JPH0363543A - Material testing machine - Google Patents

Abstract

PURPOSE:To reduce a correction cost and to improve the correction accuracy by correctly rewriting in advance a load-deflection characteristic curve for a load frame in to plural approximate functions and correcting a load- displacement characteristic of a specimen to be tested with the use of these approximate functions. CONSTITUTION:Form the load and deflection data measured at the time when the load frame LF is loaded without the specimen to be tested, the plural approximate functions divided in accordance with a shape of the load-deflection characteristic curve are obtained by arithmetic means 34. These calculated approximate functions are stored in storage means 35. Then, these approximate functions stored in the storage means 35 are selected in accordance with a detected load of displacement, and the load-displacement characteristic of the specimen SP to be tested is corrected in accordance with these selected approximate functions. The load-displacement characteristic for the object in which a deflecting portion of the load frame LF is excluded, can be accurately measured accodingly. With this arrangement, the correction adaptable to the load- displacement characteristic for every testing condition can e accurately made at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a material testing machine that accurately measures the load-displacement characteristics of a specimen.

B. Conventional technology Conventionally, for example, a 4J (shaped body) is installed in a load frame consisting of a pair of supports erected on a table and a crosshead is placed horizontally thereon, and the load cell and pulse encoder are connected while loading the specimen. A material testing machine that measures load and displacement using methods such as the above is known.

Furthermore, the load frame of the material testing machine described above is itself deformed by the load and has a certain load-deflection characteristic, so the measurement results include the deflection of the load frame as an error. This error can be reduced to a negligible level by increasing the rigidity of the load frame, but increasing the rigidity increases the load frame's size and weight, which is undesirable.

Therefore, in the past, all the data of the deflection characteristic curve against the load of the load frame was stored in advance in the internal memory of the material testing machine control section, and then the specimen was set in the load frame and the test specimen was actually tested. When measuring load and displacement, the displacement is corrected using load frame data in memory to obtain load-displacement characteristics of the specimen that do not include the amount of deflection of the load frame.

C9 Problem to be Solved by the Invention However, in the conventional material testing machine as described above, all the data of the deflection curve against the load of the load frame is stored in the memory, so the correction data required to correct the displacement of the specimen is The amount of correction data becomes enormous, necessitating a large capacity memory, and if a ROM is used as a memory for correction data, it takes a lot of time to rewrite and update the data, making it impractical.

In addition, because the material of the specimen changes, or the test conditions for the same specimen change in various ways, we prepare various memories that store the deflection data of the load frame corresponding to each of these test conditions. This further increases the memory capacity and memory cost. Therefore, there is a problem that it becomes impossible to cope with an increase in test conditions.

A technical object of the present invention is to perform corrections suitable for the load-displacement characteristics for each test condition at low cost and with high accuracy.

The present invention will be explained with reference to FIG. 1 showing an embodiment of means for solving the problems of 96.
The material testing machine according to the present invention includes a load frame 10 for placing a specimen between a pair of opposing members and applying a load, an actuator 10e for loading this specimen, and a load on the specimen sp. The load detection means 1 includes a load detection means 12 and a displacement detection means 13 for detecting the displacement of the specimen sp.
The present invention is applied to a material testing machine that determines the load-displacement characteristics of the specimen SP based on the load detected by 2 and the displacement detected by the displacement detection means 13. And the technical issues mentioned above.

A load is applied to the load frame 10 without the specimen SP installed, and the load detected by the load detection means 12 and the displacement detection means 13
a calculation means 34 for converting the load-deflection characteristic curve obtained from the detected displacement into a plurality of approximate functions according to the shape of the curve; and a storage means 35 for storing approximate function data obtained by the calculation means 34. , the load-displacement characteristics detected by the load detection means 12 and the displacement detection means 13 when the specimen SP is loaded are corrected by selecting one of a plurality of approximation functions based on the detected load or displacement. This problem can be solved by providing a correction means 21 that performs the correction.

The E1 action calculating means 34 calculates approximate functions divided into a plurality of parts according to the shape of the load-deflection characteristic curve from the load and deflection data measured when the load frame is loaded without a specimen. This calculated approximation function is stored in the storage means 35. Then, the approximation function stored in the storage means 35 is selected according to the detected load or displacement, and the load-displacement characteristic of the specimen sp is corrected based on the selected approximation function. Therefore, it is possible to accurately measure the load-displacement characteristics of the specimen from which the deflection of the load frame LF has been removed.

In the above-mentioned sections and section E, which describe the present invention in detail, figures of embodiments are used to make the present invention easier to understand, but the present invention is not limited to the embodiments.

F. Embodiment FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the same figure, 10 is a testing machine main body that applies a compressive load (or tensile load) to the specimen SP, and this testing machine main body 10
is equipped with a load frame LF.

The load frame LF has a yoke 'Oa horizontally suspended over the upper ends of a pair of screw rods 10k and 10m erected on a table 10d, and a crosshead 1 at 10m on the screw rods 10.
0b screwed together. A load motor 10e is installed on the table lod, and the rotation of this motor 10e is transmitted through a transmission 11 to a pair of screw rods 10k and 10m.
is transmitted to the screw rod 10, and the crosshead Ob is raised and lowered by a rotation of 10 m.

The crosshead 10b is provided with an upper grip 10c via a load cell 2, and the table lod is provided with a lower grip LOf. (2) 3 is a pulse encoder for detecting the displacement of the specimen SP, which is the rotation of the transmission 11 or the screw rod 10k.

Outputs pulses corresponding to 10m rotation.

The control system that controls the testing machine main body 1o includes a control circuit 21 that controls the whole and also functions as a means for performing correction calculations of load-displacement data, which will be described later, and load and deflection data of the load frame LF,
A RAM-configured memory 22 temporarily stores the load and displacement data when the specimen SP is set and loaded in the load frame LF, and various data of the compression test (or tensile test) (maximum elongation, maximum shrinkage, an operating section 23 for inputting data such as expansion/contraction speed), a counter 25 for performing counting operations according to pulses output from the pulse encoder 13, and an F for converting the output pulse frequency of the pulse encoder 13 into voltage.
/V conversion circuit 26 and speed setting section 24 in the control circuit 21
It has an adder 27 that calculates the deviation between the generated voltage pattern waveform and the output voltage of the F/V conversion circuit 26, and a motor control circuit 28 that controls the speed, that is, the rotational speed of the motor 10e in accordance with this deviation signal.

The pulse encoder 13 outputs pulses with a frequency corresponding to the rotational speed of the motor 10e that is decelerated by the transmission 11.

Therefore, this pulse output is a pair of screw rods l Q k, 1
This corresponds to the rotation speed of 0 m, that is, the displacement of the specimen SP, and the control circuit 21 can know the amount of displacement given to the specimen SP by taking in the number of pulses counted by the counter 25.

A speed setting section 24 in the control circuit 2 generates a voltage pattern waveform for setting the rotation speed of the motor 10e based on the various data input from the operation section 23.9 This voltage pattern waveform is generated by an adder 27. Then, the deviation from the output of the FV conversion circuit 26, that is, the voltage corresponding to the current rotational speed of the motor 10e, is determined, and the deviation signal is inputted to the motor control circuit 28. The motor control circuit 28 controls the motor 10e so that the difference between a certain instantaneous value of the voltage pattern waveform and the voltage corresponding to the current rotation speed becomes zero.

In addition, the control system of the material testing machine described above includes the load cell 12.
an amplifier 29 that amplifies the load signal detected by the amplifier 2;
An A/D (analog-digital) converter 30 that converts the amplified output (analog signal) of 9 into digital data, a recorder 31 that outputs a graph of the load-displacement characteristics of the specimen sp, and an output from the control interface v121. A D/A converter 3 converts the digital data to voltage and inputs it to the recorder 3■
2 and a CRT (cathode ray tube), the control port vI21
a display device 33 for displaying the processing results and for graphically displaying the load-deflection characteristics of the load frame LF or the load-displacement characteristics of the specimen SP based on the load and deflection data stored in the memory 22;

By operating the operation unit 23, the cursor generated on the screen of the display device 33 is moved along the load-deflection characteristic curve of the load frame LF displayed on the display device 33, and the approximate curve range of the load-deflection characteristic is displayed. An arithmetic circuit 34 that specifies each inflection point and calculates an approximation function from data in each approximate curve range using the least squares method, and an external memory such as a floppy that stores the approximation function obtained by this arithmetic circuit 34 through the control circuit 21. 35.

The load signal of the load cell 12 is amplified by the amplifier 29 and A/
The data is converted into digital load data by the D converter 30 and input to the control circuit 21 . The control circuit 21 includes a counter 25
Since the displacement given to the load frame LF and the specimen SP can be known from the count value of , the load - Measure displacement characteristics.

Next, the operation will be explained.

First, the load-deflection characteristics of the load frame LF are measured without the specimen sp installed. FIG. 2 is a flowchart showing a processing procedure for determining an approximate function for correction from the load and deflection (displacement) due to the load on the load frame LF.

First, under the control of the control circuit 21, a predetermined voltage pattern waveform set according to the test conditions (maximum compression, speed) is output from the speed setting section 24, and the rotation speed of the motor 10e is controlled according to this voltage pattern waveform. Then, in step S2, the count value (displacement amount) counted by the counter 25 and the load value detected by the load cell 12 are taken into the control circuit 21 at a predetermined sampling period, and the load is Load of frame LF -
Measure displacement characteristics. The measurement result data is stored in memory 2.
Based on this stored data, the load-displacement curve of the load frame LF having the characteristics as shown in FIG. 3 is displayed on the screen of the display device 33 (step S3). Once the measurement of
The control circuit 21 is set to approximate function calculation mode using the operation unit 23, and then a cursor 36 is generated on the screen of the display device 33, and this cursor 36 is moved on the load-displacement curve 37 in the direction of the arrow in FIG. Then, the approximate curve range of the characteristic curve 37 is specified for each inflection point (step S4).

For example, in the case of the characteristic curve shown in Fig. 3, the quadratic interval number y=
Since it consists of two approximate quantity lines: ax''+b and linear interval number y=cx0d, when specifying the range of these approximate curves, first operate the keys on the operation unit 23. The cursor 36 is moved from the point of zero displacement in the direction of the arrow along the characteristic curve and stopped at a point slightly over the inflection point 38 of the one-sided line.This allows the two-function number y=a x+
The range [1 of the first approximate curve corresponding to b is specified. In addition, when specifying the range ■ of the second approximate curve, move the cursor 36 upward along the curve of the linear interval y=c x+d from a point slightly below the inflection point 38, and at the end point This is done by stopping.

In this way, approximate curve range 1. When II is specified,
The calculation means 34 calculates the load frame L stored in the memory 22.
From the load-displacement (deflection) data of F, the correction coefficients a, b, c, and d of the approximate function equation for correction are calculated by the least squares method, and the approximate function equations y=ax''+b and y= of the characteristic curve 37 are calculated. Calculate = c x + d (step S5),
Then, the approximate function data for correction obtained in step S5 is stored in the external memory 35 by the control circuit 21 (step S6).

Next, the operation of measuring and correcting the load-displacement characteristics of the specimen sp will be explained based on the flowchart of FIG. 4.

First, the specimen SP is held between the upper grip 10c and the lower grip 10.
Step 511), a compressive load is applied and the output of the A/D converter 30 and the output of the counter 25 are sampled so as to obtain a load-displacement characteristic including the load-deflection characteristic of the load frame LF. (step 512). Load data and displacement data at each sampling point are stored in memory 22.

In the next step S13, an approximate function stored in the external memory 35 is selected from the displacement or load state. That is, at the initial stage of measurement, the approximate function y=ax''+b is selected.

The selected approximation function is then used to correct the displacement data of the sampling point of interest.

The displacement of the specimen SP is corrected (step 514).

When the correction for a certain sampling point is completed, the control circuit 21 first determines whether the correction has been completed for all the sampling points (step 515), and if the determination is negative, the control circuit 21 performs step 515 for the sampling points for which the correction has not been completed. The process from S13 onward is repeated. When the correction is completed for all sampling points, the corrected load-displacement characteristic is output (step 516). The corrected load data and displacement data output from the control circuit 21 are displayed on the display device 33. Or, it is drawn on the recorder 31 via the D/A converter 32.

In addition, in step 13, when it is determined from the detected load or displacement that the sampling point reaches the inflection point 38, y = cx + d is selected as the approximate function for correction, and the specimen is adjusted according to this approximate function. The displacement will be corrected and calculated.

In this way, a load is applied to the load frame LF in advance, the load-deflection characteristic curve is converted into a plurality of approximate functions, and the external memory 35
Since the load-displacement characteristics of the specimen are corrected based on this approximation function, the load-displacement characteristic of the load frame is
The amount of data on the deflection curve is reduced, the data can be stored easily and in a short time, and the storage capacity of the memory is also small, making it possible to reduce the cost of the control system.

Moreover, by using the approximation function, the influence of noise becomes less likely, and the measurement error of the load-displacement characteristic becomes smaller. In addition, since the correction load-deflection characteristic curve is shown by two approximation functions, the correction accuracy is improved especially near the inflection point, and the measurement accuracy can be improved.

Furthermore, if the external memory 35 that stores the approximate function is configured with a floppy disk, it is possible to store a large amount of data depending on the test conditions, and even if the test conditions change due to changes in jigs, etc., the floppy disk can be replaced. This enables highly accurate correction that matches the test conditions.

In addition, although the above-mentioned example described the case of a simple compression test, it is not limited to this, and a simple tensile test, a oscillating fatigue test, or a double oscillating fatigue test can be performed in the same way. Also.

Since the load-deflection characteristic curve of the load frame is converted into an approximation function and stored, the internal memory of the control system can suffice if the number of test conditions is small.

Furthermore, the approximation function for approximating the shape of the deflection curve by the least squares method for each inflection point is not limited to the linear and quadratic equations shown in the above embodiments, but also higher-order equations such as cubic and quartic equations. It is also possible to use functions. In this case, a more accurate approximation is possible. Furthermore, in the above embodiment, the load-displacement characteristics are corrected by batch processing, but the correction may be performed in real time.

As described in detail of the G6 invention, in the present invention, the curve of the load-deflection characteristic of the load frame is rewritten in advance into a plurality of approximate functions, and the load-displacement characteristic of the specimen is corrected using these approximate functions. As a result, it is possible to reduce the memory capacity of the data for correcting the displacement of the specimen, reduce the cost for correction, and improve the correction accuracy.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a flowchart showing an embodiment for determining an approximation function for correction, and Fig. 3 is an explanatory diagram showing the load-deflection characteristics of a load frame. , FIG. 4 is a flowchart showing an example of measuring the load-displacement characteristics of a specimen. tO: Testing machine main body 1-Oc: Upper grip 10e: Motor 11: Transmission 13: Pulse encoder 22: Memory 25: Counter 27: Adder 29; Amplifier 34: Arithmetic circuit 10b: Black head 10d: Table 10f: Lower grip 12: Load cell 21: Control circuit 23: Operation unit 26: FV converter 28: Motor control circuit 33: Display device 35: External memory

Claims (1)

[Claims] A load frame for installing and applying a load to a specimen between a pair of opposing members, an actuator for loading this specimen, a load detection means for detecting a load applied to the specimen, and a displacement detection means for detecting the displacement of the specimen. Displacement detection means, in which the load-displacement characteristic of a specimen is determined based on the load detected by the load detection means and the displacement detected by the displacement detection means, wherein the load-displacement characteristic is determined when the specimen is not installed. calculation means for applying a load to the frame and converting a load-deflection characteristic curve obtained from the load detected by the load detection means and the displacement detected by the displacement detection means into a plurality of approximate functions according to the shape of the curve; a storage means for storing approximate function data obtained by the calculation means; and a load detected by the load detection means and the displacement detection means when the specimen is loaded.
A material testing machine comprising: a correction means for correcting displacement characteristics by selecting one of the plurality of approximation functions based on detected load or displacement.