C-stage

The final step in the curing process for thermoset resins, resulting in irreversible hardening and insolubility. (See also A-stage, B-stage.)


CAD/CAM

Computer-aided design/computer-aided manufacturing.


Carbon fiber

Reinforcing fiber produced by the pyrolysis of an organic precursor fiber, such as PAN (polyacrylonitrile), rayon or pitch, in an inert atmosphere at temperatures above 982°C/1800°F. The term carbon is often used interchangeably with the term graphite, but the fibers differ. Carbon fibers are typically carbonized at about 1315°C/2400°F and contain 93 percent to 95 percent carbon. Carbon fibers can be converted to graphite fibers by graphitization at 1900°C to 2480°C (3450°F to 4500°F), after which they contain more than 99 percent elemental carbon. Carbon fibers are known for their light weight, high strength and high stiffness.


Carbon/carbon

Composite of carbon fiber in a carbon matrix.


Cast polymer

A nonreinforced composite (resin used without reinforcing fibers) that combines polymers, fillers and additives as composites to meet specific application requirements.


Catalyst

Substance that promotes or controls curing of a compound without being consumed in the reaction. (See also hardener.)


Catalyzed resin

A resin mixture possibly still in the workable state, after it has been mixed with catalyst or hardener.


Catenary

Uniformity of strand length in a specified length of roving stretched under tension. Poor catenary means some strands in the roving length are longer than others.


Caul plate

Plate or sheet the same size and shape as the composite layup with which it will be used. The caul plate is placed in immediate contact with the layup during curing to transmit normal pressure and provide a smooth surface on the finished part.


Centipoise (cps)

A unit of measure used to designate a fluid's viscosity (at 21°C/70°F, water is 1 cps; peanut butter is 250,000 cps).


Centrifugal casting

A processing technique for fabricating cylindrical structures, in which the composite material is positioned inside a hollow mandrel designed to be heated and rotated as resin is cured.


Ceramic-matrix composites (CMC)

Materials consisting of a ceramic or carbon fiber surrounded by a ceramic matrix, primarily silicon carbide.


Charge pattern

The ply schedule used in parts made from sheet molding compound (SMC); a pre-weighed number of SMC plies cut from an SMC sheet and oriented in such a way that the material will fill the mold cavity when placed in the mold and compressed.


Chemical vapor deposition (CVD)

Process in which the reinforcement material is deposited from the vapor phase onto a continuous core such as boron or tungsten.


Chopped strand

Continuous roving that is chopped into short lengths for use in mats, spray up or molding compounds.


Circumferential winding

Process of winding fiber perpendicular to the axis during filament winding.


Cloth

See fabric.


CMC

See ceramic-matrix composite.


Cocured

Cured and simultaneously bonded to another prepared surface.


Coefficient of expansion (COE)

A measure of the change in length or volume of an object.


Coefficient of thermal expansion (CTE)

A material's fractional change in length for a given unit change of temperature.


Cohesion

Tendency of a single substance to adhere to itself. Also, the force holding a single substance together.


Coin tap

Tapping a laminate with a coin in different spots to detect a change in sound, indicating the presence of a defect that may require repair.


Commingled yarn

Hybrid yarn made with two types of materials intermingled in a single yarn (for example, thermoplastic filaments intermingled with carbon filaments to form a single yarn).


Composite

Three-dimensional combination of at least two materials differing in form or composition, with a distinct interface separating the components. Composite materials are usually manmade and created to obtain properties that cannot be achieved by any of the components acting alone.


Compression molding

Technique for molding thermoset composites in which the part is shaped and cured in the same step. Layered reinforcing fibers and resin paste (typically precombined in a leather-like, preimpregnated sheet) are placed into an open two-part mold cavity. The mold is closed and, with the application of both heat and pressure, the resin viscosity drops, the material is forcibly distributed throughout the mold cavity to take its final shape and the part is allowed to cure.


Compressive strength

Resistance to a crushing or buckling force; the maximum compressive load a specimen sustains divided by its original cross-sectional area.


Condensation

A polymerization reaction in which simple byproducts (e.g., water) are released.


Consolidation

A processing step in which a fiber and matrix are compressed to reduce voids and achieve a particular density.


Contaminant

An impurity or foreign substance that affects one or more properties of composite materials, particularly adhesion.


Continuous filament

An individual, flexible, small-diameter fiber of indefinite length.


Continuous roving

Large bundle of parallel filaments coated with sizing, gathered together into single or multiple strands, and wound into a cylindrical package. May be used to provide continuous reinforcement in woven roving, filament winding, pultrusion, prepregs, or high-strength molding compounds (may also be used chopped).


Coordinate axes

See laminate coordinate axes.


Core

In sandwich construction, the central component to which inner and outer skins are attached; also refers to a section of a complex mold that forms undercut parts (also see honeycomb).


Core crush

Compression damage of the core.


Core depression

A gouge or indentation in the core material.


Core orientation

Used on a honeycomb core to line up the ribbon direction, thickness of the cell depth, cell size and transverse direction.


Core separation

A breaking of honeycomb core cells.


Core splicing

Joining of two core segments by bonding them together.


Cowoven fabric

Reinforcement fabric woven with two different types of fibers in individual yarns (e.g., thermoplastic fibers woven side by side with carbon fibers).


Crazing

Region of ultrafine cracks that may develop on or under a resin surface.


Creel

A device for holding the required number of roving spools or other supply packages of reinforcement in the desired unwinding position.


Creep

Time-dependent dimensional change in a material under physical load.


Crimp

Degree of waviness of a fiber, which determines its capacity to cohere.


Critical length

Minimum length of a fiber necessary for matrix shear loading to develop ultimate fiber strength.


Cross-laminated

Laminated with some of the layers oriented at one or more angles to the other layers with respect to the principal laminate axis. (See cross-ply laminate and fiber architecture.)


Crosslinking

Polymerization reactions that branch out from the main molecular chain to form a networked pattern of chemical links.


Cross-ply laminate

A laminate having plies oriented only at 0° and 90°. May or may not be symmetrical.


Crystalline

Having a molecular structure in which the atoms are arranged in an orderly, three-dimensional pattern.


CTE

See coefficient of thermal expansion.


Cure

Irreversible alteration of the molecular structure and physical properties of a thermosetting resin by chemical reaction, typically stimulated by heat and/or the presence of catalysts, with or without applied pressure. However, see ultraviolet (UV) cure.


Cure temperature

The temperature at which a material attains final cure.


Curing agent

Catalytic or reactive agent that brings about polymerization when added to a resin (also see accelerator, catalyst and hardener).


CVD

See chemical vapor deposition.