Page 87 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology EN012K-587 July 26, 2001 10:35

Plastics Engineering

R. J. Crawford
University of Auckland

I. General Types of Plastics
II. Design Considerations
III. Material and Process Selection
IV. Successful Engineering Applications for Plastics

GLOSSARY Modulus The ratio of stress to strain in a material, at a
specified level of strain.
Composite A material that is a combination of two or Speciality plastics Materials with special characteris-
more constituents, each of which retains its own iden- tics usually in regard to high-temperature proper-
tity. In the context of this article, the constituents ties.
are fibers within a thermoplastic or thermosetting Stiffness A measure of the ratio of load to deformation;
matrix. there is usually a direct correlation with modulus,
Creep The time-dependent change in the dimensions of but modulus is an inherent material property whereas
a plastic under the action of a static load. stiffness depends on the shape of the material being
Cross-linking The formation of an infusible structure by stressed.
the joining together of individual molecular chains into Thermoplastic A material capable of being repeatedly
a three-dimensional network. softened by heat and hardened by cooling.
Ductility The ability of a material to deform plastically Thermoset A plastic that when subjected to heat (or a
before fracture. chemical process) changes into an infusible, insoluble
Elastomers Plastics that exhibit the large deformation/ material.
elastic recovery characteristics of rubbery materials. Viscoelasticity A property of a material whereby it ex-
Engineering plastics A general name for plastics suit- hibits the combined effects of viscous and elastic be-
able for use in load-bearing applications. havior.
Fatigue Thefailureofamaterialasaresultoftherepeated
application of a fluctuating stress or strain.
Fiber A general term for a filament of material that has a PLASTICSarenowwellestablishedinallbranchesofen-
length at least 100 times its diameter. gineering as cost-effective, high-performance materials.
Heat-deflection temperature The temperature at which A major attraction of plastics is that when one takes into
a standard test piece deflects by a specified amount account the overall costs of conversion from raw mate-
when subjected to a specified force. rial to final product, plastics almost always come out best.

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