JPH07109392B2 - Repeated impact fatigue tester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a tester for repeatedly applying an impact load to a test piece.

B. Conventional technology In the conventional repeated impact tester, the actual load is tested by performing a feedback test so that the load acting on the test piece has a preset repeated load waveform (load pattern).

C. Problem to be Solved by the Invention However, according to such a load feedback control, the punch of the load actuator is in an uncontrolled state in the unloaded state in which the punch is separated from the test piece, and the speed at the time of punch collision is not stable. , As a result, impact force (maximum load)
Becomes unstable. Note that the load feedback control system is essentially unable to control the speed due to the control system.

Therefore, it is conceivable to carry out the test by feeding back the actual displacement of the load actuator so as to obtain a preset displacement waveform (displacement pattern), but in this case, because of deformation of the test piece due to fatigue, collision speed or The impact force changes over time.

A technical problem of the present invention is to perform control in a fatigue test by displacement feedback control so as to obtain a desired collision speed and maximum load even when a test piece is deformed.

D. Means for Solving the Problem Explaining with reference to FIG. 1 which is a claim correspondence diagram, the repeated impact fatigue testing machine according to the present invention performs a test with a displacement pattern having a waveform determined by a predetermined displacement average value, amplitude and frequency. Piece 11
Load actuator that repeatedly applies impact load to
Load detection means 12 for detecting the load acting on the test piece 11 and 10A
A displacement detection means 13 for detecting the displacement of the load actuator 10A, and a pre-test performed prior to the repeated impact test, and a substantially intermediate value between the maximum value and the minimum value of the displacement detected by the displacement detection means 13. With load actuator 10A
Pre-test correction means for correcting the displacement average value so that the collision starts with the test piece 11, and for correcting the amplitude so as to reduce the difference between the predetermined maximum load and the maximum load detected by the load detection means 12. 151 and a repeated impact test that is performed with the corrected amplitude fixed, during a test to correct the displacement average value so as to reduce the difference between the maximum load determined in advance and the maximum load detected by the load detection means 12. Correction means
152, and drive control means 15 for driving the load actuators 10A during the pre-test and the repeated test so that the test piece 11 is loaded with the displacement patterns corrected by the pre-test correction means 151 and the test-time correction means 152, respectively. The above-mentioned technical problem is solved by including.

E. Action By correcting the above displacement average value to an intermediate value between the displacement at maximum load detection and the minimum displacement at no load, the load actuator 10A always collides with the test piece 11 at the displacement average value. Further, by correcting the above amplitude so as to reduce the difference between the maximum load detected and the maximum load determined in advance,
A desired maximum load can be applied to the test piece 11. Further, the displacement average value is corrected so that the difference between the maximum load detected during each repeating cycle and the predetermined maximum load is reduced while the amplitude thus determined is fixed. As a result, in each repeated cycle, the load actuator 10A always collides with the test piece 11 at the same speed, a desired maximum load is obtained at the time of maximum displacement, and a stable test is performed.

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 the repeated impact fatigue tester according to the present invention.

In the figure, actuator 10A that applies repeated load
The fatigue tester 10 is composed of a servo valve 10B for controlling the actuator 10A and a punch 10C attached to a movable part of the actuator 10A, and the punch 10C repeatedly applies an impact load to the test piece 11. Reference numeral 12 is a load cell that detects the load acting on the test piece 11, and 13 is a displacement meter that detects the stroke of the punch 10C.

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 data from the load cell 12 and the displacement meter 13. A RAM 153 for storing the like, and an input interface 154 and an output interface 155, which are connected via a bus 156.
It is connected to the CPU 151. Here, the control device 15 constitutes drive control means, and the CPU 151 constitutes correction means.

The load cell 12 and the displacement meter 13 are connected to the input interface 154 via A / D converters 16 and 17, respectively. Further, the output interface 155 is connected to the servo valve 10B of the tester main body via the D / A converter 18.

Next, the operation of the present embodiment thus constructed will be described with reference to the flowchart of FIG.

First, when the controller 15 is started by an external command from a keyboard (not shown) or the like, the test starts in the procedure shown in FIG.

In step S1 of FIG. 3, the lamp displacement command data is read from the ROM 152 of the control device 15, and the lamp displacement command data is output. Interface 155 and D / A converter 18
To the servo valve 10B of the tester body 10 to control the displacement of the actuator 10A. Here, the displacement control is
This is a control method in which the displacement output from the displacement gauge 13 is fed back to the control device 15 to control the actuator 10A to be displaced according to the displacement command data. As a result, the maximum load Pmax ₀ preset from the no-load state to the test piece 11
Start loading statically until. At this time, the load applied to the test piece 11 is detected by the load cell 12, and the A / D converter 16
Is converted into a digital amount and input to the control device 15. Further, the stroke displacement of the actuator 10A is detected by the displacement meter 13, converted into a digital amount by the A / D converter 17, and input to the control device 15. These load and displacement data are stored in the RAM 153 as a static load-displacement diagram of the test piece 11 (step S2).

In the next step S3, based on the load-displacement diagram obtained in step S2, the displacement Sm ₀ at the point where the load starts to be generated (this is called the minimum load) is read, and this displacement Sm ₀
Is set to the displacement average set value S'm. Also, the maximum load Pm
Loading displacement Smax ₀ for ax _0, this displacement Smax ₀ and multiplied by a constant C (<1) the initial target amplitude S'a this result
Set to. Further, from the preset punch velocity V and the read displacement Smax ₀ , the frequency of the displacement pattern is obtained by f = V / 2πSmax ₀ . Then, the displacement command waveform is set to a herb-sine wave, and a load pattern signal having a frequency f, a displacement average set value S'm and an amplitude S'a as shown in FIG. 4 is supplied to the servo valve 10B. As a result, the actuator 10A vibrates and a shock load is repeatedly applied to the test piece 11 (step S4).

Next, in step S5, the load of the test piece 11 and the displacement of the actuator 10A vibrated in the displacement pattern shown in FIG. 4 are read respectively, and in step S6, the displacement at the beginning of the load application, that is, at the minimum load Displacement S ₀ of
The displacement Smax with respect to the maximum load Pmax (see FIG. 4) and the maximum displacement Smin in the no-load direction when the load is zero (see FIG. 4, referred to as minimum displacement) are measured. That is, the load cell 12
The load and the displacement detected by the displacement gauge 13 are stored in the RAM 153 of the control device 15, and based on this data,
Find S ₀ , Smax, and Smin. Then, in step S7,
The deviation amount ΔSm of the average displacement value is It is determined from | ΔSm | <εs. This is because the test piece 11 deforms with repeated impact load, and the displacement point at which the punch 10C starts to collide with the test piece 11 changes, so the displacement average set value Sm ′ of the displacement pattern is always corrected according to this deformation. This is the step of determining whether or not the correction is necessary.

That is, when it is determined that | ΔSm | is larger than the standard deviation εs, the true average displacement value of the punch 10C corresponds to the displacement S ′ ₀ corresponding to the minimum load measured in step S6 at the start of the test.
Since it is far from, go to the next step S8, Is executed to correct the displacement average set value Sm ′ of the displacement pattern. That is, when the displacement average set value Sm ′ is given during the test, the punch 10C always moves at that position at the punch 11C.
Correction is made so as to start colliding with and the process returns to step S6. When it is determined that | ΔSm | is smaller than the reference deviation εs, step S8 is skipped and the process proceeds to step S9.

In step S9, the maximum load Pmax is read from the displacement-load curve collected in step S5, and in step S10,
ΔP = Pmax ₀ −Pmax is calculated to determine whether | Pmax ₀ −Pmax | <εp. That is, it is determined whether or not the absolute value | ΔP | of the difference between the preset maximum load Pmax ₀ and the maximum value Pmax detected by the load cell 12 during vibration is smaller than the reference deviation εp.
Here, when it is determined that it is larger than εp, step S11
If it is determined that the value is smaller than εp, the process proceeds to step S12.

In step S11, Sa ′ = Sa ′ + (Pmax ₀ −Pmax)
The amplitude Sa ′ is corrected by executing the calculation of × α, and the process returns to step S6. However, α = {(Smax ₀ −Sm ₀ ) / (Pm
ax ₀ −0)} × C, which represents the slope of the load-displacement characteristic curve with good linearity. Note that C is 0 <C <1. That is, as the fatigue of the test piece 11 progresses, the maximum load does not reach Pmax ₀ even if the test piece 11 is displaced by the amplitude Sa ′ set at the start of the test. Correct so that Pmax ₀ is obtained.

By the procedure as described above, the initial steady state in which the initial displacement average value is So and the initial displacement amplitude is (Sa ') is set. After that, in order to keep the collision speed constant, the amplitude is kept constant Sa 'and the average value So is corrected to maintain the maximum load.

That is, if | ΔP | <εp is determined in step S10, the repeated impact test is continued in step S12, and load and displacement data are collected in step S13. Next, in step S14, the load S starts to be applied, that is, the displacement S at the minimum load and the maximum load Pmax are detected, and the process proceeds to step S15. In step S15, the detected displacement S
And a difference between the initial average value So and a predetermined reference value S _R are determined. If this step S15 is affirmed, the test piece 11 has been considerably deformed, so the test ends. When step S15 is denied, the process proceeds to step S16, and it is determined whether or not the absolute value | Pmax ₀ −Pmax | of the difference between the maximum load Pmax ₀ at the start of the test and the detected maximum load Pmax is smaller than the reference deviation εp. To do. If step S16 is affirmed, the procedure returns to step S12 to continue the test, and if not, proceeds to step S17, where Sm ′ = Sm ′ + (Pmax ₀ −Pmax) × α for the average value S′m. Apply correction. As a result, the amplitude is maintained constant at Sa ′ and the initial average value So is corrected according to the deformation of the test piece 11, so that the impact test is repeatedly performed with a constant maximum load while keeping the collision speed constant. That is, when the impact test is repeated, the test piece 11 becomes fatigued, and the distance between the actuator 10A and the test piece 11 gradually changes, so that the impact force is different even when the impact test is performed with the amplitude of the actuator 10A fixed. .
Therefore, in step S17 in FIG. 3, the displacement average value is always corrected so that the load starts to be applied with the displacement average value, and the impact test is performed with the amplitude determined in step S11. The collision speed and impact force can be kept constant regardless of

In this embodiment, when the impact load is repeatedly applied to the test piece by displacement control, the actuator 10A
Correct the displacement average value so that the punch 10C starts a collision with the test piece TP at the midpoint between the maximum value and the minimum value of the actual displacement of, and then correct the amplitude so that the desired maximum load is obtained, and further, This amplitude was fixed and the displacement average value was corrected so that the desired maximum load was obtained. Therefore, even if the test proceeds, as shown in FIG. 5, the maximum load is generated at the maximum value of the displacement pattern, and as shown in FIG. 6, the displacement amount under no load and the displacement amount under load are Is 1: 1 and the collision speed and impact force are maintained with high accuracy, and a highly accurate fatigue test is possible.

Further, in the conventional repeated impact fatigue testing machine, since the test is performed until the test piece is broken such as cracked or punched, the test time is long.
However, in the present embodiment, the test is stopped when the displacement of the actuator 10A when the load starts to be applied exceeds a predetermined value, so that it is not necessary to perform the test until the test piece is completely destroyed, and the test time is shortened. In addition to being able to do so, the fatigue status of the test piece can be clearly understood.

In the above examples, after the initial steady state, the amplitude was kept constant to make the collision speed constant.However, when the rigidity of the test piece fluctuates significantly, the frequency of the displacement pattern also needs to be gradually changed. There is. Further, the fatigue testing machine of the present invention,
The circuit method of the above embodiment is not limited.

G. Effect of the Invention Since the present invention is configured as described above, when performing a fatigue test by displacement control with a set displacement pattern, even if the test piece is deformed or its rigidity decreases due to fatigue, it is always constant. The load actuator can collide with the test piece at a speed and can be loaded with a desired impact load,
Stable and highly accurate tests are performed.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim according to the present invention. FIG. 2 is a block diagram of a repeated impact fatigue testing machine 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 waveform diagram of the displacement pattern. FIG. 5 shows the load of the test result by the fatigue tester of this embodiment,
It is a displacement time diagram. FIG. 6 is also a load-displacement diagram. 10: Testing machine body, 10A: Actuator 10B: Servo valve, 10C: Punch 11: Test piece, 12: Load cell 13: Displacement meter, 15: Control device 151: Correction means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keihiro Nakamura 19 Nishinokyo Shimogoicho, Nakagyo-ku, Kyoto City, Kyoto Prefecture Shimazu SDC Co., Ltd. (56) Reference JP-A-61-210925 (JP, A)

Claims (1)

[Claims] 1. A load actuator for repeatedly applying an impact load to a test piece in a displacement pattern having a waveform determined by a predetermined displacement average value, amplitude and frequency, and load detection means for detecting a load acting on the test piece. Targeting a displacement detection means for detecting the displacement of the load actuator and a pre-test conducted prior to a repeated impact test, the load is set at a substantially intermediate value between the maximum value and the minimum value of the displacement detected by the displacement detection means. A test in which the actuator corrects the displacement average value so as to start a collision with the test piece, and corrects the amplitude so as to reduce the difference between a predetermined maximum load and the maximum load detected by the load detection means. A pre-correction unit and a repeated impact test performed with the corrected amplitude fixed are targeted, and the predetermined maximum load and the load detection unit are used. Test means for correcting the displacement average value so as to reduce the difference in maximum load detected by the test piece, and the test piece is loaded with the displacement pattern corrected by the pre-test correction means and the test time correction means. As described above, the repeated impact fatigue testing machine is provided with drive control means for respectively driving the load actuators during the pre-test and the repeated test.