JPH0363541A - Material testing machine - Google Patents

Abstract

PURPOSE:To improve an accuracy of correction by using a hysteresis curve for true load-deflection of a load frame at the time of alternately loading as correction data. CONSTITUTION:The load and a displacement are detected while applying the alternating load to a specimen SP to be tested, and a curve for load- displacement is measured then corrected by the correction data in storage means 22. The load-deflection characteristic of the load frame LF having the stable hysteresis when the alternating load is applied, is stored in the storage means 22. That is, the load of both-directions swing is applied to the load frame LF in advance for specified number of times, and the characteristic of load- deflection is stored as the correction data for both-directions swing at the time when the hysteresis curve for load-displacement characteristic of the specimen to be tested is made to correct by these correction data.

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 specimen is installed in a load frame consisting of a pair of columns erected on a table and a crosshead is placed horizontally thereon, and while the specimen is loaded, a load cell, pulse encoder, etc. Material testing machines that measure load and displacement are known.

In addition, it is known that the load frame of the material testing machine described above is itself deformed by the load, and a method was developed in 1554 of 1983 to correct this deformation to obtain an accurate amount of deflection.
There is a publication No. 65 entitled "Deflection Correction Wet Material Testing Machine". In this deflection correction wet materials testing machine, the amount of deflection of the load frame itself relative to the load is determined from a functional formula or numerical table, and the amount of deflection of the actually measured specimen is corrected.

By the way, when conducting a single swing or double swing fatigue test, it is necessary to correct the deflection amount for the alternating load using correction data6. For example, in a compression swing fatigue test, when a compressive load is applied to the load frame and a predetermined load is reached, The load-deflection curve when the load is gradually unloaded becomes a hysteresis curve as shown in FIG. 5(a). Similarly, when a tensile load is applied to the load frame and the load is unloaded, as in a tensile oscillation test, the load-deflection curve becomes a hysteresis curve as shown in FIG. 5(b). Conventionally, the load is applied and unloaded only once, and the hysteresis curve of the load-deflection characteristic at that time is used as correction data.

Problems to be Solved by the C0 Invention However, the hysteresis of the load-deflection curve when applying and unloading a compressive or tensile load to a load frame is not stable unless the load is applied and unloaded a predetermined number of times. Therefore, the conventional method of creating correction data by applying and unloading the load has a problem in that the accuracy of correction deteriorates.The technical problem of the present invention is to create a true hysteresis curve. The objective is to correct the load-displacement characteristics of the specimen using the load-deflection characteristics of the load frame.

01 Means for Solving the Problems The present invention will be explained in conjunction with FIG. It is equipped with a load detection means 12 for detecting the applied load on the specimen sp and a displacement detection means 13.25 for detecting the displacement of the specimen sp.
It is applied to a material testing machine that applies an alternating load to p. The above-mentioned technical problem is solved by the storage means 22 which stores the load-deflection characteristics in a stable state by applying an alternating load to the load frame LF at a predetermined period without installing the specimen, and by applying an alternating load to the specimen sp. The load-displacement characteristic of the specimen SF' obtained from the load detected by the load detection means 12 and the displacement detected by the displacement detection means 13.25 is corrected by the load-deflection characteristic of the load frame LF. Correction means 21 to perform
This is solved by having the following.

81 action While applying an alternating load to the specimen SP, the load and displacement are detected and the load-displacement curve is measured. This is corrected using the correction data stored in the storage means 22. The storage means 22 stores the load-deflection characteristics of the load frame LF which is applied with an alternating load and has stable hysteresis. Therefore, highly accurate correction is possible.

Note that 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 figure, numeral 10 is a test machine main body that alternately applies a compressive load and a tensile load to the specimen SP.

This testing machine main body IO is equipped with a load frame LF.

The load frame LF has yokes i and oa horizontally suspended on the upper ends of a pair of screw rods 10 k and 10 m erected on a table 10 d, and a cross head 1 on the screw rods 10 and 10 m.
0b screwed together. A load motor 10e is installed on the table 10d, and the rotation of this motor], Oe is transmitted to a pair of screw rods 10 via a transmission 11 for 10 m.
is transmitted to the screw rod 10, and the crosshead 10b moves up and down by a rotation of 10 m.

An upper grip 10c is provided on the crosshead 10b via a load cell 12, and a lower grip 10f is provided on the table 10d. 13 is a pulse encoder for detecting the displacement of the specimen SP.

Rotation of transmission 11 or screw shaft 10 k, l Om
Outputs pulses according to the rotation of the

The control system that controls the test machine main body 10 includes a control circuit 21 that controls the whole, and a control system that controls the load-deflection characteristics of the load frame LF and the specimen s.
A memory 22 that stores the load-displacement characteristics of p, an operation unit 23 that performs manual input of various data of the compression-tensile test (data such as maximum elongation, maximum contraction, and expansion/contraction speed), and a pulse encoder ]-3 A counter 25 that performs a counting operation according to the output pulses, an FV conversion circuit 26 that converts the output pulse frequency of the pulse encoder 13 into voltage, and a voltage pattern waveform and FV generated by the speed setting section 24 in the control circuit 21. It has an adder 27 that calculates the deviation from the output voltage of the 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 corresponds to the rotation speed of 10 m, that is, the displacement of the specimen SP to the pair of screw rods 10, and the control circuit 21 calculates the displacement given to the specimen SP by counting this number of pulses with the counter 25. You can know the amount.

The 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 inputted from the operation section 23. This voltage pattern waveform is input to the adder 27, where the deviation from the output of the FV variable circuit 26, that is, the voltage corresponding to the current rotational speed of the motor 10e is determined, and the deviation signal is input 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.
A predetermined displacement corresponding to the voltage indicated by the voltage pattern waveform is applied to the load frame LF and the specimen sp.

In addition, the control system of the material testing machine described above has two parts on the load cell.
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 circuit 21. A D/A converter 32 converts the digital data to voltage and inputs it to the recorder 31.
and a display device 33 configured with a CRT (cathode ray tube) and displaying the processing results of the control circuit 21.

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 2■ is a counter 25
Since the displacement given to the load frame L F or the specimen SP can be known from the counted value of , this displacement and A/
By sampling the load data input from the D converter 30, the load-displacement characteristics of the specimen SP or the load-deflection characteristics of the load frame LF are measured.

Next, we will explain the case of performing a double swing test.6 First,
The double swing correction data of the load frame LF is measured without the specimen sp installed. FIG. 2 shows a flowchart for creating correction data.

First, under the control of the control circuit 21, a compression-tensile load that includes one round of the hysteresis loop is applied (step S1), a predetermined voltage pattern waveform is output from the speed setting section 24, and the motor is controlled according to this voltage pattern waveform. 1
By controlling the rotation speed of 0e, a predetermined displacement is given and a load is applied.

As shown in Fig. 5(c), the order of applying the load is, for example, first, the tensile load is gradually increased (↓↓) (O→l), then the tensile load is unloaded (1→2) and the compression is applied. The load is increased (2→3), then the compressive load is unloaded (3→4), and the tensile load is increased (4→1).

Next, the control circuit 21 determines whether the number of repetitions of the compressive load and the tensile load has reached a predetermined number (step S2
). If the predetermined number of times is not reached, the process returns to step S1 and the compressive load and tensile load are repeatedly applied. When the number of repetitions of the compressive load and the tensile load reaches a predetermined number, the control circuit 21 then measures the load-deflection characteristics of the load frame LF (step S3), and repeatedly applies the compressive load and the tensile load a predetermined number of times. This stabilizes the hysteresis of the load-deflection characteristic, so this stable characteristic is measured as oscillation correction data. The control circuit 21 receives load data input from the A/D converter 30.

The relationship with the displacement data input from the counter 25 is sequentially sampled for one cycle of the compressive load and the tensile load, and is stored in the memory 22 along with the increase/decrease status of the compressive and tensile loads (
Step S4), the measurement of the correction data is ended.

In FIG. 6 showing the load-deflection characteristics of the load frame thus obtained in FIG. 3, the vertical axis represents the load, with the positive side corresponding to the tensile load and the negative side corresponding to the compressive load. The horizontal axis indicates displacement, with the positive side corresponding to the amount of elongation of the load frame in response to a tensile load, and the negative side corresponding to the amount of contraction of the load frame in response to a compressive load.

The solid line A shows the load-deflection characteristics when the tensile load is decreased and the compressive load is increased, and the dotted line #jAB represents the load-deflection characteristics when the compressive load is decreased and the tensile load is increased. By repeating step S1 and step S2, the load-displacement characteristics shown by the solid line A and the dashed-dotted line IB are stabilized, and the solid line A and the dashed-dotted line B sampled in step S3 are stored in the memory 22 in a state where they can be individually specified. Stored.

This correction data is created by the manufacturer at the time of shipment.
Generally, it is stored in OM and provided to the user.
It may also be stored in a magnetic memory such as a floppy disk and provided to the user. If a floppy disk or the like is used, the user can easily update the correction data when using a new jig.

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, hold the specimen SP between the upper grip 10c and the lower grip ↓O.
step 5ll).

Apply tensile load and compressive load alternately and load on load frame LF -
Load-displacement characteristics including deflection characteristics are sampled using the output of the A/D converter 30 and the output of the counter 25 (step 512). Load data and displacement data at each sampling point are stored in the memory 22 along with load state information. This load state information is information for identifying whether the state is in which the tensile load is decreased and the compressive load is increased, or the compressive load is decreased and the tensile load is increased. For example, a 1-bit identifier is assigned to identify the information.

When the sampling in step S12 is completed, the control circuit 21 then reads each sampled data stored in the memory 22 and determines the load state of this sampled data. It is determined whether or not the tensile load is decreased and the compressive load is increased using the identifier stored together with each sampling data (step 813). If an affirmative determination is made, the correction data shown by the solid line A in FIG. 3 is stored in the memory 22.
The displacement data is corrected based on the load data of the sampling point of interest (step 514).
, specifically, the actual N1A corresponding to the load at the sampling point.
The displacement data on A is read out and corrected by subtracting it from the displacement data at the sampling point.

If a negative determination is made in step S3, the correction data indicated by the dashed line B in FIG. 3 is similarly read out from the memory 22 and the displacement data is corrected based on the load data of the sampling point of interest (step 515).

When the correction for a certain sampling point is completed, the control circuit 21 then determines whether the correction has been completed for all sampling points (step 516), and if the determination is negative, the control circuit 21 performs step 516 for the sampling points for which the correction has not been completed. The processing from 813 onwards is repeated. When the correction is completed for all sampling points, the corrected load-displacement characteristics are output (step 517). The corrected load data and displacement data output from the control circuit 21 are displayed on the display device 33 or drawn on the recorder 31 via the D/A converter 32.

In this way, in this embodiment, a double swing load is applied to the load frame LF a predetermined number of times (a loop of 1 → 2 → 3 → 4 → 1 is repeated multiple times), and the time point is determined when the hysteresis curve of the load-deflection characteristic becomes stable. The load-deflection characteristics were stored as oscillation correction data, and the load-displacement characteristics of the specimen were corrected using this correction data. Therefore, since the correction data shows true hysteresis, the correction accuracy is improved compared to the conventional technique.

In addition, in the compression or tension oscillation test, Fig. 5 (
Since the hysteresis curves shown in a) and (b) are obtained, the correction accuracy can be improved by creating correction data after the hysteresis curve is stabilized in the same manner as described above. Further, although the load-displacement data is corrected by batch processing in 1 or more, it may be corrected in real time. Furthermore, since the load-deflection characteristics of the load frame differ depending on the upper and lower grips, the load-deflection characteristics are measured in advance for each jig used and stored in the memory 22.
The jig to be used may be designated and selected from the operation unit 23 during the test. Yet again.

Although the load frame is a screw rod type, a hydraulic cylinder type may also be used.

As explained in detail of the G0 invention, in the present invention, the true load-deflection hysteresis curve of the load frame at the time of single swing or single swing load is used as correction data, so that the measured load of the specimen - The correction accuracy of displacement characteristics is improved.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram showing one embodiment of the present invention, Fig. 2 is a flowchart of an embodiment regarding correction data creation, Fig. 3 is an explanatory diagram of load-deflection characteristics with hysteresis of the load frame, and Fig. 4 The figure is a flowchart of an example of measuring the load-displacement characteristics of a specimen, and FIG. 5 is an explanatory diagram of hysteresis curves during single swing and double swing. 10: Testing machine main body 10b = crosshead 10c: upper grip 10d: table 10e: motor 10
f: Right above bottom grip 1: Transmission 12: Load cell 13 Nibals encoder 21: Control circuit 22: Memory 25: Counter 26: FV converter 27: Adder 29: Amplifier 28: Motor control circuit

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. In a material testing machine equipped with a displacement detecting means and adapted to apply an alternating load to the specimen, the alternating load is applied to the load frame at a predetermined period without the specimen installed, and the load-deflection is determined when the hysteresis is stabilized. storage means for storing the characteristics; and the load-displacement characteristic of the specimen obtained from the load detected by the load detection means and the displacement detected by the displacement detection means by applying an alternating load to the specimen. A material testing machine characterized by comprising a correction means for correcting based on the load-deflection characteristics of a load frame.