Elastic constants and grüneisen parameters of pyrolytic graphite

Abstract

Abstract The room-temperature elastic constants of a pyrolytic graphite were measured by an ultrasonic transmission technique and compared with values calculated on the basis of the constant strain and constant stress models from the elastic constants of compression-annealed pyrolytic graphite (CAPG). It was found that the constant stress model gives better agreement; and that the measured C 11 and C 44 can be bracketed by calculations with the basal plane shear constants of neutron-irradiated and unirradiated CAPG respectively as inputs, as would be expected because of the high mobility of dislocations in the basal plane. Grüneisen parameters, for sample temperatures between 80 and 300°k, were determined from measurements of inertial thermoelastic stress. Calculations from single-crystal thermal expansion and elastic constant values showed reasonable agreement with the measured parameters and indicated that the elastic constants of a given pyrolytic graphite, being extremely structure sensitive, can be used to estimate Grüneisen parameters from single-crystal data.