The strength of a material often is the primary
concern. The strength of interest may be measured
in terms of either the stress necessary to
cause appreciable plastic deformation or the
maximum stress that the material can withstand.
These measures of strength are used, with appropriate
caution (in the form of safety factors),
in engineering design. Also of interest is the material’s
ductility, which is a measure of how
much it can be deformed before it fractures.
Rarely is ductility incorporated directly in design;
rather, it is included in material specifications
to ensure quality and toughness. Low ductility
in a tensile test often is accompanied by
low resistance to fracture under other forms of
loading. Elastic properties also may be of interest,
but special techniques must be used to measure
these properties during tensile testing, and
more accurate measurements can be made by
ultrasonic techniques.