B-STAGE
An intermediate stage in the reaction of certain thermosetting resins in which the material swells when in contact with certain liquids and softens when heated, but may not entirely dissolve or fuse; sometimes referred to as resistol. The resin in an uncured prepreg or premix is usually in this stage. See A-stage, C-stage.

BAG MOLDING
A molding technique in which the composite material is placed in a rigid mold and covered with a flexible bag, with pressure applied by vacuum, autoclave, press, or by inflating the bag.

BALANCED LAMINATE
All lamina except those at 0/90( are placed in plus/minus pairs (not necessarily adjacent) symmetrically about the layup centerline.

BARCOL HARDNESS
Hardness value obtained by measuring the resistance to penetration of a sharp steel point under a spring load. The instrument, called the Barcol Impressor, gives a direct reading on a 0-100 scale. The hardness value is often used as a measure of the degree of cure of a plastic.

BARE GLASS
Glass (yarns, rovings, fabrics) from which the sizing or finish has been removed; also, such glass before the application of sizing or finish.

BASKET WEAVE
Woven reinforcement where two or more warp threads go over and under two or more filling threads in a repeat pattern. This weave is less stable than the plain weave but produces a flatter, stronger, more pliable fabric.

BATCH (or LOT)
Material made with the same process at the same time having identical characteristics throughout.

BEARING STRENGTH
The maximum bearing stress that will not fail a composite when applied through a cylindrical fastener surface.

BEARING AREA
The product of the pin diameter and the specimen thickness.

BEARING LOAD
A comprehensive load on an interface.

BEARING STRESS
Applied load divided by bearing area (hole diameter times thickness).

BEND TEST
A test of ductility by bending or folding usually with steadily applied forces. In some instances the test may involve blows to a specimen having a cross section that is essentially uniform over a length several times as great as the largest dimension of the cross section.

BENZOYL PEROXIDE (BPO)
The catalyst used in conjunction with aniline accelerator or where heat is used as an accelerator.

BIAS FABRIC
A fabric in which warp and fill fibers are at an angle to the length.

BIAS CUT
Fabric cut at an angle (45^o) to the warp & fill fibers.

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

BI-DIRECTIONAL LAMINATE
A reinforced plastic laminate with the fibers oriented in two directions in the plane of the laminate; a cross laminate.

BINDER
The resin or cementing constituent of a plastic compound which holds the other components together; the agent applied to glass mat or preforms to bond the fibers prior to laminating or molding.

BISMALCIMIDE - (BMI)
A type of thermoset polyimide that cures by an additional reaction, avoiding formation of volatiles, and has temperature capabilities between those of epoxy and polyimide.

BISPHENOL A
A condensation product formed by reaction of two (bis) molecules of phenol with acetone (A). This polyhydric phenol is a standard resin intermediate along with epichlorohydrin in the production of epoxy resins.

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 vacuum bagging.

BLEEDER PLY
Layer of porous material placed in a vacuum bag to absorb excess resin and allow air and gas to escape.

BLEEDOUT
The excess liquid resin appearing at the surface, primarily occurring during filament winding.

BLEND
Made by mixing traditional polymers which have already formed. The mixing results in a multi-phase system. Physical interactions between the polymers are responsible for the properties of the blend.

BLISTER
Undesirable rounded elevation of the surface of a plastic, whose boundaries may be more or less sharply defined, resembling in shape a blister on the human skin. The blister may burst and become flattened.

BMC
Bulk Molding Compound (Thermoset).

BOND PLY
The ply or fabric patch that comes in contact with the honeycomb core during repair.

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. The amount of adhesion between bonded surfaces.

BORON FIBER
A fiber usually of a tungsten-filament core with elemental boron vapor deposited on it to impart strength and stiffness.

BRAID
A system of three or more yarns which are interwoven in such a way that no two yarns are twisted around each other.

BRAID ANGLE
The acute angle measured from the axis of braiding.

BRAID, TWO-DIMENSIONAL
Braided fabric with no braiding yarns in the through thickness.

BRAID, THREE-DIMENSIONAL
Braided fabric with one or more braiding yarns in the through thickness direction.

BRAIDED, TRIAXIAL
A biaxial braided fabric with laid in yarns running in the axis of braiding.

BRAIDING
Weaving fibers into a tubular shape.

BREAKOUT
Separation or breakage of fibers when the edges of a composite part are drilled or cut.

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

BRIDGING
Fabric reinforcement extended over a curved edge that does not come into contact with the rest of the composite.

BROADGOODS
Fibers woven into fabrics that may or may not be impregnated with resin, usually furnished in rolls.

BUCKLING (composite)
A failure mode usually characterized by fiber deflection rather than breaking because of compressive action.

BURST STRENGTH
(1) Hydraulic pressure required to burst a vessel of given thickness. Commonly used in testing filament-wound composite structures. (2) Pressure required to break a fabric by expanding a flexible diaphragm or pushing a smooth spherical surface against a securely held circular area of fabric. The Mullen expanding diaphragm and Scott ball burst machine are examples of equipment used for this purpose.

BUTT JOINT
A joint in which parts are joined with no overlap.

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Glossary Section (B) Last Updated: 9/3/99 12:54 PM

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