Research On Magnetic-mechanical-Electrical Coupling Performance And Application Of Magnetorheological Plastomer

Magnetorheological plastomer(MRP)is a new type of magnetorheological material with magneto-sensitive properties formed by dispersing magnetic particles in low-cross linking polyurethane(PU).It has good plasticity like a plasticine and can be shaped into various shapes.The magnetic particles are uniformly dispersed in the PU matrix without agglomeration and sedimentation.When an external magnetic field is applied,the magnetic particles in the PU matrix can overcome the constraints of the matrix to self-assemble into chain-like structures along the direction of the magnetic field.Therefore,MRP has good stability and high magnetorheological effect.In addition,the unique magneto-induced microstructure evolution has a significant impact on the mechanical,electrical,and acoustic properties of MRP,making it a potential application prospect in the fields of damping and vibration control,flexible electronics and noise reduction.Currently,a series of research works on MRP have been carried out and the achievements in material preparation,performance testing and microstructure simulation have been achieved.However,there are only a few reports on optimization and application of MRP.It is important to further study the magnetic-mechanical-electrical coupling performance and working mechanism.Aiming at the shortcomings in the current work,the dynamic mechanical properties of MRP under high strain rates were firstly measured.Then,the mechanical-magnetic coupling working mechanism was proposed.In order to optimize the mechanical and electrical properties,carbon fibers,carbon nanotubes,liquid metals and electrolyte materials were tried to be doped in MRP.The magnetic-mechanical-electrical coupling performance and working mechanism were further analyzed.Finally,a series of magnetic-mechanical-electrical sensing devices based on MRP were designed.The specific research contents are as follows:1.The dynamic mechanical properties of MRP at high strain rates and the mechanical-magnetic coupling mechanism.The dynamic mechanical properties of MRP were investigated by using a Split Hopkinson Pressure Bar(SHPB)equipped with an electromagnetic accessory.Both the SHPB and rheological test indicated the mechanical properties of MRP increased with strain rate,which demonstrated the typical rate dependent stiffening performance.With strain rate increased from 1580 s'1 to 7900 s-1,the maximum stress of MRP increased from 31 MPa to 66 MPa.MRP also exhibited a magnetic strengthening behavior due to the magnetorheological effect.Keeping the strain rate at 6500 s-1,the maximum stress increased 19.8 MPa as the magnetic flux density increased from 0 mT to 480 mT and the increase rate of maximum stress reached to 34%.Moreover,a high-speed camera was also used to capture the deformation of MRP in different strain rates.Based on the above results,a possible mechanism was proposed to investigate the dynamic mechanical properties of the MRP.The synergistic effect between the magnetic field dependent particle structure evolution and polymer chain deformation were responded for the magnetorheological behavior and strain rate stiffening characteristic,respectively.2.Strengthening effect of 1-D carbon materials on the mechanical and electrical properties of MRP.A novel multifunctional carbon fillers-doped magnetorheological plastomer(CMRP)was developed and its magnetic-mechanical-electrical coupling properties were tested.Here,the carbon fiber(CF),carbon nanotube(CNT)and their mixtures(CF and CNT)were dispersed into the matrix to prepare CMRP.It was found that the CMRP with 7.5wt%CF and 0.5wt%CNT had the excellent magnetorheological effect(2200%)and magnetic field dependent electrical property.Specially,when the magnetic field increasing from 0 mT to 900 mT,the resistance was reduced by two orders of magnitude.Moreover,the relationship between resistance and strain was also discovered.The resistance variation increased with the increasing oscillation amplitude,and the period of the resistance variation was half of the period of the strain variation.Finally,the possible mechanism for the magnetic-mechanical-electrical properties was discussed.3.The magnetic-thermal-mechanical-electrical coupling performance of liquid metal-filled MRP.A novel multifunctional sensing material capable of responding synergistically to magnetism,temperature,and mechanical stimuli was proposed.It was a mixture of liquid metal(LM),plastic low-crosslink density polyurethane(PU)and magnetic carbonyl iron(CI)particles,named as liquid metal-filled magnetorheological plastomer(LMMRP).Excitingly,the LMMRP can change from an insulator to a conductor under a magnetic field,because the CI particles aggregated into chain-like structures along the direction of the magnetic field,forming the conductive paths with the flowing LM microdroplets.The relative resistance variation of LMMRP can reach 95%under a magnetic field of 180mT.The wide range of resistance change made the material a promising future in magneto-controlled electronic equipment.Moreover,the temperature sensitivity and force sensitivity of the LMMRP sensor were investigated,which met different sensing requirements in various situations.Furthermore,the magnetic-thermal-mechanical-electrical coupling characteristics were analyzed by microstructure simulation.It had a deep understanding of the multiple sensing mechanism.The LMMRP also exhibited the intelligent applications,such as magnetic control,environment recognition,and motion monitoring.It provided the potential application prospects in the field of intelligent electronics.4.Flexible,self-powered,magnetism/pressure dual-mode sensor based on MRP.A flexible self-powered magnetism/pressure dual-mode sensor,which consists of MRP was developed.The working mechanism of the self-powered sensor was based on the displacement reaction of Fe and CuSO4.Different from traditional flexible pressure sensors,it was not only sensitive to a slight pressure(1.3 kPa),but also responsive to a small magnetic field(12 mT).Under an external magnetic field,the micro-scale CI particles in the MRP electrode aggregated into the chain-like and the cluster-like structures,which enhanced the electrochemical activity of ions in the electrolyte of the electrode materials and formed the conductive network.The voltage increased with the magnetic field strength and the sensitivity was 4.2%at a magnetic field of 252 mT.To further explore the mechanism of sensor,the microstructure evolution of CI particles inside the electrode materials under different magnetic fields was simulated by particle-level dynamics method.Finally,a smart writing board based on a self-powered magnetism/pressure dual-mode sensor array was developed and it was sensitive to different magnetic fields without an external power supply,which demonstrated a broad potential for mobile electronic device in the non-contact state.