JP7750039B2 - Bending and torsion testing equipment - Google Patents

Description

The present invention relates to a bending/torsion testing device that applies both bending and torsional moments to a test specimen using a single driving unit.

Piping in power plants and other facilities expands thermally when heated by the fluid inside, and is also subjected to internal pressure from the fluid. Such pipes are subjected to bending and torsional moments due to thermal expansion and internal pressure. As the temperature and internal pressure of the pipes change, the bending and torsional moments also change, causing the pipes to fatigue. Therefore, it is necessary to predict the fatigue life of the pipes due to bending and torsional moments by conducting tests using mechanical testing equipment to apply bending and torsional moments to a pipe specimen. One example of such testing equipment is disclosed in Patent Document 1. The testing equipment disclosed in Patent Document 1 includes a jig that fixes one end of the specimen, a torsional load application device that applies a torsional load around the axis of the specimen to the other end of the specimen, and a bending load application device that applies a bending load perpendicular to the axis of the specimen to the center of the specimen.

JP 2013-156021 A

The testing device described in Patent Document 1 is expensive because it requires two actuators to apply both bending and torsional moments to the test specimen.

The present invention was developed in consideration of these issues, and its main purpose is to provide a bending/torsion testing device that can apply both bending and torsional moments to a test specimen using a single driving unit.

To solve the above problems, a first lever is provided, which extends from a first base end to a first tip, is rotatable around a first central axis extending from the first base end to the first tip, is swingable around a first swing axis at the first base end that is perpendicular to the first central axis, and one end of a columnar or hollow columnar test body is fixed to the first tip so that the central axis of the test body is perpendicular to the first central axis; and a second lever is provided which extends from a second base end to a second tip in a direction parallel to and opposite to the direction in which the first lever extends from the first base end to the first tip, is rotatable around a second central axis extending from the second base end to the second tip, and the second lever is fixed to the second tip. A bending/torsion testing device is provided, which includes: a second lever that is swingable around a second oscillation axis perpendicular to the second central axis at its base end, and the other end of the test body is fixed to the second tip so that the central axis of the test body is perpendicular to the second central axis; a pair of jigs that are spaced apart in the direction of the central axis of the test body and support the radial load of the test body so that the test body can rotate around the central axis of the test body; and a drive unit that displaces the pair of jigs in a direction perpendicular to the central axis of the test body so as to swing the first lever and the second lever around the first oscillation axis and the second oscillation axis, respectively.

According to the above, when the drive unit displaces the pair of jigs in a direction perpendicular to the central axis of the test piece, the test piece bends and a bending moment is generated in the test piece. Because the first lever is rotatable about its first central axis and the second lever is rotatable about its second central axis, the test piece bends significantly.
Furthermore, when the drive unit displaces the pair of jigs in a direction perpendicular to the central axis of the test specimen, the first lever swings around a first swing axis at its first base end, and the second lever swings around a second swing axis at its second base end. Because the direction in which the first lever extends from its first base end to its first tip is opposite to the direction in which the second lever extends from its second base end to its second tip, the direction in which the first lever swings around the first swing axis is opposite to the direction in which the second lever swings around the second swing axis. As a result, the test specimen twists, and a torsional moment is generated in the test specimen.
Therefore, both bending and torsional moments can be applied to the test specimen by a single driving unit.

Both bending and torsional moments can be applied to the test specimen using a single drive unit.

FIG. 1 is a front view of a bending and twisting test device. FIG. 1 is a side view of a bending and torsion test device. FIG. 2 is a perspective view of the main part of a bending and twisting test device. FIG. 2 is a perspective view of the main part of a bending and twisting test device. FIG. 2 is a front view of the main part of the bending and twisting test device. FIG. 2 is a front view of the main part of the bending and twisting test device. FIG. 2 is a front view of the main part of the bending and twisting test device. FIG. 2 is a side view of the main part of the bending and twisting test device. 10 is a graph showing a waveform of a load per cycle. 10 is a graph showing experimental results of the relationship between the number of cycles and the displacement. 10 is a graph showing experimental results of the relationship between the number of cycles and the deflection angle. 10 is a graph showing experimental results of the relationship between the number of cycles and the torsion angle. 1 is a photograph showing the state of cracks that occurred in a test specimen. 10 is a graph showing experimental results of the relationship between deflection angle and equivalent bending moment. 10 is a graph showing experimental results of the relationship between the torsion angle and the equivalent bending moment. 1 is a graph showing experimental results of the relationship between the number of cycles to fatigue failure and the equivalent bending moment.

Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are subject to various limitations that are technically preferable for implementing the present invention, but the scope of the present invention is not limited to the following embodiments and illustrated examples.

1. Bending and Torsion Test Apparatus FIG. 1 is a front view of the bending and torsion test apparatus 1. FIG. 2 is a side view of the bending and torsion test apparatus 1. FIGS. 3 and 4 are perspective views of the main parts of the bending and torsion test apparatus 1. FIGS. 5 to 7 are front views of the main parts of the bending and torsion test apparatus 1. FIG. 8 is a side view of the main parts of the bending and torsion test apparatus 1. In each figure, the X-axis, Y-axis, and Z-axis, which are mutually orthogonal, are shown as auxiliary lines indicating directions. The X-axis and Y-axis are horizontal, and the Z-axis is vertical. Since the X-axis extends left and right, the Y-axis extends front and back, and the Z-axis extends up and down, the X-axis, Y-axis, and Z-axis directions are also referred to as the left-right direction, the front-back direction, and the up-down direction, respectively. Here, in FIG. 5, the test specimen 2 set in the bending and torsion test apparatus 1 is not deformed, in FIG. 6, the test specimen 2 is bent in a downward convex shape, and in FIG. 7, the test specimen 2 is bent in an upward convex shape. In the initial state where the test specimen 2 set in the bending/torsion test device 1 is not deformed, the central axis of the test specimen 2 is parallel to the X-axis.

The bending/torsion test device 1 applies two-point loads to a cylindrical or hollow cylindrical test specimen 2, generating a bending moment and a torsion moment in the test specimen 2, and measures the deflection angle θ and torsion angle φ generated in the test specimen 2. The bending/torsion test device 1 can be used not only for static bending/torsion tests, but also for creep-fatigue tests, fatigue tests, and creep tests.

Here, the deflection angle θ refers to the angle between the central axis of the test specimen 2 in its initial state at the end of the test specimen 2 and the central axis of the test specimen 2 after deformation. The torsion angle φ refers to the angular displacement from the initial state around the central axis of the test specimen 2 at the end of the test specimen 2. The two-point load refers to a bending load applied to the test specimen 2 from two points. The test specimen 2 may be made of metal or resin. If the test specimen 2 is hollow and cylindrical, two metal round tubes butt-welded together may be used as the test specimen 2.

The bending/torsion test device 1 includes a support base 10, a first linear guide 12, a second linear guide 13, a first lever mechanism 20, a second lever mechanism 30, a load device 40, a load cell 70, a deflection angle sensor 81, a torsion angle sensor 82, and a heating furnace 90. Note that when the bending/torsion test device 1 is used for static bending/torsion testing or fatigue testing, the heating furnace 90 does not need to be provided. In Figure 4, the heating furnace 90 is omitted so that the entire test specimen 2 and first lever mechanism 20 can be seen.

(1) Support Base The support base 10 supports the weight of the first linear guide 12, the second linear guide 13, the first lever mechanism 20, the second lever mechanism 30, the load device 40, the load cell 70, the deflection angle sensor 81, the torsion angle sensor 82, and the heating furnace 90. The support base 10 is installed on an experimental table (not shown) via a plurality of adjusters for adjusting the height in the Z-axis direction. By adjusting the height of these adjusters, the upper surface of the support base 10 is adjusted to be horizontal.

(2) Linear Guide The first linear guide 12 is attached to the support base 10. The first linear guide 12 guides the first lever mechanism 20 (described later) in the left-right direction. The direction in which the first linear guide 12 guides the first lever mechanism 20 is parallel to the central axis of the test specimen 2 in its initial state set in the bending/torsion test device 1.

The second linear guide 13 is attached to the support base 10 at a position rearward and to the right of the first linear guide 12. The second linear guide 13 guides the second lever mechanism 30 (described below) in the left-right direction. The direction in which the second linear guide 13 guides the second lever mechanism 30 is parallel to the central axis of the test specimen 2.

(3) First Lever Mechanism The first lever mechanism 20 is provided on the support base 10 via a first linear guide 12. The first lever mechanism 20 holds one end of the test body 2 so that the one end can be swung up and down around a first pivot 22 (described later) as a fulcrum, and so that the one end of the test body 2 can tilt around the central axis of a first lever 23 (described later). The first lever mechanism 20 has a first pole 21, a first pivot 22, a first lever 23, a first chuck 24, a first support bar 25, and a first counterweight 26.

The first pole 21 is mounted upright on the support base 10 via the first linear guide 12. The first pole 21 is guided left and right relative to the support base 10 by the first linear guide 12. As the first pole 21 is guided by the first linear guide 12, the first pivot 22, first lever 23, first chuck 24, first support bar 25, and first counterweight 26 are also guided left and right.

The first pivot 22 is attached to the upper end of the first pole 21 via a bearing or the like so that its central axis is parallel to the left-right direction. The axial and radial loads of the first pivot 22 are supported by the bearing, allowing the first pivot 22 to rotate around its central axis.

The first lever 23 has a central axis extending from the base end of the first lever 23 on the first pivot 22 side to the tip of the first lever 23. The base end of the first lever 23 corresponds to the "first base end," the tip of the first lever 23 corresponds to the "first tip," and the central axis of the first lever 23 corresponds to the "first central axis."

The base end of the first lever 23 is attached to the first pivot 22 via a bearing or the like so that the central axis of the first lever 23 is perpendicular to the central axis of the first pivot 22. The first lever 23 extends from the first pivot 22 in a direction perpendicular to the central axis of the first pivot 22. Specifically, the first lever 23 extends rearward from the first pivot 22. The axial and radial loads of the first lever 23 are supported by the bearing, and the first lever 23 is rotatable around its central axis. Here, because the first pivot 22 is rotatable around its central axis as described above, the first lever 23 is arranged to be able to swing up and down around the central axis of the first pivot 22, with the central axis of the first pivot 22 as a fulcrum. The central axis of the first pivot 22 corresponds to the "first swing axis."

The first chuck 24 is attached to the tip of the first lever 23. The first chuck 24 secures one end of the test specimen 2 to the tip of the first lever 23 so that the central axis of the test specimen 2 is perpendicular to the central axis of the first lever 23.

The base end of the first support bar 25 is attached to the base end of the first lever 23 or the first pivot 22 so that the central axis of the first support bar 25 is coaxial with the central axis of the first lever 23. The first support bar 25 extends from the first pivot 22 in a direction perpendicular to the central axis of the first pivot 22. Specifically, the first support bar 25 extends forward from the first pivot 22.

The first counterweight 26 is attached to the first support bar 25. The position of the first counterweight 26 is adjustable along the first support bar 25.

(4) Second Lever Mechanism The second lever mechanism 30 is provided on the support base 10 via the second linear guide 13. The second lever mechanism 30 is configured to be symmetrical to the first lever mechanism 20 with respect to the vertical axis. The second lever mechanism 30 holds the other end of the test specimen 2 so that the other end of the test specimen 2 can be swung up and down around a second pivot 32 (described later) as a fulcrum, and so that the other end of the test specimen 2 can tilt around the central axis of a second lever 33 (described later). The second lever mechanism 30 has a second pole 31, a second pivot 32, a second lever 33, a second chuck 34, a second support bar 35, and a second counterweight 36.

The second pole 31 is positioned rearward and to the right of the first pole 21, and is mounted upright on the support base 10 via the second linear guide 13. The second pole 31 is guided left and right relative to the support base 10 by the second linear guide 13. As the second linear guide 13 guides the second pole 31, the second pivot 32, second lever 33, second chuck 34, second support bar 35, and second counterweight 36 (described below) are also guided left and right.

The second pivot 32 is attached to the upper end of the second pole 31 via a bearing or the like so that its central axis is parallel to the left-right direction. The axial and radial loads of the second pivot 32 are supported by the bearing, allowing the second pivot 32 to rotate around its central axis.

The second lever 33 has a central axis extending from the base end of the second lever 33 on the second pivot 32 side to the tip of the second lever 33. The base end of the second lever 33 corresponds to the "second base end," the tip of the second lever 33 corresponds to the "second tip," and the central axis of the second lever 33 corresponds to the "second central axis."

The base end of the second lever 33 is attached to the second pivot 32 via a bearing or the like so that the central axis of the second lever 33 is perpendicular to the central axis of the second pivot 32. The second lever 33 extends from the second pivot 32 in a direction perpendicular to the central axis of the second pivot 32. Specifically, the second lever 33 extends forward from the second pivot 32. The axial and radial loads of the second lever 33 are supported by the bearing, and the second lever 33 is rotatable around its central axis. Here, in the initial state in which the test specimen 2 is not deformed, the direction in which the second lever 33 extends from its base end to its tip is parallel to and opposite to the direction in which the first lever 23 extends from its base end to its tip.

As described above, the second pivot 32 is rotatable around its central axis, and the second lever 33 is arranged to be able to swing up and down around the central axis of the second pivot 32, with the central axis of the second pivot 32 as a fulcrum. The central axis of the second pivot 32 corresponds to the "second swing axis."

The second chuck 34 is attached to the tip of the second lever 33. The second chuck 34 secures the other end of the test specimen 2 to the tip of the second lever 33 so that the central axis of the test specimen 2 is perpendicular to the central axis of the second lever 33.

The base end of the second support bar 35 is attached to the base end of the second lever 33 or the second pivot 32 so that the central axis of the second support bar 35 is coaxial with the central axis of the second lever 33. The second support bar 35 extends from the second pivot 32 in a direction perpendicular to the central axis of the second pivot 32. Specifically, the second support bar 35 extends rearward.

The second counterweight 36 is attached to the second support bar 35. The position of the second counterweight 36 is adjustable along the second support bar 35.

Both ends of the test specimen 2 are fixed to the tips of the levers 23 and 33 by chucks 24 and 34, respectively, so that the assembly of the test specimen 2 and the levers 23 and 33 forms a crank shape. In the initial state when the test specimen 2 is not deformed, the weight of the counterweights 26 and 36 balances the levers 23 and 33 and the test specimen 2 horizontally.

(5) Loading Device and Load Cell The loading device 40 applies two-point loads to the test specimen 2.
The load cell 70 measures the sum of the two-point loads applied by the loading device 40. The load cell 70 outputs an output signal representing the measurement value of the sum of the two-point loads to a data logger or computer connected to the load cell 70. The data logger or computer inputs the output signal from the load cell 70 and stores the measurement value of the sum of the two-point loads measured by the load cell 70 in chronological order.

The load device 40 includes a base 41, a drive unit 42, a head 43, third linear guides 44 and 45, tilting mechanisms 46 and 47, and jigs 50 and 60.

The stand 41 is gate-shaped and consists of an upper part and a column. The stand 41 is installed on the support base 10. Lever mechanisms 20 and 30 are located on the left and right sides of the stand 41, respectively, and the test specimen 2 is passed left and right through the area surrounded by the stand 41.

The drive unit 42 is attached to the top of the base 41. The drive unit 42 is an actuator, more specifically, a hydraulic servo cylinder. The drive unit 42 is capable of both displacement control and load control. The drive unit 42 may also be an air cylinder or an electromagnetic solenoid.

The head 43 is connected to the drive unit 42 via the load cell 70. The head 43 is driven vertically by the drive unit 42. As the head 43 moves up and down, the third linear guides 44, 45, tilting mechanisms 46, 47, and jigs 50, 60 (described below) also move up and down. The load applied to the head 43 from the drive unit 42 is measured by the load cell 70, and this load is equal to the sum of the two-point loads.

The third linear guides 44, 45 are attached to the underside of the head 43, lined up on the left and right. The third linear guides 44, 45 guide the tilting mechanisms 46, 47 (described below) in the left and right directions, respectively, and the left and right movable ranges of the tilting mechanisms 46, 47 are set by the third linear guides 44, 45. The third linear guides 44, 45 are provided with centering springs, which position the tilting mechanisms 46, 47 in the center of their left and right movable ranges. When the tilting mechanisms 46, 47 are positioned, the midpoint between the jigs 50, 60 (described below) is located directly below the drive unit 42 and load cell 70.

The tilting mechanisms 46 and 47 are attached to the head 43 via third linear guides 44 and 45, respectively. Each of the tilting mechanisms 46 and 47 consists of a single-axis pivot joint. The tilting mechanisms 46 and 47 support the jigs 50 and 60 (described below) so that they can tilt about an axis perpendicular to both the displacement direction of the head 43 and the central axis of the test specimen 2. In other words, the tilting mechanisms 46 and 47 support the jigs 50 and 60 so that they can tilt about an axis extending forward and backward.

The jigs 50 and 60 are attached to tilting mechanisms 46 and 47, respectively. The jigs 50 and 60 support the radial load of the test specimen 2 so that the test specimen 2 can rotate around its central axis. Because the test specimen 2 can rotate around its central axis relative to the jigs 50 and 60, the jigs 50 and 60 do not provide resistance to torsion of the test specimen 2.
The jigs 50 and 60 are spaced apart from each other in the direction of the central axis of the test piece 2. The distance from one end of the test piece 2 to the jig 50 is equal to the distance from the other end of the test piece 2 to the jig 60. The position of the midpoint between the jigs 50 and 60 is aligned with the position of the midpoint between both ends of the test piece 2.

The jigs 50 and 60 will now be described in detail.
The jig 50 includes a first block 51 , a pair of first rollers 52 , a second block 53 , a pair of second rollers 54 , and a pair of screw-type fasteners 55 .

The first block 51 is connected to the tilting mechanism 46. The first block 51 is tiltable left and right by the tilting mechanism 46.

A pair of first rollers 52 are attached below the first block 51, lined up front and back. When the first block 51 is not tilted, the rotation axes of the first rollers 52 are parallel to the left-right direction. These first rollers 52 are applied to the outer surface of the test specimen 2 from above.

The first block 52 and the second block 53 are assembled together with the test specimen 2 placed between them. A threaded fastener 55 secures the second block 53 to the first block 51.

A pair of second rollers 54 are attached to the top of the second block 53, lined up front and back. When the first block 51 and second block 53 are not tilted, the rotation axis of the second rollers 54 is parallel to the left-right direction. These second rollers 54 are placed against the outer surface of the test specimen 2 from below, and the test specimen 2 is sandwiched between the first roller 52 and the second roller 54.

When the screw fastener 55 tightens the second block 53 to the first block 51, a clamping force is generated between the first roller 52 and the second roller 54, clamping the test specimen 2 between them. This clamping force restricts the relative movement of the test specimen 2 in the direction of its central axis relative to the jig 50.

Since jig 60 is configured in the same way as jig 50, a detailed description of jig 60 will be omitted.

When the drive unit 42 displaces the head 43, third linear guides 44, 45, tilting mechanisms 46, 47, and jigs 50, 60 downward, a downward load is applied from the jigs 50, 60 to the test specimen 2. As shown in Figure 6, the test specimen 2 bends downward in a convex shape, and the levers 23, 33 rotate around their respective central axes. As the levers 23, 33 rotate, the chucks 24, 34 tilt in an inverted V shape, and the tilt angle of the chucks 24, 34 is equal to the deflection angle θ.

When the test specimen 2 bends convexly downward, the jigs 50, 60 are tilted by the tilting mechanisms 46, 47 so that the lower portions of the jigs 50, 60 move away from each other. At this time, the levers 23, 33 are swung down so as to rotate in opposite directions around the pivots 22, 32, respectively, causing the test specimen 2 to twist. The swing angle of the levers 23, 33 is equal to the torsional angle φ of the test specimen 2.

Conversely, when the drive unit 42 displaces the head 43, third linear guides 44, 45, tilting mechanisms 46, 47, and jigs 50, 60 upward, and an upward load is applied from the jigs 50, 60 to the test specimen 2, the test specimen 2 bends upward in a convex shape, as shown in Figure 7, and the levers 23, 33 rotate around their respective central axes, causing the chucks 24, 34 to tilt in a V-shape. Due to the bending of the test specimen 2, the tilting mechanisms 46, 47 tilt the jigs 50, 60 so that their lower portions approach each other. At this time, the levers 23, 33 are swung up to rotate in opposite directions around the pivots 22, 32, respectively, causing the test specimen 2 to twist.

As the test specimen 2 bends, the distance between its ends narrows, causing the lever mechanisms 20 and 30 to move closer together, guided by the linear guides 12 and 13, respectively. When the test specimen 2 is no longer bent, the lever mechanisms 20 and 30 move away from each other.

(6) Deflection Angle Sensor and Torsion Angle Sensor The deflection angle sensor 81 and the torsion angle sensor 82 are attached to the tip of the first lever 23 via the first chuck 24. The deflection angle sensor 81 and the torsion angle sensor 82 may be attached to the second chuck 34. The deflection angle sensor 81 and the torsion angle sensor 82 are formed by tilt sensors.

The deflection angle sensor 81 measures the rotation angle of the first lever 23 around its central axis, i.e., the deflection angle θ of the test piece 2 and the tilt angle of the first chuck 24. The deflection angle sensor 81 outputs an output signal representing the measurement value of the deflection angle θ to a data logger or computer connected to it. The data logger or computer inputs the output signal of the deflection angle sensor 81 and stores the measurement values of the deflection angle θ measured by the deflection angle sensor 81 in chronological order.

The torsion angle sensor 82 measures the swing angle of the first lever 23 around the central axis of the first pivot 22, centered on the first pivot 22, and the torsion angle φ of the test specimen 2. The torsion angle sensor 82 outputs an output signal representing the measured value of the torsion angle φ to a data logger or computer connected to it. The data logger or computer inputs the output signal of the torsion angle sensor 82 and stores the measured values of the torsion angle φ measured by the torsion angle sensor 82 in chronological order.

(7) Heating Furnace The heating furnace 90 is attached to the head 43 so as to hang down from the head 43, and rises and falls integrally with the head 43. The heating furnace 90 may be detachable from the head 43. The heating furnace 90 is tubular and has an internal space. The left and right end faces of the heating furnace 90 are open, and the test specimen 2 is passed through these openings, with the center of the test specimen 2 housed in the heating furnace 90. When the test specimen 2 is passed through the opening of the heating furnace 90, the gap between the outer surface of the test specimen 2 and the edge of the opening is sealed with insulating material. The heating furnace 90 is an electric furnace, and an electric heater and a temperature sensor are provided in the heating furnace 90. The electric heater heats the internal space of the heating furnace 90 and the test specimen 2. The temperature sensor measures the temperature inside the heating furnace 90. The electric heater and temperature sensor are connected to a temperature control circuit outside the heating furnace 90. The temperature control circuit feedback controls the electric heater in accordance with the temperature measured by the temperature sensor so as to maintain the temperature inside the heating furnace 90 constant.

The heating furnace 90 is composed of an upper half and a lower half so that it can be separated into upper and lower halves. A semicircular groove is formed on the underside of the upper half, and a semicircular groove is formed on the upper surface of the lower half. The upper and lower halves are combined to form the heating furnace 90. The upper half is attached to the head 43.

2. Bending moment, torsional moment, and equivalent bending moment When the test specimen 2 is a hollow cylindrical body, i.e., a round tube, when two-point loads are applied to the test specimen 2 from the jigs 50 and 60, the bending moment, torsional moment, and equivalent bending moment generated in the test specimen 2 are as follows:

Here, M [Nm] is the bending moment, T [Nm] is the torsional moment, M _e [N] is the equivalent bending moment, P [N] is the two-point load applied to the test piece 2 from the jigs 50 and 60, L [m] is the length of the test piece 2, and L ₁ [m] is the distance from the end of the test piece 2 to the jig 50.

3. Setting the Test Specimen The method by which an operator sets the test specimen 2 in the bending/torsion test device 1 will be described.

First, loosen the screw fasteners 55 on the jig 50 and remove the second block 53 from the first block 51. Do the same for the jig 60. Remove the lower half of the heating furnace 90 from the upper half.

Next, one end of the test specimen 2 is fixed to the first chuck 24 of the lever mechanism 20. By adjusting the position of the first counterweight 26 of the lever mechanism 20, the weight of the first counterweight 26 and the weight of the test specimen 2 balance the first lever 23 of the lever mechanism 20 horizontally.

Next, the other end of the test specimen 2 is fixed to the second chuck 34 of the lever mechanism 30. By adjusting the position of the second counterweight 36 of the lever mechanism 30, the weight of the second counterweight 36 and the weight of the test specimen 2 balance the second lever 33 of the lever mechanism 30 horizontally. Therefore, the weight of the counterweights 26, 36 balances the levers 23, 33 and the test specimen 2 horizontally.

Next, move the lever mechanisms 20, 30 left and right along the linear guides 12, 13, and adjust the positions of the lever mechanisms 20, 30 so that the middle of the test specimen 2 is positioned directly below the drive unit 42 and load cell 70.

Next, the drive unit 42 is activated to lower the head 43 until the first roller 52 of the jig 50 and the first roller of the jig 60 come into contact with the test piece 2.

Next, the second block 53 of the jig 50 is assembled to the first block 51, and the test specimen 2 is sandwiched between the first roller 52 and the second roller 54. Then, a screw-type fastener 55 is attached to the second block 53 and the first block 51, and the second block 53 is tightened to the first block 51 by the screw-type fastener 55. This completes the assembly of the jig 50, and the test specimen 2 is rotatably supported by the jig 50. Similarly, the jig 60 is assembled, and the test specimen 2 is supported by the jig 60.

Next, the lower half of the heating furnace 90 is attached to the upper half, and the center of the test specimen 2 is placed in the heating furnace 90 .
Next, the gap between the edge of the opening at the end face of the heating furnace 90 and the outer peripheral surface of the test piece 2 is closed with a heat insulating material.
This completes the setting of the test specimen 2.

4. Static Bending and Torsion Test Method A static bending and torsion test method using the bending and torsion test device 1 will be described.

The test specimen 2 is set in the bending/torsion test device 1 as described above.
Next, the deflection angle sensor 81 and the torsion angle sensor 82 are calibrated to their zero points.

Next, the drive unit 42 is activated, and operates under displacement control or load control, thereby driving the head 43 to raise or lower it. As the displacement of the head 43 increases, the two-point load applied to the test specimen 2 from the jigs 50 and 60 increases. This causes the test specimen 2 to deflect and twist, increasing the deflection angle θ and the torsion angle φ. Note that the drive unit 42 may operate until the test specimen 2 breaks, or the drive unit 42 may remove the two-point load before the test specimen 2 breaks.

As the test specimen 2 is deflecting and twisting, the load cell 70 measures the sum of the two loads, and the deflection angle sensor 81 and torsion angle sensor 82 measure the deflection angle θ and torsion angle φ, respectively. The load cell 70, deflection angle sensor 81, and torsion angle sensor 82 output the measured values of the sum of the two loads, deflection angle θ, and torsion angle φ to a data logger or computer. The data logger or computer records the measured values of the sum of the two loads, deflection angle θ, and torsion angle φ in chronological order.

The loading device 40 may apply a two-point load to the test specimen 2 while the heating furnace 90 is heating the test specimen 2. The loading device 40 may apply a two-point load to the test specimen 2 while the heating furnace 90 is stopped and the temperature inside the heating furnace 90 is at room temperature.

5. Creep-Fatigue Test Method A creep-fatigue test method using the bending/torsion test device 1 will be described.

The test specimen 2 is set in the bending/torsion test device 1 as described above.
Next, when the power supply to the heating furnace 90 is turned on, the temperature control circuit feedback controls the electric heater of the heating furnace 90 based on the temperature measured by the temperature sensor of the heating furnace 90. This heats the inside of the heating furnace 90, and the temperature of the heating furnace 90 is maintained at a predetermined temperature.
Next, the deflection angle sensor 81 and the torsion angle sensor 82 are calibrated to their zero points.

Next, when the drive unit 42 operates under load control or displacement control, the drive unit 42 repeatedly raises and lowers the head 43. As a result, a two-point load is repeatedly applied to the test specimen 2 from the jigs 50 and 60. As a result, the test specimen 2 repeatedly bends in a downward or upward convex shape, or the test specimen 2 repeatedly bends in an alternating downward and upward convex shape. Note that during each cycle, the state in which the two-point load is at its maximum may be maintained for a certain period of time. Alternatively, during each cycle, the state in which the two-point load is at its minimum may be maintained for a certain period of time.

As the test specimen 2 is repeatedly deflected, the load cell 70 measures the sum of the two-point loads, and the deflection angle sensor 81 and torsion angle sensor 82 measure the deflection angle θ and torsion angle φ, respectively. The load cell 70, deflection angle sensor 81, and torsion angle sensor 82 output the measured values of the sum of the two-point loads, deflection angle θ, and torsion angle φ to a data logger or computer. The data logger or computer records the measured values of the sum of the two-point loads, deflection angle θ, and torsion angle φ in chronological order.

While the test specimen 2 is heated by the heating furnace 90, two-point loads are repeatedly applied to the test specimen 2, causing creep to occur in the test specimen 2. In other words, as the number of cycles increases, the maximum deflection angle θ and maximum torsion φ of the test specimen 2 during each cycle also increase.

The drive unit 42 may operate until the test specimen 2 experiences creep fatigue failure, or the repeated loading may be stopped or temporarily interrupted by stopping the drive unit 42 before the test specimen 2 experiences creep fatigue failure.

6. Fatigue Test Method The fatigue test method is the same as the creep-fatigue test method described above, except that the test specimen 2 is not heated by the heating furnace 90.

7. Creep Test Method The creep test method using the bending and torsion test device 1 will be described.

The test specimen 2 is set in the bending/torsion test device 1 as described above.
Next, when the power supply to the heating furnace 90 is turned on, the temperature control circuit feedback controls the electric heater of the heating furnace 90 based on the temperature measured by the temperature sensor of the heating furnace 90. This heats the inside of the heating furnace 90, and the temperature of the heating furnace 90 is maintained at a predetermined temperature.
Next, the deflection angle sensor 81 and the torsion angle sensor 82 are calibrated to their zero points.

Next, when the drive unit 42 operates under load control, the drive unit 42 raises or lowers the head 43, thereby applying a constant two-point load from the jigs 50, 60 to the test specimen 2. As a result, the test specimen 2 bends convexly downward or upward. Because a constant two-point load is applied to the test specimen 2 while it is heated by the heating furnace 90, creep occurs in the test specimen 2. In other words, the maximum deflection angle θ and maximum torsion angle φ of the test specimen 2 increase over time.

As the creep phenomenon of test specimen 2 progresses, load cell 70 measures the sum of the two-point loads, and deflection angle sensor 81 and torsion angle sensor 82 measure the deflection angle θ and torsion angle φ, respectively. Load cell 70, deflection angle sensor 81, and torsion angle sensor 82 output the measured values of the sum of the two-point loads, deflection angle θ, and torsion angle φ to a data logger or computer. The data logger or computer records the measured values of the sum of the two-point loads, deflection angle θ, and torsion angle φ in chronological order.

8. Advantageous Effects (1) When the jigs 50, 60 are displaced up and down by the drive unit 42, two-point loads are applied from the jigs 50, 60 to the test specimen 2, causing the test specimen 2 to bend. At this time, the levers 23, 33 swing so as to rotate in opposite directions around the pivots 22, 32, respectively, causing the test specimen 2 to twist. Therefore, both bending moment and torsional moment can be applied to the test specimen 2 by the single drive unit 42. Furthermore, since the test specimen 2 simulates actual piping in a power plant or the like, it is possible to realize in the test specimen 2 a mechanical state that approximates the state in which the actual piping is bent and twisted.

(2) Because the actuator used in the bending/torsion test device 1 is a single drive unit 42, the bending/torsion test device 1 can be provided at low cost. Furthermore, because the bending and twisting of the test specimen 2 are generated by the power of the single drive unit 42, there is no time lag between the timing of the bending and twisting of the test specimen 2.

(3) Because the first lever 23 is rotatable around its central axis and the second lever 33 is rotatable around its central axis, the test specimen 2 bends significantly. Here, the test specimen 2 simulates actual piping in a power plant or the like, and because the span of the actual piping is long, the piping bends significantly due to thermal expansion and internal pressure. Therefore, the significant bending of the test specimen 2 caused by the rotation of the levers 23 and 33 mimics the bending of the actual piping.

(4) Because the test specimen 2 can rotate around its central axis relative to the jigs 50 and 60, the jigs 50 and 60 do not provide resistance to torsion of the test specimen 2.

(5) When the test specimen 2 bends, the distance between both ends of the test specimen 2 becomes shorter. Even in this case, the lever mechanisms 20, 30 are guided left and right by the linear guides 12, 13, so the distance between the tips of the levers 23, 33 is adjusted to match the distance between the two ends of the test specimen 2.

(6) Because the relative movement of the test specimen 2 in the central axis direction with respect to the jigs 50 and 60 is restricted, the distance between the jigs 50 and 60 changes when the test specimen 2 bends. Even in such cases, the jigs 50 and 60 are guided left and right by the third linear guides 44 and 45, so the distance between the jigs 50 and 60 is adjusted in accordance with the bending of the test specimen 2.

(7) When the test specimen 2 bends, the jigs 50, 60 are tilted by the tilting mechanisms 46, 47, and the jigs 50, 60 move left and right by the third linear guides 44, 45. Therefore, the shape of the deflection curve of the test specimen 2 is not unique to the jigs 50, 60.

9. Experiments Using Bending and Torsion Testing Apparatus and Results Creep-fatigue tests were conducted using the bending and torsion testing apparatus 1. The details of the experiments and their results are described below.

(1) Test specimen Two metal round tubes of equal length were welded together at their ends to prepare test specimen 2. The length of test specimen 2 was 900 mm, the inner diameter of test specimen 2 was 38.14 mm, and the outer diameter of test specimen 2 was 48.3 mm.

(2) Heating Temperature The temperature inside the heating furnace 90 was controlled to be constant at 923K.

(3) Load Conditions FIG. 9 shows the waveform of the load P applied by the drive unit 42 during one cycle when the drive unit 42 is load-controlled. In FIG. 9, the vertical axis represents the load P, and the horizontal axis represents time. Table 1 shows the maximum value P _max of the load P, the holding time _th , the load P increase rate V _i , and the load decrease rate V _d . Here, the load P is the sum of the two loads, the holding time _th is the time during which the load P is held at the maximum value P _max , the increase rate V _i is the amount of change in the load P per unit time when the load _P is changed from the minimum value (almost zero) to the maximum value P _max , and the decrease rate V _d is the amount of change in the load P per unit time when the load P is changed from the maximum value P max to the minimum value. When the load when the drive unit 42 was load-controlled was measured using the load cell 70, it was confirmed that the measured values were in accordance with the settings shown in FIG. 9.

Creep-fatigue tests were conducted under the above-mentioned loading conditions (a) to (f).

(4) Change in Displacement Figure 10 is a graph showing the experimental results of the relationship between the number of cycles and displacement under load condition (b). In Figure 10, the horizontal axis represents the number of cycles, and the vertical axis represents the displacement of the head 43 when the load P is at its maximum value _Pmax or its minimum value. The displacement of the head 43 when the head 43 descends from the initial position is negative.

10, as the number of cycles increases, the absolute values of the displacement at both the maximum load and the minimum load increase, indicating that creep occurs in specimen 2.
Furthermore, when the number of cycles slightly exceeds 2000, cracks appear in test piece 2, and the fatigue life of test piece 2 is reached.

(5) Change in Deflection Angle Figure 11 is a graph showing the experimental results of the relationship between the number of cycles and the deflection angle θ under load condition (b). In Figure 11, the horizontal axis represents the number of cycles, and the vertical axis represents the deflection angle θ when the load P is at its maximum value _Pmax or its minimum value (almost zero). As is clear from Figure 11, as the number of cycles increases, both the deflection angle θ at the maximum load and the deflection angle θ at the minimum load increase.

(6) Change in torsion angle Figure 12 is a graph showing the experimental results of the relationship between the number of cycles and the torsion angle φ under load condition (b). In Figure 12, the horizontal axis represents the number of cycles, and the vertical axis represents the torsion angle when the load P is at its maximum value _Pmax or its minimum value (almost zero). As is clear from Figure 12, as the number of cycles increases, both the torsion angle φ at the maximum load and the torsion angle φ at the minimum load increase.

(7) Observation of cracks Figure 13 is a photograph showing the state of cracks that occurred in test piece 2 under loading condition (b). As shown in Figure 13, it can be seen that cracks occurred at the interface between the end of the metal round tube and the weld.

(8) Relationship between deflection angle and equivalent bending moment Figure 14 is a graph showing the experimental results of the relationship between deflection angle θ and equivalent bending moment. In Figure 14, the horizontal axis represents deflection angle θ, and the vertical axis represents equivalent bending moment. As is clear from Figure 14, hysteresis occurs in the deflection angle θ at each cycle. It is also clear that the residual deflection angle θ increases as the number of cycles increases. This indicates that creep occurs in test specimen 2.

(9) Relationship between torsion angle and equivalent bending moment Figure 15 is a graph showing the experimental results of the relationship between torsion angle φ and equivalent bending moment. In Figure 15, the horizontal axis represents torsion angle φ, and the vertical axis represents equivalent bending moment. As shown in Figure 15, it can be seen that hysteresis occurs in the torsion angle φ at each cycle. It can also be seen that the remaining torsion angle φ increases as the number of cycles increases. This indicates that creep occurs in test specimen 2.

(10) Relationship between Equivalent Bending Moment and Fatigue Life Figure 16 is a graph showing the experimental results of the relationship between the number of cycles at which fatigue failure was reached and the equivalent bending moment. In Figure 16, the horizontal axis represents the number of cycles at which fatigue failure was reached, and the vertical axis represents the equivalent bending moment. In Figure 16, the results for a holding time t _h of 1 minute are plotted with open circles, _and the results for a holding time t _h of 10 minutes are plotted with closed circles. As is clear from Figure 16, the fatigue life for a holding time t _h of 10 minutes is shorter than the fatigue life for a holding time t h of 1 minute. This shows that the torsional creep phenomenon caused by holding the load P at the maximum value P _max affects the fatigue life, and the more pronounced the creep phenomenon, the shorter the fatigue life becomes.

1... Bending/torsion test device 12... First linear guide (first guide)
13...Second linear guide (second guide)
23...First lever 33...Second lever 42...Drive unit 44, 45...Third linear guide (third guide)
46, 47... Tilting mechanism 50, 60... Jig 51... First block 52... First roller 53... Second block 54... Second roller 55... Screw-type fastener (fastener)
81... Deflection angle sensor 82... Torsion angle sensor

Claims (8)

a first lever extending from a first base end to a first tip end, rotatable about a first central axis extending from the first base end to the first tip end, and swingable at the first base end about a first swing axis perpendicular to the first central axis, one end of a columnar or hollow columnar test body being fixed to the first tip end so that the central axis of the test body is perpendicular to the first central axis;
a second lever extending from a second base end to a second tip end in a direction parallel to and opposite to the direction in which the first lever extends from the first base end to the first tip end, being rotatable about a second central axis extending from the second base end to the second tip end, and being swingable at the second base end about a second swing axis perpendicular to the second central axis, the other end of the test body being fixed to the second tip end so that the central axis of the test body is perpendicular to the second central axis;
a pair of jigs spaced apart from each other in the direction of the central axis of the test body and supporting a radial load on the test body so that the test body can rotate around the central axis of the test body;
a drive unit that displaces the pair of jigs in a direction perpendicular to the central axis of the test piece so as to swing the first lever and the second lever around the first swing axis and the second swing axis, respectively. a first guide that guides the first lever in a direction parallel to the central axis of the test body;
2. The bending/torsion test device according to claim 1, further comprising: a second guide that guides the second lever in a direction parallel to the central axis of the test piece. The bending/torsion testing device according to claim 1 or 2, further comprising a pair of tilting mechanisms that support the pair of jigs so that they can be tilted about axes perpendicular to both the displacement direction of the pair of jigs and the central axis of the test piece. The bending/torsion testing device of claim 3, further comprising a pair of third guides that respectively guide the pair of tilting mechanisms in a direction parallel to the central axis of the test specimen. The jig is
The first block,
a first roller attached to the first block so as to be rotatable about an axis parallel to the central axis of the test piece, the first roller being in contact with an outer peripheral surface of the test piece;
a second block assembled to the first block with the test specimen interposed between the first block and the second block;
a second roller attached to the second block so as to be rotatable about an axis parallel to the central axis of the test piece, the second roller being in contact with the outer peripheral surface of the test piece;
5. The bending/torsion test device according to claim 1, further comprising: a fastener that fastens the first block and the second block together and generates a clamping force that causes the first roller and the second roller to sandwich the test specimen therebetween. The bending/torsion test device according to any one of claims 1 to 5, further comprising a deflection angle sensor provided at the first tip of the first lever or the second tip of the second lever, for measuring the deflection angle of the test specimen. The bending/torsion test device according to any one of claims 1 to 6, further comprising a torsion angle sensor provided at the first tip of the first lever or the second tip of the second lever, for measuring the torsion angle of the test specimen. The bending/torsion test device described in any one of claims 1 to 7, further comprising a heating furnace that accommodates the portion of the test specimen between the pair of jigs.