Composite material curved plate outer pressure and shear combined action test piece and loading method

Abstract

The present application relates to a kind of composite material curved plate outer pressure and shearing combined action test piece and loading method, the test piece includes composite material curved plate, composite material curved plate straight edge clamping frame and composite material curved plate curved edge clamping frame, the straight edge of composite material curved plate and the curved surface near it are clamped in the middle by straight edge clamping upper frame and straight edge clamping lower frame, the curved edge of composite material curved plate and the curved surface near it are clamped in the middle by curved edge clamping upper frame and curved edge clamping lower frame, the test piece can be applied shearing load and outer pressure load by experimental device, test piece buckles under the combined action of outer pressure and shearing stress.The test piece of the present application first obtains shearing stress on test piece by applying shearing load, then fixes test piece, the advantage of this operation is that shearing stress will affect the buckling behavior of test piece under outer pressure, and this influence is controllable.

Description

Technical Field

[0001] This invention relates to a composite curved plate test specimen subjected to combined external pressure and shear and a loading method, belonging to the fields of aerospace experiment and composite structural mechanics. Background Technology

[0002] As aircraft speeds increase and service environments become more extreme, the buckling problem of composite curved plate structures under combined external pressure and shear loads must be considered. Some aircraft exhibit significant buckling deformation of composite curved plate airfoils under the combined effects of aerodynamic pressure and shear loads during high-speed maneuvering. Therefore, the buckling problem of composite curved plate airfoil skin under combined aerodynamic pressure and shear loads must be taken into account. Composite material submersibles, during deep-sea navigation, experience the combined effects of seawater pressure and shear loads on their composite curved plate structures. On June 18, 2023, the "Titan" composite material structure submersible conducted its first commercial manned dive, losing contact after 1 hour and 45 minutes of descent, and was last detected at a depth of 3800 meters. Research confirmed that the submersible had imploded. Composite material structures have certain advantages in withstanding internal pressure (fibers primarily bear tensile force), but their ability to withstand external pressure is relatively weaker, especially their buckling resistance under external pressure. When a sealed composite structure buckles under external pressure, the air inside the sealed structure is compressed rapidly, which increases the possibility of the composite structure imploding.

[0003] Currently, there are no reports, either domestically or internationally, on the combined effects of external pressure and shear loads on composite curved plate structures, and corresponding experimental specimens are lacking for such research. Compared to composite flat plate shear specimens, the clamping of the curved plate edges and nearby curved surfaces is more complex, requiring special design details for the clamping frame. Applying the combined external pressure and shear loads to composite curved plate structures is a challenge, and domestic reports are scarce. The inventors previously proposed a method for applying external pressure and shear loads to composite flat plate structures, where shear loads and external pressure are simultaneously and directly applied to the specimen through a special operation. However, research revealed several problems: when applying shear loads, the small sliding plate needs to be in a sliding state, which can cause uncontrollable interference to the buckling deformation of the specimen under external pressure. For example, when the curved plate buckles externally, it may pull or push the small sliding plate uncontrollably. This invention addresses these problems by designing an experimental specimen for studying the buckling behavior of composite curved plates under the combined effects of external pressure and shear loads. Summary of the Invention

[0004] The problems to be solved by this invention are: design and loading method of test specimens for the combined action of external pressure and shear load on composite curved plates; design of clamping and clamping frame for the straight edge and nearby curved surface of composite curved plates; design of clamping and clamping frame for the curved edge and nearby curved surface of composite curved plates; and application and control of the combined application of shear load and external pressure on the test specimen.

[0005] The technical solution adopted by this invention to solve the technical problem is: a composite curved plate test specimen and loading method under combined external pressure and shear stress. The test specimen comprises three parts: a composite curved plate, a straight-edge clamping frame for the composite curved plate, and a curved-edge clamping frame for the composite curved plate. The straight-edge clamping frame for the composite curved plate includes an upper straight-edge clamping frame and a lower straight-edge clamping frame. The straight edge of the composite curved plate and its adjacent curved surface are clamped in the middle by the upper and lower straight-edge clamping frames and fixed by countersunk screws. The curved-edge clamping frame for the composite curved plate includes an upper curved-edge clamping frame and a lower curved-edge clamping frame. The curved edge of the composite curved plate and its adjacent curved surface are clamped in the middle by the upper and lower curved-edge clamping frames and fixed by countersunk screws. This test specimen can be subjected to shear load and external pressure load through an experimental device, and the test specimen buckles under the combined action of external pressure and shear stress. The experimental device consists of a pressure vessel and a clamping system, which consists of a pair of large sliding plates and a pair of small sliding plates. The composite curved plate test specimen and the small sliding plates are rotatably connected by a rotating connecting pin. The large slide plate has a U-shaped groove at its end, which mates with the side flange of the small slide plate. The small slide plate also has a U-shaped groove at its end. The installation sequence of the small slide plate, the test piece, and the large slide plate is as follows: First, slide a small slide plate into the large slide plate to the appropriate position and fix it to the large slide plate with screws. Then slide in the test piece, with the clamping part of the test piece mates with the U-shaped groove at the end of the small slide plate and is rotatably connected to it with a rotating connecting bolt. Then slide in another small slide plate and rotatably connect it to the test piece. The testing machine clamps the two small slide plates and pulls them upward to a certain position (applying shear load; the distance of the pull controls the magnitude of the shear load). Then, fix the sliding small slide plate to the large slide plate with screws (creating shear stress on the test piece). Finally, install the large slide plate onto the pressure vessel with bolts and nuts and gradually apply external pressure.

[0006] Compared with the prior art, the advantages of the present invention are:

[0007] 1. The test specimen is first subjected to shear load to obtain shear stress, and then the test specimen is fixed. The advantage of this operation is that the shear stress will affect the buckling behavior of the test specimen under external pressure, and this effect can be controlled; 2. The straight and curved edges of the composite material curved plate can be effectively clamped by the test specimen frame; 3. The application of the combined external pressure and shear load on the test specimen is simple and feasible. Attached Figure Description

[0008] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0009] Figure 1 Three-dimensional diagram of a composite curved plate specimen subjected to combined external compression and shear load.

[0010] Figure 2 Composite material curved plate

[0011] Figure 3 Composite material curved plate with straight edge clamping the upper frame (front)

[0012] Figure 4 Composite material curved plate with straight edge clamping upper frame (back side)

[0013] Figure 5 Composite material curved plate with straight edge clamping lower frame (front)

[0014] Figure 6 Composite material curved plate with straight edge clamping lower frame (back side)

[0015] Figure 7 Composite material curved plate with curved edge clamping upper frame (front)

[0016] Figure 8 Composite material curved plate with curved edge clamping upper frame (back side)

[0017] Figure 9 Composite material curved plate with curved edge clamping lower frame (front)

[0018] Figure 10 Composite material curved plate with curved edge clamping lower frame (back side)

[0019] Figure 11 Schematic diagram of applied shear stress

[0020] Figure 12 Diagram of fixing a small skateboard

[0021] Figure 13 Schematic diagram of fixed clamping system

[0022] Figure labels: 1. Composite material curved plate; 2. Straight edge clamping the upper frame; 3. Straight edge clamping the lower frame; 4. Curved edge clamping the upper frame; 5. Curved edge clamping the lower frame; 6. Countersunk screw; 7. Rotary connecting pin; 8. Straight edge of curved plate; 9. Curved edge of curved plate; 10. Curved plate connecting hole; 11. Boss of straight edge clamping the upper frame; 12. Rotary connecting hole of straight edge clamping the upper frame; 13. Countersunk screw hole of straight edge clamping the upper frame; 14. Curved edge clamping the upper frame clamping the curved surface; 15. Curved edge clamping the lower frame clamping the curved surface; 16. Boss of curved edge clamping the upper frame; 17. Curved edge clamping the upper frame clamping the curved surface; 18. Curved edge clamping the lower frame clamping the curved surface; 19. Large sliding plate; 20. Small sliding plate; 21. Screw; 22. Rotary connecting bolt; 23. Bolt. Detailed Implementation

[0023] The following will describe in detail the implementation of the present invention with reference to the accompanying drawings and embodiments, so as to fully understand how the present invention uses technical means to solve technical problems and achieve technical effects and to implement it accordingly.

[0024] The technical solution adopted by this invention to solve the technical problem is: a composite curved plate test specimen and loading method under combined external pressure and shear stress. The test specimen includes a composite curved plate 1, a straight edge clamping frame for the composite curved plate, and a curved edge clamping frame for the composite curved plate. The straight edge clamping frame for the composite curved plate includes a straight edge clamping upper frame 2 and a straight edge clamping lower frame 3. The straight edge 8 of the composite curved plate and its nearby curved surface are clamped in the middle by the straight edge clamping upper frame 2 and the straight edge clamping lower frame 3, and are connected and fixed by countersunk screws 6. The curved edge clamping frame for the composite curved plate includes a curved edge clamping upper frame 4 and a curved edge clamping lower frame 5. The curved edge 9 of the composite curved plate and its nearby curved surface are clamped in the middle by the curved edge clamping upper frame 4 and the curved edge clamping lower frame 5, and are connected and fixed by countersunk screws 6. The test specimen can be subjected to shear load and external pressure load through the experimental device, and the test specimen buckles under the combined action of external pressure and shear stress. The experimental device consists of a pressure vessel and a clamping system, and the clamping system consists of a pair of large sliding plates 19 and a pair of small sliding plates 20. The composite curved plate test specimen is rotatably connected to the small slide plate via a rotating connecting pin 7. The end of the large slide plate 19 has a U-shaped groove, which mates with the side flange of the small slide plate 20. The end of the small slide plate also has a U-shaped groove. The installation sequence of the small slide plate, the test specimen, and the large slide plate is as follows: First, slide the small slide plate 20 into the large slide plate to the appropriate position, and use screws 21 to connect and fix the small slide plate to the large slide plate. Then, slide the test specimen in, and the clamping part of the test specimen mates with the U-shaped groove at the end of the small slide plate. Rotating connecting bolts 22 are used to rotatably connect it to the small slide plate. Then, slide in another small slide plate 20 and rotatably connect it to the test specimen. The testing machine clamps the two small slide plates and pulls the small slide plate 20 upward to a certain position (applying shear load, the pulling distance controls the magnitude of the shear load). Then, use screws 21 to fix the sliding small slide plate to the large slide plate (creating shear stress on the test specimen). Finally, use bolts 23 and nuts to install the large slide plate onto the pressure vessel and gradually apply external pressure.

[0025] Figure 1 This invention relates to a test specimen and loading method for a composite curved plate subjected to combined external compressive and shear loads. The test specimen comprises a composite curved plate, a straight-edge clamping frame for the composite curved plate, and a curved-edge clamping frame for the composite curved plate. The straight-edge clamping frame for the composite curved plate includes an upper clamping frame and a lower clamping frame. The straight edge of the composite curved plate and its adjacent curved surfaces are clamped in the middle by the upper and lower clamping frames and fixed by countersunk screws. The curved-edge clamping frame for the composite curved plate includes an upper and lower clamping frame. The curved edge of the composite curved plate and its adjacent curved surfaces are clamped in the middle by the upper and lower clamping frames and fixed by countersunk screws. This test specimen can be subjected to shear loads and external compressive loads using an experimental apparatus, and the specimen buckles under the combined action of external compressive and shear stresses.

[0026] Figure 2This is a composite material curved plate. The material of the curved plate is a continuous fiber-reinforced matrix composite. The shape of the curved plate is a square or rectangular curved plate with a certain curvature, and it has straight edges, curved edges, and connecting holes.

[0027] Figure 3 This is a straight-edge clamping upper frame (front view) for a composite curved plate. Its features include a straight-edge clamping upper frame boss, a straight-edge clamping upper frame rotating connection hole, and a straight-edge clamping upper frame countersunk screw hole, etc.

[0028] Figure 4 It is a straight-edge clamping upper frame (back side) for composite curved plates. Its features include a straight-edge clamping curved surface for the upper frame, a straight-edge clamping rotating connection hole for the upper frame, and a straight-edge clamping countersunk screw hole for the upper frame.

[0029] Figure 5 This is a straight-edge clamping lower frame (front view) for a composite curved plate. Its features include rotating connection holes for the straight-edge clamping lower frame and countersunk screw holes for the straight-edge clamping lower frame.

[0030] Figure 6 This is a straight-edge clamping frame (back side) for a composite curved plate. Its features include a straight-edge clamping surface for the lower frame, a rotating connection hole for the straight-edge clamping lower frame, and countersunk screw holes for the straight-edge clamping lower frame. The straight-edge clamping surface for the lower frame and the straight-edge clamping surface for the upper frame clamp together to hold the straight edge of the curved plate and its surrounding curved surfaces in the middle.

[0031] Figure 7 This is a curved edge clamping upper frame (front view) for composite material curved panels. Its features include a curved edge clamping upper frame boss, a curved edge clamping upper frame rotating connection hole, and a curved edge clamping upper frame countersunk screw hole, etc.

[0032] Figure 8 This is a curved edge clamping upper frame (back side) for composite material curved panels. Its features include a curved edge clamping surface for the upper frame, a rotating connection hole for the upper frame, and countersunk screw holes for the upper frame.

[0033] Figure 9 This is a curved edge clamping lower frame (front view) for composite material curved panels. Its features include rotating connection holes for the curved edge clamping lower frame and countersunk screw holes for the curved edge clamping lower frame.

[0034] Figure 10 This is a lower frame (back side) for clamping the curved edge of a composite material curved plate. Its features include a clamping surface for the lower frame, a rotating connection hole for the lower frame, and countersunk screw holes for the lower frame. The clamping surfaces of the lower and upper frames clamp the curved edge of the plate and its surrounding surfaces in the middle.

[0035] Figure 11This is a schematic diagram of applying shear stress. The lower small slide plate is fixed to the large slide plate with screws. The test piece is rotatably connected to the two small slide plates. Finally, an upward axial tensile load is applied to the top of the upper small slide plate, stretching the upper small slide plate upward to a certain position, thus forming shear stress on the test piece. The magnitude of the shear stress is controlled by the stretching distance.

[0036] Figure 12 This is a schematic diagram of fixing the small sliding plate. After shear stress is applied to the test piece, the small sliding plate is fixed with screws.

[0037] Figure 13 This is a schematic diagram of the clamping system. After securing the upper sliding plate with screws, the clamping system is fixed to the pressure vessel with bolts and nuts.

[0038] The above description only illustrates the preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All modifications made within the scope of the independent claims of this invention are also within the scope of protection of this invention.

Claims

1. A loading method for a composite curved plate test specimen subjected to combined external pressure and shear, characterized in that: The composite curved plate test specimen subjected to combined external compression and shear includes a composite curved plate, a straight-edge clamping frame for the composite curved plate, and a curved-edge clamping frame for the composite curved plate. The straight-edge clamping frame includes an upper straight-edge clamping frame and a lower straight-edge clamping frame. The straight edge of the composite curved plate and its adjacent curved surfaces are clamped in the middle by the upper and lower straight-edge clamping frames and fixed by countersunk screws. The curved-edge clamping frame includes an upper curved-edge clamping frame and a lower curved-edge clamping frame. The curved edge of the composite curved plate and its adjacent curved surfaces are clamped by the upper and lower curved-edge clamping frames. The frame is held in the middle and fixed by countersunk screws. The test piece can be subjected to shear load and external pressure load through the test device. The test piece buckles under the combined action of external pressure and shear stress. The test piece is rotatably connected to two small slide plates, one of which is fixedly connected to the large slide plate. The two small slide plates are clamped by the test machine chuck, and the other small slide plate is stretched upward to a certain position. Then, the small slide plate is fixed to the large slide plate with screws, forming shear stress on the test piece. Finally, the large slide plate is installed on the pressure vessel with bolts and nuts, and external pressure is gradually applied through the pressure vessel.

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