An integrated structure for load bearing, heat insulation, and drag reduction, and its preparation method.

Abstract

This invention discloses an integrated structure for load-bearing, heat insulation, and drag reduction, and its fabrication method, belonging to the aerospace field. Through mechanical methods, it achieves multifunctional integrated reconstruction of metal structures, solving problems such as heavy weight, low load-bearing capacity, complex structure, strict connection and assembly requirements, unfriendly heat insulation environments in engineering, and low efficiency. This invention employs a mechanical method to implant a heat-insulating lattice functional phase into a metal matrix. A reconstruction tool is used to micro-press the phase onto the alloy surface according to a set program, inducing a path-based rotational friction motion that drives the material to undergo intense plastic rheology. The plastic deformation process follows a fractal process optimization flow, further forming a surface texture structure on the metal-based ceramic or near-ceramic surface, with a gradually twisted cross-section, resulting in a seamless gradient transition from the outer side of the structure to the matrix. This invention leverages the excellent load-bearing and heat insulation effects of the heat-insulating lattice functional composite phase, and the specific texture structure on the metal-based ceramic or near-ceramic surface contributes to excellent drag and vibration reduction.

Description

Technical Field

[0001] This invention belongs to the field of aerospace technology, and in particular relates to an integrated structure that combines load-bearing, heat insulation, and drag reduction, as well as its preparation method. Background Art

[0002] Modern aircraft are characterized by high Mach numbers and long flight cycles, resulting in aerodynamic heating that places more stringent demands on the thermal corrosion resistance of hypersonic aircraft. To ensure the safety of the main structure and internal instruments of the aircraft, lightweight, efficient, and reliable thermal insulation materials are needed to prevent external heat from flowing into the aircraft's interior. Currently, aerospace thermal insulation materials mainly include ceramic heat insulation tiles and outer shell covers. However, these materials suffer from problems such as poor reliability, low load-bearing capacity, complex structure, heavy weight, and overly stringent connection and assembly requirements, making it difficult to meet the requirements of economic efficiency, reliability, and sustainability. Summary of the Invention

[0003] This invention provides an integrated structure for load-bearing, heat insulation, and drag reduction, and its preparation method. The integrated structure design for material load-bearing, heat insulation, and drag reduction is achieved through a combination of mechanical and CNC methods.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An integrated structure for load-bearing, heat insulation, and drag reduction is disclosed. The material comprises a drag-reducing textured surface, a heat-insulating lattice transition layer, and a load-bearing metal substrate. The metal substrate surface is machined with a regular array of holes, the surface and inner walls of which are smooth, burr-free, and crack-free. The array holes are filled with lattice material with certain gaps. The metal substrate filled with lattice material is compressed with a non-material-removing tool head, and subjected to rotational friction and vibration to induce plastic deformation of the material surface. The plastic deformation process follows a fractal process optimization procedure. The fractal process optimization procedure processes the textured surface according to parameters such as feed rate, single-layer pressure, and tool straightness percentage. After the processing is completed, a scaly texture composed of dynamically recrystallized fine grains is formed on the material surface. The texture is a multi-directional curved quadrilateral. The texture structure is mechanically processed to increase free energy, causing the heat-insulating material and the metal substrate to undergo a phase transition reaction and then combine with the substrate material, achieving a seamless integrated structure.

[0006] In the above-mentioned materials, the array holes are regularly distributed at equal intervals, the surface texture of the array holes is smooth and no cracks shall appear; the squamous texture is a metal-based ceramic or a near-ceramic functional surface; the lattice point material is a dense material (such as a carbon fiber composite material doped with SiC particles of different diameters); the voids can be secondarily filled with thermal insulation materials (such as aerogels, carbides, nitrides, and oxides, etc.) or drag reduction materials to achieve better effects.

[0007] A preparation method for an integrated structure of load-bearing, heat insulation and drag reduction includes the following steps:

[0008] Step 1: Establish a fractal surface texture structure expression using the W-M model

[0009]

[0010] where z(x,y) is the height of the surface texture; x,y are three-dimensional coordinate variables; D is the fractal dimension of the fractal surface. The larger the fractal dimension, the richer the structural details of the squamous texture. For this three-dimensional model, 1 < D < 3; G is the roughness coefficient. The larger G is, the rougher the squamous texture surface; γ is the spatial frequency of the texture, and γ generally takes 1.5; n is the wave number; m is the frequency coefficient; L is the sampling length; M is the overlap number of the fractal surface texture folds; is a random phase;

[0011] Step 2: Set the material properties according to the selected materials, and import the structure expression into three-dimensional design software for reverse modeling;

[0012] Step 3: Import the model obtained by modeling into software for simulation, and obtain the law of the change of the surface texture structure with process parameters according to the simulation results; control the variables of the process parameters through the law, further set the optimal process parameters, and process to obtain the desired surface texture structure;

[0013] Step 4: Adopt a mechanical implantation method. First, implant array holes on the surface of a high-strength alloy matrix through a drill bit, and then process a smooth, burr-free and crack-free hole wall in the holes and fill the lattice point material;

[0014] Step 5: Through the progressive metal surface micro-nano modification technology (MIMST), use a modification tool to compress the material surface according to the optimal process parameters, and perform rotational friction and vibration on it, so that the material surface undergoes plastic deformation and grain refinement strengthening, and the thermal insulation material and the metal matrix are densely compounded together to form a functional phase with stable physical properties, while improving the strength, hardness, plasticity and toughness of the metal;

[0015] Step 6: Repeat step 5 until the material is compressed to a predefined thickness to prepare a load-bearing, heat-insulating, and drag-reducing integrated structure with a multi-directional scaly textured metal-based ceramic or near-ceramic functional surface.

[0016] The material properties mentioned in step 2 of the above-mentioned materials include Young's modulus, density, and Poisson's ratio; the process parameters mentioned in step 3 include the diameter of the modified tool tip, the tool speed, the feed rate, the single-layer undercut, and the tool straightness percentage; when different process parameters are used, the scale-like texture produced by modification will be different, that is, the texture base length, texture height, and texture angle will change accordingly with the change of process parameters.

[0017] Beneficial Effects: This invention provides an integrated structure for load-bearing, heat insulation, and drag reduction, and its fabrication method. Through a combination of mechanical and CNC methods, it achieves multifunctional integrated reconstruction of metal structures (such as aluminum alloys, magnesium-aluminum alloys, and aluminum-lithium alloys), solving the problems of long processing time, high cost, low precision, and environmental pollution that are prevalent in current technologies. This promotes the development and application of microtexturing technology in practical industry. The structure of this invention includes a drag-reducing textured surface with surface texturing, a heat-insulating lattice transition layer, a load-bearing metal substrate, lattice points filling array holes providing support, and a path-based rotation mechanism for the reconstruction tool. Friction passing through the array holes results in a metal-based ceramic surface supported by a lattice matrix, improving structural stability and facilitating the formation of a seamless integrated structure. Due to its high strength-to-weight ratio, excellent heat dissipation performance, and vibration damping and noise reduction capabilities, the lattice matrix allows for a balance between stiffness and strength while reducing structural weight, achieving lightweighting. The voids, implanted lattice matrix materials, and secondary filling insulation materials (such as aerogels, carbides, nitrides, and oxides) primarily function as heat preservation and vibration absorption materials. Surface textures mainly serve to reduce drag and vibration. This invention is based on progressive metal surface micro / nano modification technology (MIMS). T) Establish a fractal surface texture structure expression, import the expression into 3D design software for reverse modeling; simulate to obtain the law of surface texture structure changing with process parameters, further set optimal parameters to quickly and accurately prepare the desired surface texture structure, realizing the adjustable, controllable and distributable production process; the texture structure increases free energy through mechanical treatment, causing the thermal insulation material and the metal matrix to undergo a phase change reaction and then composite with the matrix material, realizing a seamless integrated structure; the technology integrates thermal insulation, CNC technology, surface metallurgy, and microstructure drag reduction into the field of metal surface engineering; the prepared surface texture structure is... The material possesses high specific strength and specific modulus, meaning the integrated structure exhibits high strength, high rigidity, and light weight. The integrated structure prepared by this technology demonstrates excellent fatigue resistance, effectively preventing the propagation of fatigue cracks. Furthermore, the integrated structure prepared by this technology increases the natural frequency, effectively preventing resonance and providing good vibration damping performance. The integrated structure prepared by this technology also exhibits excellent high-temperature performance; the tensile strength of the ceramic textured surface remains at room temperature levels even at temperatures ranging from 1000℃ to 1200℃, demonstrating excellent high-temperature performance. This technology is suitable for large-scale sheet metal forming, is pollution-free and low-cost, and enables green production of surface engineering. Attached Figure Description

[0018] Figure 1 The preparation method described in this embodiment of the invention;

[0019] Figure 2 This is a process flow diagram in an embodiment of the present invention;

[0020] Figure 3Schematic diagram of the overall structure of the integrated structure for load-bearing, heat insulation and resistance reduction in the embodiments of the present invention;

[0021] Figure 4 Enlarged view of the surface texture structure of the integrated structure for load-bearing, heat insulation and resistance reduction in the embodiments of the present invention;

[0022] Figure 5 Drag reduction texture structure diagram of the surface texture of the integrated structure for load-bearing, heat insulation and resistance reduction in the embodiments of the present invention;

[0023] Figure 6 Contour map of the flow velocity distribution along the flow direction of the overall model set for calculating the drag reduction effect of the material in the embodiments of the present invention;

[0024] Figure 7 Contour map of the pressure distribution along the flow direction of the overall model set for calculating the heat insulation effect of the material in the embodiments of the present invention;

[0025] Figure 8 Contour map of the surface friction coefficient distribution along the flow direction of the overall model set for calculating the drag reduction effect of the material in the embodiments of the present invention;

[0026] Figure 9 Contour map of the surface heat transfer coefficient distribution along the flow direction of the overall model set for calculating the drag reduction effect of the material in the embodiments of the present invention. Specific embodiments

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] As Figure 1 and Figure 2 shown, a preparation method for an integrated structure for load-bearing, heat insulation and resistance reduction includes the following steps:

[0029] Step 1: According to the structural performance requirements, establish a fractal surface texture structure expression using the W-M model:

[0030]

[0031] where z(x, y) is the height of the surface texture; x, y are three-dimensional coordinate variables; D is the fractal dimension of the fractal surface. The larger the fractal dimension, the richer the structural details of its scaly texture. For this three-dimensional model, 1 < D < 3; G is the roughness coefficient. The larger G is, the rougher the scaly texture surface; γ is the spatial frequency of the texture, taking 1.5; n is the wave number; m is the frequency coefficient; L is the sampling length; M is the overlap number of the fractal surface texture folds; is the random phase;

[0032] Step 2: Import the expression into the 3D design software for reverse modeling. The modeling is based on Solidworks software. The specimen material is 7075-T6 aluminum alloy. The material properties are set as follows: Young's modulus is 71 GPa, density is 2810 kg per cubic meter, and Poisson's ratio is 0.3.

[0033] Step 3: Import the model into ANSYS and ABAQUS finite element software for simulation. The workpiece is made of 7075 aluminum alloy, and the surface texture generated by the machining process must be considered during the simulation. Therefore, it cannot be coupled as a rigid body. Edit the material properties, set "hardening" to isotropic in "plasticity" and input the stress-strain values ​​of 7075-T6 aluminum alloy; edit the section properties, and set the specimen type to "solid, homogeneous"; in the assembly, apply a preload to the modification tool to make it contact the specimen; edit the analysis step, set the type to "dynamic, explicit", set the time length to 6.7 seconds, and turn on the "geometric nonlinear" solver; edit the field output request, and set the scope to "entire model"; edit the interaction, select "master face" as the outer surface of the modification tool and "follower face" as the surface to be machined on the specimen; define the boundary conditions and solve to obtain the simulation results. The simulation results revealed the following pattern in which the surface texture structure changes with process parameters: When the modified tool tip diameter varies from 4mm to 16mm, the texture angle of the scaly texture first decreases monotonically, reaching its minimum of 73.28° at a tip diameter of 8mm, and then monotonically increases again within the 8mm to 16mm range. When the modified tool rotation speed ranges from 6000 rpm to 11000 rpm, the texture angle of the scaly texture increases monotonically from 73.28° to 77.91°, indicating an upward trend in surface texture angle with increasing rotation speed. When the modified tool feed rate varies from 3000 mm / min to 21000 mm / min, the texture angle of the scaly texture reaches its maximum value of 99.23° at 15000 mm / min. The process parameters include the modified tool tip diameter, tool rotation speed, feed rate, single-layer indentation, and tool straightness percentage. When processing surface textures, the variables of the above-mentioned process parameters are controlled in a regular manner, and the optimal process parameters are further set to obtain the desired surface texture.

[0034] Step 4: Using a mechanical implantation method, array holes are first implanted on the surface of the high-strength alloy substrate using a drill bit. Then, a reamer is used to process smooth, burr-free, and crack-free hole walls inside the holes. SiC particles of different diameters are filled as thermal insulation material and a certain amount of voids are left. These voids can be filled with other thermal insulation materials (such as aerogel, carbide, nitride, and oxide) to achieve better thermal insulation effect.

[0035] Step 5: Using progressive metal surface micro-nano modification technology (MIMST), the material surface is compressed according to the set optimal process parameters using a remanufacturing tool, and subjected to rotational friction, vibration, and ultrasonic excitation to induce plastic deformation and fine grain strengthening on the material surface. The thermal insulation material and the metal matrix are densely combined to form a functional phase with stable physical properties, while improving the strength, hardness, plasticity, and toughness of the metal.

[0036] Step 6: Repeat step 5 until the surface material is compressed to a predefined thickness to prepare a metal-based ceramic or near-ceramic functional surface with a multi-directional scaly texture.

[0037] like Figure 3 As shown, an integrated structure for load-bearing, heat insulation, and drag reduction is disclosed. The material comprises a drag-reducing textured surface, a heat-insulating lattice transition layer, and a load-bearing metal substrate. The metal substrate surface is machined with an array of holes whose inner walls are smooth, burr-free, and crack-free. The array holes are regularly and evenly spaced, and their surfaces are smooth and crack-free. The array holes are filled with lattice material, leaving certain gaps. The metal substrate filled with lattice material is compressed on its surface using a non-material-removing tool head, and subjected to rotational friction and vibration to further compress the material. Plastic deformation occurs on the material surface; the plastic deformation process must follow the fractal process optimization process; the fractal process optimization process processes the texture according to parameters such as feed rate, single-layer pressure, and tool straightness percentage; after the processing is completed, a scaly texture composed of dynamically recrystallized fine grains is formed on the material surface; the texture is a multi-directional curved quadrilateral; the texture structure increases free energy through mechanical treatment, causing the thermal insulation material and the metal matrix to undergo a phase change reaction and then combine with the matrix material to achieve a seamless integrated structure.

[0038] A 30-layer aluminum alloy processed by MIMST was placed under a metallographic microscope at 50x magnification to observe the surface texture. Figure 4 As shown, the surface texture is elliptical and scaly, which can be approximated as the continuous elliptical machining texture produced by the modified tool under the interaction of downward pressure and rotational friction. The parameters of the major semi-axis a and minor semi-axis b of the elliptical feature are extracted.

[0039] In this embodiment, the overall model is a right-angled triangle with a side length of 3mm and a height of 0.8mm, and an extruded thickness of 1.5mm. A surface texture is established using the wedge face of this triangular wedge as the base surface. The surface texture is created using an ellipse with rotational cutting. Considering that the MIMST-modified surface texture is a microstructure, the surface texture characteristic parameters are measured under an optical microscope. The parameters are as follows: the major semi-axis a of the ellipse is 0.13mm, the minor semi-axis b is 0.04mm, and the rotational cutting is as follows... Figure 5As shown in (b), after the excision is completed, a linear array is selected, and the spacing of the ellipses along the major axis is also set to 0.13 mm, while the spacing along the minor axis is 0.09 mm, resulting in... Figure 5 The array feature shown in (b) has a surface texture of 16×22 elliptical structures. The layer beneath the texture is a heat insulation layer, and the remaining part is an aluminum alloy wedge-shaped substrate.

[0040] The integrated structure flow field environment is set as follows: the fluid model is set to single phase, the heat transfer model is set to adiabatic, the turbulence model is set to adaptive, the fluid medium is air, the fluid velocity is 50 m / s, and the density is 1.225 kg·m³. 3 With an ambient temperature of 288.15K, the following results were obtained through calculation:

[0041] To calculate its barrier reduction and heat insulation effect, the velocity diagram of the fluid distribution along the flow direction in the integrated structure is shown below. Figure 6 As shown, the surface pressure distribution of the integrated structure is as follows: Figure 7 As shown, the surface friction coefficient distribution of the integrated structure is as follows: Figure 8 As shown, the thermal conversion coefficient distribution of the integrated structure is as follows: Figure 9 As shown.

[0042] Figure 6 (a) The blank control group consisted of aluminum alloy wedges with no surface texture and no ceramic heat insulation transition layer. After the incoming air flow of 50 m / s, the velocity gradient distribution on the wedge surface was as follows: the velocity at the bottom of the wedge was maintained at about 38.6 m / s, and the velocity increased with the increase of the wedge height, reaching a maximum of 51.3 m / s. The overall change of the wedge surface velocity was relatively slow and gradually increased with the height. Figure 6 (b) The incoming air at 50 m / s encounters the surface texture and its velocity changes abruptly, reaching a minimum of around 15.8 m / s. The velocity recovers slightly with increasing altitude, but remains below the incoming air velocity, generally hovering around 30.5 m / s. The surface velocity is significantly lower than that of the untextured model. Surface pressure is as follows... Figure 7 As shown, the pressure on the untextured surface is around 1590.7 Pa, while the pressure on the textured surface remains around 555.6 Pa, indicating that the textured surface has lower pressure. The surface friction coefficient is as follows: Figure 8 As shown, the friction coefficient of the untextured surface is around 0.003, while the friction coefficient of the textured surface remains around 0.001, indicating that the textured surface has a lower friction coefficient. Since a smaller surface friction coefficient means a smaller shear force on the fluid flowing through the texture, a smaller portion of the kinetic energy is converted into heat energy, thus the surface heat conversion coefficient is also smaller. The surface heat exchange coefficient is as follows: Figure 9 As shown, the heat transfer coefficient of the textureless surface is 118.083 W·m. -2 ·k -1 Around 72.977 W·m, the surface textured friction coefficient remains at approximately 72.977 W·m. -2 ·k-1 about.

[0043] Based on the above near-flow field calculations, the velocity of the integrated structure with surface texture can be reduced by about 33.3% compared to the untextured surface. The pressure of the textured surface is only 0.39 times that of the untextured surface, the surface friction coefficient is only 0.3 times that of the untextured surface, and the surface heat conversion coefficient is 0.618 times that of the untextured surface, proving that the surface texture has a good effect on reducing barrier and preventing heat.

[0044] The above are merely preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing an integrated structure that combines load-bearing, heat insulation, and drag reduction, characterized in that, Includes the following steps: Step 1: Establish the fractal surface texture structure expression using the WM model. ， in The height of the surface texture; is a three-dimensional coordinate variable; D is the fractal dimension of the fractal surface, the larger the fractal dimension, the richer the structural details of its scale texture; G is the roughness coefficient, the larger G is, the rougher the scale texture surface. denoted as spatial frequency of the texture; n is wavenumber; m is frequency coefficient; L is sampling length; M is the number of overlaps of the fractal surface texture folds; It is a random phase; Step 2: Set material properties according to the selected material, and import the structural expression into 3D design software for reverse modeling; Step 3: Import the model obtained from modeling into the software for simulation, and obtain the law of surface texture structure changing with process parameters based on the simulation results; control the variables of the process parameters through the law, further set the optimal process parameters, and process to obtain the desired surface texture structure; Step 4: Using mechanical implantation, array holes are implanted on the substrate surface, and then smooth, burr-free, and crack-free hole walls are machined inside the holes and filled with lattice material. Step 5: Through progressive metal surface micro-nano modification technology, the material surface is plastically deformed and fine-grained strengthening is carried out according to the optimal process parameters, and the thermal insulation material and the metal matrix are densely combined to form a functional phase with stable physical properties. Step 6: Repeat step 5 until the material is compressed to a predefined thickness to prepare a load-bearing, heat-insulating, and drag-reducing integrated structure with a multi-directional scaly textured metal-based ceramic or near-ceramic functional surface.

2. The method for preparing the integrated structure for load bearing, heat insulation, and drag reduction according to claim 1, characterized in that, The material properties mentioned in step 2 include: Young's modulus, density, and Poisson's ratio.

3. The method for preparing the integrated structure for load bearing, heat insulation, and drag reduction according to claim 1, characterized in that, The process parameters mentioned in step 3 include the modified tool tip diameter, tool rotation speed, feed rate, single-layer indentation, and tool straightness percentage.

4. The method for preparing the integrated structure for load-bearing, heat insulation, and drag reduction according to claim 1 or 3, characterized in that, When different process parameters are used, the modified scaly texture will be different, that is, the texture base length, texture height and texture angle will change accordingly with the change of process parameters.

5. The method for preparing the integrated structure for load-bearing, heat insulation, and drag reduction according to claim 1, characterized in that, Step 5 is supplemented with ultrasonic stimulation.

6. The integrated structure for load bearing, heat insulation, and drag reduction prepared by the method according to any one of claims 1-5, characterized in that, The structure includes a textured, drag-reducing surface, a thermally insulating lattice transition layer, and a load-bearing metal substrate. The surface of the metal substrate has a regularly distributed array of holes. These holes are filled with lattice material and have some voids. The surface of the metal substrate filled with the lattice material undergoes plastic deformation, forming a scaly texture composed of dynamically recrystallized fine grains. The lattice material undergoes a phase transition reaction with the metal substrate, thus becoming composite with it, achieving a seamless, integrated structure.

7. The integrated structure for load-bearing, heat insulation, and drag reduction according to claim 6, characterized in that, The texture is a multi-directional curved quadrilateral.

8. The integrated structure for load-bearing, heat insulation, and drag reduction according to claim 6, characterized in that, The array holes are regularly spaced at equal intervals.

9. The integrated structure for load-bearing, heat insulation, and drag reduction according to claim 6 or 8, characterized in that, The surface of the array aperture is smooth, and the inner wall is smooth without burrs or cracks.

10. The integrated structure for load-bearing, heat insulation, and drag reduction according to claim 6, characterized in that, The lattice gaps can be filled with heat-insulating or drag-reducing materials.

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