Investigation on energy transmission constitutive relationships by laser measurements

The problem of the energy transmission in vibrating structures is of paramount importance under practical and theoretical points of view. In this field the Statistical Energy Analysis is nowadays the most useful theory, even if the effects of its basic assumptions are difficult to evaluate. Based on the thermal behavior of mechanical energy among coupled vibratory systems, S.E.A. provides information on the stored and dissipated energy and on the transmitted power between them. Starting from the S.E.A. thermal assumptions, some energy models have been developed for the dynamic analysis of mechanical systems vibrating in the high frequency range. The basic principle of thermal propagation of mechanical energy has been examined under the theoretical point of view. The results seem to suggest that the analogy between thermal and mechanical energy propagation should be an acceptable approximation only for 1D systems but it is no longer valid for complex 2D and 3D structures. The present paper describes some experiments designed with the aim of validating the theoretical predictions developed. The experimental tests have been performed on one beam and one plate, excited in a relatively high frequency range. Consequently short characteristic wavelengths are generated and a very fine measurement grid is required. The laser measurement technique is in this case the most effective way to investigate the phenomena related to the wave mechanical energy propagation. The results of the comparison between theory and experiments confirm the dependence of the energy transmission law on the spatial scale range and the general failure of the vibrational conductivity principle.