JPS5819979B2 - Load measurement method and device for dynamic testing of materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When attempting to measure a dynamic material testing machine in the high-speed range or something with a fast response such as a collision, the present invention is designed to prevent the influence of the natural frequency of the detection device from entering the measurement data. required measurement data could not be obtained.

The present invention makes it possible to remove such natural frequency components and extract only necessary measurement data.

In recent years, the properties required of industrial materials have become even more stringent, and progress has been remarkable.

Among these properties, impact strength and brittle fracture properties are particularly good examples.

For this reason, in recent testing machines for measuring the load applied to a sample, instead of a normal load cell,
Strain gauge type load cells have been used.

This strain gauge type load cell differs from conventional load cells in that it uses a strain gauge to detect the local elastic strain of a metal material and measures the applied load, and is characterized by its simplicity, high accuracy, and high measurement frequency. be.

However, there are limits to its frequency, and in normal cases, the natural frequency as a whole is limited to 10 to 20 kHz, and the measurement frequency is limited to 3 to 5 kHz.

This is because no matter how high the natural frequency of the load cell itself is, the overall natural frequency will inevitably decrease due to the added weight of the joints, sample holder, etc.

However, as mentioned above, recent requirements for material testing are severe, and for example, measurement frequencies of 10 to 20 kHz or higher are often required.

When testing this using conventional methods, the data to be measured is buried in the overall resonance data, making it impossible to extract only the necessary data.

In addition, especially when the added mass is too large or the natural frequency of the detector itself must be lowered, the natural frequency of the entire measurement system may be about 100 Hz or less.

Therefore, the main object of the present invention is to provide a load measuring device for a material testing machine which overcomes the above-mentioned drawbacks and can be used even at high measuring frequencies.

The load measuring device according to the present invention having the above objects and advantages is obtained by extracting the configuration of a conventional typical material testing machine (FIGS. 1 and 2) and the main parts of the preferred embodiment of the present invention. It will be clearly understood from the following detailed description, taken in conjunction with the accompanying drawings in which: FIG.

FIG. 1 is a schematic configuration diagram of a typical conventional material testing machine, in which reference numeral 11 is the frame of the testing machine, 12 is an upper joint suspended from the top of the frame 11, 13 is a load cell, 14 is a lower joint, 15 is an upper sample holder, 1
6 is a sample, 17 is a lower sample holder, and 18 is a loading mechanism, the usage of which is well known and has no bearing on the gist of the present invention, so a description thereof will be omitted.

In the test machine shown in FIG. 1, the load mechanism 18 includes various types,
For example, pneumatic type, hydraulic type, electric type, explosive type, drop weight type, flywheel type, etc. are known, but when using a load cell, the configuration of the load measuring section is the same. The only difference is whether the joint is long or negligibly short.

Figure 2 shows a diagram of the mechanism of a conventional Charpy testing machine.

In the figure, 21 is a frame, 22 is a hammer, 23 is a hammer arm, 24 is a rotating shaft of the hammer arm, 25 is a blade that strikes a sample, 26 is a load cell, 27 is a sample, and 28 is a sample holder.

In this figure, the load cell is attached to the blade, but it is of course possible to attach it to the sample holder.

In the detailed description of the present invention, in order to facilitate understanding, it is assumed that the spring constant of the test piece or sample is smaller than the sum of the spring constants 11 to 15 in FIG.

When performing a tensile test, the force applied to the sample through the lower sample holder is measured using F10-Docel, and the force is f, 11~1
If the momentum of 5 is MV, then the following equation of motion holds true.

In an impact test, propagation of shock waves can be considered, but if this is ignored, the displacement of each part of 11 to 15 is proportional, so if the velocity at the point is V, then equation (2) can be transformed into (1) Substituting it into the formula, if we take the measurement point (■) at the position of the load cell, the load measured by the load cell is due to the deformation of the load cell, so it is proportional to the displacement of parts 11 to 15, and the following formula is obtained. is obtained.

The formula <3f shows the equation of motion when a forcing force is applied to a simple one-degree-of-freedom system.

Also, in formulas (2), (3) and (31), Ko
and 2 are proportionality constants.

In Equation (1) 1, when the second term on the right side is small, it is a static load test, and when the influence of the second term on the right side can no longer be ignored, it is a dynamic test using an impact load.

In the test shown in FIG. 2, if the mass of the hammer 22 is considered to be much larger than the mass of the blade 25, the same condition holds if the above M is considered as the momentum of the blade.

Therefore, in the following explanation, only FIG. 1 will be described.

A schematic block diagram of a load measuring device according to a first preferred embodiment of the present invention is shown in FIG.
32 is an accelerometer with excellent frequency characteristics, 33 is an amplifier for the load cell 31, 34 is an amplifier for the accelerometer 32, 35 is an adder, 36 is an amplifier, and 37 is a utilization device (not shown). This is the output lead that leads to
The 11 device 33 can be omitted if the load cell 31 has a high output such as a semiconductor strain gauge type.
If 2 is a piezoelectric accelerometer, high output can be obtained and amplifier 3
4 can also be omitted.

Normally, the amplifiers 33 and 34 are required to have good frequency characteristics.

In the conventional configuration, since the accelerometer 32 was not used, it was impossible to directly measure the change in the total momentum, as is clear from equation (2).

Therefore, in the present invention, an accelerometer 32 whose natural frequency is sufficiently higher than that of the load cell is attached to any of the components 12 to 15 in FIG. 1, so that equation (1) can be used.
This makes it easy to remove the effects of vibration.
The overall configuration of the testing machine and the main configuration of the load measuring device are the same as the conventional one shown in FIG.

Now, the operation of the configuration shown in FIG. 3 will be explained.

First, an impact is applied to the upper sample holder in the load direction without the sample 16 attached.

At this time, since the equation of motion (3) holds, the first term f and the second term d(MV)/dt on the right side of equation (1) become vibration waveforms.

Therefore, the output waveform of the accelerometer also becomes a vibration waveform proportional to the second term on the right side.

By the way, in formula (1), F~0 at the moment of application of impact, but F-0 after that.

Therefore, since equation (1) is, the sensitivity of the amplifier 34 to the accelerometer 32 may be adjusted so that the output 37 in FIG. 3 becomes zero.

FIG. 4 shows another embodiment of the present invention, in which a load cell 31
and a block diagram that is applied when the amplifier 33 has attenuation or phase fluctuation or when the accelerometer 32 and the amplifier 34 have similar characteristics, and therefore the components 31 to 37
is exactly the same as in FIG. are provided in between.

Since phase shifters 38 and 39 have normal functions, the overall circuit operation is equivalent to that of FIG.

FIG. 5 shows another embodiment in which a data storage device such as a transient converter using electronics, which has been rapidly developed in recent years, is used.

In this embodiment, the phase shifters 38 and 39 in FIG. 4 are replaced by a data storage device 40 of a load cell connected in series and its sensitivity adjuster 41, and a data storage device 42 of an accelerometer also connected in series. The sensitivity adjusters 43 are connected respectively.

In the case of the circuit arrangement shown in FIG. 5, the detection data of the load cell 31 and the accelerometer 32 are temporarily stored in the storage devices 40 and 41, respectively, so the sum ratio of the output of the load cell 31 and the output of the accelerometer 32 is Change it arbitrarily and output 3
The output of 7 can be adjusted as many times as necessary to obtain the optimal data.

In the examples of FIGS. 2, 3, and 4, the accelerometer and the load cell are each mounted separately, but the accelerometer may be incorporated into the load cell and formed integrally.

FIG. 6 is an example of this, and only the load cell part is extracted and shown. In the figure, the reference number 50 is the connection part of the tension type load cell, 51 is the connection screw, 52 is the tubular sensing part, 5
3 is a plurality of strain gauges attached to the sensing part 52, 54 is a protective outer cylinder, 55 is a cable relay terminal for the strain gauges 33, 56 is an accelerometer attached to a part of the load cell 13, and 57 is an acceleration This is a relay terminal for a total of 56 cables.

The shape of the sensing part 52 can be made into a shape suitable for a method of receiving a load, such as a method using bending stress such as a cantilever beam or a double support beam, or a method of detecting shear force.

Furthermore, the joint becomes longer and lateral vibration is added to the load cell.
When the acceleration output cannot accurately detect the vibration of the central axis of the load cell, two accelerometers are used as shown at 56 and 56' in Figure 7, and the effects of lateral vibration can be eliminated by adding the outputs. Can be canceled out.

8 and 9 show waveforms of the conventional load cell and the present invention after calculation when the portion of the upper sample holder 15 is hit with a hammer in FIG. 1.

As is clear from the figure, the waveform of the load cell shows a typical resonance phenomenon, but the waveform after calculation is completely different from the former, and the phenomenon at the time of impact with a hammer appears prominently.

Next, FIGS. 10 and 11 show the waveforms of the phenomenon when a mild steel smooth round bar test specimen 1 having a parallel portion diameter of 5 miφ was subjected to impact tensile fracture at a tensile speed of 5 m/sec.

Also in this figure, the difference between the case of using only a load cell and the present invention is clearly visible, and the features and effects of the present invention are clear.

Although the present invention has been described above based on preferred embodiments, the present invention is not limited to these embodiments, and may be modified in many ways without departing from the spirit and scope of the invention. Obviously, changes and modifications may be made.

[Brief explanation of the drawing]

1 and 2 are schematic block diagrams of a conventional material testing machine, FIG. 3 is a schematic block diagram of a first embodiment according to the present invention, and FIGS. 4 and 5 are a schematic block diagram of a conventional material testing machine. A schematic block diagram of the embodiment; Fig. 6 is a schematic diagram of an improved load cell used in the embodiments shown in Figs. 3, 4, and 5; Fig. 7 is only an improved part of the load cell that is further improved from Fig. 6. Figures 8 to 11 are waveform diagrams useful for explaining the effects achieved by the present invention. In Figure 8, the upper diagram shows the load cell single output, and the lower diagram The figure on the side shows the output after calculation with the accelerometer, both with a 100 kHz filter, and the horizontal axis is 1 m5ec/
Figure 9 is shown on a scale of 1 div, and Figure 9 is the 10th division when using a 10 kHz filter in Figure 8.
The upper diagram in Figure 2 shows the output of the load cell alone, and the lower diagram shows the output after calculation with the accelerometer, both of which are 10
With kHz filter, horizontal axis is 1 m5ec/1 di
FIG. 11 is the case where a 1 kHz filter is used in each case in FIG. 10. In addition, in the figure, the relationship between the main components and reference numerals is as follows. 11...Testing machine frame, 12...Upper joint, 13...Load cell, 14...
Lower joint, 15... Upper sample holder, 16...
・Sample, 17...Lower sample holder, 18...
... Load mechanism, 21 ... Frame, 22 ...
... Hammer, 23 ... Hammer arm, 24
...Shaft, 25...Blade, 26...
・Load cell, 27... Sample, 28...
・Sample holder, 31...Load cell, 32...
... Accelerometer, 33, 34 ... Multiplier, 3
5... Adder, 36... Multiplier, 38
゜39... Phase shifter, 40... Data storage device, 41... Sensitivity adjuster, 42...
・Data storage device, 43... Sensitivity adjuster, 50
...Connection part, 51 ...Connection screw, 5
2... Sensing section, 53... Strain gauge, 5
4... Protective outer cylinder, 55... Relay terminal, 56... Accelerometer, 57... Relay terminal.

Claims (1)

[Claims] 1. In a load measurement method in dynamic testing of materials, on the one hand a load cell is used to detect a load waveform corresponding to elastic deformation due to a load, and on the other hand an accelerometer is used to detect a measurement system during load application. detect the signal corresponding to the acceleration of
Both signals are expressed by formula (1), that is, F=f+A old EP
A load measuring method, characterized in that the influence of changes in momentum (MV) in the measurement system is removed from the load waveform by performing arithmetic processing so as to satisfy the following. 2. In a load measuring device for a material testing machine that includes a sample holder, a joint, a detection unit (load cell), and a load mechanism, a load cell that sends a signal in accordance with elastic deformation due to a load;
an accelerometer that is attached to any one of the sample holder, the joint, and the load cell to detect acceleration and send out an acceleration signal corresponding to the detected amount; an amplifier that adjusts or subtracts the output signal of the accelerometer; A load measuring device comprising: an adder for adding the output of the load cell and the output of the accelerometer. 3. Claims characterized in that the adder has a phase shifter that can separately adjust the phase of the input signal from the load cell and the phase of the input signal from the amplifier of the accelerometer. 2. The load measuring device according to 2. 4. The adder according to claim 2, wherein the adder has a data storage device for discriminatively storing the input signal from the load cell and the input signal from the amplifier of the accelerometer. Load measuring device.