Investigation On The Coupling Between The Surface/Interface Force And Deformation Of Slender Elastic Structures

With the rapid development of micro/nano technology and Micro Electro Mechanical Systems(MEMS),the study on surface/interface effects of objects has raised concerns among scientists and engineers.The volume forces of objects decay much faster than the surface forces,and in this case surface/interface effects play an essential role at micro/nano scale.Normally,the coupling effect between surface/interface force and slender structures deals with a lot of complex problems,such as large deformation,non-linear effect and coupling of multi physical fields.As a result,there still lack of systematic investigation on this topic,which is just an emerging problem.Firstly,we propose that the morphology of a pendant droplet adhered to a solid substrate is analogous to that of a slender rod in large deformation.The governing equation and transversality condition of the droplet is derived based on the variational theory with movable boundary conditions.The analytical solution is then explicitly solved in terms of elliptical integrations.After that,we extended the obtained solutions to analyze the pendant droplet hanging on a substrate with special curvatures,these analyses can be beneficial to the design of the morphology of substrate and analogy experiments.In succession,the coupling between capillary forces and two kinds of structures is analyzed.At first,the true axial stress of a micro-fiber filled with a droplet is calculated in use of the Mooney-Rivlin model,and the effect of capillary forces on its load capability is discussed.Next,the process of a slender fiber piercing into liquid is systematically investigated,where the variation of the buoyancy when the fiber pinned at the triple contact line is analyzed.In use of this model,the posture of the strider leg pressing water is well explained.Finally,the influence of surface stress on the internal force and buckling of a nanobeam is studied.Based on Gurtin's theory,the expressions of the shear force and bending moment of a nanobeam under different boundary conditions and loads are analytically derived,then the size effect on the internal force diagram of the nanobeam is demonstrated.Furthermore,the buckling phenomenon of a clamped-clamped beam induced by the surface stress is studied,and the postbuckling morphology of the beam is presented.