The utility of thermo-mechanical equations in the ultrafast thermo-elastic domain is tested by studying the electronic sputtering from metal-dielectric nanocomposites (NCs) induced by swift heavy ion irradiation. It is observed that the sputtering yield of metal atoms from such NC films strongly depends on the size of the metal nanoparticles (NPs) and the properties of host dielectric matrices. The decrease of the melting temperature of small NPs, superheating at the surface of NPs due to additional electron-surface scattering and transient melting of the dielectric matrices induce complex thermal effects. The dependence of the sputtering yield on the size of the NPs has been obtained by evaluating the transient stress and strain induced by thermal effects in the framework of the ultrafast thermo-elastic model.