Device and usage method for pull-off test of composite material fasteners

Abstract

The present invention relates to a device and a usage method for a pull-off test of composite fasteners, belonging to the technical field of aircraft strength tests, capable of ensuring that the test piece and the loading axis of the testing machine meet the centering requirements during the assembly process and realizing the rapid installation of the test piece; the device includes a base, an upper cover plate, a connecting rod and a centering assembly; during centering, the centering assembly is centered and connected to the upper cover plate, and the lower section of the connecting rod is centered and connected to the centering assembly; the centering connection is specifically a connection without horizontal displacement; the upper section of the connecting rod is fixedly connected to the testing machine; the base and the upper cover plate are fixedly connected; the base is fixedly connected to the testing machine; the test piece includes a composite material plate and a lug fixedly arranged on its upper surface; during the test, the base is fixedly connected to the testing machine, and the base and the upper cover plate are fixedly connected; the composite material plate is located in the space between the base and the upper cover plate, and the lug passes through the upper cover plate and is connected to the lower section of the connecting rod; the upper section of the connecting rod is fixedly connected to the testing machine.

Description

Technical Field

[0001] The invention relates to the technical field of aircraft strength testing, and in particular to a device for a pull-off test of a composite material fastener and a use method thereof. Background Art

[0002] Fastener connection is an important connection form in the field of aircraft design. In order to obtain the structural design allowable value of fastener pull-off, ASTM D7332 / D7332M-16 "Test method for measuring pull-off resistance of fiber-reinforced polymer matrix composite fasteners" is usually used for testing. According to ASTM D7332 / D7332M-16 method B, the test fixture is divided into two parts. The lower end contains a slotted part with a clearance hole, which is connected to the fixed chuck of the test machine to fix the test piece. The upper end is connected to the test piece through an ear fork to achieve loading. In order to obtain accurate and effective test data, when assembling the test piece and the test fixture, it is necessary to ensure that the test piece and the loading axis of the test machine coincide. Since the slotted part has a clearance hole, misalignment may occur when the test piece is installed. If the test piece is inconsistent with the loading direction during the assembly process, the fastener will be subjected to shear force caused by additional bending moment, which may cause the test failure mode to be invalid or the result to be inaccurate.

[0003] Chinese invention patent 201521005076.X discloses an adjustable fastener pull-off impedance test fixture, including a grooved part with a positioning step; an ear fork with a positioning circular groove; through the simple assembly of the above parts, it can be used to meet the requirements of ASTMD7332 / D7332M-09 standard for the pull-off impedance measurement of fasteners with specifications of φ10 and below. Applying this solution, all test pieces need to be reassembled with the ear fork after completion, which is suitable for a small number of tests. The repeated assembly of the test pieces themselves brings new problems. The first is whether the test unit has the qualifications to assemble the composite test piece with the ear fork through fasteners. Secondly, after the test piece is assembled, there are a series of processes, inspections and other technical and quality processes. If it is an airworthiness test, it will also involve the authority's manufacturing inspection and test witnessing, which will reduce the efficiency of the entire test. At present, in the fastener pull-off test carried out in the composite material connection design, the test pieces are manufactured in batches and furnaces according to the materials and processes. The manufacturing unit and the test unit are usually carried out separately. After the design party determines the test piece configuration, the fasteners and ear forks are fixed, and then batch production will be carried out, and the problem of adjustable bosses and ear forks will no longer be involved. Therefore, this adjustable fastener pull-off impedance test fixture is not suitable for large-scale allowable value tests.

[0004] Therefore, it is necessary to develop a new device for pull-off testing of composite fasteners to address the deficiencies of the prior art and to solve or alleviate one or more of the above problems. Summary of the invention

[0005] In view of this, the present invention provides a device and a use method for the pull-off test of composite fasteners, which can solve the problem of test alignment, ensure that the test piece and the loading axis of the testing machine meet the alignment requirements during the assembly process, and realize the rapid installation of the test piece.

[0006] On the one hand, the present invention provides a device for the pull-off test of composite fasteners, including a base, an upper cover plate, a connecting rod, and an alignment assembly;

[0007] During alignment, the alignment assembly is connected to the upper cover plate in an aligned manner, and the lower section of the connecting rod is connected to the alignment assembly in an aligned manner; the aligned connection is specifically a connection without horizontal displacement; the upper section of the connecting rod is fixedly connected to the testing machine; the base and the upper cover plate are fixedly connected; the base is fixedly connected to the testing machine;

[0008] During the test, the base is fixedly connected to the testing machine, and the base and the upper cover plate are fixedly connected; the test piece includes a composite material plate and a lug fixedly arranged on the upper surface of the composite material plate; the composite material plate is located in the space between the base and the upper cover plate, and the lug passes through the upper cover plate and is connected to the lower section of the connecting rod; the upper section of the connecting rod is fixedly connected to the testing machine.

[0009] In the above aspect and any possible implementation manner, a further implementation manner is provided, where the alignment assembly includes an alignment plate, an alignment boss, and a first alignment through hole;

[0010] The alignment boss is arranged on the upper surface of the alignment plate, and the first alignment through hole is arranged in the middle of the alignment boss; the shape and size of the first alignment through hole match the lower section of the connecting rod, and the lower section of the connecting rod is inserted into the first alignment through hole to achieve aligned connection.

[0011] In the above aspect and any possible implementation manner, a further implementation manner is provided, where the upper cover plate is provided with a second alignment through hole, and the shape and size of the second alignment through hole match the alignment boss;

[0012] The alignment boss is embedded in the second alignment through hole to achieve aligned connection.

[0013] In the above aspect and any possible implementation manner, a further implementation manner is provided, where the upper cover plate is an inverted U-shaped structure; a through hole for the lug to pass through is provided at the top of the upper cover plate; threaded holes are provided at the bottom of the upper cover plate, and the upper cover plate is fixedly connected to the base through bolts.

[0014] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. A pin connection hole is provided in the upper section of the connecting rod, and a thread is provided on the outside of the upper section and is equipped with a locking nut; the pin connection hole is pin-connected to the testing machine, and the locking nut is tightened to realize the locking and fixing of the connecting rod and the testing machine.

[0015] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. A pin connection hole is provided in the lower section of the connecting rod, and the pin connection hole is pin-connected to the ear fork.

[0016] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. The second centering through hole and the hole on the upper cover plate for the ear fork to pass through are the same through hole.

[0017] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. The upper section of the connecting rod is a cylindrical rod, and the lower section of the connecting rod is a rectangular rod.

[0018] On the other hand, the present invention provides a usage method of the device for the pull-off test of composite material fasteners as described above in any one. The steps of the method include:

[0019] S1. Assemble the upper cover plate, the base and the testing machine to realize the assembly connection among the three;

[0020] S2. Centrally connect the centering assembly with the upper cover plate;

[0021] S3. Centrally connect the connecting rod with the centering assembly;

[0022] S4. According to the result of the central connection in S3, perform the fixed connection between the connecting rod and the testing machine;

[0023] S5. Remove the centering assembly;

[0024] S6. Connect the ear fork of the test piece with the connecting rod;

[0025] S7. Perform the pull-off test.

[0026] For the aspects and any possible implementation manners as described above, a further implementation manner is provided. When removing the centering assembly and connecting the ear fork with the connecting rod, the vertical displacement of the connecting rod is realized by adjusting the testing machine, which is convenient for removing the centering assembly and connecting the ear fork with the connecting rod.

[0027] Compared with the prior art, one of the technical solutions in the above technical solutions has the following advantages or beneficial effects: The solution of the present invention conducts relevant tests based on a test piece with a determined configuration. The entire device includes a connecting rod, an upper cover plate, a base, and a centering assembly. Each part forms an assembly relationship through mechanical connection, and can be used for the test of measuring the pull-off impedance of composite fasteners to meet the requirements of ASTM D7332 / D7332M-16 standard, realizing rapid and accurate installation and testing; The connection form, test centering design, application scope, etc. of the technical solution of the present invention are significantly different from those of Chinese invention patent 201521005076.X;

[0028] Another one of the above technical solutions has the following advantages or beneficial effects: The centering assembly and the connecting rod of the present invention ensure that the test piece is consistent with the loading direction of the testing machine, reducing the test installation error and improving the test accuracy and assembly efficiency;

[0029] Another one of the above technical solutions has the following advantages or beneficial effects: The number of the whole set of test tooling is small, the assembly is simple, realizing rapid and accurate installation of the test piece, improving the overall test efficiency, and being beneficial to the rapid design verification of the structural design allowable value of the fastener pull-off.

[0030] Of course, it is not necessary for any product implementing the present invention to achieve all the above-mentioned technical effects simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 is a schematic assembly structure diagram of a test piece and a test fixture system provided by an embodiment of the present invention;

[0033] Figure 2 is an axonometric view of a centering assembly provided by an embodiment of the present invention;

[0034] Figure 3 is an axonometric view of a connecting rod provided by an embodiment of the present invention;

[0035] Figure 4 is an axonometric view of an upper cover plate provided by an embodiment of the present invention;

[0036] Figure 5 is an axonometric view of a base provided by an embodiment of the present invention;

[0037] Figure 6It is an isometric view of a test piece provided by an embodiment of the present invention.

[0038] Among them, in the figure:

[0039] 1. Base; 2. Upper cover plate; 3. Connecting rod; 4. Centering component; 5. Test piece;

[0040] 11. Base body; 12. Base connecting column; 13. Upper cover plate fixing hole;

[0041] 21. Centering round hole; 22. Cover plate fixing hole;

[0042] 31. Cylindrical section; 32. Rectangular section; 33. Locking nut;

[0043] 41. Centering square plate; 42. Circular boss; 43. Centering through hole;

[0044] 51. Test piece square plate; 52. Fork. Detailed implementation manners

[0045] In order to better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0047] The purpose of the present invention is to provide a device for the pull-off test of composite fasteners for the performance test and structural verification of the pull-off test of composite fasteners based on a test piece with a determined configuration. In Method B of ASTM D7332 / D7332M-16 standard, the test fixture is a split type, which is respectively connected to the upper and lower chucks of the testing machine. Currently, there are usually two ways to connect the upper and lower chucks of the testing machine, namely pin connection and threaded connection. However, no matter which way, due to assembly tolerances, the upper and lower test fixtures may deviate from the center after being tightened. And there is a 2-mm gap between the fixed end of the fixture described in the standard and the test piece during assembly. In the actual test process, it is easy to cause misalignment problems. The test device proposed by the present invention can easily ensure the centering requirement of the test piece and the loading axis of the testing machine. When the upper and lower parts of the test fixture are connected to the testing machine, it can easily realize the initial centering adjustment of the fixture, reasonable loading during the test process, and rapid installation of the test piece, while improving the overall test efficiency and preventing the test from being invalid or inaccurate due to test assembly errors.

[0048] The pull-off test device for composite material fasteners includes a connecting rod (connected to a testing machine), an upper cover plate, a base (connected to the testing machine), and a centering component. The components are mechanically connected to form an assembly relationship. During actual use, the test fixture itself and the test piece can be centered twice, thus ensuring the loading accuracy. The upper cover plate and the base are connected by M10 bolts. The connecting rod and the base are respectively connected to the upper and lower chucks of the testing machine through pins matching the diameter of the reserved connection holes of the testing machine and locking nuts on the connecting rod. The first centering of the above two centerings is achieved through the centering component. The centering component is a part with a circular boss. The diameter of the boss is the same as the diameter of the round hole of the upper cover plate. A rectangular hole is designed in the center of the boss, and the size of the rectangle is the same as the rectangular cross-section size of the connecting rod. The four corners of the rectangular hole adopt a design feature of eliminating chamfers to ensure the assembly of the connecting rod and the centering component. After ensuring the centering of the connecting rod and the base through the centering component, tighten the locking nut, and then remove the centering component, thus realizing the centering of the test fixture itself. The ear fork of the test piece passes through the centering round hole of the base and is connected to the connecting rod through a force-transmitting pin. The thickness dimension of the connecting rod is the same as the ear fork spacing to ensure the centering of the test piece in the axial direction of the connecting rod hole. The holes of the connecting rod and the ear fork of the test piece are connected by a pin rod, thus ensuring the centering of the test piece in the direction perpendicular to the axis of the connecting rod hole. After the test piece is centered in both directions, the test piece and the test loading direction are on the same axis.

[0049] Embodiment 1:

[0050] The specific implementation manner of a pull-off test device for composite material fasteners is as follows:

[0051] 1) As Figure 1 shown, a device for the pull-off test of composite material fasteners includes a connecting rod 3, an upper cover plate 2, a base 1, and a centering component 4; the centering component 4 is mainly used for the first centering of this test, that is, to ensure the centering among the loading axis of the testing machine, the connecting rod 3, the upper cover plate 2, and the base 1 when the test fixture and the testing machine are installed.

[0052] 2) As Figure 2As shown, it is the centering component 4 of the fixture. The centering component 4 includes a centering square plate 41 and a circular boss 42 provided in the middle of the square plate. A rectangular centering through-hole 43 for the connecting rod to pass through is provided in the middle of the boss. Arc-shaped expansion holes are provided at the four corners of the centering through-hole 43, so as to eliminate chamfers and facilitate the assembly of the connecting rod and the centering component. During assembly, pre-assembly is carried out through the centering component. The circular boss 42 of the centering component 4 is assembled into the centering circular hole 21 of the upper cover plate 2 to achieve positioning. The outer diameter of the circular boss 42 is the same as the inner diameter of the centering circular hole 21, which can ensure that the circular boss is embedded in the circular hole and the two are in close contact, thus ensuring the accuracy of positioning. The rectangular cross-section size at one end of the connecting rod matches the centering through-hole 43. When the test device is centered and installed for the first time, the test piece is not involved. The base 1 is connected to the lower chuck of the test piece, and the connecting rod 3 is connected to the upper chuck of the testing machine. After the base 1 and the connecting rod 3 are respectively connected to the testing machine through pins, before tightening their respective lock nuts, the base 1, the upper cover plate 2, and the connecting rod 3 are centered and positioned through the centering component 4. Then, the lock nut of the base 1, the connecting bolt between the base 1 and the upper cover plate, and the lock nut of the connecting rod 3 involved in the test device are tightened in sequence. The existence of the centering component 4 can ensure the centering of the fixture and the testing machine. After all the bolts are tightened, the connecting rod 3 can be separated from the centering component 4 by lifting the crossbeam of the test piece, and then the centering component 4 can be taken out;

[0053] 3) As Figure 3 shown, it is the connecting rod 3 of the fixture, which is divided into two sections: the upper section is a cylindrical section 31, and the lower section is a rectangular section 32. The rectangular section is provided with a pin connection hole for pin connection with the through-hole on the ear fork of the test piece, and the load is transmitted to the fastener and the composite material through the ear fork on the test piece 5. The structure of the test piece is as Figure 6 shown, including a test piece square plate 51 and an ear fork 52 provided on the square plate. The ear fork 52 is in a "U" shape, and symmetric through-holes are provided on its two side walls. The through-holes match the pin connection holes of the rectangular section of the connecting rod for their pin connection. After the ear fork of the test piece passes through the centering hole of the upper cover plate from bottom to top, it is pin-connected to the connecting rod. The load is transmitted to the ear fork through the connecting rod, and the composite material plate (i.e., the test piece square plate 51) of the test piece is restricted by the upper cover plate, thereby applying a pull-off load to the fastener (i.e., testing the connection strength between the ear fork and the test piece square plate). A pin connection hole is also provided near the upper end of the cylindrical section of the connecting rod for pin connection with the testing machine. An external thread is also provided on the outer surface of the cylindrical section of the connecting rod and is equipped with a lock nut 33 for locking after the connecting rod is pin-connected to the testing machine;

[0054] 4) As Figure 4As shown in the figure, it is the upper cover plate 2 of the fixture. The upper cover plate 2 is integrally in an inverted U shape. Its top is provided with a centering round hole 21. Both bottoms respectively have extension parts, and the extension parts are provided with more than two cover plate fixing holes 22 for being fixed together with the base through fixing bolts; when a pull-off load is applied to the fastener, the upper cover plate is used to limit the displacement of the composite material plate of the test piece along the pull-off direction; the designed height of the upper cover plate needs to be greater than the overall height dimension of the test piece along the axis direction of the fastener to be measured to meet the assembly of the test piece.

[0055] 5) As Figure 5 As shown in the figure, it is the base 1 of the fixture. The base 1 includes a base body 11 and base connection columns 12; the base body is in a rectangular plate shape, and four base connection columns are provided at the bottom of the rectangular plate shape; each of the four base connection columns 12 is provided with a pin connection hole for connecting with the testing machine. The outer surface of the base connection column is provided with an external thread and is equipped with a locking nut for locking after the base connection column is pin-connected with the testing machine; the rectangular plate shape is provided with upper cover plate fixing holes 13, which match the bolt holes at the bottom extension part of the upper cover plate, and the upper cover plate and the base are fixedly connected through fixing bolts.

[0056] The steps of the usage method of the above device for the pull-off test of composite material fasteners include:

[0057] S1. Assemble the upper cover plate, the base and the testing machine to achieve the assembly connection among the three;

[0058] S2. Centrally connect the centering assembly with the upper cover plate;

[0059] S3. Centrally connect the connecting rod with the centering assembly;

[0060] S4. According to the result of the central connection in S3, fixedly connect the connecting rod with the testing machine;

[0061] S5. Remove the centering assembly;

[0062] S6. Connect the fork of the test piece with the connecting rod;

[0063] S7. Conduct the pull-off test.

[0064] When removing the centering assembly and connecting the fork with the connecting rod, adjust the testing machine to realize the displacement of the connecting rod in the vertical direction, which is convenient for removing the centering assembly and connecting the fork with the connecting rod.

[0065] The above has introduced in detail a device for the pull-off test of composite material fasteners provided by the embodiments of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation of the present application.

[0066] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a commodity or system including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent in such a commodity or system. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the commodity or system including the said element. "Roughly" means within an acceptable error range, and those skilled in the art can solve the said technical problem within a certain error range and basically achieve the said technical effect.

[0067] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. In the present application, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. In addition to being able to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present application can be understood according to specific circumstances. The term "and / or" used herein is only a description of the associated relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

Claims

1. A device for the pull-off test of composite material fasteners, characterized in that, it includes a base, an upper cover plate, a connecting rod and a centering component; During centering, the centering component is centered and connected to the upper cover plate, and the lower section of the connecting rod is centered and connected to the centering component; the centered connection is specifically a connection without horizontal displacement; the upper section of the connecting rod is fixedly connected to the testing machine; the base and the upper cover plate are fixedly connected; the base is fixedly connected to the testing machine; During the test, the base is fixedly connected to the testing machine, and the base and the upper cover plate are fixedly connected; the test piece includes a composite material plate and a fork fixedly arranged on the upper surface of the composite material plate; the composite material plate is located in the space between the base and the upper cover plate, and the fork passes through the upper cover plate and is connected to the lower section of the connecting rod; the upper section of the connecting rod is fixedly connected to the testing machine; The centering component includes a centering plate, a centering boss and a first centering through hole; The centering boss is arranged on the upper surface of the centering plate, and the first centering through hole is arranged in the middle of the centering boss; the shape and size of the first centering through hole match the lower section of the connecting rod, and the lower section of the connecting rod is inserted into the first centering through hole to achieve centering connection; The upper cover plate is provided with a second centering through hole, and the shape and size of the second centering through hole match the centering boss; The centering boss is embedded in the second centering through hole to achieve centering connection; The upper section of the connecting rod is a cylindrical rod, and the lower section of the connecting rod is a rectangular rod.

2. The device for the pull-off test of composite material fasteners according to claim 1, characterized in that, the upper cover plate is an inverted U-shaped structure; a through hole for the fork to pass through is provided at the top of the upper cover plate; threaded holes are provided at the bottom of the upper cover plate, and it is fixedly connected to the base through bolts.

3. The device for the pull-off test of composite material fasteners according to claim 1, characterized in that, a pin connection hole is provided on the upper section of the connecting rod, and the outside of the upper section is provided with threads and is equipped with a locking nut; the pin connection hole is pin-connected to the testing machine, and the locking nut is tightened to achieve the locking and fixing of the connecting rod and the testing machine.

4. The device for the pull-off test of composite material fasteners according to claim 1, characterized in that, a pin connection hole is provided on the lower section of the connecting rod, and the pin connection hole is pin-connected to the fork.

5. The device for the pull-off test of composite material fasteners according to claim 1, characterized in that, the second centering through hole and the hole on the upper cover plate for the fork to pass through are the same through hole.

6. A method for using the device for the pull-off test of composite material fasteners according to any one of claims 1-5, characterized in that, the steps of the method include: S1. Assemble the upper cover plate, the base and the testing machine to achieve the assembly connection among the three; S2. Centeringly connect the centering component to the upper cover plate; S3. Centeringly connect the connecting rod to the centering component; S4. According to the result of the centering connection in S3, fixedly connect the connecting rod and the testing machine; S5. Remove the centering component; S6. Connect the fork of the test piece with the connecting rod; S7. Conduct a pull-off test.

7. According to the method of using the device for the pull-off test of composite material fasteners as claimed in claim 6, characterized in that when removing the centering component and connecting the fork with the connecting rod, the displacement of the connecting rod in the vertical direction is realized by adjusting the testing machine, which facilitates the removal of the centering component and the connection of the fork with the connecting rod.

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