A physical and mechanical discontinuity occurring within a material or part, usually consisting of solid, encapsulated foreign material. Inclusions are often capable of transmitting some structural stresses and energy fields, but in a noticeably different degree from the parent material. See also voids. A material added to a plastic to alter the end-item properties through physical rather than chemical means. Radiant heat is in this range, and infrared heaters are frequently used in the thermoforming and curing of plastics and composites.
Infrared analysis is used for identification of polymer constituents.
Also used in certain types of monomers and resins to prolong storage life. The stress produced by force in a specimen before stress relaxation occurs. See also Young's modulus. The strain produced in a specimen by given loading conditions before creep occurs. Peroxides used as sources of free radicals.