A continuous plant fiber reinforced honeycomb composite gradient damping structure, a preparation device and a preparation method

Abstract

The present application relates to a kind of continuous plant fiber reinforced honeycomb composite gradient damping structure, preparation device and preparation method, the structure includes: upper damping layer, upper panel, intermediate core layer, lower panel and lower damping layer, the upper panel, intermediate core layer and lower panel are sequentially stacked, the upper panel and lower panel are all provided with recess on, and the upper panel and lower panel with the recess constitute gradient thickness structure, the upper damping layer and lower damping layer are respectively arranged in the recess bottom of upper panel and lower panel, the intermediate core layer is gradient height honeycomb structure, and the upper panel and lower panel use multiscale continuous plant fiber reinforced honeycomb composite material.Compared with prior art, the present application has the advantages of realizing excellent broadband damping without increasing mass.

Description

Technical Field

[0001] This invention relates to the field of composite materials and vibration reduction and noise reduction, and in particular to a gradient vibration reduction structure, preparation device and preparation method of continuous plant fiber reinforced honeycomb composite material. Background Technology

[0002] With the rapid development of the aviation industry towards green and lightweight designs, aircraft interior structures not only need to meet stringent load-bearing requirements but also need to possess excellent vibration and noise reduction performance to suppress broadband mechanical vibrations generated during flight, extend equipment lifespan, and improve passenger comfort. Existing aircraft interior components mostly employ traditional homogeneous sandwich structures or artificial fiber-reinforced composite material sandwich structures. While these offer some lightweighting and load-bearing capacity, they lack effective broadband vibration suppression capabilities.

[0003] To improve the vibration reduction performance of sandwich structures, conventional designs often employ the method of adding a viscoelastic damping layer. However, this passive vibration reduction structure design, which involves "adding mass," significantly increases the overall weight of the components, failing to meet the requirements of lightweight aerospace applications. Gradient configurations based on variable thickness cross-sections offer a new approach to achieving "lightweight and high damping." Theoretically, when the panel thickness or the height of the honeycomb core layer decreases according to a specific power function (acoustic black hole effect), the phase velocity of the bending wave entering that region gradually decreases until it approaches zero, achieving efficient energy accumulation of the bending wave. While a purely gradient structural design can accumulate energy, if the intrinsic damping of the structural material itself is insufficient, the accumulated energy will still be reflected and cannot be effectively absorbed and dissipated.

[0004] Plant fibers contain unique natural micro-fiber cavities and a fine fiber-matrix interface layer, exhibiting excellent internal damping characteristics. Combined with their lightweight, high specific strength, high specific modulus, and biodegradability, they become ideal materials for fabricating lightweight, environmentally friendly, and vibration-damping interior structures. By balancing the micro-material properties of plant fibers with the macro-power function cross-sectional structure design, a gradient vibration-damping structure with macro-variable thickness panels and variable height honeycomb is constructed. This allows bending waves to focus in the gradient region and directly utilize the plant fibers for intrinsically efficient dissipation, achieving high-efficiency broadband vibration reduction without adding additional mass.

[0005] However, the fabrication process of the aforementioned multi-scale gradient composite material structures faces significant challenges. Traditional structures cannot truly achieve vibration frequency dissipation; the traditional "flat plate hot pressing + mechanical milling" processing method inevitably cuts continuous fibers directly when preparing the pre-defined functional cross-section, disrupting the continuity of stress transmission within the panel; simultaneously, the dynamic cutting force during milling easily induces interlaminar tearing and large-area debonding within the composite material, leading to a sharp decline in mechanical properties. Therefore, a novel fabrication method is urgently needed to achieve high-quality, high-continuity net-shape forming of continuous plant fiber reinforced honeycomb composite gradient vibration-damping structures, leveraging their advantages of multi-scale synergistic vibration damping and efficient load-bearing. Summary of the Invention

[0006] The purpose of this invention is to provide a gradient vibration reduction structure, preparation device, and preparation method for a continuous plant fiber reinforced honeycomb composite material that achieves lightweighting while effectively dissipating vibration energy at different frequencies.

[0007] The objective of this invention can be achieved through the following technical solutions: A gradient vibration reduction structure of continuous plant fiber reinforced honeycomb composite material includes an upper damping layer, an upper panel, an intermediate core layer, a lower panel, and a lower damping layer. The upper panel, intermediate core layer, and lower panel are stacked sequentially. Both the upper and lower panels have recesses. The upper and lower panels with the recesses form a gradient thickness structure. The upper and lower damping layers are respectively disposed at the bottom of the recesses in the upper and lower panels. The intermediate core layer is a gradient height honeycomb structure. The upper and lower panels are made of multi-scale continuous plant fiber reinforced honeycomb composite material.

[0008] Furthermore, the number of recesses opened on the upper panel or the lower panel is one or more.

[0009] Furthermore, the cross-section of the pit is composed of a truncated region, a variable thickness region, and a flat region, and the cross-section of the pit satisfies the following power-law function: , In the formula, coordinates x At the thickness, h 0 represents the thickness of the cut-off region. r 0 represents the radius of the cutoff region. It is a smoothing constant. h 1 represents the thickness of the flattened area. m The power exponent. m ≥2.

[0010] Furthermore, the multi-scale of the continuous plant fiber reinforced honeycomb composite material includes micro-fiber cavities, a meso-fiber matrix interface layer, and a macro-gradient thickness, wherein the macro-gradient thickness is achieved by the cross-section of the pits with varying thickness in the variable thickness region and the truncated region.

[0011] Furthermore, the upper damping layer and the lower damping layer are made of viscoelastic materials.

[0012] The present invention also provides a preparation apparatus for preparing the above-described continuous plant fiber reinforced honeycomb composite gradient vibration damping structure, comprising: a hot pressing mold, positioning pins, and a release film. The hot pressing mold includes an upper mold and a lower mold. The upper mold includes a punch and a base plate. The punch is mounted on the base plate, and the shape of the punch matches the shape of the recess. Positioning holes are provided at corresponding positions of the lower mold and the base plate. The positioning pins are installed in the positioning holes. The release film also has positioning holes corresponding to the lower mold. The release film has a scale pattern of circles with different radii and is laid on the lower mold through the positioning holes.

[0013] Furthermore, the cross-section of the punch satisfies the power-law function.

[0014] Furthermore, a circular groove is provided in the center of the base plate, and a circular through hole is provided in the center of the circular groove. The punch is installed on the circular groove through a transition fit.

[0015] Furthermore, it also includes a shim located on the lower mold and corresponding to the position of the flattening area to determine the thickness of the gradient damping structure.

[0016] The present invention also provides a preparation method for preparing the gradient vibration damping structure according to the hot pressing mold described above, the preparation method comprising the following steps: Step 1: The continuous plant fiber impregnation resin solution is dried and calendered to prepare a continuous plant fiber prepreg of a specific width; Step 2: Cut the continuous plant fiber prepreg into multiple layers of prepreg, with a circular hole of different radius in the center of each layer of prepreg, and the radius of the circular hole is determined according to the power law function; Step 3: Install positioning pins on the positioning holes of the lower mold, and cut a release film of the same size as the lower mold and with corresponding positioning holes. Step 4: Set a scale pattern with different radii on the release film, wherein the different radii on the scale pattern are consistent with the radii of the circular holes in the center of different layers of prepreg. Step 5: Adhere the first layer of prepreg to the first scale base map, and insert the release film through the positioning hole on it into the positioning pin on the lower mold to align with the center. Step 6: After compacting the prepreg, peel off the release film; Step 7: Repeat steps 3-6 above to process each subsequent layer of prepreg, wherein all the compacted prepregs are stacked in layers and their centers coincide, and all the circular holes of different radii after stacking form the pits. Step 8: Install the upper mold to the lower mold through the positioning hole. Place all the compacted prepreg in the upper and lower molds in layers, and place the punch in the round hole of all the compacted prepreg. Determine the thickness of the gradient damping structure by using the shim corresponding to the position of the flat area to obtain the initial upper panel with gradient thickness. Step 9: Prepare an initial lower panel that is identical to the initial upper panel according to steps 1-8 above; Step 10: The initial upper panel and initial lower panel are processed into the final upper panel and lower panel by vacuum hot pressing. Step 11: The intermediate core layer is attached between the upper panel and the lower panel, and co-cured by vacuum bag-assisted molding and autoclave process. The upper damping layer and the lower damping layer are then adhered to the recess to obtain a gradient vibration reduction structure.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The gradient vibration reduction structure of the present invention integrates the upper and lower panels of the gradient thickness structure and the continuous plant fiber reinforced honeycomb composite material, the middle core layer of the gradient height honeycomb structure, and the upper and lower damping layers at the pit. The upper and lower panels made of the composite material can achieve lightweighting of the structure while ensuring sufficient stiffness and strength. The gradient-designed panels can better match and disperse low- and medium-frequency vibrations, achieving high-efficiency vibration reduction over a wide frequency band. The gradient height honeycomb structure dissipates energy through structural deformation, and the damping layer mainly absorbs high-frequency vibrations, thereby achieving lightweighting while effectively dissipating vibration energy of different frequencies.

[0018] (2) This invention combines the unique natural micro-fiber cavities and fine fiber matrix interface layer of continuous plant fibers with macro-gradient configurations (variable thickness panels and variable height honeycomb) to obtain a gradient vibration reduction structure. Through multi-scale synergy, it achieves excellent broadband vibration reduction without increasing mass. It effectively overcomes the defects of traditional methods that add viscoelastic damping layers, which lead to increased structural weight, and the defects of pure geometric configuration designs that are more prone to energy reflection due to insufficient intrinsic material damping.

[0019] (2) The gradient recess design on the panel of the present invention (consisting of a cut-off area, a variable thickness area and a flat area) avoids abrupt changes in thickness, can smoothly transfer and disperse loads, significantly reduce stress concentration, thereby improving the fatigue life and reliability of the structure.

[0020] (3) By innovatively adopting a special mold positioning + release film scale circle layup process, the present invention has completed the high-quality preparation of composite material panels with preset power function pits, ensuring the coincidence of the center of each layer of prepreg and the continuity of the fibers, avoiding the impact of cutting force during milling, and improving the integrity and mechanical properties of the prepared structure.

[0021] (4) This invention integrates multi-scale design at the micro (fiber cavity), meso (fiber / matrix interface), and macro (gradient thickness, gradient honeycomb) levels through a repeatable process. This is not merely a composite of materials, but an integrated design and manufacturing of structural functions, enabling synergistic optimization of lightweight, vibration reduction, load-bearing, and other performance characteristics.

[0022] (5) The present invention uses continuous plant fiber as reinforcement, which has low density, high specific strength, high specific modulus and is naturally renewable; combined with porous honeycomb core structure and variable thickness lightweight cross section design, it not only meets the dual requirements of load bearing and vibration reduction of aircraft interior structure, but also has good degradability, which is highly in line with the current green and low carbon development trend of aviation industry.

[0023] (6) The preparation process of this invention forms a complete process flow, from prepreg preparation, precise cutting and lamination, to vacuum hot pressing and co-curing. This method is particularly suitable for preparing composite material structures with complex gradient shapes, has good repeatability, and is suitable for small-batch or customized production. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the gradient vibration reduction structure of the present invention; Figure 2 This is a schematic diagram of the multi-scale coordinated vibration reduction of the gradient vibration reduction structure in this invention; Figure 3 These are prepregs with different opening radii cut in this invention; Figure 4 This is a half-sectional view of the apparatus for preparing the gradient thickness panel in this invention; Figure 5 This is a schematic diagram illustrating the layer-by-layer layup of prepreg using a graduated release film in this invention. Figure 6 This is a flowchart of the vacuum hot pressing process parameters in this invention; Figure 7 This is a schematic diagram illustrating the measurement of the surface vibration response of a specimen using a laser vibrometer in this invention. Figure 8 This is a comparison of the velocity admittance curves of the gradient vibration reduction structure and the ordinary structure in this invention; 1 is the upper damping layer, 2 is the upper panel, 3 is the middle core layer, 4 is the lower panel, 5 is the lower damping layer, 6 is the upper mold, 7 is the lower mold, 8 is the punch, 9 is the base plate, 10 is the positioning pin, 11 is the release film, 12 is the prepreg, and 13 is the gasket. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] This embodiment provides a gradient vibration reduction structure of continuous plant fiber reinforced honeycomb composite material, such as... Figure 1 As shown, the gradient damping structure includes an upper damping layer 1, an upper panel 2, an intermediate core layer 3, a lower panel 4, and a lower damping layer 5. The upper panel 2 and lower panel 4 are bonded to the upper and lower surfaces of the intermediate core layer 3, respectively. The intermediate core layer has a gradient height honeycomb structure, while the upper panel 2 and lower panel 4 have a gradient thickness structure. One or more recesses are formed in the upper panel 2 and lower panel 4. The upper damping layer 1 is adhered to the bottom of the recesses in the upper panel 2, and the lower damping layer 5 is adhered to the bottom of the recesses in the lower panel 4. The recess cross-section consists of a cut-off region, a variable thickness region, and a flat region. The thickness of the cut-off region is the thickness of a single layer of composite material. The recess cross-section satisfies the following power law function: , In the formula, It is a smoothing constant; x Coordinates; m The power exponent, m ≥2; r 0 represents the radius of the cutoff region; r 1 represents the radius of the variable thickness region; coordinates x Thickness at the point; h 0 represents the thickness of the cut-off region; h 1 represents the thickness of the flattened area.

[0027] In this embodiment, the upper and lower panels have a length, width, and height of 280 mm × 280 mm × 3.96 mm. The upper and lower damping layers are made of circular butyl rubber with a diameter of 56 mm and a thickness of 2 mm. The middle core layer is made of gradient aramid honeycomb structure with a side length of 2.75 mm and a height of 5.2 mm. The upper and lower damping layers are made of viscoelastic materials such as rubber. The upper and lower panels are made of multi-scale continuous plant fiber reinforced composite materials, preferably multi-scale continuous flax fiber reinforced composite materials.

[0028] In this embodiment, the radius of the cutoff region is set. r 0=5mm, thickness of the cut-off region h 0 = 0.33 mm, cutoff diameter is 112 mm, smoothing constant The radius of the variable thickness region is r 1=56mm, thickness of the flattened area h If 1 = 3.96 mm, then the cross-section of the pit satisfies the following function: , Reference Figure 2 The multi-scale structure of continuous flax fiber reinforced composites includes microscopic hollow cavities of flax fibers, microscopic fiber matrix interfaces, and macroscopic gradient thickness. The fiber cavity size is 3-10 μm, the single fiber bundle size is 200-300 μm, and the macroscopic gradient thickness is achieved by the cross-section of the varying thickness pits in the variable thickness region and the truncated region.

[0029] This embodiment also provides a preparation apparatus for preparing the above-mentioned gradient vibration damping structure, including an aluminum alloy hot pressing mold, a positioning pin 10, and a release film 11, as shown in the reference. Figure 4 The hot press mold includes an upper mold 6 and a lower mold 7. The lower mold 7 has dimensions of 400 mm × 400 mm × 3 mm. The upper mold 6 includes a punch 8 and a base plate 9. The base plate 9 has dimensions of 400 mm × 400 mm × 5 mm. A circular groove with a radius of 75 mm and a depth of 3.5 mm is opened in the center of the base plate. A circular through hole with a radius of 15 mm is opened in the center of the groove to facilitate the removal of the punch 8. The punch 8 is installed on the circular groove of the base plate 9 through an transition fit, with its bottom part facing the circular through hole. The cross section of the punch 8 is milled to satisfy the cross section function of the recess, that is, the shape of the punch 8 matches the shape of the recess. The lower mold 7 and the base plate 9 have positioning holes with a diameter of 10 mm at their four corners. Positioning pins 10 are installed in the positioning holes. The release film 11 also has positioning holes corresponding to the lower mold 7. The release film 11 is provided with a scale pattern of circles with different radii and is laid on the lower mold 7 through the positioning holes. In addition, a metal shim 13 is included, which is located on the lower mold 7 and corresponds to the position of the flattening area. The thickness of the gradient damping structure is determined by using shims 13 of different thicknesses.

[0030] Based on the above-described preparation apparatus, this embodiment also provides a preparation method for preparing the above-described continuous plant fiber reinforced honeycomb composite gradient vibration damping structure. The preparation process is as follows: S1. Preparation of continuous flax fiber prepreg: Continuous flax fibers are impregnated with epoxy resin solution, dried and calendered to prepare a 1 m wide continuous flax fiber prepreg. S2, Reference Figure 3 Cutting of prepregs with different radii of openings: The prepared continuous flax fiber prepregs are cut into 12 layers with different radii of openings in the center using a prepreg cutting machine. Each layer of prepreg 12 has a length and width of 280mm × 280mm. The radius values ​​of the openings in the center are shown in Table 1 below: Table 1. Radius values ​​of the center hole S3. Laying Prepregs with Different Hole Sizes: The prepregs 12 with different hole sizes obtained in step S2 are laid layer by layer in the above mold at a 0° layup angle; the layer-by-layer laying process is carried out in the following manner: S3.1, reference Figure 5 Install positioning pins 10 with a diameter of 10 mm on the positioning holes at the four corners of the lower mold 7, and cut flexible release film 11 with the same size as the lower mold 7 and corresponding positioning holes with a diameter of 10 mm. Set scale patterns of circles with different radii on the release film 11, a total of 12, and the different radii on the scale patterns are consistent with the radii of the circular holes in the center of different layers of prepreg 12. S3.2. Adhere the first layer of prepreg 12 onto the first scale base map, and insert the release film 11 into the fixing positioning pin 10 of the lower mold 7 through the positioning hole to align with the center. S3.3 After compacting the prepreg 12, peel off the release film 11 and repeat the above process to ensure that the centers of all prepreg 12 layers coincide. S3.4. The punch 8 and the base plate 9 are installed with the lower mold 7 through the positioning hole of the base plate. Twelve layers of prepreg 12 with the same center are placed between the upper mold 6 and the lower mold 7. The thickness of the gradient thickness panel flat area is determined by the metal shim 13.

[0031] S4. Gradient Thickness Panel Hot Pressing: The prepreg material laid in the mold in step S3 is used to prepare the initial gradient thickness upper and lower panels through a vacuum hot pressing process, referring to... Figure 6 Heating was started from room temperature, the temperature was raised to 90 °C and held for 30 minutes, then the pressure was increased to 2 MPa and the temperature was raised to 130 °C and held for 120 minutes. After hot pressing, the structure was cooled in a vacuum hot press with the furnace to prepare the upper panel 2 and lower panel 4 with gradient thickness. S5. Gradient damping structure composite molding: The upper panel 2 and lower panel 4 with gradient thickness prepared in step S4 are bonded to the upper and lower surfaces of the intermediate core layer 3 with gradient height. They are then co-cured using vacuum bag-assisted molding and autoclave process. The upper damping layer 1 and lower damping layer 5 are then adhered to the upper and lower recesses (cut-off area + part of the variable thickness area) respectively, and the gradient damping structure is finally prepared.

[0032] Reference Figure 7 The vibration response of a conventional structure and a gradient vibration reduction structure of a continuous flax fiber reinforced honeycomb composite material were measured using a vibration signal testing system. A sudden random signal was applied for excitation, which was then amplified by a power amplifier and transmitted to the exciter. The exciter transmitted the excitation force to the sample through a push rod. A force sensor was fitted on the push rod, and the vibration force signal was transmitted to the computer through a charge amplifier. The vibration signal on the sample surface was non-contactly measured by a laser vibrometer and transmitted to the computer. Finally, the velocity admittance value was obtained by data processing in the computer.

[0033] The test results of the ordinary structure and the gradient vibration reduction structure are compared, and the results are as follows: Figure 8As shown, the gradient vibration reduction structure can achieve efficient wideband vibration reduction in the 500-3000 Hz test range, with a maximum attenuation of 6 dB.

[0034] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0035] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A gradient vibration reduction structure of continuous plant fiber reinforced honeycomb composite material, characterized in that, The material includes an upper damping layer (1), an upper panel (2), an intermediate core layer (3), a lower panel (4), and a lower damping layer (5). The upper panel (2), the intermediate core layer (3), and the lower panel (4) are stacked sequentially. The upper panel (2) and the lower panel (4) are both provided with recesses. The upper panel (2) and the lower panel (4) with the recesses form a gradient thickness structure. The upper damping layer (1) and the lower damping layer (5) are respectively located at the bottom of the recesses of the upper panel (2) and the lower panel (4). The intermediate core layer (3) is a gradient height honeycomb structure. The upper panel (2) and the lower panel (4) are made of multi-scale continuous plant fiber reinforced honeycomb composite material.

2. The continuous plant fiber reinforced honeycomb composite gradient vibration reduction structure according to claim 1, characterized in that, The number of recesses opened on the upper panel (2) or the lower panel (4) is one or more.

3. The continuous plant fiber reinforced honeycomb composite gradient vibration reduction structure according to claim 1, characterized in that, The cross-section of the pit consists of a truncated region, a variable thickness region, and a flat region, and the cross-section of the pit satisfies the following power-law function: ， In the formula, coordinates x At the thickness, h 0 represents the thickness of the cut-off region. r 0 represents the radius of the cutoff region. It is a smoothing constant. h 1 represents the thickness of the flattened area. m The power exponent. m ≥2.

4. The continuous plant fiber reinforced honeycomb composite gradient vibration reduction structure according to claim 3, characterized in that, The multi-scale components of the continuous plant fiber reinforced honeycomb composite material include micro-fiber cavities, a meso-fiber matrix interface layer, and a macro-gradient thickness, wherein the macro-gradient thickness is achieved by the cross-section of the varying thickness pits in the variable thickness region and the truncated region.

5. The continuous plant fiber reinforced honeycomb composite gradient vibration reduction structure according to claim 1, characterized in that, The upper damping layer (1) and the lower damping layer (5) are made of viscoelastic materials.

6. A preparation apparatus, characterized in that, The method for preparing a gradient vibration reduction structure of a continuous plant fiber reinforced honeycomb composite material according to any one of claims 1-5 includes: a hot pressing mold, a positioning pin (10) and a release film (11). The hot pressing mold includes an upper mold (6) and a lower mold (7). The upper mold (6) includes a punch (8) and a base plate (9). The punch (8) is mounted on the base plate (9), and the shape of the punch (8) matches the shape of the recess. Positioning holes are provided at corresponding positions of the lower mold (7) and the base plate (9). The positioning pin (10) is installed in the positioning hole. Positioning holes corresponding to the lower mold (7) are also provided on the release film (11). The release film (11) is provided with a scale pattern of circles with different radii and is laid on the lower mold (7) through the positioning holes.

7. The preparation apparatus according to claim 6, characterized in that, The cross section of the punch (8) satisfies the power law function.

8. The preparation apparatus according to claim 6, characterized in that, The base plate (9) has a circular groove in the center and a circular through hole in the center of the circular groove. The punch (8) is installed on the circular groove through a transition fit.

9. The preparation apparatus according to claim 6, characterized in that, It also includes a gasket (13) located on the lower mold (7) and corresponding to the position of the flattening area to determine the thickness of the gradient damping structure.

10. A preparation method, characterized in that, The gradient vibration reduction structure is prepared using a preparation apparatus according to any one of claims 6-9, and the preparation method includes the following steps: Step 1: The continuous plant fiber impregnation resin solution is dried and calendered to prepare a continuous plant fiber prepreg of a specific width; Step 2: Cut the continuous plant fiber prepreg into multiple layers of prepreg (12). Each layer of prepreg (12) has a circular hole of different radius in the center, and the radius of the circular hole is determined according to the power law function. Step 3: Install positioning pins (10) on the positioning holes of the lower mold (7), and cut release film (11) of the same size as the lower mold (7) and with corresponding positioning holes. Step 4: Set a scale pattern with different radii on the release film (11), wherein the different radii on the scale pattern are consistent with the radius of the circular hole in the center of the different layers of prepreg (12); Step 5: Adhere the first layer of prepreg (12) to the first scale base map, and put the release film (11) into the positioning pin (10) on the lower mold (7) through the positioning hole on it to align with the center; Step 6: After compacting the prepreg (12), peel off the release film (11). Step 7: Repeat steps 3-6 above to process each subsequent layer of prepreg (12), wherein all the compacted prepreg (12) are stacked in layers and their centers coincide, and all the circular holes of different radii after stacking form the pits. Step 8: Install the upper mold (6) and the lower mold (7) through the positioning hole. Place all the compacted prepreg (12) in the upper mold (6) and the lower mold (7) in layers. Place the punch (8) in the round hole of all the compacted prepreg (12). Determine the thickness of the gradient damping structure by the shim (13) corresponding to the position of the flat area to obtain the initial upper panel with gradient thickness. Step 9: Prepare an initial lower panel that is identical to the initial upper panel according to steps 1-8 above; Step 10: The initial upper panel and the initial lower panel are processed by vacuum hot pressing to produce the final upper panel (2) and lower panel (4). Step 11: The intermediate core layer (3) is attached between the upper panel (2) and the lower panel (4), and co-cured by vacuum bag assisted molding and autoclave process. Then the upper damping layer (1) and the lower damping layer (5) are adhered to the pit to obtain a gradient vibration reduction structure.

Images