Journal of Intelligent Material Systems and Structures

Hard magnetic particle–based magnetorheological elastomers are novel magnetoactive materials in which, unlike the soft particle–based magnetorheological elastomers, the particles provide magnetic poles inside the elastomeric medium. Therefore, the stiffness of the hard magnetic particle–based magnetorheological elastomers can be increased or decreased by applying the magnetic field in the same or opposite direction as the magnetic poles, respectively. In the present work, the viscoelastic properties of hard magnetic particle–based magnetorheological elastomers operating in shear mode have been experimentally characterized. For this purpose, hard magnetic particle–based magnetorheological elastomers with 15% volume fraction of NdFeB magnetic particles have been fabricated and then tested under oscillatory shear motion advanced rotational magneto-rheometer to investigate their viscoelastic behavior under varying excitation frequency and magnetic flux density. The influence of the shear strain amplitude and driving frequency is examined under various levels of applied magnetic field ranging from −0.2 to 1.0 T. Finally, a field-dependent phenomenological model has been proposed to predict the variation of storage and loss moduli of hard magnetic particle–based magnetorheological elastomers under varying excitation frequency and applied magnetic flux density. The results show that the proposed model can accurately predict the viscoelastic behavior of hard magnetic particle–based magnetorheological elastomers under various working conditions.

The aerospace industry is gradually moving toward “more electric aircraft” to reduce its environmental footprint. Developing all-electric actuators brings a reliability challenge because conventional geared-motor actuators are susceptible to jamming failures from their metal-to-metal gear contacts. Magnetorheological clutch actuators solve this challenge using a layer of fluid to transmit torque and are not exposed to potential jam failures, making them particularly attractive for high reliability applications such as primary flight controls. A key challenge that must be addressed for a widespread deployment of the magnetorheological fluid technology in aerospace is the ability to monitor magnetorheological fluid condition while it degrades in operation. To date, no such efforts have been reported in the literature. Recent studies on magnetorheological fluid durability have shown that mixing the magnetorheological fluid using a magnetic screw pump principle can significantly increase the life of the fluid by up to 50%. This article presents the design, prototyping, and testing of a proof-of-concept magnetorheological fluid condition monitoring sensor, capitalizing on the flow-recirculating properties of magnetic screw magnetorheological clutches to continuously provide a well-mixed and homogeneous fluid sample to the sensor. The proposed sensing principle uses optical red green blue sensor placed in the fluid circulation path to measure the fluid color during degradation. The sensor has been tested up to fluid failure on a high-torque (60 N m) magnetorheological clutch mounted on a fully instrumented durability test bench. Tests have been performed with two types of fluid: a commercially available fluid, the Lord 140CG, and a homemade fluid based on perfluoropolyether oil, the GPL-103. Results with the Lord fluid demonstrate a strong correlation between the decrease in torque-to-current performance with fluid brightness. The average of three aging tests on Lord 140CG fluid show a 12% ± 1% decrease in brightness at end-of-life regardless of operating conditions such as torque, shear rate, and dissipated power. These results suggest that, for the Lord 140CG fluid, brightness is directly linked to the fluid degradation state and independent of operating conditions, which makes it a more accurate metric to quantify durability than life dissipated energy since the latter can vary significantly depending on operating conditions. Tests made with the GPL-103 based fluid did not show such a strong correlation, which means that optical sensing of magnetorheological fluid condition must be carefully calibrated for each individual fluid and clutch design. Results from this study suggest that optical sensing is a relevant method to measure the magnetorheological fluid condition in flow-recirculating clutches.

Semi-active systems using magnetorheological fluids have been realized in many novel devices such as linear dampers, rotary dampers, brakes, and so on. Rotary vane-type magnetorheological damper is one such device that uses magnetorheological fluid as a hydraulic medium and a controllable magnetorheological valve to generate variable resistance. This device, due to its limited angle motion, lends itself to a natural application for prosthetic knee joint. In this article, a bypass rotary vane-type magnetorheological damper suitable for prosthetic knee device is designed. In the proposed design, the rotary vane chamber and the bypass magnetorheological valve are connected using hydraulic cables and ports. The design of rotary cylinder is implemented based on the largest possible dimensions within the envelope of a healthy human knee, while the magnetorheological valve is designed optimally using a multi-objective genetic algorithm optimization. Off-state braking torque, induced on-state braking torque and mass of the valve are selected as three objectives. The torque and angular velocity requirements of the normal human knee are used as design limits. The optimal solution is chosen from the obtained Pareto fronts by prioritizing the objective of weight reduction of magnetorheological valve. The optimal solution is capable of producing a damping torque of 73 Nm at a design speed of 8.4 rpm and current supply of 1.9 A. Potential benefits offered by this design when compared with multi-plate magnetorheological brake are flow mode operation, large clearance gap, and fewer design components, thus reducing the manufacturing complexity.

This work analyses the shear behavior of magnetorheological elastomers (MRE), a class of smart materials which presents interesting magneto-mechanical properties. In order to determine the effect of several variables at a time, a design of experiment approach is adopted. A set of several samples of MRE was manufactured, by varying the weight fraction of ferromagnetic material inside the viscoelastic matrix and the isotropicity of the material, by adding an external magnetic field while the elastomeric matrix was still liquid. The mechanical behavior of each sample was analyzed by conducting cyclic tests at several shear rates, both with and without an external magnetic field. Moreover, in order to estimate the maximum shear stress, the specimens were loaded monotonically up to failure. Shear stiffness, maximum shear stress and specific dissipated energy were calculated on the basis of the experimental data. The results were analyzed using an Analysis of Variance (ANOVA) to assess the statistical influence of each variable. The experimental results highlighted a strong correlation between the weight fraction of ferromagnetic material in each sample and its mechanical behavior. Moreover, the dissipated energy of the MRE drops down when the magnetic field stiffens the behavior or the shear rate increases. The ultimate failure shear stress is strongly affected by the external magnetic field, increasing it by nearly 50%. The ANOVA on the results provides a simple phenomenological model is built for each output variable and it is compared with the experimental tests. These models produce a fast and fairly accurate prediction of each analyzed response of the MRE under various shear rates and applied magnetic fields.

The main functions of automotive suspensions are to improve passenger comfort as well as vehicle dynamic performance. Simultaneously satisfying these functions is not possible because they require opposing suspension adjustments. This fundamental design trade-off can be solved with an active suspension system providing real-time modifications of the suspension behavior and vehicle attitude corrections. However, current active suspension actuator technologies have yet to reach a wide-spread commercial adoption due to excessive costs and performance limitations. This paper presents a design study assessing the potential of magnetorheological clutch actuators for automotive active suspension applications. An experimentally validated dynamic model is used to derive meaningful design requirements. An actuator design is proposed and built using a motor to feed counter-rotating MR clutches to provide upward and downward forces. Experimental characterization shows that all intended design requirements are met, and that the actuator can output a peak force of ±5300 N, a peak linear speed of ±1.9 m/s and a blocked-output force bandwidth of 92 Hz. When compared to other relevant technologies, the MR approach simultaneously shows both better force density and speeds (bandwidth) while adding minimal costs and weight. Results from this experimental assessment suggest that MR slippage actuation is promising for automotive active suspensions.

This work presents an analysis of the effect of parametric uncertainties on the vibration control performance of a rod with periodically distributed piezoelectric patches that can be either independently connected to electrical shunt circuits or interconnected through an electrical line of inductors. In both cases, the capacitance of the piezoelectric patches is considered as stochastic parameters following a known probability density function distribution. Then, Monte Carlo simulations are performed to evaluate mean values and confidence intervals of the frequency response functions to assess the robustness of each solution and to compare different solutions in terms of nominal and robust performances. Results have shown that vibration amplitude reduction worsen significantly due to the mistuning between structural natural frequency and circuit resonance frequency. Yet, interconnected circuits are more robust to these uncertainties than independent shunts because they ensure a mean response that is closer to the nominal one. It was then proposed to assess the effect of modifying the circuits’ resistance. Results have shown that increased resistance decreases variability when considering both environmental and manufacturing variabilities. This also favors the use of interconnected circuits that require increased resistance for robust vibration mitigation.

The aim of this embodiment is to present an analytical analysis of a functionally graded piezoelectric energy harvester consisting of a flexible functionally graded piezoelectric layers carrying magnetic mass at the free end. The magnetic tip mass is in interaction with a permanent magnet which is located at a distance from the top of the tip mass. The oscillation of the harvester happens via excitation of the base. Using Rayleigh’s beam theory and Hamilton’s principle and considering geometric nonlinearity, the coupled electromechanical governing equations have been developed. The nonlinear frequency response of the piezoelectric energy harvester beam has also been studied under base excitation. A parametric study has been carried out to investigate the effect of grading index and magnetic force on responses of both free vibration and induced excitation cases. The results were compared with those obtained using three-dimensional finite element model developed in COMSOL Multiphysics 5.5 commercial software and good agreement has been observed. The results from both the analytical method and simulation confirm that tuning the design parameters of grading index and magnetic gap to the optimal value results in a considerable change in the performance of the energy harvester.

Industrial robots used in manufacturing processes such as drilling of aerospace structures undergo many rapid positioning motions during each operation. Such aggressive motions excite the structural modes of the robot and cause inertial vibrations at the end-effector, which may damage the part and violate the tolerance requirements. This article presents a vibration avoidance technique based on input shaping combined with a learning-based structural dynamic model. A theoretical dynamic model is first developed for commonly used robotic arms considering the flexibilities of the first three joints of the robot. An artificial neural network is developed and used in conjunction with the dynamic model to predict the natural frequency of the system at any pose in the workspace. Transfer learning techniques are used to extend the trained artificial neural network to account for the mass of the payload with minimal data collection. To reduce the residual vibrations of the robot in rapid motions, zero-vibration derivative shapers are designed and implemented. The effectiveness of the presented methodology has been validated experimentally on a Staubli RX90CR robot with an open-architecture control system developed fully in-house. Experimental results show more than 85% reduction in residual vibrations during aggressive motions of the robot.

This paper proposes a wheel with a deployable leg that can change the apparent wheel radius to improve the runnability of a rover traversing a lunar surface covered with regolith. The driving force of the wheel was formulated according to terramechanics, and relations for the changing driving force with the different configurations were clarified. The simulated driving forces with the original wheel configuration and extended leg configuration were compared in a single-wheel experiment, and the results confirmed that the proposed extendable leg system exhibited a higher driving force than the original circular wheel. With this system, the rover can use the original wheel state for flat ground surfaces that do not require a high driving force and then switch to the proposed extendable leg system when a high driving force is required, such as escaping from local concave ground or climbing on steep slope. The proposed system is potentially applicable to efficiently traversing irregular surfaces not only on the Moon but also on other planets.

The development of the bench model of a hybrid (rigid-flexible) morphing leading edge is presented in this paper. The distinctive feature of this design centers on compounding a fully rigid nose with a flexible structure to create a seamless morphing leading edge. The rigid nose guarantees a precise shape control in the aerodynamically critical region of the wing whereas the flexible structure allows for an increase in both chord length and its camber. These improvements offer potential solutions to many of the challenges reported in the literature about the existing morphing wing designs. In order to evaluate the feasibility of the hybrid (rigid-flexible) concept and to demonstrate the aforementioned improvements, a bench model is developed and tested in-house. This paper focuses on the analysis performed to develop this model, including (1) aerodynamic shape optimization to devise the desired drooped shape; (2) geometry optimization to specify the dimensions of the rigid nose; (3) finite element analysis to characterize the skin component of the flexible structure; and (4) finite element analysis to estimate the actuation authority. Overall, the numerical and experimental results reveal the inherent advantage of the hybrid (rigid-flexible) concept from the smart structure standpoint; however, significant considerations are required to advance the technical readiness level of this design to a commercially viable solution for aircraft manufacturers.