Composites Terms

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Planar textile. Also known as cloth.

Fabric, nonwoven

Planar textile constructed by bonding or interlocking but not interlacing fibers or yarns by mechanical, chemical, thermal or solvent means.

Fabric, woven

Planar textile constructed by interlacing fibers or yarns, using a weaving process.


Process of making a composite part or tool.


Failure or deterioration of a material's mechanical properties as a result of repeated cyclic loading or deformation over time.

Fatigue strength

Maximum cyclical stress withstood for a given number of cycles before a material fails. The residual strength after being subjected to fatigue loading.


See finite-element analysis.


One or more filaments in an ordered assemblage.

Fiber architecture

The design of a fibrous preform or part in which the fibers are arranged in a particular way to achieve a desired result. Mats and braided, stitched and woven fabrics are common forms of fiber architecture.

Fiber bridging

Reinforcing fiber material bridging an inside radius of a pultruded product. The condition is caused by shrinkage stresses around such a radius during cure.

Fiber content

The amount of fiber present in a composite expressed either as a percent by weight or percent by volume. Also sometimes stated as a fiber volume fraction or expressed in ratio to the matrix content (e.g., a 60:40 fiber-to-resin ratio denotes a composite with 60 percent fiber content and 40 percent resin content).

Fiber orientation

Direction of fiber alignment in a nonwoven or mat laminate wherein most of the fibers are placed in the same direction to afford greater strength in that direction.

Fiber placement

Continuous process for fabricating composite shapes with complex contours and/or cutouts by means of a device that lays preimpregnated fibers (in tow form) onto a nonuniform mandrel or tool. Differs from filament winding in several ways: There is no limit on fiber angles; compaction takes place online via heat, pressure or both; and fibers can be added and dropped as necessary. The process can produce shapes with greater complexity and permits a faster putdown rate than filament winding.

Fiber volume fraction

See fiber content.

Fiber wash

Dislocation or displacement of reinforcing fibers placed within a mold caused by the force of the resin flow, resulting in unintended fiber distribution within the finished part.

Fiber-reinforced plastics (FRP)

General term for a polymer-matrix composite that is reinforced with cloth, mat, strands or any other fiber form. However, in practice, the term is most often used in reference to glass fiber-reinforced plastics.


Reinforcing fiber made by drawing molten glass through bushings. The predominant reinforcement used with polymer matrix composites, it is known for its good strength, processability and low cost.


Polycrystalline or amorphous individual fiber unit with a length-to-diameter ratio greater than one. The minimum diameter of a filament is not limited, but the maximum diameter may not exceed 0.010 inches. Filaments greater than about 0.002 inches in diameter are often referred to as wires.

Filament count

Number of filaments in the cross-section of a fiber bundle.

Filament winding

An automated process in which continuous reinforcing fibers, either preimpregnated with resin or drawn through a resin bath, are wound under controlled tension around a rotating form to make a composite structure. (Also see winding and mandrel.)


The fiber bundles in a woven fabric that run transverse (at a 90° angle) to the warp yarns; also known as weft or woof.


A solid constituent, usually inert, added to a matrix to modify a composite's properties (e.g., increase viscosity, improve appearance or de-crease density) or to decrease part material cost.

Filler ply

An additional patch used to fill in a depression in a repair or build up an edge.

Film adhesive

Adhesive in the form of a thin, dry resin film, with or without a carrier; commonly used for adhesion between laminate layers.


Material applied to textiles to improve the bond between the fiber and matrix; applied after sizing is removed.

Finite element analysis

Process of selecting the optimum combination of materials in a composite, based on computer-based computational modeling and analysis.

Flexural modulus

Ratio, within the elastic limit, of the applied stress on a test sample in flexure to the corresponding strain in the outermost fibers of the sample.

Flexural strength

Strength of a material in bending, usually expressed in force per unit area, as the stress of a bent test sample at the instant of failure.


A rupture in the surface of a laminate due to external or internal forces; may or may not result in complete separation.

Fracture toughness

A measure of the damage tolerance of a material containing initial flaws or cracks.


See fiber-reinforced plastics.