JP2756324B2 - Material fatigue test equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material fatigue test apparatus for testing the strength of a material against fatigue, and more particularly to an irregular variation similar to that acting on a working mechanical structure. The present invention relates to a material fatigue test device for performing a so-called random load fatigue test for testing the strength of a material with respect to the load using the load.

[Conventional technology]

An irregular fluctuating load whose frequency and amplitude change with time often acts on a mechanical structure. For this reason,
When performing a fatigue test on a mechanical structure, a load waveform that fluctuates randomly from the mechanical structure is measured, and a load simulated exactly in the same manner as this load waveform is applied to a material equivalent to the material forming the mechanical structure. By giving a test piece made of a material to obtain the fatigue strength, a test can be actually performed in a short time.

One possible method is to collect the waveform of the load actually applied to the mechanical structure and operate the tester directly with this load waveform data. Exists, it is meaningless to test with the waveform data as it is. In addition, the waveform data of the actual load has a period in which the load is concentrated and a period in which the load hardly exists. Therefore, if a test is performed using the waveform data as it is, the test takes time. There is also.

Therefore, the actual load waveform data was decomposed into fatigue damage by the rain flow method as a stress frequency counting method of the actual load waveform data measured from the mechanical structure,
A load amplitude frequency distribution suitable for damage evaluation is obtained and stored in a memory.The memory is read out by a random number generator and converted into a distribution with less frequency fluctuation such as a Rayleigh distribution. Creates load data with equivalent frequency distribution.

FIG. 14 shows a conventional apparatus for performing a fatigue test of a material using the load data created as described above. In FIG. 14, 1 indicates that the actual load created as described above is equivalent to fatigue damage. This is a memory that stores load data of various frequency distributions. Reference numeral 2 denotes a basic signal generator for generating a basic signal of a predetermined frequency having a constant amplitude, and reference numeral 3 denotes a waveform adjuster for adjusting the amplitude of the basic signal generated by the basic signal generator 2 based on data sequentially read from the memory 1. , This waveform adjuster 3
15 (a) generated by the basic signal generator 2
The load signal shown in FIG. 15 (b) in which the amplitude of the basic signal shown in FIG. 15 is irregularly changed by the load data read from the memory 1 is obtained.

The load signal obtained at the output of the waveform adjuster 3 is supplied to the electrohydraulic fatigue tester 4 as a target value signal. The electrohydraulic fatigue tester 4 operates in response to the load signal, and applies a load having a frequency distribution equivalent to the actual load and the fatigue damage to the test piece 5 made of the material to be tested. At this time, the load acting on the test piece 5 is detected by the load cell (load detector) 6, and the electrohydraulic fatigue tester 4 is feedback-controlled by the detected load.

[Problems to be solved by the invention]

In the conventional material fatigue test apparatus described above, the problem that the test when the electro-hydraulic fatigue test machine 4 is directly operated with the actually collected load waveform data takes a long time is solved. The problem of not being able to do so is reduced. However, since the electro-hydraulic fatigue detector 4 is still operated directly using the analog load signal as an oscillator, the response characteristic of the electro-hydraulic fatigue test machine 4 is affected, so that there is a problem in followability, and the target load can be accurately calculated. And it was difficult to match the load actually applied to the test piece.

Accordingly, an object of the present invention is to provide a material fatigue test apparatus capable of performing a random fatigue test by applying a load or strain that accurately matches a target value to a test piece in view of the above-described conventional problems.

[Means for solving the problem]

As shown in the basic configuration diagram of FIG. 1 (a), a material fatigue test apparatus made according to the present invention for solving the above-mentioned problem has a load or strain acting on a working mechanical structure equivalent to fatigue damage. A material fatigue test in which the electrohydraulic fatigue tester 10 is operated based on frequency distribution load or strain target value data to apply an irregularly varying load or strain to a test piece and test the strength of the material with respect to the load or strain. In the device,
Storage means 23 for recording said target value data, said means
A reading means 21a for sequentially reading the target value data stored in 23 and the electrohydraulic fatigue tester 10 detect the load or strain actually applied to the test piece to generate actual value data. Actual value data generating means 28; comparing means 21b for comparing the target value data read by the reading means 21a with the actual value data generated by the actual value data generating means 28; When the value data is larger than the actual value data, the target value signal gradually increases to a predetermined value, and when the target value data is smaller than the actual value data, the target value signal gradually decreases to a predetermined value. , The reading means 21a
And a coincidence detecting means 21d for detecting a coincidence between the target value data read by the actual value data generating means 28 and the actual value data generated by the actual value data generating means 28. The next target value data is read from the storage means 23.

In order to solve the above-mentioned problems, a material fatigue test apparatus according to the present invention has a load or strain acting on a working mechanical structure and fatigue damage as shown in a basic configuration diagram of FIG. 1 (b). Material fatigue in which the electrohydraulic fatigue tester 10 is operated based on the equivalent frequency distribution load or strain target value data to apply an irregularly variable load or strain to the test piece and test the strength of the material against the load or strain. In the test apparatus, a storage unit 23 storing the target value data, a reading unit 21a for sequentially reading the target value data stored in the storage unit 23, and a target value sequentially read by the reading unit 21a The difference between the data is divided by a constant value, a calculating means 21e for obtaining an increase / decrease speed value according to the magnitude of the difference, and a load or strain actually applied to the test piece by the electrohydraulic fatigue tester 10 are calculated. Detect And the actual value data generating means 28 for generating the actual value data, the target value data and the actual value data generating means read by the reading unit 21a
Comparing means 21 for comparing with the actual value data generated by 28
b, based on the comparison result, when the target value data is larger than the actual value data, the target value signal is calculated by the calculating means 21e.
When the target value data is smaller than the actual value data, the target value signal is calculated by the arithmetic means 21.
target value signal generating means 21c for decreasing the predetermined value obtained by e
And a coincidence detecting means 21d for detecting coincidence between the target value data read by the reading means 21a and the actual value data generated by the actual value data generating means 28,
The reading means 2 based on the coincidence detection by the coincidence detecting means 21d.
1a reads the next target value data from the storage means 23.

(Operation)

In the configuration of FIG. 1A, the storage means 23
Load or strain target value data having a frequency distribution equivalent to the load or strain acting on the actual mechanical structure and the fatigue damage is stored and sequentially read out by the reading means 21a.

The actual value data generating means 28 is an electrohydraulic fatigue tester 10
Generates actual value data on the load or strain actually applied to the test piece.

The comparing means 21b compares the target value data read by the reading means 21a with the actual value data generated by the actual value data generating means 28, and based on the comparison result, the target value signal generating means 21c When the value data is larger than the actual value data, the target value signal is increased by a predetermined value, and when the target value data is smaller than the actual value data, the target value signal is decreased by a predetermined value.

Then, the coincidence detecting means 21d detects coincidence between the target value data read by the reading means 21a and the actual value data generated by the actual value data generating means 28, and the coincidence detecting means 21d detects the coincidence. The reading means 21a
Reads the next target value data from the storage means 23.

As described above, when the target value data of the load or the strain matches the actual value data, the control based on the next target value data is performed, so that the fatigue faithful to the target value data is applied to the material under test. Can be added.

Further, in the configuration of FIG.
e divides the difference between the target value data read successively by the reading means 21a by a constant value, and obtains a value corresponding to the large difference. When the target value data is larger than the actual value data, the target value signal generating means 21c increases the target value signal by the predetermined value obtained by the arithmetic means 21e, and the target value data becomes the actual value. When the data is smaller than the data, the target value signal is reduced by a predetermined value obtained by the arithmetic means 21e.

As described above, since the change of the target value signal is changed according to the size of the target value data, and the time of each half cycle is fixed, fatigue can be intensively added at a constant frequency, The test time can be completed in a short time.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of a material fatigue test apparatus according to the present invention. In FIG. 2, reference numeral 10 denotes a well-known electro-hydraulic fatigue test machine, which includes a servo valve 11a and a load detector 1
1b, a tester main body 11 for applying a test load to a test piece (not shown), a load target signal for one input, and a load detection signal for representing the load actually applied to the test piece to the other input Are input and output the deviation signal at the output
12 and the servo signal 11a of the tester body 11 by amplifying the deviation signal
And a load amplifier 14 for amplifying the load detection signal detected by the load detector 11b.

Reference numeral 20 denotes a control device that controls the electrohydraulic fatigue tester 10 to perform a random fatigue test, and includes a microcomputer (CPU) 21 that operates according to a predetermined control program, a control program for the CPU 21, and the like. A read-only memory (ROM) 22 for storing data to be processed by the CPU 21, a read / write random access memory (RAM) 23 for temporarily storing data to be processed by the CPU 21, a random number generator 24,
A keyboard 25 as an input section for inputting various commands and data by key operation, an input / output circuit 26 for externally inputting data stored in the RAM 23 and outputting data stored in the RAM 23 to the outside; , D / A converter 27 and A
/ D converter 28, which are interconnected by a bus line 29. The RAM 23 has areas 23a to 23d as shown in FIG.

Prior to performing control for performing a random fatigue test by controlling the electrohydraulic fatigue tester 10, the control device 20 described above also performs a task of creating load target value data for control. A method of creating target value data will be described.

In order to create the load target value data, for example, the following processing may be performed. First, the load waveform data actually applied to the mechanical structure is collected, and the collected data is analyzed based on the above-mentioned rain flow method, and the load waveform as shown in FIG. p) Value data is created, and this pp value data is input via the input / output circuit 26 and stored in the predetermined area 23a of the RAM 23.

P-p value data n ₁ to n _n stored in the area 23a
Read sequentially, store each p-p value data n ₁ to n _n n _1/2 to be processed into n _n / 2, the processed are denoted by the positive and negative sign in order to area 23c in data And n as shown in FIG.
_{1/2, -n 1/2} , n 2/2, -n 2/2, ......, n n / 2, -n n / 2, ...
Create load target value data.

Next, a fatigue test performed using the load target value data created as described above will be schematically described. First, when a start of a test is instructed by a specific key operation of the keyboard 25 serving as an input unit, the CPU 21 stores the RAM 23 and the area 23c.
Reading a first one n _1/2 of the load target value data from. Load target value data n _1/2 read the can, A / D converter 2
The load is compared with the load value data of the load actually applied to the test piece by the tester main body 11 input through the input unit 8. As a result of this comparison, if the actual load value data is small, for example, a counter configured inside the CPU is counted up by a certain value. The count value of this counter is converted into an analog signal by the D / A converter 27,
The input is input as a load target value signal. The load target signal has a deviation from the actual input load value at the addition point 12 and the servo signal 11a of the tester main body 11 is servo-controlled by the deviation signal. Increases the load applied to the specimen.

Each time the CPU 21 counts up the counter, the CPU 21 compares the actual load value data from the A / D converter 28 with the load target value data, and continues the above operation while the actual load value data is small. If they match, the above-described count-up operation is stopped, and the area 2
Read the next load target value data -n _1/2 from 3c.

Then, the load target the readout value data -n _1/2 and A /
The actual load value data from the D converter 28 is compared. In this case, the result of the comparison is larger for the actual load value data, and the counter is counted down at a constant speed according to the result of the comparison. At the time of this countdown operation, the actual load value data from the A / D converter 28 is compared with the load value target value data in the same manner as described above, and the above operation is continued while the actual load value data is large. If they match, the above-described countdown operation is stopped, the next load target value data is read from the area 23c, and the above-described operation is repeated.

After ending the above-mentioned operation for the last load target value data read from the area 23c,
The first load target value data n _{1/2 of} 23c is read out, and the above-described operation is repeatedly performed until the test piece is broken or a predetermined number of times.

The details of the operation of generating the load target value data, which has been schematically described above, will be described with reference to the flowchart of FIG. 6 showing the work executed by the CPU 21 in accordance with the control program stored in the ROM 22 in advance.

The CPU 21 starts operation by a specific key operation of the keyboard 25, which is an input unit. In the first step S1, the CPU 21 activates the random number generator 24, generates a random number, and captures the random number value. Then the process proceeds to step S2, and decremented here to correspond to the p-p value of the random number R _n written in the RAM23 of the area 23a captured count data, RA
It is determined whether or not the count data stored in the area 23a of M23 is zero. If the determination in step S2 is NO, the process proceeds to step S3, and if the determination is YES, the process proceeds to step S1.
And the above operation is repeated. In step S3, it writes sequentially random number R _n to RAM23 area 23b. Then, in the subsequent step S4, p corresponding to the random value R _n
The number data of the -p value is decremented by 1, and then the process proceeds to step S5. In step S5, it is determined whether or not all of the count data stored in the area 23a is zero. If the determination is YES, the process proceeds to the next load target value data creating routine 6, where the fifth The load target value data described above with reference to the drawing is created and stored in the area 23c of the RAM 23, and all the work is completed. If the determination is NO, the process returns to step S1, and the above operation is repeated.

Next, the details of the fatigue test operation performed using the load target value data created in the above-described operation will be described with reference to the flowchart of FIG. 7 which shows the work performed by the CPU 21 according to the control program stored in the ROM 22 in advance. explain.

The CPU 21 starts a fatigue test operation using a specific key device of the keyboard 25 which is an input unit.In the first step S11, the CPU 21 uses the count value of the address counter, in which the initial value is set, as an address in a predetermined area 2
The first one of the load target value data stored in 3c is read, and this is temporarily stored in a predetermined area of the RAM 23.
Thereafter, the process proceeds to step S12, where actual load value data from the A / D converter 28 is fetched, and this is also temporarily stored in a predetermined work area 23d of the RAM 23.

Thereafter, the process proceeds to step S13, where the target load value data read out in step S11 is compared with the actual load value data fetched in step S12, and it is determined whether or not the two match. If they match, step S1
Returning to step 1, the next load target value data is read out. If they do not match and the determination is NO, the process proceeds to step S14, where it is determined whether the load target value data is larger. Steps
If the determination in S14 is YES, the process proceeds to step S15, where the CPU
The counter configured in the RAM 21 or the RAM 23 is incremented by a certain value. If the determination in step S14 is NO, the process proceeds to step S16, where the counter is down-counted by a certain value.

Subsequently, the process proceeds to step S17, where it is determined whether or not the address for reading the load target value data from the area 23c is an address for designating the final load target value data. The initial value is set in the address counter, and the process returns to step S13. If the address is not the final address, the address counter is incremented by one in step S19, and the process returns to step S13.

In the above-described material fatigue test apparatus, since the counter counts up and down a constant value, the half cycle time is short when the load target value data is small as shown in FIG. The time width changes greatly. On the other hand, since the tester main body 11 has a response characteristic, the cycle portion of the shortest time is set to be equal to the upper limit frequency reproducible by the tester main body 11.
However, in this case, when the load target value data is large, the half cycle time becomes long, and the frequency spectrum is dispersed over a wide band as shown in FIG. Become.

In order to shorten the test time, the spectrum should be concentrated near the resonance frequency f ₀ (FIG. 10), which is a practical limit of the tester main body 11, as shown in FIG. What is necessary is just to change the up / down value of the counter per unit time according to the magnitude of the load target value data for the counter that has been up / down.

Next, the details of the operation when the fatigue test is performed by changing the up / down value of the counter per unit time according to the magnitude of the load target value data as described above are executed by the CPU 21 in accordance with the control program stored in the ROM 22 in advance. The work to be performed will be described with reference to the flowchart of FIG.

The CPU 21 starts a fatigue test operation by a specific key operation of the keyboard 25 which is an input unit, and in the first step S21, the count value of the address counter in which the initial value is set is stored as an address in a predetermined area of the RAM 23. The first load target value data is read out and temporarily stored in a predetermined work area of the RAM 23. Then the process proceeds to step S22, obtains the ΔD by dividing the difference here between the present read load target value data P _n and load target value data P _-n previously read in step S21 with a constant value N.

Thereafter, the process proceeds to step S23, where actual load value data from the A / D converter 28 is fetched, and this is also temporarily stored in a predetermined work area of the RAM 23. Subsequently, the process proceeds to step S24, where the load target value data read out in step S21 is compared with the actual load value data fetched in step S23, and it is determined whether or not the two match. If both match and the determination is YES, the process returns to step S21, and the next load target value data is read out. If they do not match and the determination is NO, the process proceeds to step S25, where the load target value data is larger. It is determined whether or not. Step S25
If the determination is YES, the process proceeds to step 26, where the counter configured in the CPU 21 or the RAM 23 is counted up by the constant value ΔD obtained in step S22. Also step
If the determination in S25 is NO, the process proceeds to step S27, where the counter is down-counted by the constant value ΔD.

Subsequently, the process proceeds to step S28, where it is determined whether or not the address for reading the load target value data from the area 23c is an address for designating the final load target value data. The initial value is set in the address counter, and the process returns to step S24. If the address is not the final address, the address counter is incremented by one in step S30, and the process returns to step S24.

In the material fatigue test apparatus described above, the up / down count of the counter is changed according to the magnitude of the difference between the successive load target value data, so that the half cycle time is equal to the load target value data as shown in FIG. The tester main body 11 is always operated at the upper limit frequency at which the response characteristics can be reproduced, regardless of the magnitude, and the frequency spectrum is
11 concentrated in a narrow range around the f ₀ as shown in FIG., It is possible to shorten the test time.

(Effect)

As described above, according to the present invention, when the target value data of the load or the strain matches the actual value data, the control is performed by the next target value data.
Fatigue faithful to the target value data can be applied to the material under test, so that a load or strain that exactly matches the target value can be applied to the test piece to perform a random fatigue test.

Also, since the change of the target value signal is changed according to the size of the target value data and the time of each half cycle is fixed, fatigue can be intensively added at a constant frequency, and the test time can be reduced. It can be completed in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are block diagrams respectively showing a basic configuration of a material fatigue test apparatus according to the present invention, and FIG. 2 is an embodiment of a material fatigue test apparatus according to the present invention. FIG. 3 is an explanatory diagram showing the memory configuration of the RAM in FIG. 2, FIGS. 4 and 5 are explanatory diagrams showing data stored in each area of the RAM in FIG. FIG. 7 is a flowchart showing one job executed by the CPU in FIG. 2, FIG. 7 is a flowchart showing another job executed by the CPU in FIG. 2, and FIG. 8 is a flowchart shown in FIG. FIG. 9 is an explanatory view showing a method of a fatigue test performed by a CPU. FIG. 9 is an explanatory view showing a power spectrum in a case of a fatigue test performed by a CPU according to the flowchart of FIG. 6. FIG. Diagram showing response characteristics, Fig. 11 shows preferred power for fatigue test FIG. 12 is an explanatory diagram showing a spectrum, FIG. 12 is a flowchart showing a part of the flowchart shown in FIG. 7, and FIG. 13 is an explanatory diagram showing a method of performing a fatigue test performed by the CPU based on the flowchart shown in FIG. Is a block diagram showing a configuration example of a conventional material fatigue tester, and FIG. 15 is a view showing a target value signal in the tester shown in FIG. 10 …… Electro-hydraulic fatigue tester, 21a …… Read-out means (CP
U), 21b ... Comparison means (CPU), 21c ... Target value signal generation means (CPU), 21d ... Coincidence detection means (CPU), 21e ... Calculation means (CPU), 23 ... Storage means (RAM) ), 28 ... actual value data generating means 28 (A / D converter).

Claims (2)

(57) [Claims] 1. An electrohydraulic fatigue testing machine is operated based on load or strain target value data having a frequency distribution in which the load or strain acting on an actual mechanical structure and fatigue damage are equivalent to each other, and irregular fluctuations occur in the test piece. In a material fatigue test apparatus for applying a load or strain to test the strength of a material with respect to the load or strain, a storage unit in which the target value data is recorded, and the target value data stored in the unit are sequentially read out Reading means; actual value data generating means for detecting a load or strain actually applied to the test piece by the electrohydraulic fatigue tester to generate actual value data; and the target read by the reading means. Means for comparing value data with the actual value data generated by the actual value data generating means; and, based on the comparison result, the target value data is compared with the actual value data. A target value signal generating means for increasing the target value signal by a predetermined value when the target value data is larger than the actual value data and decreasing the target value signal by a predetermined value when the target value data is smaller than the actual value data; Coincidence detection means for detecting coincidence with the actual value data generated by the actual value data generation means, and the reading means reads the next target value data from the storage means by the coincidence detection by the coincidence detection means. Material fatigue test equipment characterized by the following. 2. An electro-hydraulic fatigue tester is operated based on load or strain target value data having a frequency distribution in which the load or strain acting on an actual mechanical structure and the fatigue damage are equivalent to each other, and the test piece is irregularly varied. In a material fatigue test apparatus for testing the strength of a material with respect to the load or the strain by applying a load or a strain, storage means for recording the target value data, and sequentially reading the target value data stored in the storage means Reading means; calculating means for dividing a difference between the target value data read successively by the reading means by a constant value to obtain a value corresponding to the magnitude of the difference; and the electrohydraulic fatigue tester Actual value data generating means for detecting the load or strain actually applied to the test piece and generating actual value data; the target value data and the actual value read by the reading means A comparison means for comparing the actual value data generated by the data generation means with a target value signal obtained by the arithmetic means when the target value data is larger than the actual value data. A target value signal generating means for reducing a target value signal by a predetermined value obtained by the arithmetic means when the target value data is smaller than the actual value data; and generating the target value data and the actual value data read by the reading means. Means for detecting a match with the actual value data generated by the means, wherein the read means reads the next target value data from the storage means by the match detection by the match detection means. Material fatigue testing equipment.