Nupol Composites

Nupol Composites
49-61 Stephen Road,
Botany, NSW, 2019
Australia
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Applications > Resources > Glossary of Terms

Glossary

Term	Description
Accelerator	A material which, when mixed with a catalysed resin, will speed up the chemical reaction between the catalyst and resin; either in polymerising of resins or vulcanisation of rubbers. Also known as 'promoter'. Examples are diethylaniline, cobalt naphthenate and cobalt octoate.
Actual End Count	The number of bundles or splits that are actually counted in one doff of roving. (This is less than the theoretical end count due to splitting efficiencies of less that 100%.)
Additive	Any substance added to another substance, usually to improve properties, such as plasticisers, initiators, light stabilisers, and flame-retardants. See also Flame Retardants, Filler.
Adherend	A body that is held to another body, usually by an adhesive. A detail or part prepared for bonding.
Adhesion	The state in which two surfaces are held together at an interface by mechanical or chemical forces or interlocking action or both.
Adhesion Promoter	A coating applied to a substrate before it is coated with an adhesive, to improve the adhesion of the plastic. Also called primer. See also - Primer.
Adhesive	A substance capable of holding two materials together by surface attachment. Adhesive can be in film, liquid, or paste form.
Adhesive Failure	Rupture of an adhesive bond such that the separation appears to be at the adhesive-adherend interface.
Adhesive Film	A synthetic resin adhesive, with or without a film carrier fabric, usually of the thermosetting type, in the form of a thin film of resin, used under heat and pressure as an interleaf in the production of bonded structures.
Adhesive Strength	Strength of the bond between an adhesive and an adherend.
Air Entrapment	Occlusion of air in a resin or resin glass system, giving rise to blisters, bubbles or voids in the system.
Air Splice	The coupling between two roving doffs which is made by a jet of air entwining/snarling the two strands together. The air splice is used instead of a knot.
Air Vent	Small outlet, to prevent entrapment of gases.
Air-Bubble Void	Air entrapment within and between the plies of reinforcement or within a bond line or encapsulated area; localised, non-interconnected, spherical in shape.
Amine Resins	A synthetic resin derived from the reaction of urea, thiourea, melamine or allied compounds with aldehydes, particularly formaldehyde.
Anisotropy	The tendency of a material to exhibit different along the directions parallel to the length or width into the lamination planes; or parallel to the thickness into the planes perpendicular to the lamination.
Anti-Static Agents	Agents which, when added to the moulding material or applied on the surface of the moulded object, make it less conducting (thus hindering the fixation of dust).
Aramid	Aromatic polyamide fibres characterised by excellent high-temperature, flame-resistance, and electrical properties.
Areal Weight	The weight of fibre per unit area (width x 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 reaction of a thermosetting resin in which the material is still soluble and fusible.
Autoclave	A closed vessel that permits application of pressure and heat used for processing composite materials.
Axial Winding	A type of filament winding in which the filaments are parallel to the axis.
Bag Moulding	A process in which the consolidation of the material in the mould is effected by the application of fluid or gas pressure through a flexible membrane.
Bag Side	The side of the part that is cured against the vacuum bag.
Bagging	Applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn.
Balanced Construction	Equal parts of warp and fill in fibre fabric. Construction in which reactions to tension and compression loads result in extension or compression deformations only and in which flexural loads produce pure bending of equal magnitude in axial and lateral directions.
Balanced Laminate	A composite laminate in which all laminate at angles other than 0o and 90o occur only in + pairs (not necessarily adjacent) and are symmetrical around the centre line.
Bare Glass	The glass as it flows from the bushing in fibre form, before a binder or sizing is applied.
Bias Fabric	A fabric in which warp and fill fibres are at an angle to the length.
Biaxial Winding	A type of filament winding in which the helical band is laid in sequence, side by side, with no crossover of the fibres.
Bi-Directional Laminate	A reinforced laminate in which the fibres are oriented in 2 directions.
Binder	A coating applied to the surface of a chopped glass mat or preform which is then cured. The binder holds the previously sized glass bundles or ends together in the roving operation into a stable shape or form.
Birdsnest	A large collection of continuous glass bundles which is tangled up and will not run through the guide eye into roving creel. In the field, a large tangled collection of roving which does not run through the tube or guide eyes to the chopper.
Bisphenol A	A condensation product formed by reaction of two (bis) molecules of phenol with acetone (A). This polyhydric phenol is a standard resin intermediate along with epichlorohydrin in the production of epoxy resins.
Bladder	An elastomeric lining for the containment of pressurisation medium in filament-wound structures, or for the manufacture of composite structures.
Blade Packing	Glass bundles or chopper fuzz which build up and pack between the blades of a chopper. This blade packing can cause poor choppability. If it falls off, it usually does not wet-through, and this can cause blisters or porosity.
Bleeder Cloth	A non-structural layer of material used in the manufacture of composite parts to allow the escape of excess gas and resin during cure. The bleeder cloth is removed after the curing process is complete and is not part of the final composite.
Bleed out	The excess liquid resin appearing at the surface primarily occurring during filament winding.
Blister	Undesirable rounded elevation of the surface of a plastic, whose boundaries may be more or less sharply defined, resembling in shape a blister on the human skin. The blister may burst and become flattened.
BMC	Bulk Moulding Compound. Thermosetting resin mixed with strand reinforcement, fillers, and so on, into a viscous compound for compression or injection moulding. See also Sheet Moulding Compound.
Bobbin	The spool or shipping package on to which textile yarns are wound.
Boron Fibre	A fibre usually of a tungsten-filament core with elemental boron vapour deposited on it to impart strength and stiffness.
Braid/Braider	A narrow tubular or flat fabric produced by intertwining a single set of yarns according to a definite pattern.
Break-Up	See Dispersion.
Breather	A loosely woven material, such as glass fabric, which serves as a continuous vacuum path over a part but does not come in contact with the resin. The breather is removed after the curing process is complete and is not part of the final composite.
Bridging	Condition in which fibres do not move into or conform to radii and corners during moulding, resulting in voids and dimensional control problems.
Broad Goods	Fibre woven to form fabric up to 1270 mm (50 in.) wide. It may or may not be impregnated with resin and is usually furnished in rolls of 25 to 140 kg. (50 to 300 lb).
Broken End	In the roving operation, a broken or severed strand (bundle) which causes the forming cake to stop running.
B-Stage	An intermediate stage in the reaction of a thermosetting resin in which the material melts when heated and dissolves in certain solvents. Materials are usually pre-cured to this stage to facilitate handling and processing prior to final cure.
Build-Up	Glass bundles or chopper fuzz which collect on the chopper, cot, static bars or machine frame.
Bulk Factor	The ratio of the volume of a raw moulding compound, reinforcement or powdered plastic to the volume of the finished solid piece produced therefrom. The ratio of the density of the solid plastic object to the apparent or bulk density of the loose moulding powder or fabric.
Bulk Moulding Compound	Thermosetting resin mixed with strand reinforcement, fillers, and so on, into a
(BMC)	viscous compound for compression or injection moulding. See also Sheet Moulding Compound.
Bundle	A discrete collection of many parallel glass filaments. A collection of Individual filaments, a sub-strand.
Bushing	Plate with holes through which molten glass is pulled to produce glass fibres.
Bushing Tip	Small tapered protrusions on the bottom of bushings each containing an orifice through which molten glass flows, from which continuous filaments are drawn.
Cabled Yarn	Yarn that is plied more than once; yarn made by plying two or more previous plied yarns.
Cake	A term applied to the glass package that is produced in the forming department. Also used as forming cake package, forming cake and cake package. All terms are synonymous.
Carbon Fibre	An important reinforcing fibre known for its light weight, high strength, and high stiffness that is commonly produced by pyrolysis of an organic precursor fibre (often polyacrylonitrile (PAN) or rayon) in an inert atmosphere.
Carbon/Carbon	A composite of carbon fibre in a carbon matrix.
Carding	The process of untangling and partially straightening fibres by passing them between two closely spaced surfaces which are moving at different speeds, and at least one of which is covered with sharp points, thus converting a tangled mass of fibres to a filmy web.

Catalyst	A substance that changes the rate of a chemical reaction without itself undergoing permanent change in composition or becoming a part of the molecular structure of the product. A substance that markedly speeds up the cure of a compound when added in minor quantity as compared to the amounts of primary reactants.
Catenary	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.
Caul Plates	Smooth metal, plastic, or rubber plates free of surface defects, used in contact with the lay-up during the curing process to transmit normal pressure and provide a smooth surface on the finished part. A caul plate must be the appropriate size and shape for the composite lay-up with which is will be used.
Cavity	The space inside a mould in which a resin or moulding compound is poured or injected. The female portion of a mould. That portion of the mould that encloses the moulded article (often referred to as the die). Depending on the number of such depressions, moulds are designated as single cavity or multiple cavity.
Cell	In honeycomb core, a cell is a single honeycomb unit, usually in a hexagonal shape.
CFRP	Carbon Fibre-Reinforced Plastic.
Chemical Size	A surface finish applied to the fibre that contains some chemical constituents other than water.
Choppability	The ease of chopping/cutting the glass fibres to a uniform length.
Chopped Strand	Continuous roving that is chopped into short lengths for use in mats, spray-up or moulding compounds.
Chopper Gun	A special piece of equipment used in the manufacture of reinforced plastic parts, which chops glass and sprays resin and catalyst simultaneously onto a moulded surface.
Co-Cured	Cured and simultaneously bonded to another prepared surface.
Compaction	The application of a temporary vacuum bag and vacuum to remove trapped air and compact the lay-up.
Composite	A homogeneous material created by the synthetic assembly of two or more materials (a selected filler or reinforcing elements and compatible matrix binder) to obtain specific characteristics and properties. Composites are subdivided into classes on the basis of the form of the structural constituents; Laminar - Composed of layer or laminar constituents; Particular -The dispersed phase consists of small particles; Fibrous -The dispersed phase consists of fibres; Flake -The dispersed phase consists of flat flakes; Skeletal -Composed of a continuous skeletal matrix filled by a second material.
Compression Mould	A mould which is open when the material is introduced and which shapes the material by heat and by the pressure of closing. See also Compression Moulding.
Compression Moulding	A technique for moulding 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.
Conditioning	Subjecting a material to a prescribed environmental and/or stress history before testing.
Conformability	Ability of the mat to conform to difficult shapes without causing wrinkles or leaving excessively resin-rich or glass-rich radii, which may craze.
Contact Moulding	A process for moulding reinforced plastics in which reinforcement and resin are placed on a mould, cure is either at room temperature using a catalyst-promoter system or by heat in an oven and no additional pressure is used.
Continuous Filament	An individual, small-diameter reinforcement that is flexible and indefinite in length.
Continuous Roving	Parallel filaments coated with sizing, gathered together in single or multiple strands and wound into a cylindrical package. It can be used to provide continuous reinforcement in woven roving, filament winding, pultrusion, pre-pregs or high-strength moulding components. It also can be chopped. See also Chopped Strand.
Conventional Roving	Roving that is assembled from several forming packages using a creel and a roving winder. Typical characteristics are multiple ends, 3-inch diameter centres, a tube core and some catenary.
Co-Polymer	A resin produced by copolymerisation, the process where unlike molecules are arranged in alternate sequence in a chain.
Core	The central component of a sandwich construction to which the sandwich faces or skins are attached; also, part of a complex mould that forms undercut parts.
Count	For fabric, number of warp and filling yarns per inch in woven cloth. For yarn, size based on relation of length and weight.
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.
Co-Woven 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.
Crazing	Fine cracks that may extend in a network on or under the surface of a plastic material.
Creel	A device for holding the required number of roving balls or supply packages in desired position for unwinding onto the next processing step.
Crimp	A fibre's waviness, which determines the capacity of the fibre to cohere.
Cross Laminated	Material laminated so that some of the layers are oriented at various angles to the other with respect to the laminate grain. A cross-ply laminate usually has plies oriented only at 0/90 degrees.
Crosslinking	The setting up of chemical links between molecule chains. This occurs in all thermosetting resins. Styrene monomer is a crosslinking agent in polyester resins.
C-Stage	The final stage of the curing of a thermosetting resin in which the material has become infusible and insoluble in common solvents.
Cure	To change the properties of a thermosetting resin irreversibly by chemical reaction, i.e., condensation, ring closure, or addition. Cure may be accomplished by addition of curing (cross-linking) agents, with or without catalyst, and with or without heat.
Cure Cycle	The time/temperature/pressure cycle used to cure a thermosetting resin system of pre-preg.
Cure Stress	A residual internal stress produced during the curing cycle of composite structures. Normally, these stresses originate when different components of a wet lay-up have different thermal coefficients of expansion.
Curing Agent	A catalytic or reactive agent that brings about polymerisation when it is added to a resin.
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 period of time during which a part is subjected to heat or pressure, or both, to cure the resin; interval of time between the instant of cessation of relative movement between the moving parts of a mould and the instant that pressure is released. (Further cure may take place after removal of the assembly from the conditions of heat or pressure.)
Cycle	The complete, repeating sequence of operations in a process or part of a process. In moulding, the cycle time is the period (or elapsed time) between a certain point in one cycle and the same point in the next.
Daylight	The distance, in the open position, between the moving and fixed tables or the platens of a hydraulic press. In the case of a multi-daylight press, daylight is the distance between adjacent platens.
De-bulking	Compacting of a thick laminate under moderate heat and pressure and/or vacuum to remove most of the air, to ensure seating on the tool, and to prevent wrinkles.
Delaminate	To split a laminated plastic material along the plane of its layers. Physical separation or loss of bond between laminate plies.
Denier	A numbering system for yarn and filament in which yarn number is equal to weight in grams of 9000 meters of yarn.
Direct Wound Roving	A roving made directly at the bushing that does not go through a roving process. Typical characteristics are single-end roving, coreless, 6-inch diameter centres and no catenary.
Direct-Sized Yarn	Specially formulated sizings on textile yarns that allow them to be resin compatible.
Dispersion	The degree to which the roving separates into discrete bundles after being chopped. Good dispersion is characterised by a bed of bundles that are uniform in width. Poor dispersion is characterised by a wide distribution in the widths of various bundles in the bed. Poor dispersion can cause poor wet-through and wet-out.
Doctor Roll; Doctor Bar	A device for regulating the amount of liquid material on the rollers of a spreader.
Draft	The tape or slope of the vertical surfaces of a mould designed to facilitate removal of moulded parts.
Drape	A property indicating the stiffness of a product. The stiffness of a mat, for example, determines the ease of conformity to moulded surfaces during initial processing.
Dry Laminate	A laminate containing insufficient resin for complete bonding of the reinforcement.
Dry Lay-Up	Construction of a laminate by the layering of pre-impregnated reinforcement (partly cured resin) in a female mould or on a male mould, usually followed by bag moulding or autoclave moulding.
Dry Loft	Height of the bed of chopped fibres.
Dry Winding	A filament winding operation in which resin is not used.
E-Glass	A borosilicate glass; the type most used for glass fibres for reinforced plastics; suitable for electrical laminates because of its high resistivity.
Ejection / De-moulding	The process of removing a moulding from the moulding impression; by mechanical means, by hand, or by the use of compressed air.
Ejection Plate	A metal plate used to operate ejector pins; designed to apply a uniform pressure to them in the process of ejection.
End	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, a "yarn" after twist has been applied. An individual warp yarn, thread, fibre, or roving.
End Count	The number of strands contained in a roving.
Epoxy Plastic	A polymerisable thermoset polymer containing one or more epoxide groups and curable by reaction with amines, alcohols, phenols, carboxylic acids, acid anhydrides, and mercaptans. An important matrix resin in composites and structural adhesive.
Exotherm	The liberation or evolution of heat during the curing of a plastic product.
Fabric, Non-woven	A material formed from fibres or yarns without interlacing (e.g., stitched bonded, non-woven broad goods).
Fabric, Woven	A material constructed of interlaced yarns, fibres or filaments produced by the weaving process.
Fabrication	The process of making a composite part or tool.
Feathered Edge	A fabric edge that tapers down in weight instead of abruptly ending.
Fibre	A general term used to refer to filamentary materials. Often, fibre is used synonymously with filament.
Fibre Architecture	The design of a fibrous part in which the fibres are arranged in a particular way to achieve the desired result. This can include braided, stitched or woven fabrics, or mats, rovings or carbon tows.
Fibre Content	The amount of fibre present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite.
Fibre Diameter	A term used to denote the diameter of continuous glass filaments. Their diameter can vary depending on the purpose for which they are to be used. Can be expressed in letter designation, microns or inches.
Fibre Direction	The orientation or alignment of the longitudinal axis of the fibre with respect to a stated reference axis.
Fibre Glass	Primarily means glass in fibre form. However, "fibre glass" is also used to describe composite processing and applications. Examples of usage: fibre glass moulding plant, fibreglass car.
Fibre Orientation	The fibre alignment in a non-woven or a mat laminate in which most of the fibres are in the same direction, thereby affording higher strength in that direction.
Fibre Pattern	Visible fibres on the surface of laminates or mouldings; the thread size and weave of glass cloth.
Fibre Prominence	The appearance of reinforcement fibres in the surface of a moulded part. Can also be termed pattern print-through, strike-through or fibre pattern.
Fibre Reinforced Plastics	A general term for composite materials or parts that consist of a resin matrix that
(FRP)	contains reinforcing fibres such as glass or fibre and have greater strength or stiffness than the resin. FRP is most often used to denote glass fibre-reinforced plastics.
Filament	The smallest unit of a fibrous material. The basic units formed during drawing and spinning, which are gathered into strands of fibre for use in composites. Filaments usually are of extreme length and very small diameter, usually less than 25 micron. Normally filaments are not used individually. Some textile filaments can function as yarn when they are of sufficient strength and flexibility.
Filament Winding	A process for fabricating a composite structure in which continuous reinforcements (filament, wire, yarn, tape, or other), either previously impregnated with a matrix material or impregnated during the winding, are placed over a rotating and removable former.
Filamentisation	A phenomenon in which a coated strand breaks up into loose individual filaments.
Fill	That part of a woven fabric in which the strands are perpendicular to the main direction of the fabric (warp), the strands running from selvage to selvage. Also called weft. See also - Weft.
Filler	A relatively inert substance added to a material to alter its physical, mechanical, thermal, electrical, and other properties or to lower cost or density. Sometimes the term is used specifically to mean particulate additives.
Film Adhesive	An adhesive in the form of a thin, dry, resin film with or without a carrier, commonly used for adhesion between layers of laminates.
Flame Retardant	Certain chemicals that are used to reduce or eliminate a resin's tendency to burn.
Flash	Excess material which forms at the parting line of a mould or die, or which is extruded from a closed mould.
Flow	The movement of resin under pressure, allowing it to fill all parts of a mould; flow or creep the gradual but continuous distortion of a material under continued load, usually at high temperature.
Flow Line	A mark on a moulded piece made by the meeting of two flow fronts during moulding. (Also, 'striae', or 'weld-mark,' or 'weld-line.').
Fly	Loose filaments of fibre that have broken from their parent strand during processing and are freely floating in the air.
FRP	Acronym for fibre glass-reinforced or fibre-reinforced plastic, polymer or polyester.
Fuzz	Detached and broken glass fibre that has collected on processing equipment.
Gate	Where molten thermoplastic or liquid thermoset resin enters the cavity in a tool.
Gel	A partial cure of plastic resins; a semi-solid, jelly-like state similar to gelatin in consistency.
Gel Coat	A resin applied to the surface of a mould and gelled prior to lay-up. The gel coat becomes an integral part of the finished laminate, and is usually used to improve surface appearance and protect the laminate from the environment.
Gel Point	The stage at which a liquid begins to exhibit pseudo-elastic properties. (This stage may be conveniently observed from the inflection point on a viscosity-time plot). Also, called gel time. See also - Gel Time.
Gel Time	Time required to change a flowable liquid resin into a non-flowing gel.
GFRP	Glass fibre-reinforced plastic, polymer or polyester.
Glass Cloth	Conventionally woven glass fibre material; certain lightweight glass fabrics are also called scrims. See also - Scrim.
Glass Content	Percentage of glass in the compound.
Glass Fibre	Reinforcing fibre made by drawing molten glass through bushings. The predominant reinforcement for polymer matrix composites, it is known for good strength, processability and low cost.
Glass Resin Ratio	The amount of glass by weight compared to the amount of resin by weight in a finished laminate or moulding.
Glass Rich	An area of moulded part that has an overabundance of glass reinforcement. The reinforcement may appear dry and un-wet with the resin.
Glint	A visual defect in a fibreglass reinforced cured organic (usually corrosion resistant resin) panel. The defect appears as many small visible un-wet or foreign substances; a salt and pepper effect. The defect is not visible before cure but appears at exotherm of the panel.
Graphite Fibres	This term is used interchangeably with carbon fibres throughout the industry.
Green Strength	The strength of a freshly moulded part that hasn't completely cured.
GRP	Glass-Reinforced Plastic, polymer or polyester.
Gun Roving	A special type of roving reinforcement designed for use in a gun or chopper gun.
Hand Lay-Up	A fabrication method in which reinforcement layers are placed in mould by hand, saturated with resin and then cured to the formed shape.
Hardener	A substance or mixture added to a plastic composition to promote or control the curing action by taking part in it.
Honeycomb	Lightweight, cellular structure made from either metallic sheet materials or non-metallic materials (e.g., resin-impregnated paper or woven fabric) and formed into hexagonal nested cells, similar in appearance to the cross section of a beehive, that serves as a core material in sandwich constructions. Honeycomb may also be metallic or polymer materials in a rigid, open-cell structure.
Hybrid	A composite laminate comprised of laminae of two or more composite material systems, e.g., graphite and glass. It also applies to woven fabrics having more than one type of fibre.
Impregnate	In reinforced plastics, the saturation of the reinforcement with a resin.
Inclusion	A physical and mechanical discontinuity occurring within a material or part, usually consisting of solid, encapsulated foreign material. Inclusions are often capable of transmitting some structural stresses and energy fields, but in a noticeably different manner from the parent material.
Inhibitor	A substance that retards polymerisation, thus extending shelf life of a monomer. Also used to influence gel time and exotherm.
Injection Moulding	Method of forming a plastic to the desired shape by forcibly injecting the polymer into the mould.
Insert	An integral part of a plastics moulding consisting of metal or other material which may be moulded into position or pressed into the moulding after the moulding is completed.
Interface	The boundary or surface between two different, physically distinguishable media. On fibres, the contact area between fibres and sizing or finish. In a laminate, the contact area between the reinforcement and the laminating resin.
Inter-laminar	Existing or occurring between two or more adjacent laminae.
Isotropic	Having uniform properties in all directions. The measured properties of an isotropic material are independent of the axis of testing.
Kevlar?	Registered trademark of E.I. Dupont de Nemours, Inc. for a strong organic fibres with high strength-to-weight ratio. Often used for applications requiring high impact resistance. Generic term Aramid.
Knitted Fabric	A textile structure produced by inter-looping one or more ends of yarn or comparable material.
Laminate	A product made by bonding together two or more layers of material or materials. Primarily means a composite material system made with layers of fibre reinforcement in a resin. Sometimes used as a general reference for composites, regardless of how made. Examples of usage laminate consumption by market, compression-moulded laminate.
Laminate Orientation	The configuration of a cross-plied composite laminate with regard to the angles of cross plying, the number of laminae at each angle, and the exact sequence of the lamina lay-up.
Laminate Ply	One layer of a laminated product.
Land	The portion of a mould which provides the separation or cut-off of the flash from the moulded article; in the screw of an extruder, the bearing surface along the top of the flights; in an extrusion die, the surface parallel to the flow of material; in a semi-positive or flash mould, the horizontal bearing surface; in a two-piece mould, a platform build up to the split line.
Lay-Up	The reinforcing material placed in position in the mould. The process of placing the reinforcing material in position in the mould. The resin-impregnated reinforcement. A description of the component materials, geometry, and so forth, of a laminate.
Loft	The height of the glass lay-down either dry (as in chopping SMC glass) or wet (as in the height of the glass/resin mixture in a spray-up on the mould before roll-out).
Loom	A mechanical device that interlaces fibres at right angles with varying degrees of weave construction (weight, thickness and design). More modern looms are air jet but rapier and more traditional shuttle equipment is still in use.
Low Profile	Resin compounds formulated for low or zero shrinkage during moulding.
Low-Pressure Moulding	The distribution of relatively uniform low pressure (200 psi or less) over a resin-bearing fibrous assembly of cellulose, glass, asbestos, or other material, with or without application of heat from external source, to form a structure possessing definite physical properties.
Mandrel	The core around which paper-, fabric-, or resin-impregnated glass is wound to form pipes, tubes, or vessels; in extrusion, the central finger of a pipe or tubing die.
Mat	A fibrous reinforcing material comprised of chopped filaments (for chopped-strand mat) or swirled filaments (for continuous-strand mat) with a binder to maintain form; available in blankets of various widths, weights, and lengths.
Mat Binder	Resin applied to glass fibre and cured during the manufacture of mat, to hold the fibres in place and maintain the shape of the mat.
Mat Strength	Ability of the mat to resist being pulled apart under tension during impregnation and moulding.
Matched Metal Moulding	A reinforced plastics manufacturing process in which matching male and female metal moulds are used (such as compression moulding) to form the part, as opposed to low pressure laminating or spray-up.
Matrix	The material in which the fibre reinforcements of a composite system are embedded. Thermoplastic and thermoset resin systems can be used, as well as metal and ceramic.
Metal-Matrix Composites	Materials in which continuous carbon, silicon carbide, or ceramic fibres are embedded in a metallic matrix material.
Milled Fibre	Continuous glass strands hammer milled into very short glass fibres. Useful as inexpensive filler or anti-crazing reinforcing fillers for adhesives.
Mould	The cavity or matrix into or on which the plastic composition is placed and from which it takes form. To shape plastic parts or finished articles by heat and pressure. The assembly of all the parts that function collectively in the moulding process.
Mould Shrinkage	The immediate shrinkage which a moulded part undergoes when it is removed from a mould and cooled to room temperature; the difference in dimensions, expressed in inches per inch between a moulding and the mould cavity in which it was moulded (at normal temperature measurement); the incremental difference between the dimensions of the moulding and the mould from which it was made, expressed as a percentage of the dimensions of the mould.
Mould Surface	The side of a laminate that faced the mould (tool) during cure.
Moulding	The forming of a polymer or composite into a solid mass of prescribed shape and size by the application of pressure and heat for given times. Sometimes used to denote the finished part.
Moulding Compounds	Plastics in a wide range of forms to meet specific processing requirements. Granules or pellets are popular forms.
Moulding Cycle	The period of time occupied by the complete sequence of operations on a moulding press requisite for the production of one set of mouldings; the operations necessary to produce a set of mouldings without reference to the time taken.
Moulding Pressure,	The unit pressure applied to the moulding material in the mould. The area is
Compression	calculated from the projected area taken at right angles to the direction of applied force and includes all areas under pressure during complete closing of the mould. The unit pressure is calculated by dividing the total force applied by this projected area, and is expressed in pounds per square inch.
Mould-Release Agent	A lubricant, liquid, or powder (often silicone oils and waxes), used to prevent sticking of moulded articles in the cavity.
Monomer	A simple molecule which is capable of reacting with like or unlike molecules to form a polymer; the smallest repeating structure of a polymer; for addition polymers, this represents the original un-polymerised compound.
Multi-filament	A yarn consisting of many continuous filaments.
Multiple-Cavity Mould	A mould with two or more mould impressions; that is, a mould which produces more than one moulding per moulding cycle.
Nol Ring	A parallel filament wound test specimen used for measuring various mechanical strength properties of the material by testing the entire ring, or segments of it.
Non-Woven Fabric	A textile structure produced by bonding or interlocking of fibres, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.
One-Part Resin System	A resin system (often used in resin transfer moulding) in which the neat resin and catalyst are mixed together by the material supplier as part of the resin production operation.
Orange Peel	An uneven surface somewhat resembling that of an orange peel; said of mouldings that have unintentionally ragged surfaces.
Oriented Materials	Composites whose constituents are aligned in a particular way.
Out Time	The time a pre-preg is exposed to ambient temperature, namely, the total amount of time the pre-preg is out of the freezer. The primary effects of our time are to decrease the drape and tack of the pre-preg while also allowing it to absorb moisture from the air.
Pan Fibres	Carbon reinforcement fibre derived from the controlled pyrolysis of poly (acrylonitrile) fibre.
Parting Line	A mark on a moulded piece where the sections of a mould have met in closing.
PBT	Polybutylene Terephthalate (Thermoplastic Polyester Resin).
Peel Ply	Layer of material applied to a pre-preg lay-up surface that is removed from the cured laminate prior to bonding operations and leaves a clean resin-rich surface ready for bonding.
Peel Strength	Adhesive bond strength, as in pounds per inch of width, obtained by a stress applied in a peeling mode.
PET	Polyethylene Terephthalate (Thermoplastic Polyester Resin).
Pinhole	A tiny hole in the surface of, or through, a plastic material; usually occurring in multiples.
Pit	Small regular or irregular crater in the surface of a plastic, usually with width approximately of the same order of magnitude as its depth.
Pitch	A residual petroleum product used in the manufacture of certain carbon fibres.
Plain Weave	A weaving pattern in which the warp and fill fibres alternate; that is, the repeat pattern is warp/fill/warp/fill, and so on. Both faces of a plain weave are identical. Properties are significantly reduced relative to a weaving pattern with fewer crossovers.
Plastic	A material that contains as an essential ingredient an organic substance of large molecular weight, is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow; made of plastic.
Platens	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. (Synonyms folded yarn, formed yarn.)
Ply	In general, fabrics or felts consisting of one or more layers (laminates, and so forth). The layers that make up a stack. Yarn resulting from twisting operations (three-ply yarn, and so forth). A single layer of pre-preg. A single pass in filament winding (two plies forming one layer).
Polyacrylonitrile (PAN)	A product used as a base material in the manufacture of certain carbon fibres.
Polyamide	A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fibre-forming.
Polyester Combination Yarn	A polyester/fibre glass hybrid yarn.
Polyesters	Thermosetting resins, produced by dissolving unsaturated, generally linear, alkyd resins in a vinyl-type active monomer such as styrene, methyl styrene, and diallyl phthalate. Cure is effected through vinyl polymerisation using peroxide catalysts and promoters, or heat, to accelerate the reaction. The resins are usually furnished in solution form, but powdered solids are also available.
Polymer	A very large molecule formed by combining a large number of smaller molecules, called monomers, in a regular pattern.
Polymerisation	A chemical reaction in which the molecules of monomers are linked together to form polymers.
Porosity	The presence of visible voids within a solid material into which either air or liquids can pass.
Positive Mould	A mould designed to apply pressure to a piece being moulded with no escape of material.
Post-Cure	Additional elevated temperature cure, usually without pressure, to improve final properties and/or complete the cure. In certain resins, complete cure and ultimate mechanical properties are attained only by exposure of the cured resin to higher temperatures than those of curing.
Pot Life	The length of time a catalysed thermosetting resin system retains a viscosity low enough for it to be suitable for processing.
PPO	Polyphenylene Oxide (Thermoplastic Resin).
PPS	Polyphenylene Sulfide (Thermoplastic Resin).
Precursor	For carbon fibres, the rayon, PAN, or pitch fibres from which carbon fibres are made.
Preform	A pre-shaped fibrous reinforcement formed by distribution of chopped fibres by air, water flotation, or vacuum over the surface of a perforated screen to the approximate contour and thickness desired in the finished part. Also, a pre-shaped fibrous reinforcement of mat or cloth formed to desired shape on a mandrel or mock-up prior to being placed in a mould press. Also, a compact "pill" formed by compressing pre-mixed material to facilitate handling and control of uniformity of charges for mould loading.
Pregel	An unintentional extra layer of cured resin on part of the surface of a reinforced plastic. (Not relating to 'gel coat.')
Pre-Mix	A moulding compound prepared prior to and apart from the moulding operations and containing all components required for moulding resin, reinforcement, fillers, catalysts, release agents, and other compounds.
Pre-Preg	Ready-to-mould material in sheet form, which may be cloth, mat, or paper pre-impregnated with resin and stored for use. The resin is partially cured to a 'B' stage and supplied to the fabricator who lays up the finished shape and completes the cure with heat and pressure.
Pressure Bag Moulding	A process for moulding 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 provided by compressed air or water, is placed against the bag, and the part is cured.
Pressure Intensifier	A layer of flexible material (usually a high-temperature rubber) used to ensure the application of sufficient pressure to a location, such as a radius, in a lay-up being cured.
Primer	A coating applied to a surface, before the application of an adhesive, lacquer, enamel, and so forth, to improve the adhesion performance or load-carrying ability of the bond.
Processing Window	The range of processing conditions, such as stock (melt) temperature, pressure, shear rate, and so on, within which a particular grade of plastic can be fabricated with optimum or acceptable properties by a particular fabricating process.
Pultrusion	An automated, continuous process for manufacturing composite rods, tubes and structural shapes having a constant cross section. Roving and other reinforcements are saturated with resin and continuously pulled through a heated die, where the part is formed and cured. The cured part is then cut to length.
Quasi-Isotropic	Approximating isotropy by orientation of plies in several directions.
Reinforcement	A material added to the matrix to provide the required properties; ranges from short fibres through complex textile complex textile forms.
Release Agent	Materials that are used to prevent cured matrix material from bonding to tooling.
Release Film	An impermeable layer of film that does not bond to the resin being cured. See also - Separator.
Resin	A material, generally a polymer that has an indefinite and often high molecular weight and a softening or melting range and exhibits a tendency to flow when it is subjected to stress. Resins are used as the matrices to bind together the reinforcement material in composites.
Resin Content	The amount of resin in a laminate expressed as either a percent of total weight or total volume.
Resin Rich	Localised area filled with excess resin as compared to consistent resin/fibre ratio.
Resin-Starved	Areas of insufficient resin, usually identified by low gloss, dry spots or fibre show.
Resin-Transfer Moulding	A moulding process in which catalysed resin is transferred into an enclosed
(RTM)	mould into which the fibre 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.
Roll-Out	A process used in spray-up and hand lay-up procedures where the resin and glass reinforcement are compacted to a uniform laminate with rollers.
Roving	A number of yarns, strands, tows, or ends collected into a parallel bundle with little or no twist.
RP	Reinforced plastic, polymer or polyester.
RTP	Sometimes used to distinguish reinforced thermoplastic from reinforced thermosetting plastic.
Rule-of-Mixtures	When combined, the properties of the composite material is some combination of the properties of the two constituent materials. The composite property equals the amount of the fibre property multiplied by the volume percentage of fibre, plus the amount of matrix property multiplied by the volume percentage of matrix.
S-Glass	A family of magnesium-alumina-silicate glasses with high mechanical strength.
SAN	Styrene Acrylonitrile (Thermoplastic Resin).
Sandwich Construction	A composite composed of lightweight core material (usually honeycomb or foamed plastic) to which two relatively thin, dense, high strength, functional, or decorative skins (also called faces) are adhered.
Scrim	A low-cost reinforcing fabric made from continuous filament yarn in an open-mesh construction. Used in the processing of tape or other B-stage material to facilitate handling. Also used as a carrier of adhesive, to be used in secondary bonding.
Scrimp	Seamann Composite Resin Infusion Moulding Process.
Secondary Bonding	The joining together, by the process of adhesive bonding, of two or more already cured composite parts, during which the only chemical or thermal reaction occurring is the curing of the adhesive itself.
Separator	A permeable layer that also acts as a release film. Porous Teflon-coated fibreglass is an example. Often placed between lay-up and bleeder to facilitate bleeder system removal from laminate after cure.
Set Up	To harden, as in curing of a polymer resin.
Shear	An action or stress resulting from applied forces which 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. Inter laminar Shear (ILS). The plane of contact is composed of resin only.
Shear Edge	The cut-off edge of the mould.
Shear Strength	The maximum shear stress that a material is capable of sustaining. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original cross-sectional area of the specimen.
Sheet Moulding Compound	A ready-to-mould glass fibre reinforced polyester material primarily used in
(SMC)	compression moulding.
Shelf Life	The length of time a material, substance, product, or reagent can be stored under specified environmental conditions and continue to meet all applicable specification requirements and/or remain suitable for its intended function.
Short Beam Shear (SBS)	A flexural test of a specimen having a low test span-to-thickness ratio (for example, 4:1), such that failure is primarily in shear.
Shrinkage	The relative change in dimension between the length measured on the mould when it is cold and the length on the moulded object 24 hours after it has been taken out of the mould.
Silicon Carbide Fibre	A reinforcing fibre with high strength and modulus; density is equal to that of aluminium. It is used in organic metal-matrix composites.
Single Yarn	The simplest strand of textile material suitable for operations such as weaving, knitting, etc.
Sink Mark	A shallow depression or dimple on the surface of an injection moulded part due to collapsing of the surface following local internal shrinkage after the gate seals; an incipient short shot.
Size	The treatment applied to the glass fibre to allow the resin and glass to adhere to one another. Also allows glass fibre to be conveniently handled.
Skin	A layer of relatively dense material used in a sandwich construction of the surface of the core.
Soft Glass	A roving product whose sizing is moderately soluble in acetone or styrene, which results in the tendency of the bundles to open readily or filamentise the matrix resin. The size is generally between 50% and 80% soluble in acetone.
Specimen	An individual piece or portion of a sample used to make a specific test; of specific shape and dimensions.
Splice	The joining of two ends of yarn by intertwining, knotting, overlapping or adhering them together.
Split Mould	A mould in which the cavity is formed of two or more components held together by an outer chase. The components are known as splits.
Spray Pattern	In connection with the spray-up process (see below), it refers to the width and uniformity of the fan of resin and glass while it is travelling between the gun and the mould. See also - Spray-Up.
Spray-Up	Techniques 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. In foamed plastics, very fast-reacting urethane foams or epoxy foams are fed in liquid streams to the gun and sprayed on the surface. On contact, the liquid starts to foam.
Stacking Sequence	A description of a laminate that details the ply orientations and their sequence in the laminate.
Staple	Filaments produced in short lengths from the bushing (usually less than 17 inches), to be gathered into strands or sliver. (See Continuous Filament.)
Starved Area	An area in a plastic part that has an insufficient amount of resin to wet out the reinforcement completely. This condition may be due to improper wetting or impregnation or excessive moulding pressure.
Storage Life	The period of time during which a liquid resin or packaged adhesive can be stored under specified temperature conditions and remain suitable for use. (Also 'shelf life.') See also - Shelf Life.
Strand	Normally an untwisted bundle or assembly of continuous filaments used as a unit, including slivers, tows, ends, yarn, and so forth. Sometimes a single fibre or filament is called a strand.
Strand Count	The number of strands in a plied yarn; the number of strands in a roving. U.S. Yardage System; the length, in hundreds of yards, of a single strand having a mass of one pound. European TEX System; the mass, in grams, of a strand 1000 meters in length.
Strand Integrity	Relating to the ability of the size to keep all the filaments of a bundle stuck together during chopping. Good strand integrity is required for good flow in or wet-through and wet-out on the mould.
Structural Adhesive	Adhesive used for transferring required loads between adherends exposed to service environments typical for the structure involved.
Structural	Bond-A bond that joins basic load-bearing parts of an assembly. The load may be either static or dynamic.
Styrene Monomer	A water-thin liquid monomer used to thin polyester resins and act as the crosslinking agent.
Surface Preparation	Physical and/or chemical preparation of an adherend to make it suitable for adhesive bonding.
Surfacing Mat	A very thin mat, usually 7 to 20 mils thick, of highly filamentised fibreglass used primarily to produce a smooth surface on a reinforced plastic laminate.
Tack	Stickiness of an adhesive or filament reinforced resin pre-preg material.
Tenacity	The term generally used in yarn manufacture and textile engineering to denote the strength of a yarn or of a filament of a given size. Numerically it is the grams of breaking force per denier unit of yarn or filament size; grams per denier, gpd. The yarn is usually pulled at the rate of 12 inches per minute. Tenacity equals breaking strength (grams) divided by denier.

Tension Device	A mechanical or magnetic device that controls tension.
Tex	A unit for expressing linear density, equal to the mass in grams of 1 km of yarn, filament, fibre or other textile strand.
Texturised Glass Yarn	A yarn processed from continuous filament yarn in such a manner to induce bulk to the yarn by disorientation of the filaments.
Thermoplastic	Capable of being repeatedly softened by an increase of temperature and hardened by an increase in temperature. Applicable to those materials whose change upon heating is substantially physical rather than chemical and that in the softened stage can be shaped by flow into articles by moulding or extrusion.
Thermoset	A material that will undergo a chemical reaction caused by heat, catalyst, etc., leading to the formation of a solid. Once it becomes a solid, it cannot be reformed.
Thickeners	Material added to the resin to thicken it or raise the viscosity index of the resin so that it will not flow as readily.
Thixotropic, Thixotropy	Concerning materials that are gel-like at rest but fluid when agitated.
Thread Count	The number of yarns (threads) per inch in either the lengthwise (warp) or crosswise (fill or weft) direction of woven fabrics.
Tow	An untwisted bundle of continuous filaments (usually carbon) usually designated by a number followed by K, indicating multiplication by 1,000 (for example, 12K tow has 12,000 filaments).
Tracer	A fibre, tow, or yarn added to a pre-preg for verifying fibre alignment and, in the case of woven materials, for distinguishing warp fibres from fill fibres.
Ultrasonic Testing	A non-destructive test applied to materials for the purpose of locating internal flaws or structural discontinuities by the use of high-frequency reflection or attenuation (ultrasonic beam).
Unidirectional	Refers to fibres that are oriented in the same direction, such as unidirectional fabric, tape, or laminate, often called UD.
Vacuum Bag Moulding	A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed over the lay-up on the mould and sealed at the edges. A vacuum is applied between the sheet and the lay-up. The entrapped air is mechanically worked out of the lay-up and removed by the vacuum, and the part is cured with temperature, pressure, and time. Also called bag moulding. See also - Bag Moulding.
Vacuum-Assisted Resin	An infusion process where a vacuum draws resin into a one-sided mould. A cover,
Transfer Moulding (VARTM)	either rigid or flexible is placed over the top to form a vacuum-tight seal.
Veil	An ultra thin mat similar to a surface mat, often composed of organic fibres as well as glass fibres.
Vent	A small hole or shallow channel in a mould that allows air or gas to exit as the moulding material enters.
Void	A physical and mechanical discontinuity occurring within a material or part which may be two-dimensional (e.g., disbonds, delaminations) or three-dimensional (e.g., vacuum-, air-, or gas-filled pockets). Porosity is an aggregation of micro-voids. Voids are essentially incapable of transmitting structural stresses or non-radiative energy fields. (See Inclusion.)
Void Content	Volume percentage of voids, usually less than 1% in a properly cured composite. The experimental determination is indirect, that is, calculated from the measured density of a cured laminate and the "theoretical" density of the starting material.
Volatiles	Materials, such as water and alcohol, in a sizing or a resin formulation, that are capable of being driven off as a vapour at room temperature or at a slightly elevated temperature.
Warp	The yarn running lengthwise in a woven fabric. A group of yarns in long lengths and approximately parallel. A change in dimension of a cured laminate from its original moulded shape.
Weave	Pattern by which a fabric is formed from interlacing yarns. In a plain weave, the warp and fill fibres alternate to make both fabric faces identical. In a satin weave, the pattern produces a satin appearance with the warp roving crossing over several fill rovings and under the next one (e.g., eight-harness satin would have warp roving over seven fill rovings and under the eighth).
Weft	The system of yarns running crosswise in a fabric. Also known as fill.
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 Winding	Filament winding wherein fibre strands are impregnated with resin immediately before they contact the mandrel.
Wet-Out	The degree and/or rate at which each individual filament is "wet" or encapsulated by the matrix polymer resin in a composite sheet. Relates to the ability of the polymer matrix resin system to move through the glass fibre bed and to attain complete encapsulation of each individual filament. A measure of the wetability of the sized glass fibre surface.
Whisker	A short single crystal fibre or filament. Whisker diameters range from 1 to 25 microns, with aspect ratios between 100 and 15,000.
Working Life	The period of time during which a liquid resin or adhesive, after mixing with catalyst, solvent, or other compounding ingredients, remains useable.
Woven Roving	A heavy glass fibre fabric made by the weaving of roving.
Wrinkle	A surface imperfection in laminated plastics that has the appearance of a crease or fold in one or more outer sheets of the paper, fabric, or other base, which has been pressed in. Also occurs in vacuum bag moulding when the bag is improperly placed, causing a crease.
X-Axis	The axis in the plane of the laminate used

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