__LONGITUDINAL STRAIN__

There are two kinds of
changes that occur as a result of natural deformation. The first which causes
changes of lengths of elements is called ** longitudinal strain** and the second
which changes the orientation of various elements or objects is called the ** shear
strain**. If the original length is lo and the length after deformation ld, then
**extension**, e, is given by

e=( ld-lo)/lo :e could be negative or positive
depending on whether the length is decreased or increased. The **
quadratic extension**, designated by l, is given
by

l=(ld/lo)^{2}
which is the same as (1+e)^{2}

and the ** reciprocal quadratic extension** designated by l'
is given by

l'=(lo/ld)^{2}
or [(1+e)^{2} ]^{-1}

The longitudinal strain can also be expressed in natural logarithmic
form as **natural strain** and designated by e.

e=log_{e} (1+e) or e=ln
(1+e) or e=log_{e} =^{ }Öl