Composites Central

Old 06-30-2009, 01:46 AM   #11

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The standard abbreviation for "structural glass," which is a magnesia/alumina/silicate glass fiber reinforcement designed to provide the very high tensile strength required in high-performance composites.

Sandwich structure

A composite component featuring a lightweight core material (usually honeycomb, foam or balsa wood) placed between (hence the term "sandwich") two relatively thin, dense, high-strength, functional and/or decorative skins. (Also see core.)


Low-cost, woven reinforcing fabric in an open mesh construction.


A paste or liquid that, when applied to a joint, hardens in place to form a seal.

Secondary bonding

The joining, by means of adhesive, of two or more already cured composite parts.

Secondary structure

Aerospace structure that is not critical to flight safety. (In contrast to primary structure.)


A permeable layer that separates and also acts as a release film (e.g., porous, Teflon-coated fiberglass). Often placed between lay up and bleeder to facilitate bleeder systems' removal from laminate after cure.


An action or stress resulting from force applied in a direction parallel to the plane of adhesion between the surfaces of two adjacent components or layers, causing or tending to cause one to slide relative to the other.

Shear strength

The maximum shear stress that a material is capable of sustaining.

Sheet molding compound (SMC)

A ready-to-mold, glass fiber-reinforced polyester material primarily used in compression molding.

Shelf life

Length of time a material can be stored and continue to meet specification requirements, remaining suitable for its intended use. (Also see storage life.)


One complete cycle on an injection-molding machine.

Shot weight

The measured amount of compound required to completely fill the mold in injection or transfer molding processes.

Silicon carbide fiber

Reinforcing fiber with high strength and modulus; density is equal to that of aluminum. May be formed as wires by chemical vapor deposition onto a carbon-filament core, or as filaments. Used in both organic and metal-matrix composites.


A chemical solution used to coat fiber filaments, facilitating operations such as weaving or braiding. Sizing protects the filament from water absorption and abrasion (to minimize fiber wear) and also can be used to bind together and stiffen warp yarns during weaving. Sizing is usually removed and replaced with finish before matrix application. Also called size.


The relatively dense laminate adhered to the outer surfaces of the core material in a sandwich structure.

Soft tool

Tool made of composites or a similar "soft" material that is vulnerable to damage during use, storage or transportation. (In contrast to hard tool.)


A liquid capable of dissolving another substance. Certain solvents find application as evaporative diluents in paints or coatings and/or as cleaning solutions in maintenance operations.


Colloquial abbreviation for "specification"; describes the required properties and characteristics a particular material or part must have in order to be acceptable to a potential user.

Specific gravity

The density (mass per unit of volume) of a material divided by the density of water at a standard temperature.


A technique in which continuous strand roving is fed into a chopper gun, which chops the roving into predetermined lengths and sprays the chopped fiber, along with a measured amount of resin and catalyst, onto an open mold.

Stacking sequence

Arrangement of ply orientations and material components in a laminate specified with respect to some reference direction (also see ply schedule).


Collection of short filaments of spinnable length.


Measure of the resistance of a material to deformation. The ratio of applied stress to resulting strain for a particular material.

Storage life

The length of time a material can be stored and retain specific properties. (Also see shelf life.)


Deformation resulting from applied stress. Measured as the change in length per unit of length in a given direction; expressed as a percentage or in inches per inch.


See tow.


Internal resistance to change in size or shape, expressed in units of force (load) per unit area.

Stress concentration

A magnification of applied stress in the region of a notch, void, hole or inclusion.

Stress corrosion

Preferential attack of areas under stress in a corrosive environment that alone would not have caused corrosion.

Stress crack

External or internal cracks in a composite caused by tensile stresses. Cracking may be present internally, externally or in combination.

Structural adhesive

An adhesive used to transfer loads between adhesively bonded surfaces.

Structural bond

A bond that joins load-bearing components in an assembly.

Structural Reaction Injection Molding (SRIM)

A closed molding process employing a fiber reinforced preform or mat that is injected with a reactive resin to impregnate the fibers and cure quickly.

Structural repair manual (SRM)

Document prepared by an OEM that designates original structural materials (both composite and metal) used for a specific aircraft. It usually includes schematics for all parts and listings of fastener types and adhesives. It also suggests general repair methodologies and curing parameters (e..g., autoclave requirements) that will maintain structural integrity. Updated periodically by OEMs based on input from repair technicians.


Material that provides the surface on which an adhesive-containing substance is applied for any purpose, such as bonding or coating.

Surfacing veil

A reinforcing fabric specifically designed to block out the fiber patterns of underlying reinforcements. It often adds ultraviolet protection to the structure as well. (Also see veil.)

Symmetric laminate

Laminate in which the stacking sequence for the plies located on one side of the geometric midplane are the mirror image of the stacking sequence on the other side of the midplane.

Synthetic fiber

Fiber made of materials other than glass or carbon, such as polyester.


Stickiness of an uncured prepreg.


Thin, unidirectional prepreg, available in up to 12-inch widths in carbon fiber. (Also see unidirectional.)

Tape laying

An automated fabrication process in which preimpregnated tape is laid side by side and/or overlapped to form a structure.

Tensile strength

The maximum tensile stress sustained by a test specimen before failure during a tension test.


A unit of linear density equal to the weight in grams of 1,000m of filament fibers, yarns or strands.


See glass-transition temperature.

Thermal conductivity

The ability to conduct heat.

Thermal stress cracking

Crazing and cracking of some thermoplastic resins from overexposure to elevated temperatures.


Wire assembly used with a control device to sense temperature.


A class of plastics that can be repeatedly softened by heating and hardened by cooling through a temperature range characteristic of the plastic, and that in the softened state can be reshaped by means of molding or extrusion.


A class of plastics that, when cured by thermal and/or chemical or other means, become substantially infusible and insoluble. Once cured, a thermoset cannot be returned to the uncured state.


Describes substances that have high static shear strength and low dynamic shear strength, which results in a predictable, time-dependent loss of viscosity under shear (e.g., when mixed, sprayed or otherwise subjected to force) and subsequent substantial to complete return to the higher at-rest viscosity when shear force is removed. Highly thixotropic resins, for example, may be applied easily with spray equipment, yet immediately afterward resist running on a vertical surface.


The mold, either one- or two-sided and either open or closed, in or upon which composite material is placed in order to make a part.

Tooling resin

A plastic resin, typically epoxy or silicone, used to make a tool.


Measure of the ability of a material to absorb energy.


Continuous, ordered assembly of essentially parallel, collimated filaments, normally continuous filaments without twist. Same as strand but used when the reference is specific to carbon fiber.

Tow size

Designates the number of filaments in a tow, denoted by a number followed by K, indicating multiplication by 1,000 (for example, 12K tow has 12,000 filaments).


A visually different or distinctive fiber, tow, or yarn added to a prepreg to verify fiber alignment or to distinguish warp fibers frfill fibers.

Triaxial fabric

Fabric with three non-interwoven layers - oriented at +45, - 45 and either 0 or 90 - which are bonded together, usually by through-the-thickness stitching, to form a single sheet of fabric. (See also biaxial fabric, quadraxial fabric.)


Measure of the number of turns per unit length that a fiber bundle makes around its axis. "Z"-twist denotes a right-handed twist, while "S"-twist denotes a left-handed twist. "U" is often used to represent no twist and "N" means never twisted.
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Old 06-30-2009, 01:47 AM   #12

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Ultrahigh molecular weight (UHMW) polyethylene

A polyethylene (PE) resin with very high molecular weight and very high abrasion resistance and impact strength.

Ultraviolet (UV) cure

The process of curing resins and adhesives with ultraviolet light.

Unidirectional (UD)

General term denoting orientation of fibers in one direction.

Vacuum-assisted resin transfer molding (VARTM)

An infusion process by which a vacuum draws resin into a one-sided mold; a cover, either rigid or flexible, is placed over the laminate and taped or otherwise fixed to form a vacuum-tight seal. (See previous entry.)

Vacuum-bag molding

Molding technique wherein a part layed up on an open mold is cured under a layer of sealed film from which entrapped air has been removed by vacuum. The technique more effectively consolidates the laminate and reduces void content, compared to conventional open molding.


An ultrathin, nonwoven mat often composed of organic fibers as well as glass fibers and used primarily as a corrosion barrier.

Vinyl esters

A class of thermosetting resins containing ester of acrylic and/or methacrylic acids.


Describes the tendency of a material to resist flow. Viscosity is measured in comparison with water, and computed in centipoise (cps). The higher the number, the greater the resistance to flow.


Any pocket of enclosed gas or air within a composite.

Volatile content

The percent of volatiles that are driven off as a vapor from a plastic or an impregnated reinforcement during cure.

Volatile organic compounds (VOCs)

Chemical substances, such as solvents, that readily evaporate or volatilize into the air. Many VOCs also are considered hazardous air pollutants (HAPs) because of potential health concerns.


Materials, such as water and alcohol, in a sizing or resin formulation that can be vaporized at ambient or slightly elevated temperatures.


Fiber bundles in a woven fabric that run parallel to the length of the loom and lengthwise along the longer dimension of the finished fabric.


Dimensional distortion in a composite.

Water absorption

Ratio of the weight of water ab-sorbed by a material to the weight of dry material.


High-pressure water stream used for cutting polymer composite parts.


To interlace fibers in a pattern, often based on a 0/90 grid; the fabric pattern formed by interlacing yarns. Interlacing patterns vary. In plain weave, for instance, warp and fill fibers alternate to make both fabric faces identical. A satin weave pattern is produced by a warp tow over several fill tows and under one fill tow (e.g., eight-harness satin features one warp tow over seven fill tows and under the eighth).


See fill.

Wet layup

Application of a resin to dry reinforcements in the mold.

Wet winding

A filament winding technique that impregnates fiber strands with resin immediately before they contact the mandrel.


Saturation with resin of all voids between reinforcement strands and filaments.

Wetting agent

A surface-active agent that promotes wetting by decreasing a liquid's cohesion.


A short, single crystal fiber or filament used as a reinforcement in a matrix.

Wind angle

Measure in degrees between the direction parallel to the filaments and an established reference point.


Any process in which continuous material is applied under controlled tension to a rotating form (mandrel) in a predetermined geometric relationship to make a structure. (See filament winding.)

Winding pattern

In filament winding, the recurring pattern of the filament path after a certain number of mandrel revolutions.


Large diameter (greater than about 2 mils) high-performance fiber (e.g., see boron fiber or silicon carbide fiber). In contrast, see filament and fiber.

Wire mesh

Fine wire screen used to dissipate the electrical charge from lighting.


Same as fill.

Woven roving

Heavy, coarse fabric produced by weaving continuous roving bundles.


Imperfection in the surface of a laminate that looks like a crease in one of the outer layers. This occurs in vacuum-bag molding when the bag is improperly placed.


Usually, the axis in the plane of the laminate used as 0 reference. Typically, the y-axis is the axis in the plane of the laminate perpendicular to the x-axis, and the z-axis is the reference axis normal to the laminate plane in the composite laminate. (See also laminate coordinate axes, off-axis laminate and principal axis.)


The axis in the plane of a laminate perpendicular to the x-axis.


A continuous, ordered assembly of essentially parallel, collimated filaments, usually with a twist.

Yield point

The first stress in a material, less than the maximum rate attainable stress, at which the strain increases at a higher rate than the stress. The point at which permanent deformation of a stressed specimen begins to take place. (Also see stress and strain.)

Young's modulus

Ratio of normal stress to the corresponding strain for tensile or compressive stresses less than a material's proportional limit.


The axis perpendicular to the plane formed by the x and y axes. In a sheet laminate, if the x and y axes are parallel to the length and width, respectively, the z-axis would indicate sheet thickness. (See x-axis and y-axis.)

Zero bleed

Laminate fabrication procedure that does not allow loss of resin during cure.

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Old 12-26-2010, 03:04 PM   #13

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Originally Posted by GGROP View Post
For an online Composites glossary and free subscription to a couple of great industry composite mags too:
Anyone know if the Free Magazine Subscriptions are still available? When I went to check it out the online request was formatted incorrectly (code everywhere). It could just be a browser thing (Google Chrome) but I thought I'd check before submitting personal information on a website. I really hate to submit personal info over an unsecured site regardless
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