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Accelerator
A material that, when mixed with a catalyst or resin, will speed up the chemical reaction between the catalyst and the resin. Also know as a promoter.
Activator
An additive used to promote and reduce the curing time of resins.
Anisotropic
Material whose physical properties vary with direction.
Aramid
A type of highly orientated organic material derived from polyamide (nylon) but incorporating aromatic ring structure.
Areal Weight
The weight of fabric or tape per unit area (width x length).
Bias Fabric
Warp and weft fibers at an angle to the length of the fabric.
Bulk Molding Compound
Thermoset resin system mixed with strand reinforcement into a viscous compound for compression molding.
Carbon fiber
A fiber produced by the pryrolysis of organic precursor fibers, either polyacrylonitrile (PAN), rayon and pitch as the starting materials heat treated in excess of 2300ºF (1260ºC).
Chopped Strand
Continuous strand fiber or roving cut up into uniform lengths.
Coefficient of thermal expansion
The change in length per unit length of a material when heated through a unit temperature. Usually express in terms of length/length/unit temperature (i.e. in/in/°F).
Compression Molding
An open mold, loaded with reinforcement, closed then heated resulting in net shape parts.
Compressive Strength
The ability of a material to resist a force that tends to crush or buckle.
Contact Molding
A process where resin and reinforcement are added to an open mold. Curing takes place through exothermic chemical reaction at room temperature or in an oven at elevated temperatures, with no additional pressure being applied.
Core
The central member of a sandwich construction to which the exterior face sheets are attached.
Coupling agent
Materials applied to fiber surfaces to improve the bond between fiber and matrix.
CTE (see coefficient of thermal expansion)
Curing Agent
A reactive agent that when added to a resin, causes polymerization. Also called a hardener.
Delamination
Separation in the layers of material within a laminate.
Drapeability
The ability of a fabric or prepreg to conform to a contoured surface.
Dry Laminate
A laminate containing insufficient resin for a complete bonding of the entire laminate. Also referred to as resin starved.
E-Glass
A family of glasses with a calcium aluminoborosilicate composition and a maximum alkali content of 2.0%. This glass is suitable for electrical laminates due to its high resistivity.
Exotherm
The amount of heat given off as a result of the resin curing.
Fatigue strength
The maximum cyclical stress a material can withstand for a given number of cyles before failure.
Fiber Direction
The orientation or alignment of the longitudinal axis of the fiber with respect to a stated reference axis.
Fibers
A general term for a material which has a long axis this is several times greater than its radius.
Filament
A single fiber which is the smallest unit of fiberous material.
Fill
Fiber orientation at right angles to the warp in a fabric – also known as weft.
Fish Eye
A circular separation in a gelcoat film which is generally caused by contaminates such as oil, dust, silicone or water.
Graphite fiber
Graphite fibers are those carbon fibers which have been subjected to a heat treatment in excess of 3000ºF (1650ºC).
Gel Time
The length of time that a catalyzed resin remains workable after the hardener is added.
Glass Transition
Reversible change in an amorphous polymer between a viscous or rubbery condition to a hard relatively brittle one.
Hand Lay-Up
The process of placing successive plies of reinforced material of resin-impregnated reinforcement in position on a mold by hand.
Hardener
Material that reacts with resin to promote or control the curing action.
Hybrid
A composite laminate consisting of laminae of two or more composite material system.
Inhibitor
A material added to resin to slow the cure cycle down by retarding polymerization.
Injection Molding
Method of forming a plastic to the desired shape by forcing the heat-softened plastic into a relatively cool mold cavity under pressure.
Interlaminar strength
A measure of the bonding strength between two or more adjacent laminae.
Isotropic
Having physical properties that do not vary with direction.
Kevlar®
An organic polymer fiber composed of aromatic polyamides. Kevlar is a registered trademark of E.I. Dupont deNemours and Company, Inc.
Lamina
A single ply or layer within a laminate made up of a series of layers.
Laminate
Multiple layers of lamina with unique orientations.
Lamination
The laying on of layers of reinforced materials and resin onto a mold.
Macroscopic
Relating to or concerned with larger units.
Mat
A fiberous material used to develop a fiber reinforced plastic consisting of randomly oriented chopped filament loosely held together by a binder.
Matrix
Material in which reinforcing fiber is embedded: polymer, metal or ceramic.
Mill
A unit used in measuring film thickness and the diameter of fiber strands of glass – one mill = 0.001”.
Modulus of Elasticity
The mathematical description of a materials tendency to be deformed elastically (i.e., non-permanently) when a force is applied.
Mold
The cavity into (female) or onto (male) which the reinforcement an resin is places and from which it takes its form.
Monomer
A single molecule that can react with like or unlike molecules to form a polymer.
Net Shape
Part fabrication resulting in final dimension that do not require machining or cutting.
Orange Peel
The gel coat surface which takes on a rough wavy texture like an orange peel.
Out-Gassing
Release of solvents, volatiles, gasses and moisture from composite parts while under vacuum.
Pan (Polyacrylonitrile)
Base material used in manufacture of some types of carbon fiber.
Peel Strength
Strength of an adhesive bond obtained by stress that is applied in a ‘peeling’ mode.
Plug
The initial model used to develop molds, also referred to as a tooling master.
Pitch fiber
A fiber produced by the pryrolysis of pitch (a residue from the distillation of coal and petroleum products), usually exhibiting higher stiffness than PAN based fibers.
Porosity
Small air bubbles in a gel coat film or composite which are generally smaller in size than a pinhole.
Preform
A preshaped fiberous reinforcement.
Prepreg
Resin impregnated cloth, fiber or mat in which the resin is partially cured and which can be stored for later use.
Pre-Release
Premature release of gel coat or laminate from the mold.
Print-Through
Transfer of the image of glass strands through a gel coated surface.
Promoter
See “accelerator”.
Reinforcement
The fiber, flake or particle added to a matrix to change some property of the matrix such as adding fiber to plastic to increase its strength and stiffness .
Release Agent
A substance used on a mold or in the compound to prevent sticking and for ease of part release.
Resin
Used in reinforced plastics to surround and hold fibers in column. Also transfers stress from outer surface to fiber columns.
Resin Infusion
To draw or force resin into a dry reinforcement which is already in a mold cavity.
Resin Rich
Localized area filled with excess resin as compared to consistent resin/glass ratio.
Resin Transfer Molding (RTM)
Molding process in which a catalyzed resin is pumped into a two sided matched mold where a fiberous reinforcement has been placed.
Roving
A collection of continuous filaments.
S-Glass
Magnesia/alumina/silicate glass reinforcement designed to provide very high tensile strength.
Shear stiffness
The resistance of a material to deformation under shear loading.
Sheet Molding Compound (SMC)
Ready-to-mold glass fiber reinforced thickened polyester material used primarily in closed molding.
Sizing
Water-soluable solution of chemical additives used to coat filaments which protect against water absorption and abrasion.
Specific stiffness
The stiffness of a material divided by the material density.
Specific strength
The strength of a material divided by the material density.
Standard Modulus Carbon Fiber
33 million PSI axial Young's Modulus fiber.
Stress
A measure of the average amount of force exerted per unit area.
Stiffness
The resistance of a material to deformation under load, usually measured under tensile loading conditions.
Strength
The stress at which a material breaks or permanently deforms.
Thermoplastic
A material that softens when heated without changing its intrinsic physical properties.
Thermoset
A plastic, that when cured changes to a substantially to an insoluble or infusible material.
Tow
An untwisted bundle of continuous filaments with a specific count.
Transverse stiffness
The resistance of a material to transverse deformation under transverse load.
Vacuum Assisted Resin Transfer Molding (VARTM)
Infusion process where a vacuum draws resin into a one sided mold.
Viscosity
A fluids resistance to flow.
Warp
The fibers running lengthwise and parallel in a fabric.
Weft
The transverse fibers in a fabric which run perpendicular to the warp. Also called fill or woof.
Woven Fabric
A planar material made by interlacing (weaving) tows in various or specific patterns.