JPH0695061B2 - Upper yield point detection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for detecting an upper yield point in a material test.

B. Conventional technology and its problems In a material test that examines the relationship between load and elongation for the material under test, the upper yield point (see Fig. 2), which is one characteristic of the material, is detected.

By the way, in the conventional data device for the material testing machine, the upper yield point is detected only on the basis of the load reduction sensitivity setting value (d). That is, as the detection algorithm, the sampling load during the test is the load (Lp
When the load decreased by more than the set load reduction sensitivity from k) and then the load again increased from the maximum load value (Lpk) up to then, this Lpk point was determined as the upper yield point. Explaining with reference to FIG. 3, the sampling value L _i of the load at the sampling time t _i is taken as the maximum load value Lpk up to t _i.
And L _i (Lpk−L _i ) satisfies Lpk−L _i ≧ d (d is the load reduction sensitivity setting value),
When L _{i + n} > Lpk is satisfied thereafter, the Lpk point is detected as the upper yield point.

However, with the detection method that only checks the load reduction sensitivity as described above, the instantaneous load reduction during the test due to external noise or chuck slip that occurs between the test piece grip (chuck) and the test piece is yielded. There was a problem that it was detected as a point (see point A in FIG. 4).

C. Means for Solving Problems The present invention has been made to overcome the above problems, and when detecting the upper yield point, it is caused by noise during the test and chuck slip. It is an object of the present invention to provide an upper yield point detection method capable of preventing false detection.

In order to achieve the above-mentioned object, the upper yield point detection method according to the present invention, the load on the material under test is decreased by more than a predetermined load reduction sensitivity, and then until the load exceeds the maximum load value (Lpk) until then. Is measured, and the Lpk point is detected as the upper yield point only when the load exceeds the maximum load value after a certain set time has elapsed as a result of this measurement.

D. Embodiment FIG. 5 is a diagram showing a schematic configuration of an embodiment of the present invention. In the figure, in the material testing machine 1, two screw knives 2 and 3 are rotated by a motor (not shown) provided in a pedestal 4, and a crosshead 5 screwed to the screw knives 2 and 3 is moved up and down. It is configured to move. Screw rod 2
The upper ends of 3 and 3 are rotatably supported by a fixed frame 6. The crosshead 5 and the fixed frame 6 are provided with chucks 7 and 8, respectively, and the chuck 7 and 8 hold the test piece 9.

Therefore, when the crosshead 5 moves up and down by the rotation of the screw rods 2 and 3, a compressive force or a tensile force is applied to the test piece 9. The material test is to examine the relationship between the tensile force applied to the test piece 9 and the elongation (or the compression force and the contraction).

A load sensor 10 is provided on the fixed frame 6 in association with the chuck 8. The load sensor 10 is for detecting the load applied to the test piece 9. In addition, the fixed frame 6,
A rotary encoder 11 is provided in association with the screw rod 3. The rotary encoder 11 is for detecting the amount of rotation of the screw rod 3 to detect the amount of movement of the crosshead 5 and thus the extension (or contraction) of the test piece 9.

The output of the load sensor 10 is applied to the load amplifier 12, amplified, and then applied to the A / D converter 13 to be converted into a digital signal. The output of the A / D converter 13 is given to the CPU 14. On the other hand, the output of the rotary encoder 11 is given to the crosshead movement amount pulse counter 17 and the output pulse number is counted. Cross head movement pulse counter
The output of 17 is given to the CPU 14.

ROM15 and RAM16 are connected to CPU14. The operation program of the CPU 14 as shown in FIG. 1 is stored in the ROM 15. The RAM 16 is for storing various data necessary for the data processing of the CPU 14, and includes a time counter Tc and a load down flag DF as a storage area of particular interest to the present invention.

FIG. 1 is a flow chart for explaining the operation of the CPU 14 shown in FIG. FIG. 6 is a graph for explaining the upper yield point detection principle in the above-mentioned embodiment, and the test piece 9
It shows the relationship between the load given to and the sampling timing.

First, the principle of upper yield point detection in this embodiment will be described with reference to FIG. The load is the maximum load value so far Lp
The minimum time set value from the time when the load reduction sensitivity d falls below k by more than the set load d until the load exceeds Lpk again is a × Δt. (Here, a is an integer, Δt is a sampling period, and in this embodiment, for example, a = 4 and Δt = 50 ms.) In this embodiment, in addition to the conventional check of the load reduction sensitivity d, the time a · The Δt is determined and the upper yield point is detected. That is, assuming that the load L _{i at} the sampling time t _i satisfies Lpk−L _i ≧ d (d: load reduction sensitivity) as compared with the maximum load value Lpk until then, the load at the subsequent time t _{i + n} Compare L _{i + n} with Lpk. If L _{i + n} > Lpk, the time is further checked.

If t _{i + n} −t _i ≧ a · Δt, that is, n ≧ a is satisfied, the Lpk point is determined as the upper yield point. If n <a, the Lpk point is not the upper yield point,
The L _{i + n} point is newly replaced with the maximum load value and the subsequent detection is continued.

Next, a more specific operation of the above embodiment will be described with reference to FIG. First, at step S1, an arbitrary time t
sampling the load _{L k} in _k. Then, in step S2, the maximum load value Lpk up to that point is detected. When the maximum load value Lpk is detected, the routine proceeds to step S3, where it is judged if the load down flag DF is set or not. Initially, the load down flag DF is reset, so the routine proceeds to step S4, where it is judged whether or not the decrease value of the load from the maximum load value Lpk has decreased by the set load decrease sensitivity d or more.
When the decrease value of the load has not dropped to the set load decrease sensitivity d, the operation returns to step S1, but the set load decrease sensitivity d
If it has decreased more than this, the load down flag DF is set in step S5. Then, in step S6, the time counter Tc is cleared. Then, the operation returns to step S1.

After the operations of steps S1 and S2, it is determined in step S3 that the load down flag DF is set, and the process proceeds to step S7. In step S7, the time counter Tc is incremented and the time counting operation is started. Succeedingly, in a step S8, it is determined whether or not the load value Lk sampled this time exceeds the maximum load value Lpk so far. Load value L _k is maximum load value Lp
If k is not exceeded, the process returns to step S1 again and a new load value is sampled. After that, steps S1 to S
A series of operations of 3, S7, S8 are repeatedly performed, and the load value L _k
When exceeds the maximum load value Lpk, the routine proceeds to step S9, where it is judged whether or not the value of the time counter Tc is larger than a preset value a. That is, the time width t between the time point t _i that drops from the maximum load value Lpk set load decreased sensitivity d or more until the time t _{i + n} to rise above the maximum load value again
_It is determined whether _{i + n-} t _i is larger than a predetermined time width a · Δt (Δt sampling period). If the time width t _{i + n} −t _i is smaller than the time width a · Δt, the load down flag DF is reset in step S10, and then the operation returns to step S1. That is, in this case, the maximum load value Lpk is not regarded as the upper yield point. On the other hand, when the time width t _{i + n} −t _i is larger than the time width a · Δt, the process proceeds to step S11 and the Lpk point is set as the yield point Yp.
Store in RAM16.

E. Effect of the Invention As described above, according to the present invention, the load after the upper yield point decreases relatively slowly and then rises, and the instantaneous load caused by external noise or chuck slip after the upper yield point. Focusing on the fact that the decrease occurs, especially since the judgment of the time width after the load decrease sensitivity falls below the set value is added to the upper yield point detection algorithm, the influence of noise and chuck slip can be eliminated accurately. Real-time detection of the upper yield point is possible.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining the operation of the CPU 14 shown in FIG. FIG. 2 is a diagram showing a load-elongation curve in a material test. FIG. 3 is a diagram for explaining a conventional upper yield point detection algorithm. FIG. 4 is a diagram for explaining the problems of the conventional upper yield point detection method. FIG. 5 is a diagram showing a schematic configuration of an embodiment of the present invention. FIG. 6 is a diagram for explaining the upper yield point detection principle of one embodiment of the present invention, and shows the relationship between the load applied to the test piece 9 and the sampling timing. 1 …… Material testing machine 5 …… Crosshead 9 …… Test piece 10 …… Load sensor 11 …… Rotary encoder 14 …… CPU 15 …… ROM 16 …… RAM Tc …… Time counter DF …… Load down flag 17 ...... Crosshead movement pulse counter

Claims (1)

[Claims] 1. A method for determining the upper yield point of a material under test in a material test for investigating the relationship between load and elongation for the material under test, the method being performed again after the load falls below a predetermined load reduction sensitivity. Load value up to (Lpk)
The time required to exceed the maximum load value (Lp) is measured only when this measurement time exceeds a certain set time.
A method for detecting an upper yield point, characterized by detecting the point k) as an upper yield point.