** **
**In a Nut Shell:
**Imagine
an arbitrary structural member say in the shape of a flat ovular
plate.
See the figure
below. Before** **loading let an arbitrary material segment, AB, in the plate be
of
length L. After loading the** **material segment may rotate and change length. Let the length of
the same material
segment become A*B*, ** **after loading be L*. Then the normal strains are
defined as
ε_{engr} =
( L* - L)/L =
engineering strain
ε_{true} = ln ( L*/L
) =
true strain
Common units of strain
are in inches/inch, millimeters/millimeter, or microstrain
(dimensionless).
Normal strain is considered
to be positive when the material segment becomes
longer and negative if
it shortens (sign convention).
Usually normal strains are
very small usually much
less than 1. | ε_{engr} |
<< 1
Click here for an
example of normal strain.
** ** |