One-Dimensional Thermoelastic Response of Solids to Pulsed Energy Deposition

Abstract

A one‐dimensional model for the thermoelastic response of materials exposed to pulsed energy deposition is presented. For the model presented, a generalized form of the Mie‐Grüneisen equation of state was used to develop a description of the free‐surface motion which includes the temperature dependence of the Grüneisen parameter Γ. This model was verified through free‐surface motion measurements of solids exposed to a pulsed electron beam, over a temperature region where Γ may be considered constant. The measured time‐dependent rear‐surface displacement and velocity histories for a single crystal of Al are compared with those quantities predicted by the one‐dimensional theory and found to agree very well. The measured thermoelastic response for Al, Ag, and Cu in both single and polycrystalline form, single crystals of Si, Ge, and InSb, and the polycrystalline alloy Kovar is presented in an equivalent form as a measurement of the Grüneisen parameter. The agreement between the measured Grüneisen parameters and their accepted value is within ± 7% for all materials studied. Empirical corrections have been made to the data to reflect the fact that the theoretical model neglects attenuation. It is concluded that the method is valid for determining the Grüneisen parameter of solids; however, it is restricted to materials for which (a) the deposited energy couples to the lattice phonons in times short compared to their acoustic relaxation time, (b) the Grüneisen parameter is relatively constant over the temperature range of the measurements, and (c) the thermal expansion of the materials is isotropic.