Glossary    

A-stage   An early stage of polymerization of thermosetting resins in which the material is still soluble in certain liquids and is fusible. Also called resole. See also B-stage and C-stage.

Ablative   A material that absorbs heat through a decomposition process called pyrolysis at or near the exposed surface.

Addition   A polymerization reaction in which no by-products are formed.

Additives   Ingredients mixed into resin to improve properties.

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

Amorphous   Polymers that have no order to their molecules, thus no crystalline component.

Anisotropic   The tendency of a material to exhibit different properties in response to stresses applied along axes in different directions.

Aramid   Aromatic polyamide fibers characterized by excellent high-temperature, flame-resistance, and electrical properties. Aramid fibers are used to achieve high-strength, high-modulus reinforcement in plastic composites.

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

Aspect ratio   The ratio of length to diameter of a fiber.

Autoclave   A closed vessel that permits application of pressure and heat used for curing composites.

Autoclave molding   A molding technique in which an entire assembly (layup) is placed into an autoclave at 50 to 100 psi, in order to consolidate layers of the part by removing entrapped air and volatiles. Usually includes application of heat to trigger curing of the resin.

Axial winding   A type of filament winding in which the filaments are parallel to the axis.

B-stage   Intermediate stage in the polymerization reaction of thermosets, following which material will soften with heat and is plastic and fusible. Also called resistal. The resin of an uncured prepreg or premix is usually in B-stage. See A-Stage and B-Stage.

Bag molding   A technique in which the composite material is placed in a rigid mold and covered with a flexible bag, with pressure applied by vacuum, autoclave, press, or by inflating the bag.

Balanced laminate   All lamina except those at 0/90 are placed in plus-minus pairs (not necessarily adjacent) symmetrically about the lay-up centerline.

Bearing strength   The maximum bearing stress that will not cause a composite to fail when applied through a cylindrical fastener surface.

Bearing stress   Applied load divided by bearing area (hole diameter times thickness).

Bias fabric   A fabric in which warp and fill fibers are at an angle to the length.

Biaxial winding   A type of filament winding in which the helical band is laid in sequence, side by side, with no crossover of the fibers.

Bidirectional laminate   A reinforced plastic laminate in which the fibers are oriented in more than one direction in the plane of the laminate.

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

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

Bleedout   The excess liquid resin appearing at the surface, primarily during filament winding.

Bond strength   The amount of adhesion between bonded surfaces. As measured by load/bond area, the stress required to separate a layer of material from that to which it is bonded.

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

Braiding   Weaving fibers into a tubular shape.

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

Broadgoods   Fibers woven into fabrics that may or may not be impregnated with resin, usually furnished in rolls.

Buckling (composite)   A failure usually characterized by fiber deflection rather than breaking because of compressive action.

Butt joint   A joint in which parts are joined with no overlap.

C-stage   The final step in the cure of a thermoset resin; results in essentially irreversible hardening and insolubility.

Carbon/carbon   A composite of carbon fiber in a carbon matrix.

Carbon fiber   An important reinforcing fiber known for its light weight, high strength, and high stiffness that is produced by pyrolysis of an organic precursor fiber in an inert atmosphere at temperatures above 1,800° F. The material may also be graphitized by heat treating above 3,000° F.

Catalyst   A substance used in small quantities to promote or control the curing of a compound without being consumed in the reaction.

Caul sheet   Plate or sheet the same size and shape used in contact with a composite layup to transmit normal pressure and temperature during cure.

Ceramic-matrix composites   Materials consisting of a ceramic or carbon fiber surrounded by a ceramic matrix, usually SiC (silicon carbide).

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

Circuit   One complete traverse of the fiber feed mechanism of a filament-winding machine.

Circumferential winding   A type of filament winding in which the filaments are perpendicular to the axis.

Co-cured   Cured and simultaneously bonded to another prepared surface.

Coefficient of thermal expansion   A material's fractional change in length for a given unit change of temperature.

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

Composite   A material created from a fiber (or reinforcement) and an appropriate matrix material in order to maximize specific performance properties. The constituents do not dissolve or merge completely but retain their identities as they act in concert.

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

Compressive strength   A material's ability to resist a force that tends to crush or buckle; maximum compressive load a specimen sustains divided by the specimen's original cross-sectional area.

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

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

Contact molding   A technique in which reinforcement and resin are placed in a mold, with cure taking place at room temperature with a catalyst/promoter system, or in a heated oven. No additional pressure is used.

Continuous filament   An individual, small-diameter reinforcement that is flexible and indefinite in length.

Continuous-filament yarn   Yarn that is formed by twisting two or more continuous filaments into a single continuous strand.

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

Core   The central component of a sandwich construction to which the sandwich faces or skins are attached; also, part of a complex mold that forms undercut parts.

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

Creep   The dimensional change in a material under physical load over time beyond instantaneous elastic deformation.

Crimp   A fiber's waviness, which determines the capacity of the fiber to cohere.

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

Cross laminated   Material laminated so that some of the layers are oriented at various angles to the other layers with respect to the laminate grain. A cross-ply laminate usually has plies oriented only at 0°/90°.

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

Cure   To change the physical properties of a material irreversibly by chemical reaction via heat and catalysts, alone or in combination, with or without pressure.

Cure temperature   The temperature at which a material attains final cure.

Curing agent   A catalytic or reactive agent that brings about polymerization when it is added to a resin.

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

Damping   Diminishing the intensity of vibrations.

Debond   An unplanned nonadhered or unbonded region in an assembly.

Delamination   The separation of a laminated plastic material along the plane of its layers.

Denier   A numbering system for yarn and filament in which yarn number is equal to weight in grams of 9000 meters of yarn.

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

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

Draft angle   A mandrel's taper or angle for ease of part removal.

Drape   The ability of prepreg to conform to the shape of a contoured surface.

Dry winding   A type of filament winding in which preimpregnated roving is used.

E-glass   "Electrical glass"; the borosilicate glass most often used for the glass fibers in conventional reinforced plastics.

Fabric, nonwoven   A material formed from fibers or yarns without interlacing.

Fabric, woven   A material constructed of interlaced yarns, fibers, or filaments.

Fatigue   The failure of a material's mechanical properties as a result of repeated stress.

Fatigue strength   Maximum cyclical stress withstood for a given number of cycles before a material fails.

Fiber orientation   The fiber alignment in a nonwoven or a mat laminate in which most of the fibers are in the same direction, thereby affording higher strength in that direction.

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

Filament winding   A process for fabricating composites in which continuous reinforcing fibers, either preimpregnated with resin or drawn through a resin bath, are wound around a rotating, removable mandrel.

Filaments   Individual fibers of indefinite length used in tows, yarns, or roving.

Film adhesive   An adhesive in the form of a thin, dry, resin film with or without a carrier, commonly used for adhesion between layers of laminates.

Finish   Material applied to fibers, after sizing is removed, to improve matrix-to-fiber coupling.

Fracture   A rupture of the surface of a laminate because of external or internal forces, with or without complete separation.

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

Glass transition   The reversible change in an amorphous polymer between a viscous or rubbery condition and a hard, relatively brittle one.

Glass-transition temperature (Tg)   The approximate temperature at which increased molecular mobility results in significant changes in properties of a cured resin. The measured value of Tg can vary depending upon the test method.

Hand lay-up   A fabrication method in which reinforcement layers, preimpregnated or coated afterwards, are placed in a mold by hand, then cured to the formed shape.

Hardener   A substance used to promote or control curing action by taking part in it; as opposed to catalyst.

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

Honeycomb   Resin-impregnated material manufactured in, usually, hexagonal cells that serves as a core material in sandwich constructions. Honeycomb may also be metallic or polymer materials in a rigid, open-cell structure.

Hoop stress   Circumferential stress in a cylindrically shaped part as a result of internal or external pressure.

Hybrid composite   A composite with two or more reinforcing fibers.

Impact strength   A material's ability to withstand shock loading as measured by the work done in fracturing a specimen.

Impregnate   To saturate the voids and interstices of a reinforcement with a resin.

Impregnated fabric   See Prepreg.

Interface   The surface between two different materials: in fibers, the area at which the glass and sizing meet; in a laminate, the area at which the reinforcement and the laminating resin meet.

Interlaminar   Existing or occurring between two or more adjacent laminae.

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

Isotropic. Having uniform properties in all directions independent of the direction of load application.

Laminate ply   One layer of a laminated product.

Lap joint   A joint made by bonding overlapped portions of two adherends.

Lay-up   The placement of layers of reinforcement in a mold.

Liquid-crystal polymers   A newer type of thermoplastic, melt processible, with high orientation in molding, improved tensile strength, and high-temperature capability.

Mandrel. The form around which resin-impregnated fiber or tape is wound to form structural shapes or tubes.

Mat   A fibrous reinforcing material comprised of chopped filaments (for chopped-strand mat) or swirled filaments (for continuous-strand mat) with a binder to maintain form; available in blankets of various widths, weights, and lengths.

Matrix   A material in which the fiber of a composite is imbedded; it can be plastic, metal, ceramic, or glass.

Metal-matrix composites   Materials in which continuous carbon, silicon carbide, or ceramic fibers are embedded in a metallic matrix material.

Modulus   A measure of the ratio of load (stress) applied to the resultant deformation of a material, such as elasticity or shear.

Multifilament   A yarn consisting of many continuous filaments.

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

Nonwoven roving   A reinforcement composed of continuous rovings loosely gathered together.

Oriented materials   Composites whose constituents are aligned in a particular way.

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

PAN   See Polyacrylonitrile.

Peel ply   Layer of material applied to a prepreg lay-up surface that is removed from the cured laminate prior to bonding operations and leaves a clean resin-rich surface ready for bonding.

Peel strength   Strength of an adhesive bond obtained by stress applied "in a peeling mode."

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

Planar winding   A type of filament winding in which the filament path lies on a plane that intersects the winding surface.

Ply   The number of single yarns twisted together to form a plied yarn; one of the layers that make up a stack or laminate.

Polar winding   A type of filament 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 of the chamber.

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

Polymer   A very large molecule formed by combining a large number of smaller molecules, called monomers, in a regular pattern.

Polymerization   A chemical reaction in which the molecules of monomers are linked together to form polymers.

Postcure   An additional elevated-temperature exposure that is performed often without tooling or pressure to improve elevated-temperature mechanical properties, for example.

Pot life   The length of time a catalyzed thermosetting resin system retains a viscosity low enough for it to be suitable for processing.

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

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

Preform   A fibrous reinforcement preshaped to approximate contour and thickness desired in the finished part.

Prepreg   Resin-impregnated cloth, mat, or filaments in flat form that can be stored for later use. The resin is often partially cured to a tack-free state called "B-staging." Catalysts, inhibitors, flame retardants, and other additives may be included to obtain specific end-use properties and improve processing, storage, and handling characteristics.

Pressure-bag molding   A molding technique in which a flexible bag is placed over the contact lay-up in the mold, sealed, and clamped in place, and pressure applied by compressed air, which forces the bag against the part while the part cures.

Pultrusion   A continuous process for manufacturing composites in rods, tubes, and structural shapes having a constant cross-section. After the reinforcement is passed through the resin-impregnation bath, it is drawn through a shaping die to form the desired cross-section; curing takes place before the laminate can depart from that cross-section.

Quasi-isotropic   Approximating isotropy by orientation of plies in several directions.

Ramping   A gradual, programmed increase or decrease in temperature or pressure to control the cure or cooling of composite parts.

Reinforcement   A material added to the matrix to provide the required properties; ranges from short fibers through complex textile forms.

Release agents   Materials that are used to prevent cured matrix material from bonding to tooling.

Release film   An impermeable film layer that does not bond to the composite during cure.

Resin   A material, generally a polymer, that has an indefinite and often high molecular weight and a softening or melting range and exhibits a tendency to flow when it is subjected to stress. Resins are used as the matrices to bind together the reinforcement material in composites.

Resin rich   Localized area filled with resin but lacking reinforcement fiber.

Resin starved   Localized area lacking sufficient resin for wetout of the fibers.

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

Roving   A collection of bundles of continuous filaments either as untwisted strands or as twisted yarns.

S-glass   Structural glass; a magnesia/alumina/silicate glass reinforcement designed to provide very high tensile strength.

Sandwich construction   A composite composed of a lightweight core material (usually honeycomb or foamed plastic) to which two relatively thin, dense, high-strength, functional, or decorative skins (also called faces) are adhered.

Scarf joint   A bonded joint in which similar segments of adherends are cut away, with cut areas overlapped and bonded.

Selvage   The narrow edge of woven fabric that runs parallel to the warp. It is made with stronger yarns in a tighter construction than the body of the fabric to prevent raveling.

Shelf life   The length of time a material can be stored and continue to meet specification requirements and remain suitable for its intended use.

Silicon carbide fiber   A reinforcing fiber with high strength and modulus; density is equal to that of aluminum. It is used in organic metal-matrix composites.

Sizing   A compound that binds together and stiffens warp yarn to provide resistance to abrasion during weaving; normally removed and replaced with finish before matrix application.

Skin   A layer of relatively dense material used in a sandwich construction on the surface of the core.

Specific gravity   The density (mass per unit volume) of a material divided by that of water at a standard temperature.

Starved joint   A joint that does not have the proper amount of adhesive because of insufficient spread or excessive pressure.

Stiffness   The relationship of load to deformation for a particular material.

Storage life   The amount of time a material can be stored and remain suitable for use.

Strain   The elastic deformation of a material as a result of stress.

Stress   The internal force that resists change in size or shape, expressed in force per unit area.

Structural adhesive   An adhesive used for transferring loads between adherends.

Structural bond   A bond joining load-bearing components of an assembly.

Tack   The stickiness of a prepreg.

Tape   A unidirectional woven prepreg, in widths up to 12 inches for carbon fiber, for example.

Tape laying   A fabrication process in which prepreg tape is laid side by side or overlapped to form a structure.

Tensile strength   The maximum tensile stress sustained by a plastic specimen before it fails in a tension test.

Thermal conductivity   The ability of a material to conduct heat.

Thermoplastic   A plastic material that is capable of being repeatedly softened by application of heat and repeatedly hardened by cooling.

Thermoset   A plastic material that is capable of being cured by heat or catalyst into an infusible and insoluble material. Once cured, a thermoset cannot be returned to the uncured state.

Tooling resins   Plastic resins, chiefly epoxy and silicone, that are used as tooling aids.

Toughness   Tendency of a material to absorb work.

Tow   An untwisted bundle of continuous filaments, usually designated by a number followed by "K," indicating multiplication by 1,000; for example, 12K tow has 12,000 filaments.

Unbond   Area of a bonded surface in which bonding of adherends has failed to occur, or where two prepreg layers of a composite fail to adhere to each other; also denotes areas where bonding is deliberately prevented to simulate a defective bond.

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

Vacuum bag molding   A molding technique in which the part is cured inside a layer of film, from which entrapped air is removed by vacuum.

Viscosity   The tendency of a material to resist flow.

Voids   Pockets of entrapped gas that have been cured into a laminate.

Volatiles   Materials in a sizing or a resin formulation that can be vaporized at room or slightly elevated temperature.

Warp   The yarns running lengthwise and parallel to the selvage in a woven fabric.

Water jet   A high-pressure stream of water used for cutting organic composites.

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

Weft   The yarns running perpendicular to the warp in a woven fabric; also called "woof."

Wet lay-up   The application of resin to dry reinforcement in the mold.

Wet winding   A type of filament winding in which the fiber strand is impregnated with resin immediately before it contacts the mandrel.

Wetout   The saturation of all voids between strands and filaments of porous materials with resin.

Wetting agent   A surface-active agent that promotes wetting by decreasing the cohesion within a liquid.

Winding pattern   The regularly recurring pattern of the filament path in a filament winding after a certain number of mandrel revolutions.

Woven roving   A heavy, coarse fabric produced by the weaving of continuous roving bundles.

Wrinkle   An imperfection in the surface of a laminate that looks like a crease or fold in one of the outer layers; it occurs in vacuum bag molding due to improper placement of the bag.

X axis   The axis in the plane of the laminate used as 0 degree reference; the Y axis is the axis in the plane of the laminate perpendicular to the X axis; the Z axis is the reference axis normal to the laminate plane in composite laminates.

Yarn   Continuously twisted fibers or strands suitable for use in weaving into fabrics.

Young's modulus   The ratio of normal stress to the corresponding strain for tensile or compressive stresses less than the proportional limit of the material.

Source: Information herein was obtained from various government agencies. None of the text within this section is copyrighted material to the best knowledge of Composites-By-Design.

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