Britannica Sources used in this answer

How is elastic energy stored when a material is stretched?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

mechanics of solids Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).

When a material is stretched within its elastic range, it stores energy as strain energy (or elastic potential energy). This process involves the work done by an external force to deform the material, which is then stored internally and can be recovered when the deforming force is removed.123

In the context of the mechanics of solids, this stored energy is represented by the area under the stress-strain curve. For a material undergoing a one-dimensional deformation, the strain energy density—the energy stored per unit volume—is determined by the relationship between the applied stress ( $σ$ ) and the resulting strain ( $e$ ).1

From a thermodynamic perspective, this energy is stored as internal energy or Helmholtz free energy, depending on whether the process is adiabatic or isothermal. At the microscopic level, this storage occurs as constituent atoms, molecules, or ions are displaced from their equilibrium positions, creating restoring forces that seek to return the material to its original state. For polymers like rubber, this energy is stored through the uncoiling of long-chain molecules.231