Influences Of Surface Stress On Mechanical Behaviors Of Microstructural Elements

The surface effect, scale effect and quantum effect are important features that affect the physical, chemical and mechanical performances of nanometer structures and/or particles. In fact, the characteristics of nanometer structures and particles result from the competition of these three factors, and the dominant factor depends on the scale of the structures and particles. For instance, in the scale above a few nanometers, the quantum effect might be negligible in comparison with the other two effects. Therefore, the surface effect should be taken into account when designing and manufacturing nanometer structures. In the previous studies, the surface stress has been considered as a constant and the coupling between the deformations on the surface and in the interior of the solid are neglected. In the present investigation, the influences of the surface effect on the mechanical behaviors and thermoelastic damping of nanometer structures are studied under different conditions based on the energy principle and the classical theory of elastic plate. The main results are as follows:Firstly, It is shown that the surface stress can destabilize the surface of cylindrical gel. Furthermore, the wavelength depends not only on the intrinsic scale of the material, but also on the radius of the cylinder, indicateing that the stability is correlating to size.In the case, the surface is treated as an elastic ultra-thin film adhering to the body without slipping, the elastic constants of the film are different from those of the interior of the solid. The normal stress is taken into account by applying Gurtin and Murdoch's relations of surface equilibrium. On the basis of Kirchhoff's hypothesis and Mindlin's theory as well as by means of Hamilton variational principle, the membrane force, bending moment and governing equation are derived. The results reveal that the mechanical behaviors of the elastic thin film with surface effect are size-dependent, and that the effects of both the rotation and normal stress can be neglected.Further, to demonstrate the influence of surface effect, the forced vibration problem of simply supported elastic film with periodic force is also studied. The approximate amplitude and frequency are obtained by applying the method of perturbation, and it shows that the vibration frequency depends on the thickness of the film. Moreover, the thermoelasticity coupling of the elastic film in forced vibration is considered. The equation of heat conduction with surface effect is derived by applying the minimum principle of latent heat flux to describe the temperature distribution and reveal the size-dependence of thermoelastic damping in the form of energy dissipation during the vibration process.