Bagging: applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn.

Bag Molding: process in which the consolidation of the material in the mold is affected by the application of fluid or gas pressure through a flexible membrane.

Balanced Construction: equal parts of warp and fill in fiber 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 Laminate: composite laminate in which all laminae at angles of 0° and 90° occur only in + or - pairs (not necessarily adjacent) and are symmetrical around the centerline.

Band width: in filament winding, the width of the reinforcement as it is applied to the mandrel.

Barcol-Shore Rockwell Hardness: property of material which describes its ability to be indented. The Rockwell method for measuring hardness forces a steel point into the material and then measures the penetration of the point. The different letters in the Rockwell reading describe the shape of the point and the load applied during the test. Units - Rockwell units with the appropriate suffix letter. The letter and number cannot be separated. Higher numbers with the same letter indicate harder materials. Harder materials have more resistance to penetration by another substance. The hardness value is often used as a measure of the degree of cure of a plastic.

Bare Glass: glass as it flows from the bushing in fiber form, before a binder or sizing is applied.

Batch: 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.

Batt: felted fabrics. Structures built by the interlocking action of compressing fibers, without spinning, weaving, or knitting.

Bearing Strength: 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: 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.

Bias Fabric: warp and fill fibers at an angle to the length of the fabric.

Biaxial Load: 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 fibers eliminated.

Bi-Directional: reinforcing fibers that are arranged in two directions, usually at right angles.

Bi-Directional Laminate: a reinforced plastic laminate with the fibers oriented in two directions in its plane. A cross laminate.

Binder: resin or cementing constituent (of a plastic compound) that holds the other components together. The agent applied to fiber mat or preforms to bond the fibers before laminating or molding. Schmelzer Industries currently offers five distinct binders for varying uses in the composites industry.

Bismaleimide (BMI): 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 polymerization of a pre-polymer terminated with tow maleimide groups. Intermediate in temperature capability between epoxy and polyimide.

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

Bleeder Cloth: woven or non-woven 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.

Blister: flaw either between layers of laminate or between the gel coat film and laminate.

BMC: Bulk Molding Compound (Thermoset).

Bond Strength: 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.

Boron Fiber: fiber produced by vapor deposition of elemental boron, usually onto a tungsten filament core, to impart strength and stiffness.

Braiding: weaving a fiber into a tubular shape instead of a flat fabric, as for graphite fiber reinforced gold club shafts.

Breathing: opening and closing of a mold to allow gas to escape early in the molding cycle. Also called “degassing”; sometimes called “bumping” in phenolic molding.

Bridging: condition in which fibers do not move into or conform to radii and corner during molding, resulting in voids and dimensional control problems.

B-Stage: intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and is plastic and fusible buy may not entirely dissolve or fuse. Also called “resistol” or “resitol.” The resin in an uncured prepreg or premix is usually in this stage.

Buckling (Composite): mode of failure generally characterized by an unstable lateral material deflection due to compressive action on the structural element involved.

Bulk Molding Composite (BMC): thermosetting resin mixed with short strand reinforcement, filler, and so on, into a viscous compound for compression or injection molding.

Bundle: general term for a collection of essentially parallel filaments or fibers.

Bushing: plate with holes through which molten glass is pulled to produce glass fibers.

Bushing Tip: small tapered protrusions on the bottom of bushings each containing an orifice through which molted glass flows, from which continuous filaments are drawn.

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