20. A
stress element shown in the figure is subjected to two-dimensional stresses 
and 
. The axial length of the element
is 
. The Poission’s ratio is 
and
the modulus of elasticity is 
. If 
and 
, estimate the mean and standarad
deviation of the axial elongation using the First Order Second Moment Method.
Note that and are independent.
Solution
The axial strain is given by
Thus, the axial elongation is
Let
where
.
Using FOSM, we have
