Analysis Of Electro-magnetic Squeeze Magnetorheological And Shape Memory Alloy Composite Transmission Performance

Smart materials and structures are an emerging discipline in the world today,which is a frontier research field.As smart materials and structures can solve many technical problems that are not easily solved by existing technologies and methods,it has attracted great attention from scholars at domestic and foreign.As typical smart materials,magnetorheological fluids and shape-memory alloys have great application prospects in smart devices and precision transmission systems because of its controllable mechanical properties,rapidly response and steady performance.In this dissertation,a magnetorheological and shape memory alloy composite transmission method with electromagnetic squeeze was proposed to address the problems of traditional magnetorheological transmission devices with small transfer torque and performance degradation under heavy load and high-temperature conditions.The aim was to improve the power density of the magnetorheological transmission device and maintain its stable transmission performance under high temperatures.The constitutive model of magnetorheological fluid and shape memory alloy was modified,and the transmission performance of the composite transmission device under the coupling effect of electric,magnetic,thermal,and force fields was analyzed using finite elements.The relationship between current and device temperature,electromagnetic force,squeeze stress,and output torque was established.The design equations for the key dimensions of the composite transmission and the dimensions of the shape memory alloy spring are derived,which provide theoretical references for the design optimization of the composite transmission.The main research contents of the full dissertation are as follows.(1)The composition of magnetorheological fluids was introduced and the chain process of magnetic particles in shear and squeeze modes was simulated by molecular dynamics algorithms.The constitutive model of the magnetorheological fluid was described,and a squeeze-strengthening model containing parameters such as volume fraction,temperature,stress-strain and magnetic flux density is established based on magnetic dipole theory.The temperature effects on the rheological properties of the magnetorheological fluids were quantitatively analyzed by experimental data.The shape memory effect and superelasticity of shape memory materials were described by taking the martensitic phase transformation.The constitutive equations of the shape memory alloys considering the martensitic phase transition rate and stress/temperature reorientation transition were established.The martensitic phase transformation equation was modified by using the logistic sigmoid function.(2)The yield flow equation and torque equation of the magnetorheological fluid in the disc gap were derived.The relationship between the minimum working gap thickness and the required torque was established,and the relationship between the load torque and the height of the magnetorheological fluid yield surface was analyzed.The relationship between the coil magnetic energy and the electromagnetic force of the armature disc was established,the coil size design method was described,and the relationship between the magnetic flux potential and the number of turns of the coil is established based on the equivalent magnetic circuit method.The magnetic field boundary conditions at multi-arc gaps were analyzed based on the flux continuity principle,and the relationship between material permeability and transmedia deflection angle was established.And the design optimization was carried out for the flux distribution at the arc gaps.(3)The relationship between shape memory alloy spring temperature,spring size,output displacement and output force was established based on the design equation of threedimensional helical springs.Two types of magnetorheological and shape-memory alloy composite actuators for electromagnetic squeeze were introduced,and the working principle of the composite actuators was described.(4)The finite element analysis was carried out for the magnetic and temperature fields of the composite transmission,and the relationship between the current and temperature,squeeze stress,output torque was established.The magnetostatic torques were obtained under the squeeze strengthening only,the squeeze strengthening and viscosity-temperature characteristics,and the compensation torque of shape memory alloy at different temperatures.Finally,the coupling torque of the transmission was obtained by torque superposition.(5)An experimental bench was built to verify the correctness of the established shape memory alloy spring driving force equation,the magnetorheological fluid squeeze strengthening equation and the torque equation.The innovations are as follows.(1)The chaining process of magnetorheological fluid was simulated by molecular dynamics algorithm,and the squeeze strengthening model in the squeeze-shear composite mode is established based on the magnetic dipole moment theory.The stress-strain relationship of the magnetorheological fluid under different magnetic flux densities was obtained.The viscosity-temperature characteristics of the magnetorheological fluid were quantitatively analyzed by experiments.(2)Based on the continuous medium mechanics’ theory and thermodynamics theory,the constitutive equations of the shape memory alloy considering the phase transformation rate,stress/temperature reorientation transition and thermoelastic deformation were established.The phase transformation equation of martensite was modified by using the logistic sigmoid function,and the thermodynamic equations of shape memory alloy spring were established based on the first law of thermodynamics.(3)The mechanism of electromagnetic force generation was analyzed,and the relationship between magnetic flux and electromagnetic force magnitude and magnetic field boundary conditions was established.The composite transmission method of magnetorheological and shape memory alloy based on electromagnetic extrusion was proposed.Its transmission performance under the coupled physical fields’ influence was analyzed to provide new ideas for the development of squeezed magnetorheological transmission technology.