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Glossary of terms

A B C D E F G H I J K L M N O P R S T :: Abbreviations

These terms are frequently used in the reinforced plastics and allied industries:

A

Ablative:
material that absorbs heat through decomposition process called pyrolysis at or near the exposed surface
Accelerator:
accelerates cure of a resin
Additives:
the term used for a large number of specialist chemicals which are added to resins/compounds to impart specific properties, for example, flame retardancy, and UV resistance
Adhesive:
substance applied to mating surfaces to bond them together by surface attachment. An adhesive can be in liquid, film or paste form.
Aramid:
high-strength, high-stiffness aromatic polyamide fibres
Aspect ratio:
the length/diameter ratio of a fibre

B

Blister, blistering:
undesirable raised areas in a moulded part caused by local internal pressure, due usually to rapped air, volatile reaction by-products or water entering by osmosis.
Bulk Moulding Compound (BMC):
polyester resin/glass fibre premix, for injection or transfer moulding, also known as dough moulding compound (DMC)

C

Carbon fibre:
reinforcing fibre known for its light weight, high strength and high stiffness.
Catalyst (also called hardener):
a chemical compound (usually an organic peroxide) which initiates polymerisation of a resin
Chlorinated paraffins:
flame-retardant additives for polyester resins
Chopped strands:
short strands cut from continuous filament strands of reinforcing fibre, not held together by any means
Coefficient of thermal expansion:
a material’s fractional change in length corresponding to for a given unit change in temperature
Composite: a material made up of resin and reinforcement (usually fibre)
Compression strength:
the crushing load at failure of a material, divided by cross-sectional area of the specimen
Contact moulding:
moulding of fibre-reinforced resins without application of external pressure
Core:
in sandwich construction, the central component to which inner and outer skins are attached. Foam, honeycomb and wood are all commonly used core materials.
Corrosion resistance:
the ability of a material to withstand contact with ambient natural factors without degradation or change in properties. For composites, corrosion can cause crazing.
Coupling agent:
a substance, which promotes or establishes a stronger bond at the resin matrix/reinforcement interface
Cracking:
actual separation of moulded material, visible on opposite surfaces of a part ad extending through the thickness (fracture)

Crazing:
fine cracks, which may extend in a network on or under the surface of a moulded part
Cure:
the process of hardening of a thermosetting resin (by cross-linking of the molecular structure), under the influence of heat
Curing agents:
chemical compounds used to cure thermosetting resins
Curing time:
the time taken for a resin to cure to its full extent

D

Delamination:
splitting, physical separation or loss of bond along the plane of layers of a laminated material
Direct roving:
roving produced by winding a large and determined number of filaments direct from a bushing

Dough moulding compound (DMC):
polyester/resin fibre premix, for injection or transfer moulding, also known as bulk moulding compound (BMC)

F

Fibre:
a unit of matter of relatively short length, characterised by a high ratio of length to thickness or diameter

Filament:
a single textile element of small diameter and very long length considered as continuous
Filler:
material (usually low cost) added to a resin to extend it, or give special properties
Finishing:
application of coupling agent to textile reinforcements to improve the fibre/resin bond
Flexural strength:
the strength of a material in bending expressed as the stress if a bent test sample at the instant of failure.
Flow:
the movement of a resinous material, thermosetting or thermoplastic, under pressure, to fill all parts of a closed mould
Fracture:
cracks, crazing or delamination resulting from physical damage.

G

Gate:
the opening through which a moulding compound is injected into a closed mould; the size, geometry and positioning of the gate can strongly influence properties of the finished moulding
Gel:
the state of a resin, which has set to a jelly-like consistency
Gelcoat:
a thin layer of unreinforced resin on the outer surface of a reinforced resin moulding; it hides the fibre pattern of the reinforcement, protects the resin/reinforcement bond, gives smooth external finish and can also provide special properties; it is usually pigmented
Glass fibre:
reinforcing fibre made by drawing molten glass through bushings. The predominant reinforcement for polymer composites, it is known for its good strength, processability and low cost.

H

Hardener:
see catalyst
HET acid anhydride:
saturated dicarboxylic acid anhydride, containing chlorine
Honeycomb:
light weight cellular structure made from either metallic sheet materials or non-metallic materials and formed into hexagonal nested cells, similar in appearance to the cross-section of a beehive
Hybrid:
a resin or reinforcement made from two or more different polymers or reinforcement materials

I

Impact strength:
a material’s ability to withstand shock loading as measured by fracturing a specimen
Impregnation:
saturation of reinforcement with liquid resin
In-mould coating (IMC):
a process used with SMC (and recently developed also for thermoplastics) in which a liquid/melt coating layer is applied to the exterior of a moulding while still in the mould, as part of the moulding cycle
Interface:
the contact area between reinforcement and resin


L

Laminate:
the structure resulting from bonding multiple plies of reinforcing fibre or fabric
Lay-up:
a resin-impregnated reinforcement in the mould, prior to polymerisation

M

Mat:
a widely used sheet-type reinforcement made up of filaments, staple fibres or strands, cut or uncut, oriented or random, lightly bonded together
Monomer:
a compound containing a reactive double bond, capable of polymerising

P

Polyester:
usual term for an unsaturated polyester resin
Polymer:
a long-chain molecule, consisting of many repeat units
Porosity:
numerous air pockets or voids in a moulded product
Post-cure:
application of external heat to bring a resin to a stable state of cure in the shortest possible time
Preform:
reinforcement pre-shaped to the general geometry of the intended moulded part; it is used on more complex and deep-draw mouldings, to optimise distribution and orientation of fibres
Premix:
a moulding compound prepared prior to, and apart from, the moulding operation, containing all components necessary for moulding
Prepreg:
a factory-made combination of reactive resins and reinforcing fibres, plus other necessary additive chemicals, ready to be moulded

R

Reactive resins:
liquid resins which can be cured by catalysts and hardeners to form solid materials
Release agent:
a substance which prevents a moulding from sticking to the mould surface; it may be a chemical compound or a solid material such as a cellulose or plastics film
Reinforcement:
key element added to resin (matrix) to provide the required properties; ranges from short fibres and continuous fibres through complex textile forms
Resin:
polymer with indefinite and often high molecular weight and a softening or melting range that exhibits a tendency to flow when subjected to stress. As composite matrices, resins bind together reinforcement fibres
Resin transfer moulding (RTM):
a moulding process in which catalysed resin is injected into a closed mould already containing the pre-formed reinforcement
Roving:
endless glass fibre bundles; a collection of parallel strands (assembled roving) or parallel filaments (direct roving) assembled without intentional twist

S

Sandwich structure:
composite composed of lightweight core material to which two relatively thin, dense, high strength, functional or decorative skins are adhered
Sheet moulding compound (SMC):
a flat pre-preg material, comprising thickened resin, glass fibre and fillers, covered on both sides with polyethylene or nylon film, ready for press-moulding
Size:
a coating applied to glass fibres or filaments during manufacture, to improve handling and protect from abrasion
Strand:
an assembly of parallel filaments simultaneously produced and lightly bonded

T

Thermoplastic:
a plastic, which softens each time it is heated
Thermoset:
a plastic which flows and then sets permanently on first heating, as s result of setting up a three-dimensional cross-linked molecular structure, and subsequently will not soften or dissolve
Thick moulding compound (TMC):
a compound similar to BMC, but continuously produced in sheet form with a thickness of 25mm or more

Void:
a pocket of gas or air trapped in a laminate or moulding
Wet-out:
complete wetting/saturation of a fibrous surface with a liquid resin


Abbreviations

ACM:
advanced composite material

AFRP:
aramid fibre reinforced polymer

BMC:
bulk moulding compound

CFRP:
carbon fibre reinforced polymer

DMC:
dough moulding compound

GFRP:
glass fibre reinforced polymer

FRP:
fibre reinforced polymer

SMC:
sheet moulding compound

TMC:
thick moulding compound