Glossary of composites manufacturing terms

Lecture PowerPoint

Review papers

Subject Index

Principal sources:.

• Anon., Boiler and Pressure Vessel Code, Section X: Fibreglass-Reinforced Plastic Pressure Vessels, American Society of Mechanical Engineers, New York 10017, 1986.
• WD Callister, Materials Science and Engineering: an introduction - fifth edition, John Wiley, New York, 2000.  ISBN 0-471-32013-7.
• NP Cheremisinoff and PN Cheremisinoff, Fibreglass-Reinforced Plastics Deskbook, Ann Arbor Science Publishers, Ann Arbor MI-48106, 1978.
• G Eckold. Design and Manufacture of Composite Structures, Woodhead, Cambridge, 1994.  ISBN 1-85573-051-0.
• CA Farnfield and PJ Alvey (editors), Textile Terms and Definitions (seventh edition), The Textile Institute, Manchester, 1975.
• DA Garvin, Managing Quality: the Strategic and Competitive Edge, The Free Press (Macmillan), New York and London, 1988.
• D Hull and TW Clyne, An Introduction to Composite Materials - second edition, Cambridge University Press, Cambridge, 1996.  ISBN 0-521-38855-4.
• ISO 8402 (1986) [BS 4778]: Quality vocabulary, Part 1: International terms, British Standards Institution, London, 1987. BS 4778: Part 2: National terms, BSI Handbook 22: Quality Assurance, Fourth Revision, May 1990, pages 15-40.
• S Lynch, Characteristics and performance of tooling fixtures for curing fibre reinforced thermosetting composites, Royal Aircraft Establishment Technical Memorandum MAT/STR 1091, Farnborough UK, 28 April 1987.
• JJ Morena, Advanced Composites World Reference Dictionary, Krieger, Malabar FL, 1997.  ISBN 0-89464-991-4.
• HE Pebly, Glossary of terms, In TJ Reinhart (editor): "Engineered Materials Handbook, Volume 1: Composites, ASM International, Metals Park OH-44073, 1987.
• LR Whittington, Whittington's Dictionary of Plastics, Technomic Publishing Co Inc, Westport CT-06880, 1978.

• A-glass: high alkali grade glass fibres, originally made from window glass (72% silica, 15% sodium oxide, 10% calcium oxide), with poor resistance to water in reinforcement form.
• A-stage: the initial stage in the reaction of thermosetting resins, in which the material is still soluble and fusible.  Also known as resol in phenolic resin systems.
• ABL bottle: an internal-pressure vessel (approx. 610 mm long by 460 mm diameter) used to test the quality and properties of filament-wound material.
• Accelerator: a substance that hastens the solidification of catalyzed thermosetting resin.
• Activation: chemical process to make a surface more receptive to bonding.
• Adherend: a component or body held to another body by an adhesive.
• Adhesive: a material which bonds parts together, usually applied as a liquid, melt, solution, or paste and caused to harden by chemical reaction, cooling or solvent evaporation.
• Alkyd resin: polyester resin with recurrent ester groups in the backbone chain and ester groups in the cross-links between chains.
• Alugatoring: wrinkling of gel coat during lamination.
• Anaerobic adhesive: an adhesive which cures only in the absence of air after being confined by the assembled parts.
• Appraisal costs: the cost of assessing the quality achieved.
• Areal weight: the weight of a tape or fabric per unit area.
• Autoclave: a closed vessel capable of controlled application of heat and pressure, used for curing pressure-bagged composites.
• Axial winding: in filament winding, the placement of fibres parallel to the longitudinal (mandrel rotation) axis.  Zero degrees helix angle.

• B-stage: an intermediate stage in the reaction of thermosetting resins, in which the material swells when in contact with certain liquids and softens when heated, but does not entirely dissolve or fuse.  The resin   in an uncured prepreg or premix is usually at this stage.  Also known as resitol in phenolic resin systems.
• Back pressure: resistance of a material, due to the viscosity, to continued flow when the mould is closing.
• Bagging: application of a sealed impermeable bag over an uncured part to allow additional consolidation by evacuation or external pressure.
• Balanced design: a laminate stacking sequence or filament winding pattern designed to produce equal stresses in all filaments.
• Balanced laminate: a laminate in which the stacking sequence is arranged such that the plate does not distort due to residual stresses built in during curing.
• Band density: the quantity of fibreglass reinforcement per 25.4 mm (inch) of bandwidth, expressed as strands (or filaments) per inch in filament winding.
• Band thickness: the thickness of the reinforcement as applied to the mandrel in filament winding.
• Bandwidth: the width of the reinforcement as applied to the mandrel in filament winding.
• Bias fibres: fibres at angles to the length of the fabric.
• Biaxial winding: a form of filament winding in which a helical band is laid in sequence, side-by-side, eliminating crossover of the fibres.
• Binder: polymer applied to hold together the fibres of mat reinforcements.
• Birds nest: entanglement of fibres in filament winding or pultrusion, usually around feed eyes.
• Bleeder cloth: a woven or non-woven layer of material used in bagging to soak up excess resin (may also serve as breather fabric).
• Bleedout: the excess resin that migrates to the surface of a laminate or filament wound component.
• Bloom: visible exudation of plasticiser or lubricant at the surface.
• BMC: Bulk Moulding Compound.
• Bobbin: a cylindrical or slightly tapered barrel, with or without flanges, for holding rovings or yarns.
• Bolted joints: attachment of sub-assemblies using mechanical fasteners.
• Bonded store: a secure place in which only those supplies that have been accepted as satisfactory by the inspection staff should be held.
• Bonding: to attach materials with adhesive compounds.
• Braiding: the process of interlacing three or more threads in such a way that they cross one another and are laid down in a diagonal formation.  Tubular, flat or solid constructions may be formed.
• Breather cloth: a woven or non-woven layer of material used in bagging to permit the escape of volatiles and entrapped air (may also serve as bleeder cloth).
• Bridging: condition in which fibres do not conform to the radii of concave corners during moulding or filament winding, resulting in poor dimensional tolerances, resin rich areas and voids.
• Bulk moulding compound (BMC): thermosetting resin mixed with short fibre reinforcement for compression or injection moulding.
• Bushing: the unit through which molten glass is drawn in making glass fibres.

• C-glass: chemical grade glass fibres (65% silica, 14% calcium oxide, 8% sodium oxide) with good resistance to acids.
• C-stage: the final stage in the reaction of thermosetting resins, in which the material is relatively insoluble and infusible.  The resin in a fully cured thermoset moulding is at this stage.  Also known as resit in phenolic resin systems.
• Cast: to form a material into shape by pouring it into a mould and allowing it to harden without external pressure.
• Cast tooling: any tool manufactured by the casting method.
• Catalyst: a reactive chemical which is mixed with a resin to produce a cured thermoset.
• Catenary: the tendency of some strands in a taut horizontal roving to sag lower than others.  A measure of the evenness of strand length (and indirectly of fibre winding tension) in a specified length of roving.
• Caul plate: a plate located to the top of a component during cure to achieve a uniform pressure distribution.  Also known as slave skin.
• Cavity: the portion of a mould which defines the outer surface of a part.
• Centrifugal casting: process for the production of tubular components, in which resin and reinforcement are applied to the inside of a heated rotating mould.
• Chopped strand mat (CSM): glass fibre reinforcement consisting of strands of fibres chopped into short (between 3-12 mm) lengths and bonded to form a planar mat.
• Circuit: one complete traverse of the fibre feed mechanism of a filament winding machine.  One complete traverse of a filament-winding band from an arbitrary point along the winding path to another point on a plane through the starting point and perpendicular to the axis.
• Circs: hoop windings.
• Circumferential winding: filament winding which is essentially perpendicular to the axis.  Ninety degree or level winding.
• Clairaut condition: that the product of the instantaneous radius and the sine of the filament winding angle is constant for (usually) a dome-ended cylinder.
• Class A surface: high-gloss finish specified for the automotive industry.
• Closed-cell foam: cellular material without interconnecting passages.
• Closing speed: the rate of approach of the two mould halves.
• Closure: complete coverage of the mandrel in filament winding.
• Co-curing: simultaneously curing a laminate whilst bonding it to another sub-assembly.
• Coextrusion: the process of extruding two or more materials through a single die with two orifices arranged so that the extrudates merge and weld together in a laminar structure before chilling.
• Co-mingled: the close inter-mixing of (usually) reinforcement and thermoplastic matrix fibres within a single tow.
• Cohesion: forces holding together two pieces of the same material .
• Coinjection: a process similar in results to the coextrusion process, but performed by modifications of the injection moulding process.
• Collimated roving: roving with better strand parallelism than standard roving.
• Commingled: see Co-mingled.
• Compact winding: see Biaxial winding.
• Compaction: application of a temporary vacuum-bag (usually without heat) to compact a partial lay-up and remove entrapped air.
• Compatibility: the suitability of the size or surface finish on a fibre for use with a particular resin type.
• Composite tooling: any mould tool manufactured with plastic composite materials.
• Compression moulding: process for shaping composites by loading a mould face with fibres and resin (or pre-pregs) and using a second mould face to define the other surface.  Heat and pressure are applied to achieve cure and the required dimensions in the finished part.
• Concession (international quality term): written authorisation to use or release a quantity of material, components or stores already produced but which do not conform to the specified requirements.
• Conditioning: subjecting material to prescribed environmental conditions before lay-up.
• Conformability: the ability of a fabric to be formed to follow a double curvature (cf.: drape).
• Conformity: the fulfilment of a specified requirement by a quality characteristic of an item or service.
• Consolidation: application of pressure to achieve higher density product.
• Contact moulding: a process for moulding reinforced plastics/composites in which the reinforcement and resin are placed on the mould.  Cure may be either at room temperature using a catalyst promoter system or by heat in an oven.  No additional pressure is used.
• Continuous fibre: reinforcement which is as long as the component being manufactured.
• Control chart: a chart with upper and/or lower control limits on which are plotted values of some statistical measures for a series of samples or subgroups.  The chart frequently shows a central line to assist detection of a trend of plotted values towards either control limit.
• Control limits: limits on a control chart that are used as criteria for action, or for judging whether a set of data does or does not indicate lack of control.
• Core: the portion of a mould that forms the inner surfaces of a moulded product, or a (usually lightweight) material or former contained within the final part.
• COSHH: UK Control of Substances Hazardous to Health Regulations 1989.
• Coupling agent: that part of the size or surface finish on a fibre which is designed to promote good bonding between the fibre and the resin.
• Creel: an apparatus for holding a number of packages of strand, yarn, roving or tape.
• Crimp: the waviness of a fibre, usually when incorporated in a fabric.
• Critical length: the minimum length of a fibre which can fail at the fibre ultimate tensile strength when in a composite. Hull and Clyne state that the critical aspect ratio (CAR) may range from ~2-3 for a strong metallic matrix, or up to >100 for a polymer composite with poor interfacial bonding.  Eckold suggests that the majority of the equivalent unidirectional strength is developed at ~4 times CAR and the full strength potential of the composite is achieved for fibre lengths ~10 times CAR.  Callister gives a range for the CAR between 20-250 times the fibre diameter. 
• Cross-linking: formation of chemical links between long-chain molecules.
• Crosby, Philip B: quality guru.  Advocate of zero defects.
• Crowfoot weave: a warp-faced weave in which the binding places are arranged with a view to produce a smooth cloth surface free from twill, with a regular interlacing shift (cf..: satin weave).
• CSM: Chopped Strand Mat.
• Cure: to change the properties of a polymer by chemical reaction, usually by the addition of reactive chemicals or heat or both, with or without pressure.  The mechanism may be polymerisation, addition crosslinking, ring opening crosslinking or condensation chain extension/branching.
• Curing temperature: temperature to which a resin or assembly is subjected in order to cure the resin.
• Curing time: the period of time required for a resin undergoing cure to attain maximum properties.

• D-glass: reinforcement fibres with low dielectric constant, and hence good transparency to radar (75% silica, 22% boria).
• Dam: boundary support or ridge to prevent excessive run out from the laminate before or during cure.
• Dancer: a roller mounted on an axis which is moveable with respect to the axes of other rollers in an apparatus, used to control or measure the tension of a continuous length of material.
• Darcy's law: law governing viscous flow in which the permeability (in darcys) is proportional to viscosity, flow rate and media thickness and inversely proportional to pressure drop and cross sectional area.
• Daylight: the distance in the open position, between fixed and moving platens of a hydraulic press.  For multi-daylight presses it is the distance between adjacent platens.
• Deep-draw: a mould having a core that is long in relation to the width of the opening, or in relation to the wall thickness.
• Defect (international quality term): the nonfulfilment of intended usage requirements.
• Debulk: a step in the laminating process where laminate thickness is reduced by the application of pressure (often by vacuum-bagging) to remove air, volatiles, vapour and other reactants.
• Deflashing: removal of excess resin from edges of a newly demoulded part.
• Deming, W Edwards: quality guru.  Most famous of the American exponents of quality control techniques, demanding a rigorous and systematic approach to solving quality problems.
• Denier: the weight in grams of nine kilometres of fibre.
• Design review (international quality term): a formal, documented, comprehensive and systematic examination of a design to evaluate the design requirements and the capability of the design to meet these requirements and to identify problems and propose solutions.
• Deviation permit (international quality term): see Production permit.
• Displacement angle: the distance advanced along the equator by the ribbon after one complete circuit in filament winding.
• DMC: Dough Moulding Compound.
• Doctor blade or bar: device for regulating the amount of resin on rollers for impregnating rovings or fabrics.
• Doily: additional reinforcement for openings, particularly planar reinforcement added to a local area in filament winding where a cutout is to be made.
• Doubler: a local area with additional integrally filament-wound fibres.
• Dough moulding compound (DMC): a mixture (usually) of glass fibres, polyester resin, fillers, lubricants and catalysts with a dough-like consistency in the uncured or partially cured state.
• Dowel: pin to maintain alignment between various sections of a mould, or to define the path taken by rovings in filament winding or pultrusion.
• Draft: the taper or shape of a 'vertical' surface of a mould bed designed to facilitate removal of the moulded parts.  Angle of clearance.
• Drape: the natural ability of a fabric to follow a double curvature (cf.: conformability).
• Drop-off: a position at which the number of plies is reduced to compensate for narrowing of the component section.
• Dry winding: filament winding without liquid resin.  This may be either to produce dry preforms or using pre-impregnated tapes.
• Durometer hardness: hardness measured by the Shore Durometer.
• Dwell: a pause in the application of pressure or heat to allow the escape of volatiles or the achievement of a predetermined viscosity.
• Dwell (filament winding): the time that the traverse mechanism is stationary while the mandrel continues to rotate to the appropriate point for the traverse to begin a new pass.

• E-glass: electrical insulation grade glass fibres (54% silica, 18% CaO, 14% alumina, 8% boria).  The most common fibre for reinforced plastics.
• Economic quality: the economic level of quality at which the cost of securing higher quality would exceed the benefits of improved quality.
• Edge dam: boundary support or ridge to prevent excessive run out from the laminate before or during cure.
• Edge injection: in resin transfer moulding, the positioning of the inlet port such that resin flow is parallel to the laminate layers.
• Edge moulding: the technique of moulding the periphery of components to net finished size.
• Egg-box: the supporting sub-structure for a mould tool, fabricated as an interlocking box assembly.
• Ejector pins: Pins or dowels which assist in the removal of parts from the mould.
• Elastomeric: a rubbery material, either silicone or non-silicone bonded, that can be cast, fabricated or extruded to requirements.
• Electroform: method of mould manufacture in which metal is electroplated on the reverse pattern of the cavity.
• End: the smallest commercially available bundle of glass fibres.  A loosely bonded bundle of continuous fibres formed and sized together (cf. strand).
• Epoxy resins: thermosetting polymers cured by a ring opening mechanism.  The epoxy (oxirane) group is a three membered ring of two carbon atoms and one oxygen atom.  The glycidyl group is a methylene group adjacent to an oxirane group.
• Equator: the line, in filament winding, described by the junction of the cylindrical portion and the end dome.
• Exotherm: the heat evolved during cure.

• Fabric: a planar assembly of fibres interlaced by weaving, braiding or knitting.
• Fabricated tooling: a mould tool manufactured by mechanically fastening, bonding or welding component tool parts together.
• Faying surface: the surfaces of materials in contact with each other and joined or about to be joined together.
• Feigenbaum, Armand: quality guru.  Proposed 'total quality control' in 1956.
• Female mould: that portion of a mould which encloses the moulded article.  The mould cavity.
• Fibre: a unit of matter characterised by flexibility, fineness and a high ratio of length to thickness.
• Fibre placement: use of robotics or automated systems for pin winding of rovings or positioning of fibres into predefined slots.
• Filament: a fibre of indefinite length.
• Filament winding: a process in which continuous reinforcement is placed over a rotating form (mandrel) in a controlled manner.  Generally the shape is a surface of revolution.
• Fill: fibres at right angles to the warp of a woven fabric.
• Fill time: the time from the start of resin injection to complete filling of the mould.
• Fillet: filling the internal angle between two surfaces.
• Film stacking: early method for producing fibre reinforced thermoplastics in which layers of reinforcement were interleaved with the matrix materials in film form.  No longer widely practised due to the problems in adequate wetting of the fibres.
• Finish: a material applied to the surface of fibres to enhance the properties of the subsequent composite.
• FIT fibre: proprietary reinforced thermoplastic feedstock with reinforcement fibres and matrix powder enclosed in a tube of matrix polymer.
• Flash: excess material around the edges of a moulded article, removed immediately on ejection from the mould.
• Forming: part of the operation in which glass fibre strands are drawn from the bushing.
• Fusible mandrel: former for the manufacture of hollow objects which may be melted out after solidification of the composite.
• Fuzz: an accumulation of short broken filaments after passing strands, yarns or rovings over a contact surface.

• Gallery: a resin channel within a mould to provide a faster flow path than that achieved from a single inlet point.
• Gap: the space between successive filament windings which were intended to lie next to one another.
• Gel: the point at which the curing resin is no longer liquid yet has not fully become solid.  This is not a clearly defined transition.
• Gel coat: a coating designed to perfectly copy a surface, usually the required surface finish for a structure.  A smooth coloured pore-free surface on a moulded article which is integral with the laminate.
• Gel point: the stage at which the viscous liquid resin changes to a gelled rubbery form with pseudo-elastic properties.
• Gel time: the time at which gel occurs, usually measured as the time to reach a preset viscosity under defined conditions.
• Geodesic: the shortest distance between two points on a (curved) surface.
• Geoform: lattice structures produced by filament winding.
• Glass stress: the stress (usually in filament wound pressure vessels) calculated assuming that the load is only carried in the cross sectional area of the fibres with no contribution from the resin.
• Glass transition: the reversible change in an amorphous (region of) polymer from a viscous or rubbery state to a hard and relatively brittle state.
• Glass transition temperature (Tg): the approximate midpoint of the temperature range over which the glass transition takes place.
• Glycidyl group: a methylene group adjacent to an oxirane group.  See Epoxy resin.
• GMT: Glass Mat Thermoplastic.
• GPD: see Grams per denier.
• Grade (international quality term): an indicator of category or rank related to features or characteristics that cover   different sets of needs for products or services intended for the same functional use.
• Grams per denier (GPD): a measure of tenacity (qv).
• Green strength: the state in which cure is not complete, but at which the material can be removed from the mould and handled without tearing or permanent distortion.

• Hand lay-up: the process of placing and working successive plies of reinforcement into position on a mould by hand.
• Handling life: see Out-life.
• Hardener: compound or mixture which promotes curing.
• Harness satin: weaving pattern producing a satin appearance.  In an n-harness satin the warp crosses over (n-1) weft and under the nth weft.
• Helical winding: filament winding in which a filament band advances along a helical path, not necessarily at a constant angle, except in the case of a cylinder.
• High frequency heating: the heating of materials by dielectric loss in a high-frequency electromagnetic field.
• High pressure moulding: moulding processes using pressures above 14 bar.
• High speed resin transfer moulding (HSRTM): RTM systems with a production rate of one part per minute or faster.
• Honeycomb: resin impregnated sheet material, or metal foil, formed into a regular array of hexagonal cells.  Lightweight core material.
• Hoop winding: filament winding at 90 degrees to the axis of rotation.
• Hot isostatic pressing (HIP): Consolidation of a (metal matrix) composite preform under fluid pressure at high temperatures and pressures in a pressure vessel.
• HSRTM: High Speed Resin Transfer Moulding.

• Impingement mixing: injection of catalyst into resin by impacting the flow streams of the two components.
• Impregnation: the thorough wetting of fibres or cloth with resin.
• Inflatable mandrel: a former for filament winding, which maintains the required shape by internal pressure, and may be removed by releasing that pressure.
• Inhibitor: material that retards chemical reaction or curing.
• Initiators: free-radical crosslinking agents.
• Injection moulding: process for forming plastics by forcing the softened polymer at high pressure into a relatively cool cavity.
• Insert: any metal or plastic component included at lay-up or subsequently positioned, to allow location to other subassemblies.
• Inspection (international quality term): activities such as measuring, testing, gauging one or more characteristics of a product or service and comparing these with specified requirements to determine conformity.
• Intensifier: flexible material used to apply high pressures into tight radii during bag moulding operations.
• Inter-penetrating network (IPN): the combination of an easily processed brittle thermosetting resin with a thermoplastic polymer which is more difficult to process, such that a continuous path can be traced through the material in either component.  Properties are dependent on both of the constituent materials and on the phase morphology.
• Interface barrier: a material applied to the surface of a tool to prevent contamination during cure.
• IPN: Inter-Penetrating Network.
• Isotensoid: constant tension, particularly in filament winding.

• JIT: See Just-in-time.
• Juran, Joseph M: quality guru.  Author of 'Quality Control Handbook' (1951) which tackled the question "how much quality is enough?".
• Just-in-time (JIT) production methods: philosophy which argues that eliminating the buffers between manufacturing processes leads to improvements in both quality and productivity.

• Kerf: the width of a cut made by whatever means.
• Knit lines: a flaw on a moulded plastic article caused by the meeting of two flow fronts during the moulding operation.
• Knitted fabric: fabrics produced by inter-looping chains of yarn.
• Knuckle: the point at the end of a way-wound roving ball where the roving reverses its axial direction.

• L-direction: The (ribbon) direction of the continuous sheets in honeycomb.
• Laminate: the act of laying up successive plies of material.
• Lap: the amount of overlay between successive (filament) windings, intended to minimise gapping.
• Latin squares: as used by Fisher to design experiments for agricultural research is one of the basic statistical tools which aims to remove type variation from experimental error from two sources.
• Lattice pattern: in filament winding, a pattern with a fixed arrangement of open voids giving a basket weave effect.
• Lay: the orientation of filament wound ribbon, usually referenced to the axis of rotation.
• Lay-up: the sequential placing of reinforcements onto/into the mould, using either wet laminating or pre-preg systems.
• Level winding: see Circumferential winding.
• Liner: the continuous, usually flexible coating on the inside surface of a filament wound vessel, used to protect the laminate from chemical attack or to prevent leakage under stress.
• Long fibre: any (discontinuous) fibre of finite length greater than the critical length.
• Longos: low angle helical or longitudinal filament windings.
• Loop tenacity: the strength obtained by pulling two loops of the same fibre against each other to demonstrate the resistance to cutting or crushing.
• Lost core: see Fusible mandrel.
• Low pressure moulding: moulding or laminating between 1-14 atmospheres.
• Lubricant: a component of most fibre sizes to improve the handling and processing properties of the strand.

• M-glass: High (110 GPa) elastic modulus glass fibre (principally 54% silica, 13% calcium oxide) with high (8%) beryllia content.
• Macerate: to chop or shred fabric for use as filler.
• Machined tooling: any mould manufactured by cutting the tool face from a solid block.
• Male mould: that portion of a mould which is enclosed by the moulded article.
• Mandrel: the former onto which filament winding is undertaken.
• Manufacturing Resource Planning (MRP II): the expansion of MRP from being simply a planning tool to one that includes operational control and thereby forms a closed loop system which allows the entire product cycle to be analysed.
• Mat: a planar assembly of randomly oriented chopped fibres, or swirled continuous strands, of reinforcement with a binder.
• Matched metal moulding: use of metal male and female moulds, with heat and pressure, to form reinforced plastics parts.
• Materials Requirement Planning (MRP): a system, invariably computer-based, which uses demand information from the master production schedule, from bills of material, and from current inventory levels to determine the timing and quantity of orders to be placed or issued.
• Mathweb: lattice structures produced by filament winding.
• Maturation: increase and levelling off of viscosity OR storage of SMC to achieve a desired viscosity.
• Melt impregnation: the process of thoroughly wetting out reinforcement fibres with molten polymer.
• Metallic tooling: any mould manufactured from a metal block.
• Milled fibre: hammer milled very short glass fibres.
• Mixing ratio: the proportions, usually measured in parts by weight, of a base material and the corresponding hardener.
• Mock leno weave: a woven fabric with an open-mesh character resulting primarily from the weave interlacing sequence.
• Mohs hardness: measure of a scratch resistance of materials by comparison.
• Mooney equation: relates the viscosity of a concentrated suspension to the particle concentration and shape.
• Mould: any properly prepared surface against which a composite is cured.
• Moulding compounds: see BMC, DMC, SMC, TMC, XMC, ZMC.
• MRP: Materials Requirement Planning.
• MRP II: Manufacturing Resource Planning.
• Multi-circuit winding: filament winding which requires more than one circuit before the band repeats by laying adjacent to the first band.
• Multi-daylight: description of a press with more than one opening.

• Needled mat: a mat of short strands, felted together in a needle loom.
• Nesting: the placing of fabric such that the yarns of one ply lie in the valleys between yarns of an adjacent ply.
• Net shape: product produced without the need for trimming.
• Netting analysis: analysis of filament wound structures which assumes that the stresses induced in the structure are carried entirely by the filaments, with the strength of the resin neglected.  The filaments are assumed to carry only axial loads with no bending or shearing stiffness.
• Node: the connection between adjacent ribbons of honeycomb.
• NOL ring: a filament wound test specimen used to establish mechanical strength properties.  The ring is usually 146 mm internal diameter, 1.52 or 3.18 mm wall thickness and 6.35 mm wide, and may be tested whole or as segments.
• Nonconformity (international quality term): the nonfulfilment of specified requirements.
• Non-crimp fabrics: assemblies of reinforcement fibres in which the fibres are substantially linear without the crimp associated with weaving.  Typically one or more layers of reinforcement are held together by stitch-interlocking.
• Non-woven fabric: a planar textile structure produced by loosely compressing together fibres, yarns, rovings, etc with or without a scrim cloth carrier.

• Open-cell foam: cellular material with interconnecting passages.
• Orthogonal arrays: of which Latin Squares is one example, are used in Taguchi Methods, to design experiments which will provide the maximum information on the effect of variables from the minimum number of trials.
• Out-life: the period of time during which a pre-preg can be out of the freezer and remain suitable for use.
• Out-time: see Out-life.
• Ovaloid: a surface of revolution symmetrical about the polar axis which forms the end closure for a filament wound cylinder.
• Oxirane: a three membered ring of two carbon atoms and one oxygen atom.  See Epoxy resin.

• Package: Units of yarn or roving capable of being handled, transported and particularly unwound for use.
• Parting agent: see Release agent.
• Parting line: a mark on a moulding indicating where sections of the mould come together.
• Peel ply: a layer of open weave release material applied on the surface of a prepreg laminate, to maintain an uncontaminated surface until a subsequent bonding operation.
• Percolation: the flow of liquid through a confined series of pores .
• Permeability: parameter indicating the rate of diffusion of resin into a fabric stack during RTM.
• Phenolic: resins produced by the condensation reaction between phenols and aldehydes.  The latter is usually formaldehyde.
• Pick: a single weft thread in a cloth as woven.
• Pin winding: process similar to filament winding, or means of obtaining complex patterns in filament winding, where the fibres are wound around pins to define the fibre paths.
• Plain weave: the simplest of all weave interlacings in which odd warp threads operate over and under the weft threads and even warp threads operate under and over the weft threads throughout the fabric.
• Planar helix winding: filament winding in which the 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: filament winding in which the path lies on a plane which intersects the winding surface.
• Plasticiser: material added to a resin to facilitate compounding and improve flexibility and other properties of the end product.
• Platen: the mounting plate of a press, to which the mould is attached.
• Plied yarn: a yarn formed by twisting together two or more single yarns in one operation.
• Ply: an individual layer in a stack.
• Polar winding: a filament winding pattern in which the path passes tangentially over the opening at each pole of the winding.  A one circuit pattern is inherent in the system.
• Pole piece: (metal) reinforcement placed at the end of the major axis of a filament wound pressure vessel.
• Polyester: a general term for all polymers in which the main chain is formed by the esterification condensation of polyfunctional alcohols and acids.  In the reinforced plastics industry, a shortened term for 'unsaturated polyester resin'.
• Port: inlet or exit point on a mould.
• Post cure: a heat treatment, usually following initial polymerisation, used to improve the heat resistance of a plastic tool or composite part.
• Pot life: the time during which the reacting resin mix is usable.
• Preform: a coherent shaped mass of reinforcement fibres.
• Premix: the admixture of resin, catalyst, reinforcements and fillers to form a complete mix ready for moulding, usually not in a web or filamentous form (cf.: pre-preg).
• Pre-preg: a material comprising of cloth pre-impregnated with a resin system and possibly fillers etc (and usually cured to the B-stage).
• Pressclave: a simulated autoclave made by using the platens of a press to seal the ends of an open chamber, providing both the force to prevent loss of the pressurising medium and the heat required for laminate cure.
• Pressure bag moulding: a process 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 maintained against the bag during cure.
• Prevention costs: the cost of any action taken to investigate, prevent or reduce defects and failures.
• Process average: the average percentage defective or average number of defects per 100 items, whichever is applicable, submitted for original inspection.
• Process capability: the limits of inherent variability within which a machine tool or other process operates as governed by prevailing circumstances.
• Process control chart: see Control chart.
• Process quality control: that part of quality control that is concerned with maintaining process variability within the required limits.
• Processing window: the time during which resin viscosity lies within limits appropriate to the next process step.
• Product liability: a generic term used to describe the onus on a producer or others to make restitution for loss related to personal injury, property damage or other harm caused by a product or service.
• Product specification: the document that describes, for manufacturing purposes, the item concerned.
• Production permit (international quality term): written authorisation, prior to production or before provision of a service, to depart from specified requirements for a specified quantity or for a specified time.
• Promoter: alternative term for accelerator.
• Puckers: local separation of prepreg from the backing paper, as blisters.
• Pulforming: pultrusion with a subsequent forming operation to produce sections with curvature or non-constant cross section.
• Pullwinding: a combination of pultrusion with overwinding of additional fibres before entry to the curing die.
• Pultrusion: a continuous process for the production of composites with constant cross-sectional shape, by pulling the reinforcement through a resin bath and heated shaping die.

• Quality: the totality of features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs.
• Quality assurance: all those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality.
• Quality audit: a systematic and independent examination to determine whether quality activities and related results comply with planned arrangements and whether these arrangements are implemented effectively and are suitable to achieve objectives.
• Quality circles: consist of a small group of volunteers who meet regularly to identify and solve quality related problems that they have identified in their own work place.   The circle will then implement their solutions with management approval.
• Quality control: the operational techniques and activities that are used to fulfil requirements for quality.
• Quality control surveillance: see Control chart.
• Quality improvement team: group of people nominated by management to work on quality related problems selected by management (cf.: Quality Circles).
• Quality loop: conceptual model of interacting activities that influence the quality of a product or service in the various stages ranging from the identification of needs to the assessment of whether these needs have been satisfied.
• Quality management: the aspect of the overall management function that determines and implements the quality policy.
• Quality manual: a document setting out the general quality policies, procedures and practices of an organisation.
• Quality plan: a document setting out the specific practices, resources and sequence of activities relevant to a particular product, service, contract or project.
• Quality policy: the overall quality intentions and direction of an organisation as regards quality, as formally expressed by top management.
• Quality programme: a documented set of activities, resources and events serving to implement the quality system of an organisation.
• Quality related costs: the expenditure incurred in defect prevention and appraisal activities plus the loss due to internal or external failure.
• Quality spiral: see Quality loop.
• Quality surveillance: the continuing monitoring and verification of the status of procedures, methods, conditions, processes, products and services, and analysis of records in relation to stated references to ensure that specified requirements for quality are being met.
• Quality system: the organisational structure, responsibilities, procedures processes and resources for implementing quality management.
• Quality system review: a formal evaluation by top management of the status and adequacy of the quality system in relation to quality policy and new objectives resulting from changing circumstances.
• Quarantine store: a secure place in which all supplies therein await proof of compliance with specified requirements.

• R-glass: European equivalent of S-glass.  Easier to produce.
• Random pattern: filament winding with no fixed pattern.  A random pattern is approached if a large number of circuits are required for the pattern to repeat.
• Reaction injection moulding (RIM): injection moulding of activated thermosetting resins using lower pressures than for thermoplastics and (usually) a high-pressure impingement type mixing head.
• Reinforced reaction injection moulding (RRIM): the RIM process with reinforcement added to the mould.
• Release agent: a material which is applied in a thin film to prevent adhesion of curing resin to the mould surface.
• Release film: a sheet of material placed adjacent to a mould surface to minimise adhesion between the mould and the curing resin.
• Reliability (international quality term): the ability of an item to perform a required function under stated conditions for a stated period of time.
• Resin applicator: the device which deposits liquid resin onto the reinforcement band before filament winding or pultrusion.
• Resin content: the amount of resin in a laminate, expressed as either a ratio or percentage, by either volume or weight.
• Resin Infusion under Flexible Tooling (RIFT): vacuum-driven RTM with one splash or film tool face.
• Resin injection: see Resin transfer moulding.
• Resin transfer moulding (RTM): a process whereby catalysed resin is drawn or injected into a mould which has previously been filled with reinforcement.
• Resit: the C-stage in phenolic resin systems.
• Resitol: the B-stage in phenolic resin systems.
• Resol: the A-stage in phenolic resin systems.
• Reverse helical winding: a multi-circuit filament winding, in which the reinforcement band is laid down with reversal of the helix direction at the polar ends (cf.: biaxial, compact or sequential winding).
• Reynolds number: the ratio of (pipe internal diameter ✗ average velocity of flow ✗ density) to the viscosity, which determines whether the flow of a viscous liquid through a pipe is streamlined (values below 2100) or turbulent (values above 3000).
• Rheology: the study of flow, particularly of non-Newtonian liquids and plastic flow of solids.
• Ribbon width: see Bandwidth.
• Ribbonization: the degree of flattening of a sized roving, expressed as the ratio of ribbon width to thickness.
• RIFT: Resin Infusion under Flexible Tooling.
• RIM: Reaction Injection Moulding.
• Roller: a serrated tool used to compact the laminate and release trapped air or volatiles.
• Roving: a bundle of continuous untwisted parallel glass fibres.
• Roving ball: a package, usually cylindrically wound, of continuous roving.
• Roving ball build: the geometry of a roving ball, including a description of the waywind.
• Roving integrity: the degree of bond between the strands in a roving.
• RRIM: Reinforced Reaction Injection Moulding.
• RTM: Resin Transfer Moulding.

• S-glass: very high tensile strength glass filaments (65% silica, 25% alumina, 10% magnesia).  European equivalent is known as R-glass.
• S-twist: clockwise rotation as the twist approaches the reference point.
• Sandwich: panel composed of high strength/stiffness faces bonded to a lightweight core.
• Sateen weave: a weft-faced weave in which the binding places are arranged with a view to produce a smooth cloth surface free from twill (cf.: satin weave).
• Satin weave: a warp-faced weave in which the binding places are arranged with a view to produce a smooth cloth surface free from twill, with an irregular interlacing shift (cf.: crowfoot and sateen weave).
• Scarf joint: joint made by cutting away similar angular segments of the two adherends to be joined.
• Scrim: a low-cost reinforcing fabric made from continuous filament yarn in an open mesh construction.
• Secondary bonding: the joining of two or more sub-assemblies by adhesive bonding, laminate overlay, or other suitable means to form a larger component.
• SCRIMP: Seeman Composites Resin Infusion Manufacturing Process (a variant of RIFT patented in the USA).
• Selvedge: the woven-edge portion of a fabric parallel to the warp.
• Sequential winding: see Biaxial winding.
• Service liability (international quality term): see Product liability.
• Sheet moulding compound (SMC): a compounded sheet of fibres, (polyester) resin, pigments, fillers and other additives produced for subsequent compression moulding.
• Shelf life: the period of time during which a material can be stored under specific temperature conditions and remain suitable for use.
• Shell tooling: a mould or bonded fixture consisting of a contoured surface shell supported by a substructure which provides dimensional stability.
• Shelling: a term applied to loops of roving falling to the base of a roving ball as the roving is payed out.
• Shewhart, Walter A: quality guru.  Published 'Economic Control of Quality of Manufactured Product' in 1931, a watershed event for the quality movement.
• Short fibre: a length of fibre which is less than the critical length, and hence does not achieve full reinforcing efficiency.
• Short shot: injection of insufficient material to fill the mould .
• Shrinkage: the dimensional difference between the mould geometry and the cured component geometry.
• Single circuit winding: filament winding in which the filament path makes a complete traverse, and the following traverse lies immediately adjacent to the previous one.
• Size: the application of compounds to a strand, to form a more or less continuous film around the strand and the individual fibres.
• Sizing: the compounds applied to a strand to hold the bundle together, enhance the handling and processability, and promote good interfacial bonding.
• Skein: a continuous strand, yarn or roving wound up to some measured length and usually used to measure various physical properties of the material.
• Skirt: the material added to the end(s) of a filament wound bottle to provide attachment points for supports.  Extension of the cylindrical portion of a rocket motor case from the equator, used for interstage connections, usually wound as an integral part of the case.
• Slave skin: a plate located to the top of a component during cure to achieve a uniform pressure distribution.  Also known as caul plate.
• Slip angle: the angle at which tensioned fibre will slide off a filament wound dome.  The value is dependent on the fibre and resin system used.
• Slipper skin: a composite skin utilised in conjunction with metallic tooling to take account of thermal expansion between the tool and the component during cure.
• SMC: Sheet Moulding Compound.
• SMC-CR: Sheet Moulding Compound with both Continuous and Random fibres.
• SMC-R: Sheet Moulding Compound containing Random fibres.
• Solution impregnation: the process of thoroughly wetting out reinforcement fibres with a solution of polymer.
• SPC: Statistical Process Control.
• Specification (international quality term): the document that describes the requirements with which the product or service has to conform.
• SPI gel time: the interval of time between introduction of the catalyst to a thermosetting resin and the formation of a gel, as defined by the US Society of the Plastics Industry.
• Splice: the joining of two ends of a yarn or strand, by interlacing or adhesion.
• Splining: a method of engendering solid geometry from plane geometry.
• Spray-up: a process for laying down a combination of chopped glass fibres and initiated resin onto a contact mould.  The spray head usually chops continuous fibres to short lengths as the resin is sprayed.
• Spiral flow test: a measure of the mouldability of SMC.
• SQC: Statistical Quality Control.
• SRIM: Structural (reinforced) Reaction Injection Moulding.
• Staging: heating a premixed resin system to start cure, but stopping the reaction before the gel point, particularly in the production of pre-pregs.
• Stamping: the rapid application of force to sheet feedstock material to produce components of shallow depth.
• Staple fibre: short fibres of sufficient length to be spun into yarn.
• Statistical process control (SPC): that part of process control in which statistical techniques are used.
• Statistical quality control (SQC): that part of quality control in which statistical techniques are used.
• Strand: one of the individual components, namely a single, a two-fold, or a multi-fold yarn, of a cabled or folded construction.
• Strand count: the number of strands in a plied yarn or roving.
• Strand integrity: the degree of bond between the filaments in a strand.
• Strand length differential: see Catenary.
• Structural reaction injection moulding (SRIM): the moulding of finished parts by injection of polymerising monomers or prepolymers into a mould containing aligned fabric reinforcement (differs from RTM in that the resins used are typically polyurethanes or polyureas, rather than epoxy or polyester, and mould fill times are in seconds rather than minutes).
• Surface mat: a very thin mat, usually 0.175 - 0.5 mm thick, used at the surface of a laminate to ensure a smooth finish on the part.
• Surface tissue: a thin mat of fine fibres used primarily to produce a smooth surface on a reinforced plastic.
• Syneresis: contraction of a gel, observed by the separation of a liquid from the gel.
• Syntactic foam: composites of hollow microspheres and resin.

• Tack: the degree of stickiness of a material, especially of prepregs.
• Taguchi, Genichi: quality guru.  His 'loss function' measures losses a product imparts to society from the time it is shipped, and suggests that a broad distribution centred on the target dimension is preferable to a narrow distribution within the specification limit but centred off target.
• Taguchi methods: the statistical design of experiments and analysis of variance methods in industrial design and production.  An extension of Statistical Process Control back into the design stage for prototyping.
• Tangent line: any diameter at the equator of a filament wound bottle.
• Tangent point: any point on the equator of a filament wound bottle.
• Tape: narrow fabrics not greater than 305 mm wide.
• Tape laying: the automated placement of prepreg (thermoplastic or thermoset) tapes onto a mould surface.  Similar to filament winding, but without a rotating mandrel to maintain fibre tension.
• Template: a pattern used as a guide for cutting and laying plies.
• Tenacity: the breaking force in grams per unit denier of yarn or filament.
• Tension control: control of the speed of release of fibre from the bobbin achieved by magnetic or friction brakes, electronic rewind or rotating scissor bars.
• Tex: a unit in the ISO system for describing the linear density (mass/unit length of fibres, filaments and yarns.  One tex is one gram per kilometre.
• Tg: glass transition temperature (qv).
• Thermal expansion moulding: process in which elastomeric tooling details are constrained within a rigid frame to generate consolidation pressure by thermal expansion during the autoclave cure cycle.
• Thick moulding compound (TMC): Three-dimensional random moulding compound typically 6-50 mm thick.
• Thixotropy: the capacity of a liquid material to have high static shear strength (viscosity) and also low dynamic shear strength.  Such a material can be stirred/mixed, but will not flow under gravity.
• TMC: Thick Moulding Compound.
• Tool life: the number of processing operations (cures) which can be successfully carried out on a particular tool.
• Tool side: the side of a component that is cured against a (single-sided) tool.
• Tooling: the moulds used for part production.
• Tow: a large number of filaments collected together into a loose strand or assemblage, substantially without twist.
• TPI: Turns Per Inch.
• Traceability (international quality term): the ability to trace the history, application or location of an item or activity, or similar items or activities, by means of recorded identification.
• Tracer yarn: strand of coloured fibre distinct from the remainder of the roving package or fabric for quality checking.
• Tumble winder: filament winding machine with the mandrel mounted on a driven inclined axis with stationary roving strands.  The tumbling mandrel describes a polar winding path.
• Turns per inch (TPI): a measure of the amount of twist produced in a yarn during the conversion from the individual strands.
• Twill weave: a weave that repeats on three or more ends and picks and produces diagonal lines on the face of the cloth.
• Twist: the rotation of yarns about the strand axis per unit length.  The direction of twist may be either S (clockwise as the twist approaches the reference point) or Z (anticlockwise as the twist approaches the reference point).

• Undercure: a condition in which insufficient time and/or temperature was allowed in curing, resulting in inadequate hardening of the part.
• Undercut: any protuberance or indentation that impedes the withdrawal of a moulded part from a two-piece mould.
• Unsaturation: the presence of double (or triple) bonds in a compound, which may take part in addition polymerisation or crosslinking.

• Vacuum assisted resin injection (VARI): the process of loading fabric reinforcement into a mould, then causing resin to flow into the mould by the action of gravity or pressure assisted by evacuation of the mould followed by curing the resin before opening the mould.
• Vacuum bag: an impervious flexible film which contains the laminate or part under vacuum pressure whilst curing.
• Vacuum bagging: curing a laminate in an evacuated bag to allow the application of additional consolidation pressure.
• Vacuum impregnation: the process of loading reinforcement fibres into a mould then causing resin to flow into the mould by applying a vacuum, followed by curing the resin before opening the mould.
• Vacuum table: an impervious rubber film, usually mounted on a frame, which contains the laminate or part under vacuum pressure whilst curing.
• VARI: Vacuum Assisted Resin Injection.
• Veil: an ultrathin mat similar to a surface mat.
• Vent: a small hole or shallow channel in a mould to allow air or gas to exit as the material enters.
• Vent cloth: see Breather cloth.
• Vibroforming: the use of vibrating rollers during consolidation in contact moulding .
• Viscometry: the measurement of viscosity.
• Viscosity: the property of resistance to flow, expressed as the relationship between applied shearing stress and the resulting rate of strain in shear.
• Vitrification: the stage during cure when the resin changes from a gelled liquid or rubber state to a glass-like solid.  The vitrification point depends on the matrix conversion and indicates that the matrix glass transition temperature is equal to the cure temperature [Gillham, 1986].  Unlike the glass transition temperature this is a one-way change during cross-linking/manufacture of the composite.
• Volatile: materials in a roving sizing or resin formulation which are capable of being driven off as a vapour at ambient or elevated temperatures.
• Volume fraction: the proportion of one component relative to the whole body by volume.
• Volume percentage: the percentage of one component relative to the whole body by volume.

• Wafer: additional reinforcement for openings.
• Waiver (international quality term): see Concession.
• Wall stress: the stress (usually in filament wound pressure vessels) calculated using the load and the entire laminate cross sectional area.
• Warp: the lengthwise thread in a fabric as woven.  The fabric production direction.
• Warp knitting: a method of making a fabric by normal knitting in which the loops made by each warp thread are formed substantially along the length of the fabric.
• Warp-insertion weft knit fabric (WIWK): weft knitted fabric into which uncrimped warp fibres are inserted within the weft knitted loops.
• Waywind: the number of wraps or turns that an end or ends make from one side of the filament wound package back to the same side.
• Weave: the manner in which fibres are interlaced.
• Weft: the widthways thread in a fabric as woven.  The shuttle direction.
• Weft knitting: a method of making a fabric by normal knitting in which the loops made by each weft thread are formed substantially across the width of the fabric.
• Weft-insertion warp knit fabric (WIWK): warp knitted fabric into which uncrimped weft fibres are inserted within the warp knitted loops.
• Weight fraction: the proportion of one component relative to the whole body by weight.
• Weight percentage: the percentage of one component relative to the whole body by weight.
• Weld mark: a flaw on a moulded plastic article caused by the meeting of two flow fronts during the moulding operation.
• Wet lay-up: the application of liquid resin to each successive ply during laminating.
• Wet out: the achievement of complete impregnation of the interior of bundles of reinforcement fibres.
• Wet winding: filament winding with the reinforcement impregnated with liquid resin immediately before being laid down on the mandrel.
• Wetting: see Wet out.
• Whisker: a short single crystal fibre or filament used as reinforcement.  Usually between 1-25 μm diameter with an aspect ratio between 100-15000.
• Wind angle: the angle between the axis of rotation and filament wound fibres.
• Winding pattern: the total number of individual circuits required to begin repeating a filament winding path by laying down immediately adjacent to the initial circuit.  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: the tension on the reinforcement fibres during filament winding onto the mandrel.
• WIWK: Weft-Insertion Warp Knit fabric, or Warp-Insertion Weft Knit fabric.
• Witness: the arrival of resin at the exit port of a mould.
• Woof: see Weft.
• Woven fabric: interlaced yarns forming a planar mesh pattern.  Styles include plain, twill, satin and mock leno.
• Woven roving: a heavy glass fibre fabric made by weaving roving or yarn bundles.

• XMC: crossed-continuous fibre moulding compound.

• Yardage: number of yards per pound of fibre for yarn, roving or strand.  The reciprocal of weight per yard.
• Yarn: a product of substantial length and relatively small cross section of fibres or filaments, with or without twist.  One strand which has been twisted.  Two or more strands which have been plied.  A generic term for a continuous strand of textile fibres, filament or material in a form suitable for knitting, weaving or otherwise intertwining to form a fabric.
• Yarn construction: a term used to indicate the number of a single yarn and the number of strands combined to form each successive unit of a plied yarn or cord.
• Yield: the number of yards per pound of reinforcement.

• Z-twist: anticlockwise rotation as the twist approaches the reference point.
• Zero bleed: a laminate fabrication procedure that does not allow loss of resin during cure.  Also prepreg designed for use in such a procedure.
• Zero defects: quality philosophy advocated by Crosby.
• ZMC: moulding compound process for minimal fibre breakdown.