JP3819616B2 - Tensile compression test method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tensile and compression test method for testing fatigue and the like of a material.
[0002]
[Prior art]
FIG. 6 is a diagram for explaining a tensile compression test method. In the figure, 21 is a loop, 21a is an initial curve portion, 21b is a negative direction curve portion, 21c is a positive direction curve portion, 22 is an elastic line, and 23 and 24 are tangents.
As a tensile compression test method, for example, as known in Japanese Examined Patent Publication No. 4-26419, there is a tensile compression test method in which a loop 21 is drawn while keeping a plastic region (plastic strain) constant. As used herein, the plastic region (plastic strain) is the difference in strain ε between two points where the loop 21 intersects the line of stress σ = 0, as indicated by ε _{pp in} the figure.
[0003]
This plastic region ε _pp is a value measured only after one cycle of the loop 21 is executed. That is, by measuring the plastic zone epsilon _pp in the first cycle of the loop 21, in accordance with the difference between the target value of the measured value and the plastic region, as plastic zone epsilon _pp the second cycle becomes the target value, 2 Tension compression is reversed in anticipation of the value of strain ε at the apex (1/2 of the total amplitude) of the loop 21 in the cycle. Similarly in the third and subsequent cycles, the value of the strain ε at the apex of the loop 21 is predicted and reversed so that the plastic area ε _pp of the next cycle becomes the target value.
[0004]
Thus, the vertex of the loop 21 must be determined empirically so that the value of the plastic zone ε _pp of the next cycle becomes the target value, and it is difficult to match the plastic zone ε _pp to the desired target value. It is. Moreover, the plastic region epsilon _pp of unless the test results kept at a target value precision becomes poor from the initial 1 cycle. Since the integration of the area of the loop 21 results in total damage, an error in the area of the first cycle becomes a large error in a test in which the test piece has an area that can be broken by several 10 to 1000 times.
[0005]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a tensile compression test method capable of easily and highly accurately performing a tensile compression test for keeping a plastic region constant. It is.
[0006]
[Means for Solving the Problems]
In the first aspect of the present invention, in the tensile and compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece, the stress and the strain Based on the detected value, the amount of strain at the point of crossing the straight line passing through the detected value and having a gradient equal to the gradient of the elastic line and the zero-stress line is calculated. From the first cycle to the subsequent cycles, the tension and compression are reversed so that it is always ½ of the target value of the plastic region.
Therefore, it is easy to keep the plastic region constant with high accuracy.
[0007]
According to a second aspect of the present invention, in the tensile and compression test method according to the first aspect, a limit value is set for each absolute value of the stress and the strain, and in the course of the first cycle, Before reaching the time of performing the reversal, when at least one of the absolute value of the detected value of the stress and the absolute value of the detected value of the strain reaches the respective limit values, the stress at the time of reaching and the A value that is twice the amount of strain calculated based on the detected strain value is reset to a new target value in the plastic region, and in the course of the subsequent cycles, 1 of the new target value in the plastic region is set. The tension / compression is reversed when / 2 corresponds to the strain amount.
Therefore, the runaway of the compression / tensile tester can be prevented, and the test can be performed safely, and valuable data for the trial of the test is not lost.
[0008]
According to a third aspect of the present invention, in the tensile and compression test method according to the second aspect, before reaching the time of performing the reversal in the process of the first cycle, the absolute value of the detected value of the stress, When at least one of the absolute values of the detected strain values reaches the respective limit values, at least the limit value among the absolute value of the detected stress value and the absolute value of the detected strain value is reached. In the course of the subsequent cycles, when the absolute value of the detected value of stress or the absolute value of the detected value of strain has reached the respective limit value, In addition, the test is stopped.
Therefore, the test can be further safely performed.
[0009]
According to a fourth aspect of the present invention, in the tensile compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece, In a period not exceeding the elastic limit of the cycle, a slope of an elastic line is calculated based on the detected values of the stress and the strain, and in a period exceeding the elastic limit of the first cycle of the tension and compression, the stress and Based on the detected value of the strain, a strain amount at a point that intersects the straight line of zero stress of a straight line that passes through the detected value and has a gradient equal to the gradient of the elastic line, and the calculated strain amount, From the first cycle of the tension compression to the subsequent cycles, the tension compression inversion is always performed so that it becomes 1/2 of the target value of the plastic region. It is.
Therefore, it is easy to keep the plastic region constant with high accuracy. Since the process of measuring the gradient of the elastic line can be performed integrally with the tensile and compression test process, the test procedure can be rationalized. Since there is no need to replace the test piece between the two test machines, human error is unlikely to occur.
[0010]
According to a fifth aspect of the present invention, in the tensile-compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece, the test piece is elastic with respect to the test piece. A first step of performing the tension and compression while performing stress control by setting a stress target value that does not exceed the limit, and obtaining a gradient of an elastic line based on the detected values of the stress and the strain, and the test piece The amount of strain at the point of crossing the straight line having zero stress and passing through the detected value and having a gradient equal to the gradient of the elastic line based on the detected value of the stress and the strain while controlling the strain From the first cycle of the tension compression to the subsequent cycle so that the calculated strain amount is always ½ of the target value of the plastic region. And it has a second process of performing inversion of tension and compression. Therefore, it is easy to keep the plastic region constant with high accuracy. Since the elastic line gradient measurement and the tensile and compression test process can be automatically performed along a continuous flow, the test procedure can be rationalized. Since there is no need to replace the test piece between the two test machines, human error is unlikely to occur.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of a tension / compression test apparatus for explaining an embodiment of the tension / compression test method of the present invention. In the figure, 1 is a target value output unit, 2 is a comparison unit, 3 is a control element, 4 is a tension / compression tester, 5 is a servo valve, 6 is a hydraulic actuator, 6a is a hydraulic cylinder, 6b is a piston, and 7 is a test piece. (Test sample), 8 is a load sensor, 9a and 9b are chucks, 10 is an elongation sensor, 11 is an amplifier for a load sensor, 12 is an amplifier for an elongation sensor, 13 is an _Epp calculation unit, 14 is a level comparator, and 15 is E A target value setting unit for _pp , 16 is a limit value setting unit for load and elongation, and 17 is a level comparator.
The tensile / compression tester 4 is controlled by a controller and a host computer, but in FIG. 1, the controller and the host computer are not distinguished from each other and are illustrated as a plurality of functional blocks.
[0012]
The target value output unit 1 outputs a target value that repeatedly increases and decreases with a predetermined gradient. This output value is output to the control element 3 by subtracting the value of the elongation εlong output from the elongation sensor amplifier 12 in the comparison unit 2. The output signal of the control element 3 is output to the servo valve 5 of the tensile / compression tester 4. In the tensile / compression tester 4, the test piece 7 is attached to the piston 6b and the load sensor 8 at both ends by chucks 9a and 9b. An elongation sensor 10 is attached to the test piece 7. As the elongation sensor 10, for example, a strain gauge type extensometer having an arm, a capacitance type extensometer, a laser type displacement measuring instrument, or the like is used. For example, a load cell is used as the load sensor 8.
[0013]
The output value of the load sensor 8 is amplified and A / D converted by the load sensor amplifier 11 and is output to E _pp arithmetic unit 13 and a level comparator 17. The output value of the stretch sensor 10 is amplified and A / D converted by the stretch sensor amplifier 12 and output to the comparison unit 2 and also to the E _pp calculation unit 13 and the level comparator 17.
[0014]
Level comparator 14, the value of E _pp output from E _pp calculation unit 13 matches the output value of the target value setting section 15 of the E _pp, it outputs an inversion command signal to the target value output unit 1.
On the other hand, in the first cycle of the loop 21, the level comparator 17 outputs the output of the load sensor amplifier 11 and the output of the extension sensor amplifier 12 to the respective limits output from the extension and load limit value setting unit 16. Compare with the value. When either the output of the load sensor amplifier 11 or the output of the elongation sensor amplifier 12 exceeds the limit value, an inversion command signal is output. At the same time, the target value of the target value setting unit 15 of E _pp is set and changed so that the output value of the E _pp calculating unit 13 at this time becomes a new target value. And each limit value set to the limit value setting part 16 of elongation and load is enlarged. The level comparator 17 also stops the test when one of the output of the load sensor amplifier 11 and the output of the elongation sensor amplifier 12 exceeds the limit value in the second cycle and thereafter of the loop 21.
[0015]
Returning to FIG. There are two definitions of the plastic region. The first definition is the one described in the above description of the prior art, and is the difference in strain between two points where the loop 21 intersects the line of stress σ = 0. , Ε _pp . On the other hand, the second definition is the difference in strain between two points where the tangents 23 and 24 of the inversion point of the loop 21 intersect the line of the stress σ = 0, and is represented by E _pp . In the present invention, this E _pp is defined as a plastic region, and a target value of this E _pp is set. As a property of the metal material, even if the number of repeated cycles advances and fatigue progresses, the tangent lines 23 and 24 have a substantially constant gradient until just before the fracture. This gradient is equal to the gradient of the elastic line 22, that is, the Young's modulus. If the Young's modulus is known, the target value for E _pp can be clearly calculated before actually intersecting the line of stress σ = 0.
[0016]
In one embodiment of the present invention, in the E _pp calculation unit 13, a straight line that passes through the current values of the stress σ and the strain ε and has a gradient equal to the gradient of the elastic line 22 obtained in advance is the load σ = A value corresponding to the strain amount at a point intersecting the straight line of 0 (a value that is 1/2 of the plastic zone E _pp ) is calculated, and this value is always equal to E _pp from the first cycle of tensile compression to the subsequent cycles. When the level comparator 14 determines that the target value set in the target value setting unit 15 has been exceeded, the increase / decrease in the target value of elongation of the target value output unit 1 is reversed, and the tension compression is reversed.
[0017]
FIG. 2 is a first diagram for explaining an embodiment of the tensile compression test method of the present invention. In the figure, parts similar to those in FIG.
The basic operation will be described with reference to FIGS. Prior to the tensile and compression test, Young's modulus is measured in advance. That is, the inclination of the elastic line 22 is obtained. By outputting a target value of the elongation εlong proportional to time from the target value setting unit 1, a load is applied to the test piece 7 while performing feedback control with a constant displacement speed, and a tensile compression test is executed.
[0018]
The E _pp calculating unit 13 tangents to the measurement points of the strain ε and the stress σ corresponding to the measured values of the load load and the elongation εlong every time t ₁ , t ₂ , t ₃ ,... (Time interval Δt). 23 calculates the strain at the point of intersection with the line of stress σ = 0 (a value that is ½ of the plastic zone E _pp ). When the level comparator 14 detects that the output of the E _pp calculation unit 13 has reached the set value of the target value setting unit 15 of E _pp at time t _n in the first cycle of the tensile and compression test, the target value output The output of part 1 is reduced and the loop 21 is inverted. The loop 21 moves from the initial curve portion 21a to the negative direction curve portion 21b. Similarly, even in a quadrant in which the stress σ (load load) and the strain ε (elongation εlong) are negative, twice the strain amount at the point where the tangent line 24 (FIG. 6) intersects the line with the stress σ = 0 is E _pp. , The loop 21 is inverted from the negative curve portion 21b to the positive curve portion 21c (FIG. 6).
[0019]
In this way, the inversion of the amplitude is repeated until the test piece 7 breaks so that the plastic zone E _pp maintains a constant target value in the subsequent cycles. As a result, the target value for E _pp can be set from the first cycle of the loop 21. Since the plastic zone ε _pp and the plastic zone E _pp are substantially equal, as described above, the plastic zone ε _pp is broken from the first cycle even if the target value is set for the plastic zone E _pp . Since it is kept almost constant until, it is highly accurate and reliable.
[0020]
FIG. 3 is a second diagram for explaining an embodiment of the tensile compression test method of the present invention. The case where the current strain ε exceeds the limit value limitε _max of the absolute value of the strain in the first cycle is illustrated. In the figure, parts similar to those in FIG. 31 is a stress limit line, 32 is a strain limit line, 33 is a half point of the target value of E _pp , 34 is a half point of the new target value of E _pp when updated, 35 Is a new limit line of stress when updated, and 36 is a new limit line of strain when updated.
[0021]
In the compression test method Tensile according plastic zone control described above, the operator sets the target value to the target value setting portion of the E _pp, while increasing the load σ and strain epsilon (INC) in or decrease (DEC), E _pp While calculating the value, the operation proceeds by inverting the loop 21 so that the value becomes the set target value. Therefore, only when the reversal point is reached, as a result, the maximum value σ _max and the minimum value σ _min (| σ _max | = | σ _min |) of the load σ, and the maximum value ε _max and the minimum value ε of the strain _min (| ε _max | = | ε _min |) is determined. These values depend on the material properties of the test piece. Therefore, at the stage where the operator first designates the target value of the plastic zone E _pp , it is impossible to manage how much σ _max and ε _max are increased. Therefore, during the test, the values of the load σ and strain ε may become too large and run away. Therefore, it is a problem to solve practically safe driving.
[0022]
Once a test piece is damaged, it cannot be used for a formal test. Therefore, the value of E _{pp that} can be safely tested can be determined by performing a tensile and compression test using another test piece 7 of the same material. However, since the test piece 7 is valuable, it is unreasonable to waste even one test piece, even for trial.
[0023]
Therefore, when at least one of the absolute values of the stress σ corresponding to the load Load and the strain ε corresponding to the elongation εlong in the first cycle reaches the stress limit line 31 and the strain limit line 32, respectively. As a new target value E _pp (new) of the plastic zone E _pp , the tangents 23 and 24 of the points of the stress σ and the strain ε at this time have twice the strain amount at the point where the straight line of the stress σ = 0 intersects. Set again. At the same time, the limit value Limitshiguma _max of the absolute value of the stress sigma, and, by increasing the limit value Limitipushiron _max of the absolute value of the distortion ε, Limitσ _max (New), and the limit value of the absolute value of the distortion ε Limitε _max (New ). That is, a new limit line 35 for stress when updated and a new limit line 36 for strain when updated are set.
[0024]
Therefore, in the subsequent tensile and compression process, twice the strain amount at the point where the tangents 23 and 24 of the measurement points of the load σ and the strain ε described above intersect the straight line with the stress σ = 0 is a new value in the plastic region E _pp . When the target value E _pp (new) is reached, the tension and compression are reversed. Also, the test is stopped when at least one of the absolute values of stress σ and strain ε reaches the respective updated limit value, Limitσ _max (new), value Limitε _max (new).
In this way, when the initially set target value of the plastic region E _pp is too large and the load σ or strain ε becomes too large and there is a risk of runaway, the target value of E _pp is set to a smaller value and the test is continued.
[0025]
FIG. 4 is a flowchart of one embodiment of the tensile compression test method of the present invention. As shown in FIG. 4, in S41, the strain ε (elongation εlong) is uniformly increased or decreased. That is, feedback control is performed so that the strain ε (elongation εlong) changes at a constant speed. In S42, based on the detected values of stress σ (load Load) and strain ε (elongation εlong) and Young's modulus, E _{pp is determined} from the strain at the intersection of tangent line 23 and stress σ = 0 line shown in FIG. Is calculated. In S43, it is determined whether E _pp exceeds the target value. When the target value is exceeded, the process proceeds to S44, and when the target value is not exceeded, the process proceeds to S45. In S44, when the strain ε is uniformly increasing, it is reversed to uniform decrease, and when the strain ε is uniformly decreasing, it is reversed to be uniformly increased, and the processing returns to S41.
[0026]
In S45, it is determined whether or not the absolute value | ε | of the strain ε exceeds the limit ε _{max. If} it exceeds, the process proceeds to S46, and if not, the process proceeds to S47. In S47, when the absolute value | σ | of the load σ exceeds limitσ _max , the process proceeds to S46, and when it does not exceed, the process returns to S41.
Therefore, when the absolute value of at least one of the strain ε or the load σ does not reach the set limit value, the steps S41 to S45 and S47 are repeated, so that the plastic zone E _pp is set to the first set target value. It will be controlled to hold.
[0027]
In S46, it is determined whether or not the current test cycle is the first first cycle of plastic zone control. If it is the first cycle, the process proceeds to S48. When it is not the first cycle, the process proceeds to S49 and the test is stopped. In S48, the target value of the plastic zone E _pp is changed. That is, a size twice as large as the amount of strain at the point where the tangent line 23 passing through the detected values of the current load σ and strain ε intersects the line of stress σ = 0 is set as a new target value of the plastic region E _pp .
[0028]
In S50, in FIG. 3, Limitσ _max (new), as shown as Limitε _max (New), by re-setting the limit value to a larger value, in the second cycle after the next, caught by the limit value Make sure there is nothing. That is, Δε (> 0) is added to the limit value limitε _max of the absolute value of the strain ε to obtain a new limit value of the absolute value of the strain ε. Further, Δσ (> 0) is added to the limit value limitσ _max of the absolute value of the load σ to obtain a new limit value of the absolute value of the load σ. In S51, when the strain ε is uniformly increasing, it is reversed to uniform decrease, and when the strain ε is uniformly decreasing, it is reversed to be uniformly increased, and the processing is returned to S41. Thereafter, until the test piece breaks, new target value of the plastic zone E _pp (New), strain new limit value of the absolute value of ε limitε _max (New), a new limit value of the absolute value of the load σ limitσ _max Drive on (new).
[0029]
In the above description, the limit value is set for both the strain ε and the stress σ, but may be set to only one of them. In S50, the absolute value of the stress σ or the limit value of the absolute value of the strain ε that has reached the limit value out of the absolute value of the stress σ and the absolute value of the strain ε may be set larger. .
[0030]
In the embodiment of the tension compression test method described above, it is necessary to know the gradient (Young's modulus) of the elastic line 22 in advance. However, if this Young's modulus is measured with another testing machine before the start of the test, the test piece 7 must be transferred, and thus a human error may occur when the test piece is attached or removed. Therefore, the reliability of the test cannot be increased. Therefore, it is reasonable that the same tensile and compression test apparatus can be used. Therefore, the gradient of the elastic line 22 can be measured by switching the function in the control program of the tensile and compression test apparatus shown in FIG.
The Young's modulus needs to be measured in the elastic region below the stress σ _ys corresponding to the yield point or the point at which the permanent set becomes a predetermined value (0.2% or 0.02%).
[0031]
The first method of measuring the Young's modulus using the same tensile and compression test apparatus is the gradient of the stress σ with respect to the strain ε at a measurement point equal to or less than σ _ys predicted in the initial curve portion 21a of the first first cycle. Is calculated, the gradient of the elastic line 22, that is, the Young's modulus can be calculated.
[0032]
The second method of measuring the Young's modulus using the same tensile compression test apparatus is a method in which the Young's modulus is first measured and then the plastic zone control test is continuously performed.
FIG. 5 is an explanatory diagram of a second method for measuring the Young's modulus using the same tensile compression test apparatus. In the figure, 61 is the value of stress σ and 62 is the value of strain ε.
In the second method of measuring the Young's modulus using the same tensile compression test apparatus, the Young's modulus is measured in the period of FB = load as a pre-process of the tensile compression test method for keeping the plastic region constant. To the test piece 7, and sets the upper target value sigma _a and a lower target value over sigma _a load sigma not exceeding the elastic range, from the target value output section, of the between the upper target and a lower target value constant Outputs a target value that increases or decreases linearly with time.
[0033]
By measuring in the elastic range, cyclic damage of the test piece 7 can be avoided. In the comparison unit 2, the target value is compared with the load Load output from the load sensor amplifier 11, thereby performing tension and compression while performing load feedback control. During this time, the Young's modulus is calculated by detecting the stress σ (load Load) applied to the test piece 7 and the strain ε (elongation εlong) generated in the test piece 7.
[0034]
After the Young's modulus is obtained, the feedback control method is switched from FB = load to FB = εlong when the stress σ = 0 (load Load = 0). In the period of FB = εlong, as described with reference to FIG. 1 and the like, the main test of tension and compression is performed while feedback control of the speed of elongation εlong is made constant. FIG. 5 shows two defined plastic zones ε _pp and E _pp .
[0035]
【The invention's effect】
As apparent from the above description, the present invention has an effect that it is easy to keep the plastic region constant with high accuracy. The test can be performed safely. Since it is not necessary to perform a test using a test piece made of the same material as that used for a formal test, valuable materials are not wasted for the test trial, and the material can be used effectively.
In addition, the measurement of the slope of the elastic line necessary for constant control of the plastic area can be performed integrally with the tensile and compression test process, so the test procedure can be rationalized, human error is unlikely to occur, and the reliability of the test is reliable. Can raise the sex.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of a tension / compression test apparatus for explaining an embodiment of a tension / compression test method of the present invention.
FIG. 2 is a first diagram for explaining one embodiment of a tensile compression test method of the present invention.
FIG. 3 is a second diagram for explaining an embodiment of the tensile compression test method of the present invention.
FIG. 4 is a flowchart of an embodiment of the tensile compression test method of the present invention.
FIG. 5 is an explanatory diagram of a second method for measuring Young's modulus using the same tensile and compression test apparatus.
FIG. 6 is a diagram for explaining a tensile compression test method.
[Explanation of symbols]
1 target value output unit, 2 comparison unit, 4 tension compression tester, 5 servo valve, 6 hydraulic actuator, 6a hydraulic cylinder, 6b piston, 7 test piece, 8 load sensor, 9a, 9b chuck, 10 elongation sensor, 21 loop 21a initial curve part, 21b negative direction curve part, 21c positive direction curve part, 22 elastic line, 23, 24 tangent

Claims (5)

In the tension compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece,
Based on the detected values of the stress and the strain, calculate the amount of strain at a point that intersects the straight line of zero stress of a straight line that passes through the detected value and has a gradient equal to the gradient of the elastic line,
A tensile and compression test method comprising performing reversal of tensile and compression so that the calculated strain amount is always ½ of the target value of the plastic region from the first cycle to the subsequent cycle of the tensile and compression. . A limit value is set for each absolute value of the stress and the strain,
At least one of the absolute value of the detected value of the stress and the absolute value of the detected value of the strain has reached the respective limit value before reaching the time of performing the reversal in the process of the first cycle. Sometimes, a value twice the amount of strain calculated based on the detected value of the stress and strain at the time of arrival is reset to a new target value of the plastic region, and in the process of the subsequent cycles, 2. The tensile compression test method according to claim 1, wherein the tensile compression is reversed when a half of a new target value of the plastic region corresponds to the strain amount. At least one of the absolute value of the detected value of the stress and the absolute value of the detected value of the strain has reached the respective limit value before reaching the time of performing the reversal in the process of the first cycle. Sometimes, among the absolute value of the detected value of the stress and the absolute value of the detected value of the strain, at least the limit value that has reached the limit value is set to a larger value. The tensile / compression test method according to claim 2, wherein the test is stopped when at least one of an absolute value of the detected value and an absolute value of the detected value of the strain reaches the respective limit value. In the tension compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece,
Calculating a slope of the elastic line based on the detected values of the stress and the strain in a period not exceeding the elastic limit of the first cycle of the tension and compression;
In a period exceeding the elastic limit of the first cycle of the tension and compression, a straight line with zero stress, a straight line having a gradient that passes through the detected value and is equal to the gradient of the elastic line, based on the detected value of the stress and the strain. The amount of strain at the point of intersection with the tension compression is calculated, and the calculated amount of strain is always ½ of the target value of the plastic region from the first cycle of the tension compression to the subsequent cycles. A tensile compression test method characterized by performing inversion. In the tension compression test method for repeatedly performing tensile compression on the test piece and detecting the stress applied to the test piece and the strain generated in the test piece,
A first process of setting a stress target value that does not exceed an elastic limit for a test piece, performing the tension and compression while performing stress control, and obtaining a gradient of an elastic line based on the detected values of the stress and the strain ,and,
While performing strain control on the test piece, based on the detected values of the stress and the strain, a point that intersects the straight line of zero stress passing through the detected value and having a gradient equal to the gradient of the elastic line A strain amount is calculated, and the calculated strain amount is always reversed from the first cycle of the tension compression to the subsequent cycles so that the tension compression is reversed so as to be ½ of the target value of the plastic region. 2. A tensile-compression test method comprising the steps of 2.

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