Terms used in the composites industry
There are many terms used in the composites industry. The following are some of the more popular terms and abbreviations.
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
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)
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
Chopped strands: short strands cut from continuous filament strands of reinforcing fibre, not held together by any means
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
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 and extending through the thickness (fracture)
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
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)
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.
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.
Hardener: see catalyst
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
Impact strength: a material’s ability to withstand shock loading as measured by fracturing a specimen
Impregnation: saturation of reinforcement with liquid resin
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
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
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
Pre-preg: a factory-made combination of reactive resins and reinforcing fibres, plus other necessary additive chemicals, ready to be moulded
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
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
Strand: an assembly of parallel filaments simultaneously produced and lightly bonded
Thermoplastic: a plastic, which softens each time it is heated
Thermoset: a plastic which flows and then sets permanently on first heating, as a result of setting up a three-dimensional cross-linked molecular structure, and subsequently will not soften or dissolve
Wet-out: complete wetting/saturation of a fibrous surface with a liquid resin
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