Provided a material obeys Hooke’s Law, strain energy stored inside it can be calculated.
Work done on an elastic material in stretching = energy stored in material as elastic strain energy.
Work done = force X displacement.
Force on material isn’t constant. It rises from zero up to force (F). To calculate work done, use average force between zero and F:
Work done = 1/2FX.
Elastic strain energy (E) = E = 1/2FX
As Hooke’s Law is being obeyed, F = Kx, F can be replaced in the equation to give:
E = 1/2kx^2.
Material stretches beyond elastic limit - some work is done separating atoms. This energy will not be stored as elastic strain energy, and so isn’t released when force is removed.
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