Study On Magnetorheological Plastomer:the Optimization And Mechanism Of Its Mechanical Properties

Magnetorheological plastomer(MRP)is a kind of magnetically sensitive soft material consisting mainly of magnetic particles and non-magnetic plastic matrix.When no magnetic field is applied,the MRP appears as plasticine,whose shape can be easily changed and retains after the external force is removed,exhibiting plasticity.When a magnetic field is applied,the magnetic particles inside the material form a chain or mesh structure,in which case the material exhibits elasticity and has a large yield stress.When the magnetic field is removed,the particles remain in the position where the magnetic field is applied,so that the microstructure formed by the particles is preserved.This feature makes it possible to simultaneously observe the internal structure of the material and the mechanical properties of the test material,which helps to study the relationship between mechanical behavior and microstructure.Since this material exhibits high magnetorheological effect and has no problem of particle sedimentation,it is a kind of excellent magnetorheological material.It has broad application prospects in the fields of vibration and noise reduction,intelligent drive and sensing.Therefore,the research on MRP is of great significance for theoretical analysis and application.As an emerging magnetorheological material,MRP performance testing,optimization design and computational simulation have achieved initial results,but lack a systematic study on it.At the same time,there are few researches on the reliability of MRP under longer and more complex loading.In view of the shortcomings of this part of the work,this thesis optimizes and expands the MRP system from the perspective of dispersed particles and matrix,and analyzes the effects of different factors on the performance of MRP.Then the mechanical properties of MRP under oscillatory shear environment are studied,and the genesis is analyzed and verified by calculation.The specific research content includes the following aspects:1.Characterization of MRPs filled with NdFeB particles.From the perspective of particles,the effect of mixed particles on the mechanical properties of MRP is studied.NdFeB particles have a large coercive force,and MRP obtained as a dispersed phase still retains remanence when the magnetic field becomes zero.This helps with the retention of the structure;the mixed system obtained by mixing the hard magnetic NdFeB particles with the carbonyl iron powders may obtain a more complicated structure under the magnetic field,but the introduction of the hard magnetic particles may cause the asymmetrical response to the magnetic field loading.For this reason,the soft/hard magnetic particles with different mixing ratios were prepared as the MRP of the dispersed phase,and the mechanical behavior under the symmetrical/asymmetric magnetic field was tested.Then changes of the hard magnetic plastomer under the step magnetic field are studied.A possible mechanism explanation is proposed.2.The effect of matrix mechanical properties on the properties of MRP.From the perspective of matrix,the magnetorheological effect and creep recovery behavior of matrix with different cross-linking degree at different temperatures were studied.Firstly,the polyurethane matrix with different length of chain extension reaction was obtained through experiments.The creep behavior was compared and the rheological curve of pure matrix was tested.Then the iron powder was mixed into the MRP to study the variation of the nonlinear interval in the oscillating shear environment,and then the magnetorheological effect in the linear interval was tested.Experiments show that MRP with incomplete cross-linking has a smaller initial modulus and higher magnetorheological effect,and is more likely to change to nonlinear interval.The creep recovery curves of the materials under different magnetic field sizes,different temperatures and different stress levels were then tested.It is further determined that there is a maximum value of the flexibility of MRPs with the change of reaction time,which is not the same as the performance of the pure matrix.To this end,a parameter between the particles and the matrix on the material is qualitatively proposed to explain such experimental phenomena.3.Study on the change of properties of MRP under oscillatory shear.When the MRP storage modulus is tested by oscillatory shear,it was found that the zero field storage modulus of MRP could not be restored to the initial value after the magnetic field was removed.The change of storage modulus and normal force of MRP under linearly varying magnetic field and step-changing magnetic field was tested.It is found that this phenomenon was only discovered when the magnetic field slowly decreased.Repeated loading indicates that the increase in storage modulus is independent of the loading history and is only related to the last variation of the magnetic field.The increase in zero field storage modulus occurs only once in repeated loadings and is restored in a stepped magnetic field.By analyzing this series of phenomena,the reason for the structural changes of MRP under the oscillating shearing magnetic field is proposed,and this phenomenon is verified by computational simulation.