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