Materials Characterization with Nonlinear Surface Acoustic Wave Pulses

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9970241 SchuesslerThis research concerns the propagation of high amplitude surface acoustic waves in solid materials and the development of a novel method for the characterization of materials based on the properties of such materials. The manifestation of nonlinear phenomena depends on the nonlinear elastic moduli of the solid, which are sensitive to the appearance of different defects in the material. The nonlinear moduli are therefore expected to give information suitable for materials characterization. In this work the third order nonlinear moduli will be determined for several materials by fitting the solutions of the nonlinear evolution equations of the nonlinear acoustic wave propagation to experimentally measured waveforms. Contact-free laser methods will be used for exciting and detecting the surface acoustic waves. The experiments will serve to test recent theoretical predictions concerning unusual properties during the propagation of such waves. These include nonlinear distortion of the wave shape, generation of high frequency spectral components, formation of a shock front with subsequent nonlinear attenuation of the energy of the wave and, under certain conditions, the formation of solitons. This project will contribute a new method for the characterization of thin films and coatings of superhard materials, as well as to the study of the visco-elastic behavior and anisotropy of materials. The results of this work will have an impact on different fields such as materials science, acoustoelectronis, nonlinear acoustics, the theory of nonlinear waves, and seismology.%%% Mechanical and elastic properties of solids are important characteristics reflecting their microscopic structure. Therefore the development of new versatile and informative methods to measure these quantities is one of the ongoing tasks of materials research. The objective of this project is to study the non-linear propagation of surface acoustic waves in solid materials and to develop a novel method of materials characterization based on the properties of such nonlinear waves. This research will test existing theoretical models that purport to describe such waves and will allow to quantify the influence of such phenomena as fatigue and crack formation on the elastic properties of materials. This research will also contribute to the development of a technique for the characterization of diamond and diamond like films and coatings, to the elastic and other properties of crystalline materials. The results of this work will have an impact on different fields such as materials science, acousto-electronics, nonlinear acoustics, theory of nonlinear waves, and seismology. An important feature of this project is the integration of research and education through the training of students in novel methods of materials science and related research areas.