A novel shear thickening magnetorheological (STMR) damper with both speed locking and semiactive controlling properties was designed and fabricated based on multifunctional smart composite materials which was defined as magnetorheological Silly Putty (MRSP). The rate sensitive property and magnetorheological effect of MRSP samples were analyzed by using a rheometer to select the best filler for the STMR damper. The mechanical properties of the STMR damper were investigated through slow, fast, and dynamic experiments. The experimental results indicate that the STMR damper exhibits an obvious rate sensitive characteristic and semiactive control property. On one hand, when the STMR damper is simulated fast enough, it can realize the “speed switch” function, which enables it to instantly lock up and act as a shock transmission unit (STU). On the other hand, when the STMR damper is applied with current, the damping force can be adjusted by magnetic field strength to realize its semiactive controlling property. In addition, a multiparameter and symmetry model was established to describe the dynamic hysteretic behavior of the STMR damper, which is consistent with the experimental data.
Magnetorheological Silly Putty (MRSP) is a smart multifunctional composite prepared by dispersing soft magnetic particles into a Silly Putty matrix with shear stiffening property [
At this stage, the vibration damper based on a single magnetorheological material requires an external magnetic field, which belongs to the active device. Magnetorheological materials are widely used in all kinds of MR dampers, and the technology is relatively mature. Lord Company of USA and BASF Company of Germany have developed many commercialized MR dampers. For example, the RD-1005-type MR damper produced by Lord Company is the earliest application of the international commercialized MR damper with damping force over 2200 N [
The single shear thickening material is used as energy dissipation fillers for small passive ST dampers. Zhang et al. developed a speed-driven damper based on the shear thickening fluid and studied the dynamic performance of the ST damper through both experiment and theory methods [
The MR damper is the most mature energy dissipation device in the field of magnetorheological vibration damping. From the point of energy, the principle of the work is to change the energy spectrum of the vibration source’s excitation to the system and reduce the passed energy to suppress the vibration. However, in the face of huge incentive loads, the vibration damping, which the MR damper depends on, does not slow down the deformation or even destruction of civil engineering structures due to insufficient stiffness; besides, the mechanism of damping is relatively simple. In addition, these MR dampers all belong to active devices, which means that in the event of a circuit failure that cannot be controlled by a magnetic field, the damper loses the significance of the semiactive vibration control. The current solutions include setting a permanent magnet to make the magnetorheological fluid in the MR damper produce certain yield strength, but the scheme makes the design of the damper more complex. Furthermore, commonly used permanent magnets are made of NdFeB material with strong temperature instability, meaning that the higher the temperature, the faster the demagnetization. The shear thickening material is mainly used in caging devices, including all kinds of speed locking devices, in order to improve the overall stiffness of the structure and achieve the purpose of seismic resistance and vibration reduction. At the moment, researchers of the world only focus on the study of the mechanisms of magnetorheological damping and shear thickening damping respectively, and there is no intersection between each other. However, there are no relevant studies that combine the characteristics of two kinds of intelligent materials as a whole to explore new intelligent dampers with double vibration damping mechanisms.
In this work, a novel shear thickening magnetorheological (STMR) damper was designed and fabricated based on MRSPs. Compared with traditional MR dampers, the STMR damper not only exhibited controllable characteristics of damping force under the adjustment of the magnetic field but also provided a “locking” function under an unexpected sudden rare load, which was more suitable for the vibration control of large civil engineering structures. In order to verify the dual vibration damping characteristics of the STMR damper, slow, fast, and dynamic mechanical property experiments were carried out. Finally, a multiparameter and symmetry model was established and deduced to describe the dynamic hysteretic behavior of the STMR damper.
The Dow Corning 3179 dilatant compound, which was purchased from Dow Corning Co., Ltd., was used as the Silly Putty matrix. The composition of the Silly Putty matrix is outlined in Table
Composition of the Silly Putty matrix.
Composition | Weight percentage |
---|---|
Polydimethylsiloxane (PDMS) | 65 |
Silica | 17 |
Thixotrol | 9 |
Boric acid | 4 |
Glycerine | 1 |
Titanium dioxide | 1 |
Dimethyl cyclosiloxane | 1 |
The dilatant compound as matrix and the different volume fractions of CI as fillers were homogeneously mixed using a two-roll mill (Nantong Hailite Rubber Machinery Inc., China, XK-160 model) at room temperature. For the mechanical mixing method, up to six different volume fractions were considered for the present study: 0, 6.98, 10.11, 15.84, 20.80, and 27.29%. The prepared samples were marked as MRSP 0, MRSP 1, MRSP 2, MRSP 3, MRSP 4, and MRSP 5, in sequence. In this work, the dynamic rheological properties of the MRSP samples were carried out using a commercial rheometer (Physica MCR 302, Anton Paar Co., Austria). During the testing procedure, a parallel plate PP20 with a diameter of approximately 20 mm was used, and a gap of 1 mm was maintained at all times. At the same time, a controllable magnetic field was generated by an external coil. Besides, all the samples for the experiment were maintained at an approximately same volume value. The MRSP sample and MCR 302 rheometer are displayed in Figure
Preparation of (a) the MRSP sample and (b) the MCR 302 rheometer.
The structure of the STMR damper is shown in Figure
Basic structure of the STMR damper.
The STMR damper mainly consists of the main cylinder controlled by magnetorheology and the accessory cylinder with displacement decoupling characteristic. This novel damper not only maintains the performance of an adjustable damping force by magnetic field, but also possesses obvious rate sensitive characteristic which provides the function of locking structure to disperse loading under high frequency or impaction. The basic structural parameters of the STMR damper are listed in Table
Main structure parameter of the STMR damper.
Working gap of the main cylinder tube | 2 mm | Working gap of the accessory cylinder | 2 mm |
External diameter of the main piston | 156 mm | External diameter of the accessory piston | 156 mm |
Wall thickness of steel tube of the main cylinder tube | 15 mm | Wall thickness of steel tube of the accessory cylinder tube | 15 mm |
Piston’s stroke limit of the main cylinder tube | 65 mm | Piston’s stroke limit of the accessory cylinder tube | 65 mm |
Length of working gap of the main cylinder tube | 206 mm | Length of working gap of the accessory cylinder tube | 117 mm |
Piston’s number of windings of the main cylinder tube | 980 | Effective stroke of decoupling spring | 7 mm |
Diameter of piston rod | 50 mm | Maximum power | <120 W |
Piston’s current range of the main cylinder tube | 0∼3 A | Designed damping force | 300 kN |
The physical object of the STMR damper is displayed in Figure
Entity of the STMR damper.
The experimental setup of the STMR damper.
In the earlier research, when there was no external magnetic field applied, the soft magnetic particles of CI were evenly dispersed in the Silly Putty matrix to form isotropic viscoelastic materials [
Besides, from the earlier research, in order to compare the shear stiffening degree of the MRSP samples, the absolute shear stiffening effect (ASTe) and relative shear stiffening effect (RSTe) are defined as the index of measurement [
However, under the condition of an external magnetic field, the soft magnetic particles of the CI powder were arranged into chain-like ordered structures along the direction of the magnetic flux line in the interior of the shear stiffening matrix, forming the anisotropic structure. The pure shear stiffening matrix MRSP 0 sample was not influenced by the magnetic field due to the absence of soft magnetic particle fillings. Figure
The shear storage modulus of MRSP samples as a function of angular frequency at different magnetic flux densities. (a) MRSP 1, (b) MRSP 2, (c) MRSP 3, (d) MRSP 4, and (e) MRSP 5.
Similarly, the ASTe and RSTe indexes are implemented to illustrate the influence of magnetic flux density on the shear stiffening effect of the MRSP samples, and the relevant parameters are listed in Table
Samples | Magnetic flux density, |
|
|
|
|
---|---|---|---|---|---|
MRSP 1 | 0 | 0.287 | 0.00346 | 0.28354 | 8194.80 |
0.102 | 0.349 | 0.01620 | 0.33280 | 2054.32 | |
0.211 | 0.480 | 0.06410 | 0.41590 | 648.83 | |
0.321 | 0.566 | 0.10900 | 0.45700 | 419.27 | |
0.430 | 0.603 | 0.13400 | 0.46900 | 350 | |
0.533 | 0.618 | 0.14400 | 0.47400 | 329.17 | |
0.627 | 0.627 | 0.15000 | 0.47700 | 318 | |
|
|||||
MRSP 2 | 0 | 0.309 | 0.00531 | 0.30369 | 5719.21 |
0.102 | 0.383 | 0.03550 | 0.34750 | 978.87 | |
0.211 | 0.873 | 0.22900 | 0.64400 | 281.22 | |
0.321 | 1.060 | 0.37000 | 0.69000 | 186.49 | |
0.430 | 1.160 | 0.44000 | 0.72000 | 163.64 | |
0.533 | 1.190 | 0.45900 | 0.73100 | 159.26 | |
0.627 | 1.200 | 0.47100 | 0.72900 | 154.78 | |
|
|||||
MRSP 3 | 0 | 0.411 | 0.0131 | 0.39790 | 3037.40 |
0.102 | 0.924 | 0.2900 | 0.63400 | 218.62 | |
0.211 | 1.280 | 0.6690 | 0.61100 | 91.33 | |
0.321 | 1.500 | 0.9190 | 0.58100 | 63.22 | |
0.430 | 1.610 | 1.0400 | 0.57000 | 54.81 | |
0.533 | 1.670 | 1.0900 | 0.58000 | 53.21 | |
0.627 | 1.710 | 1.1300 | 0.58000 | 51.33 | |
|
|||||
MRSP 4 | 0 | 0.44 | 0.0228 | 0.41720 | 1829.82 |
0.102 | 1.24 | 0.366 | 0.87400 | 238.80 | |
0.211 | 1.90 | 1.19 | 0.71 | 59.66 | |
0.321 | 2.14 | 1.59 | 0.55 | 34.59 | |
0.430 | 2.24 | 1.77 | 0.47 | 26.55 | |
0.533 | 2.31 | 1.86 | 0.45 | 24.19 | |
0.627 | 2.31 | 1.92 | 0.39 | 20.31 | |
|
|||||
MRSP 5 | 0 | 0.51 | 0.0239 | 0.4861 | 2033.89 |
0.102 | 1.67 | 0.814 | 0.8560 | 105.16 | |
0.211 | 2.15 | 1.67 | 0.48 | 28.74 | |
0.321 | 2.29 | 1.95 | 0.34 | 17.44 | |
0.430 | 2.32 | 2.04 | 0.28 | 13.73 | |
0.533 | 2.33 | 2.08 | 0.25 | 12.02 | |
0.627 | 2.34 | 2.12 | 0.22 | 10.38 |
Under a continuously changing magnetic field, the soft magnetic particles are rapidly magnetized into dipoles and are arranged into chain-like ordered structures within the interior of the matrix until the magnetic saturation is achieved. Macroscopically, the continuous variation of the shear modulus of the MRSPs eventually reaches a steady state of saturation. The magnetorheological effect determines the directional controllable performance of the MRSPs, which is usually measured by the change of modulus. Currently, the research results indicated that the lower the loading frequency was, the higher the magnetorheological effect became, and the more the conducive it was to the adjustment of the magnetic field. However, the loading frequency was higher, the matrix modulus of MRSP became larger, the chain-like resistance of soft magnetic particles in the interior of the matrix became greater, and the magnetorheological effect tended to be lower [
The shear storage modulus of MRSP samples as a function of magnetic flux density at different shear strains. (a) MRSP 1, (b) MRSP 2, (c) MRSP 3, (d) MRSP 4, and (e) MRSP 5.
Samples | Shear strain, |
|
|
|
|
---|---|---|---|---|---|
MRSP 1 | 0.5% | 0.184 | 0.0666 | 0.1174 | 176.28 |
1% | 0.167 | 0.0619 | 0.1051 | 169.79 | |
5% | 0.119 | 0.0547 | 0.0643 | 117.55 | |
10% | 0.100 | 0.0393 | 0.0607 | 154.45 | |
|
|||||
MRSP 2 | 0.5% | 0.340 | 0.0796 | 0.2604 | 327.14 |
1% | 0.281 | 0.0692 | 0.2118 | 306.07 | |
5% | 0.169 | 0.0590 | 0.1100 | 186.44 | |
10% | 0.135 | 0.0398 | 0.0952 | 239.20 | |
|
|||||
MRSP 3 | 0.5% | 1.120 | 0.2770 | 0.8430 | 304.33 |
1% | 0.934 | 0.2390 | 0.6950 | 290.79 | |
5% | 0.484 | 0.1150 | 0.3690 | 320.87 | |
10% | 0.340 | 0.0498 | 0.2902 | 582.73 | |
|
|||||
MRSP 4 | 0.5% | 1.630 | 0.4020 | 1.2280 | 305.47 |
1% | 1.360 | 0.3530 | 1.0070 | 285.27 | |
5% | 0.735 | 0.2010 | 0.5340 | 265.67 | |
10% | 0.480 | 0.0669 | 0.4131 | 617.49 | |
|
|||||
MRSP 5 | 0.5% | 1.960 | 0.4340 | 1.5260 | 351.61 |
1% | 1.770 | 0.3660 | 1.4040 | 383.61 | |
5% | 0.907 | 0.2140 | 0.6930 | 323.83 | |
10% | 0.592 | 0.0843 | 0.5077 | 602.25 |
For the transverse comparison of the samples with different contents of soft magnetic particles, the larger the volume fraction of soft magnetic particles is, the greater the magneto-induced modulus becomes, and the more obvious the absolute magnetorheological effect tends to be. For MRSP 5 with the highest particle content, the magneto-induced modulus is up to 1.5 MPa at the strain of 0.5%. The relative magnetorheological effect is mainly determined by the initial shear storage modulus, from which it can be observed that, for loading conditions at small strains of 0.5% and 1%, the relative magnetorheological effect produced by the same sample varies with no obvious difference from each other. This is for the reason that within the strain of 1%, each group of MRSP sample is in the linear viscoelastic region, which displays no obvious difference of initial modulus. However, when the strain continues to climb up to 5% and 10%, respectively, the initial modulus sharply decreases outside the linear viscoelastic region, and in turn, the magnetorheological effect becomes quite different. Besides, the relative magnetorheological effect with strain of 10% is higher than that with the strain of 5%. With the increase in the content of CI powder, the relative magnetorheological effect tends to enhance. When the strain is 0.5%, the relative magnetorheological effect of MRSP 5 reaches 352% at most; nevertheless, if the shear strain increases to 10%, the relative magnetorheological effect of MRSP 4 reaches as high as 617%, and the adjustable range of the magnetic field is relatively wide. Consequently, it is beneficial to obtain great magnetorheological effect when the volume fraction of the soft magnetic particle is high.
By comparing the rate sensitive characteristic and magnetorheological effect of each MRSP samples, the MRSP 5 sample with high magnetorheological effect was finally selected as the filling material in the main cylinder tube of the STMR damper. Since there was no soft magnetic particles filled in MRSP 0 sample, due to its higher relative shear stiffening effect, it was regarded as the filling materials for the accessory cylinder tube of the STMR damper. For the STMR damper with the locking function, when the relative speed rate of the piston to the cylinder is slower than 1 mm/s, it is considered as a slow testing, but when the speed rate is greater than 1 mm/s, it is regarded as a fast testing. Firstly, in order to meet the requirements of the slow testing, the control rates were set constantly as 0.033 mm/s, 0.083 mm/s, 0.166 mm/s, 0.33 mm/s, 0.66 mm/s, and 0.83 mm/s, respectively. Figure
Division of the displacement-resistance region.
Relationship between velocity and spring stiffness.
The fast testing displays that the STMR damper can be instantaneously locked at a certain rate to transfer the designed load. According to AASHTO, when a fast testing is carried out, the locking distance should be within 12 mm [
The relationship between displacement and resistance force.
When the amplitude is within the range of the maximum compression of the butterfly spring, only the main piston of the STMR damper works. When the amplitude exceeds the maximum compression of the butterfly spring, the main and accessory pistons work together, resulting in a greater output of damping force. Since the interior of the STMR damper is filled by MRSPs with the rate sensitive characteristic, it is necessary to confirm the dynamic rate sensitive performance. So, the excitation frequency of 0.1 Hz, 0.5 Hz, 1.0 Hz, 1.5 Hz, and 2.5 Hz were, respectively, applied under a displacement of 5 mm. The experimental results are displayed in Figure
Relationship between the damping force and displacement for the STMR damper.
In order to validate the adjustable characteristic of the mechanical properties for the STMR damper under the effect of the magnetic field, the dynamic mechanical properties were investigated under different currents, during which the same displacement control was adopted, and each working condition was circulated for 10 times. The testing conditions were as follows: the displacement was 5 mm, the frequencies were 0.1 Hz, 0.5 Hz, 1.0 Hz, and 1.5 Hz, and a current of 0 A, 1 A, 2 A, and 3 A was applied in each case, respectively. When the displacement was 55 mm and the frequency was 0.1 Hz, a current of 0 A, 1 A, 2 A, and 3 A was similarly applied; nevertheless, when the input current increased in sequence, the magnetic flux density in the working gap of the STMR damper also enhanced and the damping force of the damper also correspondingly magnified as well. Figure
Relationship between damping force and displacement for the STMR damper at different frequencies and displacements: (a) 0.1 Hz, 5 mm; (b) 0.5 Hz, 5 mm; (c) 1.0 Hz, 5 mm; (d) 1.5 Hz, 5 mm; (e) 0.1 Hz, 55 mm.
As shown in Figure
In the structural vibration control, as the external excitation frequency is not enough to make the STMR damper induce the speed locking, it is given full play to the adjustment ability of the damper in the magnetic field, which indicates that the STMR damper can be simplified to a larger traditional MR damper.
The dynamic damping force of the STMR damper can be decomposed into a superposition of three components of force: the first component of force refers to applied force
The first component of force
The second component of force
The third component of force
Based on (
For the dynamic mechanical properties of the STMR damper, it can be considered that the shear storage modulus of the MRSPs contributes to the stiffness part of the device structure, whereas the damping characteristic of the material contributes to the damping part of the device structure. Consequently, in (
The displacement hysteresis phenomenon of the STMR damper is caused by the subitem
Therefore, according to (
As a result, the stiffness coefficients
Marquardt algorithm was adopted to carry out the parameter identification on the damping mechanical model of the STMR damper. Low frequency and small displacement experimental data were selected, among which the excitation frequency was 0.1 Hz, the amplitude was 5 mm, and the current input was 0 A, 1 A, 2 A, and 3 A, respectively. From the experimental data, it can be perceived that the lagging displacement in both positive and negative directions is 2 mm, whereas 14 parameters based on the symmetric dynamic hysteretic mechanical model were identified. The identification results are listed in Table
Results of the parameter identification.
Parameters |
|
|
|
|
---|---|---|---|---|
|
−0.15 | −0.00049 | 5.35 | −48.87 |
|
33.59 | 5.85 | −13.03 | 29.70 |
|
−57.71 | −82.02 | 14.16 | −1.03 |
|
0.45 | 0.022 | 0.25 | −0.14 |
|
−0.43 | 0.027 | −0.34 | 0.09 |
|
−45.23 | 238.50 | 61.14 | 307.36 |
|
143.15 | 0.31 | 65.55 | −93.70 |
|
0.00083 | 0.94 | 2.01 | −1.45 |
|
23.20 | 60.74 | 2.55 | 26.09 |
|
1.23 | 1.35 | 0.38 | 1.02 |
|
0.033 | 0.022 | 0.50 | 0.01 |
|
0.033 | 0.022 | 0.50 | 0.01 |
|
1 | 1 | 1 | 1 |
|
0.40 | 0.40 | 0.40 | 0.40 |
The relationship between the model curve and experimental data of the STMR damper.
In this work, a novel STMR damper with rate sensitive characteristic (speed locking) and semiactive controlling property was designed and fabricated based on multifunctional composite MRSPs. Both the mechanical properties of MRSPs and the STMR damper were experimentally investigated. Firstly, the MRSP 5 and MRSP 0 samples exhibited the best magnetorheological effect and relative shear stiffening effect, respectively, which were chosen as the fillers of the main cylinder and accessory cylinder. Secondly, through slow and fast experiments, the STMR damper presented an obvious rate sensitive property and realized the speed locking function in a short time and distance when external excitation rate was fast enough. Besides, dynamic experiment results indicated that the damping force of the STMR damper could be controlled by the excitation frequency and the applied magnetic field. Finally, a multiparameter and symmetry hysteretic model was proposed to describe the dynamic hysteretic behavior of the STMR damper, which agreed well with the experimental data.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This work was supported by Primary Research and Development Plan of Jiangsu Province (Grant no. BE2017167); Natural Science Foundation of Zhejiang Province (Grant no. LY15E080015); National Natural Science Foundation of China (Grant no. 51508237); Natural Science Foundation of Jiangsu Province (Grant no. BK20140560); and Research Foundation for Advanced Talents of Jiangsu University (Grant no. 14JDG161).