Definitions /Dictionary/Glossary - nptel

Population Mean: The average of all potential measurements in a given population weighted by
their relative frequencies in the population.
Population Median: That value in the population such that the probability of exceeding it is 0.5
and the probability of being less than it is 0.5.
Population Variance: A measure of dispersion in the population.
Porosity: A condition of trapped pockets of air, gas, or vacuum within a solid material, usually
expressed as a percentage of the total nonsolid volume to the total volume (solid plus nonsolid)
of a unit quantity of material.
Positive Mold: A mold designed to apply pressure to a piece being molded with no escape of
material.
Positively Skewed: A distribution is said to be positively skewed if the distribution is not
symmetric and the longest tail is on the right.
Post Bake: See Post Cure.
Post-cure: Additional elevated temperature cure, usually without pressure, to increase the glass
transition temperature, to improve final properties, or to complete the cure.
Pot Life: It is the period of time during which a reacting thermosetting composition remains
suitable for its intended processing after mixing with a reaction initiating agent.
Potting: Similar to encapsulating, except that steps are taken to insure complete penetration of
all the voids in the object before the resin polymerizes.
Precision: The degree of agreement within a set of observations or test results obtained.
Precision involves repeatability and reproducibility.
Precure: The full or partial setting of a resin or adhesive before the clamping operation is
complete or before pressure is applied.
Precursor (for Carbon or Graphite Fiber): Either the PAN or pitch fibers from which carbon and
graphite fibers are derived.
Preform: An assembly of dry fabric and fibers which has been prepared for one of several
different wet resin injection processes. A preform may be stitched or stabilized in some other
way to hold it’s a shape. A commingled preform may contain thermoplastic fibers and may be
consolidated by elevated temperature and pressure without resin injection.
Preform Mat: Fiber reinforced mat shaped like the mold in which it will be used. It eliminates
the need for overlapping the corners in molding.