GLOSSARY OF TERMS
F

Fabricator: manufacturer of reinforced plastic products.

Fatigue: the failure or decay of mechanical properties after repeated applications of stress. Fatigue tests give information on the ability of a material to resist the development of cracks, which eventually bring about failure as a result of a large number of cycles.

Fatigue life: the number of cycles of deformation required to bring about failures of the test specimen under a given set of oscillating conditions (stresses and strains).

Fatigue limit: the stress level below which a material can be stress cyclically for an infinite number of times without failure.

Fatigue strength: the maximum cyclical stress a material can withstand for a given number of cycles before failure occurs. The residual strength after being subjected to fatigue.

Fiber: reinforcement material which is a major component in a composite matrix. Often, fiber is used synonymously with filament.

Fiber content: the amount of fiber present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite.

Fiber diameter: the measurement (expressed in hundred thousandths of an inch) of the diameter of individual filaments.

Fiber direction: the orientation or alignment of the longitudinal axis of the fiber with respect to a stated reference axis.

Fiberglass: Glass which has been extruded into extremely fine filaments. These filaments vary in diameter, and are measured in microns. Glass filaments are treated with special binders and processed similar to textile fibers. These fibers come in many forms such as roving, woven roving, mat and continuous strands. All Schmelzer Industries products are made of fiberglass.

Fiberglass reinforcement: major material used to reinforce plastic. Available as mat, roving, fabric, and so forth, it is incorporated into both thermosets and thermoplastics.

Fiber pattern: visible fibers on the surface laminates or molding. The thread size and weave of glass cloth.

Fiber Reinforced Plastic (FRP): a general term for a composite that is reinforced with cloth, mat, strands, or any other fiber form.

Filament: single thread-like fiber of extruded glass. The smallest single unit of a fibrous material.

Filament winding: process which involves winding a resin-saturated strand of glass filament around a rotating mandrel.

Fill: yarn oriented at right angles to the warp in a woven fabric.

Filler: Usually inert organic or inorganic materials which are added to plastics, resins or gel coats to vary the properties, extend volume, or lower the cost of the article being produced.

Finish: a mixture of materials for treating glass or other fibers. It contains a coupling agent to improve the bond of resin to the fiber.

Fire retardants: certain chemicals that are used to reduce the tendency of a resin to burn.

Fish Eye: effect of surface contamination which causes a circular separation of a paint or gel coat.

Flamability: measure of the extent to which a material will support combustion. How fast a material will burn under controlled conditions.

Flash: that portion of the charge which flows from or is extruded from the mold cavity during the molding. Extra plastic attached to a molding along the parting line, which must be removed before the part is considered finished.

Flash Point: lowest temperature at which a substance gives off enough vapors to form a flammable mixture.

Flexible molds: molds made of rubber or elastomeric plastics, used for casting plastics. They can be stretched to remove cured pieces with undercuts.

Flexural modulus: determines how much a sample will bend when a given load is applied. The ratio, within the elastic limit, of the applied stress on a test specimen in flexure to the corresponding strain in the outermost fibers of the specimen.

Flexural strength: also known as bending strength. The maximum stress that can be borne by the surface fibers in a beam in bending. The flexural strength is the unit resistance to the maximum load before failure by bending, usually expressed in force per unit area. It describes how much of a non-moving load can be applied before a bar yields or breaks. Units are normally thousands of pounds per square inch. (103 psi) - Mega Pascals (mPa). Higher numbers mean that material is stronger and can withstand a heavier load.

Flow: the movement of resin under pressure, allowing it to fill all parts of a mold. The gradual but continuous distortion of a material under continued load, usually at high temperatures; also called creep.

Flow line: a mark on a molded piece made by the meeting of two flow fronts during molding. Also called striae, weld mark, or weld line.

Flow marks: wavy surface appearance of an object molded from thermoplastic resins, cased by improper flow of the resin into the mold.

Foam: lightweight, cellular plastic material containing glass-filled voids. Typical foams include urethane, PVC, and polyester.

Force: the male half of the mold that enters the cavity, exerting pressure on the resin and causing it to flow. Also called punch.

Fracture: the separation of a body. Defined both as rupture of the surface without complete separation of laminate and as complete separation of a body because of external or internal forces.

Fracture stress: the true, normal stress on the minimum cross-sectional area at the beginning of fracture.

Fracture toughness: a measure of the damage tolerance of a material containing initial flaws or cracks. Used in aircraft structural design and analysis.

FRP: see Fiber Reinforced Plastic.

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