ADDITIVE - Any substance added to another substance, usually to
improve properties, such as plasticizers, initiators, light stabilizers,
and flame retardants. See also filler.
ADHEREND - A body that is held to another body, usually by an
adhesive. A detail or part prepared for bonding.
ADHESION - The state in which two surfaces are held together at an
interface by mechanical or chemical forces or interlocking action or both.
ADHESION PROMOTER - A coating applied to a substrate before it is
coated with an adhesive, to improve the adhesion of the plastic. Also
ADHESIVE - A substance capable of holding two materials together by
surface attachment. Adhesive can be in film, liquid, or paste form.
ADHESIVE FAILURE - Rupture of an adhesive bond such that the
separation appears to be at the adhesive-adherent interface.
ADHESIVE FILM - A synthetic resin adhesive, with or without a film
carrier fabric, usually of the thermosetting type, in the form of a thin
film of resin, used under heat and pressure as an interleaf in the
production of bonded structures.
ADHESIVE JOINT - The location at which two adherends or substrates
are held together with a layer of adhesive. The general area of contact
for a bonded structure.
ADHESIVE STRENGTH - Strength of the bond between an adhesive and an
AIR-BUBBLE VOID - Air entrapment within and between the plies of
reinforcement or within a bondline or encapsulated area; localized,
non-interconnected, spherical in shape.
AREAL WEIGHT - The weight of fiber per unit area (width x length)
of tape or fabric.
ASSEMBLY TIME - The time interval between the spreading of the
adhesive on the adherend and the application of pressure and/or heat to
ARAMID - Aromatic polyamide fibers characterized by excellent
high-temperature, flame-resistance, and electrical properties.
A-STAGE - An early stage in the reaction of a thermosetting resin
in which the material is still soluble and fusible.
AUTOCLAVE - A closed vessel for producing an environment of fluid
pressure, with or without heat, to an enclosed object while undergoing a
chemical reaction or other operation.
BAGGING - Applying an impermeable layer of film over an uncured
part and sealing the edges so that a vacuum can be drawn.
BAG MOLDING - A process in which the consolidation of the material
in the mold is effected by the application of fluid or gas pressure
through a flexible membrane.
BAG SIDE - The side of the part that is cured against the vacuum
BALANCED CONSTRUCTION - Equal parts of warp and fill in fiber
fabric. Construction in which reactions to tension and compression loads
result in extension or compression deformations only and in which flexural
loads produce pure bending of equal magnitude in axial and lateral
BALANCED LAMINATE - A composite laminate in which all laminate at
angles other than 0 degrees and 90 degrees occur only in +/- pairs (not
necessarily adjacent) and are symmetrical around the centerline.
BARCOL HARDNESS - A hardness value obtained by measuring the
resistance to penetration of a sharp steel point under a spring load. The
instrument, called the Barcol impressor, gives a direct reading on a 0 to
100 scale. The hardness value is often used as a measure of the degree of
cure of a plastic.
BATCH - In general, a quantity of material formed during the same
process or in one continuous process and having identical characteristics
throughout. Also called a lot.
BIAS FABRIC - A fabric in which warp and fill fibers are at an
angle to the length.
BINDER - The resin or cementing constituent (of a plastic compound)
that holds the other components together. The agent applied to fiber mat
or pre-forms to bond the fibers before laminating or molding.
BLADDER - An elastomeric lining for the containment of hydroproof
or hydroburst pressurization medium in filament-wound structures.
BLEEDER CLOTH - A nonstructural layer of material used in the
manufacture of composite parts to allow the escape of excess gas and resin
during cure. The bleeder cloth is removed after the curing process is
complete and is not part of the final composite.
BLEEDOUT - The excess liquid resin appearing at the surface
primarily occurring during filament winding.
BOND STRENGTH - The amount of adhesion between bonded surfaces. The
stress required to separate a layer of material from the base to which it
is bonded, as measured by load/bond area. See also peel strength.
BREATHER - A loosely woven material, such as glass fabric, which
serves as a continuous vacuum path over a part but does not come in
contact with the resin. The breather is removed after the curing process
is complete and is not part of the final composite.
BRIDGING - Condition in which fibers do not move into or conform to
radii and corners during molding, resulting in voids and dimensional
BROAD GOODS - Fiber woven to form fabric up to 1270 mm (50 in.)
wide. It may or may not be impregnated with resin and is usually furnished
in rolls of 25 to 140 kg. (50 to 300 lb.).
B-STAGE - An intermediate stage in the reaction of a thermosetting
resin in which the material melts when heated and dissolves in certain
solvents. Materials are usually precured to this stage to facilitate
handling and processing prior to final cure.
BULK FACTOR - The ratio of the volume of a raw molding compound or
powdered plastic to the volume of the finished solid piece produced
therefrom. The ratio of the density of the solid plastic object to the
apparent or bulk density of the loose molding powder.
BULK MOLDING COMPOUND (BMC) - Thermosetting resin mixed with strand
reinforcement, fillers, and so on, into a viscous compound for compression
or injection molding. See also sheet molding compound.
CARBON FIBERS - Fibers produced from pyrolytic degradation of
synthetic organic fibers, polyacrylonitrile (PAN) or rayon, which contain
about 92-99% carbon content and typically have modulus values up to 75 x
CATALYST - A substance that changes the rate of a chemical reaction
without itself undergoing permanent change in composition or becoming a
part of the molecular structure of the product. A substance that markedly
speeds up the cure of a compound when added in minor quantity as compared
to the amounts of primary reactants.
CAUL PLATES - Smooth metal, plastic, or rubber plates free of
surface defects. A caul plate must be the appropriate size and shape for
the composite lay-up with which it will be used. It is used in immediate
contact with the lay-up during the curing process to transmit normal
pressure and provide a smooth surface on the finished part.
CAVITY - The space inside a mold in which a resin or molding
compound is poured or injected. The female portion of a mold. That portion
of the mold that encloses the molded article (often referred to as the
die). Depending on the number of such depressions, molds are designated as
single cavity or multiple cavity.
CELL - In honeycomb core, a cell is a single honeycomb unit,
usually in a hexagonal shape.
COCURED - Cured and simultaneously bonded to another prepared
COEFFICIENT OF THERMAL EXPANSION - The fractional change in length
of a material for each unit change in temperature.
COHESION - The propensity of a single substance to adhere to
itself. The internal attraction of molecular particles toward each other.
The ability to resist partition of itself. The force holding a single
COHESIVE FAILURE - Failure of an adhesive joint occurring primarily
in an adhesive layer.
COIN TAP TEST - Using a coin to tap a laminate in different spots,
listening for a change in sound, which would indicate the presence of a
defect. A surprisingly accurate test in the hands of experienced
COMPACTION - The application of a temporary vacuum bag an vacuum to
remove trapped air and compact the lay-up.
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 MODULUS - Ration of compressive stress to compressive
strain below the proportional limit. Theoretically equal to Young’s
modulus determined from tensile experiments.
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.
CONDITIONING - Subjecting a material to a prescribed environmental
and/or stress history before testing.
CONTACT MOLDING - A molding 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.
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.
CORE CRUSH - A collapse, distortion, or compression of the core.
COUNT - For fabric, number of warp and filling yarns per inch in
woven cloth. For yarn, size based on relation of length and weight.
COUPON - Usually, a specimen for a specific test, as a tensile
CREEP - The dimensional change in a material under physical load
over time beyond instantaneous elastic deformation.
CROSS LAMINATED - Material laminated so that some of the layers are
oriented at various angles to the other with respect to the laminate
grain. A cross-ply laminate usually has plies oriented only at 0 degree/90
CROSS-LINKING - Applied to polymer molecules, the setting-up of
chemical links between the molecular chains. When extensive, as in most
thermosetting resins, cross-linking makes one infusible super-molecule of
all the chains.
C-STAGE - The final stage of the curing of a thermosetting resin in
which the material has become infusible and insoluble in common solvents.
CURE - To change the properties of a thermosetting resin
irreversibly by chemical reaction, i.e., condensation, ring closure, or
addition. Cure may be accomplished by addition of curing (cross-linking)
agents, with or without catalyst, and with or without heat.
CURE CYCLE - The time/temperature/pressure cycle used to cure a
thermosetting resin system of prepreg.
CURE STRESS - A residual internal stress produced during the curing
cycle of composite structures. Normally, these stresses originate when
different components of a wet lay-up have different thermal coefficients
CURING AGENT - A catalytic or reactive agent that brings about
polymerization when it is added to a resin.
DEBOND - A deliberate separation of a bonded joint or interface,
usually for repair or rework purposes. Also, an unbonded or nonadhered
region; a separation at the fiber-matrix interface due to strain
incompatibility. In the United Kingdom, the term often refers to
accidental damage. See also delamination.
DEBULKING - Compacting of a thick laminate under moderate heat and
pressure and/or vacuum to remove most of the air, to ensue seating on the
tool, and to prevent wrinkles.
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.
DRAFT ANGLE - The angle of a taper on a mandrel or mold that
facilitates removal of the finished part.
DRAPE - The ability of a fabric or prepreg to conform to a
DRY LAMINATE - A laminate containing insufficient resin for
complete bonding of the reinforcements. See also resin starved.
DRY LAY-UP - Construction of a laminate by the layering of
preimpregnated reinforcement (partly cured resin) in a female mold or on a
male mold, usually followed by bag molding or autoclave molding.
E-GLASS - "Electrical glass"; the borosilicate glass most
often used for the glass fibers in conventional reinforced plastics.
ELASTICITY - That property of materials by virtue of which they
tend to recover their original size and shape after removal of a force
ELONGATION - Deformation caused by stretching. The fractional
increase in length of a material stressed in tension. (When expressed as
percentage of the original gage length, it is called percentage
END - A strand of roving consisting of a given number of filaments
gathered together. The group of filaments is considered an "end"
or strand before twisting, a "yarn" after twist has been
applied. An individual warp yarn, thread, fiber, or roving.
EPOXY PLASTIC - A polymerizable thermoset polymer containing one or
more epoxide groups and curable by reaction with amines, alcohols,
phenols, carboxylic acids, acid anhydrides, and mercaptans. An important
matrix resin in composites and structural adhesive.
EXOTHERM - The liberation or evolution of heat during the curing of
a plastic product.
FATIGUE - The failure or decay of mechanical properties after
repeated applications of stress. Fatigue tests give information on the
ability of a material to resist the development of cracks, which
eventually bring about failure as a result of a large number of cycles.
FATIGUE STRENGTH - The maximum cyclical stress a material can
withstand for a given number of cycles before failure occurs. The residual
strength after being subjected to fatigue.
FAYING SURFACE - The surfaces of materials in contact with each
other and joined or about to be joined together.
FIBER CONTENT - The amount of fiber present in a composite. This is
usually expressed as a percentage volume fraction or weight fraction of
FIBER COUNT - The number of fibers per unit width of ply present in
a specified section of a composite.
FIBER DIRECTION - The orientation or alignment of the longitudinal
axis of the fiber with respect to a stated reference axis.
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-REINFORCED PLASTIC (FRP) - A general term for a composite
that is reinforced with cloth, mat, strands, or any other fiber form.
FILAMENT - The smallest unit of a fibrous material. The basic units
formed during drawing and spinning, which are gathered into strands of
fiber for use in composites. Filaments usually are of extreme length and
very small diameter, usually less than 25 fm (1 mil). Normally filaments
are not used individually. Some textile filaments can function as yarn
when they are of sufficient strength and flexibility.
FILAMENT WINDING - A process for fabricating a composite structure
in which continuous reinforcements (filament, wire, yarn, tape, or other),
either previously impregnated with a matrix material or impregnated during
the winding, are placed over a rotating and removable form or mandrel in a
prescribed way to meet certain stress conditions. Generally the shape is a
surface of revolution and may or may not include end closures. When the
required number of layers is applied, the wound form is cured and the
FILL - Yarn oriented at right angles to the warp in a woven fabric.
FILLER - A relatively inert substance added to a material to alter
its physical, mechanical, thermal, electrical, and other properties or to
lower cost or density. Sometimes the term is used specifically to mean
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
FINISH - Material applied to fibers, after sizing is removed, to
improve matrix-to-fiber coupling.
FLASH - Excess material which forms at the parting line of a mold
or die, or which is extruded from a closed mold.
FLEXURAL MODULUS - The ratio, within the elastic limit, of the
applied stress on a test specimen in flexure to the corresponding strain
in the outermost fibers of the specimen.
FRACTURE - A rupture of the surface of a laminate because of
external or internal forces, with or without complete separation.
GEL - The initial jellylike solid phase that develops during the
formation of a resin from a liquid. A semisolid system consisting of a
network of solid aggregates in which liquid is held.
GEL COAT - A quick setting resin applied to the surface of a mold
and gelled before lay-up. The gel coat becomes an integral part of the
finished laminate, and is usually used to improve surface appearance and
GEL TIME - The time required for a liquid material to form a gel
under specified conditions of temperature as measured by a specific test.
GLASS CLOTH - Conventionally woven glass fiber material; certain
lightweight glass fabrics are also called scrims.
GLASS TRANSITION TEMPERATURE (Tg) - The approximate midpoint
of the temperature range over which the glass transition takes place;
glass and silica fiber exhibit a phase change at approximately 955 C (1750
F) and carbon/graphite fibers at 2205 to 2760 C (4000 to 5000 F). The
temperature at which increased molecular mobility results in significant
changes in the properties of a cured resin system. Also, the inflection
point on a plot of modulus versus temperature. The measured value of Tg
depends to some extent on the method of test.
GRAPHITE FIBERS - A group of carbon fibers which have a carbon
content of about 99% and also have high modulus values. This term is used
interchangeably with "carbon fibers" throughout the industry.
HAND LAYUP - A fabrication method in which reinforcement layers,
pre-impregnated 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.
HARDNESS - The resistance to surface indentation usually measured
by the depth of penetration (or arbitrary units related to the depth of
penetration ) of a blunt point under a given load using a particular
instrument according to a prescribed procedure.
HEAT DISTORTION POINT - The temperature at which a standard test
bar deflects a specified amount under a stated load. Now called deflection
HEAT RESISTANCE - The property or ability of plastics and
elastomers to resist the deteriorating effects of elevated temperatures.
HEAT SINK - A contrivance for the absorption of transfer of heat
away from a critical element or part. Bulk graphite is often used as a
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
HYBRID - A composite laminate comprised of laminae of two or more
composite material systems, e.g., graphite and glass. It also applies to
woven fabrics having more than one type of fiber.
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.
INJECTION MOLDING - Method of forming a plastic to the desired
shape by forcing the heat softened plastic into a relatively cool cavity
INTERFACE - The boundary or surface between two different,
physically distinguishable media. On fibers, the contact area between
fibers and sizing or finish. In a laminate, the contact area between the
reinforcement and the laminating resin.
INTERLAMINAR - Existing or occurring between two or more adjacent
INTERLAMINAR SHEAR - A shearing force tending to produce a relative
displacement between two laminae along the plane of their interface.
ISOTROPIC - Having uniform properties in all direction. The
measured properties of an isotropic material are independent of the axis
KEVLAR - Registered trademark of E.I. Dupont de Nemours, Inc. For a
strong organic fiber similar to fiberglass but having a higher
strength-to-weight ratio. When woven into cloth and impregnated with a
thermosetting epoxy resin, it produces a material having high impact
resistance and low radio frequency attenuation. Generic term: aramid.
LAMINATE - A product made by bonding together two or more layers of
material or materials.
LAMINATE ORIENTATION - The configuration of a cross-plied composite
laminate with regard to the angles of cross-plying, the number of laminae
at each angle, and the exact sequence of the lamina lay-up.
LAY-UP - The reinforcing material placed in position in the mold.
The process of placing the reinforcing material in position in the mold.
The resin-impregnated reinforcement. A description of the component
materials, geometry, and so forth, of a laminate.
LOT - A specific amount of material produced at one time using the
same process and the same conditions of manufacture, and offered for sale
as a unit quantity.
MANDREL - The core tool around which resin-impregnated paper,
fabric, or fiber is wound to form pipes, tubes, or structural shell
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.
MIL - The unit used in measuring the diameter of glass fiber
strands, wire, and so forth (1 mil = 0.001 in.).
MILLED FIBER - Continuous glass strands hammer milled into very
short glass fibers. Useful as inexpensive filler or anticrazing
reinforcing fillers for adhesives.
MODULUS - A measure of the ratio of load (stress) applied to the
resultant deformation of a material, such as elasticity or shear.
MOISTURE CONTENT - The amount of moisture in a material determined
under prescribed conditions and expressed as a percentage of the mass of
the moist specimen, that is, the mass of the dry substance plus the
MOLD - The cavity or matrix into or on which the plastic
composition is placed and from which it takes form. To shape plastic parts
or finished articles by heat and pressure. The assembly of all the parts
that function collectively in the molding process.
MOLDING - The forming of a polymer or composite into a solid mass
of prescribed shape and size by the application of pressure and heat for
given times. Sometimes used to denote the finished part.
MOLDING PRESSURE - The pressure applied to the ram of an injection
machine or compression or transfer press to force the softened plastic to
fill the mold cavities completely.
MOLD-RELEASE AGENT - A lubricant, liquid, or powder used to prevent
sticking of molded articles in the cavity.
MOLD SURFACE - The side of a laminate that faced the mold (tool)
during cure in an autoclave or hydroclave.
NOMINAL VALUE - A value assigned for the purpose of a convenient
designation. A nominal value exists in name only. It is often an average
number with a tolerance so as to fit together with adjacent parts.
NONDESTRUCTIVE TESTING (NDT) - Broadly considered synonymous with
nondestructive inspection (NDI).
ORANGE PEEL - An uneven surface somewhat resembling that of an
orange peel; said of injection moldings that have unintentionally ragged
OUT TIME - The time a prepreg is exposed to ambient temperature,
namely, the total amount of time the prepreg is out of the freezer. The
primary effects of our time are to decrease the drape and tack of the
prepreg while also allowing it to absorb moisture from the air.
PARTING LINE - A mark on a molded piece where the sections of a
mold have met in closing.
PEEL PLY - Layer of material applied to a prepreg layup surface
that is removed from the cured laminate prior to bonding operations and
leaves a clean resin-rich surface ready for bonding.
PEEL STRENGTH - Adhesive bond strength, as in pounds per inch of
width, obtained by stress applied in a peeling mode.
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.
PLAIN WEAVE - A weaving pattern in which the warp and fill fibers
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.
PLATENS - The mounting plates of a press, to which the entire mold
assembly is bolted.
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).
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.
POST CURE - The exposure of certain resins to higher than normal
curing temperatures after the initial cure cycle. This second stage is
necessary to attain the complete cure and desired mechanical properties of
the resins involved. The higher temperatures are used separately because
they would result in an excessive reaction if applied throughout the
POT LIFE - The length of time a catalyzed thermosetting resin
system retains a viscosity low enough for it to be suitable for
PREFORM - A preshaped fibrous reinforcement formed by distribution
of chopped fibers 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 mold press.
PREPREG, PREIMPREGNATED - A combination of mat, fabric, nonwoven
material, or roving with resin, usually advanced to the B-stage, ready for
PRESSURE BAG MOLDING - A process for molding reinforced plastics in
which a tailored, flexible bag is placed over the contact lay-up on the
mold, 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.
PRIMER - A coating applied to a surface, before the application of
an adhesive, lacquer, enamel, and so forth, to improve the adhesion
performance of load-carrying ability of the bond.
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.
PROTOTYPE - A model suitable for use in complete evaluation of
form, design, performance, and material processing.
REINFORCEMENT - A material added to the matrix to provide the
required properties; ranges from short fibers through complex textile
RELEASE AGENTS - Materials that are used to prevent cured matrix
material from bonding to tooling.
RELEASE FILM - An impermeable layer of film that does not bond to
the resin being cured. See also separator.
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 CONTENT - The amount of resin in a laminate expressed as
either a percentage of total weight or total volume.
RESIN RICH - Localized area filled with resin but lacking
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 number of yarns, strands, tows, or ends collected into a
parallel bundle with little of no twist.
RT - Stands for ambient room temperature, usually between 70-77 F
SANDWICH CONSTRUCTION - A composite composed of 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.
SCRIM - A low-cost reinforcing fabric made from continuous filament
yarn in an open-mesh construction. Used in the processing of tape or other
B-stage material to facilitate handling. Also used as a carrier of
adhesive, to be used in secondary bonding.
SECONDARY BONDING - The joining together, by the process of
adhesive bonding, of two or more already cured composite parts, during
which the only chemical or thermal reaction occurring is the curing of the
SEPARATOR - A permeable layer that also acts as a release film.
Porous Teflon-coated fiberglass is an example. Often placed between lay-up
and bleeder to facilitate bleeder system removal from laminate after cure.
SET UP - To harden, as in curing of a polymer resin.
S-GLASS - Structural glass; a magnesia/alumina/silicate glass
reinforcement designed to provide very high tensile strength.
SHEAR STRENGTH - The maximum shear stress that a material is
capable of sustaining. Shear strength is calculated from the maximum load
during a shear or torsion test and is based on the original
cross-sectional area of the specimen.
SHEET MOLDING COMPOUND (SMC) - A composite of fibers, usually a
polyester resin and pigments, fillers and other additives that have been
compounded and processed into sheet form to facilitate handling in the
SHELF LIFE - The length of time a material, substance, product, or
reagent can be stored under specified environmental conditions and
continue to meet all applicable specification requirements and/or remain
suitable for its intended function.
SHORE HARDNESS - A measure of the resistance of material to
indentation by a spring-loaded indenter. The higher the number, the
greater the resistance. Normally used for rubber materials.
SHORT BEAM SHEAR (SBS) - A flexural test of a specimen having a low
test span-to-thickness ratio (for example, 4:1), such that failure is
primarily in shear.
SHRINKAGE - The relative change in dimension from the length
measured on the mold when it is cold to the length of the molded object 24
hrs. After it has been taken out of the mold.
SIZE - Any treatment consisting of starch, gelatin, oil, wax, or
other suitable ingredient applied to yarn or fibers at the time of
formation to protect the surface and aid the process of handling and
fabrication or to control the fiber characteristics. The treatment
contains ingredients that provide surface lubricity and binding action
but, unlike a finish, contains no coupling agent. Before final fabrication
into a composite, the size is usually removed by heat cleaning, and a
finish is applied.
SIZING CONTENT - The percent of the total strand weight made up by
the sizing; usually determined by burning off or dissolving the organic
sizing; known as loss on ignition.
SKIN - A layer of relatively dense material used in a sandwich
construction of 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.
SPRAY-UP - Technique in which a spray gun is used as an applicator
tool. In reinforced plastics, for example, fibrous glass and resin can be
simultaneously deposited in a mold. In essence, roving is fed through a
chopper and ejected into a resin stream that is directed at the mold by
either of two spray systems. In foamed plastics, fast-reacting urethane
foams or epoxy foams are fed in liquid streams to the gun and sprayed on
the surface. On contact, the liquid starts to foam.
STACKING SEQUENCE - A description of a laminate that details the
ply orientation and their sequence in the laminate.
STANDARD DEVIATION - A measure of dispersion of data from the
average. The root means square of the individual deviation from the
STIFFNESS - A measure of modulus. The relationship of load and
deformation. The ratio between the applied stress and resulting strain. A
term often used when the relationship of stress to strain does not conform
to the definition of Young’s modulus.
STOPS - Metal pieces inserted between die halves. Used to control
the thickness of a press-molded part. Not a recommended practice, because
the resin will receive less pressure, which can result in voids.
STORAGE LIFE - The period of time during which a liquid resin,
packaged adhesive, or prepreg can be stored under specified temperature
conditions and remain suitable for use. Also called shelf life.
STRAND - Normally an untwisted bundle or assembly of continuous
filaments used as a unit, including slivers, tows, ends, yarn, and so
forth. Sometimes a single fiber or filament is called a strand.
STRUCTURAL ADHESIVE - Adhesive used for transferring required loads
between adherends exposed to service environments typical for the
STRUCTURAL BOND - A bond that joins basic load-bearing parts of an
assembly. The load may be either static or dynamic.
SURFACE PREPARATION - Physical and/or chemical preparation of an
adherend to make it suitable for adhesive bonding.
TACK - The stickiness of a prepreg.
TEMPLATE - A pattern used as a guide for cutting and laying plies.
TENSILE STRENGTH - The maximum load or force per unit
cross-sectional area, within the gage length, of the specimen. The pulling
stress required to break a given specimen.
THERMAL CONDUCTIVITY - The ability of a material to conduct heat.
THERMOPLASTIC - Capable of being repeatedly softened by an increase
of temperature and hardened by an increase in temperature. Applicable to
those materials whose change upon heating is substantially physical rather
than chemical and that in the softened stage can be shaped by flow into
articles by molding or extrusion.
THERMOSET - A plastic that, when cured by application of heat or
chemical means, changes into a substantially infusible and insoluble
THIXOTROPY - The tendency of a material to cling to a vertical
THREAD COUNT - The number of yarns (threads) per inch in either the
lengthwise (warp) or crosswise (fill or weft) direction of woven fabrics.
TOW - An untwisted bundle of continuous filaments.
TRACER - A fiber, tow, or yarn added to a prepreg for verifying
fiber alignment and, in the case of woven materials, for distinguishing
warp fibers from fill fibers.
ULTRASONIC TESTING - A nondestructive test applied to materials for
the purpose of locating internal flaws or structural discontinuities by
the use of high-frequency reflection or attenuation (ultrasonic beam).
UNBOUND - An area within a bonded interface between two adherends
in which the intended bonding action failed to take place, of where two
layers of prepreg in a cured component do not adhere to each other. Also
used to denote specific areas deliberately prevented from bonding in order
to simulate a defective bond, such as in the generation of quality
VACUUM BAG MOULDING - A process in which a sheet of flexible
transparent material plus bleeder cloth and release film are placed over
the lay-up on the mold and sealed at the edges. A vacuum is applied
between the sheet and the lay-up. The entrapped air is mechanically worked
out of the lay-up and removed by the vacuum, and the part is cured with
temperature, pressure, and time. Also called bag molding.
VENT - A small hole or shallow channel in a mold that allows air or
gas to exit as the molding material enters.
VISCOSITY - The tendency of a material to resist flow.
VOID CONTENT - Volume percentage of voids, usually less than 1% in
a properly cured composite. The experimental determination is indirect,
that is calculated from the measured density of a cured laminate and the
"theoretical" density of the starting material.
VOIDS - Air or gas that has been trapped and cured into a laminate.
Porosity is an aggregation of microvoids. Voids are essentially incapable
of transmitting structural stresses or nonradiative energy fields.
VOLATILES - Materials, such as water and alcohol, in a sizing or a
resin formulation, that are capable of being driven off as a vapor at room
temperature or at a slightly elevated temperature.
WARP - The yarn running lengthwise in a woven fabric. A group of
yarns in long lengths and approximately parallel. A change in dimension of
a cured laminate from its original molded shape.
WATER JET - Water emitted from a nozzle under high pressure (70 to
410 MPa, or 10 to 60 ksi or higher). Useful for cutting organic
WEATHERING - Exposure of plastics to the outdoor environment.
WEAVE - The particular manner in which a fabric is formed by
interlacing yarns. Usually assigned a style number.
WET LAY-UP - A method of making a reinforced product by applying
the resin system as a liquid when the reinforcement is put in place.
WET-OUT - The condition of an impregnated roving or yarn in which
substantially all voids between the sized strands and filaments are filled
WORKING LIFE - A surface imperfection in laminated plastics that
has the appearance of a crease or fold in one or more outer sheets of the
paper, fabric, or other base, which has been pressed in. Also occurs in
vacuum bag molding when the bag is improperly placed, causing a crease.
YARN - An assemblage of twisted filaments, fibers, or strands,
either natural or manufactured, to form a continuous length that is
suitable for use in weaving or interweaving into textile materials.
Y-AXIS - In composite laminates, the axis is the plane of the
laminate that is perpendicular to the x-axis. Contrast with x-axis.
Z-AXIS - In composite laminates, the reference axis normal to the
plane of the laminate.
ZERO BLEED - A laminate fabrication procedure that does not allow
loss of resin during cure. Also describes prepreg made with the amount of
resin desired in the final part, such that no resin has to be removed