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Composites Terminology Database

This glossary is not an exhaustive list, however it does contain the majority of terms used in the composites industry and as part of the management of our website, it is updated on a continual basis.

The terms are accessed by clicking on the appropriate letter below, all the terms beginning with the letter P can be found below.

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Terms P

Click on a term and it will take you to the coresponding explanation.


package
Yarn, roving, and so forth in the form of units capable of being unwound and suitable for handling, storing, shipping, and use.


PAN
See polyacrylonitrile
"polyacrylonitrile"


parallel laminate
A laminate of woven fabric in which the plies are aligned in the same position as originally aligned in the fabric roll. A series of flat or curved cloth-resin layers stacked uniformly on top of each other.


particulate composite
Material consisting of one or more constituents suspended in a matrix of another material. These particles are either metallic or non-metallic.


parting agent
See parting agent
"mould release agent"


parting line
A mark on a moulded piece where the sections o f a mould have met in closing.


PAS
See polyarylsulfone
"polyarylsulfone"


PBI
See polybenzimidazole
"polybenzimidazole"


PEEK
See polyether etherketone
"polyether etherketone"


peel ply
A layer of open-weave material, usually fibreglass or heat-set nylon, applied directly to the surface of a prepreg lay-up. The peel ply is removed from the cured laminate immediately before bonding operations, leaving a clean, resin-rich surface that needs no further preparation for bonding, other than application of a primer where one is required.


peel strength
Adhesive bond strength, as in pounds per inch of width, obtained by a stress applied in a peeling mode.


permanence
The property of a plastic that describes its resistance to appreciable changes in characteristics with time and environment.


permanent set
The deformation remaining after a specimen has been stressed a prescribed amount in tension, compression, or shear for a definite time period and released for a definite time period. For creep tests, the residual unrecoverable deformation after the load causing the creep has been removed for a substantial and definite period of time.

Also, the increase in length, expressed as a percentage of the original length, by which an elastic material fails to return to original length after being stressed for a standard period of time.


permeability
The passage or diffusion (or rate of passage) of a gas, vapour, liquid, or solid through a barrier without physically or chemically affecting it.


pH
The measure of the acidity or alkalinity of a substance, neutrality being at pH 7. Acid solutions are less than 7, alkaline solutions are more than 7.


phenolic (phenolic resin)
A thermosetting resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. Used in high-temperature applications with various fillers and reinforcements.


phenylsilane resins
Thermosetting copolymers of silicone and phenolic resins. Furnished in solution form.


physical catalyst
Radiant energy capable of promoting or modifying a chemical reaction.


PI
See polyimide
"polyimide"


PIC
See pressure-impregnation-carbonization
"pressure-impregnation-carbonization"


pick count
The number of filling yarns per inch of woven fabric.


pin holes
Small cavities that penetrate the surface of a cured pan.


pit
A small, regular or irregular crater in the surface of a plastic, usually of a width approximately the same order of magnitude as its depth.


pitch
A high molecular weight material left as a residue from the destructive distillation of coal and petroleum products. Pitches are used as base materials for the manufacture of certain high-modulus carbon fibres and as matrix precursors for carbon-carbon composites.


plain weave
A weaving pattern in which the warp and fill fibres alternate; that is, the repeat pattern is warp/fill/warp/fill, and so on. Both faces of a plain weave are identical. Properties are significantly reduced relative to a weaving pattern with fewer crossovers.


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


planar winding
A winding in which the filament path lies on a plane that intersects the winding surface. See also polar winding
"polar winding"


planar
Lying essentially in a single plane.


plastic deformation
Change in dimensions of an object under load that is not recovered when the load is removed, as opposed to elastic deformation.


plastic flow
Deformation under the action of a sustained hot or cold force. Flow of semisolids in the moulding of plastics.


plastic memory
The tendency of a thermoplastic material that has been stretched while hot to return to its un-stretched shape upon being reheated.


plastic
A material that contains as an essential ingredient an organic polymer of large molecular weight, hardeners, fillers, reinforcements, and so forth; is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow. Made of plastic. A plastic may be either thermoplastic or thermoset.
"thermoplastic" "thermoset"


plasticiser
A material incorporated in a plastic to increase its workability and flexibility or distensibility. Normally used in thermoplastics. A lower molecular weight material added to an epoxy to reduce stiffness and brittleness, thereby resulting in a lower glass transition temperature for the polymer.


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


plied yarn
Yarn made by collecting two or more single yarns. Normally, the yarns are twisted together, though sometimes they are collected without twist.


ply
In general, fabrics or felts consisting of one or more layers (laminates, and so forth). The layers that make up a stack. Yarn resulting from twisting operations (three-ply yarn, and so forth). A single layer of prepreg. A single pass in filament winding (two plies forming one layer).


PMR polyimides
A novel class of high temperature resistant polymers. PMR represents in. situ polymerisation of monomer reactants.


Poisson's ratio
The ratio of the change in lateral width per unit width to change in axial length per unit length caused by the axial stretching or stressing of a material. The ratio of transverse strain to the corresponding axial strain below the proportional limit.


polar winding
A winding in which the filament path passes tangent to the polar opening at one end of the chamber and tangent to the opposite side of the polar opening at the other end. A one-circuit pattern is inherent in the system.


polyacrylonitrile (PAN)
Used as a base material or precursor in the manufacture of certain carbon fibres.


polyamide plastic
See nylon plastics
"nylon plastics"


polyamide
A thermoplastic polymer in which the structural units are linked by amide or thio-amide groupings (repeated nitrogen and hydrogen groupings). Many polyamides are fibre forming.


polyamideimide
A polymer containing both amide (nylon) and imide (as in polyimide) groups; properties combine the benefits and disadvantages of both.


polyarylsulfone (PAS)
A high temperature resistant thermoplastic (Tl = 275 degree C, or 527 degree F). The term is also occasionally used to describe the family of resins which includes polysultone and polyethersultone.


polybenzimidazole (PBI)
A condensation polymer of diphenyl isophthalate and 3.3'??? diaminobenzidine. Extremely high-temperature resistant. Available as adhesive and fibre.


polycarbonate resin
A thermoplastic polymer derived from the direct reaction between aromatic and aliphatic dihydroxy compounds with phosgene or by the ester exchange reaction with appropriate phosgene-derived precursors. Highest impact resistance of any transparent plastic.


polycondensation
See condensation polymerisation
"condensation polymerisation"


polyesters, thermoplastic
See thermoplastic polyesters
"thermoplastic polyesters"


polyesters, thermosetting
See thermosetting polyesters
"thermosetting polyesters"


polyether etherketone (PEEK)
A linear aromatic crystalline thermoplastic. A composite with a PEEK matrix may have a continuous use temperature as high as 250 degree C (480 degree F).


polyetherimide
An amorphous polymer with good thermal properties for a thermoplastic. Reported Tg of 215 degree C (419 degree F) and continuous-use temperature of about 170 degree C (338 degree F).


polyimide (Pl)
A polymer produced by reacting an aromatic dianhydride with an aromatic diamine. It is a highly heat-resistant resin, ³ 315 degree C (419 degree F), similar to a polyamide, differing only in the number of hydrogen molecules contained in the groupings. Suitable for use as a binder or adhesive. May be either thermoplastic or thermoset.


polymer
A high molecular weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer. For example, polyethylene, rubber, and cellulose. Synthetic polymers are formed by addition or condensation polymerisation of monomers. Some polymers are elastomers, some are plastics, and some are fibres.

When two or more dissimilar monomers are involved, the product is called a copolymer. The chain lengths of commercial thermoplastics vary from near a thousand to over one hundred thousand repeating units. Thermosetting polymers approach infinity after curing, but their resin precursors, often called prepolymers, may be relatively shortÑ 6 to 100 repeating unitsÑbefore curing.

The lengths of polymer chains, usually measured by molecular weight, have very significant effects on the performance properties of plastics and profound effects on processibility.


polymerisation
The resin portion of a reinforced or filled plastic.


polymethyl methacrylate
A thermoplastic polymer synthesised from methyl methacrylate. It is a transparent solid with exceptional optical properties; available in the form of sheets, granules, solutions, and emulsions. Used as facing material in certain composite constructions. See also acrylic plastic
"acrylic plastic"


polyphenylene sulfide (PPS)
A high-temperature thermoplastic useful primarily as a moulding compound. Optimum properties depend on slightly cross-linking the resin. Known for chemical resistance.


polypropylene
A tough, lightweight, thermoplastic made by the polymerisation of high purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.


polysulfide
A synthetic polymer containing sulfur and carbon linkages, produced from organic dihalides and sodium polysulfide. Material is elastomeric in nature, resistant to light, oil, and solvents, and impermeable to gases.


polysulfone
A high temperature resistant thermoplastic polymer with the sulfone linkage, with a Tg of 190 degree C (375 degree F).


polyurethane
A thermosetting resin prepared by the reaction of diisocyanates with polyols, polyamides, alkyd polymers, and polyether polymers. See also isocyanate plastics and urethane plastics
"isocyanate plastics" "urethane plastics"


porosity
A condition of trapped pockets of air, gas, or vacuum within a solid material. Usually expressed as a percentage of the total non-solid volume to the total volume (solid plus non-solid) of a unit quantity of material.


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


postforming
The forming, bending, or shaping of fully cured, C-staged thermoset laminates that have been heated to make them flexible. On cooling, the formed laminate retains the contours and shape of the mould over which it has been formed.


pot life
The length of time that a catalysed thermosetting resin system retains a viscosity low enough to be used in processing. Also called working life.


power factor
The cosine of the angle between voltage applied and the current resulting. Measurements are usually made at millioncycle frequencies.


PPS
See polyphenylene sulfide
"polyphenylene sulfide"


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


precursor
For carbon or graphite fibre, the rayon, PAN or pitch fibres from which carbon and graphite fibres are derived.


prefit
A process for checking the fit of mating detail parts in an assembly prior to adhesive bonding, to ensure proper bond lines. Mechanically fastened structures are sometimes prefitted to establish shimming requirements.


preform binder
A resin applied to the chopped strands of a preform, usually during its formation, and cured so that the preform will retain its shape and can be handled.


preform
A preshaped fibrous reinforcement formed by distribution of chopped fibres or cloth by air, water flotation, or vacuum over the surface of a perforated screen to the approximate contour and thickness desired in the finished part. Also, a preshaped fibrous reinforcement of mat or cloth formed to the desired shape on a mandrel or mock-up before being placed in a mould press.


pregel
An unintentional, extra layer of cured resin on part of the surface of a reinforced plastic. Not related to gel coat.


preheating
The heating of a compound before moulding or casting, to facilitate the operation or reduce the moulding cycle.


preimpregnation
The practice of mixing resin and reinforcement and effecting partial cure before use or shipment to the user. See also prepreg
"prepreg"


premix
A moulding compound prepared prior to and apart from the moulding operations and containing all components required for moulding: resin, reinforcement, fillers, catalysts, release agents, and other ingredients.


premolding
The lay-up and partial cure at an intermediate cure temperature of a laminated or chopped-fiber detail part to stabilise its configuration for handling and assembly with other parts for final cure.


preply
A composite material lamina in the raw-material stage, ready to be fabricated into a finished laminate. The lamina is usually combined with other raw laminae before fabrication. A preply includes a fibre system that is placed in position relative to all or part of the required matrix material to constitute the finished lamina. An organic matrix preply is called a prepreg. Metal matrix preplies include green tape, flamesprayed tape, and consolidated monolayers.


prepolymer
A chemical intermediate whose molecular weight is between that of the monomer or monomers and the final polymer or resin.


prepreg
Either ready-to-mold material in sheet form or ready-to-wind material in roving form, which may be cloth, mat, unidirectional fibre, or paper impregnated with resin and stored for use.

The resin is partially cured to a B-stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure. The two distinct types of prepreg available are (1) commercial prepregs, where the roving is coated with a hot melt or solvent system to produce a specific product to meet specific customer requirements, and, (2) wet prepreg, where the basic resin is installed without solvents or preservatives but has limited room-temperature shelf life.


press clave
A simulated autoclave made by using the platens of a press to seal the ends of an open chamber, providing both the force required to prevent loss of the pressurising medium and the heat required to cure the laminate inside.


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


pressure intensifier
A layer of flexible material (usually a high-temperature rubber) used to ensure the application of sufficient pressure to a location, such as a radius, in a lay-up being cured.


pressure-impregnation-carbonization (PIC)
A densification process for carbon-carbon composites involving pitch impregnation and carbonisation under high temperature and isostatic pressure conditions. This process is carried out in hot isostatic press (HIP) equipment.


pressure-sensitive adhesive
A viscoelastic material that, in solvent-free form, remains permanently tacky. Such material will adhere instantaneously to most solid surfaces with the application of very light pressure.


primer
A coating applied to a surface, before the application of an adhesive, lacquer, enamel, and so forth, to improve the adhesion performance or load-carrying ability of the bond.


printed wiring board
A completely processed conductor pattern, usually formed on a stiff, flat base (laminated plastic). It serves as a means of electrical interconnection and physical attachment for printed circuits. Also called printed circuit board.


processing window
The range of processing conditions, such as stock (melt) temperature, pressure, shear rate, and so on, within which a particular grade of plastic can be fabricated with optimum or acceptable properties by a particular fabricating process, such as extrusion, injection moulding, sheet moulding, and so forth.

The processing window for a particular plastic can vary significantly with design of the part and the mould, with the fabricating machinery used, and with the seventy of the end-use stresses.


production volume
Total production volume for this part.


promoter
A chemical, itself a feeble catalyst, that greatly increases the activity of a given catalyst. See also accelerator
"accelerator"


proof pressure
The test pressure that pressurised components shall sustain without detrimental deformation or damage. The proof pressure test is used to give evidence of satisfactory workmanship and material quality.


proof
To test a component or system at its peak operating load or pressure.


proportional limit
The greatest stress which a material is capable of sustaining without deviation from proportionality of stress and strain (Hooke's law). It is expressed in force per unit area. See also elastic limit
"elastic limit"


prototype
A model suitable for use in complete evaluation of form, design, performance, and material processing.


puckers
Areas on prepreg materials where material has locally blistered from the separator film or release paper.


pulp moulding
The process by which a resin impregnated pulp material is preformed by application of a vacuum and subsequently is oven cured or moulded.


pultrusion
A continuous process for manufacturing composites that have a constant cross-sectional shape. The process consists of pulling a fibre-reinforced material through a resin impregnation bath and through a shaping die, where the resin is subsequently cured. "pultrusion"


pyrolysis
With respect to fibres, the thermal process by which organic precursor fibre materials, such as rayon, polyacrylonitrile (PAN), and pitch, are chemically changed into carbon fibre by the action of heat in an inert atmosphere.

Pyrolysis temperatures can range from 800 to 2800 degree C (1470 to 5070 degree F), depending on the precursor. Higher processing graphitisation temperatures of 1900 to 3000 degree C (3450 to 5430 degree F) generally lead to higher modulus carbon fibres, usually referred to as graphite fibres.

During the pyrolysis process, molecules containing oxygen, hydrogen, and nitrogen are driven from the precursor fibre, leaving continuous chains of carbon.

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