Definitions /Dictionary/Glossary - nptel

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.
Significant: Statistically, the value of a test statistic is significant if the probability of a value at
least as extreme is less than or equal to a predetermined number called the significance level of
the test.
Significant Digit: Any digit that is necessary to define a value or quantity.
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.
Size System: See Finish.
Sizing: A generic term for compounds which are applied to yarns to bind the fiber together and
stiffen the yarn to provide abrasion-resistance during weaving. Starch, gelatin, oil, wax, and
man-made polymers such as polyvinyl alcohol, polystyrene, poly-acrylic acid, and polyacetatates
are employed.
Skewness: See Positively Skewed, Negatively Skewed.
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 one ply of chopped strand
mat.
Slave Pump: A catalyst pump, which is driven by the resin pump through a pair of level arms.
Sleeving: It is a common name for tubular braided fabric.
Slenderness Ratio: The unsupported effective length of a uniform column divided by the least
radius of gyration of the cross-sectional area.
Sliver: A continuous strand of loosely assembled fiber that is approximately uniform in crosssectional
area and has no twist.