THE FREE-ENERGY OF CONDENSED MATTER UNDER STRESS

The currently accepted form of the free energy of condensed matter und er stress, derived using the Helmholtz free energy, is disproved. Reco gnizing that the Gibbs free energy is the correct function of state, a new formula for the free energy-density E which is linear-rather than quadratic-in the strain is derived. For isotropic and cubic media, th e formula is E = -(c(11) + 2C(12))epsilon where the c(ij) are elastic stiffness constants and E is the strain. The formula is in accordance with published data.