JP2001074627A - Material-testing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the influence of the inertia force of a movable part in a high-cycle bending test. SOLUTION: First, a selection part 13 is set to a side B, frequency is swept with a sinusoidal wave at a small, constant amplitude and at the same time a sample 1 is vibrated by displacement control, and a frequency where the output of a load sensor 6 reaches zero is obtained and is determined as a natural frequency f0 of a system. Based on the natural frequency f0, the frequency characteristics of the ratio of a load signal being applied to a sample to force being actually applied to the sample are determined, thus obtaining an attenuation ratio Δy of a load signal corresponding to a vibration frequency fx in a test. An operation control part 14 controls the amplitude of a vibration signal to be generated from a waveform generation part 15 so that the attenuation ratio Δy can be cancelled out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for testing a material, and more particularly, to a method and an apparatus suitable for performing a bending test on a large sample at a high cycle.

[0002]

2. Description of the Related Art A bending test is performed in which a sample is supported at two points, a load is applied in the middle thereof, and a bending moment is applied to the sample. Conventionally, this bending test was performed only in a static region, but recently, for saving test time,
A repetitive load of a predetermined frequency is applied to the sample, and the test is performed in a dynamic range.

FIG. 4 is a view showing a state of a bending test. In this figure, 1 is a sample (test piece), 2 is an actuator, and 3 is a servo valve. The actuator 2 is driven by the servo valve 3 to apply a force point 4 of the sample 1. Reference numeral 5 denotes a displacement sensor such as a piston displacement meter that detects the displacement of the piston of the actuator 2 (that is, the displacement of the sample 1), 6 denotes a load sensor such as a load cell that measures the load applied to the sample, and 7 denotes the displacement sensor. The control unit controls a drive signal supplied to the servo valve 3 so that an output or an output of the load sensor 6 becomes a predetermined value. In such a configuration, a drive signal is applied from the control unit 7 to the servo valve 3 so that the actuator 2
Is driven to apply the applied point of the sample 1. Then, a load signal corresponding to the force applied to the sample from the load sensor 6 and a displacement signal corresponding to the displacement of the sample from the displacement sensor 5 are observed.

[0004]

In performing such a bending test, when performing a so-called static test in which the load applied to the force applying point 4 is gradually increased, the measured value of the load sensor 6 is true. It can be said that the applied point load is measured. However, when the operation is performed in a high cycle by applying a high-frequency repetitive load, a difference is generated between the measured value of the load sensor that measures the force applied to the sample and the stress generated in the sample. This difference is due to the inertial force generated by the mass of the moving part and is a function of frequency. Therefore, there is a problem that the value obtained from the measurement value of the load sensor cannot be observed as a true stress from the viewpoint of the sample, and it is necessary to estimate the inertial force and correct the load cell observation value.

Accordingly, an object of the present invention is to provide a material testing method and apparatus capable of removing the influence of the inertial force of a movable portion and applying a desired stress to a sample.

[0006]

According to the present invention, there is provided a material testing method for applying a load to a sample using a target load signal having a predetermined frequency. As a target displacement signal, the sine wave of the amplitude is used to vibrate the sample while sweeping its frequency, and to obtain the natural frequency of the system by observing the load applied to the sample, based on the natural frequency, Calculating an attenuation value corresponding to the frequency; and exciting the sample using the target load signal of the predetermined frequency corrected in accordance with the attenuation value.

A material testing apparatus according to the present invention is a material testing apparatus for applying a load to a sample using a target load signal having a predetermined frequency, comprising: a waveform generator for generating a target load signal; An addition unit that calculates a difference between a target load signal from the generation unit and a signal from the displacement sensor or the load sensor, a load device that loads the sample based on an output of the addition unit, and a load applied to the sample. A load sensor for detecting, a displacement sensor for detecting displacement of the sample, and a target load signal from the waveform generator based on an attenuation of the load sensor output at the predetermined frequency calculated based on a natural frequency of the system. And an arithmetic processing unit for correcting the output.

[0008]

FIG. 1 is a block diagram showing the configuration of an embodiment of a material testing apparatus to which the material testing method of the present invention is applied. In this figure, a sample 1, an actuator 2, a servo valve 3, an applied point 4, a displacement sensor 5, and a load sensor 6 are the same as those shown in FIG. 4, and these constitute a testing machine section. .

In the control section, reference numeral 11 denotes a displacement amplifier for amplifying the output of the displacement sensor 5 and performing A / D conversion as necessary and outputting the amplified signal.
The load amplifier 13 amplifies the output of the load amplifier and A / D converts and outputs the output as necessary. The load amplifier 13 selects the output of the displacement amplifier 11 or the output of the load amplifier 12 and supplies it to the subtraction input of the adder 16. A selection unit 14 for supplying an arithmetic processing unit to which the output of the displacement amplifier 11 and the output of the load amplifier 12 are input and outputs a control signal to the waveform generation unit 15, A waveform generator for generating and outputting a target load signal waveform corresponding to the target load signal from the waveform generator 15 and the selector 1
An adding unit for generating a deviation signal from the output of the displacement amplifier 11 or the output of the load amplifier 12 supplied from the output unit 3;
Reference numeral 17 denotes a PID adjusting unit to which a deviation signal from the adding unit 16 is input and performs processing such as proportionality and integration.
The output of the D adjuster 17 is supplied to the servo valve 3 as a drive signal.

[0010] In the material testing apparatus thus configured, a feedback control system is configured as is apparent from the figure, and the selector 13 is connected to the A side to select the output of the load amplifier 12. When the output is connected to the B side and the output of the displacement amplifier 11 is supplied to the adder 16, the load feedback is provided.

The principle of the material test method of the present invention executed in the material test apparatus having such a configuration will be described. In the following discussion, it is assumed that the test is performed under the following conditions. (1) The operation waveform (target load signal waveform) of the tester is assumed to be a sine wave. (2) The test is performed with load feedback. (3) The resonance frequency of the mass and the spring constant is several times or more higher than the operation frequency (excitation frequency). (4) For high cycle operation, the hysteresis between load and displacement is small, and the test shall be performed in a region that shows almost apparent elastic behavior.

FIG. 2 is a diagram showing a mechanical model of the test device shown in FIG. 1 or FIG. In this figure, M is the mass of the movable part and cannot be observed directly. K is the spring constant of the sample, C is the viscous resistance, x
(t) is the displacement of the piston, and f (t) is the applied value applied to the sample. Here, if the hysteresis can be neglected as in the above (4), the viscous resistance C is a value that hardly exists (= 0).

The equation of motion of this model can be expressed by the following equation (1).

(Equation 1) The following equation (2) is obtained by Laplace transforming the equation (1) and expressing it in the s region.

(Equation 2) Also, the natural frequency (resonant frequency) ω ₀ (= 2π) of this system
f ₀ ) is represented by the following equation (3).

(Equation 3)

In equation (2), s = jω,
The horizontal axis represents the frequency ω normalized on the natural frequency ω ₀ (= 2πf ₀ ) of the system on a logarithmic scale, and the vertical axis represents 20 log | F (jω) / K ·
The frequency characteristic expressed by taking X (jω) | is expressed as shown in FIG. This figure shows frequency characteristics when C = 0. Here, F (jω) is the force detected by the load sensor (the force applied to the sample), K · X (jω)
(K is the spring constant, X (jω) is the output of the displacement sensor) indicates the force (stress) generated in the sample. Accordingly, assuming that the assumption of C ≒ 0 holds, the 周波 数 (K / M) in the equation (3) can be determined by obtaining the natural frequency f _0, and the equation (2), ie, FIG. The curve shown can be determined.

In the frequency characteristic of FIG. 3, ω≪ω ₀ (f
In the case of {f ₀ ), 20log | F (jω) / K · X (jω) |
It becomes almost 0 dB, and F (jω) becomes almost equal to K · X (jω). However, f in f <f ₀ is toward the _{f 0, 20log | F (jω} ) / K · X (jω) | value decreases rapidly. On the other hand, in the region of f> f ₀ , the value sharply increases.
When the vibration frequency of the sample when performing the bending test of high cycle was f _x, it is desirable that f _x «f _0, since in practice a f _x <f _0, shown in FIG. Δy cannot be ignored in practical use. Then, by vibrating the sample using the signal corrected with the value of Δy, it becomes possible to give the target stress K · X (jω) to the sample.

The material testing method of the present invention is based on the above considerations. First, the natural frequency f _{0 of the} system is obtained, and based on this, the frequency characteristic shown in the above equation (2), ie, FIG. determine the curve, based on this, obtains the correction amount Δy corresponding to the excitation frequency f _x used for testing. Then, the target load signal generated by the waveform generator 15 is corrected by the correction amount Δy and supplied.

First, in order to obtain the natural frequency f _{0 of the} system, according to the present invention, in the displacement feedback control state, the vibration is applied to the sample while increasing the excitation frequency by a sine wave having a constant small amplitude. The frequency at which the observed value of the load sensor output becomes zero or the minimum value is obtained. That is, in the block diagram shown in FIG.
Is switched to the B side, and the displacement signal is used as a feedback signal. The waveform generator 15 sweeps the small amplitude sine wave signal from a low frequency to a high frequency (or from a high frequency to a low frequency). Output. Then, the output of the load amplifier 12 at this time is observed,
A frequency at which the output becomes zero or the lowest value is obtained, and this frequency is determined as a natural frequency f _{0 of the} system. In this manner, the sample can be prevented from being damaged by driving with a small amplitude sine wave.

Next, the natural frequency f obtained in this way is
√ (M / K) is obtained from ₀ , and the above equation (2), that is, the characteristic curve shown in FIG. 3 is determined. Then, in the determined characteristic curve, determining the attenuation Δy corresponding to the excitation frequency f _x used for testing. Then, after switching the selector 13 in FIG. 1 to the A side and switching to the load feedback control, the waveform generator 15 generates a desired load target signal waveform and performs a test. At this time, the amplitude of the load target signal waveform output from the waveform generator 15 is corrected and output by an amount corresponding to the value of the attenuation amount Δy.

In practice, in the arithmetic control unit 14,
Using the equation (2) determined by the natural frequency f ₀ , an attenuation amount, that is, a correction amount Δy is calculated, and the waveform generator 1 is set so that the force K · X (s) generated in the sample becomes a target value.
The control signal for correcting the amplitude of the target load signal generated from the control signal 5 is output to the waveform generator 15. Thereby, a target stress (K · X (jω)) can be generated in the sample 1.

In the above description, the bending test has been described as an example. However, the material testing method and apparatus of the present invention are not limited to the bending test, but may be a test having an effect of an inertial force generated by the mass of the movable part. The same can be applied in the case of.

[0021]

As described above, according to the material testing method and apparatus of the present invention, when performing a high cycle operation, the influence of the inertial force generated by the mass of the movable portion is eliminated, and the high accuracy is achieved. A bending test can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an embodiment of a material testing apparatus to which a material testing method of the present invention is applied.

FIG. 2 is a diagram showing a mechanical model of a test machine section.

FIG. 3 is a diagram showing frequency characteristics of the mechanical model shown in FIG. 2;

FIG. 4 is a diagram for explaining a bending test.

[Explanation of symbols]

 Reference Signs List 1 Sample 2 Actuator 3 Servo valve 4 Force point 5 Displacement sensor 6 Load sensor 7 Control unit 11 Displacement amplifier 12 Load amplifier 13 Selection unit 14 Operation processing unit 15 Waveform generation unit 16 Addition unit 17 PID adjustment unit

Claims (2)

[Claims] 1. A material testing method for applying a load to a sample using a target load signal having a predetermined frequency, wherein the sample is vibrated while sweeping the frequency using a small amplitude sine wave as a target displacement signal. Obtaining a natural frequency of the system by observing a load applied to the sample, calculating an attenuation value corresponding to the predetermined frequency based on the natural frequency, and corresponding to the attenuation value. Vibrating the sample using the corrected target load signal having the predetermined frequency. 2. A material testing apparatus for applying a load to a sample using a target load signal having a predetermined frequency, comprising: a waveform generator for generating a target load signal; and a target load signal from the waveform generator. An addition unit that calculates a difference from a signal from a displacement sensor or a load sensor; a load device that loads a sample based on an output of the addition unit; a load sensor that detects a load applied to the sample; A displacement sensor for detecting a displacement of the load sensor; and an arithmetic processing unit for correcting a target load signal output from the waveform generating unit based on an attenuation amount of a load sensor output at the predetermined frequency calculated based on a natural frequency of the system. A material testing device comprising: