Terminology

A  

Accelerator - Chemical additive that hastens cure or chemical reaction

Adhesive - Substance applied to mating surfaces to bond them together by surface attachment.

Aramid - Aromatic polyamide fibers; commonly, DuPont's Kevlar and Akzo Nobel's Twaron.

B 

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

Bag Molding - A molding 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.

Basket Weave - Woven reinforcement where two or more warp threads go over and under two or more filling threads in a repeat pattern; less stable than the plain weave but produces a flatter, stronger, more pliable fabric.

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

Bidirectional Laminate - Laminate with fibers oriented in more than one direction on the same plane.

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

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

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.

C

C-Stage - Final step in the cure of a thermoset resin, resulting in irreversible hardening and insolubility.

CAD/CAM - Computer-aided design/computer aided manufacturing.

Carbon Fiber - Reinforcing fiber known for its light weight, high strength and high stiffness produced by by pyrolysis of an organic precursor fiber in an inert atmosphere at temperatures above 1,800º F. Can also be graphitized by heat-treating above 3,000º F.

Cocured - Cured and simultaneously bonded to another prepared surface.

Composite - A material that combines fiber and a binding matrix to maximize specific performance properties. Neither element merges completely with the other. Advanced composites use only continuous, oriented fiber in polymer, metal and ceramic matrices.

Compressive Strength - Resistance to a crushing or buckling force, the maximum compressive load a specimen sustains divided by its original cross-sectional area.

Core - In sandwich construction, the central component to which inner and outer skins are attached; also refers to a section of a complex mold that forms undercut parts..

Crosslinking - Polymerization reactions that branch out from the main molecular chain to form a networked pattern of chemical links.

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 added to resin.

D

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

Debond - An unplanned nonadhered or unbonded region in an assembly.

Delaminate - The separation of ply layers due to adhesive failure. Also includes the separation of layers of fabric from the core structure. A delamination may be associated with bridging, drilling and trimming.

Delamination - In-plane separation of a laminate ply or plies due to adhesive failure.

Demold - To remove a part from a tool, or a tool from an intermediate model.

Design Allowable - A limiting value for material property that can be used to design a structural or mechanical system to a specified level of success with 95 percent statistical confidence.

Doubler - Extra layers of reinforcement for added stiffness or strength in laminate areas that incur abrupt load transfers.

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

E  

E-Glass - Stands for "electrical glass" and refers to borosilicate glass fibers most often used in conventional polymer matrix composites.

Elasticity - The property of materials to recover their original size and shape after deformation.

Elongation - The fractional increase in length of a material stressed in tension. When expressed as a percentage of the original length, it is called percent elongation.

Exotherm - Heat released during a chemical reaction. Uncontrolled exotherm can lead to violent explosion.
F INDEX

F  

Fabric, Nonwoven - A material formed from fibers or yarns with without interlacing.

Fabric, Woven - A material constructed in interlaced yarns of fiber.

Fabrication - The process of making a composite part or tool.

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

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

FEA - Finite element analysis, a process of selecting the optimum combination of materials in a composite based on software analysis.

Fiber Content - Amount of fiber in a composite expressed as a ratio to the matrix. The most desirable fiber content is a 60:40 ratio of 60 percent fiber and 40 percent matrix resin.

Fiber Orientation - Direction of fiber alignment in a nonwoven or mat laminate wherein most of the fibers are placed in the same direction to afford greater 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 of tool. Differs from filament winding in several ways: There is no limit on fiber angles; pressure of 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.

Fiber Reinforces Plastics (FRP) - Term used to designate mid -range, glass reinforced composites.

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

Fill Treads - The crosswise fibers woven a 90 ° to the warp fibers; also known as a weft or woof.

Filler - Material added to the mixed resin to increase viscosity, improve appearance, and lower density and cost.\

Filler Ply - Additional patch to fill in a depression in repair or to build up an edge.

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

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

Flexural Strength - The strength of a material in bending, usually expressed in force per unit area, as the stress of a bent test sample at the instant of failure.

Fracture - A rupture of the surface of a laminate due to external or internal forces; may or may not result in complete separation.

G  

Gel Coat - Pigmented resins applied as a coating to a mold or part to produce a smooth finish on the part.

Gel Time - Period of time from initial mixing of liquid reactants to the point when gelation occurs as defined by specific test method.

Glass Transition - Reversible change in an amorphous polymer between a viscous condition and a hard, relatively brittle condition.

Glass-Transition Temperature (Tg) - Approximate temperature at which increased molecular mobility results in significant changes in properties of a cured resin. The measured value or Tg can vary, depending on the test method.

H 

Hand Layup - 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 - Substance used to promote or control curing action by taking part in it, as opposed to a catalyst.

Heat - Term used coloquially to indicate any temperature above ambient (room) temperature to which a part of material is or will be subjected.

Heat-Distortion Temperature (HDT) - Temperature at which deflection occurs under specified temperature and stated load.

Honeycomb - Resin-Impregnated material, most commonly manufactured in hexagonal cells, that serves as a core in sandwich structure. May also be metallic or polymer in rigid, open-cell structure.


Hybrid Composite - A composite with two or more types of reinforcing fibers.

I  

Impact Strength - A materials ability to withstand shock loading as measured by fracturing a specimen.

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

Impregnated Fabric - See Prepreg.

Inclusion - Physical and mechanical discontinuity occurring within a material or part.

Interface - Surface between two materials: in glass fibers, for instance, the area at which the glass and sizing meet; in a laminate, the area at which the reinforcement and laminating resin meet.

Interlaminar - Existing or occurring between two or more adjacent laminae.

Interlaminar Shear - Shearing force that produces displacement between two laminae along the plane of their interface.

J  

No entries for this selection


K  

Kevlar - Trademark of DuPont for aramid fibers used as a reinforcement fiber.

L  

Laminate Ply - One fabric/resin or fiber/resin layer that is bonded to adjacent layers in the curing process.

Layup - Placement of layers of reinforcement in a mold.

M  

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

Matrix - Material in which reinforcing fiber of a composite is imbedded: polymer, metal, ceramic.


Modulus - Measure of the ratio of applied load (stress) to the resultant deformation of a material, such as elasticity of shear. Can be low, intermediate, high of ultrahigh.


N  

Nomex - Trademark of DuPont for nylon paper-treated material that is commonly made into honeycomb core.
Nondestructive Inspection (NDI) - Determining material or part characteristics without permanently altering the test subject. Nondestructive testing (NDT) and Nondestructive Evaluation (NDE) are broadly considered synonymous with NDI.

Nonwoven Roving - A reinforcement composed of continuous rovings loosely gathered together.

O  

One-Off - A fabrication process in which a single part is fabricated.

Original Equipment Manufacturer (OEM) - Companies that design and build products bearing their name, such as Boeing 777 aircraft or Prince tennis racquets.

Out Time - Period of time in which a prepreg remains handleable with properties intact outside a specified storage environment (a freezer, in the case of thermoset prepregs).

Outgassing - Release of solvents and moisture from composite parts under the hard vacuum of space.\

P  

Part Consolidation - A process of composites fabrication in which multiple discrete parts are designed and fabricated together into a single part, thus reducing the number of fabricated parts and the need to join those parts together.

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

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

Phenolic Resin - Thermosetting resin produced by condensation of an aromatic alcohol with an aldehyde; usually phenol with formaldehyde.


Ply - One of the layers that makes up a stack or laminate; also, the number of single yarns twisted together to form a plied.

Ply Schedule - Layup of individual plies or layers to form a laminate. Plies may be arranged in alternating fiber orientation to produce multidirectional strength in a part.

Polymer - Large molecule formed by combining many smaller molecules or monomers in a regular pattern.

Polymerization - Chemical reaction that links monomers to form polymers.

Porosity - The presence of visible voids within a solid material into which either air or liquids may pass.

Postcure - Additional exposure to elevated temperature, often occurring without tooling or pressure, that improves mechanical properties.

Pot Life - Length of time in which a catalyzed thermosetting resin retains sufficiently low viscosity for processing.

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

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. Additives such as catalysts, inhibitors and flame retardants can be added to obtain specific end-use properties and improve processing, storage and handling characteristics.

Prototype - Process of creating a test part not intended for commercial release that establishes design, material and fabrication parameters for a new product. May entail multiple iterations to arrive at final/commercial part design.
Puckers - Local areas on prepreg where material has blistered and pulled away from the separator film or release paper.

Puncture - Break in composite skin in sandwich structure that may or may not go through to the core material or completely through the part.

Q  

Quasi -isotropic - Approximating isotropy by orienting plies in several directions.

R  

Ramping - Gradual programmed increase/decrease in temperature or pressure to control cure or cooling of composite parts.

Reinforcement - Key element added to the matrix to provide the required properties (primary strength); ranges from short fibers through complex textile forms.

Release Agent - Used to prevent cured matrix material from bonding to tooling usually painted or sprayed on mold.

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

Resin - Polymer with indefinite and often high molecular weight and a softening or melting range that exhibits a tendency to flow when subjected to stress. As composite matrices, resins bind together reinforcement fibers.

Resin-Rich - Filled with excess resin as compared to consistent resin/fiber ratio.

Resin-Starved - Lacking sufficient resin for fiber wetout.

Resin Transfer Molding (RTM) - A molding process in which catalyzed resin is pumped into a two-sided, matched mold where fibrous reinforcement has been placed. The mold and/or resin may or may not be heated. RTM offers the ability to consolidate structural parts. Its major drawback is the high cost of the initial, two sided mold.

Resin Viscosity - Viscous property of a resin system or solid-to-liquid transition resistance to flow, which can be altered by temperature and pressure as necessary to achieve desired flow characteristics.

Ribbon Direction - On a honeycomb core, the way the honeycomb can be separated. The direction of one continuous ribbon.

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

S  

S-glass - Stands for "structural glass," and refers to magnesia/alumina/silicate glass reinforcement designed to provide very high tensile strength;commonly used in advanced composites.

Sandwich Structure - Composite composed of lightweight core material (usually honeycomb or foam) to which two relatively thin, dense, high-strength, functional or decorative skins are adhered.

Sealant - A paste or liquid applied to a joint that hardens in place to form a seat.

Shear - An action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relative to each other.

Shelf Life - Length of time in which a material can be stored and continue to meet specification requirements, remaining suitable for its intended use.

Sizing - Compound that binds together and stiffens warp yarn, providing abrasion resistance during weaving. Sizing is normally removed and replaced with finish before matrix application.

Skin - A layer of relatively dense materials used on the surface of the core of a sandwich structure.

Solvent - A liquid used to dissolve and clean materials.

Spec - Specification of the properties, characteristics, or requirements a particular material or part must have in order to be acceptable to a potential user of the material or part.

Specific Gravity - Density (mass per unit volume) of a material divided by that of water at a standard temperature.

Stiffness - Relationship of load to deformation for a particular material.

Storage Life - Amount of time a material can be stored and retain specific properties.

Strain - Elastic deformation resulting from stress.

Stress - Internal resistance change in size or shape, expressed in force per unit area.

Stress Crack - External or internal cracks in a composite caused by tensile stresses; cracking may be present internally, externally or in combination.

Structural Adhesive - An adhesive used to transfer loads between adherents.

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

Substrate - A material upon the surface of which an adhesive-containing substance is spread for any purpose, such as bonding or coating.

T  

Tack - Stickiness of an uncured prepreg.

Tape - Thin unidirectional prepreg in widths up to 12 inches for carbon fiber.

Tensile Strength - Maximum tensile stress sustained by a composite specimen before it fails in a tension test.

Thermal Stress Cracking - Crazing and cracking of some thermoplastic resins from overexposure to elevated temperatures.

Thermocouple - Wire assembly used with a control device to sense temperature readings.

Thermoset - Composite matrix cured by heat and pressure or with a catalyst into an infusible and insoluble material. Once cured, a thermoset cannot be returned to the uncured state.

Thixotropic - Materials that are gel-like at rest, but fluid when agitated; having high static shear strength and low dynamic shear strength at the same time; losing viscosity under stress.

Tool - the mold, either one- or two-sided and either open or closed, in or upon which composite material is placed in order to make a part.

Toughness - A measure of the ability of a material to absorb energy.

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).

U  

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

V  

Vacuum Bag Molding - Molding technique wherein the part is cured inside a layer of film from which entrapped air is removed by vacuum.

Viscosity - Tendency of material to resist flow.

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

W  

Warp - Yarns running lengthwise and parallel to the narrow edge of woven fabric.

Water Absorption - Ration of weight of water absorbed by material to the weight of dry material.

Weave - Pattern by which a fabric is formed from interlacing yarns. In plain weave, warp and fill fibers alternate to make both fabric faces identical. In satin weave, 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 - Yarns running perpendicular to the warp in a woven fabric. Also called woof.

Wet Layup - Application of a resin to a dry reinforcement in the mold. A manual creation of a form of prepreg.

Wetout - Saturation with resin of all voids between strands and filaments.

Woof - Yarns running perpendicular to the warp in a woven fabric. Also called weft.

Woven Roving - Heavy, coarse fabric produced by weaving continuous roving bundles.

Wrinkle - Imperfection in the surface of a laminate that looks like a crease in one of the outer layers. This occurs in vacuum-bag molding when the bag is improperly placed.

X  

X-Axis - The axis in the plane of the laminate used as 0° 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.

Y  

Y-Axis - See X-Axis.

Yarn - Continuously twisted fibers of strands suitable for weaving into fabrics.

Z 

Z-Axis - See X-Axis.

Zero Bleed - Laminate Fabrication procedure that does not allow loss of resin during cure