A ca i test fixture for a composite thick sandwich panel and a clamping method thereof

Abstract

The application discloses a CAI test clamp suitable for a composite thick sandwich plate and a clamping method thereof. The CAI test clamp is composed of a bottom clamping device, a side clamping device, a top clamping device and first and second slider supporting members. The bottom clamping device is provided with a base and a front and back adjustable slider, and is used for fitting the front and back wall surfaces of a test piece. The left and right symmetrical side clamping devices are installed on the two sides of the base, and are used for fitting the left and right wall surfaces of the test piece through the back plates and the front and back adjustable sliders on the back plates. The top clamping device is used for fitting the front and back wall surfaces of the top of the test piece through a top plate and a front and back adjustable slider on the top plate. The first slider supporting member is arranged on the front and back of the base and is fixed with the side clamping device, and provides simple support constraint for the lower part and the left and right sides of the test piece through a jacking screw. The second slider supporting member is fixed on the front and back of the top plate and is used for limiting the displacement of the slider on the top plate through a jacking screw. The clamp is convenient to adjust, accurate in constraint and suitable for composite thick sandwich plates with different sizes.

Description

Technical Field

[0001] This invention relates to the field of mechanical property testing of composite sandwich structures, specifically to a CAI (compression after impact) test fixture and method for composite sandwich panels of unconventional thicknesses. Background Technology

[0002] Composite sandwich structures combine a high-stiffness skin with a low-density core material. Due to their high flexural stiffness and low structural weight, these structures are increasingly used in the aerospace industry. However, they are susceptible to impacts from various external objects, leading to different forms of initial damage and reduced residual strength. Therefore, CAI (compression after impact) testing is necessary for these sandwich structures. Currently, the standard testing method both domestically and internationally is ASTM D7137—a standard test method for the compressive residual strength of damaged polymer-based composite plates. This method uses a test fixture that transfers the compressive load of the testing machine to the specimen through top and bottom plates, and provides simply supported constraints by holding the specimen's four sides with side supports. However, this fixture is mainly designed for conventional composite plates, i.e., thin composite plates with a thickness generally within 10 mm, and cannot be applied to sandwich plates with larger thicknesses.

[0003] Therefore, there is an urgent need for a simple and reliable CAI test fixture and method that can meet the clamping requirements of thick-sized composite sandwich panels. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a CAI test fixture and clamping method for thick composite sandwich panels. The fixture features replaceable parts to accommodate specimens with a wide range of thicknesses, and is easy to disassemble while ensuring reliable loading.

[0005] The present invention relates to a CAI test fixture for thick composite sandwich panels, comprising a bottom clamping device, a side clamping device, a top clamping device, a first slider support and a second slider support.

[0006] The bottom clamping device includes a base and a base slider located at the front and rear of the center of the base. The base slider has relative displacement adjustment along the front and rear direction of the base, so that the base slider fits against the front and rear walls of the bottom of the test piece.

[0007] The side clamping device includes a left clamping device and a right clamping device, both of which have the same structure, having a base plate, a back plate perpendicular to the base plate, corner plates on both sides that are connected to the base plate and the back plate, and two corner plate sliders installed on the back side of the back plate.

[0008] The base plates of the left and right clamping devices are mounted on the sides and right side of the base, respectively, with the back plates facing each other. The base plates have relative displacement adjustment along the front-rear direction of the base, allowing the back plates to fit against the left and right walls of the test piece. The two corner plate sliders on the back plates have relative displacement adjustment along the front-rear direction of the base, and the two corner plate sliders in the left and right clamping devices fit against the front and rear walls of the left and right sides of the test piece, respectively.

[0009] The aforementioned side clamping device also features a corner rib between the two corner plates. The corner rib is integrated with the back plate and bottom plate, further providing rigidity support for the back plate. Additionally, one of the corner ribs has an elongated hole, allowing it to function as a handle to assist in the movement and adjustment of the clamp during testing.

[0010] The top clamping device includes a top plate and top plate sliders located at the front and rear positions of the top plate. The top plate sliders have relative displacement adjustment along the front and rear direction of the base, so that the top plate sliders fit against the front and rear walls of the top of the test piece.

[0011] The first slider support is a U-shaped plate structure. Two first slider support plates are respectively located at the front and rear of the base, so that the two sides of the first slider support are respectively fixed to the corner plates on the same side of the two side clamping devices by bolts. Tightening screws A are also installed on both sides and the bottom of the first slider support; the two side tightening screws A contact the two corner plate sliders on the same side as the first slider support in the left and right clamping devices respectively; the bottom tightening screw A contacts the base slider on the same side as the first slider support on the base, thereby limiting the displacement of the corner plate slider and the base slider after fixation, providing simply supported constraints for the lower part and left and right sides of the test piece.

[0012] The second slider support is a rectangular plate. The two second slider support plates are respectively bolted to the front and rear sides of the top plate. A tightening screw B is also installed on the second slider support; the tightening screw B contacts the sliding plate on the same side as the second slider support in the top clamping device, thereby limiting the displacement of the top plate slider after it is fixed.

[0013] Based on the above-mentioned specimen clamping method for CAI test fixtures of composite thick sandwich panels, the steps are as follows:

[0014] Step 1: Place the base at the geometric center of the loading position of the testing machine platform.

[0015] Step 2: Install the two side clamping devices onto the base respectively.

[0016] Step 3: Install the base slider on the left and right sides of the upper surface of the base.

[0017] Step 4: Place the test specimen at the geometric center of the base.

[0018] Step 5: Adjust the position of the two side clamping devices so that the back plate walls of the two side clamping devices are in contact with the left and right walls of the test piece and then fix them.

[0019] Step 6: Adjust the position of the two base sliders so that they are in contact with the front and rear walls of the bottom of the test piece and then fix them in place.

[0020] Step 7: Adjust the position of the corner plate sliders on both sides of the clamping device so that the two corner plate sliders in the left clamping device are attached to and fixed to the front and rear left walls of the test piece, and the two corner plate sliders in the right clamping device are attached to and fixed to the front and rear right walls of the test piece.

[0021] Step 8: Fix the two first slider supports to the corner plates on the same side of the two side clamping devices; then tighten screw A to fix the base plate slider and the corner plate slider.

[0022] Step 9: Place the top plate on top of the test piece and adjust the position of the two top plate sliders so that the two top plate sliders are in contact with the front and rear walls of the top of the test piece, respectively.

[0023] Step 10: Fix the two second slider support plates to the front and rear side walls of the top plate; then adjust the top plate so that the geometric center of the top plate coincides with the test piece, and further tighten the top plate slider by screwing in the tightening screw B.

[0024] The advantages of this invention are:

[0025] 1. This invention relates to a CAI test fixture and clamping method for thick composite sandwich panels. By replacing the bottom plate slider, top plate slider, and slider support bolts, it can adapt to composite sandwich panels with a thickness range of 10mm to 80mm, thereby reducing the waste of customizing CAI test fixtures for sandwich panels of different thicknesses.

[0026] 2. The present invention relates to a CAI test fixture and clamping method for thick composite sandwich panels. Unlike existing composite sandwich panel compression fixtures, the corner rib structure of the present invention provides sufficient rigidity support for the sides and reduces the weight of the fixture as much as possible. At the same time, a slotted design is made on one corner rib to serve as a handle to assist in the movement and adjustment of the fixture during the test.

[0027] 3. The present invention relates to a CAI test fixture and its clamping method for thick composite sandwich panels. It adopts a modular design concept, which makes the fixture easy to install, disassemble and adjust quickly on the testing machine platform, reducing the impact of the weight of the test fixture on its difficulty in movement and adjustment. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the CAI test fixture of the present invention;

[0029] Figure 2This is a schematic diagram of the bottom clamping device in the CAI test fixture of the present invention;

[0030] Figure 3 This is a schematic diagram of the base structure in the bottom clamping device;

[0031] Figure 4 This is a schematic diagram of the side clamping device in the CAI test fixture of the present invention;

[0032] Figure 5 This is a schematic diagram of the angle plate slider structure in the side clamping device;

[0033] Figure 6 This is a schematic diagram of the top clamping device in the CAI test fixture of the present invention;

[0034] Figure 7 This is a schematic diagram of the top plate slider structure in the top clamping device;

[0035] Figure 8 This is a schematic diagram of the overall structure of the first slider support in the CAI test fixture of the present invention.

[0036] Figure 9 A schematic diagram showing the hole design on the first slider support;

[0037] Figure 10 This is a schematic diagram of the overall structure of the second slider support in the CAI test fixture of the present invention;

[0038] Figure 11 This is a schematic diagram of the hole design on the second slider support.

[0039] In the picture:

[0040] 1-Bottom clamping device; 101-Base; 102-Base slider; 103-Base coarse bolt; 104-Base bolt hole A; 105-Slider strip hole; 106-Base bolt hole B;

[0041] 2-Side clamping device; 201-Base plate; 202-Back plate; 203-Angle plate; 204-Angle plate slider; 205-Angle plate coarse bolt; 206-Angle rib plate; 201a-Base plate strip hole; 202a-Back plate strip hole; 203a-Angle plate bolt hole; 204a-Angle plate slider bolt hole;

[0042] 3-Top clamping device; 301-Top plate; 302-Top plate slider; 301a-Top plate strip hole; 302a-Top plate bolt hole;

[0043] 4-First slider support; 401-Support bolt A; 402-Tightening screw A; 403-Through hole A; 404-Screw hole A;

[0044] 5-Second slider support; 501-Support bolt B; 502-Through hole B; 503-Screw hole B; 504-Tightening screw B.

[0045] 6-Test Specimen Detailed Implementation

[0046] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0047] The accompanying drawings show various structural schematic diagrams according to embodiments disclosed in this invention. The shapes of the various components and features shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design components with different shapes, sizes, and relative positions according to actual needs.

[0048] This invention provides a CAI test fixture for thick composite sandwich panels, including a bottom clamping device 1, a side clamping device 2, a top clamping device 3, and a first slider support 4 and a second slider support 5, as shown below. Figure 1 As shown.

[0049] The bottom clamping device 1 is used to clamp and fix the bottom of the CAI test specimen in the thickness direction, and includes a base 101, a base slider 102, and a base bolt 103, as shown below. Figure 2 As shown.

[0050] The base 101 is an axisymmetric rectangular plate, with a set of base bolt holes A104 symmetrically designed on the left and right sides of the center. Each set of base bolt holes A104 consists of two screw holes arranged along the front and rear direction of the base 101. Figure 3As shown. The base slider 102 is a rectangular plate; two slider slots 105 are opened along its long side on the base slider 102, and the slider slots 105 are arranged along the width direction of the base slider 102. The two base sliders 102 are located at the middle of the front and rear sides of the upper surface of the base 101, respectively. The two slider slots 105 on the base slider 102 correspond to the positions of the two sets of base bolt holes A104. After the two base bolts 103 pass through the two slider slots 105, they are threaded and tightened with the corresponding base bolt holes A104 on the left and right sides to fix the base slider 102 to the base 101. When the base bolts 103 are loosened, the position of the base slider 102 in the front-rear direction of the base 101 can be adjusted so that the two base sliders 102 contact the front and rear walls of the bottom of the test piece 6, respectively, to achieve the bottom clamping of the test piece 6. Furthermore, in this invention, when the base slide 102 is installed, two base bolt holes A104 are used in conjunction with a slider coarse bolt 103. The slider coarse bolt 103 can be connected with different base thread holes 104 to adjust the movement range of the base plate slider 102 to accommodate the clamping of test pieces 6 of different thicknesses.

[0051] The lateral clamping device 2 is used to clamp the left and right sides of the CAI test specimen in the thickness direction, and simultaneously achieves the positioning of the CAI test specimen in the left-right direction. The lateral clamping device 2 includes a left clamping device and a right clamping device, used to clamp the left and right portions of the test specimen respectively. Both have the same structure, being wedge-shaped, and include a base plate 201, a back plate 202 perpendicular to the base plate 201, corner plates 203 on both sides connecting to the base plate 201 and the back plate 202, and two corner plate sliders 204 mounted on the back side of the back plate 202. Figure 4 As shown. The base plate 201 has symmetrically arranged base plate slots 201a along its front-back direction at its left and right positions. The back plate 202 has three symmetrically arranged back plate slots 202a along its left and right sides in the vertical direction, with the slots 202a arranged along the left-right direction of the back plate 202. The corner plate slider 204 is a rectangular plate structure with three corner plate bolt holes 204a evenly spaced along its length, as shown. Figure 5 As shown. The three back plate strip holes 202a on both sides of the back plate 202 correspond to the positions of the corner plate slider bolt holes 204a on the two corner plate sliders 204. The corner plate bolts 205 are threaded through the three back plate strip holes 202a and tightened into the three corner plate slider bolt holes 204a on the corner plate sliders 204, thereby fixing the corner plate sliders 204 to the back plate 202.

[0052] The left and right clamping devices of the above structure are respectively disposed on the upper surfaces of the left and right sides of the base 101, so that the base plate strip holes 201a on both sides of the base plate 201 correspond to the positions of the three base bolt holes B106 arranged at equal intervals along the left and right directions of the base 101 on the front and rear sides of the base 101. After the three base plate bolts 206 pass through the three base plate strip holes 201a, they are threaded and tightened into the three base bolt holes B106, thereby fixing the side clamping device 2 to the base 101. Then, the test piece can be clamped in the left and right directions by the back plate 202 of the left and right clamping devices. At the same time, by loosening the corner plate bolts 205 and adjusting the positions of the two corner plate sliders 204, the two corner plate sliders 102 in the left clamping device contact the front and rear left walls of the test piece 6 respectively; the two corner plate sliders 102 in the right clamping device contact the front and rear right walls of the test piece 6 respectively, thereby achieving clamping of the left and right sides of the test piece 6.

[0053] In this invention, the length of the base plate strip hole 201a in the side clamping device 2 is slightly larger than the overall length of the three corresponding base bolt holes B106. Therefore, when the base plate coarse bolt 206 is loosened, the position of the side clamping device 2 in the left-right direction of the base 101 can be finely adjusted to accommodate machining errors in the left-right thickness of the test piece. When the base plate coarse bolt 205 is loosened, the angle plate slider 204 can be adjusted in the left-right position of the back plate 202 to prevent machining errors in the left-right width caused by variations in the thickness of the test piece during design, ensuring clamping of test pieces of different thicknesses in the left-right direction. Meanwhile, in this invention, a corner rib plate 206 is designed between the two corner plates 203 in the two side clamping devices 2. The corner rib plate 206 is connected to the back plate 202 and the bottom plate 201 as a whole. Thus, while providing sufficient rigidity support for the back plate 202 through the two corner plates 203 and the corner rib plate 206, the weight of the overall clamp is reduced as much as possible. Furthermore, an elongated hole is opened on the corner rib plate 206 in one of the side clamping devices 2, so that the side corner rib plate 206 can be used as a handle to assist in the movement and adjustment of the clamp during the test.

[0054] The top clamping device 3 includes a top plate 301 and a top plate slider 302, such as Figure 6 As shown. The top plate 301 is a rectangular plate; a set of top plate slotted holes 301a are correspondingly opened on the front and rear sides of the top plate 301, each set consisting of two slotted holes arranged along the front-rear direction of the top plate 301. The top plate slider 302 is a rectangular plate structure, with two sets of top plate bolt holes 302a equally spaced along its length, each set consisting of two bolt holes, arranged along the width direction of the top plate slider 302. Figure 7As shown. The two top plate strip holes 301a on the front and rear sides of the top plate 301 correspond to the positions of the two sets of top plate slider bolt holes 302a on the two top plate sliders 302. The top plate coarse bolts 303 pass through the two top plate strip holes 301a and are threadedly connected to the corresponding top plate slider bolt holes 302a and tightened to fix the top plate sliders 302 and the top plate 301.

[0055] The top plate 301 of the above structure is placed on top of the test piece. When the top plate coarse bolt 303 is loosened, the position of the top plate slider 302 in the front-back direction of the top plate can be adjusted to accommodate the clamping of test pieces of different thicknesses. Simultaneously, the four top plate slotted holes 301a on the top plate 301 are countersunk holes, ensuring that the top plate coarse bolt 303 does not affect the load applied to the upper surface of the top plate 301 by the testing machine. Furthermore, the connection method of the top plate slider 302 is similar to that of the base slide plate 102, that is, one top plate coarse bolt 303 is engaged with two top plate bolt holes 302a. By connecting the top plate coarse bolt 303 with different top plate bolt holes 302a, the movement range of the top plate slider 302 can be adjusted to accommodate the clamping of test pieces 6 of different thicknesses.

[0056] like Figure 8 , Figure 9 As shown, the first slider support 4 is a U-shaped plate structure. Two first slider support plates 4 are respectively set in front of and behind the base 101, so that the two sides of the first slider support 4 are respectively attached to the corner plates on the same side of the two side clamping devices 2. After the support member thick bolts A401 pass through the through holes A403 opened in the upper and lower parts on both sides of the first slider support 4, they are threadedly connected to the corner plate bolt holes 203a opened in the corresponding position of the corner plate 203 and tightened to fix the first slider support 4.

[0057] The first slider support 4 has three screw holes A404 evenly spaced vertically on both sides inside the through hole A403, corresponding to the circumferential side positions of the corner plate slider 204. Simultaneously, three screw holes B404 are also evenly spaced horizontally at the bottom of the first slider support 4, corresponding to the circumferential side positions of the base slider 102. Therefore, by tightening the tightening screws A402 into the screw holes A404 on both sides of the first slider support 4, the end of the tightening screws A402 can contact and tighten the side of the corner plate slider 204. Similarly, by tightening the tightening screws A402 into the screw holes A404 at the bottom of the first slider support 4, the end of the tightening screws A402 can contact and tighten the side of the base slider 102. Therefore, by tightening the tightening screws A402 on the first slider support 4 on the front and rear sides of the base, the corner plate sliders 204 and the base slider 102 at corresponding positions on the front and rear sides of the base 101 can be tightened respectively, thereby limiting the displacement of the corner plate sliders 204 and the base slider 102 after they are fixed, and providing simple support conditions for the lower part and left and right sides of the test piece 6. Since the simple support constraint requirements for the left and right sides of the test piece are higher than those for the upper and lower sides of the test piece, in the design of the two side clamping devices 2 in this invention, the opposite side of the two corner plate sliders 204 is designed as a conical cross-section protrusion along the longitudinal direction, and the tip of the cone is designed as a rounded corner, thereby forming a line contact between the corner plate sliders 204 and the side of the test piece 6, which can provide better simple support constraints (line constraints).

[0058] like Figure 10 , Figure 11 As shown, the second slider support 5 is a rectangular plate. The two second slider support plates 5 are respectively attached to the front and rear sides of the top plate 301. After the support bolt B501 passes through the through hole B502 opened along its length on the second slider support 5, it is threadedly connected to the top plate bolt hole 301b opened at the corresponding position on the side of the top plate 301 and tightened to fix the second slider support 5.

[0059] On the aforementioned second slider support 5, below the through hole B, three screw holes B503 are equally spaced along its length. The positions of the three screw holes B503 correspond to the circumferential side positions of the top plate slider 302. Thus, by threading the tightening screw B504 into the screw holes B504 on the second slider support 5 and tightening it, the end of the tightening screw B504 can contact and press against the side of the top plate slider 302. Therefore, by tightening the tightening screws B504 on the second slider support 5 on both the front and rear sides of the top plate 301, the two top plate sliders 302 can be pressed against each other, thereby limiting the displacement of the top plate sliders 302 after they are fixed.

[0060] The specific steps for clamping CAI test pieces using the CAI test fixture with the above structure are as follows:

[0061] Step 1: Place the base 101 at the geometric center of the loading of the testing machine platform.

[0062] Step 2: Install and fix the two side clamping devices 2 to the left and right sides of the upper surface of the base 101 using the base plate coarse bolts 206. At this time, the base plate coarse bolts 206 are only connected and not tightened; at the same time, the corner plate coarse bolts 205 connecting the corner plate slider 204 are not tightened.

[0063] Step 3: Install the base slider 102 onto the left or right position on the upper surface of the base 101 using the base bolt 103. At this time, the base bolt 103 is only connected and not tightened.

[0064] Step 4: Place the test piece at the geometric center of the base 101.

[0065] Step 5: Fine-tune the two side clamping devices 2 to the appropriate position and then fix them; at this time, the back plate walls of the two side clamping devices 2 are respectively attached to the left and right walls of the test piece.

[0066] Step 6: Adjust the two base sliders 102 to the appropriate positions and then fix them; at this time, the two base sliders 102 are respectively attached to the front and rear walls of the bottom of the test piece.

[0067] Step 7: Adjust the corner plate sliders 204 on both sides of the clamping device 2 to the appropriate position and then fix them; at this time, the two corner plate sliders 204 in the left clamping device are respectively attached to the front and rear walls of the left side of the test piece, and the two corner plate sliders 204 in the right clamping device are respectively attached to the front and rear walls of the right side of the test piece.

[0068] Step 8: Fix the two first slider supports 4 to the corner plates 203 on the same side of the two side clamping devices 2 using the support bolts A401; then screw in the tightening screws A402 and tighten them to press against the bottom plate slider 102 and the corner plate slider 204.

[0069] Step 9: Place the top plate 301 on top of the test piece and adjust the two top plate sliders 302 to the appropriate positions; at this time, the two top plate sliders 302 are respectively attached to the front and rear walls of the top of the test piece.

[0070] Step 10: Fix the two second slider support plates 5 to the front and rear side walls of the top plate 301 using the support bolts B501; then adjust the top plate 301 so that its geometric center coincides with the test piece 6, and further screw in the tightening screws B504 and tighten them to press against the top plate slider 302.

[0071] The CAI test fixture of this invention clamps and fixes the lower edge and left and right edges of the test piece using the base slider 102 and the corner slider 204, respectively. Simultaneously, the upper edge of the test piece 6 is clamped by the two top sliders 302. Furthermore, by replacing the base slider 102, corner slider 204, and top slider 302 with appropriately sized ones, the fixture can clamp test pieces 6 of different thicknesses, ensuring that it can adapt to test pieces 6 of varying thicknesses to complete the CAI test.

[0072] Extensive experiments have been conducted on standard composite laminates, i.e., thinner test pieces. The displacement at failure is generally within 2mm. Therefore, the initial displacement spacing of the CAI test fixture of this invention is designed to be 4mm, that is, the vertical distance between the bottom surface of the overall top clamping device 3 and the top of the two side clamping devices 2 is 4mm, which is sufficient to ensure no collision at failure.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A CAI test fixture for thick composite sandwich panels, characterized in that: It includes a bottom clamping device, a side clamping device, a top clamping device, a first slider support, and a second slider support; The bottom clamping device includes a base and a base slider located at the front and rear positions of the middle part of the base. The base slider has relative displacement adjustment along the front and rear direction of the base, so that the base slider fits against the front and rear walls of the bottom of the test piece; The lateral clamping device includes a left clamping device and a right clamping device, both of which have the same structure. They have a base plate, a back plate perpendicular to the base plate, corner plates on both sides that connect to the base plate and the back plate, and two corner plate sliders mounted on the back side of the back plate. The base plates of the left clamping device and the right clamping device are mounted on the side and right side of the base, respectively, and the back plates are arranged opposite to each other. The base plates have relative displacement adjustment along the front-back direction of the base, so that the back plates are respectively in contact with the left and right walls of the test piece. The two corner plate sliders on the back plate have relative displacement adjustment along the front-back direction of the base, and the two corner plate sliders in the left clamping device and the right clamping device are respectively in contact with the left and right front and rear walls of the test piece. The top clamping device includes a top plate and top plate sliders located at the front and rear positions of the top plate; the top plate sliders have relative displacement adjustment along the front and rear direction of the base, so that the top plate sliders fit against the front and rear walls of the top of the test piece. The first slider support is a U-shaped plate structure; two first slider support plates are respectively set in front of and behind the base, so that the two sides of the first slider support are respectively fixed to the corner plates on the same side of the two side clamping devices by bolts; tightening screws A are also installed on both sides and bottom of the first slider support; the two side tightening screws A contact the two corner plate sliders on the same side of the first slider support in the left clamping device and the right clamping device respectively; the bottom tightening screw A contacts the base slider on the same side of the first slider support, thereby limiting the displacement of the corner plate slider and the base slider after they are fixed, and providing simple support constraints for the lower part and the left and right sides of the test piece; The second slider support is a rectangular plate; the two second slider support plates are respectively fixed to the front and rear sides of the top plate by bolts; a tightening screw B is also installed on the second slider support; the tightening screw B contacts the sliding plate on the same side as the second slider support in the top clamping device, thereby limiting the displacement of the top plate slider after it is fixed.

2. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: The base slider is connected to the base by bolts through two slotted holes designed on it, which are respectively matched with the screw holes designed on the base. Each slotted hole corresponds to two screw holes, and the two bolts pass through the two slotted holes and are connected to a set of screw holes on the left and right respectively. The range of movement of the base slider can be adjusted by connecting the bolts to different corresponding screw holes.

3. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: The top plate slider is connected to the strip holes designed on the top plate by bolts through the screw holes designed on it; and each strip hole corresponds to two screw holes. The two bolts pass through the two strip holes and are connected to a set of screw holes on the left and right respectively. The movement range of the top plate slider can be adjusted by connecting the bolts to different corresponding screw holes.

4. The CAI test fixture for thick composite sandwich panels as described in claim 3, characterized in that: The strip-shaped holes on the top plate are countersunk holes.

5. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: The base plate has strip-shaped holes arranged in the left and right directions. The screw holes on the base plate are arranged in the left and right directions of the base and are connected by bolts. The strip holes are larger than the overall length of the bolts, so as to realize the fine adjustment of the position of the side clamping device in the left and right directions of the base, and adapt to the machining error of the thickness in the left and right directions of the test piece.

6. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: Three strip-shaped holes are symmetrically opened on the left and right sides of the back plate along the vertical direction. The strip-shaped holes are arranged along the left and right direction of the back plate and respectively cooperate with the three screw holes opened on the corner plate slider and are fixed by bolts.

7. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: A corner rib is designed between the two corner plates in the side clamping device. The corner rib is integrated with the back plate and the bottom plate, which further provides rigid support for the back plate. An elongated hole is opened on one of the corner ribs to make the corner rib a handle to assist in the movement and adjustment of the clamp during the test.

8. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: In the side clamping device, the two corner plate sliders are designed with a tapered cross section protrusion on the opposite side, and the tip of the cone is designed with a rounded corner, so that the corner plate slider and the side of the test piece form a line contact.

9. The clamping method of the CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: The specific steps are as follows: Step 1: Place the base at the geometric center of the loading position on the testing machine platform; Step 2: Install the two side clamping devices onto the base respectively; Step 3: Install the base slider on the left and right sides of the upper surface of the base; Step 4: Place the test specimen at the geometric center of the base; Step 5: Adjust the position of the two side clamping devices so that the back plate walls of the two side clamping devices are in contact with the left and right walls of the test piece and then fix them. Step 6: Adjust the position of the two base sliders so that they are in contact with the front and rear walls of the bottom of the test piece and then fix them in place; Step 7: Adjust the position of the corner plate sliders on both sides of the clamping device so that the two corner plate sliders in the left clamping device are respectively attached to and fixed to the front and rear walls of the left side of the test piece, and so that the two corner plate sliders in the right clamping device are respectively attached to and fixed to the front and rear walls of the right side of the test piece. Step 8: Fix the two first slider supports onto the corner plates on the same side of the two side clamping devices; then tighten screw A to fix the base plate slider and the corner plate slider. Step 9: Place the top plate on top of the test piece, and adjust the position of the two top plate sliders so that the two top plate sliders are in contact with the front and rear walls of the top of the test piece, respectively; Step 10: Fix the two second slider support plates to the front and rear side walls of the top plate; then adjust the top plate so that the geometric center of the top plate coincides with the test piece, and further tighten the top plate slider by screwing in the tightening screw B.

10. The CAI test fixture for thick composite sandwich panels as described in claim 1, characterized in that: The vertical distance between the bottom surface of the overall top clamping device and the top of the two side clamping devices 2 is 4mm.

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