A fixture for composite v-notched shear test and method of use

Abstract

The present application relates to a kind of clamps and using method for composite V-shaped notched piece shear test, belong to composite strength test field, by increasing the overall strength of test clamp and the mixed loading mode of end surface shear force and friction force, can effectively transmit shear load to test piece, ensure test effectiveness;The clamp comprises: upper clamp, lower clamp, two groups of clamping block assemblies and two groups of V-shaped centering clamping assembly;The inner side wall of upper clamp and lower clamp is equipped with a clamping groove;Two groups of clamping block assemblies are arranged in two clamping grooves;Each group of clamping block assemblies includes L-shaped first clamping block and square second clamping block, and the test piece to be tested is clamped between first clamping block and second clamping block;Two groups of V-shaped centering clamping assembly are arranged at the two ends of test piece not clamped, and are embedded into contact connection with the V-shaped notch of test piece, for realizing the positioning and centering of test piece in assembly process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material strength test, in particular to a clamp for high-strength composite material V-shaped notch piece shear test and a use method thereof. BACKGROUND

[0002] Shear test provides basic data for material specification, material development and research, quality assurance, structure design and analysis. The foreign test method "Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method" (ASTM D7078 / 7078M--12) provides a test method for determining the shear properties of high modulus fiber reinforced composite materials by clamping the two ends of the V-shaped notch sample on two pairs of loading rails.

[0003] Due to the gradual improvement of the performance of composite materials and the actual needs of aircraft strength design, the shear strength of the test piece for V-shaped notch shear test is increasing year by year, and the original V-shaped notch shear test clamp has the phenomena of damage before the test piece and slipping of the test piece during the loading process. The strength of the clamp and the introduction method of the shear load cannot meet the needs of the high-strength composite material V-shaped notch shear test to some extent.

[0004] Therefore, it is necessary to study a clamp for high-strength composite material V-shaped notch piece shear test to overcome the shortcomings of the prior art, so as to solve or alleviate one or more of the above problems. SUMMARY

[0005] Therefore, the present application provides a clamp for high-strength composite material V-shaped notch piece shear test, which can effectively transmit the shear load to the test piece by increasing the overall strength of the V-shaped notch shear test clamp system and the mixed loading method of the end face shear force and friction, so as to obtain effective test results.

[0006] In one aspect, the present application provides a clamp for composite material V-shaped notch piece shear test, which comprises: an upper clamp, a lower clamp, two groups of clamping block assemblies and two groups of V-shaped centering clamping assemblies.

[0007] The inner side wall of the upper clamp and the lower clamp is provided with a clamping groove; the two groups of clamping block assemblies are arranged in the two clamping grooves;

[0008] Each group of clamping block assemblies comprises a first L-shaped clamping block and a second square clamping block, and the first clamping block and the second clamping block clamp the test piece to be tested therebetween;

[0009] The two groups of V-shaped centering clamping assemblies are arranged at the two ends of the test piece which are not clamped, and are in embedded contact connection with the V-shaped notch of the test piece, for realizing the positioning and centering of the test piece during assembly.

[0010] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the upper clamp and the lower clamp each comprise an L-shaped clamp body and a connecting piece arranged at the bottom end of the L-shaped clamp body, and the connecting piece is connected with the testing machine.

[0011] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the two side walls parallel to the test piece on the clamping groove are each provided with a plurality of through fixing holes.

[0012] The outer side walls of the first clamping block and the second clamping block are each provided with a plurality of non-through fixing holes.

[0013] The non-through fixing holes and the corresponding through fixing holes are connected through clamping bolts.

[0014] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the number of non-through fixing holes on the first clamping block and the second clamping block is three, and the positions of the three non-through fixing holes form a triangle.

[0015] The number of through fixing holes on the same side wall of the clamping groove is three, and the positions of the three through fixing holes form a triangle.

[0016] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the V-shaped centering and clamping assembly comprises a V-shaped centering and clamping piece body, a boss and a spacer.

[0017] The V-shaped centering and clamping piece body is in a strip shape and has a V-shaped protruding structure in a cross section, and the V-shaped protruding structure is embedded in the V-shaped notch of the test piece.

[0018] The boss is fixedly arranged at one end of the V-shaped centering and clamping piece body, and the inner surface of the boss is in contact connection with the outer side wall of the upper clamp and / or the lower clamp.

[0019] The other end of the V-shaped centering and clamping piece body is detachably provided with the spacer.

[0020] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein the spacer is provided with a through hole, and the end surface of the V-shaped centering and clamping piece body is provided with a recessed hole with an internal thread; and the V-shaped centering and clamping piece body and the spacer are detachably connected through a centering and adjusting bolt.

[0021] According to the aspect and any possible implementation manner thereof, further provided is an implementation manner, wherein one end of the connecting piece is provided with an external thread and is in threaded connection with a threaded hole arranged on the L-shaped clamp body.

[0022] The other end of the connecting piece is provided with a through hole, and is connected with the testing machine through a pin; and the end of the connecting piece is provided with an external thread and is matched with a locking nut.

[0023] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the V-shaped centering clamp body is provided with a central axis scale, the upper clamp and the lower clamp are each provided with a centering scale parallel to the loading axis; the central axis scale and the centering scale are aligned by adjusting the screwing degree of the centering adjusting bolt, so that the centering of the test piece is realized.

[0024] In another aspect, the present application provides a use method of the clamp for the V-shaped notched composite material shear test, and the steps of the method include:

[0025] S1, a set of clamping block assemblies and one clamping end of the test piece are placed into the clamping groove of the lower clamp, and a set of V-shaped centering clamp assemblies located below are assembled on the lower clamp, and the V-shaped centering clamp assemblies are embedded into the V-shaped notch at the lower end of the test piece;

[0026] S2, another set of clamping block assemblies and another clamping end of the test piece are placed into the clamping groove of the upper clamp, and a set of V-shaped centering clamp assemblies located above are assembled between the upper clamp and the lower clamp, and the V-shaped centering clamp assemblies are embedded into the V-shaped notch at the upper end of the test piece;

[0027] S3, the assembly position is adjusted to ensure the centering of the test piece, the upper clamp and the lower clamp, and the clamping strength of the whole clamp;

[0028] S4, the two sets of V-shaped centering clamp assemblies are removed;

[0029] S5, the shear test is performed according to the requirement.

[0030] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the adjustment manner of the clamping block assembly on the test piece in steps S1, S2 and S3 is that the clamping strength of the clamping block assembly on the test piece is adjusted by adjusting the screwing degree of the clamping bolt penetrating through the side wall of the clamping groove and partially screwed into the clamping block assembly.

[0031] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects: the V-shaped notch shear test clamp system of the present application has high overall strength, the shear load can be effectively transmitted to the test piece by applying the end face and the shear force applied by the friction force in a mixed manner, and effective test results can be obtained.

[0032] Another one of the above technical solutions has the following advantages or beneficial effects: the present application can solve the problem that the existing clamp cannot meet the requirement of high shear strength of new materials in terms of clamp strength and load introduction mode;

[0033] Another one of the above technical solutions has the following advantages or beneficial effects: compared with the test clamp proposed in ASTM D7078, the present application increases the overall strength of the test clamp by improving the structural design, avoids premature destruction of the clamp due to the improvement of the performance of the measured material and the large destruction load of the test piece, uses a larger diameter and higher strength clamping bolt to avoid thread failure of the bolt caused by repeated tests, and proposes a combined loading mode of end face normal pressure and side friction of the test piece, which forms a shear stress field in the V-shaped notch area of the test piece through the L-shaped holding block end face normal pressure and side friction mixed loading mode, effectively avoids unintended relative sliding between the test piece and the holding block, and thus ensures the effectiveness of the test.

[0034] Of course, implementing any product of the present application does not necessarily require achieving all the technical effects described above. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0036] Figure 1 is a schematic diagram of the assembly structure of the test piece and the test clamp system provided by an embodiment of the present application;

[0037] Figure 2 is an upper clamp axonometric view provided by an embodiment of the present application;

[0038] Figure 3 is a lower clamp axonometric view provided by an embodiment of the present application;

[0039] Figure 4 is an L-shaped holding block axonometric view provided by an embodiment of the present application.

[0040] In the drawings:

[0041] 1, upper clamp; 2, lower clamp; 3, holding block assembly; 4, V-shaped centering clamp assembly; 5, pad; 6, test piece;

[0042] 11, upper clamp body; 12, upper connecting piece; 13, first groove; 14, first fixing hole;

[0043] 21, lower clamp body; 22, lower connecting piece; 23, second groove; 24, second fixing hole;

[0044] 31, first sub-clamping block; 32, second sub-clamping block; 33, third fixing hole. DETAILED DESCRIPTION

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

[0046] It should be clear that the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0047] A clamp for composite V-shaped notch piece shear test, comprising an upper clamp, a lower clamp, two pairs of clamping block assemblies, by tightening torque, by the clamping block to the test piece contact surface to apply pressure, and by the end surface of the L-shaped clamping block to the test piece to apply end surface load, when tensile loading, the clamp transmits shear to the test piece by composite loading.

[0048] Further, the clamp improves the design of the clamping bolt compared with the ASTM D7078 standard clamp, adopts M14 bolt, which has larger diameter, improves the maximum tightening torque that the first fixing hole 14 and the second fixing hole 24 can withstand, can withstand 110 N·m at most, compared with the tightening torque value of (45-55) N·m recommended by ASTM D7078 method, improves the clamp usage margin, so that the clamp can provide greater clamping block surface contact force, thereby improving the shear load transmitted to the test piece by the clamp through friction, which can effectively avoid the thread wear failure of the fixing hole and the clamping bolt caused by repeated tests;

[0049] Further, a set of clamping blocks is changed from the traditional two rectangles to a combination of one L-shaped and one rectangular, the contact surface of the clamping block and the test piece adopts the original tungsten carbide thermal spraying design, to introduce shear load by clamping the side surface of the test piece, the L-shaped clamping block introduces shear load by applying part of the normal pressure through contact with the end surface of the test piece, so that a mixed loading mode of normal pressure and side friction is formed, in addition, the design of the L-shaped clamping block in contact with the end surface of the test piece can effectively avoid unintended relative sliding between the test piece and the clamping block, the end surface loading provided by the L-shaped block during the test piece loading process can improve the shear load that the clamp can apply to the test piece, increase the upper limit of the shear load that the clamp can apply, avoid unacceptable damage mode of test piece and clamping block sliding, and thus obtain the shear properties of high-strength materials.

[0050] Example 1:

[0051] A fixture for composite V-notch piece shear test, the specific implementation is as follows:

[0052] 1) refer to Figure 1 , including the upper clamp 1, the lower clamp 2, two sets of clamping block assemblies 3, by tightening the torque, the contact surface of the test piece is pressed by the clamping block, and the end surface of the test piece is pressed by the end surface of the L-shaped clamping block, when the tensile load is applied, the fixture transmits the shear force into the test piece by the composite loading mode; the test piece 6 is roughly square, and V-shaped notches are respectively arranged at the upper and lower ends of the test piece; a set of V-shaped centering and clamping assemblies 4 are respectively arranged at the upper and lower ends of the clamping space between the upper clamp and the lower clamp, for clamping the V-shaped notches of the test piece; the end of the V-shaped centering and clamping assembly 4 is provided with a pad 5, which is used for pad assembly at the end of the V-shaped centering and clamping body to realize the centering of the test piece, that is, the position relative to the first groove and the second groove is appropriate; the V-shaped centering and clamping body is a strip structure, and the cross section of the V-shaped centering and clamping body is a convex V-shaped structure, which is matched with the V-shaped notch of the test piece 6. One end of the V-shaped centering and clamping body is provided with a boss, and the boss is fixedly connected with the strip-shaped V-shaped centering and clamping body; since the V-shaped centering and clamping body is arranged between the upper clamp and the lower clamp, the inner surface of the boss is in contact with the outer end surface of the upper clamp and the lower clamp during assembly, so as to limit the axial position of the V-shaped centering and clamping body; the other end surface of the V-shaped centering and clamping body is provided with a threaded hole, and the pad 5 is also provided with a through hole, and the connection between the pad and the end of the V-shaped centering and clamping body is realized through a bolt, so as to fix the V-shaped centering and clamping assembly with the upper clamp and the lower clamp; the position of the pad 5 is adjusted to realize the centering by adjusting the screwing degree of the bolt; the end surface of the upper and lower clamps is provided with a scale parallel to the loading axis, and the V-shaped centering and clamping assembly is also marked with a center axis scale, and the centering of the test piece is ensured by aligning the two lines;

[0053] After assembly is completed and before test is started, the bolt at the end of the V-shaped centering and clamping body is loosened, the pad 5 is removed, and then the V-shaped centering and clamping body is pulled out along the thickness direction of the test piece from the rear end (that is, the boss end);

[0054] 2) refer to Figure 2 , the upper clamp of the fixture, including an inverted "L" shaped upper clamp body 11 and an upper connecting piece 12 arranged at the upper end of the upper clamp body; the inner side wall of the upper clamp body is provided with a first groove 13, and a plurality of first fixing holes 14 are arranged on the two side walls of the first groove; the first fixing hole 14 is a through hole; the upper connecting piece 12 is used for connecting the test fixture system and the testing machine, one end of the upper connecting piece 12 is detachably fixedly connected with the upper clamp body through a thread, the other end is designed as a through hole matched with a connecting hole of the testing machine, and the through hole is connected through a pin; in addition, a thread is arranged on the outer surface of the upper connecting piece 12, and a nut (not shown in the figure) is matched, so as to ensure the locking after the pin of the testing machine is connected;

[0055] 3) refer to Figure 3 , the lower clamp of the clamp, comprising an "L"-shaped lower clamp body 21 and a lower connecting piece 22 provided at the lower end of the lower clamp body; the inner side wall of the lower clamp body is provided with a second groove 23, and a plurality of second fixing holes 24 are provided on the two side walls of the second groove;

[0056] 4) refer to Figure 4 , the clamping block assembly 3 of the clamp, in the two groups of clamping block assemblies, each group of clamping block assemblies 3 comprises an L-shaped first sub-clamping block 31 and a cuboid-shaped second sub-clamping block 32; the first sub-clamping block 31, the second sub-clamping block 32 and the first groove 13 or the second groove 23 are matched in size; when clamping, the second sub-clamping block 32 is located on the inner bottom end face of the first sub-clamping block 31, as shown by the arrow in Figure 4 , a gap is left between the two sub-clamping blocks, the end of the test piece is located in the gap, and the two sub-clamping blocks are assembled in the groove of the upper clamp or the lower clamp to realize clamping;

[0057] The end faces of the first sub-clamping block 31 and the second sub-clamping block 32 which do not contact the test piece are each provided with a plurality of third fixing holes 33, the third fixing holes 33 are non-through holes, i.e. one end is open, and the openings all face outward; the positions of the third fixing holes 33 match the first fixing holes or the second fixing holes; when assembling, each group of clamping blocks corresponds to a groove, i.e. the first groove or the second groove, and the first fixing holes 14 on the two side walls of the first groove are connected with the third fixing holes 33 of the corresponding group of clamping blocks by bolt connection, and the second fixing holes 24 on the two side walls of the second groove are connected with the third fixing holes 33 of the corresponding group of clamping blocks by bolt connection; when specifically connecting, the fixing holes on the same side wall of the same groove are bolted with the non-through third fixing holes on the corresponding sub-clamping blocks; since the third fixing holes are non-through holes, the end of the bolt will not pass through the sub-clamping block during fixed connection, so as to ensure that the test piece clamped between the two sub-clamping blocks will not be damaged during the tightening process of the bolt;

[0058] 5) Loosen the clamping bolts in each sub-grip block enough to allow the test piece to be freely inserted into the fixture groove, and loosely insert the test piece and the V-shaped centering fixture body into the upper and lower fixtures. The root of the V-shaped centering fixture body should be clamped so that it is securely connected to the upper and lower fixtures. Adjust the three clamping bolts on one side of the fixture, center the test piece according to the centerline marking on the V-shaped centering fixture body and the scale marking on the upper and lower fixtures, and tighten the three bolts on the side of the lower fixture by hand to lightly clamp the test piece. After confirming that the test piece notch is centered with the V-shaped centering fixture body, tighten each clamping bolt with half of the maximum tightening torque, and then tighten the bolts to the required clamping torque value. Place the second fixture (the upper fixture) on the test piece using the two V-shaped centering fixture bodies used to position the test piece when installing the first fixture (the lower fixture). Again, use the V-shaped centering fixture bodies to position the test piece when installing the second fixture block. It can be necessary to loosen the root of the V-shaped centering fixture body to connect the test piece to the second fixture, and the root of the V-shaped centering fixture body should be clamped again to securely connect it to the fixture. Tighten the clamping bolts in the same way as for the first fixture block. Connect each pair of fixtures to the upper and lower ends of the testing machine, respectively. Then remove the bolts that secure the V-shaped centering fixture body, and allow the V-shaped centering fixture body to slide freely out of the installed fixture.

[0059] 6) After the test fixture system is assembled with the test piece, connect the fixture to the testing machine through the upper connector 12 and the lower connector 22, and then remove the V-shaped centering fixture assembly to perform the shear test. The testing machine moves the crossbeam, which transmits the tensile load to the upper fixture body 11 through the connector 12. The upper fixture body 11 transmits the load to the grip block through the bolts at the fixing holes, and the grip block applies the load to the test piece through the L-shaped end face and the side face, forming a shear stress field at the V-shaped notch of the test piece, thereby measuring the shear performance.

[0060] The above provides a detailed introduction to the fixture for the shear test of the composite V-shaped notched piece according to the embodiments of the present application. The above description of the embodiments is only used to help understand the method and the core idea thereof; meanwhile, for those skilled in the art, the specific implementation and the application range can be changed according to the idea of the present application, and the above description should not be understood as a limitation on the present application.

[0061] It should also be noted that the terms "comprising", "containing", or any other similar term are intended to encompass non-exclusive inclusions, such that a product or system that comprises a list of elements does not only include those elements, but can also include other elements not expressly listed, or other elements inherent to such product or system. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of other identical elements in the product or system comprising the element. "Approximately" means within an acceptable error range, and those skilled in the art can solve the technical problem within a certain error range and substantially achieve the technical effect.

[0062] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. In this application, the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings. In addition to being used to indicate the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meanings of these terms in this application can be understood according to the specific circumstances. The term "and / or" used herein is only a description of the associated relationship between the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in this article generally represents that the front and rear associated objects have an "or" relationship.

Claims

1. A fixture for use in a shear test of a composite V-notched specimen, characterized by, The clamp comprises an upper clamp, a lower clamp, two sets of clamping block assemblies and two sets of V-shaped centering clamping assemblies; Inner side walls of the upper clamp and the lower clamp are each provided with a clamping groove; the two sets of clamping block assemblies are arranged in the two clamping grooves; Each set of clamping block assemblies comprises an L-shaped first clamping block and a square second clamping block, and the first clamping block and the second clamping block clamp a test piece to be tested therebetween; The two sets of V-shaped centering clamping assemblies are arranged at two ends of the test piece which are not clamped, and are in embedded contact connection with V-shaped notches of the test piece, for realizing positioning and centering of the test piece during assembly; Through holes are arranged on two side walls of the clamping groove which are parallel to the test piece; Non-through fixing holes are arranged on outer side walls of the first clamping block and the second clamping block; The non-through fixing holes and the corresponding through fixing holes are connected through clamping bolts, and the clamping bolts are M14 bolts; The number of the non-through fixing holes on the first clamping block and the second clamping block is three, and the positions of the three non-through fixing holes form a triangle; The number of the through fixing holes on the same side wall of the clamping groove is three, and the positions of the three through fixing holes form a triangle; The V-shaped centering clamping assembly comprises a V-shaped centering clamping piece body, a boss and a pad; The V-shaped centering clamping piece body is in a strip shape, and a cross section thereof has a V-shaped protruding structure which is embedded in the V-shaped notch of the test piece; The boss is fixedly arranged at one end of the V-shaped centering clamping piece body, and an inner surface of the boss is in contact connection with an outer side wall of the upper clamp and / or the lower clamp; The other end of the V-shaped centering clamping piece body is detachably provided with the pad; A through hole is arranged on the pad, and a female thread is arranged on an end surface of the V-shaped centering clamping piece body; the V-shaped centering clamping piece body and the pad are detachably connected through a centering adjusting bolt.

2. The fixture for composite V-notched shear test of claim 1, wherein The upper clamp and the lower clamp each comprise an L-shaped clamp body and a connecting piece arranged at a bottom end of the L-shaped clamp body, and the connecting piece is connected with a testing machine.

3. The fixture for composite V-notched shear test of claim 2, wherein, One end of the connecting piece is provided with an external thread and is in threaded connection with a threaded hole arranged on the L-shaped clamp body; The other end of the connecting piece is provided with a through hole and is connected with the testing machine through a pin; and the end of the connecting piece is provided with an external thread and is fitted with a locking nut.

4. The fixture for composite V-notched shear test of claim 1, wherein A center axis scale is arranged on the V-shaped centering clamping piece body, and a centering scale parallel to a loading axis is arranged on the upper clamp and the lower clamp; the center axis scale and the centering scale are aligned by adjusting a screwing degree of the centering adjusting bolt, so that the centering of the test piece is realized.

5. A method of using the fixture for shear testing of V-notched composite material parts according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1, a set of clamping block assemblies and a clamped end of a test piece are arranged in a clamping groove of a lower clamp, and a set of V-shaped centering clamping assemblies arranged below are assembled on the lower clamp, and the V-shaped centering clamping assemblies are embeddedly arranged in V-shaped notches of a lower end of the test piece; S2, another set of clamping block assembly and another clamping end of the test piece are put into the clamping recess of the upper clamp, and the set of V-shaped centering clamping assembly is assembled between the upper clamp and the lower clamp, and the set of V-shaped centering clamping assembly is embedded in the V-shaped notch on the upper end of the test piece; S3, the assembly position is adjusted to ensure the centering of the test piece and the upper clamp and the lower clamp, and the clamping strength of the whole clamp is ensured; S4, the two sets of V-shaped centering clamping assembly are removed; S5, the shearing test is carried out according to the requirements.

6. The method of using a fixture for composite V-notched shear test of claim 5, wherein, In steps S1, S2 and S3, the adjustment mode of the clamping block assembly to the clamping strength of the test piece is that the clamping strength of the clamping block assembly to the test piece is adjusted by adjusting the screwing degree of the clamping bolt which is threaded in the side wall of the clamping recess and partially screwed in the clamping block assembly.

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