JP2012088093A - Crack opening measuring instrument under high pressure gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that, in a differential transformer type displacement measuring instrument, a detecting lever is easily disengaged from an opening of a test piece and that a development of a crack enlarges the opening of the test piece to cause a substantial displacement or an oblique tilt of a detection rod, thereby inhibiting an accurate detection of a value.SOLUTION: A crack opening displacement measuring instrument for measuring an opening width of a compact tension test piece for use in a fatigue test under high pressure gas includes: a tip portion to be screwed to the compact tension test piece; an arm having one end engaged with the tip portion; a joint section for connecting the other end of the arm to the one end by a rolling mechanism; the detection rod to be engaged with the other end of the joint section; and a detecting section for detecting the displacement of the tip end of the detection rod. This crack opening displacement measuring instrument measures the opening width of the compact tension test piece.

Description

The present invention relates to a crack opening measuring instrument such as a crack growth test and a fracture toughness test in high-pressure gas. In particular, the present invention relates to an instrument for measuring the crack opening width of a compact tension test piece according to ASTM E647-91.

Machines and structures may be subjected to repeated stress under various environments, and fatigue failure may occur, in which the cracks that are generated progress and eventually break down. In particular, in the high-pressure hydrogen gas environment, it is assumed that micro hydrogen atoms penetrate into the crack and the crack growth behavior is different. Measurement is extremely important.

Conventionally, measurement by a clip gauge method and measurement by a differential transformer method are used to measure the displacement of a crack opening. In the clip gauge method, the tip of the clip gauge detection arm is brought into contact with the opening of the test piece, a strain gauge is attached to the detection arm of the clip gauge, and the displacement of the opening of the test piece is detected by the electrical signal of the strain gauge. To do. However, in a high-pressure hydrogen gas environment, there is a problem that hydrogen gas enters the adhesion surface of the strain gauge attached to the detection arm of the clip gauge, and the strain gauge peels off from the detection arm in a very short time, so that it cannot be used.

On the other hand, the differential transformer method detects the displacement of the opening of the test piece at the end of the detection lever, and the detection rod is perpendicular to the detection lever so that the displacement can be detected by the detection coil on the opposite side of the end of the detection lever. It is connected to. In the differential transformer method, since the detection coil is outside the high-pressure hydrogen gas environment, problems such as corrosion do not occur, but the problem is that the detection lever can easily come off from the opening of the test piece, and cracks develop and the test piece opens. When the portion becomes larger, there is a problem that the detection rod is displaced from the vertical position and tilted obliquely, so that an accurate value cannot be detected.

JP 2003-329557 A

The present invention relates to a problem that the detection lever is likely to come off from the opening of the test piece in a differential transformer type displacement measuring instrument, and when the crack is developed and the opening of the test piece becomes large, the detection rod is greatly displaced from the vertical position. A crack opening displacement measuring instrument that can measure the opening width of a compact tension test piece with high accuracy is designed to solve the problem of tilting obliquely and making it impossible to detect the exact value of the displacement of the opening. The issue is to provide.

In order to solve the above problems, the present invention provides a crack opening displacement measuring instrument for measuring an opening width of a compact tension test piece used for a fatigue test in high-pressure gas, and a tip portion screwed to the compact tension test piece; An arm portion that engages at one end with the tip portion, a joint portion that connects the other end and one end of the arm portion with a rotation mechanism, a detection rod that is engaged with the other end of the joint portion, and the detection rod A crack opening displacement measuring instrument for measuring an opening width of the compact tension test piece is provided.

According to the present invention, the tip portion constituting the crack opening displacement measuring instrument is screwed to the compact tension test piece so that it does not easily come off during the test, and the arm portion is connected to one end of the joint portion by the rotation mechanism. Therefore, even if the opening portion of the compact tension test piece becomes large, the joint portion does not tilt and the displacement of the joint portion becomes small. For this reason, the detection rod engaged with the other end of the joint portion is also less displaced from the vertical position, and the detection rod is tilted obliquely so that it is less likely that an accurate value cannot be detected by the detection portion.

According to the present invention, the cross-sectional shape of the tip portion screwed to the compact tension test piece is a shape capable of coming into contact with the bottom surface of the groove cross section formed in the compact tension test piece, and the compact tension test piece includes The crack opening displacement measuring instrument is characterized in that the formed screw groove for screwing is formed deeper than the bottom surface of the cross section of the groove.

According to such a feature, the tip portion screwed to the compact tension test piece constituting the crack opening displacement measuring instrument has a shape capable of contacting not only the side surface of the groove section of the compact tension test piece but also the bottom surface. In addition, the screw groove formed on the compact tension test piece is deeper than the bottom of the groove cross section, so that the tip and the compact tension test piece are joined together without looseness, and the screw loosens during the test. The phenomenon of dripping is reduced.

In the present invention, the bottom shape of the cross section of the groove formed in the compact tension test piece is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction, and an angle of approximately 90 degrees is formed at the center of the groove. It is the crack opening displacement measuring instrument characterized by having carried out.

According to such a feature, the bottom shape of the cross section of the groove is an object up and down, and is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction, and an angle of approximately 90 degrees is formed at the center of the groove. Therefore, groove processing is easy.

The present invention is the crack opening displacement measuring instrument, wherein the rotation mechanism further comprises a bearing mechanism.

According to such a feature, since the rotation mechanism is a bearing mechanism, the stress from the arm portion is dispersed by the bearing, so that the rotation mechanism is not deformed and durability is improved. In addition, the backlash between the arm portion and the joint portion is eliminated in terms of accuracy, and the measurement accuracy is improved.

Since the crack opening displacement measuring instrument of the present invention is screwed to the compact tension test piece, the tip is not easily detached during the test, and the arm is connected to one end of the joint by a rotating mechanism. Even if the opening of the compact tension test piece is large, the displacement of the joint portion is small. For this reason, the detection rod engaged with the other end of the joint portion also has a small deviation from the vertical position, and the detection rod tilts obliquely, and the detection portion cannot detect the accurate value of the displacement of the test piece opening. Less.

FIG. 1 is a drawing showing an example of a crack opening displacement measuring instrument of the present invention and a high-pressure gas atmosphere fatigue tester that houses the crack opening displacement measuring instrument. FIG. 2 is a drawing showing an example of a compact tension test piece of the present invention. (A) Side view (b) Front view (c) Enlarged view of part A FIG. 3 is a three-side view of the tip showing an example of the crack opening displacement measuring instrument of the present invention. (A) Plan view (b) Front view (c) Side view FIG. 4 is a cross-sectional view showing the relationship between the tip, arm, screw, and compact tension test piece. (A) Vertical sectional view at the position of the insertion portion of the distal end portion (b) Vertical sectional view at the position of the through hole of the distal end portion FIG. 5 is a trihedral view showing an example of the upper part of the crack opening displacement measuring instrument of the present invention. (A) Plan view (b) Front view (c) Side view FIG. 6 is an explanatory view showing an example of the lower part of the crack opening displacement measuring instrument of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.

FIG. 1 is a view showing an example of a crack opening displacement measuring instrument 2 according to the present invention and a high-pressure gas atmosphere fatigue tester 1 for housing it.

The high-pressure gas atmosphere fatigue tester 1 fills a space sealed with a pressure vessel 10 and a pressure vessel lid 11 with a high-pressure gas from a gas supply pipe 19 and performs a fatigue test on the compact tension test piece 3 and the like. Hydrogen gas or other corrosive gas is introduced as high-pressure gas. Since hydrogen gas deteriorates metal materials and the like, hydrogen is included in the corrosive gas in a broad sense. In addition, high pressure means the pressure of 0.1 MPa or more normally.

Although not shown, the pressure vessel 10 and the pressure vessel lid 11 are fastened with bolts, and the pressure vessel lid 11 and the pull rod 16 are interposed between the pressure vessel 10 and the pressure vessel lid 11 so that the high pressure gas does not leak. O-rings 17 and 18 are attached between the two, respectively, to ensure sealing performance.

In the space sealed by the pressure vessel 10 and the pressure vessel lid 11, a support member 12 that supports one end of the compact tension test piece 3 and the other end are supported, and tensile or compressive stress is applied to the compact tension test piece 3. A pull rod 16 and an actuator (not shown) for controlling the movement of the pull rod 16 are provided. The tensile or compressive stress is applied to the compact tension test piece 3 with a sine wave, a triangular wave or the like and a period of about 0.001 Hz to 10 Hz.

The support member 12 is provided with a load cell 13 for measuring a load and an upper chuck 14 fastened with a hole and a pin in the upper part of the compact tension test piece 3. The pull rod 16 is provided with a lower chuck 15 that is fastened with a pin and a hole in the lower portion of the compact tension test piece 3.

A crack opening displacement measuring instrument 2 is attached to the compact tension test piece 3 so that the displacement of the crack opening of the compact tension test piece 3 under test can be measured. In the crack opening displacement measuring instrument 2, a tip portion 20 (see FIG. 3) and an arm portion 22 are screwed to a compact tension test piece 3 with screws 21. The other end of the arm portion 22 is joined to one end of the joint portion 23, and the other end of the joint portion 23 engages the detection rod 24. The detection unit 25 includes a differential transformer that detects the displacement of the tip portion of the detection rod 24. The displacement from both arm portions 22 is detected by the respective detection portions 25, and the displacement of the crack opening of the compact tension test piece 3 can be obtained from the difference.

2A shows a side view of the compact tension test piece 3 of the present invention, and FIG. 2B shows a front view of the compact tension test piece 3 of the present invention. The compact tension test piece 3 of the present invention conforms to ASTM E647-91, and a crack opening 30 is formed at the center of the test piece, and the tip 20 of the crack opening displacement measuring instrument 2 is inserted above and below the crack opening 30, respectively. Grooves 31 and 32 are formed. In each of the grooves 31 and 32, two screw holes 36 for screwing the tip portion 20 and the arm portion 22 to the compact tension test piece 3 with the screw 21 are formed.

FIG. 2 (c) shows an enlarged view of part A of FIG. 2 (a). The bottom surface of the groove cross section is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction. It is characterized in that it is formed at an angle of approximately 90 degrees and that the screw groove 35 for screwing is formed deeper than the bottom surface of the groove cross section.

As described above, the bottom surfaces of the grooves 31 and 32 are formed at a predetermined angle. The tip 20 of the crack opening displacement measuring instrument 2 is also formed at the same angle. This is because the contact with the bottom surface of 32 increases the restraint of the tip 20 and is coupled without rattling, and the phenomenon that the screw loosens and comes off during the test is reduced. In addition, as the predetermined angle, since the angle of the vertical object is easy to form the bottom surface of the groove section when viewed from the horizontal direction, the angle is approximately 30 degrees to approximately 75 degrees vertically when viewed from the horizontal direction. It is desirable to form at an angle of approximately 60 degrees to approximately 150 degrees, and it is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction, and is formed at an angle of approximately 90 degrees at the center of the groove. preferable.

3A, 3B, and 3C are respectively a plan view, a front view, and a side view of the distal end portion 20 of the crack opening displacement measuring instrument 2 of the present invention. In this embodiment, the distal end portion 20 includes a main body portion 210, an insertion portion 220 integrated with the main body portion 210, and a through hole 230 of the screw 21. The shape of the insertion portion 220 is formed so as to fit into the grooves 31 and 32 of the compact tension test piece 3, and the angle of the tip portion narrowed down in a wedge shape is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction. And formed so as to intersect at an angle of approximately 90 degrees at the center. In addition, the front-end | tip part is deleted so that it may not contact | abut in the center part of the bottom face of the grooves 31 and 32. FIG.

4 (a) and 4 (b), in order to show the relationship between the tip portion 20, the arm portion 22, the screw 21 and the compact tension test piece 3, the vertical direction at the position of the insertion portion 220 of the tip portion 20 is shown. A sectional view and a sectional view in the vertical direction at the position of the through hole 230 of the screw 21 are shown. The distal end portion 20 is inserted into the groove 32 of the compact tension test piece 3, but the length of the insertion portion 220 is larger than the depth of the groove 32, so that the main body portion 210 of the distal end portion 20 is connected to the compact tension test piece 3. Floating without contact. When the distal end portion 20 and the arm portion 22 are overlapped and screwed to the screw groove 35 of the compact tension test piece 3 with the screw 21, the insertion portion 220 of the distal end portion 20 becomes the bottom surface of the groove 32 formed in the compact tension test piece 3. , A high stress per unit area is generated in this portion, rattling is reduced, and the screw 21 is less likely to loosen. In addition, if the surface of the head of the screw 21 in contact with the arm portion 22 is processed to make the surface uneven, such as knurling, the rattling is further reduced. As is clear from FIGS. 4A and 4B, the screw groove 35 of the screwing formed in the compact tension test piece 3 is formed deeper than the bottom surface of the cross section of the groove 32.

5 (a) is a plan view of the upper part of the crack opening displacement measuring instrument 2 of the present invention, FIG. 5 (b) is a front view of the upper part of the crack opening displacement measuring instrument 2 of the present invention, and FIG. It is a side view of the upper part of the crack opening displacement measuring instrument 2 of this invention.

One end of the arm portion 22 is provided with a screw hole 2220 that overlaps the through hole 230 of the distal end portion 20. The tip portion 20 and the arm portion 22 are screwed to the screw groove 35 of the compact tension test piece 3 using the screw 21. In the present embodiment, the tip 20 and the arm 22 are separated, but the tip 20 and the arm 22 may be integrally formed. In that case, the arm portion on which the tip portion is formed is screwed to the compact tension test piece 3 using the screw 21. Such an integral configuration eliminates rattling or displacement between the tip 20 and the arm 22 and further improves measurement accuracy.

The other end of the arm part 22 is connected to the upper part of the joint part 23 so as to be rotatable by a pin 2210. Furthermore, in this embodiment, the rotating mechanism of the bearing mechanism 2310 using, for example, a ball bearing, is provided at the upper portion of the joint portion 23. Thereby, rattling between the pin 2210 and the bearing mechanism 2310 is eliminated, and measurement accuracy and durability are improved.

Since the arm portion 22 with which the tip portion 20 engages is thus connected to one end of the joint portion 23 by the rotation mechanism, even if the crack opening 30 of the compact tension test piece 3 becomes large, the joint portion 23 is displaced. Becomes smaller. In other words, when the arm portion 22 with which the tip portion 20 is engaged is directly connected to one end of the joint portion 23, the tip portion 20 screwed into the groove 31 is removed from the horizontal when the crack opening 30 of the compact tension test piece 3 becomes large. The tip portion 20 screwed into the groove 32 to have a positive angle has a negative angle from the horizontal, and as a result, the arm portion 22 and the joint portion 23 are inclined.

On the other hand, when the arm part 22 is connected to one end of the joint part 23 by the rotation mechanism, the joint part 23 does not tilt even if the arm part 22 is tilted, so that the shift of the joint part 23 is reduced. For this reason, the detection rod 24 engaged with the other end of the joint portion 23 is greatly displaced from the vertical position or tilted obliquely, so that the detection unit 25 cannot detect an accurate value.

In the lower part of the joint portion 23, the center portion is perforated and the detection rod 24 is inserted, and the detection rod 24 is engaged with the joint portion 23 by a screw 2320. In this embodiment, the detection rod 24 is engaged from the outside with the screw 2320, but regardless of this, the detection rod 24 may be engaged so as not to come off from the lower portion of the joint portion 23.

FIG. 6 is an explanatory view of the lower part of the crack opening displacement measuring instrument 2 of the present invention. In the present embodiment, the detection unit 25 that detects the displacement of the tip of the detection rod 24 uses a differential transformer system. A magnetic material SUS410L core 2410 is silver-plated to the tip of the detection rod 24. The detection rod 24 is inserted into a tube attached to the pressure vessel lid 11 with one end sealed, and a detection coil 2510 wound with a primary coil and a secondary coil is attached to the outside of the tube. The primary coil is excited with an alternating current to detect the induced voltage induced in the secondary coil from the core 2410 to detect the displacement of the tip of the detection rod 24.

Since the crack opening displacement measuring instrument 2 of the present invention is placed in a corrosive gas, the crack opening displacement measuring instrument 2 including the screw 21 is made of an austenitic SUS304 or SUS316 or ferrite based SUS410L or SUS430 corrosion resistant material. . However, since the core 2410 portion must be made of a magnetic material, the upper detection rod 24 needs to be a non-magnetic austenitic SUS304 or SUS316 system.

Due to the above-described configuration, the crack opening displacement measuring instrument 2 according to the present invention has the distal end portion 20 screwed to the compact tension test piece 3 so that it is difficult to come off during a fatigue test, and the arm portion 22 has a rotating mechanism. Since it is connected to one end of the joint part 23, even if the crack opening 30 of the compact tension test piece 3 becomes large, the displacement of the joint part becomes small. For this reason, the detection rod 24 engaged with the other end of the joint portion 23 is also less displaced from the vertical position, and prevents the detection rod 24 from tilting and detecting the accurate value at the detection portion 25. be able to.

DESCRIPTION OF SYMBOLS 1 High pressure gas atmosphere fatigue test machine 2 Crack opening displacement measuring instrument 3 Compact tension test piece 21 Screw 20 Tip part 22 Arm part 23 Joint part 24 Detection rod 25 Detection part

Claims (4)

In the crack opening displacement measuring instrument that measures the opening width of the compact tension test piece used for the fatigue test in high-pressure gas,
A tip that is screwed to the compact tension specimen;
An arm portion engaged at one end with the tip portion;
A joint part connecting the other end and one end of the arm part by a rotation mechanism, and a detection rod engaged with the other end of the joint part;
A crack opening displacement measuring instrument for measuring an opening width of the compact tension test piece, comprising: a detecting portion for detecting a displacement of a tip portion of the detecting rod. The cross-sectional shape of the tip portion screwed to the compact tension test piece is a shape capable of contacting the bottom surface of the groove cross section formed in the compact tension test piece,
2. The crack opening displacement measuring instrument according to claim 1, wherein a screw groove formed on the compact tension test piece is deeper than a bottom surface of the groove cross section. The bottom surface shape of the groove cross section formed on the compact tension test piece is formed at an angle of approximately 45 degrees up and down when viewed from the horizontal direction, and an angle of approximately 90 degrees is formed at the groove center. The crack opening displacement measuring instrument according to claim 2, wherein the instrument is a crack opening displacement measuring instrument. The crack opening displacement measuring instrument according to any one of claims 1 to 3, wherein the rotation mechanism includes a bearing mechanism.

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