Vibration test fixture

Abstract

A vibration testing jig (10) comprises: a base (11) that includes a placement surface (11a) on which an end portion of a test piece is placed, and that is installed on a vibration table; a top plate (12) including a slot (16) having an inner surface (16a) that presses the end portion of the test piece toward the placement surface (11a), and a wedge mating groove which is positioned in an extending direction of the slot (16) and which communicates with the slot (16), the top plate (12) being placed on the base (11), spaced apart therefrom; a wedge portion (23) which mates with the wedge mating groove (13); and a plurality of pressing members (14) which are disposed along the slot (16) to press the top plate (12) toward the base (11). An inner surface of the wedge mating groove (13) includes a bottom surface (13a) and a pair of holding surfaces (13s, 13s) which are positioned on both sides, in a width direction, of the wedge mating groove (13) and which face the bottom surface (13a) across an internal space of the wedge mating groove (13), and the wedge portion (23) is in surface contact with the bottom surface (13a) and the pair of holding surfaces (13s, 13s).

Description

[Technical field]

[0001] The present disclosure relates to a vibration test fixture that holds an end of a test piece that extends in a predetermined direction, such as a fan blade used in an aircraft engine. [Background technology]

[0002] Vibration testing is one of the tests for evaluating the fatigue properties of a test specimen. In a vibration test, a vibration that generates a certain stress is applied to the test specimen. In general, the number of times until damage such as breakage occurs (i.e., the number of cycles to break) is a predetermined value (e.g., 10 4 Low cycle fatigue is fatigue when the number of cycles is less than a certain value (for example, 10 4 Fatigue that exceeds the number of cycles at which the stress reaches the breaking point is called high cycle fatigue. In order to evaluate the correlation between stress and the number of cycles at which the specimen breaks, it is necessary to apply vibration to the specimen for a long period of time, and the test period often extends from several days to several weeks.

[0003] Patent Document 1 discloses a jig for vibration testing of rotor blades, which is attached to the vibration table of a vibration test device. The jig in Patent Document 1 includes a jig body as a base fixed to the vibration table, and a top plate. The rotor blade is placed on the mounting base of the jig body with the blade root positioned in the holding groove of the top plate. Furthermore, multiple bolts are screwed into the jig body via the top plate. By tightening these bolts, the top plate moves toward the jig body, and as a result, the blade root is pressed against the mounting base. This holds the blade root in the jig, allowing the vibration test to be carried out. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 208925 Summary of the Invention [Problem to be solved by the invention]

[0005] In the vibration test jig of Patent Document 1, a load is applied from the top plate toward the base to the root of the rotor blade, and the rotor blade is held in place. The value of this load is set according to the environment in which the test specimen is used. For example, since the test specimen in Patent Document 1 is a rotor blade, an extremely large load (e.g., 20 t) equivalent to centrifugal force is applied to the root of the rotor blade.

[0006] While the end of the test specimen is held by the jig and the specimen is vibrated, the load on the end varies according to the vibration of the test specimen. While the end of the test specimen is stationary, the jig holds it stably, but during vibration, the jig deforms and the load decreases, which may cause the test specimen to move within the jig.

[0007] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a vibration test fixture that is capable of stably holding a test object even while the test object is being vibrated. [Means for solving the problem]

[0008] A vibration test jig according to one aspect of the present disclosure is a jig that holds an end of a test piece extending in a predetermined direction, and includes a support surface on which the end of the test piece is placed, a base that is installed on a vibration table, a top plate that has a slot with an inner surface that presses the end of the test piece toward the support surface and a wedge fitting groove that is positioned in the extension direction of the slot and communicates with the slot, and is placed on the base at intervals, a wedge portion that fits into the wedge fitting groove, and a plurality of pressing members that are arranged along the slot and press the top plate toward the base, and the inner surface of the wedge fitting groove includes a bottom surface and a pair of holding surfaces that are located on both sides in the width direction of the wedge fitting groove and face the bottom surface with an internal space of the wedge fitting groove between them, and the wedge portion is in surface contact with the bottom surface and the pair of holding surfaces.

[0009] When viewed from the extending direction of the slot, a cross-sectional shape of the wedge fitting groove may be included in a cross-sectional shape of the slot. The pair of holding surfaces may be inclined with respect to the bottom surface. The pair of holding surfaces may be parallel to the bottom surface. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a vibration test fixture capable of stably holding a test object even while the test object is being vibrated. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of a fan blade, which is an example of a specimen held by a jig according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a front view of a jig according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a top view of a fixture according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a front view of the wedge fitting groove according to this embodiment. [Diagram 5] FIG. 5 is a front view of the tabletop in a bent state. [Figure 6A] FIG. 6A is a perspective view showing a state before the wedge portion according to this embodiment is fitted into the wedge fitting groove of the top plate. [Figure 6B] FIG. 6B is a front view showing a state after the wedge portion according to this embodiment has been fitted into the wedge fitting groove of the top plate. [Figure 7A] FIG. 7A is a perspective view showing a state before a wedge portion according to a modified example of the present embodiment is fitted into a wedge fitting groove of a top plate. [Figure 7B] FIG. 7B is a front view showing a state after the wedge portion according to the modified example of the present embodiment has been fitted into the wedge fitting groove of the top plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a jig 10 according to an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a perspective view of a fan blade 1, which is an example of a specimen held by the jig 10. FIG. 2 is a front view of the jig 10 according to this embodiment. FIG. 3 is a top view of the jig 10. FIG. 4 is a front view of a wedge fitting groove 13 according to this embodiment. For ease of explanation, the base 11 and blade root 3 shown in FIG. 2 are omitted in FIG. 3. Note that the same reference numerals are used to designate common parts in each drawing, and duplicate explanations will be omitted.

[0013] For ease of explanation, the X, Y, and Z directions are defined as being orthogonal to each other. The X and Y directions are parallel to an XY plane (imaginary plane) including the vibration direction of a vibration table (not shown). The X direction is the extension direction of the slot 16 (see FIG. 3). The Z direction is orthogonal to the X and Y directions.

[0014] The jig 10 according to this embodiment is attached to a vibration table (not shown) of a vibration testing device and holds an end of a test specimen. The end of the test specimen has a cross-sectional shape that is pressed against a base 11 by a top plate 12. The test specimen is a so-called long object, and has an end extending in the X direction and a main body extending from the end in a predetermined direction (e.g., the Z direction) that intersects with the XY plane. Hereinafter, a fan blade 1 used in an aircraft engine such as a turbofan engine (not shown) will be described as an example of the test specimen.

[0015] As shown in Figure 1, the fan blade 1 as a test specimen comprises an airfoil 2 as the main body of the test specimen, and an airfoil root 3 as the end of the test specimen. The airfoil 2 and the airfoil root 3 are formed as a single unit. The airfoil 2 has a leading edge 2a, a trailing edge 2b, a tip 2c, and a hub 2d. The airfoil 2 extends in the span direction SD from the airfoil root 3, via the hub 2d, to the tip 2c.

[0016] The blade root 3 is connected to the hub 2d of the blade body 2 and extends in one direction so as to fit into a groove (dovetail groove) of a rotor (not shown) to which the fan blade 1 is attached. The extension direction of this blade root 3 may coincide with the X direction.

[0017] The blade root portion 3 is placed on the mounting surface 11a of the base 11 (see FIG. 2). The blade root portion 3 has a pair of side surfaces 3a, 3a (see FIG. 2) and a bottom surface 3b (see FIG. 2). The blade root portion 3 also has a cross-sectional shape complementary to the cross-sectional shape of the groove portion (not shown) described above. That is, the blade root portion 3 includes a width that widens in the Y direction as it moves away from the blade body 2. The pair of side surfaces 3a, 3a are inclined surfaces that define this width. The bottom surface 3b is located between the side surfaces 3a, 3a and connects to each side surface. When the blade root portion 3 is placed on the mounting surface 11a of the base 11, the bottom surface 3b comes into contact with the mounting surface 11a.

[0018] As shown in Fig. 2 and Fig. 3, the jig 10 includes a base 11, a top plate 12, and a plurality of pressing members 14. The pressing members 14 are constituted by bolts 15 having threaded portions 14a and head portions 14b integrally formed therewith. Alternatively, the pressing members 14 may be constituted by a set of threaded portions 14a formed as stud bolts and nuts 14c screwed onto the threaded portions 14a (see Fig. 2). In the former case, the top plate 12 is pressed toward the base 11 by tightening the bolts 15, and in the latter case, the nuts 14c. For the sake of convenience, the following description will be given taking the bolts 15 as an example of the pressing members 14.

[0019] Base 11 is a flat plate having a predetermined thickness in the Z direction and extending in the X and Y directions, and is made of a highly rigid metal such as stainless steel. The thickness of base 11 is set to a value that provides sufficient rigidity against the axial force of bolt 15 when fastened and against stress during vibration. Base 11 is placed on a vibration table (not shown) of a vibration testing device, and is fixed with fastening members such as bolts in a state where its orientation is adjusted to obtain the desired vibration direction.

[0020] The base 11 includes a mounting surface 11a on which the blade root 3 is placed. The mounting surface 11a faces the top plate 12 and is formed, for example, as the upper surface of a mounting stand 11b that protrudes from the base 11 toward the top plate 12. The height of the mounting stand 11b according to this embodiment is set to a value that allows a gap between the base 11 and the top plate 12 to be maintained when the top plate 12 presses the blade root 3 against the mounting surface 11a.

[0021] The top plate 12 is a rectangular flat plate having a predetermined thickness in the Z direction and extending in the X and Y directions, and is placed on the base 11 with a gap therebetween. Like the base 11, the top plate 12 is also formed of a highly rigid metal such as stainless steel. The thickness of the top plate 12 is set to a value that provides sufficient rigidity against the axial force of the bolts 15 during fastening and against stress during vibration. The shape of the top plate 12 is not limited to a rectangle, and may be another shape such as a circle.

[0022] The top plate 12 has a slot (retaining groove) 16 in which at least a part of the blade root 3 is accommodated. The slot 16 extends in the X direction and opens on the upper surface 12a of the top plate 12, and also opens on the lower surface 12b of the top plate 12 as an insertion opening 18 for the mounting base 11b. A part of the blade root 3 including the bottom surface 3b is accommodated in the slot 16. In addition, wedge fitting grooves 13 (described later) are provided on both sides of the extension direction of the slot 16 (i.e., the X direction).

[0023] The slot 16 has an inner surface 16a that presses the blade root 3 positioned in the slot 16 toward the mounting surface 11a. That is, a cross section of the slot 16 perpendicular to the X direction includes a contour corresponding to the side surfaces 3a, 3a of the blade root 3 positioned in the slot 16. As a result, a part of the inner surface 16a comes into contact with the pair of side surfaces 3a, 3a of the blade root 3.

[0024] The depth of the slot 16 in the Z direction is deeper than the length in the Z direction of the part of the blade root 3 accommodated in the slot 16. In addition, the part of the slot 16 on the lower surface 12b side has a width wider than the width of the blade root 3 in the Y direction. As a result, when the blade root 3 is inserted into the slot 16 through the insertion opening 17, a sufficient gap is formed between the blade root 3 and the inner surface 16a of the slot 16, and the blade root 3 can be easily inserted into the slot 16.

[0025] The top plate 12 has a wedge fitting groove 13 extending in the X direction. As described above, the wedge fitting groove 13 is located on both sides of the slot 16 in the extension direction of the slot 16. The wedge fitting groove 13 is arranged in a row together with the slot 16 in the X direction and communicates with the slot 16. The wedge fitting groove 13 opens to the upper surface 12a of the top plate 12 and the side surface 12c of the top plate 12. Also, when viewed from the X direction, the cross-sectional shape of the wedge fitting groove 13 is included in the cross-sectional shape of the slot 16. In other words, when viewed from the X direction, the cross-sectional shape of the wedge fitting groove 13 coincides with a part of the cross-sectional shape of the slot 16. Therefore, the wedge fitting groove 13 functions as an insertion opening 17 for the blade root 3.

[0026] The inner surface of the wedge fitting groove 13 includes at least a bottom surface 13a and a pair of holding surfaces 13s, 13s. The bottom surface 13a is a surface parallel to the XY plane, and also serves as the upper surface of a connecting portion 19 that connects the plate portion 12A on one side and the plate portion 12B on the other side with respect to the slot 16. The pair of holding surfaces 13s, 13s are formed, for example, on at least a part of the pair of side surfaces 13b, 13b. The pair of holding surfaces 13s, 13s are located on both sides of the wedge fitting groove 13 in the width direction (Y direction), and face the bottom surface 13a with the internal space of the wedge fitting groove 13 between them. The pair of holding surfaces 13s, 13s are inclined with respect to the bottom surface 13a.

[0027] The bolts 15 are arranged on the top plate 12 in the X direction and screwed into the screw holes 20 provided in the base 11 through the top plate 12. When each bolt 15 is tightened, the top plate 12 moves toward the base 11. Therefore, when the bolts 15 are tightened with the blade root 3 inserted into the slot 16 and placed on the mounting base 11b, the top plate 12 gradually descends and the inner surface 16a of the slot 16 comes into contact with the side surfaces 3a, 3a of the blade root 3. Meanwhile, the blade root 3 cannot descend because it is placed on the mounting base 11b. Therefore, when the bolts 15 are tightened further, the inner surface 16a of the slot 16 presses the side surfaces 3a, 3a of the blade root 3, and the blade root 3 is pressed against the mounting surface 11a of the mounting base 11b. In this way, the fan blade 1 is held by the jig 10.

[0028] A strain sensor 22 is embedded in each bolt 15. The strain sensor 22 measures the axial force generated in the bolt 15. When the bolt 15 is tightened, a constant axial force can be set for each bolt 15 by checking the axial force measured by the strain sensor 22. Therefore, a positionally uniform load can be applied to the blade root 3 and the jig 10.

[0029] However, the load on the jig 10 periodically fluctuates in accordance with the vibration of the fan blade 1. If this fluctuation is excessively large, the top plate 12 deforms such that the slot 16 opens (see FIG. 5), and the load on the blade root portion 3 decreases. If the load on the blade root portion 3 decreases excessively, the blade root portion 3 may move within the slot 16. Therefore, the jig 10 according to this embodiment is provided with a wedge portion 23 that fits into the wedge fitting groove 13. The wedge portion 23 comes into surface contact with the bottom surface 13a, which is the inner surface of the wedge fitting groove 13, and the pair of retaining surfaces 13s, 13s.

[0030] Fig. 6A is a perspective view showing a state before the wedge portion 23 is fitted into the wedge fitting groove 13 of the top plate 12, and Fig. 6B is a front view showing a state after the wedge portion 23 is fitted into the wedge fitting groove 13 of the top plate 12. As shown in Fig. 6A, the wedge portion 23 is a metal block, and is formed from the same metal material as the top plate 12 or a metal material having higher rigidity than the top plate 12. Such a material is, for example, stainless steel or chrome molybdenum steel (SCM).

[0031] The wedge portion 23 has a bottom surface 23a, a pair of side surfaces 23b, 23b, an upper surface 23c, a front surface 23d, and a rear surface 23e. The bottom surface 23a, the pair of side surfaces 23b, 23b, and the upper surface 23c define the cross-sectional shape of the wedge portion 23 that fits into the wedge fitting groove 13. The defined cross-sectional shape coincides with the cross-sectional shape of the wedge fitting groove 13, for example. The pair of side surfaces 23b, 23b include a pair of inclined surfaces 23s, 23s. The pair of inclined surfaces 23s, 23s faces the bottom surface 23a and is inclined with respect to the bottom surface 23a at the same angle as the pair of holding surfaces 13s, 13s.

[0032] As shown in FIG. 6B, when the wedge portion 23 is fitted into the wedge fitting groove 13, the bottom surface 23a of the wedge portion 23 comes into surface contact with the bottom surface 13a of the wedge fitting groove 13. Also, the inclined surface 23s, which is a part of the side surface 23b of the wedge portion 23, comes into surface contact with the holding surface 13s of the wedge fitting groove 13. The arrows in FIG. 5 indicate a load that deflects the top plate 12 in the Z direction with respect to the XY plane. When this load is applied to the top plate 12, a local pressure increase occurs on the periphery of the contact surface between the inclined surface 23s of the wedge portion 23 and the holding surface 13s of the wedge fitting groove 13. Then, the increase in frictional force in that portion restricts the relative movement of the wedge portion 23 and the wedge fitting groove 13 along the contact surface. In addition, the retaining surface 13s of the wedge fitting groove 13 is in surface contact with the inclined surface 23s, and the bottom surface 23a of the wedge portion 23 is in surface contact with the bottom surface 13a of the wedge fitting groove 13. Therefore, even if the bottom surface 13a (the connecting portion 19 of the top plate 12) of the wedge fitting groove 13 in the YZ plane tries to bend, the movement of the wedge portion 23 in the Z direction is restricted. Therefore, the bending of the bottom surface 13a (the connecting portion 19 of the top plate 12) is restricted. In other words, the deformation of the top plate 12 that opens the opening of the slot 16 facing the Z direction is suppressed, and the excessive reduction in the load on the blade root portion 3 in the slot 16 is suppressed. Therefore, the fan blade 1 can be stably held even during the vibration of the fan blade 1.

[0033] FIG. 7A is a perspective view showing a state before the wedge portion 23 according to the modified example is fitted into the wedge fitting groove 13 according to the modified example, and FIG. 7B is a front view showing a state after the wedge portion 23 is fitted into the wedge fitting groove 13. As shown in these figures, the pair of holding surfaces 13s, 13s in the wedge fitting groove 13 may be parallel to the bottom surface 13a. For example, the wedge fitting groove 13 includes a rectangular cross section whose long side is defined by the pair of holding surfaces 13s, 13s and the bottom surface 13a. The wedge portion 23 has a cross section complementary to this rectangular cross section and fits into the wedge fitting groove 13. In this case, the upper surface 23c of the wedge portion 23 is in surface contact with the pair of holding surfaces 13s, 13s of the wedge fitting groove 13, and the bottom surface 23a of the wedge portion 23 is in surface contact with the bottom surface 13a of the wedge fitting groove 13. That is, in this example as well, the wedge portion 23 comes into surface contact with the pair of holding surfaces 13s, 13s and the bottom surface 13a of the wedge fitting groove 13, thereby restricting the deflection of the bottom surface 13a (the connecting portion 19 of the top plate 12) of the wedge fitting groove 13. Therefore, the fan blade 1 can be stably held even during vibration of the fan blade 1.

[0034] When performing the vibration test, first, the blade root 3 of the fan blade 1 is inserted into the insertion opening 17, and then moved to the slot 16, so that the blade root 3 is positioned on the mounting surface 11a. Next, the wedge 23 is inserted into the wedge fitting groove 13 to prevent the blade root 3 from coming off the slot 16. Furthermore, while changing the target of the bolts 15 to be tightened, all the bolts 15 are gradually tightened until the desired axial force is obtained. At this time, in order to prevent only a group of bolts 15 close to each other from being extremely tightened (so-called one-sided tightening), after tightening one bolt 15, the other bolts 15 that are sufficiently distant from the one bolt 15 are tightened. As a result, the bottom surface 3b of the blade root 3 comes into contact with the mounting surface 11a, and the blade root 3 is pressed toward the mounting surface 11a by the inner surface 16a of the slot 16, so that the movement of the blade root 3 is restricted. That is, the fan blade 1 is held by the jig 10. Furthermore, due to the wedge portion 23 fitting into the wedge fitting groove 13, the jig 10 stably holds the fan blade 1 even during vibration.

[0035] The present disclosure is not limited to the above-described embodiment, but is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims.

Claims

1. A vibration test fixture for holding an end of a test specimen extending in a predetermined direction, a base including a mounting surface on which the end of the test object is placed and which is installed on a vibration table; a top plate having a slot with an inner surface for pressing the end of the test specimen toward the mounting surface and a wedge fitting groove located in an extension direction of the slot and communicating with the slot, the top plate being placed on the base with a gap therebetween; a wedge portion that fits into the wedge fitting groove; a plurality of pressing members arranged along the slot and pressing the top plate toward the base; Equipped with an inner surface of the wedge fitting groove includes a bottom surface and a pair of holding surfaces located on both sides in a width direction of the wedge fitting groove and facing the bottom surface with an internal space of the wedge fitting groove therebetween; The wedge portion is in surface contact with the bottom surface and the pair of holding surfaces. Vibration test fixture.

2. 2. The vibration test fixture according to claim 1, wherein the cross-sectional shape of the wedge fitting groove is included in the cross-sectional shape of the slot when viewed from the extending direction of the slot.

3. The pair of holding surfaces are inclined with respect to the bottom surface.

2. The vibration test fixture of claim 1.

4. The pair of holding surfaces are parallel to the bottom surface.

2. The vibration test fixture of claim 1.

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