| In recent years,the polymer matrix composites have been widely used in the bionic wall-climbing robot,various intelligent mechanical equipment and other fields.Many studies are exploring how to improve the adhesion property of materials,such as changing the polymer matrix,designing multi-level adhesion arrays,adding different additives and so on,which possess some positive efficiency and breakthrough.However,the high adhesiveness of materials brings about the difficulty of desorption in the working process,which reduces the service life of materials.How to control the adhesion and desorption of materials intelligently becomes a critical problem to be solved urgently.Magnetic-sensitive rubber,as a new type of the smart material,has been proved that its mechanical properties can be rapidly and reversibly changed under the action of magnetic field.This characteristic provides a new way to solve the problem of the uncontrollable adhesion-desorption process of traditional materials.Therefore,aiming at the problems that the research of the adhesion property of the magnetic-sensitive rubber induced by the external magnetic field is not complete and the mechanism is not clear,the adhesion force measurement experiment and the surface observation experiment are designed and implemented.The experimental phenomena of magnetically controlled adhesion property of the modified magnetic-sensitive rubber are revealed.Then,based on the experimental phenomena and the existing classical adhesion contact theory,the magnetically controlled adhesion property and mechanisms of the magnetic-sensitive rubber are analyzed and explained,which can provide some reference and guidance for the application and further study of controllable adhesion property of the magnetic-sensitive rubber.The main contents of this thesis are as follows:1.The research background and significance of the magnetically controlled adhesion property of the magnetic-sensitive rubber are expounded.The research status of the magnetic-sensitive rubber and traditional adhesive materials are reviewed.And the existing adhesion-desorption control methods of wall-climbing robots and the adhesive materials are summarized.Then the shortcomings of the related researches are pointed out,and the main contents of this thesis are planned.2.In order to solve the problem that the traditional magnetic-sensitive rubber has poor surface performance,which is not suitable for use as the adhesive material,thetraditional magnetic-sensitive rubber was modified by changing the mould,adding nano-fillers and optimizing the proportion.It is found that the modified magnetic-sensitive rubber with the graphene mass ratio of 1% has the smooth surface,stable property and significant adhesion ability,which is the most suitable as the adhesive material.Then the modified magnetic-sensitive rubber samples with different structure and ferromagnetic particles volume ratio are prepared.Next,the surface roughness and the arrangement of ferromagnetic particles in the material are measured and characterized by the contact roughness tester and the scanning electron microscope,which provide experimental proofs for the subsequent theoretical derivation and the simulation research.3.The particularity of the experimental conditions is considered comprehensively,an experimental platform for measuring the adhesion force of the modified magnetic-sensitive rubber is designed and built.The adhesion force experiment results show that without the external magnetic field,the adhesion forces of the modified magnetic-sensitive rubber are increased obviously and gradually became saturated with the increase of the separation speed and the pressing force.However,with the increase of the contact time,the increase of the adhesion force of the materials is not obvious.These experimental phenomena show that the modified magnetic-sensitive rubber has good adhesion property and conforms to the experimental rules of the traditional adhesive materials.When the different magnetic fields are applied,the adhesion forces of each modified magnetic-sensitive rubber are increased,and the increase degrees of the adhesion force are varied with the different pressing force.Among them,when the pressing force is 5N and the magnetic field is about 300 mT,the adhesive force of the modified magnetic-sensitive rubber with ferromagnetic particles volume ratio of 10%increases most obviously,which is ranged from 2.11 N to 4.28 N,and the change rate is as high as 102.8%.4.In order to explore the magnetically controlled adhesion mechanism of the modified magnetic-sensitive rubber,surface observation experiments are designed and implemented,including three-dimensional surface morphology observation experiment by the white light interferometer and the two-dimensional surface profile observation experiment by the contact roughness tester.The results of white light interferometer observation show that the surface of the modified magnetic-sensitive rubber becomes smoother under the action of magnetic field.The surface profile observation experiment confirms that the surface roughness Ra and the peak value Rp of the surface convexpeak are decreased obviously after the magnetic field is applied.Among them,when the magnetic field is about 150 mT,the surface roughness Ra of the isotropic modified magnetic-sensitive rubber with volume ratio of 10% is decreased most obviously,which is ranged from 3.631 μm to 1.523 μm,and the change rate is about 58.1%.The convex peak value Rp of the isotropic magnetic-sensitive rubber with volume ratio of 5% is decreased significantly,from 10.32 μm to 3.769 μm,which decreases by 6.551 μm.Finally,the dynamic process of surface morphology change of the modified magnetic-sensitive rubber under the action of magnetic field is analyzed by the finite element simulation method.The simulation results are consistent with the experimental phenomena.5.The magnetically controlled adhesion mechanism of modified magnetic-sensitive rubber is analyzed by using the theoretical and experimental research methods.Firstly,the surface morphology change reason of the modified magnetic-sensitive rubber is revealed based on the magnetic dipole model.Then,on the basis of the traditional JKR contact model,the contact model of magnetic-sensitive rubber under ideal condition is established.The analysis shows that the adhesion force of magnetic sensitive rubber is proportional to the actual contact area.Therefore,without the external magnetic field,when the pressing force is increased,the number of convex peaks become more numerous,the actual contact area is increased,and the adhesion force of materials is increased.After applying the magnetic field,the surface observation experiment proved that the height of the surface convex peak is decreased,the number of convex peaks contacted with the silicon wafer is increased,and the contact area is increased,which leads to the increase of the adhesion force of the material.The experimental phenomena and mechanism are explained by theoretical analysis,which is helpful for the intelligent control of the adhesive property of the magnetic-sensitive rubber. |
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