JPH0545270A - Repetitive fatigue testing device - Google Patents

Abstract

PURPOSE:To provide a repetitive fatigue testing device, with which the max. strain signal value of a load cell is made constant through changing of the alternate voltage value to be impressed on electrostrictive element layers, and equip the device with possibility of driving with resonance frequency. CONSTITUTION:A fatigue testing device is furnished with a display device 30 to indicate the alternate voltage value to be impressed on electrostrictive element layers 5a, 5b. It is made practicable to check the alternate voltage value so as to enable selecting the frequency (resonance frequency) at which the voltage value in checking minimizes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cyclic fatigue test apparatus for inspecting the strength of ceramic test pieces and the like.

[0002]

2. Description of the Related Art In a cyclic fatigue test of a ceramic test piece or the like, one surface is held at two points, the other surface is held at the center, and a three-point bending test in which a dynamic load is applied from one surface side There is a method of measuring bending fatigue. Conventionally, in the cyclic fatigue test apparatus used in this method, a mechanical linear reciprocating drive mechanism such as a piston and a cylinder is used as a drive source, and a dynamic load is applied from one surface side of the test piece. By the way, in such a conventional configuration, it is troublesome to adjust and change the driving force, a driving force of high frequency cannot be generated, a large driving sound is generated, and further mechanical friction causes mechanical friction. Wear is severe,
There were drawbacks such as difficulty in keeping the test conditions constant.

Therefore, as shown in FIG. 5, a diaphragm a having an electrostrictive element layer c disposed on at least one surface of a curved plate b.
One end or both ends of the test piece p are supported on the base d, and the holding member e for the test piece p is attached to the swinging surface of the diaphragm a, and the test piece p is held on the holding member e by the holding member e. It has been proposed that a load cell f provided with a test piece pressing end g for sandwiching is provided (Japanese Patent Application No. 62-250208).

In such a structure, when an alternating voltage of a predetermined frequency is applied to the front and back electrodes of the electrostrictive element layer c, bending vibration is generated in the bending plate b. Along with this, the holding member e supported on the swing surface of the diaphragm a vibrates. Therefore, one surface is supported by the holding member e and the other surface is pressed by the pressing end g.
The test piece p held by means of the vibration of the holding member e,
As shown in FIG. 6, a dynamic load based on a voltage having a predetermined resonance frequency is applied, and eventually damage occurs. At this time, the strength of the test piece can be detected by measuring the speed of failure and the frequency of the dynamic load.

Therefore, in this structure, by repeatedly selecting the alternating applied voltage to the electrostrictive element layer c, the repetitive stress and the cycle thereof can be adjusted, and various test conditions can be arbitrarily set. Further, unlike the conventional means for applying a dynamic load by the mechanical linear reciprocating drive mechanism, there is an advantage that the generation of noise and wear due to mechanical friction are small and it is easy to maintain the same test condition.

With such a construction, when inspecting the strength of the test piece p in a high temperature atmosphere, if strain is applied by high temperature creep, the entire apparatus will be stretched or the test piece will be gradually deformed. By the way, the bending stress (center value of bending stress in FIGS. 3 and 6; F _mean ) in the state where no voltage is applied to the electrostrictive element layer c applied to the intermediate position of the test piece p is as shown in FIG. The screw rod h screwed to the frame i is manually moved up and down to determine the position of the pressing end g thereof.
The pressing end g is a fixed point. Therefore, when the test piece p is deformed as described above, since the initially set position of the pressing end g is a fixed point, the center value F _mean of the bending stress waveform is gradually increased as shown by the chain line in FIG. The maximum value F _max becomes smaller than the initial value. For this reason, there is a drawback that stable test results cannot be obtained.

[0007]

In order to eliminate the above-mentioned problems, the maximum strain signal value from the load cell is compared with a predetermined strain signal value set in advance. It has recently been proposed by the present inventors to provide a voltage control means for increasing the alternating voltage value applied to the layers. In this configuration, when the repeated fatigue test is performed in a high temperature atmosphere, the entire device is stretched due to high temperature creep and the test piece p is plastically deformed, and the bending stress of the solid line of FIG. The median value F _mean of F falls. Along with this, the maximum strain signal value from the load cell also decreases. Therefore, the predetermined strain signal value f _max of the load cell is held in advance and compared with this value. If it is smaller than this value, the alternating voltage value applied to the electrostrictive element layer is increased to increase the vibration of the diaphragm. The amplitude becomes large. Therefore, the maximum strain signal value F _max from the load cell approaches the predetermined strain signal value f _max , and finally becomes equal to this as shown by the chain line in FIG. Thus, since the maximum strain signal value F _max is always corrected to the predetermined strain signal value f _max , the same dynamic load is applied to the test piece, and an accurate test result can be obtained.

In the conventional structure shown in FIGS. 5 and 6, the alternating voltage value applied to the electrostrictive element layer is always constant as shown in FIG. The bending vibration is generated in the bending plate b by the maximum distortion signal value of, that is, the frequency (resonance frequency) that generates the maximum amplitude. As described above, in such means, since the bending frequency is generated in the bending plate b by the resonance frequency, it is possible to efficiently apply the voltage.

By the way, as described above, in the structure in which the alternating voltage value is changed and corrected to the predetermined distortion signal value f _max , the theoretical resonance frequency is previously calculated from the spring constant of the diaphragm and the frequency adjustment weight. Although the index is calculated and the resonance frequency is tested and detected in advance, in the actual test condition, an error occurs with the resonance frequency set in advance by the above-mentioned means, and this error is It cannot be confirmed by the signal value from the load cell as in the conventional configuration described above. Therefore, a high voltage is unnecessarily applied to the electrostrictive element layer, and overcurrent flows, power is consumed, and deterioration of polarization is accelerated to shorten the life of the piezoelectric bimorph. Occurs. The present invention aims to solve such technical problems.

[0010]

The present invention compares a maximum strain signal value from a load cell with a predetermined strain signal value set in advance, and if the maximum strain signal value is less than this, an alternating voltage applied to an electrostrictive element layer is compared. It is characterized in that it is provided with a voltage control means for increasing the voltage value, and is provided with a display device for displaying an alternating voltage value applied to the electrostrictive element layer.

[0011]

The function is most efficient when bending vibration is generated in the diaphragm at the resonance frequency. Therefore, as shown in FIG. 4, when the maximum distortion signal value is constant, the resonance frequency is at the lowest alternating voltage value. Therefore, by providing a display device for displaying the alternating voltage value, it becomes possible to adjust the applied frequency to a resonance frequency, and it is possible to vibrate the diaphragm so as to generate a predetermined maximum strain at the lowest alternating voltage. It will be possible.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. Reference numeral 1 denotes a base having an elastic support material 17 such as soft rubber, sponge, and metal spring disposed on the lower surface thereof, which is fixed to the installation surface 18 in a semi-floating manner. A vibration plate 2 having a bimorph structure serving as a drive source is supported on the base 1 in a cantilever manner at one side by a support shaft 3a screwed to the base 1 and a nut 3b. The diaphragm 2 is, as shown in FIG.
Electrostrictive element layers 5a and 5b having electrodes on the front and back are provided on the upper and lower surfaces of the rectangular curved plate 4, and a weight 6 is fixed to the other side of the curved plate 4. ing.

The electrostrictive element layers 5a and 5b are polarized in opposite directions, their outer electrodes are connected to the power supply generator 15, and their inner electrodes are grounded via the curved plate 4, and the voltage is applied thereto. The wiring is such that when one expands, the other contracts. As shown in FIG.
As shown in, a sample holding member 7 having two support ends 8 located in the width direction is provided on the upper portion. A loadle 12 supported by a screw rod 11 screwed onto a machine frame 14 is disposed above the vibrating plate 2, and a lower end of the load cell 12 is provided between the support ends 8 of the sample holding member 7. There is provided a sample pressing end 13 which is located at the position a and contacts the upper surface of the test piece p.

In the above-mentioned structure, the test piece p is mounted on the supporting ends 8 of the sample holding member 7, and the screw rod 11 is manually rotated and moved up and down to bring the screw rod 11 to an appropriate position. It descends and the pressing end 13 is brought into contact with the test piece p between the supporting ends 8 to support it at three points. At this time, when the screw rod 11 is slightly lowered from the proper position, the elastic support member 17 arranged on the lower surface of the base 1 is compressed and the vibrating body 2 and the base 1 are displaced downward. The test piece p is always held with a constant pressing force without breaking. After that, the electrostrictive element layers 5a, 5
An alternating voltage having a predetermined resonance frequency is applied from the power source generator 15 to b.

As a result, strain is generated in the electrostrictive element layers 5a and 5b, and the other piece is held by the inertial force of the weight 6 to generate bending vibration. Then, the test piece p is pressed from below on both sides by the up-and-down movement of the supporting ends 8 and 8 due to the bending vibration, and bending strain is periodically imparted around the pressing end 13. And this fatigue causes fatigue,
Eventually, it will be damaged, and by measuring the time until this damage, the applied voltage, the number of times of bending, etc., it becomes possible to measure the strength such as the transverse rupture force of the sample p.

The cyclic fatigue test apparatus is provided with voltage control means for controlling the value of the alternating voltage output from the power source generator 15. The configuration will be described below.

The voltage control means includes the power source generator 1.
5, distortion amplifier 20, reference voltage setting device 21, comparator 22 and the like. That is, the distortion voltage signal from the load cell 12 is amplified by the distortion amplifier 20, and the maximum distortion signal value F _max is extracted from this. This maximum distortion signal value F _max is displayed on the display 23 and its value can be confirmed. On the other hand, a predetermined distortion signal value f _max is set in advance in the reference voltage setter 21, and the maximum distortion signal value F _max is compared with the predetermined distortion signal value f _max by the comparator 22. Information is input to the generator 15, the applied alternating voltage is amplified, and a larger voltage is applied to the electrostrictive element layer 5.
applied to a and 5b, a large amplitude is generated in the diaphragm 2,
The strain applied to the test piece p increases. Therefore, the maximum distortion signal value F _max becomes high, and by repeating the above steps, the maximum distortion signal value F _max matches the predetermined distortion signal value f _max .

As described above, since the above-mentioned voltage control means is provided, the strain applied to the test piece p is adjusted so that the maximum strain amounts become equal in the above-mentioned configuration.
Even if the fatigue applied to the test piece p becomes equal, the test piece p is deformed by the high temperature creep, and the center value F _{mean of the} bending stress falls below the initial value of the solid line in FIG. The maximum distortion signal value F _max becomes constant because the waveform is amplified like a three-dot chain line. Therefore, the maximum strain amount applied to the test piece p becomes equal, and it becomes possible to obtain a good test result under the same dynamic load. The predetermined distortion signal value f
_max is the initial maximum strain signal value F when the sample p is mounted
_Max may be input, and in this case, the initial maximum distortion signal value F _max can be maintained even in a high temperature state. This is achieved by manually inputting the initial value shown on the display 23 to the reference voltage setting device 21, or by making it possible to automatically set the initial value by an input operation of the initial setting switch. ..

By measuring the time, the applied voltage, the number of times of bending, etc., which lead to such damage, the strength of the test piece p, such as the transverse rupture force, can be properly measured.

On the other hand, a display device 30 including a voltmeter for displaying the value of the applied alternating voltage to be output is connected to the power generation device 15 so that the applied voltage is constantly displayed. Therefore, the frequency of the alternating voltage generated from the power supply generator 15 is adjusted so that the applied alternating voltage becomes the lowest. The frequency of this minimum value becomes the resonance frequency. For this reason, the electrostrictive element layers 5a and 5b are driven at the resonance frequency so as to generate a predetermined maximum strain at the lowest applied voltage. Therefore, the lowest alternating voltage is applied, resulting in power consumption. Is small and deterioration of polarization can be suppressed as much as possible.
The life of 5b can be extended. In addition, although the present invention is particularly useful for a three-point bending test, it is also suitable for a test mode in which the entire circumference of the test piece p is held by a supporting edge and the pressing end is brought into contact with the center of the test piece p. obtain.

[0021]

As described above, according to the present invention, the predetermined strain signal value of the load cell is held in advance and compared with this value. When this is small, the alternating voltage applied to the electrostrictive element layer is applied. The amplitude of the diaphragm is increased by increasing the value to make the maximum strain amount applied to the test piece p equal, and the alternating voltage value applied to the electrostrictive element layer by the display device is confirmed. Therefore, it is possible to select the frequency (resonance frequency) that minimizes the voltage value, which makes it possible to efficiently apply bending vibration to the diaphragm at such resonance frequency and reduce power consumption. In addition, there is an excellent effect that the service life of the diaphragm can be extended.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a stress waveform diagram according to the present invention.

FIG. 4 is a waveform diagram showing the relationship between the maximum distortion signal value F _max , the applied voltage, and the frequency according to the present invention.

FIG. 5 is a schematic side view of a conventional configuration.

FIG. 6 is a stress waveform diagram according to a conventional configuration.

FIG. 7 is a waveform diagram showing the relationship between the maximum distortion signal value F _max , the applied voltage, and the frequency according to the conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 substrate 3 vibrating plate 4 curved plates 5a, 5b electrostrictive element layer 12 load cell 15 power supply generator 20 strain amplifier 21 reference voltage setting device 22 comparator 30 display device p test piece

Claims (1)

[Claims] 1. A vibrating plate having an electrostrictive element layer disposed on at least one surface of a curved plate, holding one or both ends of the vibrating plate on a base, and further mounting a sample holding member on the moving surface of the vibrating plate. Mounting, on the sample holding member, provided with a load cell for sandwiching the test piece with the holding member, further comparing the maximum strain signal value from the load cell with a preset strain signal value,
If it is less than this, the voltage control means is arranged to increase the alternating voltage value applied to the electrostrictive element layer, and an alternating voltage of a predetermined frequency is applied to the electrostrictive element layer to bend the diaphragm. A repetitive fatigue test apparatus configured to generate vibration, comprising a display device for displaying an alternating voltage value applied to the electrostrictive element layer.