Energy Changes in Stressed Bodies Due to Void and Crack

It is demonstrated that the removal of material or the creation or extension of cracks always reduces the total potential energy of any non-linear or linear stable elastic body under fixed load and displacement boundary conditions. A weaker statement that crack extension releases potential energy in excess of plastic dissipation is established for stable elastic-plastic bodies, with certain strong but reasonable restrictions on the path of traction removal from the new surface. Crack healing, however, always absorbs energy. Implications for the Griffith theory of fracture, including its extension to inelastic materials, and the mechanical aspects of stress corrosion cracking are discussed.