JPH0545269A - Yield point sensing method for tensile test and tensile testing device - Google Patents

Abstract

PURPOSE:To easily and precisely sense the yield point without being influenced by the device accuracy, etc., by comparing the time-to-time stress incremental rate with the reference stress incremental rate continuously, and performing judgement that the yielding phenomenon has commenced and that the yield region is passed. CONSTITUTION:A lower cross-head 6 is sunk by a driving means to give a tension to a specimen 7. The load applied to the specimen 7 is transmitted from a rod 3 to a load receptacle table 2 and a load measuring part 10. This part 10 measures the load at certain intervals using the data given from a timer 13, and the resultant data is stored in a load data memory 12. A calculation part 14 calculates the time-to- time stress incremental rate from the load data and compares it with the reference stress incremental rate. When the time-to-time stress incremental rate is below the allowable reference down-limitation range, it is judged that the yielding phenomenon is commenced, and the yield point is sensed. When the time-to-time stress incremental rate exceeds the allowable yield over-limitation range, it is judged that the yield region is passed. After completion of the test, the data obtained is passed to a printer 19 and also stored in a recorder device 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a yield point detecting method capable of accurately detecting a yield point of a test material in a tensile test of the test material, and a tensile test apparatus used for this method.

[0002]

2. Description of the Related Art As is well known, when performing a tensile test on a test material, the test material is fixed by a chuck, a load is applied parallel to the axial direction, and the test material is stretched, gradually stretched, and finally broken. Then, the relationship between load and elongation is sought. In the yield phenomenon that occurs during the stretching of the test material, a yield point appears in many materials, and detecting the yield point is one of the purposes of the tensile test. There are several known methods for detecting the yield point (mainly the upper yield point), and typical examples thereof will be described below. The tensile load observed during the tensile test increases and decreases with the progress of tension, and the load obviously decreases after passing the yield point. Utilizing this phenomenon, there is a method of visually observing the movement of a pointer (for example, a stylus) that displays a load, or providing a means for detecting a decrease in the load and determining this as the yield point. Further, as another method, there is a method of predicting a load region including a yield point in advance and determining the maximum load in this load region as the yield point.

[0003]

However, of the conventional measurement methods, the former method requires a resident observer,
There is a problem that the efficiency is poor, and when the load value is mistakenly lowered due to slippage at the chuck part, this may be detected as the yield point, and the reliability of the measurement accuracy is high. There is a problem of being low. Further, in the latter method, it is necessary to set the load area in advance, which is troublesome, and it may be difficult to detect the yield point itself unless the area is set accurately. .. In addition, since it is difficult to set an accurate load area in advance for a material whose load-elongation characteristics are unknown, it is necessary to confirm the load area by trial and error, which causes a significant increase in the amount of work. There is.

Further, in any of the above-mentioned methods, it is difficult to confirm the yield phenomenon in a material in which the yield point does not appear clearly, and whether the yield point has failed to be detected or the yield point is detected depending on the nature of the material. There is also a problem that it is not possible to judge whether or not it could not be done, and in the end, human beings have no choice but to make a final judgment based on experience by visually observing the load-elongation curve. You will need it. Even when adjusting the tensile speed of the tensile tester, the mechanical yield point detection is not reliable, and it is difficult to grasp and control the accurate state. Then, it is necessary for an experienced worker to adjust the speed while judging the state, and there is a problem that the work is troublesome.
This invention was made against the background of the above circumstances,
An object of the present invention is to provide a method of detecting a yield point in a tensile test and a tensile test device capable of accurately and easily detecting a yield point without requiring an expert and also reliably and easily adjusting a pulling speed. And

[0005]

In order to solve the above-mentioned problems, the first invention of the present invention is to continuously measure the load and the time in a tensile test of a test material, and successively measure the loads having a time difference. Calculate the stress increase rate, set the sequential stress increase rate in the initial stage of the test as the standard stress increase rate, and continuously compare the sequential stress increase rate with the reference stress increase rate. If the value falls below the lower limit of the permissible standard, that point is set as the yield phenomenon start time, and the reference stress increase rate is replaced by the successive stress increase rate. When the allowable yield upper limit region is exceeded from the standard increase rate, the yield area passing judgment is performed, and the peak of the measured load used to calculate the sequential stress increase rate is yielded from the start of the yield phenomenon to the yield area passing judgment. point Characterized in that it.

According to a second aspect of the present invention, in the first aspect, when the sequential stress increase rate further exceeds the allowable reference upper limit region from the reference stress increase rate before the yield phenomenon starts, the reference stress increase rate is set to Substituting with the successive stress increase rate, and after the yield phenomenon has started and before the yield area passage judgment, if the successive stress increase rate is lower than the standard stress increase rate beyond the lower limit of the allowable yield area, It is characterized in that the reference stress increase rate is replaced with this sequential stress increase rate.

A third aspect of the present invention is a tensile tester for fixing a test material with a chuck to perform a tensile test, having a load measuring section and a time measuring section, and further measuring load data by the load measuring section. A load data storage unit that holds at least temporarily according to time, a calculation unit that calculates a sequential stress increase rate, a stress increase rate storage unit that holds the stress increase rate at least temporarily, and a central process that determines the yield phenomenon start and the yield region passage. The apparatus is characterized by having a device and a speed control unit for giving a speed control signal to the tension speed adjusting device in response to a command from the central processing unit.

Incidentally, the continuous measurement of the load may be carried out not only continuously but also at a constant time interval, for example, every few seconds. Also, the time difference between the loads in the calculation of the stress increase rate can be selected as appropriate, but if it is done at too short an interval it will be susceptible to temporary fluctuations due to errors, etc. Since it is not possible to accurately grasp it, it is decided taking these into consideration. For example, it is calculated using a load at intervals of several seconds. Furthermore, when the initial sequential stress increase rate is set to the reference stress increase rate, it is possible to use the stress increase rate after a predetermined time from the start in order to prevent disturbance at the time of starting, and further, for example, the prediction 10% of the load range (tentative name) of 120 to 150% of this load, based on the tensile strength load
It is also possible to determine the reference stress increase rate after the arrival.
This makes it possible to eliminate the influence of load reduction due to slippage in the chuck. Since this numerical value is not strict, it is not essential to recognize an accurate tensile strength load in advance, but it may be an approximate value.
Further, the above-mentioned allowable lower limit range, upper limit range and allowable yield range lower limit range, upper limit range can be expressed, for example, as a percentage with respect to a reference stress increase rate, and can be determined in consideration of load measurement accuracy and the like. ..

[0009]

In other words, according to the first aspect of the present invention, the reference stress increase rate and the successive stress increase rate are compared, and the allowable reference lower limit region is set. The variation error of the stress increase rate can be eliminated, and since elongation is not an element, the start of the yield phenomenon can be accurately grasped without being influenced by the accuracy of the extensometer. After the start of the yield phenomenon detection, the new reference stress increase rate and the successive stress increase rate were compared, and the upper limit of the allowable yield area was set.Therefore, even when there is no peak value, the test material has a yield point. It is easily and accurately found that the material does not appear clearly. And, the detection of the yield point, since the measured load used to calculate the stress increase rate in the above-mentioned yield region is targeted, it is possible to determine the load in a narrow range without removing the yield point, and the accuracy increases,
Moreover, the yield point can be easily detected. Also,

Further, according to the second aspect of the invention, it is possible to eliminate the influence of slippage of the chuck and the like, and to set the sequential stress increase rate during stable tension as the reference stress increase rate. After the yield point is detected, the reference stress increase rate corresponding to the yield elongation that occurs in the material in which a clear yield point appears can be determined, and the passage through the yield region can be accurately determined. According to the third aspect of the invention, the sequential stress increase rate is calculated using the load measuring unit, the time measuring unit, and the arithmetic unit, and the central processing unit compares the sequential stress increase rate with a predetermined reference stress increase rate. By doing so, the start of the yielding phenomenon and the determination of the yielding region passing can be accurately performed. Furthermore, the central processing unit can issue a command based on these judgments so that the pulling can be performed at the optimum speed for the pulling situation, and the pulling speed adjusting unit can be accurately controlled by the action of the speed control unit. it can.

[0011]

EXAMPLES The tensile tester 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.

A load measuring section 10 for measuring the load from the load receiving base 2 is built in the base 1, and the lower cross head 6 receives the driving force from the driving means.
A hydraulic valve (speed adjusting unit) 11 for adjusting the moving speed of is built in. The load measuring unit 10 includes a measuring unit 10
A load data storage unit 12 for receiving the load data from the memory and storing the load data is connected to the drive means (not shown).
A timer (timekeeping unit) 13 that measures the time after the start of tensioning is connected. The load data recording unit 12 and the timer 13 are connected to a calculation unit 14 that calculates a stress increase rate, and the calculation unit 14 is connected to a stress increase rate storage unit 15 and a central processing unit 16. The central processing unit 1
The stress increase rate storage unit 15 is connected to 6.
Further, the central processing unit 16 includes a speed control unit 17 and a CRT.
Display unit 18, printer 19, FDD or HD
The controller 17 is connected to the recording device 20 composed of D.
Is connected to the solenoid valve of the hydraulic valve 11.

Next, the operation of the tension device will be described with reference to the flow charts of FIGS. 2 and 3 and the graph of FIG. First, the condition setting in the control of the device is performed at the same time as the start of the yield point detection operation (step P1). In this setting, the load measurement time interval is set to 0.3 seconds, the time difference ΔT between the loads used to calculate the stress increase rate is set to 3 seconds,
Further, the cross-sectional area A of the test material is obtained. Further, the calculation time of the initial standard stress increase rate is set to the time when the 15% load range is reached, and the target stress increase rate is set to 2 kg / mm ² / sec. Further, before the yield phenomenon is detected, the allowable standard upper limit area which is a condition for replacing the standard stress increase rate is set to a range of 110% or less with respect to the standard stress increase rate, and the allowable standard lower limit area used for detecting the yield phenomenon is the standard stress increase rate. To 30% or more.
The increase replacement of the reference stress increase rate takes into consideration a state in which the stress increase rate increases until it becomes stable in the initial stage of the test, and the error range is within 10%.

When the reference stress increase rate is replaced with the successive stress increase rate after the yield phenomenon is detected, and the successive stress increase rate exceeds 0.3 Kg / mm ² , the reference stress increase rate is replaced with the successive stress increase rate as it is, and 0 .3kg / mm ² or less of the time, sets the reference stress increase rate to 0.3 kg / mm ^2. 0.3 kg / mm ² was used as the standard because the rate of sequential stress increase gradually near the onset of the yield phenomenon, and in general, for materials that show a clear yield point, −0.1 to −0.1.
A material showing a leveling value of 0.2 kg / mm ^{2 and} a material that does not show a clear yield point shows a value of 0 to 0.2 kg / mm ² , but the above values were used as a reference in consideration of measurement accuracy. Then, when the rate of sequential stress increase is 0.3 kg / mm ² or less, the numerical value is small, so the compared ratio becomes large even with a slight change.
In order to eliminate the effect, a constant value was used for 0.3 kg / mm ² or less. Note that this replacement is a setting that depends on the value of the incremental stress increase rate, and is replaced by the incremental stress increase rate according to the incremental stress increase rate.

The lower limit of the allowable yield area is set to a range of 90% or more of the reference stress increase rate, and the upper limit of the allowable yield area used for judging the passage of the yield area is 150% of the reference stress increase rate.
The range is less than or equal to%. The replacement by decreasing the standard stress increase rate takes into consideration that the stress increase rate further decreases in the yield elongation state, and the error range is 10%. Further, in the determination of passing the yield area, the upper limit area of the allowable yield area is set so as not to be affected by the yield point and the measurement accuracy. The initial setting may be performed every time the yield point is detected, or the setting conditions registered in advance in the 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 load applied to the test material is transmitted from the rod 3 to the load receiving base 2 and the load measuring unit 10.
In the load measuring unit 10, according to the stress increase rate Zi calculation subroutine (step S1), the load Pi is measured at intervals of 0.3 seconds by the data from the timer 13 (step SP).
1), the data is stored in the load data storage unit 12 (step SP2). In the calculation unit 14, the load data and 1
The 5% load range is compared (step SP3), and load measurement and data comparison are repeated until the load data exceeds the 15% load range. When the load data reaches the 15% load range, the load data at the present and 3 seconds ago is read from the load data recording unit 12 (step SP4), and the difference is set as ΔP, and the sequential stress increase rate Zi is calculated by the following formula. Calculate (step SP5), and use the data as the stress increase rate storage unit 1
5 (step SP6) and displayed on the display unit 18 (step SP7). Zi = ΔP / (ΔT × A) (kg / mm ² / sec)

The value of this stress increase rate is set as the initial reference stress increase rate Zs (step P2). The value was within the range of 1 to ³ kg / mm ² / sec. After that, the stress increase rate is successively calculated (step S
2) Compare with the reference stress increase rate (step P4). As a result, the rate of sequential stress increase is within the allowable upper limit (110% Z
If it exceeds s), the reference stress increase rate is replaced by the successive stress increase rate at that time (to step P2), and the successive stress increase rate is calculated. Further, if the successive stress increase rate is within the permissible reference upper limit region (110% Zs) and within the permissible reference lower limit region (30% Zs), the sequential stress increase rate is repeatedly calculated (to step S2). At this time, the sequential stress increase rate is the target stress increase rate (2 kg / mm ²
/ sec), the central processing unit issues a command to the speed control unit 17 to control the opening amount of the hydraulic valve 11 to be maintained (step P3).

When the rate of successive stress increase is below the lower limit of the permissible standard (30% Zs), it is assumed that the start of the yield phenomenon is detected, the yield point is detected, and 3 seconds before the start of the yield phenomenon. Load data storage unit 12 for all of the load data
Read from, compare three consecutive loads, Pi-
When the condition of 2 ≧ Pi−1 ≧ Pi is satisfied, Pi-2 is determined to be a peak. Note that Pi-2 and Pi-1 are load data measured two times before and one time before the Pi measurement, respectively. Furthermore, when the start of the yielding phenomenon is detected, the buzzer,
It is also possible to notify the measurer by notification means such as a lamp.

After the yield phenomenon starts, the reference stress increase rate is replaced with the sequential stress increase rate at the time of detecting the yield phenomenon (step P
6) Then, the stress increase rate Zi is successively calculated (step S3). Then, similarly to the above, the measured load from the present measurement to the two times before is read from the load data storage unit 12 to detect the yield point (step P7). Next, as a result of the calculation of the sequential stress increase rate Zi, in step P8, if Zi is 0.3 kg / mm ² / sec or less, Zs
Is set to 0.3 kg / mm ² / sec and Zi is calculated repeatedly (to step S3). If Zi exceeds 0.3 kg / mm ² / sec, compare Zi and Zs as they are. (Step P9), when Zi is within the lower limit of the allowable yield region (90% Zs), Zs is replaced with the Zi (step P5).
To), and the calculation of Zi is repeated. Also, Zi is 0.3 kg / m
m ² / sec is exceeded, and Zi is the allowable upper limit of yield (150
% Zs) is exceeded, it is assumed that the breakdown area passage detection has been performed.

If the yield point is not detected by comparing the loads between the start of the yield phenomenon and the passage of the yield region, it is determined whether the yield point is unclear. After that, although not shown in the flow chart, if the measured load is monitored and the load data from the measurement two times before to the current measurement satisfies the same condition as the yield point detection, the load of the measurement two times before is pulled. Identify as a strength load.

After the test is completed, the load data, the stress increase rate data, the peak value, etc. obtained so far are output to the printer 19 together with the time after the start of the test, and stored in the recording device 20. FIG. 4 is a load-time graph ejected by the printer after the end of the test, but it is also possible to eject the load over time during the test. It should be noted that the obtained yield point was compared with the case where the same material was scrutinized by reading a conventional pointer, the numerical value was correct, and the yield point was accurately detected. Moreover, the yield point was digitally displayed on the display unit in almost real time during the test, and was not affected by the skill of the measurer. Further, even when the load was temporarily reduced due to the slip of the chuck, this was not erroneously recognized as the yield point.

[0022]

As described above, according to the method for detecting the yield point of the present invention, the yield stress initiation is achieved by using the successive stress increase rate and continuously comparing it with the reference stress increase rate. And since the judgment of passing through the yield area is performed, no skilled worker is required, and the influence of the elongation measurement accuracy of the device and the slippage of the chuck can be eliminated, and the yield point can be detected accurately and easily. can do.
Moreover, the detection of the yield point can be known in real time during the tensile test. Further, according to the tensile test apparatus of the present invention, the yield point can be detected accurately and in real time, so that the tensile control can be appropriately performed according to the state of the test material.

[Brief description of drawings]

FIG. 1 is a schematic view of a tensioning device according to an embodiment.

FIG. 2 is a flowchart showing a yield point detection method according to an embodiment.

FIG. 3 is a flowchart showing a stress increase rate calculation procedure.

FIG. 4 is a stress increase rate-time graph obtained by a tensile test.

[Explanation of symbols]

 7 Test Material 8 Chuck 9 Chuck 10 Load Measuring Section 11 Hydraulic Valve 12 Load Data Storage Section 13 Timer 14 Computing Section 15 Stress Increase Rate Storage Section 16 Central Processing Unit 17 Speed Control Section

Claims (3)

[Claims] 1. In a tensile test of a test material, a load and a time are continuously measured, and a sequential stress increase rate is continuously calculated between loads having a time difference, and a sequential stress increase rate at an initial stage of the test is increased as a reference stress. Rate, the sequential stress increase rate and the reference stress increase rate are continuously compared, and the sequential stress increase rate is
When the value falls below the lower limit of the allowable standard from the standard stress increase rate, the yield stress starts at that time, and the standard stress increase rate is replaced with the successive stress increase rate. When the rate exceeds the upper limit of the allowable yield rate from the standard increase rate, the yield area passage determination is performed, and the peak of the measured load used to calculate the sequential stress increase rate from the yield phenomenon start to the yield area passage determination. Method for Detecting Yield Point in Tensile Tests, Wherein Yield Point 2. The sequential stress increase rate before the yield phenomenon starts,
When the standard stress increase rate exceeds the upper limit of the allowable standard, the standard stress increase rate is replaced with this successive stress increase rate. Is lower than the reference stress increase rate by more than the lower limit of the allowable yield region, the reference stress increase rate is replaced with the successive stress increase rate, and the yield point in the tensile test according to claim 1. Detection method 3. A tensile test apparatus for fixing a test material with a chuck to perform a tensile test, having a load measuring section and a time measuring section, and further temporarily holding load data by the load measuring section according to a measuring time. A load data storage unit, a calculation unit that sequentially calculates the stress increase rate, a stress increase rate storage unit that temporarily holds the stress increase rate, a central processing unit that performs a yield phenomenon start and a yield region passage determination, and a central processing unit And a speed control unit for giving a speed control signal to the tensile speed adjusting device in response to a command from the tensile tester.