Properties of Metals
DOE-HDBK-1017/1-93
STRAIN
STRAIN
When stress is present strain will be involved also. The two types of strain will
be discussed in this chapter. Personnel need to be aware how strain may be
applied and how it affects the component.
EO 1.3
DEFINE the following terms:
a.
Strain
b.
Plastic deformation
c.
Proportional limit
EO 1.4
IDENTIFY the two common forms of strain.
EO 1.5
DISTINGUISH between the two common forms of strain
according to dimensional change.
EO 1.6
STATE how iron crystalline lattice structures,
g
and
a
, deform
under load.
In the use of metal for mechanical engineering purposes, a given state of stress usually exists in
a considerable volume of the material. Reaction of the atomic structure will manifest itself on
a macroscopic scale. Therefore, whenever a stress (no matter how small) is applied to a metal,
a proportional dimensional change or distortion must take place.
Such a proportional dimensional change (intensity or degree of the distortion) is called strain and
is measured as the total elongation per unit length of material due to some applied stress.
Equation 2-2 illustrates this proportion or distortion.
(2-2)
Strain e
d
L
where:
e = strain (in./in.)
d = total elongation (in.)
L = original length (in.)
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