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Composites Terminology Database

This glossary is not an exhaustive list, however it does contain the majority of terms used in the composites industry and as part of the management of our website, it is updated on a continual basis.

The terms are accessed by clicking on the appropriate letter below, all the terms beginning with the letter B can be found below.

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Terms B

Click on a term and it will take you to the coresponding explanation.

The ''B'' mechanical property value is the value above which at least 90% of the population of values is expected to fall, with a confidence of 95%. See also:

An intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated, and is plastic and fusible but may not entirely dissolve or fuse. Also called resistol. The resin in an uncured prepreg or premix is usually in this stage. See:

back pressure
Resistance of a material, due to its viscosity, to continued flow when mould is closing.

back pressure
A process in which the consolidation of the material in the mould is effected by the application of fluid or gas pressure through a flexible membrane.

back pressure
The side of the pan that is cured against the vacuum bag.

Applying an impermeable layer of film over an uncured pan and sealing the edges so that a vacuum can be drawn.

balanced construction
Equal pans of warp and fill in fibre 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 directions.

balanced design
In filament-wound reinforced plastics, a winding pattern so designed that the stresses in all filaments are equal.

balanced laminate
A composite laminate in which all laminae at angles other than 0°ree; and 90°ree; occur only in + pairs (not necessarily adjacent) and are symmetrical around the centreline. See also symmetrical laminate

balanced twist
An arrangement of twists in a combination of two or more strands that does not cause buckling or twisting on themselves when the yarn produced is held in the form of an open loop.

balanced-in-plane contour
In a filament wound pan a head contour in which the filaments are oriented within a plane and the radii of curvature are adjusted to balance the stresses along the filaments with the pressure loading.

band density
In filament winding, the quantity of fibreglass reinforcement per inch of band width, expressed as strands (or filaments) per inch.

band thickness
In filament winding, the thickness of the reinforcement as it is applied to the mandrel.

band width
In filament winding, the width of the reinforcement as it is applied to the mandrel.

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 impression, gives a direct reading on a O to 100 scale. The hardness value is often used as a measure of the degree of cure of a plastic.

bare glass
Glass, such as yarns, rovings, and fabrics, from which the sizing or finish has been removed. Also, such glass before the application of sizing or finish.

barrier coat
An exterior coating applied to a composite wound structure to provide protection.

barrier film
The layer of film used to permit removal of air and volatiles from a composite lay-up during cure while minimising resin loss.

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.

Felted fabrics. Structures built by the interlocking action of compressing fibres, without spinning, weaving, or knitting.

bearing area
The diameter of the hole times the thickness of the material. The cross-section area of the bearing load member on the sample.

bearing strain
The ratio of the deformation of the bearing hole, in the direction of the applied force, to the pin diameter. Also, the, stretch or deformation strain for a sample under bearing load.

Bearing strength
The maximum bearing stress that can be sustained. Also, the bearing stress at that point on the stress-strain curve where the tangent is equal to the bearing stress divided by n% of the bearing hole diameter.

bearing stress
The applied load in pounds divided by the bearing area. Maximum bearing stress is the maximum load in pounds sustained by the specimen during the test, divided by the original bearing area.

bending-twisting coupling
A property of certain classes of laminates that exhibit twisting curvatures when subjected to bending moments.

bias fabric
Warp and fill fibres at an angle to the length of the fabric.

biaxial load
A loading condition in which a laminate is stressed in two different directions in its plane. A loading condition of a pressure vessel under internal pressure and with unrestrained ends.

biaxial winding
In filament winding, a type of winding in which the helical band is laid in sequence, side by side, with crossover of the fibres eliminated.

bi-directional laminate
A reinforced plastic laminate with the fibres oriented in two directions in its plane. A cross laminate. See also unidirectional laminate.
("unidirectional laminate" "unidirectional laminate")

A small ingot of non-ferrous metal.

The resin or cementing constituent (of a plastic compound) that holds the other components together. The agent applied to fibre mat or preforms to bond the fibres before laminating or moulding.

bismaleimide (BMI)
A type of polyimide that cures by an addition rather than a condensation reaction thus avoiding problems with volatiles formation and which is produced by a vinyl-type polymerisation of a prepolymer terminated with two melamine groups. Intermediate in temperature capability between epoxy and polyimide.

An elastomeric lining for the containment of hydroproof or hydroburst pressurisation medium in filament-wound structures.

Fibre or fabric plies that have been laid up in a complete assembly and placed on or in the mould all at one time (flexible bag process). Also, the form of bag in which the edges are sealed against the mould.

bleeder cloth
A woven or nonwoven 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 and is not part of the final composite.

The removal of excess resin from a laminate during cure. The diffusion of colour, out of a plastic part into the surrounding surface or part.

The excess liquid resin that migrates to the surface of a winding. Primarily occurs in filament winding.

A visible local exudation or finish change on the surface of a plastic. Bloom can be caused by a lubricant or plasticiser or by atmospheric contamination.

See: bulk moulding compound

body putty
A past like mixture of plastic resin (polyester or epoxy) and talc used in repair of metal surfaces, such as auto bodies.

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: peel strength

A metric or parameter that posses boolean characteristics. The values can be any pair that can represent an OR state of a parameter or a variable: (True False), (Yes No), (A B) , (T ), etc.

boron fibre
A fibre produced by valour deposition of elemental boron, usually onto a tungsten filament core, to impart strength and stiffness.

Projection on a plastic part designed to add strength, to facilitate alignment during assembly, or to provide for a fastening.

Weaving of fibres into a tubular shape instead of a flat fabric as for graphite fibre reinforced golf club shafts.

branched polymer
In molecular structure of polymers a main chain with attached side chains in contrast to a linear polymer.

breaking extension
The elongation necessary to cause rupture of a test specimen. The tensile strain at the moment of rupture.

breaking factor
The breaking load divided by the original width of a test specimen, expressed in lb/in.

breaking length
A measure of the breaking strength of yarn. The length of a specimen whose weight is equal to the breaking load.

Fibre separation or break on surface plies at drilled or machined edges.

A loosely woven material that serves as a continuous vacuum path over a part but is not in contact with the resin.

The opening and closing of a mould to allow gas to escape early in the moulding cycle. Also called degassing; sometimes called bumping in phenolic moulding.

Condition in which fibres do not move into or conform to radii and corners during moulding, resulting in voids and dimensional control problems.

broad goods
Fibre 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).

buckling (composite)
A mode of failure generally characterised by an unstable lateral material deflection due to compressive action on the structural element involved.

bulk density
The density of a moulding material in loose form (granular, nodular, and so forth), expressed as a ratio of weight to volume.

bulk factor
The ratio of the volume of a raw moulding 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 moulding powder.

bulk modulus
The ratio of the hydrostatic pressure to the volume strain.

bulk moulding compound (BMC)
Thermosetting resin mixed with strand reinforcement, fillers, and so on, into a viscous compound for compression or injection moulding. See:

A general term for a collection of essentially parallel filaments or fibres.

Showing evidence of thermal decomposition or charring through some discoloration, distortion, destruction, or conversion of the surface of the plastic, sometimes to a carbonaceous char.

burst strength (bursting strength)
Measure of the ability of a material to withstand internal hydrostatic or gas dynamic pressure without rupture. Hydraulic pressure required to burst a vessel of given thickness.

An electrically heated alloy container encased in insulating material, used for melting and feeding glass in the forming of individual fibres or filaments. Also, special extra heavy load-carrying short cylinder inserted in bolt or pin holes.

butt joint
A type of edge joint in which the edge faces of the two adherends are at right angles to the other faces of the adherends.

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