| Magnetostrictive film-substrate microcantilever inspired by the external magnetic field where it made the isolation between the bending displacement of free end and constant contact with the base,which will achieve the function of micromechanical switches turned on and off.During the process of dynamic contact-isolation with the base of rough surfaces between th beam and the base,if the cantilever structure parameters select inappropriately,and it may result in rough surfaces contact with higher loads that makes the unnecessary plastic deformation of the material and causing micro-mechanical system failure.This may greatly reduce the safety and the reliability of products.In this paper,the magnetostrictive effect is equivalent to the effect of thermal expansion,which is made use of the positive use of magnetostrictive effect driving magnetostrictive thin film-substrate micro-cantilever produce downward bending displacement.It benefits to built the contact-separation model of rough surfaces contact between the end of the beam and base by considering of elasto-plastic deformation of material,the interaction of asperity,the elastic recovery of micro-cantilever and the hysteresis,and a contact model of rough surfaces contact between the cantilever and the base which consider of magnetic field and different parameters(e.g.micro-beam length,width,the ratio of film/substrate thickness,magnetic field)of cantilever is established.A variety of changes on the surface of the base are analyzed,such as the contact area,contact force,stress,strain,energy of the system and so on.The results show that:(1)In the entire contact process,only minorities of high asperities occur the actual contact,the contact area just only a tiny part of the name of contact area.Besides,under the influence of the hysteresis and the resiliency elasticity of micro-cantilever,the relationship between the contact force and the contact area with the magnetic field showed a complex nonlinear relationship.The contact area and the normal contact force increases non-linear with width and thickness of the beam,and they are fluctuated with increasing length in a range.(2)When the ratio of magnetostrictive film/substrate thickness is k<0.5,the node of the minimum bending displacement appears different.The k is closer to 0.5,the minimum appears in the middle of free end of cantilever,and there is a larger difference between maximum and minimum.While k is>0.5,the microprocessor maximum and minimum cantilever bending displacement appear on the both ends of micro-cantilever free ends.The bending displacement is decrease by non-linear decrease,the difference between maximum and minimum is very large.(3)Different structural parameters of the beam have little effect on base rough surface VonMises equivalent stress while the longer the length of the beam corresponding to the base of the rough surface is densely distributed.This is because the length of the beam,the greater magnetic force during a long time applied magnetic field,the higher asperities gradually flattened,and more contact points.(4)Keeping the total thickness of the cantilever invariant,when the ratio of magnetic film/substrate thicknesses is 1/2 and 1/3,the equivalent plastic strain and VonMises equivalent stress reaches maximum.The distribution of the base rough surfaces' equivalent plastic strain increasing non-linear with the thickness,and it reaches the maximum at a length of 175 ?m.The equivalent stresses on the base rough surface decreases approximately while magnetic field is increasing.The results of this study have certain theoretical significance and application value on promoting the performance of the contact micro-cantilever design and the reliability of similar product for micro-mechanical switches. |
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