S-BASIS (OR S-VALUE)
The mechanical property value which is usually the specified minimum value of the appropriate government specification or SAE Aerospace Material Specification for the material.

S-GLASS
A family of magnesium-alumina-silicate glasses with a certified chemical composition which conforms to an applicable material specification and which produces high mechanical strength. (ASTM D578-90)

S-2 GLASS FIBER
The Owens Corning trademarked brand of high tensile strength "S" glass fibers.

SAGS/RUNS
Sag - slumping of the gel coat or resin film. Run - draining of the gel coat film or laminating resin.

SAMPLE
A small portion of a material or product intended to be representative of the whole. Statistically, a sample is the collection of measurements taken from a specified population.

SANDWICH CONSTRUCTION
A composite composed of a lightweight core material (usually honeycomb or foamed plastic) to which two relatively thin, dense, high-strength, functional, or decorative skins (also called faces) are adhered.

SANDWICH LAY-UP
A lamination composed of two outside layers of reinforced material such as glass mat and an inside layer or layers of honeycomb, glass cloth, or other light-weight core material.

SATURATION
An equilibrium condition in which the net rate of absorption under prescribed conditions falls essentially to zero.

SCARF JOINT
A bonded joint in which similar segments of adherends are cut away, with cut areas overlapped and bonded.

SCRIM
A low cost, non-woven open-weave reinforcing fabric made from continuous filament yarn in an open mesh construction.

SCRIMP
A patented variation of the RTM process.

SEALANT
Applied to a joint in paste or liquid from that hardens in place to form a seal.

SECONDARY BONDING
The joining together, by the process of adhesive bonding, of two of more already-cured composite parts, during which the only chemical or thermal reaction occurring is the curing of the adhesive itself.

SECONDARY STRUCTURE
Aircraft or Aerospace structure that is not critical to flight safety.

SELF EXTINGUISHING
Ceases to burn when the source of flame is removed.

SELVAGE
The narrow edge of woven fabric that runs parallel to the warp. It is made with stronger yarns in a tighter construction than the body of the fabric to prevent raveling.

SET
To convert a resin into a fixed or hardened state by chemical or physical action, such as condensation, polymerization, vulcanization or gelation.

SET-UP
To harden, as in curing.

SHEAR
An action or stress resulting from applied forces which causes or tends to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their plane of contact. Inter laminar Shear (ILS). The plane of contact is composed of resin only.

SHEAR EDGE
The cut-off edge of the mold.

SHEET MOLDING COMPOUND (SMC)
A ready-to-mold glass fiber reinforced polyester material primarily used in compression molding.

SHELF LIFE
The length of time a material can be stored and continue to meet specification requirements, remaining suitable for its intended use.

SHORE HARDNESS
A measure of the resistance of a material to indentation by a spring loaded indenter. A higher number indicates greater resistance.

SHRINKAGE
The relative change in dimension between the length measured on the mold when it is cold and the length on the molded object 24 hours after it has been taken out of the mold.

SKIN COAT
The first layer of laminate next to the gel coat, generally one ply of chopped strand mat.

SILICON CARBIDE FIBER
A reinforcing fiber with high strength and modulus; density equal to that of aluminum. It is used in organic metal-matrix composites.

SINK MARK
A shallow depression or dimple on the surface of an injection molded part due to collapsing of the surface following local internal shrinkage after the gate seals; an incipient short shot.

SISAL
A white fiber produced from the leaves of the agave plant. Used as a reinforcing filler, in short chopped lengths, to impart moderate impact resistance.

SIZING
A compound that binds together and stiffens yarn, providing resistance to abrasion during weaving; normally removed and replaced with finish before matrix application.

SKEIN
A continuous filament, strand, yarn, roving, etc., wound up to some measurable length, and usually used to measure various physical properties.

SKIN
A layer of relatively dense material used in sandwich construction on the surface of the core.

SKIN COAT
The first layer of laminate next to the gel coat. Generally only 1/16" thick to afford good rollout and to reduce heat.

SLAVE PUMP
A catalyst pump, which is driven by the resin pump through a pair of level arms.

SLEEVING
A common name for tubular braided fabric.

SOFT TOOL
A tool made of composites or a similar "soft" material which is vulnerable to damage during use, storage, or transportation.

SOLVENT RESISTANCE
The non-swelling of a material and, of course, the impossibility for it to be dissolved by the solvent in question.

SOLID
The amount of sizing on the glass expressed as a percentage of the total weight.

SOLUTE
The dissolved material

SOLVENT
A liquid used to dissolve and clean materials.

SPEC
Specifications of the properties, characteristics, or requirements a particular material or part must have in order to be acceptable to a potential user of the material or part.

SPECIFIC GRAVITY
The ratio of the weight of any volume of a substance to the weight of an equal volume of another substance taken as standard at a constant or stated temperature. Solids and liquids are usually compared with water, and air or hydrogen for gases.

SPECIFIC HEAT
(Thermal Capacity) The quantity of heat required to raise the temperature of a one pound unit of mass one degree Fahrenheit under specified conditions. Units = BTUs per pound per degree Fahrenheit (BTA/lb/(F); = Joules/Kilogram Kelvin (J/KgK). Higher numbers means that it takes more input heat energy to raise the temperature of a material.

SPECIMEN
An individual piece or portion of a sample used to make a specific test; of specific shape and dimensions.

SPLICE
The joining of two ends of glass fiber yarn or strand, usually by means of an air drying glue.

SPLIT MOLD
A mold in which the cavity is formed of two or more components held together by an outer chase. The components are known as splits.

SPRAY-UP
Techniques in which a spray gun is used as the processing tool. In reinforced plastics, for example, fibrous glass and resin can be simultaneously deposited in a mold. In essence, roving is fed through a chopper and ejected into a resin stream which is directed at the mold by either of two spray systems. In foamed plastics, very fast-reacting urethane foams or epoxy foams are fed in liquid streams to the gun and sprayed on the surface. On contact, the liquid starts to foam.

STABILIZER
And additive for polyesters to maintain liquid characteristics such as; gel time, viscosity and liquidity.

STAPLE
Either naturally occurring fibers or lengths cut from filaments.

STARVED AREA
An area in a plastic part, which has an insufficient amount of resin to wet out the reinforcement completely. This condition may be due to improper wetting or impregnation or excessive molding pressure.

STARVED JOINT
A joint that does not have the proper amount of adhesive because of insufficient spread or excessive pressure.

STIFFNESS
The relationship of load and deformation; a term often used when the relationship of stress to strain does not conform to
the definition of Young's modulus.

STOP MOTION
A device on a creel that quickly stops the winder when a strand breaks so that the strand can be repaired/replaced for further winding.

STORAGE LIFE
The period of time during which a liquid resin or packaged adhesive can be stored under specified temperature conditions and remain suitable for use. (Also "shelf life.")

STRAIN
The elastic deformation of a material as a result of stress.

STRANDS
A primary bundle of continuous filaments (or slivers) combined in a single compact unit without twist. These filaments (usually 51, 102 or 204) are gathered together in the forming operations.

STRAND COUNT
The number of strands in a plied yarn; the number of strands in a roving.

STRAND INTEGRITY
The degree to which the individual filaments making up the strand or end are held together by the sizing applied.

STRENGTH, FLEXURAL
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 prior to failure by bending, usually expressed in pounds per square inch.

STRESS
The internal force that resists change in size or shape, expressed in force per unit area.

STRESS CONCENTRATION
The 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, where such an environment alone would not have caused corrosion.

STRESS CRACK
External or internal cracks in a composite caused by tensile stresses; cracking can be present internally, externally or in combination.

STRESS-STRAIN
Stiffness, expressed in pounds per square inch or kilograms per square centimeter, at a given strain.

STRESS-STRAIN CURVE
Simultaneous readings of load and deformation, converted to stress and strain, are plotted as ordinates and abscissae, respectively, to obtain a stress-strain diagram.

STRUCTURAL ADHESIVE
An adhesive used for transferring loads between adherends.

STRUCTURAL BOND
A bond joining load-bearing components of an assembly.

STRUCTURAL ELEMENT
A generic element of a more complex structural member (for example, skin, stringer, shear panels, sandwich panels, joints, or splices).

STRUCTURAL GLASS
A magnesia/alumina/silicate glass reinforcement designed to provide very high tensile strength.

STRUCTURAL REPAIR MANUAL (SRM)
Document prepared by an OEM that designates original structural materials (both composite and metal) used for specific aircraft. It usually includes schematics for all parts and listings of fastener types and adhesives. It also suggests general repair methodology so that structural integrity can be maintained.

STYRENE MONOMER
An unsaturated hydrocarbon, used in plastics. In polyester, it is a co-reactant diluent.

SUBSTRATE
A material upon the surface of which an adhesive-containing substance is spread for any purpose, such as bonding or coating.

SURFACING AGENT
A material that allows the surface of polyesters to cure. It limits adhesion of another coat of resin if the first is thoroughly cured. It may be removed by sanding or rubbing with steel wool.

SURFACING MAT
A very thin mat, usually 7 to 20 mils thick, of highly filamentized fiberglass used primarily to produce a smooth surface on a reinforced plastic laminate.

SURFACING VEIL
Used with other reinforcing mats and fabrics to enhance the quality of the surface finish.  Designed to block out the fiber patterns of the underlying reinforcements; also called surfacing mat.

SURFACTANT
Chemicals used to modify or change the surface of a layer of resin or polymer.  Usually used to form a film on a curing resin, producing a tack-free surface.

SYNTACTIC FOAM
A foam made by mixing microspheres with a resin.

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Glossary Section (S) Last Updated: 7/28/00 12:22 PM

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