Question

Find an expression for the energy density in terms of stress and strain.

Answer 1

The definition of density of the energy is analogous to the definition of the density of mass. It is the energy stored per unit volume.

Number of joules stored in 1 m^3 of material 

Thus the formula for energy density

D = 1/2 * Stress * Strain

 = 1/2 F.e / A.l
where
F =  applied force
e is the extension
A is the area
and l is the length