| Magnetorheological(MR)technology is a newly established research domain that combine the control of material characteristic with machining and mechanical transmission in the field of me-chanical engineering.A serial of machine works such as damping,shock absorption,micro removal of material can be done by using MR fluids' characteristic that swiftly transition from liquid phase to solid phase.One of the features of MR technology is materials like MR fluids or MR polish-ing fluids etc.,its MR effect can be indirectly controlled by micro computer to what extents,the changing of material properties accelerate the mechanical design to change accordingly,hence in recent 20 years,MR technology quickly become one of the hot topics in the machining area,both domestic and foreign.Magnetorheological fluids(MR fluids)can be classified into an excellent functional material by the definitions of smart material:"self-adj us table characteristics while some external motivations applied".Therefore,numerous researches on rheological characteristics of magnetorheological fluids are focused on the macro and micro mechanical properties,and various industrial applications such as:machining,hydraulic transmission,damper are already implemented with magnetorheological technology.In this paper,features and scope of application about dozens of magnetorheological fluids' rhe-ology models,both continuum and discrete approach,are studied comparatively.Focused on the connection between variation of mechanical properties and micro-structure change while magnetic field is exerted,MR fluids' micro rheological characteristics,chain-like structure forming thresh-old and MR polishing material removal model are discussed with the combination of theoretical,experimental and numerical simulation methods.By using Monte Carlo simulation,position and magnetic moment of particles in MR fluids cell system are calculated,and by which the relationship between micro weighted distance of CIPs and rheological mechanical features of MR suspension is built.A distance weighted shear stress model is proposed,this model is furthermore applied to a new reciprocating magnetorheological polishing device,on the basic of shear stress parameter,a surface material removal model is built.The main research contents in this paper are listed as following:According to the given parameters of"5-levels&3-factors" central composite design(CCD)scheme,ferrofluids and MR fluids are simulated by Monte Carlo method,and thermal couple co-efficient ? and the share of magnetic energy,Van der waals energy and steric energy are further calculated.The simulation results proves the effectiveness that employing thermal couple coeffi-cient ? to evaluate aggregation features of MR fluids system.Using calculating ? value in response surface method,the contribution of MR fluids performance parameters had on particles aggregation are analyzed,a further fitting expression about thermal couple coefficient varies with these param-eters is acquired by linear regression,and the aggregation threshold of particle size in ferrofluids is calculated by response surface optimization analysis.Our research found that the effect levels to? of these factors successively were average particle size,volume concentration and magnetic field strength.On the basic of Ampere" Molecular Current Hypothesis",the interaction force formula(dis-crete approach)of neighboring particles in chain is deduced.The calculation error that standard isolated-chain shear stress model applied to the high concentrated MR suspension is analyzed.Using Monte Carlo method to simulate and calculate the carbonyl iron particles coordinate of cell system,a new isolated-chain-based shear stress model improved by distance-weighted factors is proposed.In this model,an idea:"effective magnetic chain" is raised,incorporated with distance-weighted coeffi-cients,interaction of neighboring chains and the overlapping of local magnetic field of chain can be quantified;moreover,Frohlich-Kennelly model is induced for measuring nonlinear magnetized pro-cess of MR fluids.The saturation magnetization of carbonyl iron particles fitted by the B-H data,which helps to explain the shear stress behavior of MR fluids while the particles are fully saturation magnetized.For validating the new rheology model,a high concentration self-prepared aqua-based magnetorheological fluids(38.7 vol.%)is tested in MCR301 rheometer(Anton Paar,Austria),the experimental data of shear stress ? with external magnetic strength H is collected and compared with counterparts of three commercial hydrocarbon-based magneto-rheological(MR)fluid(33.58vol.%?44.79vol.%,LORD(?)).Results verified that much greater accuracy can be achieved by the new distance-weighted model in high volume concentrated MR fluids in contrast to the standard isolated chain-based model.A water-based magnetorheological finishing fluids is prepared for polishing silicate frosted glass planar parts with 28mm diameter by using a new type of reciprocating magnetorheological polishing device.The influence that different velocity ratio(spindle axis rotation and translational motion of liquid trough)had on surface quality of workpiece are investigated.A motion simulation model is built by Multibody Toolbox in MATLAB/Simulink,according to the calculating results of particle's trajectory in workpiece surface with various combination of parts' rotational speed and trough's translational velocity,a conclusion can be drawn that the speed components of parts' spindle axis and trough should be coprime during MR polishing.On the basic of Preston equation,material removal model applied for reciprocating magne-torheological polishing device is proposed by using two parameters:surface pressure and shear stress,respectively.Considering that measuring and collecting magnetic strength data of polish-ing zone at real time is rather difficult,a parameterized 2-D symmetrical finite element model is programmed by ANSYS(?)/APDL.The surface magnetic intensity simulating data with different pa-rameters of spacing interval and external magnetic strength are employed to calculate the magnetic pressure distribution in surface of workpiece;Comparing calculating roughness values of material removal model with spline fitting surface contour that reconstructed by scattering roughness points measured by roughometer,it is confirmed that the changing trend of material removal rate(MRR)is close to the experimental data,and from center position to the nearly edge part of workpiece,a linear growth trend of MRR is observed in reciprocating MR polishing device. |
PDF Full Text Request