JPH0690121B2 - Fatigue test equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fatigue test device for a spring test piece or the like, and is particularly suitable for a fatigue test of a spring test piece having a load-displacement characteristic such as a disc spring. Regarding the device.

B. Prior Art A spring material such as a disc spring generally has a load-displacement characteristic in which a load near zero load changes little with respect to displacement, as shown in FIG.

In a spring specimen having such characteristics, when a compressive fatigue test is carried out by applying a maximum load P ₁ from the point where the load starts to occur, the preset cyclic load waveform (load pattern) should be obtained. When the test is performed by feeding back the actual load to, the displacement near the zero load cannot be determined.
In addition, when the actual displacement is fed back and tested so that the waveform (displacement pattern) of the repeated displacement from the minimum displacement to the maximum displacement that is set in advance is performed, the spring constant of the spring specimen becomes smaller due to fatigue due to the repeated load. According to
The load obtained at the maximum displacement is less than the desired maximum load P ₁ , and an accurate spring fatigue test cannot be performed.

Therefore, conventionally, the minimum load as shown in Figure 6 is set to P ₂ non-zero, the maximum load from minimum load P ₂
The fatigue test of the spring specimen was carried out by the load feedback control by the repeated load of P ₁ .

C. Problem to be Solved by the Invention However, in the conventional spring compression fatigue test apparatus as described above, in order to set the minimum load to a load P ₂ which is not zero,
There is a problem that the fatigue test accuracy of the spring test piece is reduced because the test near the zero load of the minimum load P ₂ or less is ignored.

A technical problem of the present invention is to perform a fatigue test with high accuracy between a desired maximum load value and a minimum load at which a load starts to occur even in a fatigue test by displacement feedback control, even if the spring test piece is fatigued. .

D. Means for Solving the Problem Explaining with reference to FIG. 1 which is a diagram corresponding to claims, the fatigue test apparatus according to the present invention has a specimen 11 with a displacement pattern that vibrates between a set maximum displacement and minimum displacement. A load mechanism 10 for repeatedly applying a compressive load, a load detecting means 12 for detecting a load acting on the specimen 11, a displacement detecting means 13 for detecting a displacement of the specimen 11, and a displacement while feeding back the detected displacement. A drive control means 15 for driving the load mechanism 10 so that the sample 11 is loaded in a pattern, and both detection means 12, 13
In accordance with the detection result from, the storage means 153 for storing the initial minimum displacement and the initial maximum load at the minimum load at the start of the test, and the displacement detection means 13 in each repeated cycle.
Using the minimum value of the displacement detected from the stored initial minimum displacement, the minimum displacement set so as to reduce the difference between the two displacement values is corrected, and is detected from the load detecting means 12 in each repeating cycle. Correction means for correcting the set maximum displacement so as to reduce the difference between these load values by using the maximum value of the load and the stored initial maximum load.
151 is provided to solve the above technical problem.

E. Action If the difference between the minimum displacement detected during each repeated cycle and the initial minimum displacement at the time of the minimum load at the beginning of the test due to fatigue of the specimen 11, the difference between both displacement values becomes small. Thus, the minimum displacement of the displacement pattern is corrected. As a result, the set minimum displacement in each repeated cycle is
The load will start to occur at the place given to 11.

Also, the maximum load detected during each repeated cycle,
When a difference from the initial maximum load at the start of the test occurs, the maximum displacement of the displacement pattern is corrected so that the difference between both load values becomes small. As a result, the initial maximum load is always obtained when the set maximum displacement in each repeated cycle is applied to the test piece 11.

In the above D and E for explaining the configuration of the present invention, the reference numerals of the embodiments are used to make the present invention easy to understand, but the present invention is not limited to the embodiments.

F. Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 2 is an overall configuration diagram showing an embodiment of a fatigue test apparatus for a spring specimen according to the present invention.

In the figure, 10 is a main body of the tester that constitutes the load mechanism of FIG. 1, and includes a crosshead 10b attached to a yoke 10a so as to be vertically movable, and an upper jig 10c attached to the crosshead 10b via a load cell 12. An actuator 10e for loading repeated load installed in the base 10d and a lower jig 10f attached to a movable part of the actuator 10e are provided, and a disc spring or the like is provided between the lower jig 10f and the upper and lower jigs 10c. Spring specimen
11 are intervening. Reference numeral 13 is a differential transformer that detects the stroke of the actuator 10e, that is, the displacement during repeated loading.

The control device 15 is composed of a microcomputer, and has a CPU (central processing unit) 151 for controlling the whole, a ROM 152 for storing a processing program described later, a calculation result in the CPU 151 and detection from the load cell 12 and the differential transformer 13. A RAM 153 for storing data and the like, an input interface 154, and an output interface 155 are provided, and these are connected to the CPU 151 via a bus 156. Here, the controller 15 constitutes drive control means, the RAM 153 constitutes storage means, and the CPU 151 constitutes correction means.

The load cell 12 and the differential transformer 13 are connected to the input interface 154 via A / D converters 16 and 17, respectively. The output interface 155 has a D
Servo valve for actuator 10e via A / A converter 18
0e1 is connected.

Next, the operation of this embodiment configured as described above will be described with reference to the flowchart of FIG.

In the fatigue test of the spring test piece 11 such as a disc spring having the load-displacement characteristic shown in FIG. 4, when the control device 15 is started by an external command from a keyboard (not shown), the test is performed in the procedure shown in FIG. Begins.

First, as shown in step S1 of FIG.
The lamp displacement command data is read from the ROM 152, and the lamp displacement command data is output to the servo valve 10e1 of the tester body 10 through the output interface 155 and the D / A converter 18 to control the displacement of the actuator 10e. Here, the displacement control is a control system in which the displacement output from the differential transformer 13 is fed back to control the actuator 10e so that the spring test piece 11 is deformed according to the displacement command data. As a result, the spring test piece 11 between the jigs 10c and 10f is statically started to be loaded from the unloaded state to the preset maximum load P ₁ . At this time, the load applied to the spring test piece 11 is detected by the load cell 12, converted into a digital amount by the A / D converter 16, and input to the control device 15. The stroke displacement of the actuator 10e is detected by the differential transformer 13, converted into a digital amount by the A / D converter 17, and output to the control device 15.

In the next step S2, the spring specimen 11
When loading from the unloaded state to the specified maximum load P ₁ ,
Displacement of the point where load starts to occur (this is called the minimum load)
V ₀ and (see FIG. 4), the displacement V ₁ to the maximum load P ₁ (4
(Refer to the drawing) is detected by the differential transformer 13, fetched in the CPU 151, and stored in the RAM 153. After that, the actuator 10e is returned to the state of the displacement V ₀ , and the process proceeds to step S3. Step
In S3, the displacement command waveform that gives a repetitive load is a herb-sine wave, and its frequency is f, and
When V ₀ (initial minimum displacement) is set as the minimum displacement Vm and C × (V ₁ −V ₀ ) is set as the amplitude Va, the displacement pattern becomes as shown in FIG. Here, C ₁ is a constant given by 0 << C <1. After such setting, when the actuator 10e is vibrated by the displacement control and the load is repeatedly applied to the spring specimen 11, the spring specimen 11 has a minimum displacement Vm and a minimum displacement.
It deforms repeatedly between Vm and Va.

The amplitude Va is small enough not to be overloaded when the spring test piece 11 is maximally displaced.

Next, in step S4, the maximum load Pmax of the spring test piece 11 when excited by the displacement pattern shown in FIG. 5, the maximum displacement Vmax at this time, the minimum load Pmin, and the minimum displacement Vmin at this time, and the intermediate Measure the values P ₃ and V ₃ . That is, the maximum value Pmax and the minimum value Pmax are obtained by loading the load on the spring test piece 11 detected by the load cell 12 into the CPU 151 of the control device 15.
The min and the intermediate value P ₃ are identified and stored in RAM 153. In addition, the spring specimen 11 detected by the differential transformer 13
The maximum value Vmax by entrapping CPU151 of the displacement control device 15, identifies the minimum value Vmin and the intermediate value V _3, RAM of
Store in 153.

In the next step S5, based on the above setting data and detection data Is executed by the CPU 151 to determine whether or not the displacement amplitude due to vibration exceeds N% of the initial amplitude (N is a preset reference value). Here, the displacement amplitude by Vmax-Vmin is V ₁ -
When it is determined that the initial amplitude due to V ₀ exceeds N%, the test of the spring test piece 11 is terminated.

If it is determined that it is N% or less, step S6.
To proceed, | determines whether the <ε _V | _{V 0} -Vmin. This is because the spring constant of the spring test piece 11 decreases with repeated load, so it is necessary to always correct the displacement of the minimum displacement Vm of the displacement pattern according to this decrease, but this is a step of determining whether or not the correction is necessary. .

That is, when it is determined that the difference of | V ₀ −Vmin | is larger than the standard deviation εv, the minimum value Vmin is far from the initial minimum displacement V ₀ corresponding to the minimum load measured at the start of the test, and therefore, the process proceeds to step S7 _{in, Vm = Vm + (V 0} -Vmin) / 2
Is executed to correct the minimum displacement Vm of the displacement pattern. That is, when the minimum displacement Vm is given during the test,
It is always corrected so that the spring 11 is deformed by the minimum load at the beginning of the test. When it is determined that the difference of | V ₀ −Vmin | is smaller than the reference deviation ε _V, step S7 is skipped and the process proceeds to step S8.

In step S8, | determines <ε _P | _{P 1} -Pmax. That is, it is determined whether or not the difference between the preset maximum load P ₁ and the maximum value Pmax detected by the load cell 12 during vibration is smaller than the reference deviation ε _P. Here, when it is determined that it is smaller than ε _P , the process returns to step S4, and when it is determined that it is greater than ε _P , the process proceeds to step S9. In this step S9, the corrected amplitude Va by performing the calculation of _{Va = Va + (P 1 -Pmax} ) × α. However, α = {(V ₁ −V ₃ ) /
(P ₁ −P ₃ )} × C, which represents the slope of the load-displacement characteristic curve with good linearity. That is, if the spring constant of the spring test piece 11 decreases, the maximum load does not become P ₁ even if the spring test piece 11 is displaced by the amplitude Va set at the start of the test, so when the amplitude Va is given by the above correction, the maximum load becomes P _1. Correct the amplitude Va so that the load P ₁ is obtained.

In the next step S10, it is determined whether the displacement value exceeds the measurement range. If it is within the measurement range here, step
When returning to S4 and exceeding the measurement range, no further correction is possible, so the test of the spring specimen ends.

In the present embodiment as described above, when the spring is repeatedly loaded by the displacement control, when the minimum displacement Vm of the displacement pattern is given to the spring, the minimum displacement Vm is always generated from that position. And the maximum load is always applied at that position when a displacement of amplitude Va is applied to the spring.
The amplitude Va is corrected so that P ₁ is generated, and if there is an increase of N% in amplitude with respect to the initial amplitude, it is determined that the life has ended and the test is ended. Therefore, as shown in FIG. 4, for a spring specimen such as a disc spring having a wide zero load range, a fatigue test should be performed between the minimum load near zero load and a predetermined maximum load as if the load was controlled. It is possible to perform highly accurate tests.

The fatigue test apparatus of the present invention is not limited to the circuit system of the above embodiment.

G. Effect of the Invention As described above, according to the present invention, when a fatigue test is performed by displacement control according to a set displacement pattern, the minimum displacement and the maximum displacement of the displacement pattern are sequentially corrected as if the load was zero. It is possible to carry out a test so as to control the load between a load and a predetermined maximum load, and it is possible to perform a fatigue test on a test piece having a wide spring property in the zero load range with high accuracy up to near the zero load.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim according to the present invention. FIG. 2 is a configuration diagram of a fatigue test apparatus for a spring specimen showing an embodiment of the present invention. FIG. 3 is a flow chart showing the operation procedure of the fatigue test process in this embodiment. FIG. 4 is a load-displacement characteristic diagram for explaining the spring test piece in the present embodiment. FIG. 5 is a waveform diagram of the displacement pattern in this embodiment. FIG. 6 is a load-displacement characteristic diagram of a conventional spring test piece. 10: Load mechanism, 11: Spring specimen 12: Load cell, 13: Differential transformer 15: Controller, 151: Correction means 153: Storage means

Claims (1)

[Claims] 1. A load mechanism for repeatedly applying a compressive load to a sample in a displacement pattern that oscillates between a maximum displacement and a minimum displacement that have been set, load detection means for detecting a load acting on the sample, and Displacement detecting means for detecting the displacement of the sample, drive control means for driving the load mechanism so that the sample is loaded in the displacement pattern while feeding back the detected displacement, and both the detecting means. Storage means for respectively storing the initial minimum displacement and the initial maximum load at the minimum load at the start of the test according to the detection result, the minimum value of the displacement detected by the displacement detection means in each repeating cycle, and the stored initial minimum Displacement is used to correct the set minimum displacement so as to reduce the difference between these displacement values, and at the same time, the load detection means A fatigue test comprising: a correction means for correcting the set maximum displacement so as to reduce the difference between the load values by using the maximum value of the detected load and the stored initial maximum load. apparatus.