Strain Energy Formula

Strain Energy Formula

Strain energy is defined as the energy stored in a body due to deformation. The strain energy per unit volume is known as strain energy density and the area under the stress-strain curve towards the point of deformation. When the applied force is released, the whole system returns to its original shape. It is usually denoted by U.

The strain energy formula is given as,

U = Fδ / 2


δ = compression,

F = force applied.

When stress σ is proportional to strain ϵ, the strain energy formula is given by,

Strain energy formula


σ = stress

 = strain

V = volume of body

Regarding Young’s modulus E, the strain energy formula is given as,

U = σ2 / 2E × V.


σ = stress,

E = Young’s modulus,

V = volume of body.

Solved Examples

Example 1

When a force of 1000 N is applied on a body, it gets compressed by 1.2 mm. Determine the strain energy.



Force F = 1000 N,

Compression δ = 1.2 mm

Strain energy formula is given by,

U = Fδ / 2

   = 1000 ×1.2×10−3 / 2

Therefore, U = 0.6 J.

Example 2

A rod of area 90 mm2 has a length of 3 m. Determine the strain energy if the stress of 300 MPa is applied when stretched. Young’s modulus is given as 200 GPa.



Area A = 90 mm2

Length l = 3m

Stress σ = 300 MPa

Young’s modulus E = 200 GPa

Volume V is given by the formula

V = area*length

  = (90 × 10−6) × 3

V = 270 10−6 m3

The strain energy formula is given as,

U = σ2 / 2E× V

  = (300×106)2 / 2 x 200×109 x 270 x 10-6

Therefore, U = 83.3 x 106 J

Therefore, the strain energy of the rod is 83.3 x 106 J

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