Research On Test Method And Device Of Magnetorheological Fluid's Response Time

Magnetorheological Fluids(In Short MRF)is a suspension formed by dispersing micron-sized particles in a carrier liquid.It combines the fluidity of the liquid with the magnetism of a magnetic substance so that its rheological characteristics change with an applied magnetic field,and the response process is of the millisecond order.Therefore,magnetorheological fluids are widely used in aerospace,weapons and military industry,automobile engineering,ship engineering and medicine.The response time of magnetorheological devices greatly affects their control effect,so the response time is an important indicator of magnetorheological devices.The response time of magnetorheological devices is divided into electromagnetic response time and MRF response time.In order to better improve the dynamic performance of magnetorheological devices,scholars have conducted a lot of exploration and research on the response time and electromagnetic response time of magnetorheological devices,but there are few research results on the response time of magnetorheological fluids.According to the magnetorheological effect,the shear yielding strength of magnetorheological fluid changes with the change of magnetic field.In this paper,SineWave Current signal is used to form sinusoidal magnetic field to obtain sinusoidal torque,find out the peak time difference between torque signal and magnetic field signal,and measure the response time of magnetorheological fluid.Based on this method,a set of device for measuring the response time of magnetorheological fluid is designed.The main work and achievements of this paper are as follows:(1)Briefly classify and explain the methods for measuring the response time of magnetorheological fluid.Understand that the current methods for measuring the response time of magnetorheological fluid are divided into direct method and indirect method,analyze the problems existing in measuring the response time of magnetorheological fluid from microscopic chain formation analysis,using slit shearing device and disk shearing device,and propose the research work of the paper;(2)Parameter identification of Herschel-Bulkley model(HB model for short)is carried out to ensure that it can be applied to the measurement of response time of magnetorheological fluid,and then the torque transmission formula of double shear disk model is deduced.The relation between sinusoidal current signal and torque transmission is introduced to obtain the variation relation of torque with time.Based on this,a method is proposed to find the response time of magnetorheological fluid by using the peak time difference between sinusoidal input and output signals.At the same time,the micro-dynamic model of rheological behavior of magnetorheological fluid was studied.Through simulation,the relationship between MRF response time and volume fraction was obtained.Then,from the microscopic point of view,the relationship between magnetic induction intensity,shear rate and other factors is qualitatively analyzed.It is concluded that if the volume fraction of magnetorheological fluid is increased below the critical point,the response time of magnetorheological fluid will be shortened.Beyond the critical point,the response time of MRF decreases with the increase of volume fraction.The shear rate is not sensitive to the response time.(3)Design the magnetic circuit and mechanical system of the device.Firstly,the magnetic circuit of the device is designed,and the basic design of the magnetic circuit is carried out through the magnetic circuit design principle to determine the initial coil and magnetic circuit parameters.Then,ANSYS finite element analysis is used for further quantitative analysis,and magnetic circuit design is optimized based on the design mode of combining the two with circulation.After the magnetic circuit design is completed,the mechanical core parts of the device are designed,including the shearing mechanism and supporting structure of the device,the size and tolerance of each part are determined,and the mechanical standard parts are selected.According to the estimated torque,shear rate and other parameters,the rotor motor,lifting motor and sliding table of the device are selected.(4)Set up the sensing and data acquisition system of the device.Torque sensor is used to detect the change of transmission torque.Current sensor and magnetic field probe are used to measure the change of current intensity and magnetic induction intensity.The current sensor is placed outside the device,the magnetic field probe is placed on the shear plate,and the torque sensor is placed on the shear rotating shaft.The data acquisition system and mechanical system are integrated,assembled and debugged,so that the device can successfully measure the response time of magnetorheological fluid under different conditions.(5)Set current,power supply,control system,etc.to make experimental tests on the response time of magnetorheological fluid under different conditions,measure the relationship between the response time of magnetorheological fluid and volume fraction,magnetic induction intensity and shear rate respectively,and make comparison with theoretical analysis.It is found that within the critical point,the larger the volume fraction of magnetorheological fluid is,the faster the response time will be.If the volume fraction exceeds the critical point,the response time will decrease.The greater the magnetic induction intensity,the faster the response time of magnetorheological fluid;Moreover,shear rate is not an important factor affecting the response time of magnetorheological fluid.The possible errors and their sources in measuring the response time of magnetorheological fluid are analyzed.It is considered that the testing device basically meets the design requirements.