Device for measuring cross-sectional deformation of elbow pipe under cyclic bending

Abstract

The present invention relates to a device for measuring cross-sectional deformation of an elbow pipe, and more specifically, to a device for accurately measuring the degree of cross-sectional deformation occurring in the curved portion of an elbow pipe during a repeated bending test of the elbow pipe. The present invention enables the acquisition of reliable cross-sectional deformation data of the curved section, as the linear displacement sensor moves along with the elbow section when the center of the curved section shifts due to deformation of the elbow pipe during a repetitive bending test, thereby maintaining the contact position between the curved section and the linear displacement sensor. Furthermore, the present invention allows for the acquisition of cross-sectional deformation data of the curved section during a repetitive bending test on an elbow pipe specimen performed under dynamic loads, such as seismic loads.

Description

Technology Field

[0001] The present invention relates to a device for measuring cross-sectional deformation of an elbow pipe, and more specifically, to a device for accurately measuring the degree of cross-sectional deformation occurring in the curved portion of an elbow pipe during a repeated bending test of the elbow pipe. Background Technology

[0002] Power plants and other high-energy facilities consist of numerous piping systems. Various types of elbow pipes are installed within these systems to ensure layout flexibility, accommodate thermal deformation, and absorb energy through plastic deformation in the event of excessive external forces. Due to their geometric characteristics, these elbow pipes are vulnerable to deformation and damage under large-amplitude repetitive loads compared to other piping components.

[0003] Therefore, in order to ensure the structural integrity of elbow pipes under large seismic load conditions and to develop and verify methods for evaluating this, repeated bending tests are being performed on elbow pipes using a fatigue testing machine as shown in Fig. 1.

[0004] It is known that the main damage mode of an elbow pipe during a cyclic bending test is crack formation on the flank of the bend. When cyclic bending is applied to an elbow pipe, the cross-section (AA) of the bend is periodically deformed as shown in Fig. 2, and the periodic deformation of the cross-section of the bend not only causes cyclic strain of tension and compression on the flank of the bend but also promotes crack formation through the accumulation of gradual deformation.

[0005] Therefore, to accurately determine the damage behavior of elbow piping during repeated bending tests, it is important to accurately measure the deformation of the cross-section of the curved section while the repeated bending is applied.

[0006] To do this, as shown in Fig. 3, a square frame is installed around the curved section of the elbow pipe, and a linear variable displacement transducer (LVDT) is mounted on the square frame to measure the deformation of the cross-section of the curved section while repeated bending is applied to the elbow pipe.

[0007] However, when bending is applied to a pipe elbow, as shown in Fig. 2, the shape of the cross-section of the curved section changes depending on the direction in which the bending load is applied (opening mode, closing mode), and the shape of the cross-section may not be symmetrical.

[0008] Therefore, determining the deformation pattern of the cross-section by measuring deformation only at specific locations within the curved section has limitations, and it is necessary to simultaneously measure deformation at various locations along the circumference where significant deformation is predicted to occur.

[0009] Furthermore, as the cross-section of the bend gradually deforms during repetitive bending of the elbow pipe, the contact point between the linear displacement sensor and the bend shifts from its original position, thereby reducing measurement reliability. In particular, when performing bending tests at dynamic loading velocities such as seismic loads, it is nearly impossible to continuously measure cross-sectional deformation at the original contact point.

[0010] Therefore, in order to reliably measure the cross-sectional deformation of the elbow pipe due to repeated bending, it is important for the linear displacement sensor measuring the deformation to maintain its original contact position. Prior art literature

[0011] C. Karvelas, G. Chatzopoulou, AD Zervaki, N. Stathas, E. Strepelias, The problem to be solved

[0012] The present invention was created to improve upon the above-mentioned problems, and its purpose is to provide a cross-sectional deformation measuring device for an elbow pipe that can reliably measure cross-sectional deformation when performing a repetitive bending test in in-plane mode on an elbow pipe.

[0013] In addition, the present invention aims to provide a cross-sectional deformation measuring device for an elbow pipe, wherein when the center of the curved section shifts due to deformation of the elbow pipe during a repetitive bending test, the linear displacement sensor also moves together, thereby maintaining the contact position between the curved section and the linear displacement sensor. means of solving the problem

[0014] The cross-sectional deformation measuring device of the elbow pipe under repeated bending conditions according to the present invention for achieving the above objective comprises: a sensor fixing frame formed to surround the curved portion of a pipe specimen; linear displacement sensors (LVDTs) installed on the sensor fixing frame such that their ends contact the outer surface of the curved portion to measure the cross-sectional deformation of the curved portion; and a support member installed on the pipe specimen to support the sensor fixing frame, which allows the sensor fixing frame to move when the curved portion moves as the pipe specimen bends due to a bending load applied to the pipe specimen.

[0015] The above support member comprises a first support frame coupled to a first straight pipe portion extending from one end of the curved pipe portion, a second support frame coupled to a second straight pipe portion extending from the other end of the curved pipe portion, and a pantograph unit connecting the first and second support frames to the sensor fixing frame.

[0016] The above pantograph unit comprises a guide coupled to the sensor fixing frame, a slider movable along the guide, a first support member having one side hinge-coupled to the first support frame and the other side hinge-coupled to the slider, a second support member having one side hinge-coupled to the second support frame and the other side hinge-coupled to the slider, a third support member having one side hinge-coupled to the first support frame and the other side hinge-coupled to the sensor fixing frame, and a fourth support member having one side hinge-coupled to the second support frame and the other side hinge-coupled to the sensor fixing frame.

[0017] The above pantograph unit further comprises an auxiliary slider movable along the guide, a first auxiliary support having one side hinged to the first support and the other side hinged to the auxiliary slider, and a second auxiliary support having one side hinged to the second support and the other side hinged to the auxiliary slider.

[0018] The above linear displacement sensors are each mounted on a sensor holder coupled to the sensor fixing frame and aligned at the measurement position of the curved section.

[0019] The sensor holder comprises a body having a sensor insertion hole into which the linear displacement sensor is inserted, a fixing means for fixing the linear displacement sensor to the body by changing the size of the sensor insertion hole, an insertion projection formed protruding from the upper part of the body so as to be inserted into a position adjustment hole formed in the sensor fixing frame, and a fastening projection formed on the upper part of the insertion projection to which a nut is fastened.

[0020] The position adjustment hole is formed in a curved shape so that the sensor holder can move along the circumferential direction of the curved section.

[0021] A plurality of scales are marked around the position adjustment hole to allow setting the position of the insertion projection inserted into the position adjustment hole, and an alignment line is formed on the sensor holder to align with any one of the scales.

[0022] A contact tip is installed at the end of the above linear displacement sensor and contacts the outer surface of the above curved pipe portion.

[0023] The above contact tip is formed convexly in the direction of the outer surface of the above curved tube portion. Effects of the invention

[0024] As described above, in the present invention, when the center of the curved section shifts due to the deformation of the elbow pipe during a repetitive bending test, the linear displacement sensor also moves together, so the contact position between the curved section and the linear displacement sensor can be maintained, thereby enabling reliable cross-sectional deformation data of the curved section to be obtained.

[0025] In addition, the present invention can obtain cross-sectional deformation data of the curved section in a repeated bending test on an elbow pipe specimen performed under dynamic loads such as seismic loads. Brief explanation of the drawing

[0026] FIG. 1 is a schematic diagram showing the configuration of a fatigue testing machine for a repeated bending test of an elbow pipe, and FIG. 2 is a figure illustrating the deformation of the cross-section of the curved section according to the direction in which the bending load is applied (opening mode, closing mode), and Figure 3 is a photograph showing the appearance of a cross-sectional deformation measuring device for an elbow pipe according to conventional technology, and FIG. 4 is a front view of a cross-sectional deformation measuring device for an elbow pipe according to an example of the present invention, and FIG. 5 is a perspective view of FIG. 4, and FIG. 6 is an exploded perspective view of the sensor fixing frame applied in FIG. 5, and FIG. 7 is a plan view of the sensor fixing frame of FIG. 6, and FIG. 8 is a plan view of the sensor fixing frame of FIG. 6 in a state where the sensor holder is not installed, and FIG. 9 is a left side view of FIG. 8, and FIG. 10 is an exploded perspective view of the first support frame applied to FIG. 5, and FIG. 11 is a perspective view showing the contact tip of the linear displacement sensor applied in FIG. 5, extracted and shown. FIG. 12 is a plan view of FIG. 11, and FIG. 13 is a side view of FIG. 11, and FIG. 14 is a cross-sectional view showing the main part of the sensor holder applied in FIG. 6, and FIG. 15 is a front view of a cross-sectional deformation measuring device for an elbow pipe according to another example of the present invention. Specific details for implementing the invention

[0027] Hereinafter, a device for measuring cross-sectional deformation of an elbow pipe under repeated bending conditions according to a preferred embodiment of the present invention will be described in detail.

[0028] Referring to FIGS. 4 to 14, the cross-sectional deformation measuring device of the elbow pipe of the present invention comprises a sensor fixing frame (10) formed to surround a curved section (2) of a pipe specimen (1), linear displacement sensors (LVDTs) (5) installed on the sensor fixing frame (10) so as to have their ends in contact with the outer surface of the curved section (2) to measure cross-sectional deformation of the curved section (2), and a support member installed on the pipe specimen (1) to support the sensor fixing frame (10).

[0029] A pipe specimen (1) for performing a repeated bending test consists of a curved section (2) and first and third straight sections (3)(4). The curved section (2) is a section of the pipe specimen (1) that is bent in an elbow shape. The first and second straight sections (3)(4) are formed by extending straight from both ends (2a, 2b) of the curved section (2).

[0030] The sensor fixing frame (10) is formed to surround the curved portion (2) of the pipe specimen (1). The sensor fixing frame (10) is supported by a support member. The sensor fixing frame (10) surrounds the curved portion (10) without contacting the curved portion (2).

[0031] The sensor fixing frame (10) is structured to be divided into two unit fixing frames (20). The two unit fixing frames (20) have the same structure. The two unit fixing frames (20) can be positioned to face each other with the curved section (1) in between, and then joined together using a bolt (18) and a nut (19).

[0032] Each unit fixed frame (20) is provided with a base plate (21) and a side plate (27) formed to be bent downward from the edge of the base plate (21).

[0033] When two unit fixed frames (20) are combined, a circular center hole (11) is formed in the center of the sensor fixed frame (10). The curved portion (2) of the pipe specimen (1) passes through the center hole (11).

[0034] Side plates (27) are formed in the front, rear, left, and right directions of the sensor fixing frame (10). Among the four side plates (27), a support cap (25) is attached to the side plates (27) located at the front and rear. The support cap (25) is attached to a screw hole (28) formed in the side plate (27). A third support member and a fourth support member, which will be described later, are hinge-connected to the support cap (25). A pass hole (26) is formed in the support cap (25) for the linear displacement sensor (5) to pass through. Additionally, a pass hole (29) is formed in each of the remaining two side plates (27) to which the support cap (25) is not attached. The pass holes (26) and (29) are formed horizontally so as not to hinder the movement of the linear displacement sensor (5) when the linear displacement sensor (5) moves along the circumferential direction of the curved section (2).

[0035] A position adjustment hole (23) is located in each direction where the side plate (27) is positioned. The position adjustment hole (23) is formed in the base plate (21). In the illustrated example, two position adjustment holes (23) are formed in each unit fixing frame (20). Thus, a total of four position adjustment holes (23) are formed in one sensor fixing frame (10). The position adjustment holes (23) can be arranged at 90° intervals centered around the center hole (10).

[0036] Each position adjustment hole (23) is formed to be bent in a curved shape. These position adjustment holes (23) can be bent with the same curvature as the outer surface curvature of the curved section (2). An insertion projection (37) of a holder, which will be described later, is inserted into the position adjustment hole (23). The length of the position adjustment hole (23) is formed to be larger than the length of the insertion projection (37), so that the insertion projection (37) can move along the position adjustment hole (23). Accordingly, the sensor holder (30) can move within a certain range along the circumferential direction of the curved section (2) around the curved section (2).

[0037] The linear displacement sensor (5) is installed on the sensor fixing frame (10). The end of the linear displacement sensor (5) contacts the outer surface of the curved section (2). When the cross-section of the curved section (2) is deformed, the linear displacement sensor (5) changes its output value.

[0038] A linear variable displacement transducer (LVDT) is a sensor capable of precisely measuring the cross-sectional deformation of a curved section (2) by converting the amount of movement of a rod (7) inserted into a sensor housing (6) into an electrical signal and outputting it when the rod (7) moves.

[0039] A plurality of linear displacement sensors (5) are installed at regular intervals on the sensor fixing frame (10). In the illustrated example, one linear displacement sensor (5) is installed in each of the front-rear, left-right, and right directions. Accordingly, cross-sectional deformation in the front-rear direction and cross-sectional deformation in the left-right direction of the curved pipe portion (2) can be measured.

[0040] A contact tip (8) is installed at the end of the rod (7) of the linear displacement sensor (5) and contacts the outer surface of the curved section (2). The position where the contact tip (8) of each linear displacement sensor (5) contacts the outer surface of the curved section (2) is the measurement position for measuring cross-sectional deformation.

[0041] The contact tip (8) has a constant length and vertical width as shown in FIGS. 12 and 13. For example, the length of the contact tip (8) may be 0.2 times the outer diameter of the curved section (2), and the vertical width of the contact tip (8) may be 0.1 times the outer diameter of the curved section (2). Since the contact tip (8) is formed to have a constant length and width in this way, the cross-section of the curved section (2) is asymmetrically deformed, so that the cross-section deformation can be measured even if the position of maximum cross-section deformation deviates slightly from the initial linear displacement sensor (5) measurement position.

[0042] The contact tip (8) is formed convexly in the direction of the outer surface of the curved section (2). Accordingly, the contact tip (8) contacts the outer surface of the curved section (2).

[0043] The linear displacement sensor (5) can be installed directly on the sensor fixing frame (10), but preferably, the linear displacement sensor (5) is mounted on the sensor holder (30) and installed on the sensor fixing frame (10).

[0044] The sensor holder (30) is coupled to the sensor fixing frame (10) to align the sensor holder (30) to the measurement position of the curved section (2). At the same time, the sensor holder (30) is made to move along the circumferential direction of the curved section (2) within a certain range so that the cross-sectional deformation of the curved section (2) can be measured at various measurement positions.

[0045] The illustrated sensor holder (30) comprises a body (31) having a sensor insertion hole (32) into which a linear displacement sensor (5) is inserted, a fixing means for fixing the linear displacement sensor (5) to the body (31) by changing the size of the sensor insertion hole (32), an insertion projection (37) formed protruding from the upper part of the body (31) so as to be inserted into a position adjustment hole (23) formed in the sensor fixing frame (10), and a fastening projection (38) formed on the upper part of the insertion projection (37) to which a nut (36) is fastened.

[0046] The body (31) is made of a rectangular block. The body (31) may be formed of an elastic metal material or a synthetic resin material.

[0047] A sensor insertion hole (32) is formed in the body (31). The diameter of the sensor insertion hole (32) is formed to be larger than the diameter of the sensor housing (6) of the linear displacement sensor (5) so that the linear displacement sensor (5) can be inserted into the sensor insertion hole (32).

[0048] The fixing means changes the size of the sensor insertion hole (32) to fix the linear displacement sensor (5) to the body (31).

[0049] It consists of a split slit (33) formed to be connected from the bottom surface of the body (31) to the sensor insertion hole (32) as a fixing means, and a fixing bolt (35) coupled to the body (31) to change the width of the split slit (33) to change the size of the sensor insertion hole (32).

[0050] The lower part of the body (31) is divided into two parts by the split slit (33). The fixing bolt (35) controls the width of the split slit (33). A screw groove (34) is formed in the lower part of the body (31) so that the fixing bolt (35) can be connected to the body (31).

[0051] With the linear displacement sensor (5) inserted into the sensor insertion hole (32), if the fixing bolt (35) is inserted into the screw groove (34) and rotated, the width of the split slit (33) gradually narrows. Accordingly, as the size of the sensor insertion hole (32) decreases, the linear displacement sensor (5) is fixed to the body (31).

[0052] The insertion projection (37) is formed to protrude from the upper part of the body (31). The insertion projection (37) is formed to be bent with the same curvature as the position adjustment hole (23). The insertion projection (37) is inserted into the position adjustment hole (23). While inserted into the position adjustment hole (23), the insertion projection (37) can move along the position adjustment hole (23). Thus, the position of the linear displacement sensor (5) mounted on the holder (30) can be adjusted within a limited range.

[0053] A fastening projection (38) is formed on the upper part of an insertion projection (37). When the insertion projection (37) is inserted into the position adjustment hole (23), the fastening projection (38) protrudes upward from the upper part of the sensor fixing frame (10). Screw threads are formed on the outer surface of the fastening projection (38). When a nut (36) is fastened to the fastening projection (38), the upper part of the body (31) comes into close contact with the lower surface of the base plate (21), thereby fixing the sensor holder (30). Then, when the nut (36) is loosened, the position of the sensor holder (30) can be adjusted. A conventional wing nut can be used as the nut (36).

[0054] A center line (39) is formed on the upper part of the fastening projection (38). The position of the sensor holder (31) can be accurately verified through the scale formed around the position adjustment hole (23) and the center line (39) formed on the fastening projection (38).

[0055] A support member is installed on a pipe specimen (1) to support a sensor fixing frame (10). The support member allows the sensor fixing frame (10) to move when the pipe specimen (1) bends due to a bending load applied to the pipe specimen (1) and the curved section (2) moves. Accordingly, when the center (C) of the curved section (2) moves due to deformation during a repeated bending test, the sensor fixing frame (10) also moves together, so that the measurement position of the linear displacement sensor (5) can be maintained. Therefore, reliable cross-sectional deformation data of the curved section (2) can be obtained while repeated bending is applied.

[0056] The illustrated support member comprises a first support frame (40) coupled to a first straight section (3) extending from one end of a curved section (2), a second support frame (50) coupled to a second straight section (4) extending from the other end of a curved section (2), and a pantograph unit connecting the first and second support frames (40)(50) to a sensor fixing frame (10).

[0057] The first support frame (40) is equipped with a pair of first support brackets (41). The pair of first support brackets (41) are joined to each other by a bolt (42) and a nut (43) with the first straight section (3) in between. Accordingly, the first support brackets (41) are firmly fixed to the first straight section (3). A first hinge shaft (47) is connected to the first support bracket (41). The first hinge shaft (47) is screw-connected to a screw groove (45) formed in the first support bracket (41). A first support member and a third support member, to be described later, are hinge-connected to the first hinge shaft (47).

[0058] The second support frame (50) is constructed with the same structure as the first support frame (40), differing only in its installation location. The second support frame (50) is equipped with a pair of second support brackets (51). The pair of second support brackets (51) are joined to each other by a bolt (52) and a nut with the second straight section (3) in between. A second hinge shaft (57) is connected to the second support bracket (51). The second hinge shaft (57) is screw-connected to a screw groove formed in the second support bracket (51). The second support member and the fourth support member, which will be described later, are hinge-connected to the second hinge shaft (57).

[0059] The pantograph unit connects the first and second support frames (40)(50) to the sensor fixing frame (10).

[0060] The pantograph unit comprises a guide (60) coupled to a sensor fixing frame (10), a slider (65) movable along the guide (60), a first support member (70) hinged to a first support frame (40) on one side and hinged to a slider (65) on the other side, a second support member (75) hinged to a second support frame (50) on one side and hinged to a slider (65) on the other side, a third support member (80) hinged to a first support frame (40) on one side and hinged to a sensor fixing frame (10) on the other side, and a fourth support member (85) hinged to a second support frame (50) on one side and hinged to a sensor fixing frame (10) on the other side.

[0061] The guide (60) is connected to a side plate (27) located on the left side of the sensor fixing frame (10) by a bolt (61). To this end, a screw hole (62) is formed in the side plate (27). The guide (60) is formed to extend a certain length in the left direction of the sensor fixing frame (10).

[0062] The slider (65) is formed in a rod shape so that it can slide along the guide (60). The slider (65) is installed on the guide (60) and can move along the guide (60) within a limited range. A guide hole (63) is formed in the guide (60) in an elongated left-right direction. The slider (65) is inserted into the guide hole (63), and both ends protrude outward from the guide (60).

[0063] The first support member (70) connects the first support frame (40) and the slider (65). The first support member (70) consists of a pair. The pair of first support members (70) are spaced apart in the front-rear direction. In the illustrated example, the pair of first support members (70) are connected to each other by a connecting member (71).

[0064] One side of the first support (70) is hinged to the first hinge shaft (47), and the other side of the first support (70) is hinged to the slider (65).

[0065] The second support member (75) connects the second support frame (50) and the slider (65). The second support member (75) is made up of a pair. The pair of second support members (75) are spaced apart in the front-rear direction. In the illustrated example, the pair of second support members (75) are connected to each other by a connecting member (76).

[0066] One side of the second support (75) is hinged to the second hinge shaft (57), and the other side of the second support (75) is hinged to the slider (65).

[0067] A bolt (67) is attached to the end of the slider (65) to prevent the first and second supports (70) (75), which are hinged to the slider (65), from coming off the slider (65).

[0068] The third support member (80) connects the sensor fixing frame (10) and the first support frame (40). The third support member (80) is formed as a pair. The pair of third support members (80) are spaced apart in the front-rear direction. One side of the third support member (80) is hinge-connected to the support cap (25), and the other side of the third support member (80) is hinge-connected to the first hinge shaft (47). Since the gap on the lower side of the pair of third support members (80) is larger than the gap on the upper side, the third support members (80) are formed to be bent.

[0069] The fourth support member (85) connects the sensor fixing frame (10) and the second support frame (50). The fourth support member (85) is formed as a pair. The pair of fourth support members (85) are spaced apart in the front-rear direction. One side of the fourth support member (85) is hinged to the support cap (25), and the other side of the fourth support member (85) is hinged to the second hinge shaft (57). Since the gap on the upper side of the pair of fourth support members (85) is larger than the gap on the lower side, the fourth support members (80) are formed to be bent.

[0070] The sensor fixing frame (10) can move in the forward and backward directions by means of the pantograph unit described above. Therefore, when bending is applied to the curved section (2), the slider (65) slides, and the sensor fixing frame (10) also moves the same distance as the center (C) of the curved section (2) moves forward and backward. Accordingly, the measurement position of the linear displacement sensor (5) can be maintained.

[0071] In order to measure the cross-sectional deformation of the curved portion of an elbow pipe using the present invention, a pipe specimen is mounted on a fatigue testing machine as shown in FIG. 1. Then, before installing the sensor fixing frame (10), the outer diameter of the curved portion (2) for which cross-sectional deformation is to be measured is measured.

[0072] Next, the cross-sectional deformation device of the present invention is installed on the pipe specimen (1). A first support frame (40) is mounted on the first straight section (3) of the pipe specimen (1), and a second support frame (50) is mounted on the second straight section (4). Then, a sensor fixing frame (10) is positioned on the curved section (2), and the sensor fixing frame (10) and the first and second support frames (40)(50) are connected using a pantograph unit. Then, the position of the sensor holder (30) is appropriately adjusted so that the contact tip (8) of the linear displacement sensor (5) comes into contact with the measurement position on the outer surface of the curved section (2).

[0073] In the initial state, each linear displacement sensor (5) is initialized to set the displacement value to '0', and then repeated bending is applied to the pipe specimen (1). By measuring the displacement value at each linear displacement sensor (5) while the repeated bending is applied, the amount of deformation in each direction of the cross-section of the curved pipe section (2) can be obtained.

[0074] Meanwhile, as illustrated in FIG. 15, the pantograph unit may further comprise an auxiliary slider (not shown) movable along the guide (60), a first auxiliary support (95) with one side hinged to the first support (70) and the other side hinged to the auxiliary slider, and a second auxiliary support (97) with one side hinged to the second support (75) and the other side hinged to the auxiliary slider.

[0075] Although not shown, the auxiliary slider is formed in a rod shape so that it can slide along the guide (60). This auxiliary slider is formed in the same shape as the slider. The auxiliary slider is installed on the guide (60) and can move along the guide (60) within a limited range. An auxiliary guide hole (90) is formed in the guide (60) in an elongated left-right direction. The auxiliary slider is inserted into the auxiliary guide hole (90), and both ends protrude outward from the guide (60).

[0076] The first auxiliary support (95) connects the first support (70) and the auxiliary slider. The first auxiliary support (95) consists of a pair. The pair of first auxiliary supports (95) are spaced apart in the front-rear direction. One side of the first auxiliary support (95) is hinge-connected to a first auxiliary hinge shaft (91) installed on the first support (70). The other side of the first auxiliary support (95) is hinge-connected to the auxiliary slider.

[0077] The second auxiliary support (97) connects the second support (75) and the auxiliary slider. The second auxiliary support (97) consists of a pair. The pair of second auxiliary supports (97) are spaced apart in the front-rear direction. One side of the second auxiliary support (97) is hinge-connected to a second auxiliary hinge shaft (93) installed on the second support (75). The other side of the second auxiliary support (97) is hinge-connected to the auxiliary slider.

[0078] A bolt (99) is attached to the end of the auxiliary slider to prevent the first and second auxiliary supports (95) (97), which are hinged to the auxiliary slider, from coming off the auxiliary slider.

[0079] The first and second auxiliary supports (95)(97) described above can support the movement of the sensor fixing frame more stably.

[0080] Hereinafter, a method for measuring the cross-sectional deformation of an elbow pipe under repeated bending conditions using the cross-sectional deformation measuring device of the present invention described above will be briefly explained.

[0081] First, the outer diameter of the curved section is measured before installing the cross-sectional deformation measuring device on the pipe specimen. By measuring the outer diameter of the curved section before deformation, it can be compared with the outer diameter of the deformed section after the test. The length of the outer diameter passing through the center of the curved section is measured at the location where cross-sectional deformation is to be measured, that is, at the location where the contact tip of the linear displacement sensor makes contact. The outer diameter of the curved section in the front-rear direction (D IOi ), outer diameter in the left-right direction (D LRi Each can be measured.

[0082] Next, the measuring device of the present invention is installed and fixed to the pipe specimen. Each linear displacement sensor mounted on the sensor holder of the measuring device is positioned to come into contact with the curved section at an appropriate location where cross-sectional deformation is to be measured, taking into account the contact force and measurement range with the curved section. A total of four linear displacement sensors are prepared so that cross-sectional deformation can be measured in the front-rear, left-right, and right directions of the curved section as shown in Fig. 7.

[0083] Next, each linear displacement sensor is initialized to set the displacement value to '0', and then a test is conducted by applying a repetitive bending load to the pipe specimen. When the cross-sectional deformation of the curved section occurs, each linear displacement sensor measures the displacement value, and the measured displacement value is stored in the storage unit.

[0084] Assuming the displacement values ​​at each measured linear displacement sensor position are d1 (forward), d2 (backward), d3 (left), and d4 (right), the deformation amount of the cross-section in each direction of the curved section can be calculated as follows.

[0085] - Amount of cross-sectional deformation in the front-rear direction (△ D I0 ): △ D I0 = d1+ d2

[0086] - Amount of cross-sectional deformation in the left-right direction ( △ D LR ): △ D LR = d3+ d4

[0087] Reliable cross-sectional deformation data of the curved pipe portion can be obtained by using the cross-sectional deformation measuring device of the present invention in the manner described above.

[0088] In addition, the outer diameter of the deformed section of the curved pipe during repeated bending can be calculated as follows.

[0089] - Outer diameter in the front-rear direction (D I0 ): D I0 = D I0i + △ D I0

[0090] - Outer diameter in the left-right direction (D LR ): D LR = D LRi + △ D LR

[0091] In addition, the present invention allows cross-sectional deformation and outer diameter data to be easily obtained at other locations by moving the measurement position of the linear displacement sensor in the circumferential direction of the curved section.

[0092] The present invention has been described above with reference to one embodiment, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent embodiments are possible therefrom. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims. Explanation of the symbols

[0093] 1: Pipe specimen 2: Curved pipe section 3: First intuitive area 4: Second intuitive area 5: Linear displacement sensor 10: Sensor fixing frame 40: 1st support frame 50: 2nd support frame 60: Guider 70: First Support 75: Second support 80: Third support 85: 4th support

Claims

Claim 1 A measuring device for measuring cross-sectional deformation of a curved portion of a pipe specimen during a repetitive bending test of the pipe specimen using a fatigue testing machine, comprising: a sensor fixing frame formed to surround the curved portion without contacting the curved portion; linear displacement sensors (LVDTs) installed on the sensor fixing frame such that their ends contact the outer surface of the curved portion to measure cross-sectional deformation of the curved portion; and a support member installed on the pipe specimen to support the sensor fixing frame, which allows movement of the sensor fixing frame when the curved portion moves as the pipe specimen bends due to a bending load applied to the pipe specimen; wherein the support member comprises a first support frame coupled and fixed to a first straight portion extending from one end of the curved portion, a second support frame coupled and fixed to a second straight portion extending from the other end of the curved portion, and the first and second support frames are the A device for measuring cross-sectional deformation of an elbow pipe under repeated bending conditions, comprising a pantograph unit connected to a sensor fixing frame, wherein the pantograph unit comprises a guide coupled to the sensor fixing frame, a guide hole formed in the guide, a slider inserted into the guide hole and capable of moving along the guide, a first support member having one side hinge-coupled to the first support frame and the other side hinge-coupled to the slider, a second support member having one side hinge-coupled to the second support frame and the other side hinge-coupled to the slider, a third support member having one side hinge-coupled to the first support frame and the other side hinge-coupled to the sensor fixing frame, and a fourth support member having one side hinge-coupled to the second support frame and the other side hinge-coupled to the sensor fixing frame. Claim 2 delete Claim 3 delete Claim 4 A measuring device for cross-sectional deformation of an elbow pipe under repeated bending conditions, wherein the pantograph unit further comprises an auxiliary slider movable along the guide, a first auxiliary support having one side hinged to the first support and the other side hinged to the auxiliary slider, and a second auxiliary support having one side hinged to the second support and the other side hinged to the auxiliary slider. Claim 5 A cross-sectional deformation measuring device for an elbow pipe under repeated bending conditions, characterized in that, in claim 1, the linear displacement sensors are each mounted on a sensor holder coupled to the sensor fixing frame and aligned at the measurement position of the curved pipe portion. Claim 6 A device for measuring cross-sectional deformation of an elbow pipe under repeated bending conditions, wherein the sensor holder comprises a body having a sensor insertion hole into which the linear displacement sensor is inserted, a fixing means for fixing the linear displacement sensor to the body by changing the size of the sensor insertion hole, an insertion projection formed protruding from the upper part of the body so as to be inserted into a position adjustment hole formed in the sensor fixing frame, and a fastening projection formed on the upper part of the insertion projection to which a nut is fastened. Claim 7 A measuring device for cross-sectional deformation of an elbow pipe under repeated bending conditions, characterized in that, in claim 6, the position adjustment hole is formed in a curved shape so that the sensor holder can move along the circumferential direction of the curved pipe portion. Claim 8 A measuring device for cross-sectional deformation of an elbow pipe under repeated bending conditions, characterized in that, in claim 7, a plurality of scales are marked around the position adjustment hole to set the position of the insertion projection inserted into the position adjustment hole, and an alignment line is formed on the sensor holder to align with any one of the scales. Claim 9 A cross-sectional deformation measuring device for an elbow pipe under repeated bending conditions, characterized in that, in claim 1, a contact tip is installed at the end of the linear displacement sensor to contact the outer surface of the curved pipe portion. Claim 10 A measuring device for cross-sectional deformation of an elbow pipe under repeated bending conditions, characterized in that, in claim 9, the contact tip is formed convexly in the direction of the outer surface of the curved pipe portion.

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