Yanming Liu

Sensing Behavior of Magnetorheological Elastomers

A magnetorheological elastomer (MRE) is comprised of ferromagnetic particles aligned in a polymer medium by exposure to a magnetic field. The structures of the magnetic particles within elastomers are very sensitive to the external stimulus of either mechanical force or magnetic field, which result in multiresponse behaviors in a MRE. In this study, the sensing properties of MREs are investigated through experimentally characterizing the electrical properties of MRE materials and their interfaces with external stimulus (magnetic field or stress/strain). A phenomenological model is proposed to understand the impedance response of MREs under mechanical loads and magnetic fields. Results show that MRE samples exhibit significant changes in measured values of impedance and resistance in response to compressive deformation, as well as the applied magnetic field.

A comparative study of thermal behavior of iron and copper nanofluids

Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids. It was shown that thermal conductivity can be enhanced by up to 70% for copper nanofluids. It was also demonstrated that for a given particle concentration, copper nanofluids are superior in thermal conductivity compared to iron nanofluids.Nanofluids consist of nanoparticles dispersed in heat transfer carrier fluid and are typically used for enhancing thermal conductivity in devices and systems. This study investigated the synthesis of iron and copper nanoparticle-based thermal fluids prepared using a two-step process. Chemical precipitation was used for the synthesis of the powders, and ultrasonic irradiation was used to disperse the nanoparticles in the carrier fluid (ethylene glycol). The size distributions of the nanopowders in the carrier fluid were determined using dynamic light scattering resulting in average particle sizes of around 500 nm. The crystallite sizes of the powders were below 20 nm. Thus, both types of nanofluids are comparable with regard to crystallite size, particle size, and morphology resulting in a direct comparison of material properties and their effect on thermal conductivity of the nanofluids. A guarded hot parallel-plate method and dynamic tests were used to compare the thermal conductivities of the nanofluids...

Particle size effects in the thermal conductivity enhancement of copper-based nanofluids

We present an analysis of the dispersion characteristics and thermal conductivity performance of copper-based nanofluids. The copper nanoparticles were prepared using a chemical reduction methodology in the presence of a stabilizing surfactant, oleic acid or cetyl trimethylammonium bromide (CTAB). Nanofluids were prepared using water as the base fluid with copper nanoparticle concentrations of 0.55 and 1.0 vol.%. A dispersing agent, sodium dodecylbenzene sulfonate (SDBS), and subsequent ultrasonication was used to ensure homogenous dispersion of the copper nanopowders in water. Particle size distribution of the copper nanoparticles in the base fluid was determined by dynamic light scattering. We found that the 0.55 vol.% Cu nanofluids exhibited excellent dispersion in the presence of SDBS. In addition, a dynamic thermal conductivity setup was developed and used to measure the thermal conductivity performance of the nanofluids. The 0.55 vol.% Cu nanofluids exhibited a thermal conductivity enhancement of approximately 22%. In the case of the nanofluids prepared from the powders synthesized in the presence of CTAB, the enhancement was approximately 48% over the base fluid for the 1.0 vol.% Cu nanofluids, which is higher than the enhancement values found in the literature. These results can be directly related to the particle/agglomerate size of the copper nanoparticles in water, as determined from dynamic light scattering.

Heating of a High-torque Magnetorheological Fluid Limited Slip Differential Clutch

Theoretical and experimental studies on heating of a high-torque, multi-plate magnetorheological (MR) fluid limited slip differential (LSD) clutch are presented. A lumped parameter system approach is assumed for theoretical heating analysis. The experimental study is conducted to examine the temperature rise of the clutch. Electric power input and slippage effects are investigated both theoretically and experimentally. The effect of temperature increase on the torque performance of the clutch is also examined. The results show that the transferred torque is insensitive to clutch temperature increase. For all cases, theoretical and experimental results are in good agreement.

Response time and performance of a high-torque magneto-rheological fluid limited slip differential clutch

In this study, the response time and system characterization analyses of a high-torque magneto-rheological (MR) fluid limited slip differential (LSD) clutch are presented. The response time of the clutch is examined based on the objective of keeping the relative velocity difference of the shafts of the clutch less than a predetermined threshold value. The experimental setup allows the application of an external disturbance to the system, so that the relative velocity difference exceeds the threshold value. A velocity-based, closed-loop control system is designed and tested. Additionally, system identification experiments are performed to determine system parameters such as bearing friction coefficients, dry and viscous torque coefficients. These parameters are utilized in the theoretical response time analyses of the MR fluid LSD clutch. It is demonstrated that the overall response time of the system varies between 20 and 65 ms as a function of operating velocity and electromagnet current, including the response times of the controller, solenoid inductance and MR fluid and inertia effects. The response time reduces by increasing solenoid current and increasing the operating velocity.

Full-Scale Magnetorheological Fluid Dampers for Heavy Vehicle Rollover

A unique magnetorheological fluid (MRF) bypass damper for heavy vehicle controllable suspension systems is designed, fabricated, and tested. The damper can generate nearly 8000 N which meets the maximum force requirement for preventing heavy vehicle rollover under certain crucial circumstances. A dynamic simulation of the rollover performance of a heavy vehicle incorporated with four MRF dampers is carried out using a vehicle dynamic software. Emergency maneuver and rollover scenario are simulated. The results show that the MRF dampers could achieve better performance for protection from the vehicle rollover. It is estimated that the roll angle can be reduced by 45% compared to the regular original equipment manufacturer (OEM) passive dampers.

High-torque magnetorheological fluid clutch

This study focuses on the design and characterization of a radial double-plate magneto-rheological fluid (MRF) clutch. The clutchs torque output can be controlled by adjusting the applied magnetic field. Electromagnetic finite element analysis (FEA) is performed to design and optimize the clutch. The shear stress distribution in MRF between the plates is theoretically predicted using the magnetic flux density distribution evaluated from the FEA. The output torque of the clutch is derived by using the Bingham plastic constitutive model. The output torque values are recorded for different input velocities and applied magnetic fields, and they are compared with the theoretical results. It was demonstrated that the clutch is capable of producing high controllable torques.

Response time of magnetorheological fluids and magnetorheological valves under various flow conditions

In this study, the response times of magnetorheological fluids and magnetorheological fluid valves are studied under various flow configurations. Two types of valving geometries, annular flow and radial flow, are considered in the magnetorheological fluid valve designs. The transient pressure responses of magnetorheological fluid valves are evaluated using a diaphragm pump with a constant volume flow rate. The performance of each magnetorheological valve is characterized using a voltage step input as well as a current step input while recording the activation electric voltage/current, magnetic flux density, and pressure drop as a function of time. The variation of the response time of the magnetorheological valves under constant volume flow rate is experimentally investigated. The Maxwell model with a time constant is employed to describe the field-induced pressure behavior of magnetorheological fluid under a steady flow. The results demonstrate that the pressure response times of the magnetorheological fluid and the magnetorheological valves depend on the designs of the electric parameters and the valve geometry. Magnetorheological valves with annular flow geometry have a slower falling response time compared to their rising response time. Magnetorheological valves with radial flow geometry demonstrate faster pressure response times both in rising and in falling states.

Development of Mesoporosity in Scandia-Stabilized Zirconia: Particle Size, Solvent, and Calcination Effects

We present the mechanisms of formation of mesoporous scandia-stabilized zirconia using a surfactant-assisted process and the effects of solvent and thermal treatments on the resulting particle size of the powders. We determined that cleaning the powders with water resulted in better formation of a mesoporous structure because higher amounts of surfactant were preserved on the powders after washing. Nonetheless, this resulted in agglomerate sizes that were larger. The water-washed powders had particle sizes of >5 μm in the as-synthesized state. Calcination at 450 and 600 °C reduced the particle size to ∼1-2 and 0.5 μm, respectively. Cleaning with ethanol resulted in a mesoporous morphology that was less well-defined compared to the water-washed powders, but the agglomerate size was smaller and had an average size of ∼250 nm that did not vary with calcination temperature. Our analysis showed that surfactant-assisted formation of mesoporous structures can be a compromise between achieving a stable mesoporous architecture and material purity. We contend that removal of the surfactant in many mesoporous materials presented in the literature is not completely achieved, and the presence of these organics has to be considered during subsequent processing of the powders and/or for their use in industrial applications. The issue of material purity in mesoporous materials is one that has not been fully explored. In addition, knowledge of the particle (agglomerate) size is essential for powder handling during a variety of manufacturing techniques. Thus, the use of dynamic light scattering or any other technique that can elucidate particle size is essential if a full characterization of the powders is needed for achieving postprocessing effectiveness.

Magnetorheological elastomer mount for shock and vibration isolation

A novel magnetorheological elastomer (MRE) mount is designed, fabricated, and tested to provide a wide controllable compression static stiffness range for protecting a system with variable payload from external shock and vibration. The shear static stiffness and compression dynamic stiffness were also studied. MRE is a field-controllable material in which the stiffness properties can be altered by changing the applied magnetic field. A MRE mount is developed by using 0.5-inch thick MRE layers and built-in electromagnets. The performance of the 2-layer MRE mount is characterized by compression, shear, vibration, and shock tests. The tests demonstrate that the variable-stiffness MRE mount can be used for shock and vibration isolation applications.