Composite Terminology



We have compiled a comprehensive list of the most commonly used terminology in the composites industry.

The list includes explanation of basic terms and abbreviations, as well as brief description of processes and some everyday application problems. 

A

AAP
Acetyl Acetone Peroxide: a chemical which acts as an initiator (catalyst) in composite processing.
 
ABRASION
Wearing away by friction.
 
ABSORPTION
The take up and retention of fluid into the interior of a material.
 
ACCELERATOR
A chemical that is used to speed up the reaction between the promoter and initiator especially where low temperatures are present. Also used when Benzoyl Peroxides are used as the Initiator. Sometimes they are also known as co-promoters.
 
ACOUSTIC EMISSION
A measure of integrity of a material as determined by sound emission when the material is stressed. Ideally, emissions can be correlated with defects.
 
ADDITIVE
An ingredient which is mixed into the resin, usually to improve its properties.
 
ADHEREND
A body that is held to another body by an adhesive.
 
ADHESIVE
A substance applied to mating surfaces to bond them together by surface attachment. May be liquid, film or paste.
 
ADHESIVE FAILURE
Rupture of an adhesive bond such that the separation occurs at the adhesive-adherend interface.
 
ADSORPTION
The adhesion, in an extremely thin layer, of a liquid to the surface of a solid body with which it is in contact.
 
AIR ENTRAPMENT
Occlusion of air in a laminate giving rise to bubbles voids or blisters.
 
AIRLESS SPRAYING
Application of resin and catalyst using equipment consisting of a fluid pump at high pressure, hose and spray nozzle to produce atomisation of the fluid without the use of compressed air or other propellant.
 
AIR SPLICE
The coupling of two rovings which is made by a jet of air entwining the two strands together. The air splice is used instead of a knot.
 
ALLIGATORING
Wrinkling of the gel coat resembling alligator hide. Also called triping.
 
ANISOTROPY
The characteristic of a material where it exhibits different properties along its different directions.
 
ANTIMONY TRIOXIDE
Fire retardant additive for use with resins.
 
ARAMID
Aromatic polyamide fibres. Common trade names are Kevlar and Twaron.
 
AREAL WEIGHT
Weight of a fibre reinforcement per unit area of tape or fabric.
 
ASPECT RATIO
The ratio of length to diameter of a fibre.
 
AUTOCLAVE
A closed vessel in which heat and pressure are applied for processing composites.
 
AXIAL WINDING
Filament winding where the filaments are parallel to the axis.                                                    

                                       

B

BAG MOULDING
A manufacturing process where an airtight film is placed over the laminate on the mould then pressure is applied by a vacuum, an autoclave, a press or by inflating the bag. Heat may be applied. When an autoclave is used the process is also known as autoclave moulding.
 
BAGGING
A manufacturing process where an impermeable layer of film is sealed to airtight over an uncured part and vacuum drawn to consolidate the laminate.
 
BALANCED LAMINATE
A  laminate in which all laminas except those at 0°/90° are placed in plus/minus pairs (not necessarily adjacent) symmetrically about the lay-up centreline.
 
BARCOL HARDNESS
Hardness of a laminate as measured by the Barber-Coleman lmpresser (Bar Col), generally model 934-1.
 
BIAXIAL WINDING
Filament winding where helical bands are laid in sequence, side by side with no gaps or overlap between the fibre.
 
BINDER
A bonding agent used to hold individual fibres together in the manufacture of glass fibre (or fibreglass) reinforcement, especially those in mat construction.  May be in the form of an emulsion or a powder.
 
BLEEDER CLOTH
A layer of fabric that allows excess gas and resin to escape during cure.  The bleeder cloth is removed and does not form part of the final composite.
 
BLEEDOUT
Excess  liquid resin appearing at the surface primarily during filament winding.
 
BLOOMING, FIBRE
A surface condition in pultrusion exhibiting a fibre prominence that usually has a white or bleached colour and a spark appearance.
 
BOG
Resin/filler putty: used for filling gaps.
 
BPO
Benzoyl Peroxide: a chemical which acts as an initiator (catalyst) in composite processing.
 
BREATHER 
A loosely woven fabric that does not come in contact with the resin but ensures a continuous vacuum path over a part in production. The breather is removed after cure and does not form part of the final composite.
 
BRIDGING

  1. Fibres which do not conform to sharp concave radii.

  2. Fabric plies over a curved edge that do not come in full contact with the core (refer to sandwich construction).

  3. Resin that has formed on edges during cure.

B-STAGE
An intermediate stage in processing where the resin has been allowed to partially cure.
 
BUILD UP
Glass bundles or chopper fuzz which collect on the chopper, cot, static bars or machine frame. Term can also be from resin / glass overspray and wax residue on mould surfaces.
 
BULK MOULDING COMPOUND (BMC)
A premixed blend of thermosetting resin, reinforcements, catalysts and fillers for use in compression, transfer or injection moulding processes.

C

CAD/CAM
Computer Aided Design / Computer Aided Manufacturing.
 
CAST POLYMER/CASTING
Cured unreinforced resin.
 
CATALYST
A chemical which initiates or speeds up a chemical reaction without being consumed in the reaction. This term is commonly, but incorrectly used in the composites industry to refer to the initiator.  The true catalysts used in the polyester resins used in the composites industry are the Promoters.
 
CATENARY
The loop caused by a difference in length of the strands in a specified length of roving.
 
CAUL SHEET
Smooth plate or sheet the same size and shape as the part used in contact with a composite lay-up during curing to transmit normal pressure and provide a smooth surface on the finished part.
 
CAVITY
The space between matched moulds in which the laminate is formed. Commonly used term for a female (cavity) mould.
 
CENTIPOISE (CPS)
Measurement of a fluid's viscosity as compared to water (1 centipoise at 21°C).
 
CENTRIFUGAL CASTING
A processing method for composites where the resin and reinforcement is placed inside a rotating hollow cylindrical mandrel which is then heated as the resin cures.
 
CFRP
Carbon Fibre Reinforced Plastic.
 
CHALKING
Dry, powder like appearance on gelcoat surface.
 
CHEESE
A tubeless cylindrical package consisting of wound glass roving.  Otherwise referred to as a doff, pack or spool.
 
CHOPPED STRAND
Continuous strand yarn or roving cut up into short uniform lengths, usually from 1 to 60 mm.
 
CHOPPED STRAND MAT (CSM)
A mat form of reinforcement consisting of a randomly distributed multitude of glass filament bundles cut to approximately 50mm long and bound together with a styrene soluble binder, in either emulsion or powder form.
 
CHOPPER GUN
A spray depositor which chops glass rovings into pre-determined lengths and deposits them together with catalysed resin onto the mould.  Used for spray-up laminating.
 
CLOTH
A fine weave of woven glass fibre.
 
CO-CURED
Cured and simultaneously bonded to another prepared surface.
 
COHESION
Tendency of a single substance to adhere to itself. Also, the force holding a single substance together.
 
COMPOSITE
A material composed of two or more substituents. Nuplex Composites and their customer use this term to refer to a material composed of a thermosetting resin matrix reinforced with fibres.
 
COMPRESSION MOULDING
A processing method where fibre and resin are placed into a mould cavity, the mould is closed and heat and pressure are applied until the material has cured.
 
CONFORMABILITY
Ability of reinforcements to conform to tight radii without Springback or Bridging.
 
CONTACT MOULDING
A alternative term used to refer to a processing method which uses open one sided moulds.  See Hand lay-up or Spray-up.
 
CONTINUOUS FILAMENT
An individual small diameter reinforcement that is flexible and of great length.
 
CONTINUOUS ROVING
Parallel filaments coated with sizing, gathered together into a single strand with no catenary.  Supplied wound into a cylindrical package.
 
CO-PROMOTED
The use of more than one promoter in a resin to alter the speed of the curing reaction. This may be to achieve a long gel time and quick cure.
 
CORE
The central component of a sandwich construction to which the inner and outer skins are attached.
 
COUNT
For woven fabric, the number of warp or weft yarns per inch.
 
COUPLING AGENT
A chemical designed to react with the reinforcement and resin to form a bond at their interface.
 
CRAZING
Ultra-fine cracks that may develop on or under a resin surface.
 
CREEL
Shelves or racks for holding the required number of roving spools or other supply packages in position for unwinding.
 
CREEP
Dimensional change (beyond instantaneous elastic deformation) in a material which is under stress over a long time.
 
CROSS LINKING
The process of forming a network of chemical links between polymer chains.  This occurs upon curing as the resin turns from a liquid to a solid.
 
CHP
Cumene Hydroperoxide: a chemical which acts as an initiator (catalyst) in composite processing.  In some parts of the world, CHP also refers to cyclo hexanone peroxide - make sure which is being referred to.
 
CURE
An irreversible chemical reaction where links are formed between polymer chains. This changes thermosetting resins from liquid to solid.
 
CURE TIME
The time required for the liquid resin to reach a solid cross-linked state after the catalyst (initiator) is added.

D - E

DAMPING
Diminishing the intensity of vibrations.
 
DEBOND
An unplanned separation of bonded surfaces. In composites this usually relates to separation of laminate layers.
 
DELAMINATE 
In plane separation of ply layers due to adhesive failure. This also includes the separation of layers of fabric from the core.
 
DEMOULD
Removal of a part from a tool/mould.
 
DENIER
A numbering system for yarn and filament in which yarn number is equal to weight in grams of 9000m of yarn.
 
DENSITY
Measurement of the mass of a substance per cubic volume (i.e. kg/m3).  However, commonly used term when referring to mat or fabric reinforcements, but refers to the mass per square metre (g/m2). i.e. 450g/m2 chopped strand mat.
 
DILUENT
Diluting (reducing or thinning) agent. Solvent.
 
DMA
Dimethylaniline: a promoter used with polyester and vinyl ester resins.
 
DOUBLER
Extra layers of reinforcement added to provide stiffness or strength.  This is usually positioned where fasteners are to be applied or other abrupt load transfers occur.
 
DRAFT ANGLE
A tool's (or mandrel's) taper or slope for ease of part removal.
 
DRAIN OUT
The leaking of resin from the laminate.
 
DRAPE 
The ability of fabric to conform to the shape of a contoured surface.
 
DRY FIBRE
A condition in which fibres are not fully encapsulated or wet-out by resin during laminating. In a defined area this is called a dry spot.
 
DRY LAMINATE
A laminate containing insufficient resin for complete bonding of the reinforcement.

E-GLASS
Commonly type of glass used for manufacture of continuous glass fibre utilised as reinforcement. Characterised by its high electrical resistance.
 
EMULSION BOUND MAT
Commonly called Emulsion Mat. Chopped strand mat in which the fibres are bound together with an emulsion (often poly-vinyl acetate) which is both water and styrene soluble.
 
END
A strand of roving consisting of a given number of filaments gathered together.
 
END COUNT
The number of strands contained in a roving.
 
EPOXY RESIN
A thermosetting polymer characterised by epoxide groups.
 
EXOTHERM
The heat released during a chemical reaction (e.g. curing).
 
EXTENDERS
Low cost materials added to resins to increase volume without significantly increasing cost or decreasing properties.                                                     

F

FABRICATION
The process of making a composite part or tool.
 
FABRIC (NON WOVEN)
A material formed by fibres or yarns without interlacing.
 
FABRIC (WOVEN)
A material constructed of interlaced yarns, fibres or filaments. Produced by the weaving process.
 
FADING
Loss of colour in the gelcoat.
 
FATIGUE
A failure mechanism of materials when they are exposed to repeated stress over time.
 
FATIGUE STRENGTH
Maximum cyclical stress withstood for a given number of cycles before a material fails.
 
FEA
Finite Element Analysis.
 
FEATHER EDGE
The process of tapering the edge of an overlapping material to blend with the adjoining surface.
 
FEEDERS
Components on a filament winding machine through which roving is dispensed onto the mandrel.
 
FIBRE / FIBER
An individual rod/filament of glass of sufficiently small diameter to be flexible.
 
FIBRE CONTENT
The amount of fibre in a composite relative to resin.  Expressed as either a volume or weight ratio or percentage.
 
FIBREGLAS S / FIBERGLASS

  1. Glass fibres constructed in various forms to act as a reinforcement medium.

  2. Abbreviation referring to a composite laminate consisting of a resin matrix reinforced with glass fibre reinforcement.

FIBRE ORIENTATION
Direction of fibre alignment in a composite laminate. Refers to where most of the fibres are placed in the same direction to give higher strength in that direction.
 
FIBRE REINFORCED PLASTICS / POLYMER (FRP)
A composite that consists of a resin matrix and reinforcing fibres. Often used to describe glass fibre reinforced plastics (GFRP).
 
FIBRE WHITENING
An incompatibility between the resin and glass within the laminate to produce visual white fibres upon laminate curing.
 
FILAMENT
Individual fibres of very small diameter and extremely long length.
 
FILAMENT WINDING
A manufacturing process for composites where tape, roving or single strands are fed from a creel through a bath of resin and onto a rotating mandrel. The mandrel may be cured at room temperature or in an oven.
 
FILL THREADS
Fibres woven at 90° to the warp fibres in a woven fabric. Fibres woven across the fabric from edge to edge. Also called weft.
 
FILLERS
Relatively inert materials added to resin, gel coat or flow coat to alter its properties or lower cost.
 
FISH EYE
A circular separation in a gelcoat film generally caused by contamination such as silicone, oil, dust or water.
 
FLAME RETARDANT
In composites terms this refers to a substance that reduces the flammability or delays combustion of the finished laminate.
 
FLEXURAL MODULUS
The ratio, within the elastic limit, of the applied stress on a sample in flexure to its strain in the outermost fibres of the sample. Simply put “how much a sample bends when load is applied”. 
 
FLEXURAL STRENGTH
The strength of a material in bending expressed as the stress of a bent test sample at the instant of failure.
 
FLOW LINE
A mark on a moulded product made by the meeting of two liquid fronts during moulding. Also called striae, weld-mark or weld-line.
 
FLY
Loose filaments of fibre that have broken from their strand and are freely floating in the air.
 
FRP
Fibre Reinforced Plastics.

G - H

GEL
A partial cure stage of resins. A description of the resin at the point in curing when the liquid first forms a jelly-like solid.
 
GELATION
The formation of a gel.
 
GELCOAT
Clear or pigmented resin which becomes an integral part of the finished laminate as the outer surface to give visual impact and protect the laminate from the environment.
 
GEL TIME
Period of time from initial mixing of liquid reactants (resin & catalyst or part A and part B) to the point when gelation occurs.
 
GLASS FIBRE
Reinforcing fibre made by drawing molten glass through bushings.
 
GLASS RESIN RATIO
The amount of glass by weight compared to the amount of resin by weight in a laminate.
 
GLASS RICH
An area of moulded part that has an overabundance of glass reinforcement.  The reinforcement may appear dry and un-wet within the resin.
 
GLASS TRANSITION TEMPERATURE
The temperature above which a hard/glassy polymer becomes rubbery due to increased molecular mobility with heat.
 
GRAPHITE FIBRES
Fibres containing greater than 95% carbon. The term graphite fibresis often used interchangeably with carbon fibres. Carbon fibres contain ≤ 95% carbon.
 
GREEN
A description of a low state of cure also called green strength, the earliest time that a laminate, or part, can be handled.
 
GFRP
Glass Fibre Reinforced Plastics.
 
GRP
Glass Reinforced Plastic.

HARDENER
It is the substance that reacts with resin to enable curing, also called Part B.
 
HEAT DISTORTION TEMPERATURE (HDT)
It is the temperature at which a test bar deflects a certain amount under specified temperature and load.
 
HONEYCOMB
A low density sheet material formed into hexagonal shaped cells nested together.  Used as a core material in composites.
 
HOOP
Ply laid onto a mandrel at a 90° angle.
 
HOOP STRESS
It is the circumferential stress in a cylindrical part.
 
HUMIDITY
Moisture content of air.
 
HYBRID COMPOSITE
A composite made with two or more types of reinforcing fibres.

I - J

IMPACT STRENGTH
Material's ability to withstand shock impact loading as measured by fracturing a sample.
 
IMPREGNATE
To saturate the voids and interstices of a reinforcement with resin.
 
INCLUSION
Foreign matter that is either encapsulated or embedded in the laminate.
 
INHIBITOR
Chemical that is added to the resin to slow curing. This allows a longer shelf life of uncatalysed resin and can be used to slow gel and cure time during fabrication.
 
INITIATOR
Chemical which initiates or speeds up the chemical curing reaction of resin and is consumed in the process.
 
INTERFACE
Surface between two materials. In glass fibres, the area at which the glass and sizing meet. In a laminate the area at which the reinforcement and resin meet.
 
LNTERLAMINAR
Between two or more adjacent laminae.
 
LNTERLAMINAR SHEAR
Shearing force that produces displacement between two laminae along the plane of their interface.
 
ISO
It is the abbreviation of isophthalic type resins and gelcoats.
 
ISOPHTHALIC
A polyester resin based on isophthalic acid.
 
ISOTROPIC
Fibre directionality with the same properties in all directions. An arrangement of reinforcing materials in a random manner, resulting in equal strength in all directions.
 
JACKSTRAWING 

  1. Prominence or white appearance of glass strands in the laminate. Formed by the glass separating from the resin due to excessive exothermic heat, usually associated with thick, resin rich laminates.

  2. Can also be the binder on the glass becoming insoluble in the resin as gel takes place. Quite common in vinyl ester, and some types of polyester laminates where it is a cosmetic effect and does not affect composite strength.

K - L

KEVLAR
Trademark of DuPont for strong, lightweight aramid fibre, used as a reinforcing fibre in composites.
 
KNITTED FABRIC
A textile material made by inter-looping yarns.
 
LAMINATE
The structure produced by bonding multiple plies of reinforcing fibre or fabric with resin.
 
LAMINATE PLY
One layer of reinforcement and resin in a laminate.
 
LAP JOINT
A joint made by placing one material over the other so that the joint consists of two layers of material.
 
LAY UP
The process of placing reinforcement into the mould and applying resin. Also used to describe the finished laminate itself.
 
LOFT
The height of the glass layer either dry or wet (with resin before consolidation).
 
LOW PROFILE
Resins formulated for low or zero shrinkage during moulding.

M - N

MANDREL
Mould, usually cylindrical, around which resin-impregnated fibre or tape is to produce a composite part.
 
MAT
A form f reinforcement composed of chopped filaments (for chopped-strand mat) or swirled filaments (for continuous-strand mat) with a binder applied or stitching to maintain form.
 
MATCHED METAL MOULDING
A composite fabrication method which uses matching male and a female metal moulds mounted in a hydraulic press. Matched die moulding is the same process using non-metal moulds.
 
MATRIX
Binder in which the reinforcing fibre of a composite is embedded. The general “Composites” terms usually assumes the matrix is a thermosetting resin.
 
MEKP
Methyl Ethyl Ketone Peroxide. A chemical which acts as an initiator (catalyst) in composite processing.
 
MEK SOLVENT
Methyl Ethyl Ketone. A colourless, flammable liquid which acts as solvent and is used in cleaning.
 
MIL
Unit of measure. 1mil = 0.001inch
 
MILLED FIBRE
Very short glass or carbon fibres formed by hammer milling.
 
MODULUS
Measurement of stiffness of a material. Ratio of applied load (stress) to the resultant deformation of a material (strain). High modulus indicates a stiff material.
 
MONOMER
A single molecule that can react with itself or other molecules to form a polymer
 
MOULD
The tool into/onto which resin and reinforcement is placed to form a composite part.
 
MOULD RELEASE AGENT
S
ubstance or chemical use to coat the mould to provide easy release of the part.
 
MOULDING
The forming of composite parts over a mould. A term sometimes used to refer to the finished part.
 
MSDS
Material Safety Data Sheet. A sheet which must be provided by suppliers, providing information on identification, health hazard, precautions for use, safe handling and other information on the chemical.
 
MULTIFILAMENT
A yarn consisting of many continuous filaments.
 
NONWOVEN ROVING
A reinforcement composed of continuous fibre strands loosely gathered together.
 
NPG
Neopentyl Glycol. A component in the manufacture of some types of polyester resin.

O - P

ONE PART RESIN SYSTEM
A resin system (often used in resin transfer moulding) in which the neat resin and initiator (catalyst) are mixed together by the supplier. These systems generally require heat, or UV, to cure.
 
ORANGE PEEL
Backside of the gel coated surface that has the rough wavy texture of an orange peel often from spray pattern.
 
ORTHO
Abbreviation for orthophthalic type resins and gelcoats.
 
ORTHOPHTHALIC
A polyester resin based on orthophthalic acid or anhydride.
 
OUTGASSING
Release of solvents, dissolved air and moisture from composite parts under a vacuum.
 
OUT-TIME
Period of time in which a prepreg retains acceptable handling and other properties outside a specified storage environment (e.g. freezer).
 
PAN
Polyacrylonitrile. Base material in the manufacture of some carbon fibres.
 
PATTERN
The original model for making fibreglass moulds.
 
PEEL PLY
A layer of fabric that is applied to a laminate surface to give a clean, resin rich surface ready for bonding. The fabric is removed from the cured laminate so as to not form part of the final composite.
 
PEEL STRENGTH
Strength of an adhesive bond obtained by stress applied in a peeling mode.
 
PHENOLIC RESIN
Thermosetting resin produced by condensation polymerisation of an aromatic alcohol (phenol) with an aldehyde (formaldehyde).  These are usually specified for their fire retardant properties.
 
PINHOLES
Small air bubbles or holes in the gel coat. Generally larger in size than porosity.
 
PITCH
A residual petroleum product used in the manufacture of some carbon fibres.
 
PLUG
The pattern or tool used to build moulds for the manufacture of composites. Also called master.
 
PLY
One of the layers that makes up a laminate. Also the number of single yarns twisted together to form a plied yarn.
 
PLY SCHEDULE
A description of the arrangement of individual plies in a laminate.
 
POLYESTER
A polymer containing the ester group. In composites unsaturated polyester resins are used. These are made by the reaction between dihydroxy alcohols and dibasic acids, one of which is unsaturated to permit crosslinking. A monomer such as styrene is then added.
 
POLYMER
A large molecule formed by combining many smaller molecules called monomers, in a regular pattern.
 
POLYMERIZATION
The chemical reaction that links monomers together to form polymers.
 
POROSITY
Small air bubbles or holes in the gel coat film. Smaller than pinholes.
 
POST CURE
Exposure of the cured resin to higher temperatures than used during curing.  This additional processing step, often performed in an oven, gives a composite a more complete cure and higher mechanical properties.
 
POT LIFE
Length of time before a catalysed resin has gelled to an unworkable state.  Same as gel time.
 
PREFORM
A pre-shaped fibrous reinforcement.
 
PREMIX
A mix of reinforcement, resin and usually pigment, filler and catalyst.
 
PRE-RELEASE
Premature release of the gelcoat or laminate from the mould.
 
PRINT THROUGH
Appearance of the image/form of the reinforcement through the gelcoat.
 
PRIMER
A coating applied as the first coat to a surface, which improves the adhesion performance or load-carrying ability of the bond.
 
PROMOTER
A chemical which, when mixed with a catalysed resin, reacts with the catalyst initiating the cross linking of the resin. Promoters can speed up or slow this chemical reaction.  Also called an activator or promoter.
 
PREPREG
Reinforcement impregnated with resin in flat form that can be stored for later use. The resin is often partially cured to B stage.
 
PROFILE RETENTION
A measure of the ability of composite sheeting (usually corrugated) to retain its shape after being subjected to elevated temperatures.
 
PULTRUSION
An automated, continuous process for fabricating composite shapes of constant cross section. Roving and other reinforcements are saturated with resin and continuously pulled through a heated die, where the part is formed then cured and cut to length.

Q - R

QUASI-ISOTROPIC
Approximating isotropy by orienting plies in several directions.


RAMPING
Gradual increase/decrease in temperature or pressure to control cure or cooling of composite parts.
 
REINFORCEMENT
Material combined with resin to provide improved properties such as strength and stiffness. Forms include short fibres, continuous fibres and fabrics.
 
RELEASE AGENT
Chemical used to prevent laminate from sticking to the tool.
 
RELEASE FILM
An impermeable film layer that does not bond to the composite during cure.
 
RESIN
Polymer, the matrix component in a composite which binds the reinforcement together and protects the part from the environment.
 
RESIN CONTENT
The amount of resin in a laminate expressed as either a percentage of total weight or volume.
 
RESIN RICH
Area with excess resin relative to reinforcement.
 
RESIN STARVED
An area lacking sufficient resin for fibre wet-out. The area can be identified by low gloss, dry spots or fibre show.
 
RESIN TRANSFER MOULDING (RTM)
A composite fabrication process where catalysed resin is injected into a two sided, matched mould in which fibrous reinforcement has been placed. Heat may be used.
 
RESIN TEARING
A gelcoat surface defect produced by a separation of gelcoat solids leaving resin filled voids. Usually seen as black wavy lines.
 
ROLL OUT
A process used in hand lay-up and spray-up where the resin and reinforcement are consolidated to a uniform height with a roller.
 
ROVING
A collection of continuous filaments in a parallel bundle with little or no twist.
 
RUNS
Draining of the gel coat or laminating resin.

S

SAGS
Slumping of the gel coat or laminating resin.
 
SANDWICH CONSTRUCTION
A laminate composed of a core with a relatively thin skin of reinforcement and resin adhered to either side.
 
SECONDARY BONDING
The joining together, by the process of adhesive bonding, of two or more already cured composite parts.
 
S-GLASS
“Structural Glass". Magnesia-alumina-silicate glass reinforcement which has very high tensile strength.
 
SHEAR
An applied stress which tends to cause two adjacent parts of a body to slide relative to each other in a direction parallel to their plane of contact. In interlaminar shear the plane of contact is composed of resin only.
 
SHEAR STRENGTH
The maximum shear stress that a material can sustain.
 
SHEET MOULDING COMPOUND (SMC)
A ready to mould mix of glass fibre reinforcement and resin primarily used in compression moulding.
 
SHELF LIFE
The length of time an un-catalysed resin or other chemical remains workable while stored under specified conditions in a tightly sealed container.
 
SHRINKAGE
Reduction in volume which occurs upon the curing of liquid resin to a solid product.
 
SINK MARK
A shallow depression on the surface of an injection moulded part due to collapsing of the surface following local internal shrinkage.
 
SIZING
A proprietary soluble solution of chemical additives used to coat filaments used for reinforcement purposes. Acts as a binder which protects the fine, brittle filaments during processing.  Imparts characteristics such as abrasion resistance, static reduction, dispersion, conformability, wet-out rate etc. to the final reinforcement. Components of the sizing determine the compatibility of the reinforcement with the laminate matrix, and contribute significantly to an effective reinforcement:laminate interface.
 
SKIN
A layer of relatively dense material used on top of the core in a sandwich structure.
 
SKIN COAT
The first layer of laminate next to the gelcoat. Generally a thin laminate layer to minimise exotherm, and utilising fine, lightweight reinforcement to avoid fibre show/print through on the laminate surface.
 
SOLVENT
A substance in which another material will dissolve. e.g. acetone is a solvent for polyester resin.
 
SPECIFIC GRAVITY
Density (mass per unit volume) of a material divided by that of water at a standard temperature.
 
SPLICE
The joining together of two ends of yarn by intertwining them.
 
SPLIT MOULD
A mould in which the cavity is formed of two or more components held together by an outer case.
 
SPRAY PATTERN
The width and uniformity of the fan of resin and glass when it leaves the gun in the spray-up process.
 
SPRAY-UP
A composite fabrication process in which chopped glass fibres, resin and catalyst are simultaneously deposited in a mould by the use of a spray gun.
 
SPRING-BACK
Reinforcement filaments straightening over convex curves in the laminate.
 
STORAGE LIFE
The length of time a material can be stored and retain specific properties.
 
STRAND
A bundle of continuous filaments combined in a single compact unit without twist.
 
STRAIN
The change in dimension per unit length of a member when it is subject to a stress.
 
STRESS
Internal resistance to change in size or shape, expressed in force per unit area.
 
STRESS CONCENTRATION
The magnification of applied load in the region of a notch, void, hole or inclusion.
 
STRESS CORROSION
Preferential attack of areas under stress in a corrosive environment, where such an environment alone would not have caused corrosion.
 
STRESS CRACK
External and/or internal cracks in a composite caused by tensile stresses.
 
STRUCTURAL ADHESIVE
An adhesive used to transfer loads between two or more adherents.
 
STYRENE MONOMER
A type of liquid monomer used to thin polyester resins and act as the crosslinking agent.
 
SURFACE VEIL/TISSUE
A thin lightweight reinforcing mat made of fibres. This is used to give a resin rich surface layer for laminates, assisting in resistance to corrosive liquid or fumes. It is also used to block out the fibre pattern of the underlying reinforcement, providing an improved surface finish.                    

T - V

TACKY
Sticky.
 
TENSILE STRENGTH
Maximum stress sustained by a composite specimen before it fails in a tension test.
 
TEX
A unit of linear density. Mass in grams per 1000 metres of yarn, fibre or other strand.  Also known as Bundle Tex or Strand Tex.
 
THERMAL CONDUCTIVITY
Ability to transfer heat.
 
THERMOPLASTIC
A polymer based material that will repeatedly soften when heated and harden when cooled.
 
THERMOSET
A polymer based material that will undergo or has undergone a chemical cross linking reaction by the action of heat, catalyst, ultraviolet light etc, leading to a solid state which cannot be reversed.
 
THIXOTROPIC
Materials which are gel-like at rest but flow easily when agitated. These materials have a high static shear strength and a low dynamic shear strength.
 
THIXOTROPIC INDEX
A measurement of thixotropic nature using a Brookfield viscometer, calculated as the low speed viscosity divided by the high speed viscosity.
 
TISSUE
An ultra-thin non-woven mat of reinforcing fibres. The tissue supports a resin rich layer in a laminate. It is also called veil.
 
TOOL
The mould, either open or closed, in or upon which composite materials re-formed.
 
TOW
An untwisted bundle of continuous filaments. Tow is usually written in the form of a number followed by K e.g. 16K, where K indicates multiplication by 1000 (16K tow has 16,000 filaments).
 
TRACER
A fibre, tow or yarn, usually a contrasting colour added to a fabric to verify fibre alignment.
 
TRIPE
Wrinkling of gelcoat caused by styrene attack of under-cured gelcoat when the backing resin is applied.


UNDERCUT
Negative or reverse draft on the mould. Split moulds are necessary to shape parts that are undercut.
 
UNIDIRECTIONAL (UD)
Fabric, tape or laminate where the fibres are all oriented in the same direction (straight, parallel and continuous).
 
VACUUM ASSISTED RESIN TRANSFER MOULDING (VARTM)
A composite fabrication process using infusion. A vacuum draws resin into a one-sided (open) mould which has a rigid or flexible cover placed over the top to form a vacuum tight seal.
 
VACUUM BAG MOULDING
A composite fabrication process where the reinforcement and resin are applied by hand lay-up or spray-up and then a flexible bag is sealed over the part and a vacuum drawn whilst the part cures.
 
VEIL
An ultra-thin non-woven mat of reinforcing fibres. The veil supports a resin rich layer in a laminate. Also called tissue.
 
VINYL ESTER RESIN
A type of thermosetting resin that is usually derived from an epoxide, glycol and unsaturated acid, with styrene monomer added.
 
VISCOSITY
The tendency of a fluid to resist flow.
 
VOID
A pocket of entrapped gas that has been cured into a laminate.
 
VOLATILE ORGANIC COMPOUNDS (VOCS)
Carbon containing chemical compounds (e.g. solvents and styrene) that evaporate readily at ambient temperatures. Regulations often limit exposure to VOCs so that low VOC content is preferable.

W - Z

WARP
The yarns running lengthwise in a woven fabric.
 
WARPAGE
Dimensional distortion in a composite part.
 
WEAVE
Pattern by which a fabric is formed from interlacing yarns.
 
WEFT
Yarns running perpendicular to the warp in a woven fabric. The yarns which run across the fabric from one edge to the other.
 
WETTING AGENT
A surface-active chemical that promotes wetting by decreasing the cohesion within a liquid.
 
WET-OUT
Saturation of strands and filaments and all voids between these with resin.
 
WET-OUT RATE
The speed with which the reinforcement can be completely saturated with resin.
 
WET-THROUGH
The impregnation of resin through the reinforcement matrix.
 
WET WINDING
Filament winding where fibre strands are impregnated with resin immediately before they contact the mandrel.
 
WINDING PATTERN
In filament winding, the regularly recurring pattern of the filament path after a certain number of mandrel revolutions.
 
WORKING LIFE
The period of time between addition of catalyst or hardener to a resin and gelation. Also called gel-time.
 
WOVEN ROVING
Heavy, course fabric produced by weaving continuous rovings.
 
WRINKLE
Imperfection in the surface of a laminate that looks like a crease.
 
X-AXIS
The axis in the plane of the laminate used as a 0° reference.
 
YARN
An assembly of twisted fibres or strands which forms a continuous length.
 
Y-AXIS
The plane of the laminate perpendicular to the X axis.
 
YOUNG'S MODULUS
Ratio of normal stress to the corresponding strain for tensile or compressive stresses less than the proportional limit of the material.
 
Z-Axis
The axis perpendicular to the laminate plane.