Thick film resistors (TFRs) were screen-printed and fired on fluorophlogopite glass ceramic (FGC) and alumina ceramic substrate as smart aggregates. Performances of smart aggregates under compressive load were tested before and after embedded in mortar specimens. Compared to alumina ceramic substrate, the TFRs on FGC shows better compatibility and matching performance, the matching error between sensor and mortar decreased from 0.734 to 0.187, the output strain ratio between sensor and mortar increased from 0.0837 to 0.421, and the test results confirmed the theoretical calculation results. When embedded in mortar, the TFRs on FGC shows better repeatability than that on alumina ceramic under repeated compressive load.
This paper investigates a scouring sensor using electrical properties of carbon nanotubes(CNTs)-filled cement-based composite. First, for specimens filled with different amount of CNTs, the electrical behavior and the principle which it followed were studied. The effect of the different magnetic field intensity on the arrangement of CNTs in the base was presented. Furthermore, the environment effects (temperature and humidity) on sensors and its causes were revealed. Also, the design of the temperature and humidity self-compensation sensor based on separated electrode was proposed. Finally, by comparison of the sensitivity of the scouring electrode and the stability of the reference electrode, the optimal scheme of the electrode was determined.
Previous studies did by some scholars proved applying a magnetic field during the manufacture process
of polymer-bonded Terfenol-D could orient the magnetic easy direction of the particles along the field
direction and form a pseudo-1-3 structure. Compared to the 0-3 composites composed of Terfenol-D
particles dispersed randomly in a polymer matrix, pseudo-1-3 magnetostrictive composites present
much larger magnetostrictive performance. In this paper, magnetostrictive composites based on
Terfenol-D particles in an unsaturated polyester resin matrix were fabricated under different magnetic
fields. Magentostriction was tested and compared to get the detail effects of orientation fields on
magnetostrictive properties of magnetostrictive composites. Scanning electron microscopy was used to
observe their microstructures. Image analysis was applied to describe the microstructures. The
distribution of the angles between the major axis of the particles and the magnetic field direction was
used to evaluate the arrangement of particles in the matrix quantitatively. The results confirm particle
chain-like structures in composites prepared under larger magnetic field, and show that particle
arrangement changes with the strength of the orientation field, which is result in the changes of
magnetostrictive performance.
Response time is an important parameter which determines the applied fields and practical vibration reduction effects of
magnetorheological (MR) dampers. However, up to now, only a few papers discuss the test and analysis of response
times. In this paper, the response time of a large-scale MR damper at different velocities and currents was firstly tested.
Then, the transient magnetic field excited by the time-variant excitation current was simulated by finite element method
(FEM). Based on the variation of the shear yield stress of magnetorheological fluids in the gap between the cylinder and
the piston, the response time of the MR damper was investigated. Influences of eddy current and excitation current
response time on the damper's response were also explored. Results show that by utilizing finite elements method, the
calculated average effective shear yield strength can be used to predict the response time of a MR damper.
Electromagnetic response is the predominant factor influencing the response time of a MR damper, and reducing eddy
currents is the key to accelerate the response of a MR damper. Moreover, influence of eddy currents is much larger
under stepping down excitation currents than stepping up currents, and with a same magnitude of step, no matter when
the current increases or decreases, the smaller the initial current, the greater the eddy current affects a damper's response
and the longer the response time of damping force is. A fast response excitation current may induce large eddy currents
which reduce the response of the damper instead.
Compared to the double-ended magnetorheological (MR) dampers, single-ended MR dampers are more suitable in
limited-space required fields for their larger strokes. An accumulator is needed for a single-ended MR damper to balance
the volume changes as the piston pulled out and back into the cylinder. Since an accumulator has a great influence on the
damper's performances, this influence should be taken into account in the damper's designing procedure. In this paper,
damping force formula is deduced for the single-ended MR damper with spring accumulator. Then both the method of
determination main parameters of regular spring accumulator and its inherent drawbacks are presented. Finally, by
utilizing the pseudoelastic character of shape memory alloy (SMA), a SMA spring accumulator is proposed and its
design method is given as well.
In the past ten years, there have been several investigations on the effects of particle size on magnetostrictive properties
of polymer-bonded Terfenol-D composites, but they didn't get an agreement. To solve the conflict among them,
Terfenol-D/unsaturated polyester resin composite samples were prepared from Tb0.3Dy0.7Fe2 powder with 20% volume
fraction in six particle-size ranges (30-53, 53-150, 150-300, 300-450, 450-500 and 30-500μm). Then their
magnetostrictive properties were tested. The results indicate the 53-150μm distribution presents the largest static and
dynamic magnetostriction among the five monodispersed distribution samples. But the 30-500μm (polydispersed)
distribution shows even larger response than 53-150μm distribution. It indicates the particle size level plays a doubleedged
sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to
prepare polymer-bonded Terfenol-D, whose composition is Tb0.3Dy0.7Fe2, is resulted from the competition between the
positive effects and negative effects of increasing particle size. At small particle size level, the voids and the
demagnetization effect decrease significantly with increasing particle size and leads to the increase of magnetostriction;
while at lager particle size level, the percentage of single-crystal particles and packing density becomes increasingly
smaller with increasing particle size and results in the decrease of magnetostriction. The reason for the other scholars got
different results is analyzed.
In this paper, experimental investigation on vibration control is carried out on a stay cable model incorporated with one
small size magnetorheological fluid (MR) damper. The control efficiency of the MR dampers to reduce the cable
vibration under sinusoidal excitation using passive control strategy is firstly tested. The dynamic coupling between the
cable and MR damper with the passive control strategy is obviously observed. Dynamic coupling models between stay
cable and MR damper with constant and fluctuating current input are proposed respectively. The proposed dynamic
coupling model corresponding to the MR damper with constant current input is validated by the numerical simulations of
the measured experimental data. Furthermore, using the proposed dynamic coupling corresponding to the MR damper
with fluctuating current input, experimental investigation on the cable vibration control subjected to sinusoidal excitation
using semi-active control strategy is then conducted. Experimental results demonstrate that the semi-active MR damper
can achieve much better mitigation efficacy than the passive MR dampers with different constant current inputs due to
negative stiffness provided by the semi-active MR damper.
Consideration of demagnetization effect, the model used to calculate the magnetostriction of single particle under the
applied field is firstly built up. Then treating the magnetostriction particulate as an eigenstrain, based on Eshelby
equivalent inclusion and Mori-Tanaka method, the approach to calculate average magnetostriction of the composites
under any applied field as well as saturation is studied. Results calculated by the approach indicate that saturation
magnetostriction of magnetostrictive composites increases with increasing of particle aspect, particle volume fraction
and decreasing of Young' modulus of matrix, and the influence of applied field on magnetostriction of the composites
becomes more significant with larger particle volume fraction or particle aspect.
To provide a practical design method for Magnetorheological fluid damper (MRFD), mechanical model is established for
two-exserted-pole gap type (TEP-GT) MRFD and the relationship between damping force and internal sizes is given.
The magnetic circuit is studied and the materials and structures of main components are discussed. A practical design
method for TEP-GT MRFD is obtained and several key expressions are provided. A kind of TEP-GT MRFD for the
cable-stayed vibration control system is designed and manufactured.
In this paper, the response time of one magnetorheological fluid (MR) damper with maximum damping force of 250kN
was tested. Experimental results show that, when electric current increase, response time is about 0.1 to 0.3s; when
current decrease and not to zero, response time is about 0.2 to 0.3s, higher change of current induce longer of response
time. Experimental results also show that, when electric current decrease to zero, response time is about 0.6 to 0.7s,
which is much longer than expected. Further experiment results show that, if subtracting response of coil, when current
increase, the response time is about 60 to 70ms, when current decrease and not to zero, the response time is about 140 to
150ms.
Due to possessing virtue of simple structure, small volume, fast response and good controllability, the actuator made
with Terfenol-D exhibits widely potential application in the field of vibration control, precision machine and instrument,
micro-driven and sonar system. One key technology for designing above devices is gain efficient and uniform bias
magnetic field. In this paper, using software of ANSYS, the distribution character of magnetic field of magnetostrictive
actuator was analyzed; methods to improve uniformity of magnetic field were also discussed.
In recent years, influence of volume, size and shape of particulate, stiffness of the polymeric matrix and mechanical
preload on the magetostrictive property of polymer-bonded Terfenol-D composites have been investigated by several
papers, however, few studies on the effects of the blending soft magnetic particles. In this study, polymer-bonded
Terfenol-D composites composed with 20% volume fraction of Terfenol-D particulate and different volume percentage
of carbonyl iron particle (i.e. 0, 10%, 20%, 30% and 40%) are fabricated. The changes of magnetostriction and magnetic
permeability with changing applied field are tested. The experimental results indicate that with increases of fraction of
carbonyl iron particle, the permeability of the composites increases, but the magnetostrictive property declines. The
change of permeability is explained based on two ideal models, while the change of magnetostriction is explained from
the perspective of energy transforming and mechanical property of matrix.
A novel electric current sensor based on FBG and magnetostrictive composites, which is made from epoxy resin and
Terfenol-D particulates, was fabricated. The relationship between the strain of the sensing head and the magnetic field
intensity was obtained. The new sensor exhibited a good linearity and repeatability, which indicates its potential to be a
practical electric current sensor.
An experimental study on vibration control of one stay cable using a magnetorheological fluid (MR) damper is described in the paper. A 14m-long stay cable model, which is a 1:16 scale model of a 220m-long prototype stay cable in the actual structure, is established for the experimental investigation.The planar sinusoidal excitations with the resonant frequencies are generated by the exciter installed perpendicular to the stay cable model at a point near the low anchorage. The modal testing on the unimpeded stay cable is first performed to identify the actual modal properties and the dynamic performances. Then a series of vibration control tests are conducted on the stay cable incorporated with a small-size MR damper near the low anchorage under the sinusoidal excitations with the first two modal resonant frequencies. The control efficacies and the dynamic performances of the combined cable/MR damper system corresponding to the different current inputs to the MR damper and the semi-active MR damper are investigated comparatively. The experimental results of the vibration control of the stay cable model indicate that the semi-active MR damper can achieve much better control efficacy than the passive MR dampers supplied with constant currents, and the reason can be attributed to the pseudo-negative stiffness generated by the semi-active MR damper.
In recent years, increasing research efforts have been devoted to the development of new controllable dampers, in the aim of mitigating vibration of mechanical equipment, automobile, civil construction and so on. Most of the new controllable dampers are made with special performance of smart materials, such as MR/ER fluid, piezoelectric ceramic and shape memory alloy. Although has similar smart performance such as rapid response time, low power requirement and large driving force with those smart materials, magnetostrictive material, especially magnetostrictive composite material is only got attention by a few researchers. In this paper, by analysis character of magnetosrtrictive effect, the possible applications of magnetosrtrictive composite material in area of vibration control are discussed; several new dampers, made with magnetosrtrictive composite material, such as smart friction or viscous dampers are presented.
The possibility of reducing offshore structural response under strong external excitations such as wind storm, sea ice and
earthquake via control systems is attracting the interest of a large number of researchers. Up to now, lots of dampers
have been installed on different offshore platforms. As one new kind of effective semi-active device, magnetorheological
fluid (MRF) damper has been used in the field of mechanical equipment, automobile and civil buildings, however, the
practical application for vibration control of offshore platform has not seen before. In this paper, 8 MRF dampers with
maximum damping force of 100kN for vibration control of one offshore platform with total weight of 650t have been
manufactured and tested. The general situation of MRF damper system and the offshore platform include manufacturing
issues, powering, range of variability of the mechanical parameters and response time are introduced.
Carbon fiber reinforced cement (CFRC), which mainly composed of hardened cement and short cut carbon fibers, possesses piezoresistive effect, and could be used to produce new type of compressive stress sensors. As having character of low cost, good compatibility with concrete and high durability, CFRC sensor extraordinary adapt to be used in the field of long time health monitoring of concrete structures. Based on large quantity of duplicate tests, the influence of temperature and humidity on electrical specific resistance of CFRC was studied. The function of volume content of carbon fiber or silica fume on above influence is also discussed. Results show that specific resistance of CFRC will decrease with increase of temperature or relative humidity, and above changing have no relationship with carbon fiber or silica fume volume content.
As having ability of changing its apparent viscosity in presence of magnetic field in millisecond, magnetorheological fluids (MRF) exhibit widely potential application in devices or systems for controlling vibration and noise. In addition to shear stress strength, another import performance index of MRF is its stability under long time static state. For most applied conditions, without hard agglomeration is more important than higher shear stress strength. However, up to now, only a few reports pay attention to evaluate method of MRF's settling. This make it is difficult to optimize manufacturing technique of MRF and study its principle. A novel testing instrument, which made based on theory of that varying magnetic particle's volume content of MRF would induce its correspondingly changing of magnetic conductivity, designed and fabricated. And settling state of several MRF were tested by that instrument, factors which influence accuracy of that instrument is also discussed. Research shows that, the novel settled and laminated testing instrument (NSLTI) is potential to be used to evaluate settling stator and monitor settling process of magnetic particles. Moreover, study also shows that strength of magnetic field, position of magnetic field sensor, sensitivity of Tesla meter, type of MRF and testing time may influence accuracy of NSLTI.
Due to their character of low power requirement, rapid-response and large force, the dampers that made based on the special rheologic performance of magnetorheological fluid (MRF) have shown to be one kind of ideal semi-active vibration control devices for civil engineering structures and vehicles. In this paper, the character of magnetic circuit of MRF damper was firstly studied; based on above results, a large-scale MRF damper whose adjustable multiple is about 16 and maximum damping force is about 170kN was then designed and tested. Experimental results show that, under lower electrical current, same or opposite of electric current direction of multi-coils winding on the piston do not influence damping performance of MRF damper; however, under higher electrical current, inverse connecting of adjacent coils is apt to improve damping force of MRF damper.
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