| Magnetorheological fluid and shape memory alloy are new smart materials which can respond to external stimuli.Because of its rapid sensing function,strong controllability and reversible characteristics,it is often used in construction engineering,intelligent automobile,rehabilitation medicine,intelligent robot and other industrial fields.Aiming at the defect of the magnetorheological fluid braking device that decreases braking performance at high temperature,this paper proposed the combined braking method of magnetorheological fluid and shape memory alloy based on the viscose-temperature characteristics of magnetorheological fluid,the squeezing strengthening effect and the shape memory effect of shape memory alloy,and described the braking process and working mechanism of the combined brake device.The key structure size of the joint brake device is designed,the magnetic field and temperature field of the joint brake device are analyzed by finite element software,and the braking performance of the joint brake device is studied and analyzed by combining theoretical analysis and experimental research.The main research contents of this paper are as follows:(1)The basic material composition,magnetorheological effect and constitutive model of magnetorheological fluid were introduced,and the influence of magnetic field intensity,temperature and extrusion stress on the shear yield stress of magnetorheological fluid under shear working mode was analyzed.The shape memory effect,hyperelastic effect and constitutive model of shape memory alloy are introduced.(2)Based on the constitutive model of magnetorheological fluid,the braking performance of disc and cylinder magnetorheological fluid braking devices was compared and analyzed.Based on the thermodynamic equilibrium equation and shear constitutive model of shape memory alloy,the restoring force equation of the electrothermal shape memory alloy spring is derived,and the electrothermal mechanical characteristics of the electrothermal shape memory alloy spring are obtained.(3)The working principle of the combined magnetorheological fluid and shape memory alloy friction brake device is introduced.The structure size and magnetic circuit of the combined magnetorheological fluid and shape memory alloy friction brake device are designed and analyzed,and the key structure size of the combined brake device and the relevant parameters of the excitation coil are obtained.(4)The magnetic induction intensity and temperature distribution of the combined braking device of magnetorheological fluid and shape memory alloy friction were analyzed by finite element software.The electrothermal mechanical characteristics of the electrothermal shape memory alloy spring as a force driver were analyzed based on the finite element method,and the finite element analysis value was basically consistent with the theoretical calculation value.Combined with the analysis of magnetic field,thermal field and electro-mechanical characteristics,the influence of the current loaded by the excitation coil on the braking performance of the brake device is studied.(5)The braking performance of the magnetorheological fluid braking part of the combined braking device of Magnetorheological fluid and shape memory alloy friction was tested by setting up the disc magnetorheological fluid braking performance experimental research platform of electrothermal shape memory alloy spring extrusion,which verified the feasibility of electrothermal shape memory alloy spring extrusion magnetorheological fluid working gap to improve the braking performance of the brake device;The driving performance and response time of the electrothermal shape memory alloy spring were tested by setting up an experimental research platform.The theoretical analysis of electrothermal mechanical characteristics of electrothermal shape memory alloy spring is verified.The innovation of this paper lies in:(1)Based on the thermodynamic equilibrium equation and the shear constitutive model of shape memory alloy,the relationship among loading current,temperature,material parameters,geometric parameters and restoring force when the electrothermal shape memory alloy spring is used as a force driver is established.(2)The two different driving and trigger modes of the electric heating shape memory alloy spring and shape memory alloy spring were introduced into the magnetorheological fluid brake device,and the theoretical model of the combined friction braking between magnetorheological fluid and shape memory alloy was established.In order to improve the braking performance of magnetorheological fluid,magnetorheological fluid was squeezed by the extrusion disk driven by the electrothermal shape memory alloy spring.The shape memory alloy spring is used to passively drive the friction slider to generate friction torque and ensure the stability of the brake device under high temperature. |
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