JPS587935B2 - Zairiyoushikenhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a material testing device, particularly for measuring yield point load, yield elongation, etc. in a tensile test.

In general, there is no need to explain the importance of accurately measuring various properties of materials in material tests, but for example, in tensile tests, stress-strain curves (S stress
-S train Curve...゜hereinafter S
-S curve) is drawn as shown in FIG.

Among these, the yield point includes the maximum load point just before the start of yielding (upper yield point) and the stress at the lowest load during the progression of the yielding phenomenon (excluding the point affected by the initial inertial force) (lower yield point). Although the former has conventionally been automatically measured, it is difficult to accurately determine such a minimum load when measuring the latter, and conventionally there has been no device that can automatically measure this.

In addition, the elongation during the descending phenomenon period (yield elongation) is also related to the workability of the material. For example, in order to minimize wrinkles during press forming, thin sheets are manufactured to minimize the yield elongation, and quality control is carried out. For example, it is also done artificially by applying a ruler to the S-S curve drawn on a recorder chart, but this varies from person to person, and even when using a computer, After point A appears, point A' reaches the upper yield point load again.
It has been attempted to use the extension AA' as a substitute, but this was only a very rough approximation.

The present invention takes the above circumstances into consideration and provides a method for accurately and automatically measuring the lower yield point and yield elongation.

Examples of the present invention will be described below.

FIG. 2 is a schematic configuration diagram of the material testing apparatus of the present invention, and 1
2 is a sample to be tested, 2 and 2' are chuck parts for gripping the sample, 2 is fixed, and 2' is connected to a loading device (not shown).

Reference numeral 3 denotes an extensometer that measures the elongation of the sample 1 and generates a signal corresponding to the elongation, and is configured using, for example, a differential transformer.

4 is a load detection device that generates a signal proportional to the load on the sample.

5 and 6 are AD converters, respectively, 7 and 8 are gate circuits, 9 is a CPU of a data processing computer, 10 is a storage device, 11 is an arithmetic device, 12 is a control device, and 1
2, a sampling command pulse is generated every predetermined minute time and applied to the gates 7 and 8, and the AD-converted elongation signal and load signal are stored in the storage part A of the storage device 10.
, B are stored in association with addresses.

In the configuration shown in FIG. 2, the operation of calculating the upper yield point and yield elongation can be performed by a hardware circuit configuration or by a program.

The storage portion D of the storage device 10 in FIG. 3 contains a program for this purpose.

FIG. 3 shows an example of a flowchart showing the general flow of this program.

The measurement operation will be explained below based on the flowchart shown in FIG.

When the program starts, the CPU first applies a sampling command to the gate circuits 7 and 8 every minute time t of about 20 milliseconds, and the sampled values of load and elongation are stored in the memory area 10 [load/elongation]. Sampling storage step a].

On the other hand, the extreme value of the load (
[extreme value detection step b].

Then, it is determined that the first minimum value (point B) affected by the inertial force has been exceeded [extreme value number determination step number c], and after this, the extreme value (C, D, E, F in Figure 2) is exceeded. corresponding) to the register [extreme value extraction step d].

Then, when the number of extreme values taken out in the register reaches a certain value [extreme value extraction number determination step e], their average value Y=C is calculated and stored [lower yield point load value calculation step f] lower yield point load value is output from the CPU and printed out.

In some cases, it may be easier to average only several extreme values of the load signals after the third extreme point among the sampled values at each time t.

In addition, in step e for determining the number of times of extreme value extraction, the difference between the extreme value extracted last time and the extreme value extracted this time has reached a predetermined value or less, or the load value for each period t corresponding to the above case is determined. It can also be replaced with a step of determining whether it has been taken out.

On the other hand, after the first extremely thick load (upper yield point load) is detected, this maximum load value is always compared with the load value sampled at every time t, and points on the S-S curve showing the same load value are Find [first extreme value corresponding point detection step g].

Then, constants d and b of Y=dX+b that are tangent to the SS curve at this point are calculated [tangent calculation step h].

From the equation obtained earlier, the following equation (1.>(2) is solved as a simultaneous equation to obtain X=(c-b)/a-'X2.

This X-X20 point Q is very close to the final stage of yield elongation, so X2 and the elongation at the upper yield point measured earlier = X
, X3 in the following equation (3) is found to be a value very close to the yield elongation [yield elongation calculation step i].

Then, the output is printed out from the CPU.

X3-X2-X1 (3) As is clear from the above general description, according to the present invention, the lower yield point and yield elongation in a tensile test can be accurately and automatically measured.

Note that the present invention is applicable not only to tension tests but also to compression tests.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a material testing method according to the present invention, FIG. 2 is a schematic diagram of an apparatus according to the present invention, and FIG. 3 is a diagram showing an example of a program for determining the lower yield point and yield elongation according to the present invention. 1...Sample, 2,2'...Chuck, 3...Extensometer, 4
...Load detection device, 5, 6...AD converter, 7, 8...
Gate circuit, 9...CPUo

Claims (1)

[Claims] 1. A material characterized by detecting extremely thick and extremely small values after the third extreme value of a load signal on a load (or stress)-strain curve, and determining the lower yield point by averaging these. Test method. 2 Find a straight line tangent to the curve from the point where the load (or stress)-strain curve again reaches a load approximately equal to the first maximum load, and calculate the yield from this tangent and the lower yield point found according to claim 1. A material testing method characterized by determining the final stage of elongation.