Vibration test fixture

Abstract

A vibration test jig (10) comprises: a base (11) that includes a placing surface (11a) on which an end portion of an object under test is placed and that is installed on a shaker table; a top plate (12) that has a slot (16) having an inner surface (16a) for pressing the end portion of the object under test toward the placing surface (11a) and that is placed over the base (11) with a space therebetween; a reinforcement part (13) that is placed along the slot (16); and a plurality of pressing members (14) that press the reinforcement unit (13) toward the base (11) and that are arranged along the slot (16). The thickness of the reinforcement unit (13) varies along the slot (16) according to the magnitude of fluctuating load generated in the top plate (12) during shaking.

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, a very large load (e.g., 20 t) equivalent to the centrifugal force is applied to the root of the rotor blade. Therefore, a similar large load is applied to the jig as a reaction force.

[0006] While the test specimen is vibrating, the load on the jig varies in accordance with the vibration of the test specimen. In the case of a test specimen with a twisted shape overall, such as a rotor blade, the fluctuating load during vibration varies depending on the position in the jig. In other words, there are steadily positions where the fluctuating load is large and positions where the fluctuating load is small. Meanwhile, as mentioned above, vibration tests are carried out continuously over several days to several weeks. Therefore, plastic deformation is likely to occur in locations where the fluctuating load is relatively large. If such fatigue, such as plastic deformation, occurs partially, it becomes difficult for the jig to apply a uniform load (pressure) to the end of the test specimen, which shortens the product life (usable period) of 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 can reduce excessive fluctuating loads that occur within the fixture when a test specimen is vibrated. [Means for solving the problem]

[0008] A vibration test jig according to one embodiment 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 and 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 is placed at intervals on the base, and a plurality of pressing members that are arranged along the slot and press the reinforcing portion toward the base, and the thickness of the reinforcing portion changes along the slot depending on the magnitude of the fluctuating load generated in the top plate during vibration.

[0009] The reinforcing portion may be divided into reinforcing segments for each of the pressing members. The jig may include a plate member sandwiched between each of the pressing members and the reinforcing portion. The plate member may have a rigidity lower than that of the reinforcing portion. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a vibration test fixture capable of reducing excessive fluctuating loads generated within the fixture when a test specimen is 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 4A] FIG. 4A is a graph showing fluctuating loads at positions along the X direction in a region where a reinforcement portion is placed according to an embodiment of the present disclosure. [Figure 4B] FIG. 4B is a side view of a reinforcement portion having a thickness set based on the graph of FIG. 4A. [Figure 5A] FIG. 5A is a graph showing fluctuating loads at positions along the X direction in a region where a reinforcement portion is placed according to an embodiment of the present disclosure. [Figure 5B] FIG. 5B is a side view of a reinforcement portion having a thickness set based on the graph of FIG. 5A. [Figure 6] FIG. 6 is a side view of a modified example of a reinforcing portion according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a side view of a washer according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A jig 10 according to an embodiment of the present disclosure will now 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. 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 a plane (imaginary plane) that includes the vibration direction of the vibration table (not shown). The X direction is the extension direction of the slot 16 (see FIG. 3), and is also the direction from the side 12c to the side 12d of the top plate 12 parallel to the slot 16. The Z direction is orthogonal to the X and Y directions. The thickness of each part described below refers to the thickness (length) along the Z direction.

[0014] The jig 10 according to this embodiment is a jig for vibration testing. The jig 10 is attached on 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 (for example, 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, a reinforcing portion 13, and a plurality of pressing members 14. The pressing member 14 is formed by a bolt 15 having a threaded portion 14a and a head portion 14b integrally formed therewith. Alternatively, the pressing member 14 may be formed by a set of a threaded portion 14a formed as a stud bolt and a nut 14c screwed onto the threaded portion 14a (see Fig. 2). In the former case, the bolt 15 is tightened, and in the latter case, the nut 14c is tightened to press the reinforcing portion 13 toward the base 11. For convenience of explanation, the following description will be given taking the bolt 15 as an example of the pressing member 14.

[0019] The base 11 is a flat plate having a predetermined thickness, and is made of a highly rigid metal such as stainless steel. The thickness of the base 11 is set to a value that provides sufficient rigidity against the axial force of the bolts 15 when fastened and against stress during vibration. The base 11 is placed on a vibration table (not shown) of a vibration testing device, and is fixed with fastening members such as bolts after 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, and is placed on the base 11 with a gap therebetween. Like the base 11, the top plate 12 is also made 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 opens on the upper surface 12a of the top plate 12 and extends in the X direction. The slot 16 also opens on at least one of the side surfaces 12c, 12d (see FIG. 3) of the top plate 12 as an insertion opening 17 for the blade root 3. In the example shown in FIG. 3, the slot 16 extends from one of the side surfaces 12c, 12d of the top plate 12 to the other. In this case, the insertion opening 17 is provided on each of the side surfaces 12c, 12d of the top plate 12.

[0023] The slot 16 also opens in the lower surface 12b of the top plate 12 as an insertion opening 18 for the mounting base 11b. This insertion opening 18 penetrates from a bottom surface 16b, which is a part of the inner surface 16a of the slot 16, to the lower surface 12b of the top plate 12.

[0024] 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.

[0025] 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. Also, the width of the bottom surface 16b of the slot 16 in the Y direction is 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.

[0026] The portion of the slot 16 that includes the bottom surface 16b and extends in the Y direction functions as a connecting portion 19 that connects the plate portion 12A on one side of the slot 16 to the plate portion 12B on the other side. On both sides along the slot 16, there are formed screw holes 20 (see FIG. 2) into which the bolts 15 are screwed. The screw holes 20 are lined up at predetermined intervals in the X direction.

[0027] The reinforcing portion 13 is a flat plate-like member (rod-like member) having a predetermined width in the Y direction and extending along the slot 16 (i.e., in the X direction). The reinforcing portion 13 is placed on each of both sides along the slot 16. The reinforcing portion 13 is provided with through holes 21 (see FIG. 4B) into which the bolts 15 are inserted. The through holes 21 are arranged in the X direction at a predetermined interval. This interval is equal to the interval between the screw holes 20 adjacent in the X direction. The reinforcing portion 13 is formed of a metal material that is more rigid than the top plate 12. Such a material is, for example, chrome molybdenum steel (SCM).

[0028] The bolts 15 are arranged in the X direction on the reinforcing portion 13 and are screwed into the base 11 via the reinforcing portion 13 and 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.

[0029] 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.

[0030] However, the load on the jig 10 periodically fluctuates in accordance with the vibration of the fan blade 1. Furthermore, when a test specimen whose overall shape is twisted around the extension direction, such as the fan blade 1, is vibrated, the maximum value of the fluctuating load changes for each position in the jig 10. As described above, plastic deformation is likely to occur in locations of the jig 10 where the fluctuating load is relatively large. Furthermore, it becomes difficult for the jig 10 to apply a uniform load to the blade root 3, which shortens the product life (usable period) of the jig 10.

[0031] Therefore, in this embodiment, the thickness t of the reinforcing portion 13 varies along the slot 16 according to the magnitude of the fluctuating load generated in the top plate 12 when the fan blade 1 is vibrated. That is, when the fan blade 1 is held by the jig 10 having a configuration other than the reinforcing portion 13 and vibrated, the distribution of the fluctuating load generated in the top plate 12 is calculated in advance, and the thickness t of the reinforcing portion 13 is set according to the magnitude of the fluctuating load at each position along the slot 16 (e.g., each position of the bolt 15) in the calculated distribution. Therefore, the thickness of the reinforcing portion 13 increases as the fluctuating load increases in the area where the reinforcing portion 13 is placed. The distribution of the magnitude of the fluctuating load may be calculated by an analysis method such as a numerical analysis using the finite element method, or may be calculated from an actual measurement value by the strain sensor 22.

[0032] 4A to 5B are diagrams for explaining the setting of thickness t of reinforcing portion 13. Fig. 4A and Fig. 5A are graphs showing an example of fluctuating load at a position along the X direction in the region where reinforcing portion 13 is placed. Fig. 4B is a side view of reinforcing portion 13 having a thickness set based on the graph of Fig. 4A. Fig. 5B is a side view of reinforcing portion 13 having a thickness set based on the graph of Fig. 5A.

[0033] As shown in Fig. 4A, when the maximum value of the fluctuating load at a certain position increases as the position moves in the X direction, as shown in Fig. 4B, the thickness t of the reinforcing part 13 at a certain position also increases as the position moves in the X direction. The thickness of the top plate 12 may increase stepwise for each position of the through hole 21 as shown in Fig. 4A, or may increase continuously. In either case, the portion with which the head part 14b of the bolt 15 comes into contact is formed as a plane perpendicular to the insertion direction of the bolt 15 (the opposite direction to the Z direction in this embodiment).

[0034] As shown in Fig. 5A, when the maximum value of the fluctuating load at a certain position decreases as the position moves in the X direction, as shown in Fig. 5B, the thickness t of the reinforcing part 13 at a certain position also decreases as the position moves in the X direction. However, as described above, the thickness of the top plate 12 may decrease stepwise for each position of the through-hole 21 as shown in Fig. 5A, or may decrease continuously.

[0035] The distribution of the maximum values ​​of the fluctuating load along the X direction varies depending on the shape, dimensions, and material of the fan blade 1 (i.e., the test specimen) held by the jig 10, the vibration direction of the fan blade 1, and the like. Accordingly, the thickness t of the reinforcement part 13 at each position along the X direction is also set. Therefore, the change in the thickness t of the reinforcement part 13 at each position along the X direction is not limited to a monotonous increase or decrease.

[0036] According to this embodiment, by placing the reinforcing portion 13 on the top plate 12, it is possible to increase the rigidity of the portion where the fluctuating load was large. Therefore, it is possible to reduce the excessive fluctuating load generated in the jig 10 when the test object is vibrated. As a result, the unevenness of the load distribution is also mitigated, the progress of localized plastic deformation can be suppressed, and a uniform load (pressure) on the end portion of the test object can be maintained. In other words, it is possible to suppress the shortening of the product life (usable period) of the jig 10.

[0037] 6 is a side view of a modified example of the reinforcing portion 13 according to this embodiment. As shown in this figure, the reinforcing portion 13 may be divided into reinforcing segments 13S for each bolt 15 (pressing member 14). In this case, reinforcing segments 13S of different thicknesses can be used and arranged in accordance with the distribution of various fluctuating loads. For example, a reinforcing portion 13 having a thickness that matches changes in the vibration mode of a test specimen can be configured simply by changing the arrangement of the reinforcing segments 13S.

[0038] 7 is a side view of the plate member 23 according to this embodiment. The jig 10 according to this embodiment may include the plate member 23 that is sandwiched between the bolt 15 (pressing member 14) and the reinforcing portion 13. The plate member 23 has an insertion hole 24 through which the screw portion 14a is inserted, and is formed, for example, in an annular shape.

[0039] The rigidity of the plate member 23 is lower than that of the reinforcing portion 13, for example, 1 / 2 or less of the rigidity of the reinforcing portion 13. The material of the plate member 23 is selected from light metals such as aluminum and magnesium, hard rubber, hard resin, etc. Plate members made of different materials may be stacked.

[0040] When holding the fan blade 1, the bolts 15 to be tightened are changed and gradually tightened until the desired axial force is obtained. At this time, in order to prevent only a group of bolts 15 that are close to each other from being extremely tightened (so-called uneven tightening), after tightening one bolt 15, the other bolts 15 that are sufficiently distant from that one bolt 15 are tightened.

[0041] On the other hand, the base 11, top plate 12, reinforcing portion 13, and pressing member 14 are made of metals with relatively high rigidity, such as stainless steel and SCM, to avoid excessive deformation due to the load. Therefore, even if the bolt 15 is tightened only slightly, the axial force of the bolt 15 increases rapidly. In addition, an extreme increase in the axial force may cause the axial force of the adjacent bolts 15 to decrease. In other words, since the increase in the axial force per one turn of the bolt 15 is large, it is difficult to tighten the bolts appropriately, and it takes a huge amount of time to perform the work to obtain the above-mentioned uniform axial force.

[0042] When the bolt 15 is tightened, the plate member 23 is sandwiched between the head portion 14b of the bolt 15 and the reinforcing portion 13. Because the plate member 23 is softer than the reinforcing portion 13, the increase in axial force per rotation of the bolt 15 is reduced compared to when the plate member 23 is not provided. In other words, the rotation angle of the bolt 15 required to obtain a desired increase in axial force can be increased. This makes it easier to adjust the axial force of the bolt 15, easing the work required to obtain a uniform axial force for multiple bolts 15 (pressing members 14), and allowing the reinforcing portion 13 and the top plate 12 to be attached to the base 11 with an appropriate axial force.

[0043] 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 an inner surface with a slot for pressing the end of the test specimen toward the placement surface, the top plate being placed on the base with a gap therebetween; a reinforcing portion that is placed on the top plate along the slot; a plurality of pressing members arranged along the slot and pressing the reinforcing portion toward the base; Equipped with The thickness of the reinforcing portion varies along the slot in accordance with the magnitude of the fluctuating load generated in the top plate during vibration. Vibration test fixture.

2. The reinforcing portion is divided into reinforcing segments for each of the pressing members.

2. The vibration test fixture of claim 1.

3. a plate member sandwiched between each of the pressing members and the reinforcing portion, The plate member has a rigidity lower than that of the reinforcing portion.

3. A vibration test fixture according to claim 1 or 2.

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