Journal of Intelligent Material Systems and Structures current issue

Spherical Brake with MR Fluid as Multi Degree of Freedom Actuator for Haptics

Senkal, D., Gurocak, H. — Thu, 12 Nov 2009 03:08:42 PST

This research explored design of a magnetorheological (MR) spherical brake as a multi-DOF actuator. To the best of our knowledge, our design is the first ever multi-DOF spherical brake using MR fluid. The primary goal was to design a compact but powerful brake using the serpentine flux path approach. An optical position measurement system was also designed to eliminate the gimbal mechanisms that are typically used in spherical joints for position measurement. It was found that the braking torque scales up proportionally to the cube of the brake radius. This enables making much more powerful brakes without increasing the overall size significantly. A prototype spherical brake was built with 76.2 mm diameter and 3.7 Nm braking torque. Experiments were conducted to identify the characteristics of the prototype brake and to test it in virtual wall collision, damping and Coulomb friction simulations for haptics. A joystick was built as a haptic device using the MR spherical brake. Virtual wall collision experiments showed crisp reaction force at initial contact and very high rigidity during the contact.

Recursive Memory-based Hysteresis Modeling for Solid-state Smart Actuators

Bashash, S., Jalili, N., Evans, P., Dapino, M. J. — Thu, 12 Nov 2009 03:08:42 PST

This article presents a new modeling approach for the memory-dependent hysteresis phenomenon in a broad class of smart structures and systems. We propose a recursive formulation to relate the minor hysteresis trajectories to their surrounding loops. More specifically, each internal (minor) trajectory targets its previous turning point and converges to its neighboring loop with a tunable exponential rate. By applying the ‘curve alignment’ and the ‘wiping out’ properties at the turning points, we present a new strategy within the context of a memory-based hysteresis modeling framework. A Galfenol-driven micropositioning actuator and a piezoelectrically driven nanopositioning stage are used to experimentally validate the model. Galfenol exhibits large butterfly-type nonlinearity with a small hysteresis effect, while the piezoelectric actuator exhibits wide hysteresis loops. The model is able to precisely predict the major and minor hysteresis loops in both the Galfenol and piezoelectric actuators, and is expected to be effectively and conveniently applicable to general systems exhibiting memory-dependent hysteresis.

Reduction of Structural Acoustic Radiation Via Left and Right Eigenvector Assignment Approach

Wu, T.Y., Wang, K.W. — Thu, 12 Nov 2009 03:08:42 PST

The objective of this research is to investigate the feasibility of utilizing a new left—right eigenvector tailoring method in reducing the acoustical radiations of flexible structures. The structural sound pressure radiation can be expressed in terms of a combination of vibration modes, where its magnitude is also a function of the external disturbance distribution. In other words, the radiated sound pressure level depends on both the right eigenvectors (related to the structural mode shapes) and left eigenvectors (related to the system disturbance rejection ability) of the vibrating structure. The basic idea of the proposed approach is to simultaneously modify the structural modal velocity distribution and the system capability of disturbance rejection through active left—right eigenvector assignment control actions, so that the sound pressure radiated from the vibrating structure can be reduced. Numerical simulations are performed to evaluate the effectiveness of the proposed method on structural noise reduction. Frequency responses of sound pressure at a receiver in the selected frequency range are illustrated. It is shown that with the proposed active control method, one can re-shape the modal velocity distribution and enhance disturbance rejection, and hence can effectively minimize the structural sound pressure radiation.

Finite Deformations of Tubular Dielectric Elastomer Sensors

Son, S., Goulbourne, N.C. — Thu, 12 Nov 2009 03:08:42 PST

This article describes a numerical model validated with experimental results for a large stretch tubular sensor. The sensor is a dielectric elastomer (DE) membrane with electrical properties that can be accurately correlated with mechanical strain, for strains well over 50%. The DE sensor is a passive capacitive sensor. To illustrate the concept, the sensor is attached to the inner surface of a fiber-reinforced elastomer actuator, which serves as the host substrate. Fiber-reinforced elastomers configured for pneumatic operation are employed as actuators in robotic, prosthetic, and morphing applications. An electromechanical model for the two-layer composite consisting of the fiber-reinforced elastomer and the sensor is derived. For several illustrative loading profiles, the model yields a strain output for an input capacitance value. Using identical loading cases, an experimental setup was designed to measure sensor output for two different sensor materials: silicone and polyacrylate. The sensitivity of the DE sensor was also evaluated for varying geometrical parameters and is mainly dependent on the initial thickness. Comparison of experimental data and numerical results is very good with an overall error of 3—6%. This work shows that the model is robust in the large strain range and furthermore predicts non-linear strain behavior.

Unsteady Fluid Flow in Hybrid Hydraulic Actuators

John, S., Chaudhuri, A., Cadou, C., Wereley, N. M. — Thu, 12 Nov 2009 03:08:42 PST

The ability of smart materials like piezoelectrics to deliver large blocking forces in a small package while operating at high frequencies makes them extremely attractive for converting electrical energy to mechanical power. This led to the development of hybrid actuators consisting of co-located smart material actuated pumps and hydraulic cylinders that are connected by a set of fast-acting valves. The overall success of the hybrid concept hinges on the effectiveness of the coupling between the smart material and the fluid. This, in turn, is strongly dependent on the resistance to fluid flow in the device. This article presents results from 3D simulations of unsteady fluid flow in the pumping chamber of a prototype hybrid actuator powered by a piezoelectric stack. The results show that the forces associated with moving the fluid into and out of the pumping chamber exceed 10% of the piezo stack blocked force at relatively low frequencies near 100 Hz and approach 80% of the blocked force at 800 Hz. This reduces the amplitude of the piston motion in such a way that the volume flow rate remains approximately constant above operating frequencies of 600 Hz. As the driving frequency is increased beyond 800 Hz, the flow rate starts to decrease. This study also presents a decomposition of the pressure loss into its Fourier components and identifies the important harmonics.

Temperature Dependence of Magneto-rheological Materials

Sahin, H., Wang, X., Gordaninejad, F. — Thu, 12 Nov 2009 03:08:42 PST

The properties of magneto-rheological (MR) materials are temperature dependent. Compared to MR fluids, MR greases (MRGs) are more sensitive to temperature due to their inherent behavior of carrier materials. In this study, MRGs are studied to examine the temperature effect on their yield stress and apparent viscosity. Experimental data are obtained for magnetic fields ranging from 0.14 T to 0.53 T and temperatures ranging from 10^°C to 70^°C. It is observed that temperature has a significant effect on the field-induced yield stress of MRGs. A new yield stress model, based on an extended Herschel—Bulkley constitutive relation, in which the shear yield stress is a function of magnetic field and temperature, is proposed. Excellent agreement between the theoretical results and experimental data is obtained.

Equivalent Circuit Modeling of Piezoelectric Energy Harvesters

Yang, Y., Tang, L. — Thu, 12 Nov 2009 03:08:42 PST

Last decade has seen growing research interest in vibration energy harvesting using piezoelectric materials. When developing piezoelectric energy harvesting systems, it is advantageous to establish certain analytical or numerical model to predict the system performance. In the last few years, researchers from mechanical engineering established distributed models for energy harvester but simplified the energy harvesting circuit in the analytical derivation. While, researchers from electrical engineering concerned the modeling of practical energy harvesting circuit but tended to simplify the structural and mechanical conditions. The challenges for accurate modeling of such electromechanical coupling systems remain when complicated mechanical conditions and practical energy harvesting circuit are considered in system design. In this article, the aforementioned problem is addressed by employing an equivalent circuit model, which bridges structural modeling and electrical simulation. First, the parameters in the equivalent circuit model are identified from theoretical analysis and finite element analysis for simple and complex structures, respectively. Subsequently, the equivalent circuit model considering multiple modes of the system is established and simulated in the SPICE software. Two validation examples are given to verify the accuracy of the proposed method, and one further example illustrates its capability of dealing with complicated structures and non-linear circuits.

Coil-based Electromagnetic Damper and Actuator for Vibration Suppression of Cantilever Beams

Cheng, T.-H., Oh, I.-K. — Thu, 12 Nov 2009 03:08:42 PST

In this study, both an eddy current coil damper and an electromagnetic actuator were developed for the vibration suppression of a cantilever beam integrated with a copper coil and a permanent magnet. The control system for the vibration suppression of the electro-magneto-mechanically coupled beam that consists of a coil attached to an aluminum beam and a permanent magnet installed below the coil was proposed. Alternatively, the conductive coil can be passively and actively used as a damper and an actuator. The effects of various coil shapes including a cylindrical tube, a square tube and a circular sheet were investigated to determine optimal vibration suppression for the cantilever beam. The frequency response function of a beam with the theoretical model of the magnetic eddy current damping system was predicted and its accuracy was compared to the experimentally measured frequency response. Also, the results of the active control with a positive position feedback method were compared with those of the passive eddy current dampers with open and closed circuits. The experimental data showed that the tube type coils had much higher vibration suppression efficiency than the sheet type coil and the active vibration control strategy can be alternatively used to improve the electromagnetic damper system.

Detecting Water Accumulation in Honeycomb Sandwich Structures by Optical-fiber-based Distributed Temperature Measurement

Minakuchi, S., Tsukamoto, H., Takeda, N. — Thu, 12 Nov 2009 03:08:42 PST

Water accumulation in honeycomb sandwich structures is a perceived problem for aircraft operators since it significantly degrades the structural integrity. The authors developed a fiber-optic-based technique to detect water accumulation in large-scale aircraft honeycomb sandwich structures. An optical-fiber network was formed in the adhesive layer and a Brillouin-based sensing system with high spatial resolution (specifically, pre-pump pulse Brillouin optical time domain analysis (PPP-BOTDA)) was utilized to detect the non-uniform internal temperature distribution during cooling in aircraft ascent. First, the temperature change during the ascent was investigated to evaluate the feasibility of the proposed technique. A verification test was then conducted using a Nomex honeycomb sandwich panel. The non-uniform temperature induced by water accumulation was detected from the peak-frequency distributions and the width of the Brillouin gain spectrum, which is the output of the PPP-BOTDA. The spectrum width, which represents the temperature non-uniformity within the spatial resolution of the PPP-BOTDA, could indicate the presence of smaller water accumulations compared to the peak frequency, which represents the temperature averaged over the spatial resolution, thus confirming the importance of evaluating the spectrum width. The developed system is quite useful for continuously monitoring large-scale aircraft sandwich structures.

Modeling and Experimental Study of Simultaneous Creep and Transformation in Polycrystalline High-Temperature Shape Memory Alloys

Lagoudas, D. C., Chatzigeorgiou, G., Kumar, P. K. — Thu, 12 Nov 2009 03:08:42 PST

The viscoplastic behavior in high-temperature shape memory alloys and its interaction with the transformation behavior is investigated in this work. Standard creep tests and isobaric transformation-induced tests were conducted for a TiPdNi high-temperature shape memory alloy on a uniaxial frame fitted with a custom high-temperature setup. Motivated by the experimental observations indicating simultaneous creep and phase transformation, a 1D constitutive model is presented that aims to capture the coexistence of the rate-independent transformation and the rate-dependent viscoplastic behavior. Based on continuum thermodynamics, the evolution equations for forward and reverse transformation and viscoplasticity are properly chosen. The material parameters needed for the model calibration are identified from the experimental data. The predicted material response by the proposed constitutive model is in good agreement with the experimental results.

Shaped Modal Sensors for Linear Stochastic Beams

Adhikari, S., Friswell, M.I. — Thu, 12 Nov 2009 03:08:42 PST

Modal sensors and actuators using distributed piezoelectric material have a wide range of applications, for example in vibration control and piezoelectric transformers. The design of these transducers usually ignores any uncertainty and variability in the host structure, which can have a significant effect on their performance. This article investigates the design of shaped piezoelectric sensors for beam structures that are robust with respect to uncertainties in the system. The modal transducers are defined using a discrete approximation to the equations of motion for linear stochastic systems and their shapes are represented using the underlying finite element shape functions. The optimal shape design has been coupled with the stochastic finite element method to consider parametric uncertainty described using random fields, using a first-order perturbation-based approach to obtain the second-order covariance of the modal matrix. The numerical results for linear elastic beam structures showed that the shape of the sensors of the stochastic system can differ significantly from the corresponding deterministic system. However, sensors with shapes designed using a smoothness criterion also perform very well for structures with uncertainty.

Strain and Back Cavity of Tunnel Engineering Surveyed by FBG Strain Sensors and Geological Radar

Li, C., Zhao, Y.-G., Liu, H., Wan, Z., Xu, J.-C., Xu, X.-P., Chen, Y. — Thu, 12 Nov 2009 03:08:42 PST

A differential fiber Bragg grating strain sensor is developed, thereinto, the strain of a gage rod is translated into the deflection of the cantilever beam, on which the fiber Bragg gratings suffer the strain and shift their Bragg wavelengths. In this scheme, temperature compensation is achieved by the differential operation between the Bragg wavelength shifts of sensing gratings mounted on the top and bottom surfaces of the beam. The loading experiment indicates that the least-square linearity between the strain of the gage rod and the difference of the Bragg wavelength shifts of the sensing gratings is 0.3% in the range of the strain -1500 to 1500 µ, the maximum error is 20 µ, and the measure precision is 0.007. According to the flaws of the second lining of Shan Xin-Po Tunnel explored by the geological radar, these differential fiber Bragg grating strain sensors are installed on the lining. During the backfill period of 53 days and the operation period of 341 days, the strain survey results that the strains are related to the distribution of back cavity in the backfill period; however, the strains became gradually stable in the operation period.