A reusable rocket stage interstage and method of making the same

Abstract

The present application relates to aerospace structure manufacturing technical field, disclose a kind of reusable rocket stage and preparation method thereof, comprising: 4~12 carbon fiber / epoxy resin modular grid reinforcing units formed by hot die pressing, which is internally provided with grid-shaped reinforcing rib structure comprising helical rib and ring rib, and fillet transition is provided at the intersection of rib; Standardized interface is provided at the end of unit, and detachable connection of adjacent units is realized by metal connecting component; High-temperature-resistant protective layer is coated on the outer surface. The preparation method comprises mold manufacturing, local reinforcement of prepreg at intersection, hot die pressing curing, laser alignment assembly and surface spraying. The present application uses modular design and metal connecting component to establish physical boundary, limits local damage in a single module and blocks crack propagation path; Only damaged unit needs to be replaced by removing mechanical constraint during maintenance, avoiding complex destructive repair process and reducing repair difficulty.

Description

Technical Field

[0001] This invention relates to the field of aerospace structural component manufacturing technology, specifically to a reusable rocket stage intersection and its preparation method. Background Technology

[0002] With the development of reusable launch vehicle technology, the interstage section, as a key load-bearing structure connecting the upper and lower stages of a rocket, needs to withstand multiple loads during multiple launches and recoveries, including axial tension and compression, alternating bending moments, localized impacts, and aerodynamic heating. Currently, in order to meet the weight reduction targets of spacecraft, the interstage section mostly uses carbon fiber reinforced resin matrix composite materials and relies on large autoclave equipment for integral molding and manufacturing.

[0003] While composite material components with this monolithic continuous structure possess high structural efficiency, they present challenges for post-construction maintenance under conditions of frequent reusability. When interstage sections are subjected to localized impacts during separation, landing recovery, or transport, or when experiencing fatigue loads during long-term service, microscopic damage such as interlaminar debonding or matrix cracking can easily occur within the material. Because the monolithic component lacks physical boundaries to block the transmission of force, the continuous resin matrix objectively becomes a medium for the propagation of microcracks. This causes initially localized damage to continue to expand under subsequent alternating loads, ultimately affecting the overall load-bearing capacity of the structure.

[0004] For damaged integral composite components, conventional maintenance methods typically employ a patch-and-repair process, which involves removing the damaged area, applying new material, and then subjecting it to secondary heat curing. This repair process is lengthy and cumbersome. Furthermore, localized reheating and curing can easily generate residual thermal stress at the interface between the old and new materials, making it difficult for the repaired area to meet initial design requirements in terms of mechanical properties. With increasing service life, the combined effects of damage propagation and repeated heat repairs accelerate material aging, increasing the risk of overall structural failure and making it unsuitable for the high-frequency, low-cost demands of commercial space launches. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a reusable rocket stage intersegment and its preparation method, which solves the problems that microcracks in existing integrally molded composite rocket stage intersegments are prone to continuous propagation within the continuous matrix after local damage, and that traditional local patching repair processes are complex and prone to generating residual thermal stress.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a reusable rocket stage intersection, comprising: 4 to 12 modular mesh reinforcement units. The modular mesh reinforcement units are made of carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% by thermoforming. The modular mesh reinforcement units have a mesh-like reinforcing rib structure inside. The ribs of the mesh-like reinforcing rib structure include spiral ribs and ring ribs. The width of the spiral ribs is 4.91 mm, the width of the ring ribs is 3.37 mm, the height of the mesh-like reinforcing rib structure is 26.12 mm, and the intersection of the ribs of the mesh-like reinforcing rib structure is provided with a rounded transition structure with a radius of 2 mm to 5 mm. A standardized interface is provided at the connection end of the modular mesh reinforcement unit for detachable connection between adjacent modular mesh reinforcement units; Connecting components, installed at standardized interfaces, are made of metal and used to fix modular mesh reinforcement units together; An external skin protective layer is formed on the outer surface of the reusable rocket stage section. The external skin protective layer is a 0.3 mm thick zirconium dioxide thermal barrier coating or a silicon-based high-temperature resistant coating.

[0007] By adopting the above technical solution, the modular grid reinforcement unit serves as the core component, utilizing the inherent properties of carbon fiber composite materials to construct the foundation. The stress pattern of the overall shell is altered by the presence of the internal reinforcing rib network. Specifically, the helical ribs primarily handle axial tension, compression, bending moment, torque, and shear loads, while the circumferential ribs, working in conjunction with them, restrict the radial displacement of the helical ribs and resist circumferential pressure. The interweaving of these two types of ribs suppresses buckling instability of the outer skin. A 2mm to 5mm rounded corner transition design is introduced at the rib intersection area, altering the sharp abrupt change in the original geometry and allowing the load to transition smoothly at the node area, thereby alleviating stress concentration and reducing the probability of shear failure. Regarding the assembly method, metal connecting components are combined with standardized interfaces, breaking down the originally integrated large-size cylindrical section into multiple independently operable structural units. If local overload damage occurs, operators only need to separate and replace the specific unit through the interface, controlling subsequent maintenance costs. In the face of a pneumatic heating environment, the outer skin protective layer, with its low thermal conductivity, weakens the penetration of external heat flow into the internal carbon fiber resin matrix, preventing the epoxy resin from undergoing thermal degradation or experiencing a drop in glass transition temperature.

[0008] Preferably, the carbon fiber / epoxy resin prepreg adopts a quasi-isotropic layup, with the layup sequence being a symmetrical layup of [0° / 45° / −45° / 90°]n or [0° / 45° / −45° / 90°]n, where n is the number of repetitions.

[0009] By adopting the above technical solution, the quasi-isotropic layup design endows the composite laminate with uniform elastic modulus and Poisson's ratio in all directions within the plane. This homogenization of physical properties ensures that the reinforcing unit does not exhibit local stiffness deficiencies or early interlaminar cracking due to directional differences when facing multi-directional coupled loads during rocket flight.

[0010] Preferably, the joints formed by the connection of adjacent modular mesh reinforcement units are coated with a high-temperature sealant that can withstand temperatures up to 300°C.

[0011] By employing the above technical solution, the high-temperature sealant filling the assembly gaps blocks the infiltration path of external airflow, helping to maintain the relative balance of the thermodynamic environment inside the equipment compartments. In addition to its sealing effect, its inherent elasticity can also buffer the mechanical friction at the joints under vibration.

[0012] Preferably, the mesh spacing of the grid-like reinforcing rib structure is 115mm×112mm; the standardized interface is a bolt connection interface or a slot-type quick-release structure; the connecting parts are made of TC4 titanium alloy, aluminum alloy or GH 4169 high-temperature alloy.

[0013] By adopting the above technical solution, a specific grid spacing establishes a proportional balance between the overall structural weight and the critical buckling load. Various combinations of metal materials and interface types allow operators to select appropriate options based on the stress conditions and thermal environment of different load levels, ensuring the integrity of the connection points.

[0014] Secondly, the present invention provides a method for preparing a reusable rocket stage intersection, comprising the following steps: Manufacturing a modular mold system, which includes modular mesh-reinforced unit molding dies and connecting component molding dies; Carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% was cut into sheets; The cut carbon fiber / epoxy resin prepreg is laid layer by layer in the modular mesh reinforcement unit molding mold, and local reinforcement layers are laid at the intersection of the ribs corresponding to the mesh-like reinforcing rib structure to be formed. After the mold is closed, it is placed in a press for hot molding. The temperature is set at 120-180℃, the pressure is 5-10MPa, and the holding time is 30-60min. After complete curing and cooling, it is demolded and polished to obtain a modular mesh reinforcement unit. A standardized interface is set at the connection end of the modular mesh reinforcement unit. The connecting components are fabricated in a mold for forming the connecting components; Multiple modular mesh reinforcement units are placed on the assembly fixture, and laser positioning is used to ensure the alignment of standardized interfaces. Connecting components are installed at the standardized interfaces for fixation, forming a reusable rocket stage section. The outer surface of the reusable rocket stage intersection is sprayed to form a 0.3mm thick zirconium dioxide thermal barrier coating or a silicon-based high-temperature resistant coating as an external skin protective layer.

[0015] By adopting the above technical solution, the local reinforcing layup at the intersection nodes provides physical compensation for the fiber distribution differences that are easily caused by resin flow in complex mold cavities, thus compensating for the loss of node strength caused by fiber deflection. After entering the hot molding stage, the set external pressure (5-10 MPa) drives the epoxy resin to flow throughout the mold cavity, penetrating into the carbon fiber network. Through extrusion, air and volatiles trapped between layers are released, achieving the purpose of controlling porosity. During this period, in conjunction with the increase in ambient temperature, the cross-linking and curing reaction between epoxy resin molecular chains is triggered, and the original linear molecules gradually build into a three-dimensional network structure, ultimately curing into a dense reinforcing matrix. As for the assembly stage, the introduced laser positioning equipment limits the cumulative tolerance of splicing, ensuring that the stress centers of each assembly module remain aligned.

[0016] Preferably, the modular mesh reinforcement unit forming mold is made of H13 mold steel. The working surface of the modular mesh reinforcement unit forming mold is machined with grooves and protrusions corresponding to the mesh-like reinforcing rib structure, and the modular mesh reinforcement unit forming mold is designed as a four-piece detachable structure.

[0017] By adopting the above technical solution, H13 mold steel is mainly used to take advantage of its resistance to thermal fatigue in order to cope with the micro-deformation that may be caused by repeated hot molding cycles. The four-piece detachable structure, combined with the internal concave and convex shape, makes the mold separation trajectory conform to the draft angle of the grid unit, reducing the risk of scratching the surface of the carbon fiber part due to forced demolding.

[0018] Preferably, the parameters for hot molding are as follows: temperature is set to 120℃, pressure is 5MPa, and holding time is 60min; after demolding and polishing, the dimensional tolerance of the obtained modular mesh reinforcement unit is no greater than 0.2mm.

[0019] By adopting the above technical solution, the temperature and pressure settings provide the basic activation energy for the curing kinetics of the epoxy resin system. After a constant-duration heat and pressure holding process, the residual stress generated inside the part due to high-temperature molding is released. The 0.2mm dimensional tolerance limit aims to reduce the forced assembly stress induced by dimensional mismatch during subsequent multi-module assembly.

[0020] Preferably, when the standardized interface is a bolted connection interface, M8 bolts are used to fix the connecting parts, and the tightening torque is set to 15 N·m; a high-temperature sealant with a temperature resistance of 300°C is applied to the connection seam formed by the connection of adjacent modular mesh reinforcement units after fixing; the absolute value of the overall length error of the reusable rocket stage section after assembly is not greater than 1 mm.

[0021] By adopting the above technical solution, the tightening torque of the constraint bolts provides a uniform preload on the assembly surface, preventing displacement of the connection nodes in the flight vibration environment or crushing of the composite laminate due to excessive pressure. Limiting the final error of the overall length lays the foundation for the smooth aerodynamic shape during the subsequent docking stage of the rocket's various sections.

[0022] Preferably, an inspection hole with a diameter of 50 mm is opened on the reusable rocket stage section according to design requirements, and a sealing cover is installed at the inspection hole.

[0023] By adopting the above technical solution, the inspection holes are reserved to provide physical maintenance paths for internal electrical cables and pipes, while the added sealing cover fills the defects on the outer surface caused by the holes and maintains the continuity of the aerodynamic shape of the outer edge of the structure.

[0024] Preferably, the preparation method further includes reusable maintenance of the molded reusable rocket stage section: visual inspection and ultrasonic C-scan non-destructive testing are used to inspect the recovered reusable rocket stage section to identify damaged modular mesh reinforcement units or damaged connecting parts; the damaged modular mesh reinforcement units or damaged connecting parts are disassembled and replaced with undamaged modular mesh reinforcement units or undamaged connecting parts of the same model; the modular mesh reinforcement units and connecting parts are re-fixed, and the external skin protective layer is re-sprayed on the replacement parts; finally, a static loading test of 1.5 times the design load is carried out to restore the structural function.

[0025] By adopting the above technical solution, ultrasonic C-scanning can locate hidden damage by relying on the change in acoustic impedance as sound waves pass through the material interface, thus mimicking internal debonding and delamination phenomena that are difficult to detect with the naked eye. After identifying the damaged area, the method of individually removing and replacing specific unit components replaces the original overall scrapping mechanism. The shell after the new component assembly must withstand static verification loading exceeding the design benchmark to confirm the strain distribution and load-bearing state of the reassembled node area, providing data reference for the structure's secondary flight.

[0026] This invention provides a reusable rocket stage intersection and its preparation method. It has the following beneficial effects: 1. This invention employs modular mesh reinforcement units and metal connecting components to construct the interstage structure of a rocket. When the structure suffers localized damage under stress, the physical boundary formed by the metal connecting components and the composite material confines crack propagation within a single damaged module, preventing through-type failure of the overall structure. The standardized interface allows operators to replace damaged modules individually by releasing mechanical constraints, eliminating the need for destructive cutting and secondary curing processes required for traditional composite materials, and simplifying the inspection and maintenance process of the interstage section during its reuse cycle. 2. This invention incorporates a grid-like reinforcing rib within the modular unit and a rounded transition structure at the intersection of the spiral and ring ribs to mitigate the abrupt changes in cross-section caused by right-angle intersections. Under alternating spatial loads, the rounded corner structure allows the carbon fiber bundles to be laid along the geometric shape, reducing fiber cutting and resin-rich area defects, lowering stress concentration at intersections, mitigating plastic yielding and microcrack initiation in the resin matrix, and improving the fatigue life of the structure under multi-directional composite stress conditions. 3. This invention coats the outer surface of the module with a thermal barrier coating or a silicon-based high-temperature resistant coating, and applies high-temperature sealant to the joints between the modules, maintaining the stability of the structure under external thermal and pressure differential environments. The external coating blocks some of the heat, preventing the epoxy resin matrix in the carbon fiber prepreg from softening or pyrolyzing due to exceeding its glass transition temperature; the cured sealant at the joints fills the assembly gaps, reducing the sliding of adjacent modules under stress while cutting off the path for internal gas to permeate outward, ensuring the structural airtightness. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the rocket stage intersection structure of the present invention; Figure 2 The figures are a comparison of the static bearing capacity and displacement / strain of the present invention, wherein (a) is a comparison trend of axial bearing capacity; (b) is a trend of lateral elastic limit displacement under lateral bending moment loading; and (c) is a distribution of maximum local strain data under the ultimate bearing state. Figure 3 The diagram shows the partial disassembly and repeated assembly performance test of the present invention, wherein (a) is a maintenance time distribution diagram; (b) is a cumulative dimensional deviation curve after multiple disassembly and assembly cycles; and (c) is a stiffness attenuation (torque loss) trend diagram after multiple assembly cycles. Figure 4 The diagrams are for evaluating the structural sealing and thermal insulation performance of the present invention, wherein (a) is a curve for evaluating the degree of pressure leakage; (b) is a curve for the peak temperature of the outer surface under heat; and (c) is a curve for the conduction response of the inner wall. Figure 5The following is a comparison chart of the impact damage and repair performance of the present invention, wherein (a) is a comparison chart of the damage diffusion range; (b) is a comparison chart of the time and cost of structural function recovery; and (c) is a trend chart of the strength recovery level after the repair operation. Figure 6 The figures are a comparison of structural fatigue and stress concentration tests of the present invention, wherein (a) is a comparison trend of local strain under maximum cyclic tensile load; and (b) is a trend chart of structural fatigue cycle data. Figure 7 The figures are comparison charts of the torsional and combined stress conditions of the present invention, wherein (a) is a trend chart of the failure torque under pure torsional force; (b) is a trend chart of the in-plane shear modulus under equivalent force; and (c) is a comparison chart of the combined failure torque under combined tension and torsional conditions. Figure 8 The following are the vibration response and micro-damage assessment diagrams of the present invention, wherein (a) is a broken line graph of vibration transmissibility; (b) is a line graph of remaining interlaminar shear strength retention rate; and (c) is a graph of cumulative length of surface microcracks.

[0028] Among them: 1. Modular mesh reinforcement unit; 2. External skin protective layer. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0030] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a modular mesh reinforcement unit, including the following steps: The modular mesh reinforcement unit 1 forming mold in the manufacturing combination mold system is made of H13 mold steel and is designed as a four-piece detachable structure. The working surface is machined with grooves and protrusions corresponding to the mesh-like reinforcing rib structure to be formed. Carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% was cut into sheets using quasi-isotropic layup, with the layup sequence set as [0° / 45° / −45° / 90°]n, where n is the number of repetitions; The cut carbon fiber / epoxy resin prepreg is laid layer by layer in the molding mold of the modular mesh reinforcement unit 1. Local reinforcement layers are laid at the intersection of the ribs of the mesh reinforcement structure to be formed. The spiral rib width of the mesh reinforcement structure to be formed is 4.91mm, the ring rib width is 3.37mm, the height is 26.12mm, and a rounded corner transition structure with a radius of 2mm is provided at the intersection. After the mold is closed, it is placed in a press for hot molding. The temperature is set at 120℃, the pressure is 5MPa, and the holding time is 60min. After complete curing and cooling, the modular mesh reinforcement unit 1 is demolded and polished. The dimensional tolerance of the obtained modular mesh reinforcement unit 1 is no more than 0.2mm. Finally, a standardized interface is set at the connection end of the modular mesh reinforcement unit 1.

[0031] Preparation Example 2: This preparation example provides a method for preparing a modular mesh reinforcement unit, including the following steps: The modular mesh reinforcement unit 1 forming mold in the manufacturing combination mold system is made of H13 mold steel and is designed as a four-piece detachable structure. The working surface is machined with grooves and protrusions corresponding to the mesh-like reinforcing rib structure to be formed. Carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% was cut into sheets using a quasi-isotropic layup. The layup sequence was set as a symmetrical layup of [0° / 45° / −45° / 90°]n, where n is the number of repetitions. The cut carbon fiber / epoxy resin prepreg is laid layer by layer in the molding mold of the modular mesh reinforcement unit 1. Local reinforcement layers are laid at the intersection of the ribs of the mesh reinforcement structure to be formed. The spiral rib width of the mesh reinforcement structure to be formed is 4.91mm, the ring rib width is 3.37mm, the height is 26.12mm, and a rounded corner transition structure with a radius of 5mm is provided at the intersection. After the mold is closed, it is placed in a press for hot molding. The temperature is set at 180℃, the pressure is 10MPa, and the holding time is 30min. After complete curing and cooling, the modular mesh reinforcement unit 1 is demolded and polished. The dimensional tolerance of the obtained modular mesh reinforcement unit 1 is no greater than 0.2mm. Finally, a standardized interface is set at the connection end of the modular mesh reinforcement unit 1.

[0032] Preparation Example 3: This preparation example provides a method for preparing a modular mesh reinforcement unit, including the following steps: The modular mesh reinforcement unit 1 forming mold in the manufacturing combination mold system is made of H13 mold steel and is designed as a four-piece detachable structure. The working surface is machined with grooves and protrusions corresponding to the mesh-like reinforcing rib structure to be formed. Carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% was cut into sheets using a quasi-isotropic layup. The layup sequence was set as a symmetrical layup of [0° / 45° / −45° / 90°]n, where n is the number of repetitions. The cut carbon fiber / epoxy resin prepreg is laid layer by layer in the molding mold of the modular mesh reinforcement unit 1. Local reinforcement layers are laid at the intersection of the ribs of the mesh reinforcement structure to be formed. The spiral rib width of the mesh reinforcement structure to be formed is 4.91mm, the ring rib width is 3.37mm, the height is 26.12mm, and a rounded corner transition structure with a radius of 3.5mm is provided at the intersection. After the mold is closed, it is placed in a press for hot molding. The temperature is set at 150℃, the pressure is 8MPa, and the holding time is 45min. After complete curing and cooling, the modular mesh reinforcement unit 1 is demolded and polished. The dimensional tolerance of the obtained modular mesh reinforcement unit 1 is no greater than 0.2mm. Finally, a standardized interface is set at the connection end of the modular mesh reinforcement unit 1.

[0033] Examples 1-3: Example 1: This example provides a method for preparing a reusable rocket stage interstage, such as... Figure 1 As shown, its specific preparation method includes the following steps: The modular mesh reinforcement unit 1 prepared by four preparation examples 1 was used, and the mesh spacing of the mesh-like reinforcing rib structure was set to 115mm×112mm; Connecting components made of TC4 titanium alloy are fabricated in the forming mold of connecting components in a combined mold system, and the standardized interface adopts a bolt connection interface; Four modular mesh reinforcement units 1 were placed on the assembly fixture, and laser positioning was used to ensure the alignment of standardized interfaces; M8 bolts are used to fix the connecting parts at the standardized interface, and the tightening torque is set to 15 N·m. High-temperature sealant with a temperature resistance of 300℃ is applied to the joint formed by the connection of adjacent modular mesh reinforcement units 1 after fixing, forming a reusable rocket stage section. The absolute value of the overall length error of the reusable rocket stage section after assembly is no more than 1 mm. According to design requirements, a 50mm diameter inspection hole is opened on the reusable rocket stage section, and a sealing cover is installed at the inspection hole. Finally, the outer surface of the reusable rocket stage intersection is sprayed to form a ZrO2 thermal barrier coating with a thickness of 0.3 mm as the outer skin protective layer 2.

[0034] Example 2: This example provides a method for preparing a reusable rocket stage interstage, including the following steps: The modular mesh reinforcement unit 1 prepared by 12 preparation examples 2 was used, and the mesh spacing of the mesh-like reinforcing rib structure was set to 115mm×112mm; Connecting components made of GH 4169 high-temperature alloy are processed and prepared in the forming mold of connecting components of the combined mold system. The standardized interface adopts a slot-type quick-release structure. Twelve modular mesh reinforcement units 1 were placed on the assembly fixture, and laser positioning was used to ensure the alignment of standardized interfaces. Install connecting components at the standardized interface for fixation, apply high-temperature sealant with a temperature resistance of 300℃ to the joint formed by the connection of adjacent modular mesh reinforcement units 1 after fixation, and form a reusable rocket stage section. The absolute value of the overall length dimension error of the reusable rocket stage section after assembly is no greater than 1mm. According to design requirements, a 50mm diameter inspection hole is opened on the reusable rocket stage section, and a sealing cover is installed at the inspection hole. Finally, the outer surface of the reusable rocket stage section is sprayed to form a 0.3mm thick silicon-based high-temperature resistant coating as the outer skin protective layer 2.

[0035] Example 3: This example provides a method for preparing a reusable rocket stage interstage, including the following steps: The modular mesh reinforcement unit 1 prepared by 8 preparation examples 3 was used, and the mesh spacing of the mesh-like reinforcing rib structure was set to 115mm×112mm; Connecting components made of aluminum alloy are fabricated in the forming mold of the connecting components of the combined mold system, and the standardized interface adopts the bolt connection interface; Eight modular mesh reinforcement units 1 were placed on the assembly fixture, and laser positioning was used to ensure that the standardized interfaces were aligned. M8 bolts are used to fix the connecting parts at the standardized interface, and the tightening torque is set to 15 N·m. High-temperature sealant with a temperature resistance of 300℃ is applied to the joint formed by the connection of adjacent modular mesh reinforcement units 1 after fixing. The absolute value of the overall length error of the reusable rocket stage section after assembly is no more than 1 mm. According to design requirements, a 50mm diameter inspection hole is opened on the reusable rocket stage section, and a sealing cover is installed at the inspection hole. A ZrO2 thermal barrier coating with a thickness of 0.3 mm is sprayed onto the outer surface to form an outer skin protective layer 2; After launch and recovery, the interstage section of the rocket undergoes reusable maintenance. Visual inspection and ultrasonic C-scan non-destructive testing were used to inspect the recovered reusable rocket stage section to identify damaged modular mesh reinforcement units 1 or damaged connecting parts; the damaged modular mesh reinforcement units 1 or damaged connecting parts were disassembled and replaced with undamaged modular mesh reinforcement units 1 or undamaged connecting parts of the same model; the modular mesh reinforcement units 1 and connecting parts were re-fixed, and the external skin protective layer 2 was re-sprayed on the replacement area; finally, a static loading test of 1.5 times the design load was carried out to restore the structural functionality.

[0036] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that the rocket stage section is integrally molded using carbon fiber / epoxy resin prepreg, without modular segmentation, and without standardized interfaces and connecting parts; all other aspects are the same.

[0037] Comparative Example 2: Compared with Example 1, the difference is that the grid-like reinforcing ribs inside the modular grid reinforcing unit 1 do not have rounded corner transition structures at the intersection of the ribs, and the ribs intersect directly at right angles, while the rest are the same.

[0038] Comparative Example 3: Compared with Example 1, the difference is that the layup sequence of the carbon fiber / epoxy resin prepreg adopts an orthogonal alternating layup of [0° / 90°]n, instead of a quasi-isotropic layup of [0° / 45° / −45° / 90°]n, while the rest are the same.

[0039] Comparative Example 4: Compared with Example 1, the difference is that the joints formed by the connection of adjacent modular mesh reinforcement units 1 are not coated with high-temperature sealant with a temperature resistance of 300°C, but the rest are the same.

[0040] Test Examples 1-7: Test Example 1: Experimental steps: The reusable rocket stage intersections prepared in Examples 1 to 3 and the integral rocket stage intersection prepared in Comparative Example 1 were transferred to the multi-channel coordinated loading structure test rig, respectively.

[0041] Connect the bottom end face of the rocket stage section to the fixed flange of the test rig base, and use high-strength tie rods evenly along the circumference to tighten it, thus establishing the bottom fixed constraint boundary conditions.

[0042] Resistance strain gauges are attached to the intersections of the grid-like reinforcing ribs in the interstage section of the rocket, the areas where connecting components are located, and the outer wall of the middle section of the structure. Linear variable differential transformer displacement sensors are installed in four orthogonal directions at the top, middle, and bottom cross sections of the interstage section of the rocket to collect radial and axial deformation data.

[0043] An axial compressive load was applied to the top end face of the rocket stage section using a hydraulic servo loading system. The loading rate was set to 5 kN / s and the loading continued until the structure physically failed. The peak load output by the pressure sensor was recorded as the axial compressive failure load, and the maximum local strain value at the moment of failure was also recorded.

[0044] Replace the test sample and apply a lateral load to the top of the interstage section of the rocket to generate a bending moment. The lateral loading rate is set to 2 kN / s. Monitor the linear proportional relationship between load and displacement during the loading process and record the lateral displacement when it deviates from the critical point of the linear relationship as the lateral elastic limit displacement.

[0045] Table 1. Overall Static and Stiffness Test Data of Rocket Stage Intersection

[0046] From Table 1 and Figure 2 The comparison trend of axial bearing capacity in sub-figure (a) shows that the ultimate bearing capacity of Examples 1 to 3 is distributed between 1245.3kN and 1312.7kN. The data points marked with solid lines in the figure are all higher than the 1195.6kN of Comparative Example 1. The structure composed of modular mesh reinforcement unit 1 and metal connecting parts exhibits a similar or higher bearing capacity to the integral molded structure in terms of axial bearing capacity. Its load transfer path is distributed along the fastening structure of the standardized interface. The connecting parts bear the main axial compressive stress. With the local reinforcement of the mesh intersection area, the probability of local instability buckling caused by pressure on the ends of the composite material is reduced.

[0047] Under transverse bending moment loading conditions, such as Figure 2 As shown by the trend of the dashed line in subfigure (b), the lateral elastic limit displacement of Examples 1 to 3 is in the range of 17.5 mm to 18.8 mm, which is lower than the 21.4 mm of Comparative Example 1. The reduction in displacement parameters reflects the increase in the overall bending stiffness of the structure. Under stress, the in-plane shear resistance provided by the quasi-isotropic layup and the geometric support of the grid reinforcement are superimposed, and the mechanical fasteners at the standardized interfaces and the high-temperature sealant work together to limit the relative slippage of adjacent modules at the joints and maintain the dimensional stability of the structure.

[0048] from Figure 2As shown by the dashed line data distribution in subfigure (c), the maximum local strain values ​​of Examples 1 to 3 under the ultimate bearing state range from 8540 με to 8910 με, which is higher than the 7950 με of Comparative Example 1, indicating a higher overall pre-failure ultimate strain bearing capacity. During the loading process leading to structural failure, the boundaries of the modular splicing limit the cross-regional extension of cracks in the matrix. When stress is transferred to adjacent units, it is affected by the metal connecting components, which confines the interlaminar delamination or fracture of the composite matrix to a single stressed unit region, avoiding through-tearing of the overall structure and verifying the feasibility of modular design supporting local disassembly and replacement.

[0049] Test Example 2: Experimental steps: The reusable rocket stage segments prepared in Examples 1 to 3 were transferred to a three-dimensional assembly platform equipped with a laser interferometry system, a coordinate reference was established, and the overall length of the structure in the initial state of each stage segment was collected and recorded.

[0050] A single modular disassembly and reassembly process is performed for each stage of the process. A reverse operation is applied to the standardized interface to release mechanical constraints, and residual high-temperature sealant is cleaned from the physical joints of adjacent modular mesh reinforcement units 1. The individual modular mesh reinforcement unit 1 and its corresponding metal connecting components are then removed. Subsequently, modular mesh reinforcement units 1 of the same specifications and connecting components are returned to their original positions, and the mechanical connection of the standardized interface is restored using the originally set locking parameters. High-temperature sealant is then reapplied to the joints, and the time consumed for this complete disassembly and assembly cycle is recorded.

[0051] For each rocket stage segment sample from Examples 1 to 3, the disassembly and assembly cycle in step 2 is repeated continuously until a total of 20 disassembly and assembly processes are completed.

[0052] After the 20th disassembly and reassembly operation is completed, the laser interferometry system is restarted to scan the structure and obtain the overall length of the structure after multiple disassembly and reassembly. The absolute deviation of this value from the initial size in step 1 is calculated.

[0053] High-precision mechanical testing equipment (such as a digital torque tester or in-situ tension / compression sensor) was used to test the connection status of standardized interface positions (including bolted connections and quick-release structures) after 20 disassembly and assembly cycles. The current residual locking parameters (such as residual tightening torque or residual slot locking force) were measured, and the stiffness attenuation rate of the mechanical connection node compared to the initial set value was calculated. Table 2. Data on Modular Assembly / Disassembly and Dimensional Stability Tests of Rocket Stage Intersections

[0054] From Table 2 and Figure 3As shown in sub-figure (a), the maintenance time distribution line indicates that the operation time for Examples 1 to 3 ranges from 35.8 min to 46.3 min. The trend formed by the thick dotted line and the pentagram marker in the figure illustrates that local replacement operations have a time advantage. The standardized interface uses a mechanical connection method that allows operators to release the constraints between adjacent modules without damaging the composite material. This structure restricts the replacement operation of the damaged area to the boundary of a single module, eliminating the steps of destructive cutting and secondary curing of the composite material, indicating that local maintenance operations are controllable in terms of time.

[0055] from Figure 3 The cumulative dimensional deviation curve in sub-figure (b) shows that the total length dimensional deviation after 20 disassembly and assembly cycles is within the range of 0.39mm to 0.74mm. The data distribution recorded in the figure with solid lines and hollow rhombuses verifies that the repeated assembly operation has good geometric consistency, meeting the requirement that the absolute value of the overall error after assembly is no greater than 1mm. The positioning datum provided by the assembly tooling and the tolerance established by the mold limit the geometric consistency of the module. Under repeated disassembly and assembly operations, the metal connecting parts are subjected to mechanical friction, which reduces the transmission of operating stress to the carbon fiber connecting hole walls, avoids fiber breakage and matrix wear, and maintains the structural geometry after repeated loading.

[0056] from Figure 3 As shown by the dashed stiffness decay trend in sub-figure (c), the torque loss after multiple assembly cycles in the embodiment ranges from 2.6% to 4.1%. The data points marked with hexagonal stars in the figure exhibit lower decay rates, reflecting that the interface still maintains high connection reliability after multiple disassemblies, indicating that the connection interface maintains stable mechanical stiffness. The metal connectors and composite material ends form a physical interlock, and the high-temperature sealant applied to the gaps fills the gaps caused by mechanical tolerances after curing. The synergistic effect of mechanical locking and sealant reduces connection resistance during disassembly and restricts relative displacement between modules after reassembly, allowing the connection structure to maintain its predetermined load-bearing capacity under repeated disassembly and assembly conditions.

[0057] Test Example 3: Experimental steps: The reusable rocket stage sections prepared in Examples 1 to 3 were sequentially positioned inside a high-temperature heat flow simulation test chamber. The top and bottom openings of the stage sections were sealed with sealing blind plates made of high-temperature resistant silicone rubber, and a gas pressurization pipeline and a high-precision pressure transmitter were connected to the bottom sealing blind plate.

[0058] Fifteen K-type thermocouples are evenly arranged along the distribution area of ​​the grid-like reinforcing rib structure on the inner wall of the rocket stage section and the connection seam area of ​​adjacent modular grid reinforcing units 1, for synchronously collecting local temperature parameters on the inner side of the structure.

[0059] Nitrogen gas is introduced into the interstage section of the rocket through a gas pressurization line until the internal static pressure reaches the set initial positive pressure level, at which point the gas valve is closed. The section is then left to stand at a constant temperature for 30 minutes, and the pressure drop value output by the pressure transmitter is recorded to assess the amount of gas leakage originating from the standardized interfaces and inspection port areas.

[0060] After releasing the internal pressure, the infrared quartz heating lamp array in the high-temperature heat flow simulation test chamber was activated to apply thermal radiation loading to the outer surface of the rocket stage interstage at a heating rate of 20℃ / s until the outer wall surface temperature reached approximately 500℃. This external thermal environment was maintained for 600s, and the highest peak temperature output by the K-type thermocouples arranged in the inner wall region during this process was recorded.

[0061] Table 3. Test Data on Integrated Thermodynamic Environment and Airtightness of the Rocket Interstage Section

[0062] According to Table 3 and Figure 4 As shown in the pressure leakage assessment curve of sub-figure (a), under closed pressurization conditions, the pressure drop values ​​in Examples 1 to 3 remained within the range of 0.9 kPa to 1.5 kPa over 30 minutes. The trend formed by the dashed line and the rightward-pointing triangle in the figure represents a relatively low numerical level, reflecting the pressure-holding capacity of the structure. During mechanical assembly, high-temperature sealant filled the tolerance gaps between the metal connecting parts and the ends of the composite material. The cured sealant established a continuous physical barrier in the interface area, slowing down the penetration and diffusion of nitrogen along the gaps, verifying the role of the local sealing structure in maintaining the internal pressure environment.

[0063] Under external heat radiation input, a 0.3mm thick thermal barrier coating or silicon-based high-temperature resistant coating forms a heat insulation layer between the outer surface of the interstage section and the internal composite material. (Comparative observation) Figure 4 The temperature curves in sub-figures (b) and (c) reveal that when the outer surface reaches 498.7℃~512.1℃ (as shown by the solid line and crosshair markings in the figure, the coating material reduces the rate of heat transfer inward along its thickness, limiting the peak temperature of the inner wall to 79.2℃~88.1℃ (corresponding to the conduction response trend marked by the inverted triangle in the figure). The difference between the inner and outer wall temperatures reflects the overall thermal insulation performance of the structure. This mechanism prevents the internal epoxy resin matrix from softening or pyrolyzing due to overheating, ensuring the stability of the composite material panel.

[0064] In the combined environment, the metal connectors maintained a constant gap size and did not undergo deformation that would have caused seal failure. Simultaneously, the high-temperature sealant at the gaps did not exceed its tolerance limit, maintaining its elastic filling properties. The material parameters of the module units, external coating, metal connectors, and sealant were matched, collectively maintaining the structure's sealing performance under high temperature and differential pressure conditions.

[0065] Test Example 4: Experimental steps: The rocket stage sections prepared in Example 1 and Comparative Example 1 were respectively fixed on the base of a large drop hammer impact testing machine. The fixing clamps were adjusted to ensure that the impact punch of the drop hammer was vertically aligned with the central area of ​​the grid-like reinforcing rib structure on the side wall of the rocket stage section.

[0066] The counterweight mass and drop height of the drop hammer impact testing machine were set, and a drop hammer impact energy of 150J was applied to the test areas of Example 1 and Comparative Example 1. The physical morphology of the structural surface was recorded after the impact event.

[0067] Non-destructive testing of the impacted area was performed using an ultrasonic C-scanning device. The scanning frequency was set to 5MHz to obtain the interlaminar debonding and fiber fracture interface characteristics within the structure, and the projected area of ​​internal damage indicated by the ultrasonic reflection signal was calculated and recorded.

[0068] Structural function restoration operations were performed on the damaged rocket stage intersegment. For Example 1, the mechanical connection at the edge of the damaged modular mesh reinforcement unit 1 was disconnected, the damaged unit was removed and replaced with a newly fabricated unit of the same specifications, a tightening torque of 15 N·m was reapplied, and high-temperature sealant was injected. For the integrally molded structure of Comparative Example 1, a stepped patching operation was performed on the damaged area using a grinding tool, carbon fiber prepreg patches with the same layup sequence were applied, and vacuum bag-pressed in-situ curing was performed using a heating blanket at 120°C. The actual physical time consumed by both restoration operations was recorded.

[0069] The samples from Example 1 and Comparative Example 1, after undergoing structural restoration, were transferred to a static loading test bench and subjected to axial compressive load at a loading rate of 2 kN / s until physical failure occurred. The axial compressive failure load after repair was recorded, and its ratio to the initial axial compressive failure load recorded in Test Example 1 was calculated to obtain the strength recovery rate.

[0070] Table 4. Comparative Test Data on Local Damage Tolerance and Repair Efficiency of Rocket Stage Intersections

[0071] From Table 4 and Figure 5 As can be seen from the comparison of the damage diffusion range in sub-figure (a), when subjected to an impact energy of 150J, the damage area of ​​Example 1 is 382.7mm². 2As shown at the beginning of the solid line marked with an asterisk in the figure, its value is lower than 814.3 mm in Comparative Example 1. 2 In Comparative Example 1, the integrally molded structure is continuous on a composite matrix. The stress wave and interlaminar shear force induced by impact diffuse outwards, leading to matrix cracking and fiber delamination. The modular assembly of Example 1 introduces physical boundaries between adjacent units. The acoustic impedance difference between the metal and the sealing layer dissipates the shock wave, and the small damage area indicates that the structure can control mechanical damage within a single module.

[0072] from Figure 5 The comparison of the time and cost of structural function restoration in neutron diagram (b) reveals that the reset time for Example 1 is 1.15 hours, while the patching operation in Comparative Example 1 takes 47.6 hours. The trend represented by the dashed lines and crosses in the diagram illustrates the difference in time cost between the two repair methods. Example 1, based on the properties of bolted connections, involves unscrewing metal fasteners, replacing modules, and re-injecting sealant, avoiding the polymerization reaction of composite materials. The restoration process in Comparative Example 1 includes cutting, grinding, laying multiple layers of prepreg, and several hours of heating and vacuuming. The modular design transforms the post-damage treatment process from chemical curing of materials to mechanical assembly, reducing time consumption.

[0073] from Figure 5 As shown by the trend of the dashed line indicating the strength recovery level in sub-figure (c), the static loading test shows that the strength recovery rate after the replacement operation in Example 1 is 98.8%, as indicated by the data points marked with a left triangle in the figure. This result is close to the 100% complete repair benchmark, while the strength recovery rate of Comparative Example 1 after partial patching and curing is 77.3%. The new module replaced in Example 1 has the same parameters as the original damaged unit, and the load transfer path of the assembled structure conforms to the initial design. The partial patching in Comparative Example 1 interrupted the extension of the continuous carbon fiber, and the porosity defects at the interface between the patch and the base material increased, leading to a decrease in its load-bearing limit value.

[0074] Test Example 5: Experimental steps: Test specimens containing the intersection nodes of the complete mesh-like reinforcing rib structure were cut from the modular mesh reinforcement unit 1 prepared in Example 1 and Comparative Example 2, and installed between the upper and lower hydraulic clamping ends of the servo hydraulic fatigue testing machine.

[0075] Miniature high-frequency resistance strain gauges were attached to the surface of the intersection nodes of the spiral and annular ribs of the test specimen (the specimen in Example 1 has a rounded transition structure with a radius of 2 mm, while the specimen in Comparative Example 2 has a right-angle intersection structure) to measure the local micro-strain during the initial loading stage. At the same time, broadband acoustic emission sensors were arranged near the clamping area to collect acoustic impact signals reflecting the initiation state of microcracks inside the material.

[0076] Configure the loading parameter matrix for the servo-hydraulic fatigue testing machine. Set the loading mode to axial tension-compression alternating cyclic load, the stress ratio to R=0.1, and the loading frequency to 5Hz. Set the maximum cyclic tensile load to 80kN.

[0077] Start the fatigue testing machine and apply continuous cyclic alternating loads to the test specimen. Record the maximum local strain peak value output by the resistance strain gauge within the initial 100 load cycles.

[0078] The loading program runs continuously, synchronously monitoring the total number of impact signals and energy jump points of the acoustic emission sensors, while periodically acquiring images of the cross-node surface through a microscopic vision system. When the monitoring system records a step increase in the acoustic emission signal and the microscopic vision system identifies a continuous surface crack with a length of 2 mm in the cross-node area, a stop command is triggered, and the cumulative load cycle count output by the testing machine at this time is recorded.

[0079] Table 5. Fatigue life test data of interstage mesh reinforcement unit under alternating load in rocket stage.

[0080] According to Table 5 and Figure 6 The strain comparison trend in subfigure (a) reveals that under a maximum cyclic tensile load of 80 kN, the maximum local strain recorded in the intersection region of the Comparative Example 2 test specimen is 9324 με, while the local strain in Example 1, as indicated by the data points marked with pure black squares, is reduced to 4851 με. The right-angle intersection configuration used in Comparative Example 2 causes abrupt changes in the cross-section of the intersection region, and the internal stress transmission path contracts towards the right-angle tip. As indicated by the figure legend, the higher strain value reflects local stress concentration. The rounded transition structure of Example 1 increases the cross-sectional area of ​​the intersection, and the change in shape disperses the stress along the rounded edges, reducing the peak value of local micro-strain.

[0081] A comparison of structural fatigue cycle data shows that the first macroscopic crack initiation cycle in Example 1 was 845,612 cycles, while in Comparative Example 2 it was 127,849 cycles. Figure 6 In subfigure (b), the data connected by the dashed line and the hollow circle demonstrates the better fatigue resistance of Example 1. Under continuous input of alternating load, the epoxy resin matrix in the high-strain region undergoes plastic yielding and shear deformation. In Comparative Example 2, stress concentration at the right angle leads to interlaminar debonding at the carbon fiber-resin interface. The debonded region expands under alternating stress, forming macroscopic cracks and causing a reduction in the load-bearing cross-section.

[0082] Example 1, with its localized reinforcing layup at the intersection and rounded corner transition structure, ensures continuous carbon fiber bundles are laid and extended along the rounded corner contour, reducing fiber cutting or resin-rich area defects. The superposition of quasi-isotropic layup and rounded corner geometric boundaries increases the proportion of shear-resistant fibers in the intersection region. This structure alters the energy consumption path of microcrack propagation, reduces the accumulation rate of matrix micro-damage under alternating loads, and improves the fatigue life of the reinforcing element, consistent with the fatigue cycle count results recorded in the chart.

[0083] Test Example 6: Experimental steps: The rocket stage interstage section prepared in Example 1 and the rocket stage interstage section prepared in Comparative Example 3 (the test sample structure was the same as in Example 1, except that the layup sequence of the carbon fiber / epoxy resin prepreg was modified to [0° / 90°]n orthogonal layup) were respectively transferred to a multi-channel multiaxial composite loading test system. The top and bottom end flanges of the rocket stage interstage section were respectively fixedly connected to the upper and lower rigid torsion discs of the test system with bolts.

[0084] On the outer skin surface of the modular mesh reinforcement unit 1 in the middle section of the rocket stage, four sets of triaxial strain rosettes are arranged at equal intervals along the circumference to simultaneously collect in-plane strain parameters in the 0°, 45° and 90° directions.

[0085] A pure torsion test procedure was performed on the installed rocket stage intersegment. The lower torsion disk was fixed, and the upper torsion disk applied a torsional load around the central geometric axis of the structure at a constant angular velocity of 0.1° / s until macroscopic physical fracture occurred in the outer wall of the structure. The highest value output by the torque sensor during this process was recorded as the pure torsional failure torque, and the equivalent in-plane shear modulus of the structure was calculated based on the slope of the torque-torsion angle linear segment at the initial loading stage.

[0086] Replace the test specimens of Example 1 and Comparative Example 3 with new test specimens of the same specifications. Set up the test system to first apply and maintain an axial tensile load of 500.0 kN, and then, while keeping the axial tensile force constant, add torsional displacement at an angular velocity of 0.1° / s until the structure physically breaks. Record the peak torque at this point as the tensile-torsional combined failure torque.

[0087] Table 6. Test Data of Multi-directional Composite Loads in the Interstage Section of Rocket

[0088] Combined with Table 6 and Figure 7The curve spans in subgraphs (a) and (b) reveal that, under pure torsional loading, the pure torsional failure torque of Example 1 is 864.2 kN·m, and the equivalent in-plane shear modulus is 37.14 GPa. The corresponding values ​​for Comparative Example 3 are shown as the troughs of the dashed and solid lines, at 358.5 kN·m and 14.82 GPa, respectively. The data trends marked with upward triangles and hollow pentagrams in the attached figures reflect that Example 1 possesses good basic torsional stiffness and pure torsional bearing capacity. When a thin-walled cylindrical structure is subjected to pure torsional load, the shear stress generated on the surface can be decomposed into principal tensile and compressive stresses in the ±45° direction. The orthogonal layup used in Comparative Example 3 lacks carbon fiber distribution in the ±45° direction, and load transfer relies on the shear deformation of the resin matrix, leading to premature interlaminar fracture. The quasi-isotropic layup of Example 1 distributes continuous carbon fibers along the principal stress direction, with the carbon fiber bundles bearing the tensile and compressive loads, reducing the deformation proportion borne by the resin matrix.

[0089] In a combined tensile-torsional load condition with a superimposed 500.0 kN axial tensile load, from Figure 7 Subgraph (c), with its contrasting trends formed by dashed lines and black hexagons, shows that Example 1 has a combined failure torque of 712.9 kN·m, possessing the corresponding comprehensive bearing capacity under complex stress fields, while Comparative Example 3's torque decreases to 246.7 kN·m. The axial tensile load increases the initial tension of the fibers in the 0° direction, causing microcracks to form in Comparative Example 3 under multi-directional combined shear force, leading to a decrease in bearing capacity. The layup configuration of Example 1 reduces the difference in elastic modulus in different directions, making the stiffness values ​​in all in-plane directions more consistent. The mesh structure within the reinforcing unit provides out-of-plane stiffness in the combined stress field, dispersing the coupling effect of normal tensile stress and tangential shear stress.

[0090] When torsional shear stress is transmitted outward through the module edges, the bolted connections at the standardized interfaces utilize the shear resistance of the metal material to reduce tangential slippage at the gaps. Simultaneously, the high-temperature sealant filling the gaps between adjacent modules prevents microscopic displacement between the interfaces. This design, where multi-directional fibers internally bear the stress distribution and metal and sealant externally constrain displacement, enhances the structure's ability to resist asymmetric torsional loads.

[0091] Test Example 7: Experimental steps: The reusable rocket stage sections prepared in Examples 1 to 3 and the integral rocket stage section prepared in Comparative Example 1 were transferred to an environmental testing laboratory. They were rigidly fixed to the extended platform of a multi-axis electric vibration table using high-strength bolts through the metal flanges on the bottom end face to simulate the assembly boundary conditions of the rocket body.

[0092] Triaxial piezoelectric accelerometers were fixed using rigid adhesives at the intersections of the mesh-like reinforcing ribs on the outer surface of each test specimen, in the central region of the outer skin, and at the adjacent composite material ends of the metal connecting parts. Simultaneously, Bragg fiber grating sensors were embedded between the carbon fiber composite matrix layers of the mesh reinforcing ribs to collect high-frequency micro-strain parameters within the structure.

[0093] Start the multi-axis electric vibration table and input a broadband random vibration spectrum excitation covering a frequency range of 20Hz to 2000Hz along the three orthogonal spatial axes of X, Y, and Z. Set the total root mean square acceleration input value to 18.5g and maintain this loading state for 600s. Record the signal output by the accelerometer and calculate the peak vibration transmissibility of each measuring point relative to the base excitation.

[0094] After the random vibration test, rectangular specimens with dimensions of 20 mm long, 10 mm wide, and 2 mm thick were cut from the intersection area of ​​the mesh-like reinforcing ribs of each test sample. The specimens were placed in a universal testing machine, and a transverse load was applied at a constant displacement rate of 2 mm / min according to the short beam shear test procedure. The ultimate load value leading to interlaminar failure was recorded, and the remaining interlaminar shear strength was calculated. This calculated value was divided by the baseline interlaminar shear strength value of the original specimens in the same batch that had not undergone vibration testing to obtain the interlaminar shear strength retention rate. The cumulative total length of microcracks on the outer surface of the structure was measured using a microscopic vision device.

[0095] Table 7. Random Vibration Transit Rate and Interlayer Mechanical Test Data of Rocket Stage Intersection

[0096] From Table 7 and Figure 8 As shown in the vibration transmissibility trend line of sub-figure (a), the data for Examples 1 to 3 are distributed between 2.39 and 2.58, as indicated by the solid line marked with a hollow square in the figure. The trend is low and flat, lower than the 6.82 generated in Comparative Example 1. The integral molded structure of Comparative Example 1 lacks a damping dissipation interface, resulting in the superposition of broadband input vibrational mechanical energy, causing the dynamic displacement amplitude to amplify at specific frequency points. The examples introduce discontinuous boundaries through the splicing of modular units and metal connectors. The sealant and mechanical fasteners at the interface form a damping layer. When high-frequency vibration waves pass through the connection interface, some mechanical energy is converted into frictional heat energy and elastic deformation energy of the interface, dissipating the vibrational energy. This corresponds to the structural vibration reduction and dissipation capability noted in the figure, reducing the dynamic response of the structure.

[0097] Regarding the parameters after vibration testing, observe Figure 8In subfigure (b), the line connecting the retention rates formed by the pure black pentagram and the dashed line reveals that the remaining interlaminar shear strength retention rates of Examples 1 to 3 range from 92.1% to 95.8%, demonstrating good interlaminar bond stability, while Comparative Example 1 has a retention rate of 61.4%. Meanwhile, in Figure 8 In subfigure (c), the cumulative length of surface microcracks decreased from 89.3 mm in Comparative Example 1 to 10.9 mm–14.7 mm in the Example group, as recorded by the dotted line trend marked with hexagons. The rounded transition structure of the mesh reinforcement altered the geometric features at the intersection nodes, avoiding abrupt changes in cross-section. Under alternating stress induced by random vibration, the rounded transition structure guided the carbon fibers to transmit stress along a smooth trajectory, resulting in a more uniform distribution of shear stress. The quasi-isotropic layup ensured the existence of a fiber skeleton resisting external loads in all directions, reducing the probability of resin yield fracture and maintaining the bonding state within the composite material.

[0098] In terms of structural geometry preservation mechanisms, modular design confines material-level damage to localized areas. When alternating stress induces microcracks, the cracks encounter the metal connecting components and high-temperature sealant at the module edges during propagation. This boundary prevents the crack tip from extending further. The fracture toughness of the metal and the elastic deformation of the sealant prevent the crack from penetrating into adjacent modules. This modular assembly design limits the coalescence of microcracks into through-cracks, ensuring the structural stability of its load-bearing cross-sectional area and load-bearing capacity after undergoing dynamic loading cycles.

Claims

1. A reusable rocket stage intersection, characterized in that, include: 4 to 12 modular mesh reinforcement units (1), wherein the modular mesh reinforcement unit (1) is formed by hot molding of carbon fiber / epoxy resin prepreg with a resin mass fraction of 35%, wherein the modular mesh reinforcement unit (1) is provided with a mesh-like reinforcing rib structure inside, wherein the ribs of the mesh-like reinforcing rib structure include spiral ribs and ring ribs, wherein the width of the spiral rib is 4.91 mm, the width of the ring rib is 3.37 mm, the height of the mesh-like reinforcing rib structure is 26.12 mm, and the intersection of the ribs of the mesh-like reinforcing rib structure is provided with a rounded corner transition structure with a radius of 2 mm to 5 mm; A standardized interface is provided at the connection end of the modular mesh reinforcement unit (1) for detachable connection between adjacent modular mesh reinforcement units (1); The connecting component, installed at the standardized interface, is made of metal and is used for fixing the modular mesh reinforcement units (1) together; An outer skin protective layer (2) is formed on the outer surface of the reusable rocket stage section. The outer skin protective layer (2) is a ZrO2 thermal barrier coating or a silicon-based high-temperature resistant coating with a thickness of 0.3 mm.

2. The reusable rocket stage intersection according to claim 1, characterized in that, The carbon fiber / epoxy resin prepreg adopts a quasi-isotropic layup, with the layup sequence being a symmetrical layup of [0° / 45° / −45° / 90°]n or [0° / 45° / −45° / 90°]n, where n is the number of repetitions.

3. The reusable rocket stage intersection according to claim 1, characterized in that, The joints formed by the connection of adjacent modular mesh reinforcement units (1) are coated with high-temperature sealant with a temperature resistance of 300°C.

4. The reusable rocket stage intersection according to claim 1, characterized in that, The mesh spacing of the mesh-like reinforcing rib structure is 115mm × 112mm; The standardized interface is either a bolt connection interface or a slotted quick-release structure; The connecting components are made of TC4 titanium alloy, aluminum alloy, or GH 4169 high-temperature alloy.

5. A method for preparing a reusable rocket stage intersection as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Manufacturing a modular mold system, the modular mold system comprising a modular mesh reinforcement unit (1) forming mold and a connecting component forming mold; Carbon fiber / epoxy resin prepreg with a resin mass fraction of 35% was cut into sheets; The cut carbon fiber / epoxy resin prepreg is laid layer by layer in the molding mold of the modular mesh reinforcement unit (1), and local reinforcement layers are laid at the intersection of the ribs of the mesh-like reinforcing rib structure to be formed. After the mold is closed, it is placed in a press for hot molding. The temperature is set to 120-180℃, the pressure is 5-10MPa, and the heat and pressure holding time is 30-60min. After complete curing and cooling, it is demolded and polished to obtain the modular mesh reinforcement unit (1). A standardized interface is set at the connection end of the modular mesh reinforcement unit (1). The connecting component is manufactured in the forming mold of the connecting component; Multiple modular mesh reinforcement units (1) are placed on the assembly fixture for positioning and alignment, and the connecting parts are installed at the standardized interface for fixation to form the reusable rocket stage section; The outer surface of the reusable rocket stage section is sprayed to form a ZrO2 thermal barrier coating or a silicon-based high-temperature resistant coating with a thickness of 0.3 mm as an external skin protective layer (2).

6. The preparation method according to claim 5, characterized in that, The molding die for the modular mesh reinforcement unit (1) is made of H13 mold steel. The working surface of the molding die for the modular mesh reinforcement unit (1) is machined with grooves and protrusions corresponding to the mesh-like reinforcing rib structure. The molding die for the modular mesh reinforcement unit (1) is designed as a four-piece detachable structure.

7. The preparation method according to claim 5, characterized in that, The specific parameters for the hot molding process are as follows: The temperature was set to 120℃, the pressure to 5MPa, and the holding time to maintain the temperature and pressure to 60min. After demolding and polishing, the dimensional tolerance of the obtained modular mesh reinforcement unit (1) is no greater than 0.2 mm.

8. The preparation method according to claim 5, characterized in that, Laser positioning is used to ensure the alignment of the standardized interfaces; When the standardized interface is a bolted connection interface, M8 bolts are used to fix the connecting parts, and the tightening torque is set to 15 N·m. Apply a high-temperature sealant with a temperature resistance of 300°C to the joint formed by connecting adjacent modular mesh reinforcement units (1) after the fixation is completed; The absolute value of the overall length error of the reusable rocket stage section after assembly is no greater than 1 mm.

9. The preparation method according to claim 5, characterized in that, An inspection hole with a diameter of 50 mm is opened on the reusable rocket stage section as required by the design, and a sealing cover is installed at the inspection hole.

10. The preparation method according to claim 5, characterized in that, The preparation method also includes reusable maintenance of the formed reusable rocket stage intersection: Visual inspection and ultrasonic C-scan non-destructive testing were used to inspect the recovered reusable rocket stage section to identify damaged modular mesh reinforcement units (1) or damaged connecting components; Disassemble the damaged modular mesh reinforcement unit (1) or the damaged connecting component and replace it with an undamaged modular mesh reinforcement unit (1) or an undamaged connecting component of the same model; The modular mesh reinforcement unit (1) was re-fixed to the connecting component, and the outer skin protective layer (2) was re-sprayed at the replacement site. Finally, a static loading test of 1.5 times the design load was carried out to restore the structural function.

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