On Dynamics And Magnetic Control Of Slender Soft Structures Under Large Deformation

Owing to their wide applications in the fields of soft robots,stretchable electronics and flexible biomedical devices,soft materials have great improvements in the aspects of preparation technology and mechanical property in the past years.To achieve more accurate and efficient performances,it is necessary to model and analyze the mechanical behaviors of soft structures.In the existing works,the predications of the large-deformation behaviors of soft structures mainly rely on the experimental tests and the simulations via commercial software,which decreases the efficiency of mechanical analyses and increases the difficulty of revealing the underlying mechanism.As a new subject between the classical solid mechanics and the classical fluid mechanics,mechanics of soft structures needs more novel basic theories to develop.Therefore,the present work carries out the in-depth theoretical studies and mechanical analyses of the slender soft structures.By embedding the hard-magnetic microparticles into a soft material matrix,a new type of soft active materials named as the hard-magnetic soft(HMS)materials was recently fabricated.This work carries out the investiagtions of the deformation and vibration of the slender soft structures made of the HMS materials,which has important significances both in theory and practice.By exactly considering the geometric nonlinearities,a series of large-deformation theoretical models of the HMS beams are proposed,where the straight and curved beams,the two-dimensinal and three-dimensional deformations,and the statical and dynamical responses are included.Based on these novel large-deformation theories,some basic mechanical behaviors,deformation designs and property-improved methods are given via both analytical and numerical methods.In addition,this work uses the HMS materials and an external magnetic field for adjusting the large-deformation behaviors of the fluid-conveying pipes for the first time.The geometrically exact dyncamical models of the soft pipes conveying fluid are proposed to precisely predict the large-deformation behaviros of pipes,where the straight and curved pipes,and the planar and nonplanar oscillations are included.The newly derived governing equations can be degenerated into the wildely used euqations of small-amplitude vibrations.These novel theoreties can deal with many complicated problems that is unabled by using small-deformation theories.The validations of the current theoretical models and calculating results are ensured by comparing with the results of simulations,experiments,and absolute node coordinate method.When a magnetic field is applied upon a HMS beam,the magnetization direction of the HMS materials will align with the direction of the external magnetic field by the deformation of beam with bending,twisting and stretching etc.Various functional and complex transformations of the HMS beams can be realized by designing the magnetization of beam and the applied magnetic field.If the hard-magnetic microparticles are emdeded in a functionally graded form,the magnetic sensibility of HMS strcutures may be improved,and thus the deformation of HMS structures will be larger under the same acuation of magnetic field.It is also found that the static deformation,stability and large-deformation vibration of the fluid-conveying pipe can be effectively controlled by the proposed magnetic adjustment method in this work.In summary,the theoretical modeling and mechanical analyses of the slender soft structures are provided with particular attention to HMS beams and fluid-conveying pipes.The present work developes the theoretical frame of the mechanics of soft structures,and solves a series of significant and typical problems in the fields of HMS materials and flow-induced vibrations.This work also offers important theoretical foundations in the later investigations of the mechanical behaviors of complicated soft structures,e.g.soft plates and shells,and the studies of the vibration utilizations and controls of flexible structures.