JP4075987B2 - Outer diameter measuring instrument for tensile test - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tensile test method for performing a tensile test of the material, in particular true stress even under high-speed tensile relates to an outer diameter measuring instrument used in the practice of the tensile test method of enabling automatic measurement of the true strain.
[0002]
[Prior art]
In the standard tensile test method specified by JIS Z2241 (metal material tensile test method), JIS K7113 (plastic tensile test method), etc., the load applied to the test piece is the original cross-sectional area of the parallel part of the test piece. The stress is obtained by slowing down, but in the plastic region after yielding, the test piece is constricted (cross-sectional reduction), so if the load is divided by the original cross-sectional area as described above, the true stress is obtained. It cannot be expressed, and a true stress-strain relationship cannot be obtained.
Therefore, for example, in Patent Documents 1 and 2, a non-contact type outer diameter measuring device using a laser beam or the like is arranged around a test piece set in a tensile testing machine, and this outer diameter measuring device is used during a tensile test. The outer diameter of the test piece is continuously measured while reciprocating in the axial direction of the test piece, and the true stress can be obtained by using the minimum outer diameter obtained by this measurement.
[0003]
Recently, for example, in the field of vehicle manufacturing, material properties at high deformation speeds that contribute to collision analysis have become important. To meet this demand, so-called high-speed tension (10000 mm / min or more) is used. It is necessary to understand the characteristics. However, the tensile tests described in Patent Documents 1 and 2 are all statically pulled at a low speed (500 mm / min or less), and when this method is applied to high-speed tension, the constriction in the parallel portion is caused. Since the location cannot be predicted, the minimum outer diameter cannot be measured in real time, and it is difficult to obtain a true stress-strain relationship. In addition, in the thing of these patent documents 1 and 2, when a narrowing arises to some extent, it is made to reciprocate an outer diameter measuring device focusing on a constriction location (the 2nd page lower left column 18th page of patent document 1). Line 20, paragraph [0010] of Patent Document 2), such a method cannot be adopted by high-speed tension.
[0004]
On the other hand, in Non-Patent Document 1, by drawing a line at a predetermined pitch on a parallel portion of a flat plate tensile test piece for a resin material, and observing a change in the line during a high-speed tensile test with a video tape recorder, It is disclosed to determine a true stress-strain correlation.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-103442 [Patent Document 2]
JP 7-113732 A Non-Patent Document 1
Hideaki Arimoto and three others, “A study on Energy-Absorbing Mechanism of Plastic Ribs”, Proceeding of IBEC '98, USA, SAE International, 1998.CE-4 (Figures 4-6)
[0006]
[Problems to be solved by the invention]
However, according to the method described in Non-Patent Document 1, since it is necessary to determine the elongation and change in cross-sectional area by processing a video image for each frame, data analysis is performed after the test, and true during the test. It is impossible to automatically measure stress and true strain, and it takes time to understand material properties.
In a high-speed tensile test of a resin material, the strain rate increases rapidly due to the occurrence of necking. Therefore, it is necessary to feedback-control the actuator on the tensile tester side so that the strain rate is almost constant. According to the method described in (1), since the data analysis after the test is performed, the feedback control described above is impossible, and the reliability of the obtained characteristic value is particularly low for the resin material.
The present invention has been made in view of the above-described conventional problems, and the problem is that the true stress and true strain can be automatically measured with high accuracy even in high-speed tension, thereby shortening the test time. An object of the present invention is to provide an outer diameter measuring instrument for a tensile test that greatly contributes to improvement in reliability of the obtained characteristic value.
[0007]
[Means for Solving the Problems]
In the tensile test method performed using the outer diameter measuring instrument according to the present invention, a bar-shaped test piece provided with an arc shape or a U-shaped notch in a part of a parallel portion is set in a tensile tester, and the test is performed during a tensile test. The outer diameter of the cutout bottom of the piece is continuously measured.
In the tensile test performed in this way, strain is intensively generated at the notch bottom of the bar-shaped test piece. Therefore, even when high-speed tension is performed, the outer diameter can be measured in real time by focusing on the notch bottom. Further, since the strain rate can be grasped from the result of the outer diameter measurement, the feedback control for making the strain rate substantially constant becomes possible.
In this test method, the method for measuring the outer diameter of the notch bottom is arbitrary, but a thread, preferably silk thread, is wound around the notch bottom of the test piece, and the outer diameter of the notch bottom is determined from the change in length of the thread. A method of measuring change can be employed. In this case, even if the circular cross section of the test piece is deformed into a non-circular state, the change in the cross sectional area can be grasped with high accuracy from the change in the length of the filamentous body.
The test specimen material used in this test method may be a metal material or a resin material, but since the strain rate can be made almost constant as described above, the influence of the strain rate is greatly increased. This is particularly useful when the target resin material is used.
[0008]
The outer diameter measuring instrument according to the present invention used in the above tensile test method is provided between the upper and lower clamp means fixed to the test piece with the notch interposed between the notched bar test piece set in the tensile tester. A measuring instrument main body that is detachable so as to be floatable in the axial direction, a silk thread wound around the notch bottom of the test piece, or a filament having an elongation characteristic and flexibility equivalent to that of the silk thread, and provided in the measuring instrument main body Displacement detecting means for detecting a change in the length of the silk thread or filament wound around the notch bottom of the test piece.
In the outer diameter measuring device configured in this way, the length of the silk thread or filamentous body extends according to the cross-sectional reduction of the notch bottom of the test piece. Therefore, the extension of the silk thread or filamentous body is measured by the displacement detection means. The average diameter, that is, the cross-sectional area of the notch bottom of the test piece can be accurately grasped. In addition, the measuring instrument body is attached to the test piece so that it can float by the upper and lower clamp means with the notch in between, so even if the test piece is stretched, the outer diameter measurement position can always be kept at the notch bottom, outer diameter measurement of the cutout bottom of the specimen Ru can be performed even more accurately.
In the outer diameter measuring apparatus, the measuring instrument body has a frame shape having test piece insertion holes in the upper and lower plate portions, and is elastic between upper and lower clamp means that are detachably fixed to the test piece. It can be set as the structure clamped through a body, and a measuring device main body can be easily floated using the elastic force of this elastic body.
Further, the displacement detection means includes a movable body having one end fixed to the measuring instrument main body and engaged with the other end of the silk thread or the thread- like body wound around the notch bottom of the test piece, and the movable body at all times. An urging means for urging the silk thread or the filamentous body in a direction to apply tension and a displacement sensor for measuring the displacement of the movable body can be used. In this case, as the displacement sensor, it is desirable to use an eddy current displacement sensor that is relatively small and excellent in measurement accuracy.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows one embodiment of a tensile test method according to the present invention. In the figure, 1 is a fixed table of the press machine, 2 is a movable table of the press machine, and both tables 1 and 2 are provided with chucks 3 and 4 for supporting both ends of a test piece 10 described later. ing. The movable table 2 is driven up and down by an actuator (not shown) and fast-forwarding means (not shown). During the tensile test, the movable table 2 is raised by driving the actuator, so that the test piece 10 A tensile load is applied, and this load is detected by a load measuring device (load sensor) 5 attached to the chuck 3 on the fixed table 1 side.
[0010]
As shown well in FIG. 2, the test piece 10 used in the present embodiment has a rod shape as a whole, and an arc-shaped notch 11 is formed at an intermediate portion in the longitudinal direction. For example, the test piece 10 has a total length of 150 mm, a diameter D of a rod-like part (parallel part) of 10 mm, a diameter d of the bottom of the notch 11 of 3 mm, and a radius R of the bottom of the notch 11 of 7 mm. The shape is set. The notch 11 may be U-shaped.
[0011]
In the tensile test, the outer diameter measuring device 20 according to the present invention is attached to the test piece 10 set in the tensile tester via both chucks 3 and 4. The outer diameter measuring device 20 continuously measures the diameter of the bottom of the notch 11 of the test piece 10 (hereinafter referred to as the notch bottom) during the tensile test. The measuring instrument main body 21 that is detachable so as to be floatable in the direction, the silk thread (filamentous body) 22 wound around the notch bottom of the test piece 10, and the displacement detection means 23 that detects a change in the length of the silk thread 22. Has been.
[0012]
The measuring device main body 21 has a rectangular frame shape, and is provided with insertion holes 25 that allow the test piece 10 to be inserted into two opposing wall portions 24. The measuring device main body 21 is set on the test piece 10 in a state where the test piece 10 is inserted through the insertion hole 25 and is fixed between the upper and lower clamp means 26 and 27 detachably fixed to the test piece 10. It is clamped via the elastic body 28.
More specifically, each of the upper and lower clamp means 26 and 27 has a pair of L-shaped plates each having a semicircular fitting portion 29a that can be fitted to the test piece 10, as shown in FIGS. 29 and a pair of bolts and nuts 30 for integrating each pair of L-shaped plates 29. The pair of L-shaped plates 29 are fitted together with the respective fitting portions 29a along the test piece 10, and in this state, the pair of L-shaped plates 29 are fastened and fixed to the test piece 10 using the pair of bolts and nuts 30. . Thus, the upper and lower clamp means 26 and 27 are fixed to the test piece 10 with a gap slightly larger than the outer dimension between the opposing wall portions 24 of the measuring device main body 21 with the notch 11 therebetween. . As a result, each elastic body 28 is interposed between the measuring device main body 21 and the upper / lower clamp means 26 and 27 in an appropriately compressed state. As a result, the measuring device main body 21 is arranged in the axial direction of the test piece 10. It becomes possible to float. The type of the elastic body 28 is not particularly limited, but it is preferable to use a sponge having viscoelasticity. In this case, the elastic body 28 is adhered to the outer surface of the opposing wall portion 24 of the measuring device main body 21. To.
[0013]
The displacement detecting means 23 includes a movable body 31 having one end fixed to the measuring instrument main body 21 and engaged with the other end of the silk thread 22 wound around the notch bottom of the test piece 10, and the movable body 31 is normally attached to the movable body 31. It comprises a disc spring (biasing means) 32 that urges the silk thread 22 in the direction of applying tension, and an eddy current displacement sensor 33 that measures the displacement of the movable body 31. Here, the eddy current displacement sensor 33 is opposed to the movable body 31 by using a bolt 35 on a fork-like upright piece 34a of a bracket 34 integrally formed with the L-shaped plate 29 on one side constituting the lower clamp means 27. So that the positioning is fixed.
A displacement detection circuit 37 is connected to the eddy current displacement sensor 33 via a signal line 36. The displacement detection circuit 37 has a function of detecting the distance between the eddy current displacement sensor 33 and the movable body 31 from the change in the high-frequency magnetic field, and the detection signal is sent to the arithmetic unit 38. It has become so. The arithmetic device 38 has a function of calculating stress and strain based on signals from the displacement detection circuit 37 and the load measuring device 5 and obtaining a stress-strain correlation.
[0014]
Hereinafter, a tensile test method performed using the test piece 10 and the outer diameter measuring device 20 will be described.
In the tensile test, first, with the movable table 2 of the tensile tester raised, the chuck 3 of the fixed table 1 supports one end of the test piece 10, and then, from the notch 11 of the test piece 10. A pair of L-shaped plates 29 constituting the lower clamp means 27 are fastened and fixed using bolts and nuts 30 to a part separated downward by a predetermined distance. At this time, an eddy current displacement sensor 23 is attached to a bracket 34 that is integral with one of the pair of L-shaped plates 29, and at the same time the lower clamp means 27 is fixed to the test piece 10, the eddy current displacement sensor 23. Is positioned at a side position facing the notch 11 of the test piece 10.
[0015]
Thereafter, the measuring instrument main body 21 is seated on the lower clamping means 27 from above while passing the test piece 10 through the insertion hole 25 of the measuring instrument main body 21, and then a pair of L-shaped plates constituting the upper clamping means 26. 29 is fastened and fixed to the test piece 10 using bolts and nuts 30. At this time, an appropriate load is applied to the upper clamp means 26 to compress the upper and lower elastic bodies 28 by a predetermined amount, so that the measuring instrument body 21 can float between the upper and lower clamp means 26 and 27. Sandwiched between.
[0016]
Next, the silk thread 22 having one end engaged with the measuring device main body 21 in advance is wound around the notch 11 of the test piece 10, and the other end is engaged with one end of the movable body 31. The movable table 2 is lowered at a high speed by the operation of a rapid feed means (not shown), and the other end portion of the test piece 10 is supported by the chuck 4. When the preparation is completed, the movable table 2 is raised at a constant speed by the operation of the actuator of the tensile tester. Then, after elastically deforming, the test piece 10 yields and undergoes plastic deformation, and the cutout bottom gradually decreases in cross section (reduced diameter) due to this plastic deformation. Then, the length of the silk thread 22 gradually increases according to the cross-sectional reduction of the notch bottom, and the movable body 31 approaches the eddy current displacement sensor 33 side by the biasing force of the disc spring 32 accordingly. As described above, the signal of the eddy current displacement sensor 33 is sent to the arithmetic unit 38 via the displacement detection circuit 37, and the arithmetic unit 38 determines whether or not the test piece 10 is based on the signal from the displacement detection circuit 37. The average diameter, that is, the cross-sectional area of the notch bottom is calculated, and the true stress is calculated by dividing the load data obtained by the load detector 5 by the cross-sectional area. On the other hand, since the true strain rate can be found from the change in the outer diameter of the notch bottom of the test piece 10, the arithmetic unit 38 seems to obtain a predetermined strain rate when the strain rate is greater than a preset value. The actuator of the tensile tester is feedback controlled.
[0017]
In this way, the tensile test proceeds under a substantially constant strain rate, and finally the test piece 10 breaks from the bottom of the notch 11. During this tensile test, the true stress and true strain are continuously measured by signals from the displacement detecting means 23 and the load detector 5, so that even if the resin material is pulled at high speed, the true stress-true strain is measured. It becomes possible to accurately grasp the correlation.
Particularly in the present embodiment, even if the test piece 10 is stretched, the measuring device main body 21 floats via the elastic body 28 and maintains the neutral position with respect to the notch 11 of the test piece 10. The outer diameter of the notch bottom of the test piece 10 can be accurately measured. Here, the elongation of the test piece 10 having the notch 11 as described above is at most 2 to 3 mm, and the floating function is sufficiently maintained even when the flat elastic body 28 is used. Further, since the silk thread 22 constituting the outer diameter measuring device 20 has a small elongation, and has flexibility to follow a change in the outer diameter of the test piece 10, the notch bottom of the test piece 10 is open. Even when the cross section is reduced in a circular shape, the change in the cross sectional area of the notch bottom can be accurately obtained from the change in the length of the silk thread 22.
[0019]
【The invention's effect】
As described above, according to the outer diameter measuring instrument for a tensile test according to the present invention, the outer diameter of the notch bottom is accurately measured from the change in the length of the silk thread or filament wound around the notch bottom of the test piece. As a result, true stress and true strain can be measured in real time even when high-speed tension is applied, and the strain rate can be controlled to be almost constant, reducing the test time and improving the reliability of the obtained characteristic values. It will greatly contribute.
[Brief description of the drawings]
FIG. 1 is a side view showing an embodiment of a tensile test method according to the present invention and the structure of an outer diameter measuring instrument used for the tensile test.
FIG. 2 is a side view showing the shape of a test piece used in the tensile test.
FIG. 3 is a plan view showing a structure of a clamping means for attaching a measuring device main body constituting the outer diameter measuring device to a test piece.
FIG. 4 is a side view showing a structure of a measuring instrument main body constituting the outer diameter measuring instrument.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixed table of tensile tester 2 Movable table 3 of tension tester 4, 4 Chuck 5 Load measuring device 10 Test piece 11 Notch 20 of test piece Outer diameter measuring device 21 Measuring device main body 22 Silk thread (filament)
23 Displacement measuring means 26, 27 Clamping means 31 Movable body 32 Disc spring (biasing means)
33 Eddy current displacement sensor

Claims (4)

A measuring instrument main body which is attached to a bar-shaped test piece with a notch set in a tensile tester and is detachable so as to be floatable in the axial direction between upper and lower clamping means fixed to the test piece with the notch interposed therebetween, and the test A silk thread or a filament having elongation characteristics and flexibility equivalent to that of a silk thread wound around the notch bottom of the piece, and a silk thread or filament wound around the notch bottom of the test piece provided in the measuring instrument body An outer diameter measuring instrument for tensile testing, comprising: a displacement detecting means for detecting a change in length of the tensile test. The measuring instrument body has a frame shape having test piece insertion holes in the upper and lower plate portions, and is sandwiched between the upper and lower clamp means detachably fixed to the test piece via an elastic body. The outer diameter measuring instrument for a tensile test according to claim 1. A displacement detecting means includes a movable body having one end fixed to the measuring instrument main body and engaged with the other end of the silk thread or filament wound around the notch bottom of the test piece, and the movable body is normally connected to the silk thread or thread. The outer diameter measuring instrument for a tensile test according to claim 1 or 2 , comprising an urging means for urging the body in a direction of applying tension and a displacement sensor for measuring the displacement of the movable body . The outer diameter measuring instrument for a tensile test according to claim 3 , wherein the displacement sensor is an eddy current displacement sensor and is disposed to face the movable body .

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