HIGH-PRESSURE EQUATION OF STATE AND SOUND VELOCITIES TO FOURTH ORDER ELASTIC-CONSTANTS - APPLICATION TO SODIUM-CHLORIDE TO 270 KBARS

Using the theory of small deformation superposed on a finite strain, we expand the strain energy to fourth order in terms of the strain invariants, and derive an athernal expression for the equation of state and the longitudinal and shear velocities of sound of a homogeneous Isotropic material to fourth order elastic constants. We evaluate reported velocity data in sodium chloride by Voronov and Grigorev to 80 kbar in terms of our formulation, to predict the equation of state to 270 kbar. Experiments performed in our laboratory (Frankel, Rich, and Homan) to 270 kbar which use ultrasonic interferometry to obtain resonance frequency intervals in the specimen were also evaluated. Both results are in good agreement with Decker's equation of state. © 1979.