JPH07109391B2 - Fatigue testing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a fatigue tester in which the combination of frequency and amplitude of repeated load in a fatigue test is limited by the capacity of a hydraulic source.

B. Conventional technology In this type of fatigue testing machine, the load pattern waveform is set by the load average value, the amplitude and the frequency of the repeated load, and the load pattern is set while feeding back the load acting on the test piece. The test is carried out as loaded at. Usually, this type of fatigue testing machine uses a hydraulic cylinder driven by pressure oil supplied from a hydraulic source,
The test conditions are limited by the combination of the amplitude and the frequency based on the capacity of the hydraulic pressure source (for example, the discharge capacity). FIG. 3 is an amplitude characteristic diagram of the hydraulic power source, and the test can be performed within the range surrounded by the solid line SL, the horizontal axis and the vertical axis.

C. Problem to be Solved by the Invention However, if the rigidity of the test piece TP decreases and the amplitude of the load actuator becomes larger than the initial value, the range shown in FIG. 3 may be exceeded. Therefore, conventionally, an alarm is issued by detecting a deviation from the range.

However, the fatigue test generally takes a long time, and the operator does not constantly monitor the testing machine. Therefore, if the test condition is not manually changed when the alarm is issued, the test machine automatically stops, and the test piece TP that has been subjected to the fatigue test for a long time is wasted.

A technical problem of the present invention is to automatically continue the fatigue test even when the range deviates from the range defined by the amplitude characteristic diagram of the hydraulic power source.

D. Means for Solving the Problem To explain with reference to FIG. 1 showing an embodiment, a fatigue tester according to the present invention outputs a load pattern waveform of a predetermined frequency for repeatedly loading a test piece. And a hydraulic actuator 21 that is vibrated based on this load pattern waveform to load the test piece, a hydraulic source 22 of this actuator 21, and a load detection means that detects the load acting on the test piece.
13 and the actuator so that the detected load is fed back and the test piece is loaded with the load pattern waveform.
Drive control means 16 and 19 for driving 21 and a determination means 12 for determining whether or not the capacity of the hydraulic power source 22 exceeds when the momentum of the actuator 21 increases as the rigidity of the test piece decreases during the feedback control. And the frequency changing means 12 for reducing the frequency of the waveform output from the waveform generation circuit 11 when the capacity over is detected by the determination means 12, so as to avoid the capacity over. Is solved.

E. Action For example, the limit curve SL of the amplitude characteristic diagram of the hydraulic power source shown in FIG.
Fatigue tests are performed on load pattern waveforms with frequencies and amplitudes inside. When the rigidity of the test piece decreases with the fatigue test, the momentum (amplitude) of the actuator 21 increases in order to generate a load commensurate with the load pattern. As a result, the intersection of the frequency and the amplitude tends to deviate from the limit curve SL, but when this is determined by the determination means 12, the frequency of the waveform output from the waveform generation circuit 10 is a value within the range of the limit curve SL. Will be reset to. As a result, the fatigue test automatically continues.

It should be noted that, in the above-mentioned items D and E for explaining the configuration of the present invention, the drawings of the embodiments are used to make the present invention easy to understand, but the present invention is not limited to the embodiments.

F. Example FIG. 1 is a block diagram showing the overall configuration of a fatigue testing machine according to the present invention.

Reference numeral 10 denotes a waveform generation circuit that outputs a load pattern such as a sine waveform or a ramp waveform determined by the weighted average value, the amplitude, and the frequency input from the operation unit 11. FIG. 4 shows an example of a sine waveform load pattern.

Reference numeral 12 is a well-known microcomputer including a CPU, ROM, RAM, and the like, and the ROM stores the amplitude characteristic diagram of the hydraulic power source shown in FIG. That is, the limit curve SL and
The recommended curve DL and the inside thereof are stored. Reference numeral 13 is a load cell that detects the load acting on the test piece, and 14 is a displacement meter that detects the stroke of a load actuator 21 that loads the test piece. Reference numeral 15 is a load amplifier that amplifies the output signal of the load cell 13, and 16 is a deviation device that takes the deviation between the load pattern waveform signal output from the waveform generation circuit 10 and the actual load waveform signal output from the load amplifier 15. . 17 is a forward gain setting device that multiplies the output signal of the deviation device 16 by gain, and 18 is an actuator that amplifies the output signal.
It is a servo amplifier that supplies a drive signal to 21 servo valves 19. Reference numeral 20 is a stroke amplifier that amplifies the output signal of the displacement gauge 14, and 22 is a hydraulic pressure source of the actuator.

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

In step S1, the current test is the servo amplifier.
It is judged whether it is within the range of 18 auto gain control (hereinafter called AGC), and if it is within the range, the test is continued as it is. When it deviates from the AGC range, the process proceeds to step S2, and it is determined whether or not the test piece is broken by detecting the maximum actual load or the minimum actual load. If the result is affirmative, the test ends in step S9. If step S2 is denied, the process proceeds to step S3, and it is determined whether the test is completed. This can be determined, for example, by monitoring the strain amount of the test piece and determining whether it exceeds a predetermined value. If the result is affirmative, the test ends in step S9, and if the result is negative, the signal from the stroke amplifier 20 is fetched in step S4 to obtain the current amplitude of the actuator. Next, in step S5, the current frequency is read and the process proceeds to step S6.

In step S6, it is determined whether or not the intersection of the read amplitude and frequency is within the range of the limit curve SL in FIG.
If affirmative, it will return to step S1 as it is, and if negative, it will progress to step S7. In this step S7, the read amplitude is used to find the frequency from the recommended curve DL in FIG. 3, the oscillation frequency of the waveform generating circuit 11 is changed to the found frequency in step S8, and the process returns to step S1.

According to such a procedure, the fatigue test reduces the rigidity of the test piece and applies the same load to the actuator 21.
When the intersection of the amplitude and the frequency deviates from the range of the limit curve SL in the amplitude characteristic of the hydraulic power source shown in FIG. 3 when the amplitude of increases, the preset recommended curve DL is used for the current amplitude. The frequency corresponding to the capacity of the hydraulic power source is automatically set, and the fatigue test is continued. Therefore, even at night when there is no operator, the tester automatically changes the test conditions and the fatigue test continues, and the test piece that has been fatigue tested halfway is not wasted, improving test efficiency. To do.

It should be noted that the frequency may be changed by selecting a value that is inside the limit curve SL at a certain ratio regardless of the recommended curve DL.

G. Effect of the Invention Since the present invention is configured as described above, when the capacity of the hydraulic source becomes insufficient due to the rigidity of the test piece, the frequency of the repeated load is automatically reduced to avoid the capacity overrun. The fatigue test continues and the test efficiency improves.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a fatigue testing machine according to the present invention, FIG. 2 is a flow chart showing a procedure for changing a frequency, FIG. 3 is an amplitude characteristic diagram of a hydraulic source, and FIG. 4 is a load pattern. It is a figure which shows an example. 10: Waveform generation circuit, 12: CPU 13: Load cell, 14: Displacement meter 16: Deviation device, 19: Servo valve 21: Actuator, 22: Hydraulic power source

Claims (1)

[Claims] 1. A waveform generating circuit for outputting a load pattern waveform of a predetermined frequency for repeatedly loading a test piece, a hydraulic actuator for vibrating based on this load pattern waveform to load the test piece, and a hydraulic pressure of this actuator. A source and a load detecting means for detecting a load acting on the test piece,
Drive control means for driving the actuator so that the detected load is fed back and the test piece is loaded with the load pattern waveform, a displacement meter for detecting displacement of the actuator, and the test piece during the feedback control. Determination means for determining whether or not the capacity of the hydraulic power source is over when the momentum of the actuator detected by the displacement gauge increases with the decrease in the rigidity of the actuator, and when the overcapacity is detected by the determination means. A fatigue testing machine, comprising: frequency changing means for reducing the frequency of the waveform output by the waveform generating circuit so as to avoid the overcapacity.