|
[ B ]
Back
Pressure
Resistance of a material, because of its viscosity, to
continued flow when a mould is closing.
Bag
Molding
A
technique in which the consolidation of the material in the
mould is affected by the application of fluid pressure
through a flexible membrane.
Balanced
Design
In
filament-wound reinforced plastics, a winding pattern so
designed that the stresses in all filaments are equal.
Balanced
Laminate
All
laminate plies, except those at 0°/90°, are placed in
plus/minus pairs (not necessarily adjacent) symmetrically
about the lay-up centreline. This minimises distortion on
demoulding.
Balanced
Twist
An
arrangement of twist in a plied yarn or cord which will not
cause twisting on itself when the yarn of cord is held in
the form of an open loop.
Barcol
Hardness
A
hardness value obtained by measuring the resistance to
penetration of a sharp steel point under a spring load. The
instrument, the Barcol Impressor, gives a direct reading on
a scale of 0 to 100. The hardness value is often used as a
measure of the degree of cure of a plastic.
Bare
Glass
Glass
(yarns, roving or fabrics) from which the sizing or finish
has been removed or before it has been applied.
Barrier
Cream
A cream
used to protect the skin from contact with resins.
Base
The
reinforcing material (glass fibre, paper, cotton, asbestos,
etc.) which is impregnated with resin in the forming of
laminates.
Bearing
Stress
The
applied load divided by the bearing area. (Maximum bearing
stress is the maximum load sustained by the specimen during
the test divided by the original bearing area.)
Benzoyl
Peroxide (BPO)
An
initiator for curing polyester resin. BPO is used with
aniline accelerators or where heat is used to cure the
resin.
Bias
Fabric
A fabric
in which warp and weft fibre are at an angle (usually ±45°)
to the length.
Biaxial
Load
A
loading condition in which a laminate is stressed in at
least two different directions in the plan of the laminate.
Biaxial
Winding
In
filament winding, a type of winding in which the helical
band is laid in sequence, side by side, with no crossover of
fibres.
Bidirectional Laminate
A
reinforced plastic laminate with the fibres oriented in two
directions (usually, but not necessarily, 0/90°) in the
plane of the laminate. (See also Unidirectional Laminate.)
Binder
The
agent applied to glass mat or preforms to bond the fibres
before laminating or moulding.
Bismaleimide
A type
of polyimide resin 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 non-woven material, not a part of the composite,
that allows excess gas and resin to escape during cure.
Bleedout
The
excess liquid resin that migrates to the surface of a
laminate in any pressure moulding process.
Blister
Undesirable rounded elevation of the surface of a plastic
with boundaries that are more or less sharply defined,
resembling in shape a blister on the human skin.
Block
Copolymer
An
essentially linear copolymer in which there are repeated
sequences of polymer segments of different chemical
structure some of which may be crystalline in nature, others
of which may be amorphous.
Bond
Strength
The
amount of adhesion between bonded surfaces; a measure of the
stress required to separate a layer of material from the
base to which it is bonded. (See also Peel Strength.)
Boron
Fibre
A fibre
usually of a tungsten-filament core with elemental boron
vapor deposited on it to impart strength and stiffness.
Braiding
A
process for assembling fibres into a tubular shape.
Breather
A
usually non-woven material that does not come in contact
with the resin but serves as a continuous vacuum path over a
part in production.
Bridging
A region
of a contoured part which has cured without being properly
compacted against the mould.
B Stage
An
intermediate stage in the reaction of certain thermosetting
resins. The resin in an uncured prepreg or premix is usually
in this stage. (See also A Stage, C Stage.)
Bubble
A
spherical internal void; globule of air or other gas trapped
in a plastic.
Buckling
Crimping
of fibres in a composite material, often occurring in
glass-reinforced thermoset due to resin shrinkage during
cure.
Bulk
Density
The
density of a moulding material in loose form (granular,
nodular. etc.), expressed as a ratio of weight to volume.
Burst
Strength
Hydraulic pressure required to burst a vessel of given
thickness; commonly used in testing filament-wound composite
structures.
[Back to Top]
[ C ]
CAD
Computer-aided design.
CAM
Computer-aided manufacturing.
Carbon-carbon
A
composite of carbon fibre in a carbon matrix.
Carbon
Fibre
An
important reinforcing fibre known for its light weight, high
strength, and high stiffness that is produced by pyrolysis
of an organic precursor fibre in an inert atmosphere at
temperatures above 1800°F (982°C). The material may also be
graphitised by heat treating above 3000°F (1649°C).
Casting
The
process of pouring a mixture of resin, fillers and/or fibers
into a mold as opposed to building up layers through
lamination. This technique produces different physical
properties from laminating.
Catalyst
A
substance which changes the rate of a chemical reaction
without itself undergoing permanent change in its
composition; a substance which markedly speeds up the cure
of a compound when added in small quantity compared with the
amounts of primary reactants.
Catenary
A
measure of the difference in length of the strands in a
specified length of roving as a result of unequal tension;
the tendency of some strands in a taut horizontal roving to
sag lower than the others.
Caulk
An
elastic material used to protect joints or connections from
external elements, particularly moisture.
Caul
Plate
A sheet
the size of the platens used in hot pressing, or other
pressure moulding processes.
Cavity
The
space between a male and female mold set in which the part
is formed. Sometimes used to refer to a female mold.
Centipoise
A unit
of measure used to describe the viscosity of a liquid.
Viscosity is measured with a Brookfield Viscometer for most
polyester resin applications.
Centrifugal Casting
A high
production technique for cylindrical composites, such as
pipe, in which chopped fibre and resin is positioned inside
a hollow mandrel designed to be heated and rotated as resin
is added and cured.
Ceramic
Matrix Composites
Materials consisting of a ceramic or carbon fibre surrounded
by a ceramic matrix, usually silicon carbide.
Chalking
A
surface phenomenon indicating degradation of a cosmetic
surface. Chalking is a powdery film which appears lighter
than the original color.
Charge
The
measurement or weight of material (liquid, preformed, or
powder) used to load a mould at one time or during one
cycle.
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.
Chill
(1) To
cool a mould by circulating water through it. (2) To cool a
moulding with an air blast or by immersing it in water.
Chopped
Strand Mat
A
fiberglass reinforcement consisting of short strands of
fiber arranged in a random pattern and held together with a
binder. Mat is generally used in rolls consisting of 3/4
oz/ft2 material to 2 oz/ft2 material.
Circuit
In
filament winding (1) one complete traverse of the fibre-feed
mechanism of a winding machine; (2) one complete traverse of
a winding band from one arbitrary point along the winding
path to another point on a plane through the starting point
and perpendicular to the axis.
Circumferential (“circ”) Winding
In
filament-wound reinforced plastics a winding with the
filaments essentially perpendicular to the axis.
Clamping
Pressure
In
injection moulding and transfer moulding the pressure
applied to the mould to keep it closed, in opposition to the
fluid pressure of the compressed moulding material.
Cloth
A
fiberglass reinforcement made by weaving strands of glass
fiber yarns. Cloth is available in various weights measured
in ounces per square yard or Kg/m2.
Co-curing
Simultaneous bonding and curing of components, or dissimilar
materials.
Coefficient of Elasticity
The
reciprocal of Young’s modulus in a tension test.
Coefficient of Expansion
The
fractional change in dimension of a material for a unit
change in temperature. Also called coefficient of thermal
expansion.
Coefficient of Friction
A
measure of the resistance to sliding of one surface in
contact with another surface.
Coefficient of Thermal Expansion
The
change in length per unit length produced by a unit rise in
temperature.
Cohesion
(1) The
propensity of a single substance to adhere to itself. (2)
The internal attraction of molecular particles toward each
other. (3) The force holding a single substance together.
Cohesive
Failure
Failure
of a bonded joint within the adhesive itself.
Cold-setting Adhesive
A
synthetic resin adhesive capable of hardening at normal room
temperature in the presence of a hardener.
Color
Stability
The
ability of a surface coating or pigment to resist
degradation due to environmental exposure.
Co-mingled 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
homogeneous material created by synthetic assembly of two or
more materials (selected filler or reinforcing elements and
compatible matrix binder) to obtain specific characteristics
and properties. Composites are subdivided into the following
classes on the basis of the form of the structural
constituents; fibrous: the dispersed phase consists of
fibers; flake: the dispersed phase consists of flat flakes;
laminar: composed of layers of laminate constituents;
particulate: dispersed phase consists of small particles;
skeletal: composed of a continuous skeletal matrix filled by
a second material.
Compression Molding
A
technique for molding thermoset plastics in which a part is
shaped by placing the fibre and resin into an open mould
cavity, closing the mould, and applying heat and pressure
until the material has cured or achieved its final form.
Compression Molding Pressure
The
pressure applied to the moulding material in the mould.
Compressive Modulus Ec
Ratio of
compressive stress to compressive strain below the
proportional limit. Theoretically equal to Young’s modulus
determined from tensile experiments.
Compressive Strength
(1) The
ability of a material to resist a force that tends to crush.
(2) The crushing load at the failure of a specimen divided
by the original sectional area of the specimen.
Compressive Stress
The
compressive load per unit area of original cross section
carried by the specimen during the compression test.
Condensation Reaction
A
polymerisation reaction in which simple by-products (for
example, water) are formed.
Connection
Where
two panels are attached to each other or a panel is attached
to the building.
Consolidation
A
processing step that compresses fibre and matrix to reduce
voids and achieve a desired density.
Contact
Molding
A
process for molding reinforced plastics in which
reinforcement and resin are placed on an open mould, cure is
at room temperature using a catalyst-promoter system or by
heat in an oven, and no additional pressure is used.
Continuous Filament
An
individual flexible fibre of glass of small diameter and
great or indefinite length.
Continuous-filament Yarn
Yarn
formed by twisting two or more continuous filaments into a
single continuous strand.
Continuous Laminating
An
automated process for forming panels and sheeting in which
fabric or mat is passed through a resin bath, brought
together between covering sheets, and passed through a
heating zone for cure. Squeeze rolls control thickness and
resin content as the various plies are brought together.
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 moulding compounds, or it may be used chopped.
Cooling
Fixture
A
fixture used to maintain the shape or dimensional accuracy
of a moulding after it is removed from the mould and until
the material is cool enough to hold its shape.
Core
(1) The
central member of a sandwich construction to which the faces
of the sandwich are attached. (2) A channel in a mould for
circulation of heat-transfer media.
Count
(1) For
fabric the number of warp and weft yarns per cm in woven
cloth. (2) For yarn the size based on relation of length and
weight. Basic unit is a tex which is the weight in grammes
of 1000 linear metres of the fibre.
Coupling
Agent
Any
chemical substance designed to react with both the
reinforcement and matrix phases of a composite material to
form or promote a stronger bond at the interface; a bonding
link.
Cowoven
Fabric
A
reinforcement fabric woven with two different types of
fibres in individual yarns, for example, thermoplastic
fibres woven side by side with carbon fibres.
Crazing
Fine
cracks which may extend in a network on or under the surface
of a plastic material.
Creel
A device
for holding the required number of fibre bobbins in the
desired position for unwinding.
Creep
The
change in dimension of a plastic under load over a period of
time not including the initial instantaneous elastic
deformation; at room temperature it is called cold flow.
Crimp
The
waviness of a fibre, particularly in a woven fabric.
Critical
Length
The
minimum length of a fibre necessary for matrix shear loading
to develop fibre ultimate strength by a matrix.
Critical
Strain
The
strain at the yield point.
Crosswise Direction
Refers
to cutting specimens and to application of load. For rods
and tubes, crosswise is the direction perpendicular to the
long axis. For other shapes or materials that are stronger
in one direction than in another, crosswise is the direction
that is weaker. For materials that are equally strong in
both direction, crosswise is an arbitrarily designed
direction at right angles to the length.
Crystallinity
The
quality of having a molecular structure with atoms arranged
in an orderly, three-dimensional pattern.
C Stage
The
final stage in the reaction of certain thermosetting resins
in which the material is relatively insoluble and infusible.
The resin in a fully cured thermoset moulding is in this
stage. (See also A Stage, B Stage.)
Cure
To
change the properties of a resin by chemical reaction, which
may be condensation or addition; usually accomplished by the
action of heat or catalyst, or both, and with or without
pressure.
Curing
Agent
Hardener, a catalytic or reactive agent added to a resin to
cause polymerisation. Curing agents participate in the
polymerisation process. They may be latent - curable only at
elevated temperatures - or they may be activated at room
temperature (25°C).
Curing
Temperature
Temperature at which a cast, moulded, or extruded product, a
resin impregnated reinforcement, an adhesive, etc., is
subjected to curing.
Curing
Time
The
length of time a part is subjected to heat or pressure, or
both, to cure the resin. (Further cure may take place after
removal of the assembly from the conditions of heat or
pressure.)
Cycle
The
complete, repeating sequence of operations in a process or
part of a process. In moulding, the cycle time is the
elapsed time between a certain point in one cycle and the
same point in the next.
[Back to Top]
[ D ]
D Glass
A
high-boron-content glass made especially for laminates
requiring precisely controlled dielectric constant.
Damage
Tolerance
A
measure of the ability of structures to retain load carrying
capability after exposure to sudden loads (for example,
ballistic impact).
Damping
(Mechanical)
Mechanical damping gives the amount of energy dissipated as
heat during the deformation of a material. Perfectly elastic
materials have no mechanical damping. Damping also
diminishes the intensity of vibrations.
Daylight
The
distance in the open position between the moving and fixed
tables (platens) of a hydraulic press. For a multidaylight
press, daylight is the distance between adjacent platens.
Debond
An
unplanned nonadhered or unbonded region in an assembly.
Deflection Temperature Under Load
The
temperature at which a simple beam has deflected a given
amount under load (formerly called heat-distortion
temperature).
Deformation Under Load
The
dimensional change of a material under load for a specific
time following the instantaneous elastic deformation caused
by the initial application of the load; also called cold
flow or creep.
Delaminate
To split
a laminated plastic material along the plane of its layers.
(See also Laminate.)
Delamination
Physical
separation or loss of bond between laminate plies.
Denier
A yarn
and filament numbering system in which the yarn number is
equal numerically to the weight in grams of 30,000 ft (9144
m) (used for continuous filaments). The lower the denier the
finer the yarn.
Density
A
comparison of weight per volume, measured in pounds per
cubic foot.
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 of 100. A-basis allowable: material property
exceeds the design allowable 99 times out of 100.
Dielectric
A
nonconductor of electricity.
Dielectric Constant
(1) The
ratio of the capacity of a capacitor having a dielectric
material between the plates to that of the same capacitor
when the dielectric is replaced by a vacuum. (2) A measure
of the electrical charge stored per unit volume at unit
potential.
Dielectric Strength
The
value of a material as an electrical insulator or the
resistance to the flow of electric current.
Dimensional Stability
Ability
of a plastic part to retain the precise shape to which it
was moulded, cast, or otherwise fabricated.
Displacement Angle
In
filament winding the distance of advance of the winding
ribbon on the equator after one complete circuit.
Distortion
A change
in shape form that which is intended.
Doctor
Roll
A device
for regulating the amount of liquid material on the rollers
of a spreader; also called doctor bar or doctor blade.
Doily
In
filament winding the planar reinforcement applied to a local
area between windings to provide extra strength in an area
where a cutout is to be made, e.g. port openings.
Dome
In
filament winding the portion of a cylindrical container that
forms the integral ends of the container.
Doubler
Localised area of extra layers of reinforcement, usually to
provide stiffness or strength for fastening or other abrupt
load transfers.
Draft
The
taper or slope of the vertical surfaces of a mould designed
to facilitate removal of moulded parts.
Draft
Angle
The
angle between the tangent to the surface at that point and
the direction of ejection.
Drape
The
ability of preimpregnated broad goods or dry fabrics to
conform to an irregular 3-D shape; textile conformity.
Dry
Winding
Filament
winding using preimpregnated roving, as differentiated from
wet winding. (See also Wet Winding.)
Dry
Lay-up
Construction of a laminate by layering preimpregnated
reinforcement in a female or male mould, usually followed by
bag moulding or autoclave moulding.
DSC
Differential scanning calorimeter. Instrumentation for
measuring chemical reactions by observing exothermic or
endothermic (heat output or heat input) reactions of
materials - usually over a programmed temperature cycle.
Dwell
(1) A
pause in the application of pressure to a mould, made just
before the mould is completely closed, to allow gas to
escape from the moulding material. (2) In filament winding
the time the traverse mechanism is stationary while the
mandrel continues to rotate to the appropriate point for the
traverse to begin a new pass. (3) A pause in the temperature
rise of a cure cycle, where the part being cured is held at
a constant temperature for a period.
[Back to Top]
[ E ]
Edgewise
Refers
to the application of load. The load is applied edgewise
when it is applied to the edge of the original sheet or
specimen.
E Glass
A
borosilicate glass; the type most used for glass fibres for
reinforced plastics; suitable for electrical laminates
because of its high resistivity. (Also called electric
glass.)
Ejection
Removal
of a moulding from the mould impression by mechanical means,
by hand, or by using compressed air.
Elastic
Deformation
The part
of the total strain in a stressed body which disappears upon
removal of the stress.
Elasticity
The
property of plastics materials by virtue of which they tend
to recover their original size and shape after deformation.
Elastic
Limit
The
greatest stress which a material is capable of sustaining
without permanent strain remaining upon the complete release
of the stress. A material is said to have passed its elastic
limit when the load is sufficient to initiate plastic
(nonrecoverable) deformation.
Elastic
Recovery
The
fraction of a given deformation that behaves elastically.
Elastic
recovery = elastic extension
total
extension
Electroformed Moulds
A mould
made by electroplating metal on the face of a mould.
Elongation
Deformation caused by stretching; the fractional increase in
length of a material stressed in tension. (When expressed as
percentage of the original gauge length, it is called
percentage elongation.)
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 and a yarn after twist has been
applied): an individual warp yarn, thread, fibre, or roving.
Encapsulating
Completely surrounding an object with resin or a fiber resin
composite.
EpoxyResin
A
polymer resin characterized by epoxide molecule groups.
Even
Tension
The
process whereby each end of roving is kept in the same
degree of tension as the other ends.
Exotherm
The
liberation or evolution of heat during curing of a plastic
product.
[Back to Top]
[ F ]
Fabric
A
material constructed of interlaced yarns, fibres, or
filaments, usually planar.
Fabric,
nonwoven
A
material formed from fibres or yarns without interlacing.
Fabric,
woven
A
material constructed of interlaced yarns, fibres, or
filaments.
Fabricating, fabrication
The
manufacture of plastic products from moulded parts, rods,
tubes, sheeting, extrusions, or other form by appropriate
operations such as punching, cutting, drilling, and tapping.
Fabrication includes fastening plastic parts together or to
other parts by mechanical devices, adhesives, heat sealing,
or other means.
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
Life
The
number of cycles of deformation required to bring about
failure of the test specimen under a given set of
oscillating conditions (pressure/load).
Fatigue
Limit
The
stress below which a material can be stressed cyclically for
an infinite number of times without failure.
Fatigue
Strength
(1) The
maximum cyclic stress a material can withstand for a given
number of cycles before failure occurs. (2) The residual
strength after being subjected to fatigue.
Felt
A
fibrous material made from interlocked fibres by mechanical
or chemical action, moisture, or heat; made from asbestos,
cotton, glass, etc.
Female
Mold
A
concave mold used to precisely define the convex surface of
a molded part.
Fibre-composite Material
A
material consisting of two or more discrete physical phases,
in which a fibrous phase is dispersed in a continuous matrix
phase. The fibrous phase may be macro-, micro-, or
submicroscopic, but must retain its physical identity so
that it can be removed from the matrix intact.
Fibre
Glass
An
individual filament made by extruding fibres from molten
glass.
Fibre
Diameter
The
measurement of the diameter of individual filaments.
Fibre-matrix Interface
The
region separating the fibre and matrix phases, which differs
from them chemically, physically, and mechanically. In most
composite materials, the interface has a finite thickness
(nanometers to thousands of nanometers) because of diffusion
or chemical reactions between the fibre and matrix. Thus,
the interface can be more properly described by the terms
interphase or interfacial zone.
Fibre
Pattern
(1)
Visible fibres on the surface of laminates or mouldings. (2)
The thread size and weave of fabrics.
Fibre
Placement
A
continuous process for fabricating composite shapes with
complex contours and/or cutouts by means of a device that
lays preimpregnated fibres (in tow form) onto a non-uniform
mandrel or tool. It differs from filament winding (below) in
several ways: there is no limit on fibre angles; compaction
takes place online via heat, pressure, or both; and fibres
can be added and dropped as necessary. The process produces
more complex shapes and permits a faster putdown rate than
filament winding.
Filament
Any
fibre whose aspect ratio (length to effective diameter) is
for all practical purposes infinity, i.e. a continuous
fibre.
Filament
Winding
A
process for fabricating a composite structure in which
continuous reinforcements (filament, wire, yarn, tape, or
other) impregnated with a matrix material either previously
or during the winding are placed over a rotating removable
form or mandrel in a prescribed way to meet certain stress
conditions. When the right number of layers has been
applied, the wound form is cured and the mandrel removed.
Fill
(Also
known as weft). Yarn oriented at right angles to the warp in
a woven fabric.
Filler
A
relatively inert material added to a plastic mixture to
reduce cost, modify mechanical properties, serve as a base
for colour effects, or improve the surface texture.
Fillet
A
radiused joint of adhesive between two surfaces being
bonded.
Filling
Yarn
The
transverse threads or fibres in a woven fabric, i.e. fibres
running perpendicular to the warp; also called weft.
Film
Adhesive
A
synthetic resin adhesive in the form of a thin dry film of
resin with or without a carrier.
Finish
A
material applied to the surface of fibres in a fabric used
to reinforce plastics, and intended to improve the physical
properties of the reinforced plastics over those obtained
using reinforcement without finish. Not to be confused with
"size" (q.v.).
Fish Eye
The
effect of surface contamination which causes a circular
separation of a paint or gel coat.
Flame
Resistance
Ability
of a material to not support flame once source of heat is
removed.
Flame
Retardants
Chemicals used to reduce or eliminate the tendency of a
resin to burn.
Flame-retarded Resin
A resin
compounded with certain chemicals to reduce or eliminate its
tendency to burn.
Flammability
A
measure of the extent to which a material will support
combustion.
Flange
An
extension around the perimeter of a mold or part for the
purpose of demolding, stiffening or connecting two
components.
Flash
Point
The
lowest temperature at which a substance gives off enough
vapors to form a flammable mixture.
Flatwise
Refers
to cutting specimens and the application of load. The load
is applied flatwise when it is applied perpendicular to the
flat face of the original sheet or specimen.
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 fibres of the specimen.
Flexural
Rigidity
(1) For
fibres this is a measure of the rigidity of individual
strands or fibres; the force couple required to bend a
specimen to unit radius of curvature. (2) For plates the
measure of rigidity is D = El. where E is the modulus of
elasticity and I is the moment of inertia.
Flexural
Strength
(1) The
resistance of a material to breakage by bending stresses.
(2) The strength of a material in bending expressed as the
tensile stress of the outermost fibres of a bent test sample
at the instant of failure. For plastics this value is
usually higher than the straight tensile strength. (3) The
unit resistance to the maximum load before failure by
bending.
Flow
The
movement of resin under pressure, allowing it to fill all
parts of a mould.
Foam
A
lightweight, cellular plastic material containing gas-filled
voids. Typical foams include urethane, PVC and polyester.
Foamed
Plastics
Resins
in sponge form; may be flexible or rigid; cells may be
closed or interconnected.
Foam-in-place
The
process of creating a foam by the combination of two liquid
polymers. See In-Situ.
Fracture
Toughness
A
measure of the damage tolerance of a material containing
initial flaws or cracks.
FRP
Fibrous
reinforced plastic, any type of plastic-reinforced cloth,
mat, strands, or any other form of fibrous material.
FVF
Fibre
Volume Fraction. The ratio of the volume of fibre in a
laminate to the total volume of fibre and resin.
FWF
Fibre
Weight Fraction. The ratio of the weight of fibre in a
laminate to the total weight of fibre and resin.
[Back to Top]
[ G ]
Gauge
Length
Length
over which deformation is measured.
Gap
In
filament winding the space between successive windings,
which are usually intended to lie next to each other.
Gel
The
initial jellylike solid phase that develops during the
formation of a cured resin from a liquid.
Gelation
The
formation of a gel.
Gel Time
For
thermosetting resins the time between introduction of a
catalyst or hardener into a resin and gel formation.
Gelcoat
A filled
resin applied to the surface of a mould before Iay-up. (The
gelcoat becomes an integral part of the finished laminate
and is usually used to improve surface appearance, etc.)
Glass
Filament
A form
of glass that has been drawn to a small diameter and extreme
length. Most filaments are less than 0.005 (130 microns) in
diameter.
Glass
Finish
A
material applied to the surface of a glass reinforcement to
improve its effect upon the physical properties of the
reinforced plastic.
Glass
Flake
Thin,
irregularly shaped flakes of glass typically made by
shattering a continuous thin-walled tube of glass.
Glass
Transition
The
reversible change in an amorphous polymer or in amorphous
regions of a partially crystalline polymer from (or to) a
viscous or rubbery condition to (or from) a hard and
relatively brittle state. The glass transition generally
occurs over a relatively narrow temperature region and is
similar to the solidification of a liquid to a glassy state;
it is not a phase transition. The glass transition
temperature is the approximate midpoint of the temperature
range over which glass transition takes place. See extra
notes in Formulated Products Article.
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 on
the test method.
Good
Side
The side
of a molding in contact with a mold surface.
Green
Resin
which has not completely cured and is still rather soft and
rubbery.
Greige
Fabric
before finishing; yarn or fibre before bleaching or dyeing.
Also called grey goods, greige goods, greige grey.
GRP
Glass
reinforced plastics. Generally based on polyester resin. See
FIBERGLASS, FRP
[Back to Top]
[ H ]
Hand
The
softness of a piece of fabric, as determined by the touch
(individual judgement).
Hand
Lay-up
The
process of placing (and working) successive plies of
reinforcing material or resin-impregnated reinforcement in
position on a mould by hand, then cured to the formed shape.
Hardener
A
substance or mixture added to a plastic composition to
promote or control the curing action by taking part in it.
Hardness
The
resistance to surface indentation, usually measured by the
depth of penetration (or arbitrary units related to depth of
penetration) of a blunt point under a given load using a
particular instrument according to a prescribed procedure.
(e.g. Barcol hardness, Rockwell hardness number.)
Heat-distortion Temperature
Temperature at which a test bar deflects a certain amount
under specified temperature and a stated load.
Heat
Resistance
The
property or ability of plastics and elastomers to resist the
deteriorating effects of elevated temperatures.
Het-acid
Resin
Polyester resin with exceptional fire qualities.
HM
High-modulus. Often applied to carbon fibres having a
tensile modulus >350 GPa.
Honeycomb
Manufactured product of resin-impregnated sheet material
(paper, glass fabric, etc.) or sheetmetal formed into
hexagonal-shaped cells; used as a core material in sandwich
construction.
Hoop
Stress
The
circumferential stress in a material of cylindrical form
subjected to internal or external pressure.
Hybrid
Fabric
Two or
more reinforcing fibres in a fabric, such as aramid and
glass, or carbon and aramid.
Hydraulic Press
A press
in which the moulding force is created by the pressure
exerted on a fluid.
Hydrophilic
Capable
of absorbing water.
Hydrophobic
Capable
of repelling water.
Hygroscopic
Capable
of absorbing and retaining atmospheric moisture.
[Back to Top]
[ I ]
IM
lntermediate-modulus often applied to carbon fibres having a
tensile modulus of approximately 300 GPa.
Impact
Strength
The
ability of a material to withstand shock loading; the work
done in fracturing a test specimen in a specified manner
under shock loading.
Impregnate
In
reinforced plastics, to saturate the reinforcement with a
resin.
Impregnated Fabric
A fabric
impregnated with a synthetic resin. (See also Prepreg.)
Inert
Filler
A
material added to a plastic to alter its properties through
physical rather than chemical means.
Inhibitor
A
substance which retards a chemical reaction; used in certain
types of monomers and resins to prolong storage life.
lnjection Molding
A
technique developed for processing thermoplastics which are
heated and forced under pressure into closed moulds and
cooled.
In-situ
In the
position which it will finally occupy, e.g. molding or
forming foam.
Instron
A make
of mechanical testing instrument used to determine the
tensile and compressive properties of materials.
Insulating Resistance
The
electric resistance between two conductors or systems of
conductors separated only by insulating material.
Interface
The
junction point or surface between two different media; on
fibres, the contact area between the fibre and sizing or
finish; in a laminate, the contact area between the
reinforcement and the laminating resin.
lnterlaminar
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.
Interlaminar Shear Strength
The
maximum shear stress existing between layers of a laminated
material.
Internal
Stress
Stress
created within a laminate due to different rates of
contraction or expansion of the fibres and resin system.
Intumescent
A
fire-retardant technology which causes an otherwise
flammable material to foam, forming an insulating barrier
when exposed to heat.
Isophthalic
A
polyester resin based on isophthalic acid, generally higher
in properties than a general purpose or orthothatic
polyester resin.
Isotropic
The
description of equal strength properties in all orientation.
Isoptropic composites are usually achieved by random fiber
orientation.
Isotropic Laminates
One in
which the strength properties are equal in all directions.
Izod
Impact Test
A
destructive test designed to determine the resistance of a
plastic to the impact of a suddenly applied force.
[Back to Top]
[ J ]
Jackstrawing
A visual
effect of glass fiber turning white in a cured laminate.
This usually does not effect the strength of a laminate, but
could be an indication of materials incompatibility.
JIG
Any
fixture for holding parts in position, while joining them
together or to maintain their shape.
Joint
A line
or distinction formed when two panels are connected. Also
referred to as a seam.
[Back to Top]
[ K ]
[Back to Top]
[ L ]
Laminant
The
product of lamination. A composite consisting of a layer or
layers of thermoset polymer and fiber reinforcement.
Laminate
To place
into a mold a series of layers of polymer and reinforcement.
The process of applying FRP materials to a mold. To lay up.
Lamination
Applying
layers of glass and resin to a mold. Also used to describe a
single ply of laminate.
Layer
A single
ply of lay up or laminate.
Lay Up
The act
of building up successive layers of polymer and
reinforcement. Layers of catalyzed resin and fiberglass or
other reinforcements are applied to a mold in order to make
a part.
Low-pressure Laminates
Laminated, molded and cured using pressures from 400 psi
down to and including the pressure obtained by the mere
contact of the plies.
[Back to Top]
[ M ]
Male
Mold
A convex
mold where the concave surface of the part is precisely
defined by the mold surface.
Master
(plug)
A full
scale representation of the intended part, usually retained
as a reference and the part from which production molds are
made.
Mat
See
Chopped Strand Mat.
Matched
Die Molding
Technique for producing long runs of identical parts with
two finished sides.
Matched
Molds
Two or
more tools arranged in a set as a male and female mold.
Normally used in a press.
Matrix
The
liquid component of a composite or laminate.
MEK
Peroxide (MEKP)
An
initiator often referred to as catalyst and used to initiate
polymerization of a resin. Methyl Ethyl Ketone Peroxide.
MEK
Solvent
Methyl
Ethyl Ketone; a colorless, flammable liquid sometimes used
in clean up procedures.
Microballoons
Microscopic bubbles of glass, ceramic or phenolic, used as
filler or to create syntactic foam or putty mixtures.
MIL (MIL
Thickness)
The unit
used in measuring film thickness.
One mil
equals one thousandth of an inch (l mil = .001 ").
Milled
Fibers
Glass
fiber processed by a hammer mill into lengths of 1/32" to
1/8". Commonly used as a reinforcement in polyester putty.
Modulus
of Elasticity
An
engineering term used to describe a material's ability to
bend without losing its ability to return to its original
physical properties.
Mold
The tool
used to fabricate the desired part shape. Also used to
describe the process of making a part in a mold.
Molding
The
process of using a mold to form a part.
Mold
Release
A wax or
polymer compound that is applied to the mold surface which
acts as a barrier between the mold and the part, thus
preventing the part from bonding to the mold.
Monomer
One of
the constituents of polyester resin.
[Back to Top]
[ N ]
Nesting
In
reinforced plastics placing plies of fabric so that the
yarns of one ply lie in the valleys between the yarns of the
adjacent ply (nested cloth).
NDI (Non
Destructive Inspection)
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
Fabric
Fabric
produced by loosely bonding together yarns, rovings, etc.
Notch
Sensitivity
Extent
to which the sensitivity of a material to fracture is
increased by the presence of a surface inhomogeneity such as
a notch, a sudden change in section, a crack, or a scratch.
Low notch sensitivity is usually associated with ductile
materials and high notch sensitivity with brittle materials.
Novolac
A
phenolic-aldehyde resin which remains permanently
thermoplastic unless a source of methylene groups is added;
a linear thermoplastic B-staged resin.
NPG Gel
Coat
Neopentyl glycol gel coat has enhanced weatherability
compared to non-NPG gel coat.
[Back to Top]
[ O ]
Offset
Yield Strength
The
stress at which the strain exceeds by a specific amount (the
offset) an extension of the initial proportional portion of
the stress-strain curve.
Orange
Peel
An
uneven surface of a coating resembling that of orange peel.
Organic
Designating or composed of matter originating in plant or
animal life or composed of chemicals of hydrocarbon origin,
natural or synthetic.
Orthophthalic or Ortho Resin
A
polyester resin based on orthophthalic acid, also known as a
general purpose resin (GP).
Orthotropic
Having
three mutually perpendicular planes of elastic symmetry.
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.
Overlap
A simple
adhesive joint, in which the surface of one adherend extends
past the leading edge of another.
[Back to Top]
[ P ]
PAN
Polyacrylonitrile. The precursor for most carbon fibres.
Parallel-laminated
Laminated so that all the layers of material are oriented
approximately parallel with respect to the grain or
strongest direction in tension.
Parting
Agent
See Mold
Release and PVA
Parting
Line
The
location on a molded product between different segments of
the mold used to produce the product.
Pattern
The
initial model for making fiberglass molds. See Plug.
Peel Ply
A
tightly woven polyester or nylon fabric which is applied to
the outside layer of a laminate. This is removed or
sacrificed to achieve improved bonding of additional plies
and leaves a clean, resin-rich surface ready for bonding.
Peel
Strength
Bond
strength, obtained by peeling apart layers. (See also Bond
Strength.)
Permanent Set
The
deformation remaining after a specimen has been stressed in
tension a prescribed amount for a definite period and
released for a definite period.
Phenolic, Phenolic Resin
A
synthetic resin produced by the condensation of an aromatic
alcohol with an aldehyde, particularly of phenol with
formaldehyde. (See also A stage, B stage, C stage, Novolac.)
Phenolics have particularly good fire-resistance properties.
Pick
An
individual filling yarn, running the width of a woven fabric
at right angles to the warp, also called fill, woof, weft.
Pigment
A
colorant added to gel coat or resin.
Pigment
Separation
Occurs
when the pigment is not thoroughly mixed into the gel coat
during formulation or the gel coat is improperly mixed prior
to use. It is characterized by a non homogeneous surface
color.
Pinhole
A tiny
hole in the surface of, or through a coating material.
Pit
Small
regular or irregular crater in the surface of a moulding,
usually with width about the same order of magnitude as the
depth.
Pitch
A
residual petroleum product used in the manufacture of
certain carbon fibres.
Planar
Helix Winding
A
winding in which the filament path on each dome lies on a
plane which intersects the dome while a helical path over
the cylindrical section is connected to the dome paths.
Planar
Winding
A
winding in which the filament path lies on a plane
intersecting the winding surface.
Plastic
A
material that contains, as an essential ingredient, an
organic substance of high molecular weight, is solid in its
finished state and, at some stage in its manufacture or
processing into finished articles, can be shaped by flow;
made of plastic. A rigid plastic is one with a stiffness or
apparent modulus of elasticity greater than 690 MPa at 23°C.
A semirigid plastic has a stiffness or apparent modulus of
elasticity between 69 and 690 MPa at 23°C.
Plastic
Deformation
Change
in dimensions of an object under load that is not recovered
when the load is removed; opposite of elastic deformation.
See also Elastic Recovery.
Platens
The
mounting plates of a press, to which the entire mould
assembly is bolted.
Plied
Yarn
A yarn
formed by twisting together two or more single yarns in one
operation.
Plug
A
composite industry term for a pattern or model.
Ply
One of
the layers that make up a stack or laminate.
PMR-15
A type
of Polyimide resin.
Poisson's Ratio n
A
constant relating to change in cross-sectional area to
change in length when a material is stretched; n = 1/2 for
rubbery materials, 1/4 to 1/2 for crystals and glasses.
Polyacrylonitrile (PAN)
A
product used as a base material in the manufacture of
certain carbon fibres.
Polyamide
A
polymer in which the structural units are linked by amide or
thioamide groupings; many polyamides are fibre-forming.
Polyesters
Thermosetting resins produced by dissolving unsaturated,
generally linear alkyd resins in a vinyl active monomer,
e.g. styrene, methyl styrene, or diallyl phthalate.
Polyimide
A
polymer produced by heating polyamic acid; a highly
heat-resistant resin [> 600°F(> 316°C)] suitable for use as
a laminating resin or an adhesive.
Polymer
A
high-molecular-weight organic compound, natural or
synthetic, whose structure can be represented by a repeated
small unit (mer), e.g. polyethylene, rubber, cellulose.
Synthetic polymers are formed by addition or condensation
polymerisation of monomers.
Polymerization
A
chemical reaction in which the molecules of a monomer are
linked together to form large molecules whose molecular
weight is a multiple of that of the original substance. When
two or more monomers are involved, the process is called
copolymerization or heteropolymerization.
Polymerize
To unite
molecules of the same kind into a compound having the
elements in the same proportion but possessing much higher
molecular weight and different physical properties.
Polyvinyl Alcohol (PVA)
A
parting film applied to a mold for part releasing.
Porosity
Entrapped gas bubbles or voids in a gel coat film.
Postcure
Additional elevated-temperature cure, usually without
pressure, to improve final properties and/or complete the
cure. Complete cure and ultimate mechanical properties of
certain resins are attained only by exposure of the cured
resin to temperatures higher than those of initial curing.
Pot Life
The
length of time a quantity of catalysed resin system in a
container remains liquid prior to gelation, also called
working life.
PPS
Polyphenylene sulfide.
Precure
The full
or partial setting of a synthetic resin or adhesive in a
joint before the clamping operation is complete or before
pressure is applied.
Precursor
For
carbon fibres, the rayon, PAN, or pitch fibres from which
carbon fibres are made.
Preform
A
preshaped fibrous reinforcement of mat or cloth formed to
the desired shape on a mandrel or mock-up before being
placed in a mould press, or RTM tool.
Preform
Binder
A resin
applied to the chopped strands of a preform, usually during
its formation, and cured so that the preform will retain its
shape and be handleable.
Preimpregnation
The
practice of mixing resin and reinforcement and effecting
partial cure before use or shipment to the user. ( See also
Prepreg.)
Premix
Reinforcing material mixed with resin, and usually with
pigment, filler and catalyst, before placing in the mold.
Prepreg
Ready-to-mould material in rolled-sheet form, which may be
cloth, mat or fibres impregnated with resin and stored for
use. The resin is partially cured to a soft and slightly
sticky B stage and supplied to the fabricator, who lays up
the finished shape and completes the cure with heat and
pressure.
Pressure
Force
measured per unit area.
Pressure-bag Molding
A
process for molding reinforced plastics, in which a tailored
flexible bag is placed over the contact lay-up on the mould,
sealed, and clamped in place. Fluid pressure, usually
compressed air, is exerted on the bag, and the part is
cured.
Primary
Structure
The main
structure.
Primer
A
coating applied to a surface before the application of an
adhesive or lacquer, enamel, or the like to improve the
performance of the bond.
Print
Through
A
distortion in the surface of a part which allows the pattern
of the core or fiberglass reinforcement to be visible
through the surface. Also known as print out, telegraphing
or read through.
Promoter
See
Accelerator.
Proportional Limit
The
greatest stress which a material is capable of sustaining
without deviation from proportionality of stress and strain
(Hooke's Law); it is expressed in force per unit area.
Pultrusion
Reversed
extrusion of resin-impregnated roving in the manufacture of
rods, tubes, and structural shapes of a permanent cross
section. After passing through the resin dip tank the roving
is drawn through a die to form the desired cross section.
Putty
A
thickened mixture of resin made by adding fillers,
thixotrophs and reinforcing fibers.
[Back to Top]
[ Q ]
Quasi-isotropic
Approximating isotropy by orientation of plies in several
directions.
[ R ]
Ramping
A
gradual, programmed increase/decrease in temperature or
pressure, during the cure cycle of composite parts.
Reinforcement
A strong
inert material bonded into a plastic to improve its
strength, stiffness, and impact resistance. To be effective,
the reinforcing material must form a strong adhesive bond
with the resin.
Reinforced Molding Compound
Compound
consisting of a polymer and a reinforcement fiber or filler
supplied by raw material producer in the form of
ready-to-use materials.
Reinforced Plastic
A
plastic with strength properties greatly superior to those
of the base resin, resulting from the presence of
reinforcements embedded in the composition.
Release
Agent
A
material which is applied in a thin film to the surface of a
mould to keep the resin from bonding to it. See also Mould
Release.
Release
Film
A thin
plastic film applied on top of a laminate stack before it is
cured. It is usually perforated, allowing excess resin to
flow out and be absorbed by a bleeder cloth.
Resilience
(1) The
ratio of energy returned on recovery from deformation to the
work input required to produce the deformation (usually
expressed as a percentage). (2) The ability to regain an
original shape quickly after being strained or distorted.
Resin
A solid,
semisolid, or pseudo-solid organic material which has an
indefinite (often high) molecular weight, exhibits a
tendency to flow when subjected to stress, usually has a
softening or melting range. Most resins are polymers. In
reinforced plastics the material used to bind together the
reinforcement material, the matrix. See also Polymer.
Resin
Content
The
amount of resin in a laminate expressed as a percentage of
total weight.
Resin-rich Area
Space
which is filled with resin and lacking reinforcing material.
Resin-starved Area
Area of
insufficient resin, usually identified by low gloss, dry
spots, or fibre show.
Resin
Tearing
Separation of pigments in a gel coat affecting cosmetic
appearance.
RIFT
Resin
Infusion under Flexible Tooling.
Ribbon
A fibre
having essentially a rectangular cross section, where the
width-to-thickness ratio is at least 4:1.
RIM
Reaction-injection moulding.
Rockwell
Hardness Number
A value
derived from the increase in depth of an impression as the
load on an indenter is increased from a fixed minimum value
to a higher value and then returned to the minimum value.
Room
Temperature-curing Adhesives
Adhesives that set (to handling strength) at 20 to 30°C and
later reach full strength without heating.
Roving
A loose
assembly of continuous filaments of glass fibre
substantially without twist.
RRIM
Reinforced reaction-injection moulding.
RTM
Resin-transfer molding. A molding process in which catalyzed
resin is transferred into an enclosed mould 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 mould
large structural parts.
[Back to Top]
[ S ]
S Glass
A
magnesia-alumina-silicate glass, especially designed to
provide filaments with very high tensile strength.
Sandwich
Constructions
Panels
composed of a lightweight core material (honeycomb, foamed
plastic, etc.) to which two relatively thin, dense,
high-strength faces or skins are adhered.
Satin
A
particular, fairly flat weave pattern in fabrics in which
each warp fibre flocks over 4 or more weft fibres, and vice
versa.
Scarf
Joint
See
Joint.
Scrim
A
nonwoven open-weave reinforcing fabric made from
continuous-filament yarn in an open-mesh construction. Often
used to support an adhesive film.
Seam
See
Joint.
Secondary Structure
A
structure of secondary importance.
Self-extinguishing Resin
A resin
formulation which will burn in the presence of a flame but
which will extinguish itself within a specified time after
the flame is removed.
Self-tapping Screws
Hardened
screws which cut their own thread as they are set.
Selvage
The edge
of a woven fabric finished off so as to prevent the yarns
from unravelling.
Set
(1) To
convert into a fixed or hardened state by chemical or
physical action, such as condensation polymerisation,
oxidation, vulcanisation, gelation, hydration, or
evaporation of volatiles. (2) The irrecoverable deformation
or creep usually measured by a prescribed test procedure and
expressed as a percentage of original dimension.
Set Up
To
harden, as in curing.
Shear
An
action or stress resulting from applied forces and tending
to cause two contiguous parts of a body to slide relative to
each other in a direction parallel to their plane of
contact.
Shear
Modulus G
The
ratio of shearing stress t to shearing strain g within the
proportional limit of a material.
Shelf
life
The
allowable storage time before a product must be used.
Ship Lap
Method
of joining two panels together by means of one panel having
a recessed shelf to receive the other panel on top of it
leaving a flush surface.
Short-beam Shear Strength
The
interlaminar shear strength of a parallel-fibre-reinforced
plastic material as determined by three-point flexural
loading of a short segment.
Shrinkage
The
tendency of a resin system to contract in volume when
transitioning from the liquid to the used state.
Silicon
Carbide Fibre
A
reinforcing fibre with high strength and modulus: density is
equal to that of aluminium. It is used in organic- and
metal-matrix composites.
Size
Any
treatment consisting of starch, gelatin, oil, wax, or other
suitable ingredient applied to yarn or fibres at the time of
formation to protect the surface and facilitate handling and
fabrication or to control the fibre characteristics. The
treatment contains ingredients which provide surface
lubricity and binding action but, unlike a finish, 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 the organic sizing (ñloss
on Ignitionî).
Skein
A
continuous filament, strand, yarn, roving, etc. wound up to
some measurable length and generally used to measure various
physical properties.
Skin
The
laminate part of a sandwich structure.
SMC
Sheet-moulding compound.
S-N
Curve
Stress
per number of cycles to failure. Used to define fatigue
behaviour.
Specific
Gravity
The
ratio of the weight of any volume of a substance to the
weight of an equal volume of another substance, usually
water, taken as standard at a constant or stated
temperature.
Specific
Heat
The
quantity of heat required to raise the temperature of a unit
mass of a substance 1 degree under specified conditions.
Specimen
An
individual piece or portion of a sample used to make a
specific test.
Splice
To join
two ends of fibre yarn or strand, usually by means of an
air-drying glue. Such a join.
Split
Mold
An open
mold made in two or more pieces.
Spray-up
Technique in which a spray gun is used as the processing
tool. In reinforced plastics, for example, fibrous glass and
resin can be simultaneously deposited in a mould. In
essence, roving is fed through a chopper and ejected into a
resin stream, which is directed at the mould by either of
two spray systems.
Sprayed-metal Molds
Molds
made by spraying molten metal onto a master until a shell of
predetermined thickness is achieved. The shell is then
removed and backed up with plaster, cement, casting resin,
or other suitable material. Used primarily as a mould in
sheet-forming process.
Starved
Joint
An
adhesive joint which has been deprived of the proper film
thickness of adhesive due to insufficient adhesive spreading
or application of excessive pressure during lamination.
Stiffness
The
relationship of load and deformation; a term often used when
the relationship of stress to strain does not conform to the
definition of Young's modulus. (See Stress-strain.)
Strain
As
applied to composite laminates: The resultant change in
dimension of a material when subjected to a stress,
expressed as a fraction or percentage of the original
dimension.
Stress
Most
commonly defined as engineering stress; the ratio of the
applied load P to the original cross-sectional area A
Stress
Concentration
Magnification of the level of an applied stress in the
region of a notch, void, or inclusion.
Stress
Corrosion
Preferential attack of areas under stress in a corrosive
environment, where this factor alone would not have caused
corrosion.
Stress
Crack
External
or internal cracks in a plastic caused by tensile stresses
less than that of its basic mechanical strength. The
stresses which cause cracking may be present internally or
externally or may be combinations of these stresses.
Stress
Relaxation
The
decrease in stress under sustained constant strain, also
called stress decay.
Stress-strain Curve
Simultaneous readings of load and deformation, converted
into stress and strain, plotted as y and x-axes,
respectively, to obtain a stress-strain diagram.
Structural Adhesive
An
adhesive used for transferring loads between adherends.
Structural Bond
A bond
that joins basic load-bearing parts of an assembly; the load
may be either static or dynamic.
Styrene
Monomer
A
component of polyester resin that provides crosslinking
sites and reduces the polyester to a workable viscosity.
Surfacing Mat
A very
thin mat, of highly filamentized fibers used primarily to
produce a smooth surface on a reinforced plastic laminate.
Surface
Treatment
A
treatment applied to carbon fibre during its manufacture to
alter the fiber’s surface chemistry.
Surfactant
Chemicals used to modify or change the surface of a layer of
resin or polymer. Usually used to form a film on a curing
resin, producing a tack-free surface.
Syntactic Foam
A
cellular plastic which is put together by incorporating
hollow spheres or microballoons in a resin matrix; opposite
of foamed plastic, in which the cells are formed by gas
bubbles released in the liquid plastic by chemical or
mechanical action.
[Back to Top]
[ T ]
Tack
Stickiness of an adhesive, resin or prepreg material.
Tack
Free
A
surface which is not sticky after cure.
Tape
A form
of unidirectional prepreg consisting of continuous fibres
that are aligned along the tape axis parallel to each other
and held together purely by the impregnating resin.
Tape
Laying
A
fabrication process in which prepreg tape is laid side by
side or overlapped to form a structure. The process can be
automated with robotic arms.
Tenacity
The
strength of a yarn or of a filament of a given size; equals
breaking strength divided by denier.
Tensile
Modulus
The
ratio of the tension stress to the strain in the material
over the range for which this value is constant.
Tensile
Strength or Stress
The
maximum tensile load per unit area of original cross
section, sustained by the specimen during a tension test.
Tensile strength is interpreted to mean the maximum tensile
load sustained by the specimen during the test, whether this
coincides with the tensile load at the moment of rupture or
not.
Tex
A
measure of the mass of 1000lm of a fibre, tow or strand
expressed in grammes. Sometimes expressed as dtex (decitex)
where 1dtex equals 0.1x tex and is equivalent to the mass in
grammes of 10,000lm of fibre, tow or strand.
Thermal
Coefficient of Expansion
Measures
dimensional change of a material when heated or cooled.
Measured in inches per inch per degree.
Thermal
Conductivity
Ability
of a material to conduct heat; the physical constant for
quantity of heat that passes through a unit cube of a
substance in unit time when the difference in temperature of
two faces is 1 degree.
Thermoplastic
A
plastic material capable of being repeatedly softened by
increase of temperature and hardened by decrease in
temperature; applicable to those materials whose change upon
heating is substantially physical rather than chemical and
which can be shaped by flow into articles by moulding and
extrusion. Examples include, polypropylene, ABS, nylon,
polyethylene.
Thermoset
A
plastic material which changes into a substantially
infusible and unmouldable material after it is cured by
application of heat or by chemical means. Although a
thermoset material will soften at its Tg, it will never
return to its precured liquid state. Examples include epoxy
and unsaturated polyester.
Thixotropic
Gel-like
at rest but fluid when agitated; having high static shear
strength and low dynamic shear strength at the same time.
Thixotropic Index (T.I.)
A
measure of thixotropy using a Brookfield Viscometer. The low
speed viscosity divided by the high speed viscosity.
Thread
Count
The
number of yarns (threads) per inch (millimetre) in either
lengthwise (warp) or crosswise (weft) direction of woven
fabrics.
Tooling
gel coat
A gel
coat formulated for mold surfaces.
Torsional Rigidity (Fibres)
The
resistance of a fibre to twisting.
Toughness
The
resistance of a material to crack propagation.
Tow
A large
bundle of continuous filaments, generally 1000 or more,
usually designated by a number followed by ñK,î indicating
multiplication by 1000; for example, 12K tow has 12,000
filaments. Normally applied to carbon fibre.
Transition Temperature
The
temperature at which the properties of a material change.
Translucent
Permits
a percentage of light to pass but not optically clear like
window glass.
Twist
The
turns about its axis per unit of length in a yarn or other
textile strand.
[Back to Top]
[ U ]
UHM
Ultra-high modulus.
Ultimate
Elongation
The
elongation at rupture of a material. Also called ïElongation
at break' or ïStrain to failure'.
Ultimate
Tensile Strength
The
ultimate or final stress sustained by a specimen in a
tension test; at moment of rupture.
Ultraviolet (UV)
Zone of
invisible radiations beyond the violet end of the spectrum
of visible radiations. Since ultraviolet wave lengths are
shorter than the visible, their photons have more energy,
enough to initiate some chemical reactions and to degrade
most plastics.
UV
Stabilizer
A
chemical compound which improves resistance to degradation
from ultraviolet radiation.
Unidirectional
Refers
to fibres that are oriented in the same direction, such as
unidirectional fabric, tape, or laminate, often called UD.
Unidirectional Laminate
A
reinforced plastic laminate in which substantially all the
fibres are oriented in the same direction.
Undercut
An area
of a part or mold that has an acute angle between two
surfaces. If a part has an undercut a split mold is
necessary.
[Back to Top]
[ V ]
Vacuum-bag Molding
A
process for moulding laminates in which a sheet of flexible
material is placed over the lay-up on the mould and sealed.
A vacuum is applied between the sheet and the lay-up. The
entrapped air is pulled out of the lay-up and removed by the
vacuum. Atmospheric pressure provides the consolidation
pressure.
Veil
An ultra
thin mat similar to a surface mat, often composed of organic
fibres as well as glass fibres.
Viscosity
The
property of resistance to flow exhibited within the body of
a liquid or semi-solid expressed in terms of relationship
between applied shearing stress and resulting rate of strain
in shear.
Void
Content
The
percentage of voids in a laminate.
Voids
Gaseous
pockets trapped and cured into a laminate usually within the
matrix.
Volatile
Content
The
percent of volatiles driven off as a vapour from a plastic
or an impregnated reinforcement.
Volatiles
Materials in a sizing or a resin formulation capable of
being driven off as a vapour at room temperature or slightly
above.
[Back to Top]
[ W ]
Warp
(1) The
yarn running lengthwise in a woven fabric; a group of yarns
in long lengths and approximately parallel, put on beams or
warp reels for further textile processing, including
weaving. (2) A change in dimensions of a cured laminate from
its original moulded shape.
Water
Absorption
Ratio of
the weight of water absorbed by a material upon immersion to
the weight of the dry material.
Water
Jet
A high
pressure stream of water used for cutting composites and
other materials.
Wax
A
compound used as a release agent. See RELEASE AGENT
Weathering
The
exposure of materials outdoors. In artificial weathering,
plastics are exposed to cyclic laboratory conditions of high
and low temperatures, high and low relative humidities, and
ultraviolet radiant energy, with or without direct water
spray, in an attempt to produce changes in their properties
similar to those observed on long continuous exposure
outdoors. Laboratory exposure conditions are usually
intensified beyond those in actual outdoor exposure to
achieve an accelerated effect.
Weave
The
particular manner in which a fabric is formed by interlacing
yarns. In plain weave, the warp and weft fibres alternate to
make both fabric faces identical; in satin weave, the
pattern produces a satin appearance, with the warp tow over
several weft tows and under the next one (for example,
eight-harness satin would have warp tow over seven weft tows
and under the eighth).
Web
A
textile fabric, paper or a thin metal sheet of continuous
length handled in roll form, as contrasted with the same
material cut into sheets.
Weft
The
transverse threads of fibres in a woven fabric running
perpendicular to the warp; also called fill, and woof.
Wet
Lay-up
A
process in which liquid resin is applied as the
reinforcement is laid up.
Wet-out
The
condition of an impregnated roving or yarn wherein
substantially all voids between the sized strands and
filaments are filled with resin.
Wet-out
Rate
The time
required for a resin to fill the interstices of a
reinforcement material and wet the surface of the
reinforcement fibres; usually determined by optical or
light-transmission means.
Wetting
Agent
A
surface-active agent usually in a resin formulation that
promotes wetting by decreasing the cohesion within a liquid.
Wet
Winding
In
filament winding the process of winding glass on a mandrel
where the strand is impregnated with resin just before
contact with the mandrel.
Whisker
A very
short fibre form of reinforcement, usually crystalline.
Winding
Pattern
In
filament winding: (1) The total number of individual
circuits required for a winding path to begin repeating by
laying down immediately adjacent to the initial circuit. (2)
A regularly recurring pattern of the filament path after a
certain number of mandrel revolutions, leading to the
eventual complete coverage of the mandrel.
Winding
Tension
In
filament winding the amount of tension on the reinforcement
as it makes contact with the mandrel.
Woven
Fabrics
Fabrics
produced by interlacing strands at more or less right
angles.
Woven
Roving
A heavy
glass-fibre fabric made by weaving glass roving.
[Back to Top]
[ X ]
[Back to Top]
[ Y ]
Yarn
An
assembly of twisted fibres or strands, natural or
manufactured, to form a continuous yarn suitable for use in
weaving or otherwise interweaving into textile materials.
Yield
Point
The
first stress in a material, less than the maximum attainable
stress, at which an increase in strain occurs without an
increase in stress. Only materials that exhibit this unique
phenomenon of yielding have a yield point.
Yield
Strength
The
stress at which a material exhibits a specified limiting
deviation from the proportionality of stress to strain; the
lowest stress at which a material undergoes plastic
deformation. Below this stress, the material is elastic;
above it, plastic.
[Back to Top]
[ Z ]
[Back to Top]
|
