsaturated, generally linear alkyd resins in a vinyl active monomer, e.g. styrene, methyl styrene, or diallyl phthalate.



A polymer produced by heating polyamic acid; a highly heat-resistant resin [> 600░F(> 316░C)] suitable for use as a laminating resin or an adhesive.



A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit (mer), e.g. polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerisation of monomers.



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



To unite molecules of the same kind into a compound having the elements in the same proportion but possessing much higher molecular weight and different physical properties.


Polyvinyl Alcohol (PVA)

A parting film applied to a mold for part releasing.



Entrapped gas bubbles or voids in a gel coat film.



Additional elevated-temperature cure, usually without pressure, to improve final properties and/or complete the cure. Complete cure and ultimate mechanical properties of certain resins are attained only by exposure of the cured resin to temperatures higher than those of initial curing.


Pot Life

The length of time a quantity of catalysed resin system in a container remains liquid prior to gelation, also called working life.



Polyphenylene sulfide.



The full or partial setting of a synthetic resin or adhesive in a joint before the clamping operation is complete or before pressure is applied.



For carbon fibres, the rayon, PAN, or pitch fibres from which carbon fibres are made.



A preshaped fibrous reinforcement of mat or cloth formed to the desired shape on a mandrel or mock-up before being placed in a mould press, or RTM tool.


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 be handleable.



The practice of mixing resin and reinforcement and effecting partial cure before use or shipment to the user. ( See also Prepreg.)



Reinforcing material mixed with resin, and usually with pigment, filler and catalyst, before placing in the mold.



Ready-to-mould material in rolled-sheet form, which may be cloth, mat or fibres impregnated with resin and stored for use. The resin is partially cured to a soft and slightly sticky B stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure.



Force measured per unit area.


Pressure-bag Molding

A process for molding reinforced plastics, in which a tailored flexible bag is placed over the contact lay-up on the mould, sealed, and clamped in place. Fluid pressure, usually compressed air, is exerted on the bag, and the part is cured.


Primary Structure

The main structure.



A coating applied to a surface before the application of an adhesive or lacquer, enamel, or the like to improve the performance of the bond.


Print Through

A distortion in the surface of a part which allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through.



See Accelerator.


Proportional Limit

The greatest stress which a material is capable of sustaining without deviation from proportionality of stress and strain (Hooke's Law); it is expressed in force per unit area.



Reversed extrusion of resin-impregnated roving in the manufacture of rods, tubes, and structural shapes of a permanent cross section. After passing through the resin dip tank the roving is drawn through a die to form the desired cross section.



A thickened mixture of resin made by adding fillers, thixotrophs and reinforcing fibers.

                                                                                                                    [Back to Top]

[ Q ]


Approximating isotropy by orientation of plies in several directions.

[ R ]



A gradual, programmed increase/decrease in temperature or pressure, during the cure cycle of composite parts.



A strong inert material bonded into a plastic to improve its strength, stiffness, and impact resistance. To be effective, the reinforcing material must form a strong adhesive bond with the resin.


Reinforced Molding Compound

Compound consisting of a polymer and a reinforcement fiber or filler supplied by raw material producer in the form of ready-to-use materials.


Reinforced Plastic

A plastic with strength properties greatly superior to those of the base resin, resulting from the presence of reinforcements embedded in the composition.


Release Agent

A material which is applied in a thin film to the surface of a mould to keep the resin from bonding to it. See also Mould Release.


Release Film

A thin plastic film applied on top of a laminate stack before it is cured. It is usually perforated, allowing excess resin to flow out and be absorbed by a bleeder cloth.



(1) The ratio of energy returned on recovery from deformation to the work input required to produce the deformation (usually expressed as a percentage). (2) The ability to regain an original shape quickly after being strained or distorted.



A solid, semisolid, or pseudo-solid organic material which has an indefinite (often high) molecular weight, exhibits a tendency to flow when subjected to stress, usually has a softening or melting range. Most resins are polymers. In reinforced plastics the material used to bind together the reinforcement material, the matrix. See also Polymer.


Resin Content

The amount of resin in a laminate expressed as a percentage of total weight.


Resin-rich Area

Space which is filled with resin and lacking reinforcing material.


Resin-starved Area

Area of insufficient resin, usually identified by low gloss, dry spots, or fibre show.


Resin Tearing

Separation of pigments in a gel coat affecting cosmetic appearance.



Resin Infusion under Flexible Tooling.



A fibre having essentially a rectangular cross section, where the width-to-thickness ratio is at least 4:1.



Reaction-injection moulding.


Rockwell Hardness Number

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.


Room Temperature-curing Adhesives

Adhesives that set (to handling strength) at 20 to 30░C and later reach full strength without heating.



A loose assembly of continuous filaments of glass fibre substantially without twist.



Reinforced reaction-injection moulding.



Resin-transfer molding. A molding process in which catalyzed resin is transferred into an enclosed mould into which the fiber reinforcement has been placed; cure normally is accomplished without external heat. RTM combines relatively low tooling and equipment costs with the ability to mould large structural parts.

                                                                                                                     [Back to Top]

[ S ]


S Glass

A magnesia-alumina-silicate glass, especially designed to provide filaments with very high tensile strength.


Sandwich Constructions

Panels composed of a lightweight core material (honeycomb, foamed plastic, etc.) to which two relatively thin, dense, high-strength faces or skins are adhered.



A particular, fairly flat weave pattern in fabrics in which each warp fibre flocks over 4 or more weft fibres, and vice versa.


Scarf Joint

See Joint.



A nonwoven open-weave reinforcing fabric made from continuous-filament yarn in an open-mesh construction. Often used to support an adhesive film.



See Joint.


Secondary Structure

A structure of secondary importance.


Self-extinguishing Resin

A resin formulation which will burn in the presence of a flame but which will extinguish itself within a specified time after the flame is removed.


Self-tapping Screws

Hardened screws which cut their own thread as they are set.



The edge of a woven fabric finished off so as to prevent the yarns from unravelling.



(1) To convert into a fixed or hardened state by chemical or physical action, such as condensation polymerisation, oxidation, vulcanisation, gelation, hydration, or evaporation of volatiles. (2) The irrecoverable deformation or creep usually measured by a prescribed test procedure and expressed as a percentage of original dimension.


Set Up

To harden, as in curing.



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


Shear Modulus G

The ratio of shearing stress t to shearing strain g within the proportional limit of a material.


Shelf life

The allowable storage time before a product must be used.


Ship Lap

Method of joining two panels together by means of one panel having a recessed shelf to receive the other panel on top of it leaving a flush surface.


Short-beam Shear Strength

The interlaminar shear strength of a parallel-fibre-reinforced plastic material as determined by three-point flexural loading of a short segment.



The tendency of a resin system to contract in volume when transitioning from the liquid to the used state.


Silicon Carbide Fibre

A reinforcing fibre with high strength and modulus: density is equal to that of aluminium. It is used in organic- and metal-matrix composites.



Any treatment consisting of starch, gelatin, oil, wax, or other suitable ingredient applied to yarn or fibres at the time of formation to protect the surface and facilitate handling and fabrication or to control the fibre characteristics. The treatment contains ingredients which provide surface lubricity and binding action but, unlike a finish, no coupling agent. Before final fabrication into a composite, the size is usually removed by heat-cleaning and a finish is applied.


Sizing Content

The percent of the total strand weight made up by the sizing, usually determined by burning off the organic sizing (˝loss on Ignitionţ).



A continuous filament, strand, yarn, roving, etc. wound up to some measurable length and generally used to measure various physical properties.



The laminate part of a sandwich structure.



Sheet-moulding compound.


S-N Curve

Stress per number of cycles to failure. Used to define fatigue behaviour.


Specific Gravity

The ratio of the weight of any volume of a substance to the weight of an equal volume of another substance, usually water, taken as standard at a constant or stated temperature.


Specific Heat

The quantity of heat required to raise the temperature of a unit mass of a substance 1 degree under specified conditions.



An individual piece or portion of a sample used to make a specific test.



To join two ends of fibre yarn or strand, usually by means of an air-drying glue. Such a join.


Split Mold

An open mold made in two or more pieces.



Technique in which a spray gun is used as the processing tool. In reinforced plastics, for example, fibrous glass and resin can be simultaneously deposited in a mould. In essence, roving is fed through a chopper and ejected into a resin stream, which is directed at the mould by either of two spray systems.


Sprayed-metal Molds

Molds made by spraying molten metal onto a master until a shell of predetermined thickness is achieved. The shell is then removed and backed up with plaster, cement, casting resin, or other suitable material. Used primarily as a mould in sheet-forming process.


Starved Joint

An adhesive joint which has been deprived of the proper film thickness of adhesive due to insufficient adhesive spreading or application of excessive pressure during lamination.



The relationship of load and deformation; a term often used when the relationship of stress to strain does not conform to the definition of Young's modulus. (See Stress-strain.)



As applied to composite laminates: The resultant change in dimension of a material when subjected to a stress, expressed as a fraction or percentage of the original dimension.



Most commonly defined as engineering stress; the ratio of the applied load P to the original cross-sectional area A


Stress Concentration

Magnification of the level of an applied stress in the region of a notch, void, or inclusion.


Stress Corrosion

Preferential attack of areas under stress in a corrosive environment, where this factor alone would not have caused corrosion.


Stress Crack

External or internal cracks in a plastic caused by tensile stresses less than that of its basic mechanical strength. The stresses which cause cracking may be present internally or externally or may be combinations of these stresses.


Stress Relaxation

The decrease in stress under sustained constant strain, also called stress decay.


Stress-strain Curve

Simultaneous readings of load and deformation, converted into stress and strain, plotted as y and x-axes, respectively, to obtain a stress-strain diagram.


Structural Adhesive

An adhesive used for transferring loads between adherends.


Structural Bond

A bond that joins basic load-bearing parts of an assembly; the load may be either static or dynamic.


Styrene Monomer

A component of polyester resin that provides crosslinking sites and reduces the polyester to a workable viscosity.


Surfacing Mat

A very thin mat, of highly filamentized fibers used primarily to produce a smooth surface on a reinforced plastic laminate.


Surface Treatment

A treatment applied to carbon fibre during its manufacture to alter the fiber’s surface chemistry.



Chemicals used to modify or change the surface of a layer of resin or polymer. Usually used to form a film on a curing resin, producing a tack-free surface.


Syntactic Foam

A cellular plastic which is put together by incorporating hollow spheres or microballoons in a resin matrix; opposite of foamed plastic, in which the cells are formed by gas bubbles released in the liquid plastic by chemical or mechanical action.

                                                                                                                    [Back to Top]

[ T ]



Stickiness of an adhesive, resin or prepreg material.


Tack Free

A surface which is not sticky after cure.



A form of unidirectional prepreg consisting of continuous fibres that are aligned along the tape axis parallel to each other and held together purely by the impregnating resin.


Tape Laying

A fabrication process in which prepreg tape is laid side by side or overşlapped to form a structure. The process can be automated with robotic arms.



The strength of a yarn or of a filament of a given size; equals breaking strength divided by denier.


Tensile Modulus

The ratio of the tension stress to the strain in the material over the range for which this value is constant.


Tensile Strength or Stress

The maximum tensile load per unit area of original cross section, sustained by the specimen during a tension test. Tensile strength is interpreted to mean the maximum tensile load sustained by the specimen during the test, whether this coincides with the tensile load at the moment of rupture or not.



A measure of the mass of 1000lm of a fibre, tow or strand expressed in grammes. Sometimes expressed as dtex (decitex) where 1dtex equals 0.1x tex and is equivalent to the mass in grammes of 10,000lm of fibre, tow or strand.


Thermal Coefficient of Expansion

Measures dimensional change of a material when heated or cooled. Measured in inches per inch per degree.


Thermal Conductivity

Ability of a material to conduct heat; the physical constant for quantity of heat that passes through a unit cube of a substance in unit time when the difference in temperature of two faces is 1 degree.



A plastic material capable of being repeatedly softened by increase of temperature and hardened by decrease in temperature; applicable to those materials whose change upon heating is substantially physical rather than chemical and which can be shaped by flow into articles by moulding and extrusion. Examples include, polypropylene, ABS, nylon, polyethylene.



A plastic material which changes into a substantially infusible and unmouldable material after it is cured by application of heat or by chemical means. Although a thermoset material will soften at its Tg, it will never return to its precured liquid state. Examples include epoxy and unsaturated polyester.



Gel-like at rest but fluid when agitated; having high static shear strength and low dynamic shear strength at the same time.


Thixotropic Index (T.I.)

A measure of thixotropy using a Brookfield Viscometer. The low speed viscosity divided by the high speed viscosity.


Thread Count

The number of yarns (threads) per inch (millimetre) in either lengthwise (warp) or crosswise (weft) direction of woven fabrics.


Tooling gel coat

A gel coat formulated for mold surfaces.


Torsional Rigidity (Fibres)

The resistance of a fibre to twisting.



The resistance of a material to crack propagation.



A large bundle of continuous filaments, generally 1000 or more, usually designated by a number followed by ˝K,ţ indicating multiplication by 1000; for example, 12K tow has 12,000 filaments. Normally applied to carbon fibre.


Transition Temperature

The temperature at which the properties of a material change.



Permits a percentage of light to pass but not optically clear like window glass.



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

                                                                                                                     [Back to Top]

[ U ]



Ultra-high modulus.


Ultimate Elongation

The elongation at rupture of a material. Also called ´Elongation at break' or ´Strain to failure'.


Ultimate Tensile Strength

The ultimate or final stress sustained by a specimen in a tension test; at moment of rupture.


Ultraviolet (UV)

Zone of invisible radiations beyond the violet end of the spectrum of visible radiations. Since ultraviolet wave lengths are shorter than the visible, their photons have more energy, enough to initiate some chemical reactions and to degrade most plastics.


UV Stabilizer

A chemical compound which improves resistance to degradation from ultraviolet radiation.



Refers to fibres that are oriented in the same direction, such as unidirectional fabric, tape, or laminate, often called UD.


Unidirectional Laminate

A reinforced plastic laminate in which substantially all the fişbres are oriented in the same direction.



An area of a part or mold that has an acute angle between two surfaces. If a part has an undercut a split mold is necessary.

                                                                                                                    [Back to Top]

[ V ]


Vacuum-bag Molding

A process for moulding laminates in which a sheet of flexible material is placed over the lay-up on the mould and sealed. A vacuum is applied between the sheet and the lay-up. The entrapped air is pulled out of the lay-up and removed by the vacuum. Atmospheric pressure provides the consolidation pressure.



An ultra thin mat similar to a surface mat, often composed of organic fibres as well as glass fibres.



The property of resistance to flow exhibited within the body of a liquid or semi-solid expressed in terms of relationship between applied shearing stress and resulting rate of strain in shear.


Void Content

The percentage of voids in a laminate.



Gaseous pockets trapped and cured into a laminate usually within the matrix.


Volatile Content

The percent of volatiles driven off as a vapour from a plastic or an impregnated reinforcement.



Materials in a sizing or a resin formulation capable of being driven off as a vapour at room temperature or slightly above.

                                                                                                                    [Back to Top]

[ W ]



(1) The yarn running lengthwise in a woven fabric; a group of yarns in long lengths and approximately parallel, put on beams or warp reels for further textile processing, including weaving. (2) A change in dimensions of a cured laminate from its original moulded shape.


Water Absorption

Ratio of the weight of water absorbed by a material upon immersion to the weight of the dry material.


Water Jet

A high pressure stream of water used for cutting composites and other materials.



A compound used as a release agent. See RELEASE AGENT



The exposure of materials outdoors. In artificial weathering, plastics are exposed to cyclic laboratory conditions of high and low temperatures, high and low relative humidities, and ultraviolet radiant energy, with or without direct water spray, in an attempt to produce changes in their properties similar to those observed on long continuous exposure outdoors. Laboratory exposure conditions are usually intensified beyond those in actual outdoor exposure to achieve an accelerated effect.



The particular manner in which a fabric is formed by interlacing yarns. In plain weave, the warp and weft fibres alternate to make both fabric faces identical; in satin weave, the pattern produces a satin appearance, with the warp tow over several weft tows and under the next one (for example, eight-harness satin would have warp tow over seven weft tows and under the eighth).



A textile fabric, paper or a thin metal sheet of continuous length handled in roll form, as contrasted with the same material cut into sheets.



The transverse threads of fibres in a woven fabric running perpendicular to the warp; also called fill, and woof.


Wet Lay-up

A process in which liquid resin is applied as the reinforcement is laid up.



The condition of an impregnated roving or yarn wherein substantially all voids between the sized strands and filaments are filled with resin.


Wet-out Rate

The time required for a resin to fill the interstices of a reinforcement material and wet the surface of the reinforcement fibres; usually determined by optical or light-transmission means.


Wetting Agent

A surface-active agent usually in a resin formulation that promotes wetting by decreasing the cohesion within a liquid.


Wet Winding

In filament winding the process of winding glass on a mandrel where the strand is impregnated with resin just before contact with the mandrel.



A very short fibre form of reinforcement, usually crystalline.


Winding Pattern

In filament winding: (1) The total number of individual circuits required for a winding path to begin repeating by laying down immediately adjacent to the initial circuit. (2) A regularly recurring pattern of the filament path after a certain number of mandrel revolutions, leading to the eventual complete coverage of the mandrel.


Winding Tension

In filament winding the amount of tension on the reinforcement as it makes contact with the mandrel.


Woven Fabrics

Fabrics produced by interlacing strands at more or less right angles.


Woven Roving

A heavy glass-fibre fabric made by weaving glass roving.

                                                                                                                    [Back to Top]

[ X ]

                                                                                                                    [Back to Top]

[ Y ]



An assembly of twisted fibres or strands, natural or manufactured, to form a continuous yarn suitable for use in weaving or otherwise interweaving into textile materials.


Yield Point

The first stress in a material, less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. Only materials that exhibit this unique phenomenon of yielding have a yield point.


Yield Strength

The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain; the lowest stress at which a material undergoes plastic deformation. Below this stress, the material is elastic; above it, plastic.


                                                                                                                    [Back to Top]

[ Z ]


                                                                                                                    [Back to Top]


Relevant topics
AEG Legal Notice -