Glossary for Composite

A-STAGE: An early stage in the reaction of a thermosetting resin in which the material is still soluble and fusible.

ANISOTROPIC: Not isotropic; having mechanical and/or phydcal properties which vary with direction relative to natural reference axes inherent in the material.

AUTOCLAVE: A closed vessel for producing an environment of fluid pressure, with or without heat, to an enclosed object while undergoing a chemical reaction or other operation.

AUTOCLAVE MOLDING: The lay-up is covered by a pressure bag, and the entire assembly is placed in an autoclave capable of providing heat and pressure for curing the part.

B-STAGE: An intermediate stage in the reaction of a thermosetting resin in which the material melts when heated and dissolves in certain solvents. Materials are usually pre-cured to this stage to facilitate handling and processing prior to final cure.

BLEEDER CLOTH: A nonstructural 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 is complete and is not part of the final composite .

BREATHER: A loosely woven material, such as glass fabric, which serves as a continuous vacuum path over a part but does not come in contact with the resin. The breather is removed after the curing process is complete and is not part of the final composite.

C-STAG E: The fi nal stage of the cu ri ng of a thermosetting resin in which the material has become infusible and insoluble in common solvents.

CARBON FIBERS: Fibers produced from pyrolytic degradation of synthetic organic fibers, polyacrylonitrile (PAN) or rayon, which contain about 92-99%

CAUL PLATES: Smooth metal, plastic, or rubber plates free of surface defects. A caul plate must be the appropriate size and shape for the composite lay-up with which itwill be used. Itis used in immediate contact with the lay-up during the curing process to transmit normal pressure and provide a smooth surface on the finished part.

COEFFICIENT OF THERMAL EXPANSION: The fractional change in length of a material for each unit change in temperature.

COMPOSITE MATERIAL: Composites are combinations of materials differing in composition or form on a macroscale. The constituents retain their identities in the composite; that is, they do not dissolve or otherwise merge completely into each other although they act in concert. Normally, the components can be physically identified and exhibit an interface between one another.

CONSOLIDATION: The physical process of compacting thermoplastic prepregs with heat and pressure into a unified continuous part.

CURE: To change the properties of a thermosetting resin irreversibly by chemical reaction, i.e., condensation, ring closure, or addition. Cure may be accomplished by addition of curing (cross-linking) agents, with or without catalyst, and with or without heat.

DRAPE: The ability of the prepreg to conform to surfaces, molds, and bends.

END: An untwisted bundle of continuous filaments. A term commonly used in referring to fiberglass or aramid fibers.

FAB RIG: A material constructed of i nte rlaced yarns, fibers, or filaments, usually a planar structure. In fabric lamina, the warp direction is considered the longitudinal (L) direction, analogous to the filament direction in a fiiamentary lamina.

FIBER CONTENT: The amount of fiber present in a composite. This is usually expressed as a

FILAMENT: Fiberthat is characterized by extreme length, such that there are normally no filament ends within a part except at geometric discontinuities.

FILAMENT WINDING: An automated process in which continuous filament (or tape) is treated with resin and wound on a removable mandrel in a pattern.

FILL: Yarn oriented at right angles to the warp in a woven fabric.

GEL TIME: The time required for a liquid material to form a gel under specified conditions of temperature as measured by a specific test.

GLASS CLOTH: Conventionally woven glass fiber material; certain lightweight glass fabrics are also called scrims.

GRAPHITE FIBERS: A group of carbon fibers which have a carbon content of about 99% and also have high modulus values. This term is used i nterchangeably with "carbon fi bers" th roughout the industry.

HYBRID: A composite laminate comprised of laminae of two or more composite material systems, e.g., graphite and glass. It also applies to woven fabrics having more than one type of fiber.

INTERLAMINAR SMEAR: A shearing force tending to produce a relative displacement between two laminae along the plane of their interface.

ISOTROPIC: Having uniform properties in all directions. The measured properties of an isotropic material are independent of the axis of testing.

KEVLAR": Registered trademark of E. I. Du Pont de Nemours, Inc. for aramid, a strong organic fiber with a high strength-to-weight ratio. When woven into cloth and impregnated with a thermosetting epoxy resin, it produces a material having high impact resistance and low radio frequency attenuation.

LAMINA: A single ply or layer in a laminate made of a series of layers.

LAMINATE: A product made by bonding together two or more layers of material or materials.

LAY-UP: A process of fabrication involving the placement of successive layers of materials.

LOT: In general, a quantity of material formed during the same process and having identical characteristics throughout. A lot of prepreg tape produced from a single batch of matrix material. The prepreg tape lot is not necessarily produced at one time, but all sub-lots are produced in the same equipment under identical conditions.

MATRIX: The essentially homogeneous material i n which the fiber system of a composite is imbedded.

MODULUS: A mathematical value which describes the degree of stiffness of a material by measuring its deflection or change in length under loading.

ORTHOTROPIC: Having three mutually perpendicular planes of elastic symmetry.

PEEL PLY: A sacrificial nylon, polyester, or nonporous Teflon ply; usually the last ply placed on the lay-up before curing. The peel ply may serve two functions: i) When removed from the laminate, it provides a smooth surface for subsequent bonding operations. It also tends to fracture the resin when removed, thus eliminating sanding work. 2) When removed from the laminate, it helps eliminate bag wrinkles, thus providing a smoother surface.

POST CURE: The exposure of certain resins to higher than normal curing temperatures after the initial cure cycle. This second stage is necessary to attain the complete cure and desired mechanical properties of the resins involved. The higher temperatures are used separately because they would result in an excessive reaction if applied throughout the entire cure.

PREPREG, PREIMPREGNATED: A combination of mat, fabric, nonwoven material, or roving with resin, usually advanced to the B-stage, ready for curing.

RESIN: An organic material with indefinite and usually high molecular weight and no sharp melting point.

RESIN CONTENT: The amount of matrix present in a composite either by percent weight or percent volume.

ROVING: A preimpregnated tow used in the filament winding process. Term is used interchangeably with "filament prepreg."

RT: Stands for ambient room temperature, usually between 70-77"F (21-25"C).

SANDWICH CONSTRUCTION: A structural panel consisting, in its simplest form, of two thin facesheets bonded to and separated by a lightweight core.

SELVAGE: The finished edge of a woven fabric.

SHELF LIFE: The length of time a material, substance, product, or reagent can be stored under specified environmental conditions and continue to meet all applicable specification requirements and/or remain suitable for its intended function.

TACK: Qualitatively, the stickiness of a prepreg. Affected by numerous factors including temperature, humidity and resin content.

TOW: A loose, untwisted bundle of filaments.

VACUUM BAG MOLDING: A process in which the lay-up is cured under pressure generated by drawing a vacuum in the space between the lay-up and the flexible sheet placed over it and sealed at the edges.

VOID: A physical and mechanical discontinuity occurring within a material or part which may be 2D (e.g., disbonds, delaminations) or 3-D (e.g., vacuum-, air, or gas-filled pockets). Porosity is an aggregation of micro-voids. Voids are essentially incapable of transmitting structural stresses or nonradiative energy fields.

WARP: The lengthwise yarns or tows of a woven fabric that run parallel to its selvage edge.

WET STRENGTH: The strength of an organic matrix composite when the matrix resin is conditioned, possibly to saturation, with absorbed moisture. (Saturation is an equilibrium condition in which the net rate of absorption under prescribed conditions falls essentially to zero.)

YARN: Generic term for strands of fibers or filaments in a form suitable for weaving or othemise intertwining to form a fabric.