The Contact Analysis Of Rough Surfaces Between Micro-cantilever And Substrate Using Piezoelectric Driving

Piezoelectric micro-cantilever has been widely applied in Micro Electro-Mechanical System due to its excellent properties,as a micro driving execution,contact-separation occurs constantly between cantilever and substrate under the action of voltage driving.From the microscopic point of view,actual contact between surfaces occurs only among a small number of high asperities and the contact instantaneous impact is very large.The elastic restoring force generated by micro-cantilever bending makes the end of the cantilever bounce from the substrate several times before it reaches the situation of stable contact.This will exacerbate the damage of micro component due to the impact caused by the circulation,thereby greatly reducing the life of the product and the level of commercial applications.In this paper,based on the piezoelectric theory,the inverse piezoelectric effect of piezoelectric materials is used to drive micro-cantilever bending,so as to realize the contact-separation of rough surfaces between the end of the cantilever and substrate.It has the function of micro execution driving.Considering of the elasto-plastic deformation of material,the elastic recovery of micro-cantilever,the adhesion of contact interface and the interaction of asperities,a contact model of rough surfaces between micro-cantilever and substrate using piezoelectric driving is established according to the actual structure characteristics of micro components in MEMS devices.Then the contact-separation process under single/multiple voltage driving is simulated dynamically in ABAQUS finite software,and a variety of changes on the surface of the substrate are analyzed,such as the contact force,contact area,contact pressure,stress,strain,energy of the system.This paper also compares the effects of different voltages on the variables in the whole process.The results of the research show that micro-cantilever is in bending mode when the voltage signal is less than the first resonance frequency of piezoelectric micro-cantilever,which the change of terminal bending displacement is linear with the applied voltage.In every process of piezoelectric driving,the rough surfaces of micro-cantilever and substrate has appeared several contact-separation case due to the elastic restoring force of cantilever,the non-linear relationship between the contact force and terminal bending displacement of cantilever has become extremely complex.With the increase of the number of driving,the contact of rough surface gradually stabilized,and the occurrence of secondary contact-separation reduced.Due to the changing of micro convex body size,position and contact time,resulting in the distribution of contact pressure,stress,strain and so on is uneven,the maximum value and the location of them are also changing.When the cantilever is separated from the substrate,the maximum equivalent stress value of the contact area is located at the edge of contact asperity,which is the beginning separation point of the asperity contact pairs.The maximum z to tensile stress and compressive stress of the rough contact surface is located on both sides of the larger deformation of micro convex body.In the circular piezoelectric driving process,the surface of asperities and a certain area at a certain depth from the surface endure the cycle tensile stress and compressive stress with the constant contact-separation between cantilever and substrate,it is very easy to cause the fatigue failure of materials.Under different driving voltages,the characteristics of contact-separation between micro-cantilever and substrate are very different,with the increase of the voltage,the contact-separation becomes more dense in each pre-applied voltage,but the stable contact time enhanced in the late.The results of the research provide a theoretical foundation for the improvement of the rationality of design and operational reliability of micro-mechanical devices.