The behaviour of magnetorheological fluids in squeeze mode

Magnetorheological (MR) fluids possess rheological properties, which can be changed in a controlled way. These rheological changes are reversible and dependent on the strength of an excitation magnetic field. MR fluids have potentially beneficial applications when placed in various applied loading (shear, valve and squeeze) modes. The squeeze mode is a geometric arrangement where an MR fluid is sandwiched between two flat parallel solid surfaces facing each other. The distance between these two parallel surfaces is called the gap size. These surfaces are either pushed towards or pulled apart from each other by orthogonal magnetic-induced forces. In this study, a test rig was designed and built to perform the experiments with three different types of MR fluids. One type of water-based and two types of hydrocarbon-based MR fluids were activated by a magnetic field generated by a coil using different magnitudes of DC electrical current. To finalize the design, a Finite Element Method Magnetics (FEMM) was used to predict the magnetic field strength throughout the MR fluids. For each trial, combination of three process parameters were experimented in both compression and tension modes on each type of MR fluid. The three process parameters were the electric current applied to the coil, the initial gap size and the compressive or tensile speed. In every test, the speed and the current in the coil were kept constant, while the instantaneous compressive and tensile forces were recorded. Experimental results showed that MR fluids have distinct unique behaviour during the compression and tension processes. The behaviour of MR fluids was dependent on the relative movement between the solid magnetic particles and the carrier fluid in both squeeze modes. A high ratio of solid particles to carrier liquid in the MR fluid is an indication of high magnetic properties. The water-based MR fluid had a relatively large solids-to-liquid ratio. At a given applied current, significant increases in compressive and tensile stresses were obtained in this fluid type. On the other hand, the hydrocarbon-based MR fluids had relatively lower solids-to-liquid ratios, whereby, less significant increases in compressive and tensile stresses were obtained. The magnetic field strength was proportional to the applied current. Consequently, the MR effect, in terms of resulting stresses, was directly proportional to the current. When plotting stress against strain for each experiment, the slopes of the curves were found to be larger in general when the initial gap sizes were smaller. This was due to higher magnetic fields generated in smaller initial gap sizes. However, the stress-strain relationships were slightly affected by changing the compressive or tensile speeds. In general, the compressive stresses were much higher than the tensile stresses for the same experimental parameters throughout this study

Preliminary study on decision making factors to replace medical equipment in hospital

Maintaining medical equipment in hospital is a cost-deprived process yet is a crucial process that needs to be looked into. Maintaining is an ongoing process that starts with installation and ended up with disposed. The cost for maintaining equipment is often held a large portion in life cycle costing and huge amount of money need to be allocated to complete this process. The cost invested on maintaining the medical equipment should be worth the value without comprising the safety requirement and regulations. However, there are circumstances where hospitals are unable to decide when to dispose the equipment especially when the equipment reach the end of its life, incur high repairing cost, aging, and frequent failed to function. Management of hospital come into dead end solution as there are lack of proper guidelines on maintaining medical equipment and therefore the equipment may be over maintained or under maintained. This paper provides a review of 100 papers from credible sources on maintaining activities of equipment to identify factors that are important for decision making to replace the medical equipment

A Conceptual Framework to determine Medical Equipment Maintenance in Hospital Using RCM Method

Maintenance services are performed to ensure the equipment is operating according to manufacturer standard and maintained at a desired level of quality. The implementation of maintenance services may prevent unexpected breakdown and disruption of operations in a hospital. However, there were numbers of cases reported on the frequent breakdown of medical equipment even though the maintenance program is in place and practised. Therefore, the reliability of the maintenance services was questioned especially when the breakdowns occurred after the maintenance services being performed. This paper proposes a conceptual framework to determine the accurate maintenance program for medical equipment in the hospital using Reliability Centred Maintenance (RCM) method. The recommendation from the RCM will assist to identify the root cause of the breakdown and minimize the number of breakdown for medical equipment in the hospital. RCM process is known as one of the most effective maintenance approaches to reduce the number of maintenance activities and hence minimizing the cost of maintenance incurred

Study on the potential application of electronic wedge brake for vehicle brake system

This paper presents a study of the potential application of an electronic wedge brake for vehicle brake system using human-in-the-loop simulation. Simulation was made in MATLAB Simulink software which interfaces an imaginary vehicle with a real time input from a human, such as throttle and brake input. The imaginary vehicle model that is used is a vehicle dynamic model that has been validated experimentally using an instrumented experimental vehicle. A validated electronic wedge brake actuator model was then used as the brake actuator model where a suitable control strategy, namely proportional-integral-derivative and proportional-integral controllers, was utilised as the force and gapping control respectively. To verify the effectiveness of the proposed actuator in a vehicle, the simulation results are compared with the results of human-in-the-loop simulation of a vehicle using a conventional hydraulic brake and the response of the experimental vehicle using the same dynamic test, namely the sudden braking test. The simulation results show that the proposed simulation method and actuator with appropriate controller strategy have similar behaviour to a hydraulic brake in terms of its capability to produce the desired braking force to reduce the speed and halt the vehicle. The outcomes from this study can be considered in design optimisation and implementation in a real vehicle

Swelling, Thermal, and Shear Properties of a Waste Tire Rubber Based Magnetorheological Elastomer

In this study, the achievement of revulcanization, thermal stability, and rheological behaviors of waste tire rubber (WTR), based magnetorheological elastomers (MREs), were evaluated to convince their applicability as one of smart material possessing the field-dependent tuning capability of material characteristics such as complex modulus. The cross-linking density of the MREs was assessed through the swelling test to ratify the degree of reclaiming. The behavior of MREs to the temperature enhancement was evaluated via thermogravimetric analysis and thermomechanical analysis. Meanwhile, the alteration of shear stress depending on the magnetic fields was investigated at both steady and oscillatory states, measured using a rheometer. It has been shown that the increment of shear stress is proportional to the increment of the magnetic field. More specifically, it has been found that the WTR based MRE can achieve the maximum static stress ranging from 9 to 13 kPa (at 656 mT) with a linear viscoelastic (LVE) region above 3% strain amplitude. In addition, from the oscillatory test it has been determined that the highest MR effect of 24.71% can be achieved, which directly indicates the augmentation of both storage and loss moduli under ramped frequency and strain. Finally, it has been shown that the highest degree of reclamation based on swelling test can be achieved up to 54%, confirming the occurrence of the crosslinking during the reclamation process

A review of design and modeling of magnetorheological valve

Following recent rapid development of researches in utilizing Magnetorheological (MR) fluid, a smart material that can be magnetically controlled to change its apparent viscosity instantaneously, a lot of applications have been established to exploit the benefits and advantages of using the MR fluid. One of the most important applications for MR fluid in devices is the MR valve, where it uses the popular flow or valve mode among the available working modes for MR fluid. As such, MR valve is widely applied in a lot of hydraulic actuation and vibration reduction devices, among them are dampers, actuators and shock absorbers. This paper presents a review on MR valve, discusses on several design configurations and the mathematical modeling for the MR valve. Therefore, this review paper classifies the MR valve based on the coil configuration and geometrical arrangement of the valve, and focusing on four different mathematical models for MR valve: Bingham plastic, Herschel-Bulkley, bi-viscous and Herschel-Bulkley with preyield viscosity (HBPV) models for calculating yield stress and pressure drop in the MR valve. Design challenges and opportunities for application of MR fluid and MR valve are also highlighted in this review. Hopefully, this review paper can provide basic knowledge on design and modeling of MR valve, complementing other reviews on MR fluid, its applications and technologies

Declining performance of silicone-based magnetorheological elastomers after accelerated weathering

Magnetorheological elastomers (MRE)-based products are usually located in an area directly exposed to sunlight and rain. However, there is no specific research on the behavior of MRE after accelerated weathering. Therefore, in this study, the changes to the chemical and rheological properties of both isotropic and anisotropic MRE after accelerated weathering were examined. Treated and untreated specimens were compared. MRE specimens with 40% by weight CIP were prepared with no current excitation and another sample was prepared with 1.5 T of magnetic flux density. Each specimen was treated in an accelerated weathering machine, Q-Sun Xe-1 Xenon Test Chamber, under a UV light exposure cycle and water spray. A material characterization was carried out using FTIR and a rheometer to determine the changes to the chemical and rheological properties. The morphological analysis results showed that after the weather treatment, the surface was rough and more cavities occurred. The rheometer test results showed a significant decrease in the storage modulus of each treated MRE specimen, unlike the untreated MRE specimens. The decrease in the storage modulus value with currents of 0, 1, 2, and 3 Amperes was 66.67%, 78.9%, 85.2%, and 80.5%, respectively. Meanwhile, FTIR testing showed a change in the wave peak between the untreated and treated MRE specimens. Thermogravimetric analysis (TGA) also showed a decrease in MRE weight for each specimen. However, for both treated and untreated MRE specimens, the decrease in TGA was not significantly different. In all the tests carried out on the MRE samples, weather acceleration treatment caused significant changes. This is an important consideration for developers who choose silicone as the MRE matrix

Wheel slip control based on composite nonlinear feedback

To produce faster vehicle acceleration and avoid wheelspin on slippery roads, the wheel slip must be controlled to achieve maximum traction. Recent researches in slip control always had to compromise between speed of time response and overshooting. This research studies the application of Composite Nonlinear Feedback (CNF) controller for vehicle wheel slip control, particularly for in-wheel electric vehicle. A strategy for applying the CNF controller which involves feedback linearization is proposed. The CNF is a combination of a linear feedback law and a nonlinear feedback law without any switching element. The CNF control focuses on improving the transient performance. The proposed control strategy is validated by simulation

Field-dependent viscoelastic properties of graphite-based magnetorheological grease

This paper highlights the effect of graphite on the dynamic viscoelastic properties of magnetorheological grease (MRG). Two types of MRG namely MRG and graphite-MRG, GMRG with 0 wt.% and 10 wt. % of graphite respectively was synthesized by using a mechanical stirrer. The rheological properties of both sample at various magnetic field strength from 0 to 0.603 T was analyzed via rheometer under oscillatory mode with strain ranging from 0.001 to 1% with fixed frequency at 1 Hz for strain sweep and frequency ranging from 0.1 to 80 Hz at a constant strain of 0.01 % for frequency sweep. Based on the result obtained, the value of storage and loss modulus are dependent on the graphite content. A high value of storage modulus was achieved in the GMRG sample at all applied magnetic field strengths within all frequency ranges. These phenomena related to the contribution of graphite to forming the chain structure with CIPs and offered a more stable and stronger structure as compared with MRG. Moreover, the reduction in the value of loss modulus in GMRG was noticed compared to MRG at on-state conditions reflected by the stable structure obtained by GMRG. Lastly, both samples displayed a strong solid-like (elastic) behavior due to the high value of storage modulus, G’ acquired compared to loss modulus, G’’ at all frequency ranges. Therefore, the utilization of graphite in MRG can be used in wide applications such as brake and seismic dampers

Modelling and control of a fixed calliper-based electronic wedge brake

This paper presents a new design of an electronic fixed calliper-based wedge brake system. The movement of both sides of the brake piston is activated by a wedge block mechanism. The proposed fixed calliper-based electronic wedge brake system is a class of hydraulic-free device. The mechanism consists of two sets of wedge blocks, a ball screw drive shaft, a sliding beam and an electric motor. In this mechanism, the rotation of the shaft of the electric motor is converted into linear motion by using a ball screw drive shaft while the linear motion of the drive shaft will force the sliding beam to be displaced linearly. This will activate the wedge mechanism, which will cause the pad to be displaced tangentially to the disc brake. The movement of the pad in pressing the disc will generate clamping force and produce brake torque when the wheel rotates. In this study, the mathematical model of the system that generates the clamping force was identified. The model was based on a second order transfer function. The proposed mathematical model was then validated experimentally using a brake test rig installed with several sensors and input-output (10) device. The performance of the brake mechanism in term of rotational input of the drive shaft and clamping force produced by the brake were observed. Accordingly, a torque tracking proportional-integral-derivative (PID) control of the system was proposed and studied through simulation and experiment. Comparisons between experimental results and model responses were made. It is found that the trend between simulation results and experimental data are similar, with an acceptable level of error