JP3206371B2 - Automatic elongation detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automatic measurement of elongation in a tensile test, and more particularly to a method useful for application to an automated tensile tester.

[0002]

2. Description of the Related Art In a tensile test, elongation (hereinafter referred to as elongation means elongation (%). To convert the elongation length into elongation, the value obtained by dividing the elongation length by the original distance between gauge points is 100. In order to determine the elongation, it is essential that the test piece breaks within the gauge section, but in some cases, it may break outside the gauge section. Therefore, it is necessary to repeat the test until the test piece breaks within the gauge section.

[0003] Considering the automation of the tensile test, a major problem is that the test piece breaks outside the gauge section. In other words, when a break occurs outside the gauge section, not only the retest must be performed, but also the test data that has broken outside the gauge section must be searched out from a series of data groups and the data must be removed. There were difficult problems such as these, which hindered automation.

[0004] As means for solving the problem 1, (1) a multi-point setting method, (2) conversion by the Oliver equation, and the like have been proposed.

In the multi-point setting method of (1), the distance between a plurality of points is set, and after the test piece is broken, it is visually observed and the most preferable point-to-point distance is selected, and the elongation for it is determined. Is the standard elongation.

The Oliver-type conversion of (2) is a method in which a test piece having a gage length longer than a predetermined gage distance is tested and converted into an elongation of the gage distance. Since the distance is long, there is an advantage that the probability of breakage outside the gauge section is reduced.

[0007]

However, the multipoint setting method described above does not solve the problem that automation is difficult because a human judgment of visual observation is required on the way.

[0008] In the Oliver-type conversion, even if the distance between the gauges is longer than a predetermined gauge length, it is inevitable that a break occurs outside the gauge length section. Absent. In addition, although the constants are strictly different depending on the material, they are conversion formulas that consider them constant, and there is a problem in the reliability of the elongation value obtained by this method.

Further, as a completely different problem from the above,
Since the elongation in the tensile test shows an apparently different value depending on the breaking position, there is a problem in that if the breaking does not occur at the center between the mark points, the elongation value contains an error. Regarding this problem, no method or apparatus has been invented which rationally corrects the elongation due to the difference in the breaking position.

The present inventors have made an invention which solves these problems, and have filed a patent application as Japanese Patent Application No. 6-11002. This patent application discloses, "On one test piece, the elongation lengths of three or more gage sections having different lengths are detected, and from the elongation length, the length of the gage section and the mutual positional relationship,
Correct the elongation detected by the tensile tester "
The specific mode of correction is as follows: "Solution of a simultaneous equation composed of the elongation length, the length of the gauge point section and the mutual positional relationship, and a previously given elongation length distribution function, Based on the method of correcting the elongation based on the elongation length, the length of the reference point section and the mutual positional relationship, the coefficient of the elongation length distribution function given in advance is determined by regression calculation, and the elongation length distribution function is determined. A method of correcting elongation based on a mathematical expression obtained by substituting coefficients.

The present invention relates to improvements of these inventions, and has as its object to correct elongation by a simpler method.

[0012]

The object of the present invention is to determine the elongation length of three or more types of gauge sections having different lengths on one test piece, and to determine the extension length, the length of the gauge section, and the mutual length. From the positional relationship, in the automatic elongation detection method of the tensile test to correct the elongation detected by the tensile tester, of the three or more types of gauge length of the stretch length, the largest gauge length of the gauge length section is The automatic elongation detection method of the tensile test is characterized in that the elongation is obtained by estimating from the total elongation and uniform elongation or local elongation obtained from other gauge points.

As a preferred example of a method of correcting the elongation detected by the tensile tester, the elongation length, the length and the mutual positional relationship of the gauge section, and the elongation length distribution function given in advance are used. The automatic elongation detection method for tensile test according to claim 1, which is a method for solving simultaneous equations and correcting the elongation based on the obtained solution, and the elongation length, the length of the gauge point section and the mutual positional relationship. The automatic elongation detection method of the tensile test, which is a method of determining the coefficient of the elongation length distribution function given in advance by regression calculation and correcting the elongation based on the equation obtained by substituting the coefficient into the elongation length distribution function, Recommended.

[0014]

The present inventors have found that when the gauge sections are set equally on both sides around the break point, the elongation length in each gauge section is accurately expressed by the following equation. Note that, in the following example, the midpoints of each gauge point section all match.

Y = AX ** B (X ≧ 0) (1) Y = −A (−X) ** B (X <0) (1a) where X is the origin of the fracture point and the axis of the test piece. Direction coordinates Y: Displacement amount of position X with respect to the origin A, B: Constant **: Symbol indicating power, for example, X ** B means X to the Bth power.

Further, the breaking point is a distance X from the midpoint of the gauge section.
When the position is 0 away, Y = A (X0 + X) ** B (X0 + X ≧ 0) (2) Y = -A ｛-(X0 + X)｝ ** B (X0 + X < 0) (2a) Here, X, Y, A, B, and ** are the same as those in Expression (1).

FIG. 2 shows a comparison between the equations (2) and (2a) and the distribution of the actual elongation length, and the equations (2) and (2a) accurately represent the distribution of the actual elongation length. You can see that.

Next, assuming that the test piece breaks at the position shown in FIG. 3 in the actual tensile test, the elongation lengths in the three gauge sections are respectively expressed by the following equations.

E1 = Y11-Y12 = A (X0 + X1) ** BA (X0-X1) ** B (3) E2 = Y21-Y22 = A (X0 + X2) ** B-｛-A [- (X0-X2)] ** B｝ (4) E3 = Y31-Y32 = A (X0 + X3) ** B- ｛-A [-(X0-X3)] ** B｝ (5) However, E1 , E2, E3 ： Measured elongation length corresponding to the gauge length section with the gauge length 2X1,2X2,2X3 which shares the middle point of the gauge length section respectively X0 ： Between the break position and the middle point of the gauge length section Distances (3), (4), and (5) are simultaneous equations for A, B, and X0, and can therefore be solved mathematically.

Using the values A, B, and X0 obtained by solving the simultaneous equations, E0 calculated by the following equation (6) is the elongation at the time of breaking at the center of the gauge point section 2X1.

E0 = AX1 ** (B-1) × 100 (6) Assuming that the length of the reference point section 2X1 is the reference point section distance of the standard reference point section, the standard expansion is achieved by adopting E0. Can be requested.

In this example, three types of gauge sections are set. However, when three or more types of gauge sections are set, for example, five types of gauge sections are selected, three sets are arbitrarily selected from the five types. E0 may be obtained by the above method. Furthermore, 3
Since there are several combinations of how to select a set, E0 is obtained for each combination and E0 with higher accuracy can be obtained by regarding the average value as E0.

Next, as a second example of mathematical means, 3
The means to obtain standard elongation by regression calculation using more than one kind of elongation length is described. In this method, the greater the number of measured elongation lengths, the higher the accuracy. However, if at least three types of elongation lengths are used, standard elongation can be obtained with an accuracy that does not cause any practical problem.

In this example, as in the first example, a case is considered in which three types of elongation lengths are used, and all the midpoints of each gauge point section match.

The three types of elongation lengths obtained are given by equations (3), (4) and (5), respectively. In these equations, the unknowns are A, B, and X0. If the difference between the left side and the right side of the equations (3), (4), and (5) is e1, e2, and e3, the following equation is obtained.

E1 = A (X0 + X1) ** BA (X0-X1) ** B-E1 (7) e2 = A (X0 + X2) ** B-｛-A [-(X0-X2)] ** B｝ -E2 (8) e3 = A (X0 + X3) ** B-｛-A [-(X0-X3)] ** B｝ -E3 (9) Equations (7), (8), (9) ), The unknowns A, B, and X0 are determined by regression calculation so that W3 represented by W3 = e1 ** 2 + e2 ** 2 + e3 ** 2 (10) is minimized. By substituting this into equation (6), a standard elongation can be obtained.

Here, if the measured elongation lengths are n types, Wn = e1 ** 2 + e2 ** 2 + e3 ** 2 +... + En ** 2 (11) Unknowns A, B, X0 so that Wn is minimized
Should be determined.

Furthermore, the first and second examples are both cases where the midpoint positions of the respective gauge points coincide with each other, but it is essential that the midpoint positions coincide with each other in the method of the present invention. Not a condition. That is, when the midpoint positions of the respective gauge sections do not match, the coordinate transformation corresponding to the shift of each middle point from the midpoint position of the reference gauge section is represented by equations (3) to (5). Then, E0 can be obtained by the same mathematical means as above.

The device of the present invention is specifically configured as follows. (1) Three or more types of reference point sections having different lengths are set in the parallel portion of the tensile test piece, and an elongation detecting device for detecting the elongation length of the section is attached to two or more sections. It is not necessary to attach the elongation detecting device to all the gauge sections, but it is necessary to attach the elongation detecting device to at least two gauge sections.

(2) At the time of conducting a tensile test, a control device for detecting and determining the time of breakage of the test piece is installed.

(3) An arithmetic unit for calculating a standard elongation by a mathematical operation using at least three types of elongation lengths including the detected substitute value is installed.

The above is the outline of the invention according to Japanese Patent Application No. 6-11002. The gist of the invention is to automatically measure at least three types of elongation lengths and obtain a standard elongation from them. The calculation formula for elongation may be different from the formula described here.

The inventors can estimate the extension length of the above-mentioned maximum gauge point section from the total elongation obtained from the other gauge point sections and the uniform elongation or local elongation, and there is no need for actual measurement. And completed the present invention.

That is, the extension length of the maximum gauge section (given as a provisional value) can be estimated by, for example, the following method.

(A) A method of estimating from the automatically measured uniform elongation. E3 = E2 + ε1 (2X3−2X2) / 100 E3 ′ = (E3 / 2X3) × 100 where E3 ′: Elongation at an arbitrary maximum target section distance 2X3 E3: Elongation length at an arbitrary maximum target section distance 2X3 E2: Automatically measured elongation length other than 2X3 of the maximum gauge length section 2X3: Temporary value for processing a physical expression with the distance of an arbitrary maximum gauge length section. In an arbitrary section larger than 2 × 2, for example, 2 × 2 or 1.5 times of 2 × 2, the distance between the gripping jigs may be used. 2X2: Distance of gauge point section when E2 is automatically measured ε1: Uniform elongation automatically measured Here, uniform elongation is “permanent elongation corresponding to maximum tensile load” in JIS G0202 steel term (test) No. 1173 For example, the elongation obtained from the elongation length at the time of the maximum tensile load automatically measured by the elongation detector 5 may be ε1.

(B) A method of estimating from the automatically measured local elongation. In the equation in (a), the total elongation (elongation at break) is the sum of the uniform elongation and the local elongation. Therefore, the uniform elongation ε1 can be obtained from the following equation. ε1 = E2′−ε2 Here, ε2 is an automatically measured local elongation. The local elongation is JIS G0202 Steel term (test) No. 11
74 describes "permanent elongation until reaching fracture after reaching uniform elongation". For example, elongation obtained from the elongation length from the maximum tensile load to the fracture automatically measured by the elongation detector 5 May be set to ε2.

(C) A method of estimating uniform elongation by giving it as a material constant. In the equation in (a), since ε1 has no relation to the shape of the test piece, a calculation is performed by giving a value as a material constant.

(D) Estimate ε1 by other methods,
E3 'is obtained using the equation (a). (Here, the purpose is to estimate E3 'from the uniform elongation, and the uniform elongation can be obtained by any method.) Here, the longest gauge section among at least three types of gauge sections Is generally equal to the parallel part of the test piece, or the interval between the grips of the test piece, but this is not an essential requirement of the present invention, that is, the longest gauge section is the parallel part of the test piece. The present invention is effective even if the length is sufficiently shorter than the length of the test piece or the distance between the grips of the test piece.

E0 can be obtained by using the extension length of the maximum gauge point section obtained in this way.

[0040]

EXAMPLES In order to confirm the effects of the present invention, a tensile test was actually performed, and the elongation obtained by the present invention was compared with the elongation obtained by the conventional method.

In the experiment, a tubular test piece defined in JIS Z2201 was used, three types of gauge sections were set, an extension detector was attached to each section, and the extension length of each section was automatically read. As the elongation detector, a magnescal was used in principle, but a method of electrically reading the moving amount of the gripper during the tensile test was used only at the reference point 3 in Experiment 1. Here, the method of elongation detection is not the essence of the present invention, and may be, for example, an operating transformer or an optical method.

FIG. 1 is a view showing a tensile test method of the present invention. 1 is a tubular tensile test piece, 2 is a cored bar, 3 is a test piece gripper, 4 and 5 are automatic elongation detectors, and 6 is a hypothetical. An automatic extension detector for the maximum gauge length section, 7 is a specification setting section for setting conditions such as a distance between gauge points, and 8 is a standard length using the extension length automatically detected by the automatic extension detectors 4, 5, and 6. This is an operation unit that calculates elongation.

Table 1 shows the conditions and results of Example 1 of the present invention.
Shown in Table 1 is an example of a tensile test of a steel pipe having a diameter of 60 mm and a thickness of 5.4 mm. In the table, “standard elongation” is the elongation with respect to the standard mark section 1, which is a standard mark section, and at the center of the mark section. Means the calculated value of elongation at break. The standard elongation was calculated by solving simultaneous equations.

[0044]

[Table 1]

In Example 1, the breaking point was broken at a position 13 mm away from the middle point of the standard gauge section. For this reason, the elongation is 61% in the prior art, but according to the present invention, a value of 63% was obtained as the standard elongation.

Table 2 shows the results of Example 2 of the present invention. Table 2 shows an example of a tensile test of a steel pipe having a diameter of 22 mm and a thickness of 2.7 mm. The standard elongation was calculated by solving simultaneous equations in the same manner as in Example 1.

[0047]

[Table 2]

The second embodiment is an example in which a break occurs outside the section between the reference points 1 and 2. In this example, since the fracture occurred outside of the standard mark section 1, which is the standard mark section, the automatically measured value was determined to be invalid in the prior art and a retest was required. According to the present invention, the automatically measured value was determined. From E1 to E3, the standard elongation E0 (elongation value at the time of breaking at the standard gauge point section and at the midpoint of the gauge point section) is obtained. Therefore, according to the present invention, no retest is required. You can see that.

Example 3 is an example in which a standard elongation was obtained by using regression calculation using the same test results as in Example 2, and the results are shown in Table 3.

In the third embodiment and the second embodiment, the coefficients A, B, X0
Is slightly different, but the standard elongation obtained is significant figure 2
It was confirmed that the values were well matched in the range of the digits, and that there was no practical problem.

[0051]

[Table 3]

Table 4 shows the results of Example 4 of the present invention. This is an example when E3 is estimated from uniform elongation. Table 4 shows an example of a tensile test of a steel pipe having a diameter of 43 mm and a thickness of 4.9 mm. The standard elongation was calculated by solving simultaneous equations as in Example 1.

In the present embodiment, it is not necessary to measure the extension of the maximum gauge length section. For example, if the maximum gauge length is 250 mm,
The above equation, E3 = E2 + ε1 (2X3−2X2) / 10
0, automatic measurement value E2 = 41.5 mm (33%), ε
1 = 19.1%, predetermined 2X3 = 250m
m, 2X2 = 125 mm, the extension length of the maximum gauge length section is E3 = 41.5 + 19.1 (250−12)
5) /100=65.38 (mm), expressed in%, E3 ′ = 65.38 / 250 × 100 = 26.2
(%). As described above, E3 'can be obtained without actually measuring. This is in good agreement with 26 (%) of E3 ′ actually measured for verification.

[0054]

[Table 4]

The fourth embodiment is an example in which a break occurs outside the section of the reference point 1 and within the section of the reference point 2. In this example, since the fracture occurred outside of the standard mark section 1, which is the standard mark section, the automatically measured value was determined to be invalid in the prior art and a retest was required. According to the present invention, the automatically measured value was determined. ε1, E1, E2
From the above, E3 (E3 ') is obtained with high accuracy, and the standard elongation E0 (elongation at the time of breaking at the standard point section and at the midpoint of the point section) is obtained. It turns out that retesting is not necessary.

Although the present embodiment shows an example of a tubular test piece, the object of the present invention is not limited to a tubular test piece, and the present invention can be applied without any problem even if the shape of the test piece is cylindrical or plate-like.

Table 5 shows another embodiment. FIG. 4 shows the correlation between E3 '(E3'-h) and E3'(E3'-a) measured according to the present invention, which shows a good correlation.

[0058]

[Table 5]

FIG. 5 shows the correlation between the elongation correction estimated value according to JIS Z2241 of E1 'and the estimated value according to the present invention. JI
It is in good agreement with the corrected estimated value of S.

FIG. 6 shows the correlation between the elongation correction estimated value according to JIS Z2241 of E1 'and the actually measured value (conventional method). It can be seen that if the breaking position is not corrected manually after the test, there is a large variation.

[0061]

As described above, according to the present invention, a standard elongation can be automatically measured in a tensile test.
This is an invention with great industrial effects.

[Brief description of the drawings]

FIG. 1 is a diagram showing a tensile test method of the present invention in a tensile test.

FIG. 2 is a diagram comparing an elongation distribution function with an actual elongation distribution.

FIG. 3 is a diagram showing a relationship between each gauge point section and a fracture position of a test piece in a tensile test actually performed.

FIG. 4 is a diagram showing a correlation between an actually measured value of E3 ′ and an estimated value according to the present invention.

FIG. 5 is a diagram showing a correlation between a JIS correction value of E1 ′ and an estimated value according to the present invention.

FIG. 6 is a diagram showing a correlation between a JIS correction value of E1 ′ and an actually measured value (conventional method).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tubular tensile test piece 2 Core metal 3 Test piece gripping tool 4, 5 Automatic elongation detector 6 Temporary elongation detector 7 Data setting section such as distance between gauge points 8 Calculation section 9 Test piece fracture section 10 Mark section Midpoint 11, 12 Marking section 13 Temporary marking section

──────────────────────────────────────────────────続 き Continued on the front page (72) Akira Murayama, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Megumi Tanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-60-238740 (JP, A) JP-A-62-170835 (JP, A) JP-A-5-249011 (JP, A) JP-A-52-50280 (JP, A A) JP-A-7-218407 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 3/00-3/62 JICST file (JOIS)

Claims (3)

(57) [Claims] An elongation length of three or more gauge sections having different lengths is determined on one test piece, and a tensile tester is determined from the stretch length, the length of the gauge section and the mutual positional relationship. In the automatic elongation detection method of the tensile test to correct the elongation detected in, in the elongation length of the three or more types of gauge point section,
An automatic elongation detection method for a tensile test, wherein the elongation length of a maximum gauge section is obtained by estimating the total elongation obtained from other gauge sections and uniform or local elongation. 2. A method for correcting an elongation detected by a tensile tester, comprising: a simultaneous system comprising an elongation length, a length and a mutual positional relationship of a gauge section, and an elongation length distribution function given in advance. The method for detecting an automatic elongation in a tensile test according to claim 1, wherein the method is a method for solving an equation and correcting the elongation based on the obtained solution. 3. A method of correcting an elongation detected by a tensile tester, comprising: calculating a coefficient of an elongation length distribution function given in advance based on an elongation length, a length of a gauge point section and a mutual positional relationship by regression calculation. An automatic elongation detection method for a tensile test, which is a method of determining and correcting elongation based on a mathematical expression obtained by substituting a coefficient into an elongation length distribution function.