Method for testing in-plane shear performance of sandwich-structured composite material

Abstract

A method for testing the in-plane shear performance of a sandwich-structured composite material, comprising the following steps: preparing a test piece having a sandwich structure, the test piece having a sandwich structure comprising a core (1), and a non-test face sheet (2) and a test face sheet (3) which are adhered to the upper end face and the lower end face of the core (1); and bonding three reinforcing sheets on the test face sheet (3) at intervals along the width direction, the three reinforcing sheets being respectively a middle reinforcing sheet (31) and two side end reinforcing sheets (32), gaps (33) being formed between the middle reinforcing sheet (31) and the corresponding side end reinforcing sheets (32), and the middle reinforcing sheet (31) and the two side end reinforcing sheets (32) respectively extending out of the test face sheet (3) in opposite directions, wherein a first connection hole (311) is formed in the extension end of the middle reinforcing sheet (31), a fixture connection hole (321) is formed in the extension end of each of the two side end reinforcing sheets (32), kerfs (21) having one-to-one correspondence to the gaps (33) in the vertical direction are formed in the non-test face sheet (2), and the kerfs (21) extend into the core (1). The present invention solves the problems of complexity and low testing efficiency of existing test fixtures for airliner cabin floors.

Description

A method for testing in-plane shear properties of sandwich composite materials Technical Field

[0001] The present 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 structure composite materials. Background Art

[0002] Sandwich composite materials, with their high specific stiffness, light weight, and design flexibility, are widely used in aviation, aerospace, rail transportation, and other fields. In aviation composite manufacturing, sandwich composites are used to manufacture wall panels, leading edges, and passenger and cargo compartment floors. Civil aircraft cabin floors are secondary load-bearing structural components, necessitating evaluation of their in-plane shear properties.

[0003] The commonly used test method for civil aviation cabin floors is ASTM D8067, which requires a complex test fixture, as shown in patents 201520711183.8 and 201810279052.5. This test method requires complex fixtures and high-precision fittings. The test specimens and reinforcement sheets (made of a specific material, two required per specimen) are CNC-milled to the specified shape, then bonded with epoxy adhesive and holes punched into the specimen to accommodate the fixture. Before testing, the specimens and fixtures must be installed. This process is cumbersome and complex, making it difficult to fit the fixture after drilling the test pieces. Each specimen requires 40 screws and nuts (to a specific torque), resulting in low testing efficiency.

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

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a method for testing the in-plane shear properties of sandwich structure composite materials, so as to solve the problems of complex test fixtures and low test efficiency in existing civil aviation cabin floors.

[0007] A method for testing the in-plane shear properties of sandwich composite materials, comprising the following steps:

[0008] preparing a test piece having a sandwich structure, the test piece having a sandwich structure comprising a core panel, non-test panels adhered to the upper and lower end surfaces of the core panel, and a test panel;

[0009] Three reinforcing plates are bonded to the test panel at intervals along the width thereof, namely 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 connection hole is provided at the extended end of the middle reinforcing plate, and a fixture connection hole is provided at the extended end of the two side reinforcing plates. Saw cuts are provided on the non-test panel corresponding to the upper and lower ends of each gap, and the depth of each saw cut extends into the test piece.

[0010] Prepare a fixture for clamping the two side end reinforcement plates, the fixture comprising a long plate with a slot on one side of the long plate, the slot being connected to the side end reinforcement plate via a detachable connector, and a second connection hole on the long plate for connecting to the stretching mechanism on the stretching machine;

[0011] Connect the fixture and the extended end of the middle reinforcing plate to the stretching mechanism on the stretching machine respectively, and load until the test piece is broken. According to the formula The in-plane shear strength of the test piece 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 piece, in mm, and the in-plane shear strength of the core material 1 is obtained.

[0012] Preferably, the sawing width is 2.5 mm to 3 mm.

[0013] Preferably, both the non-test panel and the test panel are glass fiber reinforced epoxy resin panels.

[0014] Preferably, the thickness of the test panel is 0.2 mm to 0.6 mm.

[0015] Preferably, the detachable connecting member includes reinforcing plate connecting holes located on the long plate corresponding to the clamp connecting holes one by one, and fixing bolts screwed to each reinforcing plate connecting hole, and the reinforcing plate connecting holes are connected to the slots.

[0016] Preferably, the gap width between the middle reinforcing plate and the adjacent side reinforcing plate is 2.9 mm-3.1 mm.

[0017] Preferably, the length of the reinforcement plate is 95mm-125mm, the width is 22mm-24mm, and the thickness is 1.3mm-1.7mm.

[0018] Preferably, the reinforcing plate is made of aluminum alloy.

[0019] Preferably, the thickness of the clamp is 8mm-10mm; the width of the slot is 1.7mm-2.3mm, and the depth is 35mm-45mm.

[0020] Preferably, the reinforcing plate is sandblasted and then cleaned with a volatile solvent such as acetone or alcohol.

[0021] Preferably, when the thickness of the test panel and the non-test panel is the same, any one panel is selected to paste the first reinforcing plate, the second reinforcing plate and the third reinforcing plate, and the remaining panel is sawed; when the thickness of the test panel and the non-test panel is inconsistent, a thinner panel is selected to paste the first reinforcing plate, the second reinforcing plate and the third reinforcing plate, and a thicker panel is selected to open the saw.

[0022] The present invention provides a method for testing the in-plane shear properties of sandwich composite materials, which has the following advantages over the prior art:

[0023] The test piece processing method is simple, the assembly is efficient, and the calculation steps are streamlined, so as to achieve the in-plane shear test requirements for efficiently evaluating civil aviation cabin floors. The present invention is also applicable to the in-plane shear performance test and evaluation of general composite material thin plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] FIG1 is a flow chart of the method for testing the in-plane shear properties of sandwich structure composite materials according to the present invention;

[0026] FIG2 is a schematic structural diagram (stereoscopic view) of the test piece according to the present invention;

[0027] FIG3 is a schematic diagram (stereoscopic view) of the sawing structure of the present invention;

[0028] FIG4 is a schematic diagram (perspective view) of assembling the test piece and the first reinforcing plate, the second reinforcing plate, and the third reinforcing plate according to the present invention;

[0029] FIG5 is a schematic diagram (stereoscopic view) of the clamp structure of the present invention;

[0030] FIG6 is a schematic diagram (stereoscopic view) of assembling the clamp and the first reinforcing plate, the second reinforcing plate and the third reinforcing plate according to the present invention.

[0031] Explanation of the accompanying drawings: 1. Core board; 2. Non-test panel; 21. Saw seam; 3. Test panel; 31. Middle reinforcement plate; 311. First connection hole; 32. Side reinforcement plate; 321. Clamp connection hole; 33. Gap; 4. Clamp; 41. Slot; 42. Second connection hole; 43. Reinforcement plate connection hole; 44. Fixing bolt. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present 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 the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0035] The present invention provides a method for testing the in-plane shear properties of a sandwich composite material, comprising the following steps: preparing a test piece having a sandwich structure, wherein the test piece having a sandwich structure comprises a core plate 1, a non-test panel 2 and a test panel 3 adhered to the upper and lower end surfaces of the core plate 1;

[0036] Three reinforcing plates are bonded to the test panel 3 at intervals along its width. These are 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 plates 32. The middle reinforcing plate 31 and the side reinforcing plates 32 extend out of the test panel 3 in opposite directions. A first connection hole 311 is defined at the extended end of the middle reinforcing plate 31, and a fixture connection hole 321 is defined at the extended ends of the side reinforcing plates 32.

[0037] Saw slits 21 are provided on the non-test panel 2, corresponding to the upper and lower sides of each gap 33, and the depth of each saw slit 21 extends into the core material 1;

[0038] Prepare a fixture 4 for clamping the two side end reinforcement plates 32. The fixture 4 includes a long plate with a slot 41 on one side. The slot 41 is connected to the side end reinforcement plate 32 via a detachable connector. The long plate also has a second connection hole 42 for connecting to the stretching mechanism on the stretching machine.

[0039] Connect the extension ends of the fixture 4 and the middle reinforcing plate 31 to the stretching mechanism on the stretching machine respectively, and load until the core material 1 is broken. According to the formula

[0040] The in-plane shear strength of the test piece 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 piece, in mm, and the in-plane shear strength of the core material 1 is obtained.

[0041] According to the present invention, the core material 1 is processed into a rectangular parallelepiped with a length of (75±1) mm×(75±1) mm and a width of (75±1) mm×(75±1) mm, and the thickness direction is not processed. The panel fiber direction of the core material 1 is parallel to the edge direction of the core material 1. The upper end surface and the lower end surface of the core material 1 are the non-test panel 2 and the test panel 3, respectively. The test panel 3 is polished with (120-300 mesh) sandpaper, but the fibers of the test panel 3 must not be exposed or damaged. Then, the middle reinforcement plate 31 and the two side reinforcement plates 32 are pasted on the test panel 3. The gap 33 between the two side reinforcement plates 32 and the middle reinforcement plate 31 is 2.5 mm-3 mm. Then, saw slots 21 corresponding to the upper and lower gaps 33 are opened on the non-test panel 2, and the saw slots 21 extend into the interior of the core material 1.

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

[0043] The width of the saw cut 21 in this embodiment is 2.5 mm to 3 mm.

[0044] The present invention destroys the non-test panel 2 through the above design, so that the performance measured can only be the test panel 3 bonded to the reinforcement plate, ensuring the accuracy of the experiment.

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

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

[0047] The present invention ensures that the experiment proceeds smoothly through the above design. If the test panel 3 is too thick, the test accuracy will be affected.

[0048] The detachable connector of this embodiment includes reinforcing plate connection holes 43 located on the long plate corresponding to the clamp connection holes 111 , and fixing bolts 44 screwed to each reinforcing plate connection hole 43 . The reinforcing plate connection holes 43 are connected to the slots 41 .

[0049] The present invention can recycle the clamp 4 through the above design, thus saving manufacturing costs.

[0050] In this embodiment, the width of the gap 33 between the middle reinforcing plate 31 and the adjacent side reinforcing plate 32 is 2.9 mm to 3.1 mm.

[0051] According to the above design of the present invention, the distance between the reinforcing plates cannot be too large, otherwise it will affect the failure mode and make the test data inaccurate.

[0052] The reinforcing plates of this embodiment are all 95 mm to 125 mm in length, 22 mm to 24 mm in width, and 1.3 mm to 1.7 mm in thickness.

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

[0054] 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 through the above design, thereby ensuring that the experiment proceeds smoothly.

[0055] The thickness of the clamp 4 in this embodiment is 8 mm to 10 mm; the width of the slot 41 is 1.7 mm to 2.3 mm, and the depth is 35 mm to 45 mm.

[0056] Through the above-mentioned 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] The reinforcing plate of this embodiment is sandblasted and then cleaned with a volatile solvent such as acetone or 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, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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: The steps include: A test piece with a sandwich structure is prepared, wherein the test piece with a sandwich structure comprises a core panel (1), a non-test panel (2) and a test panel (3) adhered to the upper end surface and the lower end surface of the core panel (1); Three reinforcing plates are bonded to the test panel (3) at intervals along the width, 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 plates (32); the middle reinforcing plate (31) and the side reinforcing plates (32) extend out of the test panel (3) in opposite directions, wherein a first connection hole (311) is provided at the extended end of the middle reinforcing plate (31), and a fixture connection hole (321) is provided at the extended end of the side reinforcing plates (32); saw cuts (21) corresponding to the upper and lower sides of each gap (33) are provided on the non-test panel (2), and the depth of each saw cut (21) extends into the test piece (1); A clamp (4) for clamping the two side end reinforcing plates (32) is prepared, the clamp (4) comprising a long plate, a slot (41) is provided on one side of the long plate, the slot (41) is connected to the side end reinforcing plate (32) via a detachable connecting piece, and a second connecting hole (42) for connecting to a stretching mechanism on a stretching machine is also provided on the long plate; The fixture (4) and the extended ends of the intermediate reinforcing plate (31) are respectively connected to the stretching mechanism on the stretching machine, and loaded until the test piece (1) is destroyed. According to the formula The in-plane shear strength of the specimen is obtained; wherein, τ is the in-plane shear strength, in N / mm; F ​​is the limit load, in N; b is the specimen width, in mm, and the in-plane shear strength of the specimen (1) is obtained.

2. The method for testing the in-plane shear properties of sandwich composite materials according to claim 1, characterized in that: The width of the saw seam (21) is 2.5mm-3mm.

3. The method for testing the in-plane shear properties of sandwich composite materials according to claim 2, characterized in that: The non-test panel (2) and the test panel (3) are both glass fiber reinforced epoxy resin panels.

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

5. The method for testing the in-plane shear properties of sandwich composite materials according to claim 4, characterized in that: The detachable connecting member comprises reinforcing plate connecting holes (43) on the long plate corresponding to the clamp connecting holes (321) one by one, and fixing bolts (44) threadedly connected to each reinforcing plate connecting hole (43), and the reinforcing plate connecting holes (43) are connected to the slots (41).

6. The method for testing the in-plane shear properties of sandwich composite materials according to claim 5, characterized in that: The width of the gap (33) between the middle reinforcing plate (31) and the adjacent side end reinforcing plate (32) is 2.9 mm to 3.1 mm.

7. The method for testing the in-plane shear properties of sandwich composite materials according to claim 6, characterized in that: The length of the reinforcement plates is 95mm-125mm, the width is 22mm-24mm, and the thickness is 1.3mm-1.7mm.

8. The method for testing the in-plane shear properties of sandwich composite materials according to claim 7, characterized in that: The reinforcement plate is made of aluminum alloy.

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

10. The method for testing the in-plane shear properties of sandwich composite materials according to claim 9, characterized in that: The reinforcement plate is sandblasted and then cleaned with volatile solvents such as acetone and alcohol.

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