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Due to the rapid development of micro-nano acoustic devices, their core acoustic structures have entered the nanoscale category. The influence of surface effects on the mechanical properties of thin-film materials at the nanoscale becomes increasingly prominent, and the classical elasticity theory struggles to describe mechanical behavior at this scale. In this paper, a mechanical model of nano-SiO2/Si heterostructured thin films considering surface effects is established based on surface elasticity theory by introducing the key parameter of surface energy density. In this paper, a mechanical model of heterostructured nano-SiO2/Si films is created based on the surface elasticity theory, taking into account surface effects by introducing the key parameter of surface energy density. Using the Fourier integral transform method, analytical expressions for stress and displacement fields under surface traction are systematically derived, revealing the influence of surface effects on the mechanical behavior of materials at the nanoscale by comparing the analytical solution with the classical theory. The results show that when the surface stress distribution differs by 3% from that predicted by the classical theory, the microscopic properties of the material are dominant and the surface effect cannot be neglected within a range of 5 times the width of the excitation region 2a. As the size of the excitation region decreases, the surface effect is significantly enhanced and the stress distribution within the excitation region and near the boundary becomes more concentrated than in the classical theory. The shear stress is no longer zero, and an extreme value is observed at the boundary, which differs significantly from that predicted by the classical theory of elasticity. The transverse and longitudinal displacements are reduced compared with the classical theory, and the surface stiffness and deformation resistance of the material are greatly improved. Significant surface effects occur on nanoscale heterostructured thin films, leading to large deviations in stress and displacement distributions from elasticity theory. Therefore, the classical elasticity assumptions are no longer applicable within the corresponding nanoscale range. The results demonstrate that the propagation of ultrahigh frequency nano length acoustic waves in nanoscale solid film surfaces is significantly affected by the scale effect. The failure of the classical elastic wave theory at the nanoscale is valuable for the study of nanoscale acoustic theory. Furthermore, these findings provide a theoretical basis for the subsequent development of a more precise model of interfacial effects and a more detailed investigation of the influence of the film-substrate modulus ratio.
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Keywords:
- Surface elasticity theory /
- Nanoscale /
- Surface effects /
- Failure phenomenon
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