Strain energy quantifies the energy stored within a material due to deformation under loading conditions, a fundamental concept in materials science and engineering. The strain energy can be modeled when a material is subjected to axial loading with uniformly distributed stress. In this scenario, the stress experienced by the material is the internal force divided by the cross-sectional area, and the strain induced is directly proportional to this stress through the modulus of elasticity.

If the stress distribution is uniform, the strain energy density, defined as the product of stress and strain, can be integrated over the entire volume of the material to yield the total strain energy stored.

However, calculating strain energy becomes more complex for materials with non-uniform stress distributions. In such cases, the strain energy density must be defined for the small volumes to account for local variations in stress and strain. The total strain energy is the sum of these densities across the material's volume.

This consideration assumes elastic behavior, where the deformation is reversible, and the material returns to the original shape when the load is removed. Understanding and calculating strain energy is vital for designing materials and components that can withstand operational stresses without failure.