JPH0552724A - Proof-stress measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain an apparatus which can detect proof stress accurately without setting a loading point and without the requirement for manual line drawing. CONSTITUTION:A load measuring part 12, an elongation measuring part 10, a display part 22, an elongation-data memory part 11 and a central processing unit 15 for detecting proof stress are provided. A tension controlling part 21 is connected to the central processing unit 15. Therefore, the setting of a loading point and manual line drawing are not required, working can be simplified and proof stress can be accurately guided out. Furthermore, the result of the measurement can be displayed on the display part in real time. The tension speed can be accurately controlled based on the detection of the proof stress by controlling the tension controlling part with the central processing unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proof stress measuring device capable of accurately detecting a proof stress in a tensile test of a test material and displaying a measurement result in real time.

[0002]

2. Description of the Related Art Generally, in a tensile test of a test material, a yield strength is derived from a material whose yield point does not clearly appear. As a method of deriving the yield strength, an offset method or a total elongation method is used. (JIS Z2241).
Specifically, the offset method defines a base line along the load-stretch diagram within a proportional limit in which Hooke's law is established on the load-stretch diagram obtained by a tensile test, and determines this base line in advance. Further, the total elongation (for example, permanent elongation ratio 0.2%) is offset, and the load at the intersection of this offset base line and the load-total elongation diagram is taken as the proof load. Further, in the total elongation method, the measured load at the total elongation corresponding to the specified permanent elongation is defined as the proof load. The proof stress is derived by dividing the proof load thus obtained by the initial cross-sectional area of the test material.

As a method of determining the baseline in the offset method, it is considered that the baseline is manually drawn along a part of the load-stretch diagram which is considered to be the proportional limit, or it is considered to be within the proportional limit. There is a method in which a load value of a point is determined and these two points are connected on a diagram to form a base line. When setting the load values at two points, the low load value should be considered as the maximum allowable test load value (for example, tensile strength) in consideration of mechanical play that occurs at the initial stage of the extensometer test and slip on the chuck. 120 ~
A load value of a constant ratio to a value of 150%, hereinafter referred to as a load range) is used as a guide, and it is set to exceed at least this load value. The high load value is determined from the relationship between the tensile strength and the yield ratio (material characteristic value). These numerical values are set in advance based on the tensile strength predicted before the test, or based on the tensile strength measured during the test.

[0004]

However, the manual work method in the offset method requires a lot of work, and there is a problem in that the results vary depending on the operator. On the other hand, in the method of setting the load in the offset method, the setting of the load point in advance requires accurate prediction of tensile strength, and it is necessary to determine the yield ratio by understanding the characteristics of the material.
When the work is troublesome and the setting is improper, there is a problem that the tolerance error becomes very large. Also,
When the tensile strength is detected and set during the test, the yield strength cannot be derived in real time, and the result also depends on the measurement accuracy of the tensile strength.

In the load-elongation diagram obtained by the measurement, undulation is usually generated in the diagram due to the measurement accuracy of the measuring instrument and the influence of the shift of the latch timing on the load / elongation measurement value. It is difficult to detect the limits and elastic limits clearly. For this reason, even if the two load points are accurately set based on the tensile strength, there is a problem in that the base line varies, and it is not possible to know the exact yield strength. Moreover, if the base line is determined based on the cyclically measured load, by selecting the load data that goes back and forth, for example, a Young's modulus of ± 50 kg / mm ² is generated, and the base line also has a large difference. Occurs. Further, even in the case of the total elongation method, there is a problem that the obtained data may vary due to the measurement accuracy of the extensometer. The present invention has been made in view of the above circumstances, and provides a proof stress measuring device capable of deriving and displaying a proof stress accurately and in real time and capable of accurately controlling a pulling speed based on the proof. To do.

[0006]

In order to solve the above problems, a first invention of the present invention is a load measuring section for measuring a load applied to a test material, and an elongation for measuring elongation of the test material. A measurement unit and a display unit for displaying the measurement result,
The central processing unit has at least a storage unit for temporarily holding measured data, and the central processing unit has a load / elongation displacement ratio based on load data obtained by the load measuring unit and elongation data obtained by the elongation measuring unit. And a second processing unit that sequentially determines the reference load / elongation displacement ratio and sequentially compares the reference load / elongation displacement ratio with the sequential load / elongation displacement ratio, and a sequential load / elongation displacement ratio. When the load changes from the reference load / elongation displacement ratio by a predetermined amount or more, a third processing unit that derives a load-total elongation relationship by regression analysis of the measured load from the determination of the reference load / elongation displacement ratio to the change of a predetermined amount or more And a fourth processing unit that derives a load-total elongation proportional relationship according to the load-total elongation relationship.

In addition to the first aspect of the present invention, the second aspect of the present invention provides the central processing unit with an offset proportional relationship in which the load-total elongation proportional relationship is offset by a predetermined total elongation amount, and the measured elongation is offset. The present invention is characterized by having a fifth processing unit that performs proof stress detection when the value is equal to or greater than the elongation in the proportional relationship. Further, the third invention is characterized in that the tension control unit is connected to the central processing unit.

[0008]

According to the first aspect of the present invention, load data is obtained from the load measuring unit and elongation data is obtained from the elongation measuring unit during the tensile test, and these data are temporarily stored in the storage unit. At the same time, the load / elongation displacement ratio is sequentially calculated by being used by the first processing unit of the central processing unit. The load / elongation displacement ratio is monitored in the second processing section and compared with the reference load / elongation displacement ratio. Further, in the third processing unit, when the load / elongation displacement ratio changes by a certain amount or more in response to the comparison result in the second processing unit, the load after the determination of the reference load / elongation displacement ratio is subjected to regression analysis, and the data A load-total elongation relationship excluding undulations is derived. According to this total elongation-load relationship, the load-total elongation proportional relationship of a linear function corresponding to a straight line on the diagram is derived in the fourth processing unit.

Further, in the fifth processing unit of the second invention, an offset proportional relationship is derived by offsetting the load-total elongation proportional relationship by the total elongation amount, and the measured elongation is monitored and the measured elongation is offset. When the relationship grows beyond the limit, proof stress detection is performed. The proof stress is obtained by dividing the measured load at the time of detection into the proof load and dividing the proof load by the initial cross-sectional area of the test material. These measurement results can be displayed on the display unit immediately after detecting the proof stress in the form of numerical values or in the form of a diagram. In the third invention, a control signal is sent from the central processing unit to the speed control unit in accordance with the detection of the proof stress, and the speed control unit controls the pulling device so that the pulling test can be continued at the optimum pulling speed.

[0010]

EXAMPLES A proof stress measuring device used in the examples of the present invention will be described below. Two cylindrical rods 3 and 3 are erected on the upper surface of the load receiving base 2 on the base 1 at a predetermined interval, and inside the rods 3 and 3, an inner rod 4 supported by the base 1 is provided. 4 is penetrated and arranged. An upper crosshead 5 is fixed to the rod 3, and a lower crosshead 6 is attached to the inner rod 4. The lower crosshead 6 can be moved up and down along the inner rods 4 and 4 by a driving means (not shown).

The test material 7 is fixed by chucks 8 and 9 provided so as to face the upper crosshead 5 and the lower crosshead 6, respectively.
0 is placed. The extensometer 10 is connected to an extensometer data storage unit 11 that temporarily holds the extensometer data. A load measuring unit 12 for measuring the load from the load receiving base 2 is built in the base 1, and the load measuring unit 12 receives the load data from the measuring unit 12 and temporarily holds the load data. The load data storage unit 13 is connected.
Further, in the base 1, a hydraulic valve 1 for adjusting the moving speed of the lower crosshead 6 by receiving the driving force from the driving means.
4 is built in.

The elongation data storage unit 11 and the load data recording unit 13 are connected to a central processing unit 15,
In the central processing unit 15, it is input to the first processing unit 16 that sequentially calculates the load / elongation displacement ratio. The central processing unit 15 further determines a reference load / elongation ratio and sequentially compares the reference load / elongation displacement ratio with the sequential load / elongation displacement ratio. Fifth processing unit 18 for deriving a load-total elongation by regression analysis of load, fourth processing unit 19 for deriving a load-total elongation proportional relationship, deriving an offset proportional relationship, and performing proof stress detection
And a processing unit 20. Further, the central processing unit 15
Is connected to the speed control unit 21.
The output end of is connected to the hydraulic valve 14. In addition, the central processing unit 15 includes a display unit 2 including a CRT.
2, a printer 23, a recording device 24 including an FDD or HDD are connected.

Next, the operation of this pulling device will be described with reference to the flowchart of FIG. In this embodiment, the load / elongation displacement ratio is expressed by Young's modulus, and first, the condition setting in the control of the device is performed at the same time as the operation starts (step P1). With this setting, the load measurement time interval is 0.3 seconds, and the Young's modulus calculation interval is 0.01% in terms of elongation.
mm, and the original cross-sectional area A and gauge length l of the test material are obtained. Further, the determination time of the initial Young's modulus is set to the time when the load reaches the 5% load range. When the Young's modulus exceeds the initial Young's modulus by 10% or more during the measurement,
The initial Young's modulus is replaced with this numerical value, and the yield phenomenon is detected when the Young's modulus change is 25% or more lower than the initial Young's modulus. However, fluctuations within these ranges are not replaced as errors or permissible change ranges.

The initial setting may be performed for each proof stress measurement work, or the setting conditions registered in advance in a recording device may be called and used as it is. Next, the apparatus is operated to lower the lower crosshead 6 by a driving means (not shown) to apply a tensile force to the test material 7. The stress applied to the test material 7 is transmitted from the rod 3 to the load receiver 2 and the load measuring unit 12. The load measuring unit 12 measures the load Pi, and the load data is 0.
The data is sequentially stored in the load data storage unit 13 at intervals of 3 seconds.
The elongation of the test material 7 is measured by the extensometer 10, and the total elongation λi is sequentially stored in the elongation data storage unit 11 in synchronization with the load data storage.

In the first processing section 16, the load data displacement (Pi-Pi-1) and the elongation data displacement (λi-λi-) during the measurement cycle are measured.
1) and the original cross-sectional area A of the test material and the gauge length l,
Young's modulus Ei is sequentially calculated according to the following equation (step S
1). Ei = (Pi−Pi−1) × l / ((λi−λi−1) × A) In the second processing unit 17, the measured load data is compared with the 5% load range, and the load data is 5%. When the load range is exceeded, the subsequent processing is performed. That is, when the 5% load range is exceeded, the Young's modulus at that time is set as the reference Young's modulus (step P2), and thereafter the Young's modulus is sequentially calculated (step S2), and the successive Young's modulus and the reference Young's modulus are calculated. And are compared (step P3). And as a result of the comparison,
When the sequential Young's modulus exceeds the reference Young's modulus by 10% or more, the value of the sequential Young's modulus replaces the standard Young's modulus.

Further, when the Young's modulus is successively lower than the reference Young's modulus by 25% or more, the process goes to the third processing section 18 as detection of the yielding phenomenon (step P4). The third processing unit 18 receives the comparison result of the second processing unit 17, and performs a regression analysis of the load-total elongation data from the determination of the reference Young's modulus to the detection of the yield phenomenon to derive the load-total elongation relationship. In addition, the regression analysis is performed by the method of expressing the load data by a quadratic function of the total elongation data, and the quadratic of y = ax ² + bx + c (y: load data, x: total elongation data, a, b, c: constant) Get the regression equation.

The fourth processing unit derives a load-total elongation proportional relationship based on the load-total elongation relationship. Specifically, in the regression equation, the load-total elongation proportional relationship can be obtained by obtaining the tangent line at the load at the reference Young's modulus determination point and the yield phenomenon detection point or the midpoint of the total elongation. In the fifth processing unit, the load-total elongation proportional relationship is offset in the total elongation direction by a predetermined prescribed permanent elongation λm (offset amount, permanent elongation m%) to derive an offset proportional relationship. Note that λm is calculated by the following equation. λm = m × GL / 100 (m: permanent elongation ratio, GL:
Specified gauge length) Further, in the fifth processing unit, the load data-total elongation is sequentially monitored, and for a certain total elongation, the yield strength is detected when the elongation data is equal to or larger than the offset proportional relationship, The load at that time is defined as the proof load, and the proof stress is obtained by dividing by the original cross-sectional area A. If the measured load data does not match the offset proportional relationship when the proof stress is detected, the two adjacent measured loads are proportionally distributed to calculate the load data that matches the offset proportional relationship, and this is calculated as the proof load. And

Then, in the central processing unit 15, the speed control unit 21 is operated based on the detection of the yield strength to control the hydraulic valve 14 to control the pulling speed (step P).
5). Further, the display unit 22 announces the detection of the yield strength and displays the obtained yield strength numerically (step P6). The display unit 22 can also draw a load-total elongation line according to the measurement. It is also possible to draw a base line based on the load-total elongation proportional relationship or an offset base line based on the offset proportional relationship. The various data and the load-total elongation diagram obtained by the measurement are printed by a printer as desired (step P7) and recorded in the recording device 23 (step P8).

Next, another embodiment has a sixth arithmetic unit (not shown) in place of the fifth arithmetic unit of the central processing unit 15, and the sixth arithmetic unit obtains the fourth arithmetic unit. The given load-total elongation proportional relationship is offset by the total elongation corresponding to the specified permanent elongation, the total elongation at which the load becomes 0 is determined by the proportional relationship, and the measured load for the total elongation amount is defined as the proof load. If the total elongation does not match the measured value, the two measured loads in the adjacent total elongations are proportionally distributed, and the load data corresponding to the total elongation is calculated and used as the proof load. ..

[0020]

As described above, according to the proof stress measuring apparatus of the present invention, since the load measuring section, the elongation measuring section, the display section, the storage section and the central processing unit are provided, the setting of the load point and the manual operation are performed. It is possible to derive the proof stress accurately without the need for line drawing by, the work is simplified, and the accuracy of the extensometer is not affected. Moreover, the measurement result can be displayed in real time on the display unit. Further, by controlling the tension control device by the central processing unit, the tension speed can be accurately controlled by detecting the yield strength.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment.

FIG. 2 is a flow chart showing a control procedure of the embodiment as well.

[Explanation of symbols]

 7 Test Material 8 Chuck 9 Chuck 10 Extensometer 11 Elongation Data Storage Section 12 Load Measuring Section 13 Load Data Storage Section 14 Hydraulic Valve 15 Central Processing Unit 16 First Processing Section 17 Second Processing Section 18 Third Processing Section 19 Fourth Processing Part 20 Fifth processing part 21 Speed control part 22 Display part

Claims (3)

[Claims] 1. A load measuring section for measuring a load applied to a test material, an elongation measuring section for measuring an elongation of the test material, a display section for displaying a measurement result, and a memory for temporarily holding measurement data. And a central processing unit, wherein the central processing unit sequentially calculates a load / elongation displacement ratio based on load data obtained by the load measuring unit and elongation data obtained by the elongation measuring unit. And a second processing unit that determines the reference load / elongation displacement ratio and sequentially compares the reference load / elongation displacement ratio with the sequential load / elongation displacement ratio, and the sequential load / elongation displacement ratio becomes the reference load / elongation displacement ratio. On the other hand, when there is a change over a predetermined amount, the measured load from the determination of the standard load / elongation displacement ratio to the change over a predetermined amount is subjected to regression analysis and the load-
A proof stress measuring device comprising a third processing unit for deriving a total elongation relationship and a fourth processing unit for deriving a load-total elongation proportional relationship according to the load-total elongation relationship. 2. In the central processing unit, the load-total elongation proportional relationship obtained in the fourth processing section is offset by a predetermined total elongation amount to derive an offset proportional relationship, and the measured load is expanded in the offset proportional relationship. The yield strength measuring apparatus according to claim 1, further comprising a fifth processing unit that detects the yield strength when the value becomes the above value or more. 3. The proof stress measuring device according to claim 1 or 2, wherein a pulling speed controller is connected to the central processing unit.