Page 188 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology EN012c-598 July 26, 2001 15:59

Polymers, Mechanical Behavior

Garth L. Wilkes
Virginia Polytechnic Institute and State University

I. Introduction VI. Stress Relaxation and Creep Behavior
II. Types of Deformation VII. Effect of Crystallinity on Properties
III. Important Stress–Strain Deformation VIII. Effect of Covalent Cross-Linking
Parameters IX. Effect of Fillers on Mechanical Behavior
IV. Effect of Temperature on Stress–Deformation X. Molecular Orientation and Anisotropic Systems
Behavior
XI. Miscellaneous Considerations and Final
V. Time and Temperature with Respect to Remarks
Molecular Considerations

GLOSSARY within the time frame of the experiment. It applies only
to amorphous regions of a material.
Bulk modulus In the limit of small pressures, it repre- Loss modulus Parameter that is related to the viscous
sents a change in hydrostatic pressure with change in dissipation of a material undergoing small cyclic de-
volume when a material is placed under hydrostatic formations; generally obtained by dynamic mechanical
loading. This parameter is related to the compressibil- spectroscopy techniques.
ity of a material. Mechanical hysteresis Important parameter that is re-
Deborah number D e Dimensionless parameter related lated to the amount of energy dissipated during cyclic
to the ratio of the molecular relaxation time of a mate- deformation. No hysteresis would be obtained if the un-
rial to that of the time frame over which the material is loading stress–strain profile were identical to the load-
observed, that is, the experimental time window. ing profile.
Engineering stress Force obtained in extension divided Permanent set Parameter that is related to the degree of
by the sample’s original cross-sectional area. irrecoverable flow that exists after a material has been
Extension ratio Variable expressing how a given dimen- deformed in either shear or tension.
sion is changing in a sample with deformation; de- Poisson’s ratio Variable indicating whether a material
finedasthedeformedlengthdividedbytheundeformed undergoes dilation during extensional deformation;
length in the same direction. usually denoted by µ.
Glass transition temperature T g Important parameter Secant modulus Slope of the line that extends from the
that is related to the temperature at which the onset origin of an engineering stress–strain curve and in-
of cooperative segmental motion occurs for a polymer tersects that curve at a given elongation. The secant

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