JP2013181090A - Magnetic particle-containing composite viscoelastic body, and variable rigidity type dynamic vibration absorber using the viscoelastic body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic particle-containing composite viscoelastic body excellent in changeability of viscoelasticity, and also to provide a variable rigidity type dynamic vibration absorber using the viscoelastic body.SOLUTION: A magnetic particle-containing composite viscoelastic body is formed by dispersing a magnetic particle having an average grain size of <50 μm in a viscoelastic material so as to become 20-70 vol% with respect to a composite elastic body, wherein after mixing the magnetic particle with the viscoelastic material, a magnetic flux having the intensity of a magnetic flux density of 50 mT or higher is applied to cure the mixture.

Description

  The present invention relates to a magnetic particle composite viscoelastic body whose viscoelastic characteristics are variable by an external magnetic field, and a variable stiffness type dynamic vibration absorber using the viscoelastic body.

Structural vibration control measures are classified into three measures: passive vibration control, semi-active vibration control and active vibration control.
Passive vibration control means something that does not require any input of energy such as electric power.
Semi-active damping means that the coefficient is dynamically changed when the vibration of a structure is expressed by a state equation.
Active vibration suppression means adding a new term when the vibration of a structure is represented by a state equation.
Among these, magnetic fluid (Magneto Rheological Fluid) is known as a vibration control method classified as semi-active vibration control.
The magnetic fluid disperses magnetic particles in a dispersion medium such as oil.
Although the surface of the magnetic particles is specially treated with a surfactant so that the magnetic particles do not aggregate, the dispersion medium is also a fluid. There is a problem of subsequent aggregation, and the fluid sealability becomes a problem when held in a predetermined shape.
Patent Document 1 discloses a magnetic fluid in which secondary aggregation is prevented by connecting magnetic particles having an average particle diameter of about 400 nm or less in a chain shape. However, the above problem caused by the dispersion medium being a fluid has been sufficiently solved. I can't say that.
Patent Document 2 discloses a variable elastic modulus material in which particles that are magnetically polarized by the action of a magnetic field are dispersed in a flexible polymer material so that the magnetic fluid does not have a specific shape and has formability. Is disclosed.
However, the elastic modulus variable material disclosed in the publication is obtained by dispersing iron powder having a particle size of 50 μm and 150 μm in a flexible polymer material.
Patent Document 3 discloses a magnetically responsive material in which a non-spherical magnetic particle is dispersed in a viscoelastic material so that the elastic modulus is variable when an external magnetic field is applied.
However, the magnetic particles disclosed in the publication must be in the form of needles, columns, rods, fibers, rectangles, or whiskers, and the elastic modulus is reduced by an external magnetic field.

Japanese Patent Laid-Open No. 2005-41896 JP-A-4-266970 JP 2008-195826 A

An object of this invention is to provide the magnetic particle composite viscoelastic body which is excellent in the variability of a viscoelastic characteristic.
Another object of the present invention is to provide a variable stiffness type dynamic vibration absorber using the magnetic particle composite viscoelastic body.

  The magnetic particle composite viscoelastic body according to the present invention is obtained by dispersing magnetic particles having an average particle diameter of less than 50 μm in a viscoelastic material so as to be 20 to 70% by volume with respect to the composite elastic body. After mixing the particles with the viscoelastic raw material, the particles are cured in a state where a magnetic field having a magnetic flux density of 50 mT or more is applied.

Here, the viscoelastic material includes both a thermosetting elastomer and a thermoplastic elastomer.
In view of easy dispersion-molding of the magnetic particles, the raw material composition for molding the elastomer is liquid and can be cured and molded after mixing the magnetic particles, and an elastomer having rubber elasticity is desirable after curing.
The rubber material is not particularly limited as long as it has rubber elasticity.
Silicone rubber is preferable in terms of excellent electrical characteristics, heat resistance, block resistance, weather resistance, and the like.
The silicone rubber is preferably a two-pack type silicone rubber because it has a one-pack type and a two-pack type, and the curing reaction proceeds uniformly with the surface and inside regardless of the thickness and shape of the molded body.
Moreover, RTV rubber which hardens | cures at room temperature can be used for silicone rubber.
The viscoelastic material according to the present invention includes a gelled material.

The magnetic particles are not limited as long as they have magnetic properties, such as iron, iron nitride, iron carbide, carbonyl iron, magnetic iron oxides, ferrites, nickel, cobalt, or cobalt iron alloys, magnetite, goethite, etc. Take as an example.
The reason why the average particle diameter of the magnetic particles is set to be less than 50 μm in the present invention is to facilitate the dispersion of the magnetic particles in the viscoelastic material.
Therefore, the magnetic particles are preferably substantially spherical.

  The reason for curing in the present invention in a state where a magnetic field having a magnetic flux density of 50 mT or more is applied is to allow a plurality of magnetic particles to form clusters in a chain shape.

The magnetic particle composite viscoelastic body according to the present invention (hereinafter referred to as MRE as required) changes its apparent rigidity by an external magnetic field, so that the magnetic particle composite and magnetic field generation for applying a magnetic field thereto A semi-active vibration damping device can be obtained with the means.
In this case, a variable stiffness type dynamic vibration absorber can be obtained by providing a function as a movable mass body with the magnetic particle composite viscoelastic body and the magnetic field generating means.
Here, the dynamic vibration absorber is intended to reduce the vibration of the main system structure by adjusting its natural frequency in the vicinity of the problematic frequency in the main system structure.
Since the magnetic particle composite viscoelastic body according to the present invention can vary its rigidity by an external magnetic field, the external magnetic field is strong against unsteady disturbances or disturbances with a frequency outside the design range. By changing the height, the natural frequency of the dynamic vibration absorber can be adjusted in a direction corresponding to the disturbance.

The magnetic particle composite viscoelastic body according to the present invention has a large change in rigidity when the viscoelastic characteristics are changed by an external magnetic field and the molded body is cured in a magnetic field having a magnetic flux density of 50 mT or more.
By combining such a magnetic particle composite viscoelastic body and a magnetic field generating means, it is possible to obtain a variable rigidity dynamic vibration absorber having a simple structure and high reliability.

The manufacturing method of a MRE sample is shown, (a) shows no magnetic field, (b) shows the state which applied the magnetic field. (A) shows the cross-sectional photograph of the sample manufactured in the state without a magnetic field, (b) shows the cross-sectional photograph of the sample manufactured in the state which applied the magnetic field. An evaluation system for static tests is shown. The displacement and stiffness change rate with respect to shear force are shown. The stiffness change rate when the thickness of the sample is changed is shown. The rigidity change rate when the blending ratio of iron powder is changed is shown. An evaluation system for a dynamic test is shown. The spring constant change by the presence or absence of the application of a magnetic field is shown. The spring constant change at the time of changing the mixture ratio of iron powder is shown. A variable stiffness control model is shown. Indicates the setting value of the simulation parameter. The simulation result is shown. A semi-active vibration suppression evaluation system is shown. The semi-active vibration suppression evaluation results are shown. A numerical model of a two-degree-of-freedom vibration system including a one-degree-of-freedom main vibration system and a variable stiffness type dynamic vibration absorber is shown. The schematic diagram of the variable rigidity type vibration vibrator which used MRE as a spring element is shown. (A) shows the measurement result of the change of the natural frequency of the dynamic vibration absorber with respect to the applied current, and (b) shows the damping ratio. Each parameter at each mass ratio is shown. The amplitude response of the main system when the natural frequency of the dynamic vibration absorber is tuned to the disturbance frequency for a mass ratio of 0.3 is shown. The response comparison of the dynamic vibration absorber for each mass ratio is shown. The system example of a variable-rigidity type dynamic vibration absorber is shown.

  The magnetic particle composite viscoelastic body according to the present invention was prototyped and evaluated, and will be described below. However, the present invention is not limited to this.

Two-part silicone RTV rubber is mixed with iron powder with an average particle size of about 10 μm, and the contents of 25 mm x 25 mm x H (10, 15, 20 mm) are sealed in a container and cured by holding at room temperature for 24 hours. did.
A schematic diagram of the obtained magnetic particle composite viscoelastic body (MRE) is shown in FIG.
The dispersion state of the magnetic particles 2 in the viscoelastic material is schematically shown.
During the progress of this curing reaction, both the state where no magnetic field was applied as shown in FIG. 1A and the state where a magnetic field was applied using a coil as shown in FIG. 1B were performed.
FIG. 2A shows an internal micrograph of a magnetic particle composite viscoelastic body (hereinafter referred to as MRE) obtained in the state of FIG. 1A, that is, in the absence of a magnetic field, and shows a magnetically cured MRE. An internal micrograph is shown in FIG.
What hardened | cured in the magnetic field formed the chain | strand-shaped cluster in the direction where the iron powder applied the magnetic field.
When a permanent magnet is used as a magnetic field application method, there is a problem that magnetic particles are attracted to the permanent magnet side.
Therefore, as shown in the present embodiment, a magnetic field is applied in a state where the forming container is disposed inside the coil, and the magnetic flux density is preferably 50 mT to 1 T.
In addition, as a procedure for mixing iron powder with two-pack type silicone RTV rubber, the main agent and iron powder are stirred and mixed, then added with a curing agent and further mixed, and then placed in a molding container, and a decompression device such as a vacuum chamber is installed. It is preferable to use and defoam the bubbles mixed in the raw material composition.
This is because if bubbles remain in the MRE, the stiffness variable control is affected.

Since the sample obtained by the above method was evaluated, it will be described below.
<Static test>
Using the evaluation system as shown in FIG. 3, the change characteristic of the restoring force in the shear direction with respect to the magnetic field was evaluated.
The applied current was changed from 0 to 2.0 A.
This change corresponds to a magnetic flux density of 0 to 62 mT.
The result is shown in the graph of FIG.
4 (a) and 4 (b) are graphs showing the displacement with respect to the weight in the shearing direction depending on the presence or absence of a magnetic field, and FIG. 4 (c) shows the change in rigidity in a graph.
As a result, the rigidity of the material cured in the magnetic field increased about three times at maximum.
FIG. 5 is a graph showing the results of investigation of changes due to the thickness of the sample.
As a result, it became clear that the influence of the sample thickness was small.
FIG. 6 shows the results of investigating the influence of the mixing ratio of iron powder.
As a result, the sample with a volume content of iron powder of 44% (substrate: iron powder = 10: 8) showed the largest change in rigidity.
From this graph, it was found that the volume content of iron powder should be in the range of 40 to 70%.
<Dynamic test>
A change in viscoelastic properties in the shear direction with respect to the magnetic field was evaluated using an evaluation system as shown in FIG.
The result is shown in the graph of FIG.
The dimensionless spring constant changed about 1.5 times when there was a magnetic field hardened in the magnetic field.
FIG. 9 shows a graph of the results of investigating changes due to the iron powder blending ratio.
As a result, the sample with an iron powder volume content of 44% showed the largest change in rigidity.

Based on the above results, application to semi-active vibration control was examined.
FIG. 10 shows a variable stiffness control model.
The result of setting the simulation parameters as shown in FIG. 11 is shown in the graph of FIG.
It can be understood that there is a vibration control effect by performing on-off variable control on the rigidity of the Low and High states.
Therefore, a vibration suppression evaluation experiment was performed using an evaluation system as shown in FIG.
Here, ~ 50 Hz random noise was input to the displacement excitation, the state of energization off was defined as rigidity Low, and the state of 2.0 A energization on was defined as rigidity High.
The evaluation results are shown in the graph of FIG.
From this, it was confirmed that there was a vibration control action by on / off control.

Next, the application to the dynamic vibration absorber was examined.
First, a two-degree-of-freedom numerical calculation model was constructed.
FIG. 15 shows a numerical model of a two-degree-of-freedom vibration system including a one-degree-of-freedom main vibration system and a variable stiffness type dynamic vibration absorber.
Regard spring element k ₂ of the dynamic vibration reducer, provide a variable resistance based on the measured value to be described later.
When the spring constant k ₂ is constant, the equation of motion of the vibration system with the symbol shown in Figure is described as follows.
Here, in defining the variable range of the dynamic vibration absorber natural frequency, it is easier to understand qualitatively using the non-dimensionalized equation of motion than to consider individually giving numerical values for mass, spring constant, etc. Equation (1) is made dimensionless with respect to time and displacement as follows.
However, each parameter of Formula (2) is as follows.

As a method for designing a dynamic vibration absorber to obtain a wide range of vibration damping effects, optimum tuning and optimum damping conditional expressions are well known.
Therefore, the response of the dynamic vibration absorber based on these design theories was used as a comparison object as a guideline for evaluating the performance of the variable stiffness dynamic vibration absorber.
The optimum tuning condition for determining the natural frequency ratio is expressed as follows, where the mass ratio is μ.
Further, the damping ratio ζ _{opt applied} to the dynamic vibration absorber is determined as follows as the optimum damping condition.

Next, a dynamic vibration absorber as shown in FIG. 16 was prototyped and evaluated.
A steel part was used for a frame portion having a width of 70 mm, a height of 60 mm, and a depth of 20 mm to form a closed magnetic circuit.
The central coil generates a magnetic field and has a movable mass (about 350 g) of the dynamic vibration absorber.
Two MREs according to the present invention having a diameter of 20 mm and a thickness of 10 mm are arranged above and below the coil, and the apparent rigidity changes when magnetic flux passes through the MRE.
As the MRE, an iron powder having a mean particle size of about 10 μm and an iron powder volume ratio of 50% was used.
In order to evaluate the basic performance of the variable stiffness type dynamic vibration absorber, changes in the natural frequency and damping ratio of the dynamic vibration absorber when current was applied to the coil were investigated.
The free vibration waveform when the dynamic vibration absorber of FIG. 16 was rigidly coupled to the base and an impact force was applied to the coil portion was measured.
A plurality of periods and amplitude ratios were read from adjacent peaks of the obtained waveform, and the natural frequency and damping ratio were obtained as average values.
The current value applied to the coil was set to 0 to 4 A in 0.5 A steps.
FIG. 17 is a plot of the dynamic vibration absorber natural frequency and the damping ratio with respect to the applied current.
The natural frequency increases to 29 Hz when 4 A is applied to 15 Hz in the absence of a magnetic field (approximately 1.9 times), and changes linearly in proportion to the current.
On the other hand, the damping ratio tends to increase with respect to the current, but the dependence on the magnetic field is small, and can be regarded as being constant at about 0.15.
Based on these measurement results, a constant value of 0.15 is given to the damping ratio of the dynamic vibration absorber in the following numerical studies, and the natural frequency ratio is to be treated as changing up to 1.9 times the reference value. It was.

Next, based on the dimensionless equation (2) and the above measurement results, numerically examined the damping characteristics of the variable stiffness type dynamic vibration absorber.
The mass ratio between the main system and the dynamic vibration absorber was set at three levels of 0.1, 0.3, and 0.5.
The frequency ratio range corresponding to the variable stiffness range for each mass ratio is shown in the table of FIG. 18 together with the values of optimum tuning and optimum damping.
The variable range was determined such that the frequency ratio when the dynamic vibration absorber mass was fixed to the main system was at the center of the variable range, taking into consideration the variable magnification of 1.9 times.
As a rigidity switching rule for variable dynamic vibration absorbers, the lowest value is maintained in the low range and the maximum value in the high range, and the natural frequency is changed in synchronization with the external force frequency in the variable range. It was.

FIG. 19 shows the result of numerically determining the amplitude response of the main system when the natural frequency of the variable stiffness type dynamic vibration absorber is synchronized with the disturbance frequency with respect to a mass ratio of 0.3.
For comparison, the response of a conventional dynamic vibration absorber during optimum tuning is also shown.
With a dynamic vibration absorber that applies optimum tuning and damping, the damping effect is limited by the height of the fixed point, but with the variable rigidity type, a response curve that follows the antiresonance point in the variable frequency range is drawn. It can be seen that the vibration can be clearly reduced.

FIG. 20 shows a comparison of the responses of variable stiffness type dynamic vibration absorbers for the three mass ratios.
When the mass ratio is μ = 0.1, the amplitude is generally lower than the response of the dynamic vibration absorber to which the optimum condition is applied, but the peak is conspicuous in the main system response.
If the mass is small even with the same damping ratio, it is considered that the amplitude near the antiresonance point cannot be sufficiently reduced.
On the other hand, the damping effect increases as the mass of the dynamic vibration absorber increases. However, since it is difficult to set a large mass ratio in practice, the mass of the MRE itself can be reduced or the mass can be reduced if the attenuation ratio remains as it is. A suitable ratio is considered to be around 0.2 to 0.3.

FIG. 21 shows a system example of a vibration damping device using the dynamic vibration absorber 10 according to the present invention.
In this example, the dynamic vibration absorber 10 is attached to the main vibration body, the vibration of the main vibration body is detected by an acceleration sensor or the like, and the signal value is converted by the control means to control the current value applied to the MRE.
The dynamic vibration absorber according to the present invention can be widely applied not only to structures but also to vibration control of moving bodies such as vehicles.

1 Viscoelastic material 2 Magnetic particle 10 Dynamic vibration absorber

Claims (3)

  Magnetic particles having an average particle diameter of less than 50 μm dispersed in a viscoelastic material so as to be 20 to 70% by volume with respect to the composite elastic body, and after mixing the magnetic particles with the viscoelastic raw material, the magnetic flux density A magnetic particle composite viscoelastic body which is cured in a state where a magnetic field having a strength of 50 mT or more is applied.   A vibration damping device comprising: the magnetic particle composite viscoelastic body according to claim 1; and a magnetic field generating means for applying a magnetic field to the magnetic particle composite viscoelastic body.   A variable stiffness type dynamic vibration absorber, wherein the magnetic particle composite viscoelastic body and the magnetic field generating means have a function as a movable mass body.