A method for testing in-plane shear performance of sandwich structure composites

Abstract

The application relates to a method for testing the in-plane shear performance of a sandwich structure composite material, comprising the following steps: preparing a test piece with a sandwich structure, wherein the test piece with the sandwich structure comprises a core plate, non-test panels and test panels adhered to upper and lower end surfaces of the core plate; bonding three reinforcing plates on the test panels at intervals along the width, which are respectively a middle reinforcing plate and two side end reinforcing plates, gaps are arranged between the middle reinforcing plate and the corresponding side end reinforcing plates, the middle reinforcing plate and the two side end reinforcing plates extend out of the test panel in opposite directions, wherein a first connecting hole is arranged at the extending end of the middle reinforcing plate, and clamp connecting holes are arranged at the extending ends of the two side end reinforcing plates; saw slits corresponding to the upper and lower gaps of each gap are arranged on the non-test panels, and the depths of the saw slits extend into the test piece; and the problems of a complex test fixture and low test efficiency of a civil aviation cabin floor test are solved through the above design.

Description

Technical Field

[0001] This invention relates to the field of material mechanical property testing, and in particular to a method for testing the in-plane shear properties of sandwich composite materials. Background Technology

[0002] Sandwich composite materials possess advantages such as high specific stiffness, light weight, and strong design flexibility, and are widely used in aviation, aerospace, and rail transportation fields. In the field of aerospace composite manufacturing, sandwich composite materials are used to manufacture wall panels, leading edges, and passenger and cargo cabin floors. Among these, the passenger cabin floor of civil aircraft is a secondary load-bearing structural component, requiring evaluation of its in-plane shear properties.

[0003] The commonly used testing method for civil aviation cabin floors is ASTM D8067, which has complex test fixtures, as shown in patents 201520711183.8 and 201810279052.5. This test method involves complex tooling and fixtures with high precision requirements. The test specimen and reinforcing plates (of a specific material, requiring two reinforcing plates per specimen) are CNC milled to a specified shape, then bonded with epoxy adhesive, and holes are drilled in the test specimen to fit the fixture. Before testing, the adapted test specimen and test fixture need to be installed. This process is cumbersome and complex, making it difficult to fit the fixture after drilling the test specimen. Each test specimen requires tightening 40 screws and nuts (with a specific torque), resulting in low testing efficiency.

[0004] Therefore, in order to address the above problems, the present invention urgently needs to provide a method for testing the in-plane shear properties of sandwich composite materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the in-plane shear properties of sandwich composite materials, thereby solving the problems of complex and inefficient testing fixtures for existing civil aviation cabin floor testing.

[0006] A method for testing the in-plane shear properties of sandwich composite materials includes the following steps:

[0007] Prepare a test specimen with a sandwich structure, the test specimen with a sandwich structure includes a core plate, a non-test panel and a test panel adhered to the upper and lower ends of the core plate;

[0008] Three reinforcing plates are bonded to the test panel at width intervals: a middle reinforcing plate and two side reinforcing plates. A gap is provided between the middle reinforcing plate and the corresponding side reinforcing plates. The middle reinforcing plate and the two side reinforcing plates extend out of the test panel in opposite directions. A first connecting hole is provided at the extension end of the middle reinforcing plate, and a clamp connecting hole is provided at the extension ends of the two side reinforcing plates. Saw kerfs are provided on the non-test panel, corresponding to the upper and lower gaps, and the depth of each saw kerf extends into the test piece.

[0009] A fixture for clamping two end reinforcing plates is prepared. The fixture includes a long plate with a slot on one side. The slot is connected to the end reinforcing plate via a detachable connector. The long plate also has a second connection hole for connecting to the stretching mechanism on a stretching machine.

[0010] Connect the clamps and the extended end of the intermediate reinforcing plate to the tensile mechanism on the tensile machine, and load the specimen until it fails, according to the formula... The in-plane shear strength of the test specimen is obtained; where τ is the in-plane shear strength in N / mm; F ​​is the ultimate load in N; and b is the width of the test specimen in mm. The in-plane shear strength of core material 1 is obtained.

[0011] Preferably, the kerf width is 2.5mm-3mm.

[0012] Preferably, both the non-test panel and the test panel are glass fiber reinforced epoxy resin panels.

[0013] Preferably, the thickness of the test panel is 0.2mm-0.6mm.

[0014] Preferably, the detachable connector includes reinforcing plate connecting holes on the long plate that correspond one-to-one with the clamp connecting holes, and fixing bolts screwed into each reinforcing plate connecting hole, wherein the reinforcing plate connecting holes are in communication with the slot.

[0015] Preferably, the gap width between the middle reinforcing plate and the adjacent side reinforcing plate is 2.9mm-3.1mm.

[0016] Preferably, the length of the reinforcing plate is 95mm-125mm, the width is 22mm-24mm, and the thickness is 1.3mm-1.7mm.

[0017] Preferably, the reinforcing plate is made of aluminum alloy.

[0018] Preferably, the clamp thickness is 8mm-10mm; the slot width is 1.7mm-2.3mm; and the depth is 35mm-45mm.

[0019] Preferably, the reinforced plate is sandblasted and then cleaned with volatile solvents such as acetone and alcohol.

[0020] Preferably, when the thickness of the test panel and the non-test panel are the same, the first reinforcing plate, the second reinforcing plate and the third reinforcing plate are pasted on any one panel, and a saw slit is made on the other panel; when the thickness of the test panel and the non-test panel are different, the first reinforcing plate, the second reinforcing plate and the third reinforcing plate are pasted on the thinner panel, and a saw slit is made on the thicker panel.

[0021] The in-plane shear performance testing method for sandwich composite materials provided by this invention has the following advantages compared with the prior art:

[0022] The test specimen processing method is simple, the assembly is efficient, and the calculation steps are simplified, so as to achieve the requirements of efficient evaluation of in-plane shear test of civil aviation cabin floor. This invention is also applicable to the in-plane shear performance test and evaluation of general composite thin plates. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the in-plane shear performance testing method for sandwich composite materials described in this invention;

[0025] Figure 2 This is a schematic diagram (three-dimensional view) of the test specimen structure described in this invention;

[0026] Figure 3 This is a schematic diagram (three-dimensional view) of the saw kerf structure described in this invention;

[0027] Figure 4 This is a three-dimensional view showing the assembly of the test piece with the first reinforcing plate, the second reinforcing plate, and the third reinforcing plate described in this invention.

[0028] Figure 5 This is a schematic diagram (perspective view) of the clamp structure described in this invention;

[0029] Figure 6 This is a perspective view showing the assembly of the clamp described in this invention with the first reinforcing plate, the second reinforcing plate, and the third reinforcing plate.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Core board; 2. Non-test panel; 21. Saw kerf; 3. Test panel; 31. Intermediate reinforcing plate; 311. First connecting hole; 32. Side reinforcing plate; 321. Fixture connecting hole; 33. Gap; 4. Fixture; 41. Slot; 42. Second connecting hole; 43. Reinforcing plate connecting hole; 44. Fixing bolt. Detailed Implementation

[0032] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] This invention provides a method for testing the in-plane shear properties of sandwich composite materials, comprising the following steps: preparing a test specimen with a sandwich structure, the test specimen including a core plate 1, a non-test panel 2 and a test panel 3 adhered to the upper and lower ends of the core plate 1;

[0036] Three reinforcing plates are bonded to the test panel 3 at width intervals, namely a middle reinforcing plate 31 and two side reinforcing plates 32. A gap 33 is provided between the middle reinforcing plate 31 and the corresponding side reinforcing plate 32. The middle reinforcing plate 31 and the two side reinforcing plates 32 extend out of the test panel 3 in opposite directions. A first connecting hole 311 is opened at the extended end of the middle reinforcing plate 31, and a clamp connecting hole 321 is opened at the extended end of the two side reinforcing plates 32.

[0037] On the non-test panel 2, saw slits 21 are made corresponding to the upper and lower parts of each gap 33, and the depth of each saw slit 21 extends into the core material 1.

[0038] A clamp 4 is prepared for clamping the two end reinforcing plates 32. The clamp 4 includes a long plate, and a slot 41 is provided on one side of the long plate. The slot 41 is connected to the end reinforcing plate 32 by a detachable connector. The long plate is also provided with a second connection hole 42 for connecting to the stretching mechanism on the stretching machine.

[0039] Connect the clamp 4 and the extended end of the intermediate reinforcing plate 31 to the tensioning mechanism on the tensioning machine, and load until the core material 1 fails. According to the formula...

[0040] The in-plane shear strength of the test specimen is obtained; where τ is the in-plane shear strength in N / mm; F ​​is the ultimate load in N; and b is the width of the test specimen in mm. The in-plane shear strength of core material 1 is obtained.

[0041] Through the above design, the present invention processes the core material 1 into a cuboid with a length of (75±1)mm×(75±1)mm and a width of (75±1)mm×(75±1)mm, without any treatment in the thickness direction. The fiber direction of the core material 1 is parallel to the edge direction of the core material 1. The upper and lower end surfaces of the core material 1 are respectively the non-test panel 2 and the test panel 3. The test panel 3 is polished with (120~300 grit) sandpaper, but the fibers of the test panel 3 must not be exposed or damaged. Then, the middle reinforcing plate 31 and the two side end reinforcing plates 32 are pasted on the test panel 3. The gap 33 between the two side end reinforcing plates 32 and the middle reinforcing plate 31 is 2.5mm-3mm. Then, saw cuts 21 are made on the non-test panel 2 that correspond one-to-one with the upper and lower gaps 33. The saw cuts 21 extend into the interior of the core material 1.

[0042] The clamp 4 is connected to the side reinforcing plate 32, the tensile mechanism of one side of the testing machine is connected to the first connecting hole 311 of the middle reinforcing plate 31, and the tensile mechanism of the other side of the testing machine is connected to the clamp 4. The testing machines on both sides stretch from the left and right sides respectively until the test panel 3 bonded to the three reinforcing plates is destroyed, thereby completing the in-plane shear performance test of the sandwich structure composite material.

[0043] In this embodiment, the kerf width 21 is 2.5mm-3mm.

[0044] Through the above design, the non-test panel 2 is destroyed, so that the performance measured can only be obtained from the test panel 3, which is bonded to the reinforcing plate, thus ensuring the accuracy of the experiment.

[0045] In this embodiment, both the non-test panel 2 and the test panel 3 are glass fiber reinforced epoxy resin panels.

[0046] The thickness of the test panel 3 in this embodiment is 0.2mm-0.6mm.

[0047] The present invention ensures the smooth conduct of the experiment through the above design. If the test panel 3 is too thick, it will affect the accuracy of the test.

[0048] The detachable connector in this embodiment includes reinforcing plate connecting holes 43 on the long plate that correspond one-to-one with the clamp connecting holes 111, and fixing bolts 44 that are screwed into each reinforcing plate connecting hole 43. The reinforcing plate connecting holes 43 are in communication with the slots 41.

[0049] Through the above design, the fixture 4 can be recycled, saving manufacturing costs.

[0050] In this embodiment, the gap 33 between the intermediate reinforcing plate 31 and the adjacent side reinforcing plate 32 is 2.9mm-3.1mm wide.

[0051] Through the above design, the spacing between the reinforcing plates in this invention should not be too large, otherwise it will affect the failure mode and make the test data inaccurate.

[0052] In this embodiment, the length of the reinforcing plate is 95mm-125mm, the width is 22mm-24mm, and the thickness is 1.3mm-1.7mm.

[0053] The reinforcing plates in this embodiment are all made of aluminum alloy.

[0054] Through the above design, the present invention ensures that the reinforcing plate does not break when the testing machines on both sides are stretched from the left and right sides respectively, thus ensuring the smooth progress of the experiment.

[0055] In this embodiment, the clamp 4 has a thickness of 8mm-10mm; the slot 41 has a width of 1.7mm-2.3mm and a depth of 35mm-45mm.

[0056] Through the above design, the present invention ensures that the side end reinforcing plate 32 can be inserted into the slot 41 while ensuring the overall stability of the clamp 4.

[0057] In this embodiment, the reinforcing plate is sandblasted and then cleaned with volatile solvents such as acetone and alcohol.

[0058] The present invention cleans and roughens the surface of the reinforcing plate through the above design, thereby improving its mechanical properties and fatigue resistance.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the in-plane shear properties of sandwich composite materials, characterized in that: Includes the following steps: Prepare a test specimen with a sandwich structure. The test specimen with a sandwich structure includes a core plate (1), a non-test panel (2) and a test panel (3) adhered to the upper and lower ends of the core plate (1). Three reinforcing plates are bonded to the test panel (3) at width intervals, namely a middle reinforcing plate (31) and two side reinforcing plates (32). A gap (33) is provided between the middle reinforcing plate (31) and the corresponding side reinforcing plate (32). The middle reinforcing plate (31) and the two side reinforcing plates (32) extend out of the test panel (3) in opposite directions. A first connecting hole (311) is opened at the extension end of the middle reinforcing plate (31), and a clamp connecting hole (321) is opened at the extension end of the two side reinforcing plates (32). Saw slits (21) corresponding to the upper and lower gaps (33) are opened on the non-test panel (2). The depth of each saw slit (21) extends into the core board (1). Prepare a clamp (4) for clamping the two end reinforcing plates (32). The clamp (4) includes a long plate with a slot (41) on one side. The slot (41) is connected to the two end reinforcing plates (32) by a detachable connector. The long plate is also provided with a second connecting hole (42) for connecting to the stretching mechanism on the stretching machine. The clamp (4) and the extended end of the intermediate reinforcing plate (31) are respectively connected to the tensioning mechanism on the tensioning machine, and the load is applied until the core plate (1) breaks. According to the formula... The in-plane shear strength of the test specimen is obtained; where τ is the in-plane shear strength in N / mm; F ​​is the ultimate load in N; b is the width of the test specimen in mm. The in-plane shear strength of the core board (1) is obtained; the kerf (21) width is 2.5mm-3mm; both the non-test panel (2) and the test panel (3) are glass fiber reinforced epoxy resin panels.

2. The method for testing the in-plane shear properties of sandwich composite materials according to claim 1, characterized in that: The thickness of the test panel (3) is 0.2mm-0.6mm.

3. The method for testing the in-plane shear properties of sandwich composite materials according to claim 2, characterized in that: The detachable connector includes reinforcing plate connecting holes (43) on the long plate that correspond one-to-one with the clamp connecting holes (321), and fixing bolts (44) that are screwed into each reinforcing plate connecting hole (43). The reinforcing plate connecting holes (43) are in communication with the slots (41).

4. The method for testing the in-plane shear properties of sandwich composite materials according to claim 3, characterized in that: The gap (33) between the middle reinforcing plate (31) and the adjacent side reinforcing plate (32) is 2.9mm-3.1mm wide.

5. The method for testing the in-plane shear properties of sandwich composite materials according to claim 4, characterized in that: The length of the reinforcing plates is 95mm-125mm, the width is 22mm-24mm, and the thickness is 1.3mm-1.7mm.

6. The method for testing the in-plane shear properties of sandwich composite materials according to claim 5, characterized in that: The reinforcing plate is made of aluminum alloy.

7. The method for testing the in-plane shear properties of sandwich composite materials according to claim 6, characterized in that: The clamp (4) is 8mm-10mm thick; the slot (41) is 1.7mm-2.3mm wide and 35mm-45mm deep.

8. The method for testing the in-plane shear properties of sandwich composite materials according to claim 7, characterized in that: The reinforced plate is sandblasted and then cleaned with volatile solvents such as acetone or alcohol.

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