Alan Fuchs

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 Semi-Active, High-Torque, Magnetorheological Fluid Limited Slip Differential Clutch

The design, development, and performance characterization of a magnetorheological (MR) fluid clutch for automotive limited slip differential (LSD) applications is presented in this study. The controllability of MR fluids provides an adjustable torque transmission and slippage for the LSD application. Three-dimensional electromagnetic finite element analysis (FEA) is performed to optimize the magnetic circuit and clutch design. Based on the results obtained from the FEA, the theoretical torque transfer capacity of the clutch is predicted utilizing Bingham-Plastic constitutive model. The clutch is characterized at different velocities and electromagnet electric input currents. Both the torque transfer capacity and the response time of the clutch were examined. It was demonstrated that the proposed MR fluid LSD clutch is capable of transferring controllable high torques with a fast response time. DOI: 10.1115/1.2203308

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.

A Low Force Magneto-rheological (MR) Fluid Damper : Design, Fabrication and Characterization

This study focuses on the theoretical analysis, design, fabrication and characterization of a small Magneto-Rheological (MR) fluid damper. It can be potentially applied to a horizontal axis, front-loading washing machine. In such washing machines, although washing cycle is slow, spin cycle is much faster. During acceleration from washing cycle to spin cycle, the tub passes through its resonant speed requiring relatively high damping. On the other hand, high damping results in increased force transmission to the housing and noise at high-speed spin cycle. Controllability of the MR fluid damper allows adjustment of damping requirements for different cycles and helps to reduce the noise at high speed spin cycle while limiting the tub motion at resonance. A patented geometry of an MR valve developed by Composite and Intelligent Materials Laboratory at the University of Nevada, Reno is used as the basis of this new design to satisfy the requirements of the application. Fabricated prototype damper is characterized using harmonic displacement input. Test results are in good agreement with the theoretical predictions and design values.

Mechanical Disruption of Tumors by Iron Particles and Magnetic Field Application Results in Increased Anti-Tumor Immune Responses

The primary tumor represents a potential source of antigens for priming immune responses for disseminated disease. Current means of debulking tumors involves the use of cytoreductive conditioning that impairs immune cells or removal by surgery. We hypothesized that activation of the immune system could occur through the localized release of tumor antigens and induction of tumor death due to physical disruption of tumor architecture and destruction of the primary tumor in situ. This was accomplished by intratumor injection of magneto-rheological fluid (MRF) consisting of iron microparticles, in Balb/c mice bearing orthotopic 4T1 breast cancer, followed by local application of a magnetic field resulting in immediate coalescence of the particles, tumor cell death, slower growth of primary tumors as well as decreased tumor progression in distant sites and metastatic spread. This treatment was associated with increased activation of DCs in the draining lymph nodes and recruitment of both DCs and CD8(+)T cells to the tumor. The particles remained within the tumor and no toxicities were observed. The immune induction observed was significantly greater compared to cryoablation. Further anti-tumor effects were observed when MRF/magnet therapy was combined with systemic low dose immunotherapy. Thus, mechanical disruption of the primary tumor with MRF/magnetic field application represents a novel means to induce systemic immune activation in cancer.

Temperature-dependent skyhook control of HMMWV suspension using a fail-safe magnetorheological damper

In this paper, a theoretical study is presented to examine the behavior a fail-safe magneto-rheological fluid (MRF) damper based on a temperature compensated skyhook strategy for a quarter car model of a High Mobility Multi-purpose Wheeled Vehicle (HMMWV). A fail-safe MRF damper is a controllable semi-active device that in the event of power or control system failure behaves as a passive damper with certain viscous damping capacity. The dampers viscous force changes significantly with temperature. Vehicle suspension system is required to operate in a wide range of temperature. The temperature effects on the performance of MRF damper should be considered in the control system design. Displacement and acceleration response of the vehicle sprung mass for the quarter car model are discussed at the operating temperature range of a MRF damper. Simulation results under off-road excitation demonstrated that the compensated skyhook control system improves MRF damper performance in reducing the sprung mass displacement and acceleration compared to the uncompensated skyhook control system.

A new modular magnetorheological fluid valve for large-scale seismic applications

This study presents a modular, large-scale, magneto-rheological (MRF) by-pass valve to be used in seismic damper retrofits for energy mitigation. The by-pass valve is designed, constructed and tested. The MR valve can be used to retrofit a commercial passive seismic damper as a semi-active device. The performance of the MRF valve was characterized by means of quasi-static characterizations. A new MR fluid is also developed for the seismic by-pass MRF damper application. This MR fluid has low off-state viscosity and high field-dependent yield strength. The field-dependent rheology of the MR fluid is evaluated with a MR shear rheometer. In addition, a theoretical model is developed taking into account geometric dimensions, fluid properties and applied magnetic field strength. Three-dimensional electromagnetic finite element analysis is used to determine and maximize the magnetic field strength inside the by-pass MRF valving region. Both experimental and theoretical results show that the modular large-scale by-pass MRF damper can generate sufficient dynamic force range which meets the high-force requirements of large-scale structures subjected to seismic or other significant hazards.