A high-energy-absorbing light-weight sandwich structure imitating the beetle shell of the pine bark beetle and a preparation method thereof

Abstract

This invention discloses a high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine knot weevil and its preparation method, belonging to the field of additive manufacturing technology for lightweight energy-absorbing structures. The structure includes an upper panel, a lower panel, and a core layer structure disposed between them. The core layer structure is formed by splicing together an array of structural units. Each structural unit includes a central elliptical cavity and two hollow cylindrical supports on either side, with the elliptical cavity and the hollow cylindrical supports connected to form a load-bearing system. In the three-layer structure, the middle layer structural unit array is staggered along the axis of the elliptical cavity, and process communication holes are provided on the shared middle panel of adjacent layers. This structure can be integrally formed using selective laser melting, and features good energy absorption performance, reliable connection, and easy powder removal, making it suitable for UAV fuselages and other lightweight protective structures.

Description

Technical Field

[0001] This invention belongs to the field of high energy absorption lightweight structure design and additive manufacturing technology, specifically relating to a high energy absorption lightweight sandwich structure that mimics the elytra of a pine nodule weevil and its preparation method. Background Technology

[0002] When performing reconnaissance, transport, or combat missions, unmanned aerial vehicles (UAVs) require a structural design that possesses sufficient static strength and rigidity to meet the demands of long-endurance flight, while also exhibiting excellent energy absorption capabilities to withstand impacts during takeoff and landing, crashes, or shrapnel penetration in complex battlefield environments. In such applications, the structure must be lightweight while maintaining stable load-bearing and buffering capabilities under localized pressure or repeated impacts.

[0003] Currently, the mainstream lightweight structures used in drone fuselages are mostly aluminum honeycomb sandwich panels, foam core panels, and point frame support structures. The honeycomb core layer is usually bonded to the upper and lower panels using adhesive bonding, which can achieve structural weight reduction to some extent. However, the following problems still exist in practical engineering applications.

[0004] First, traditional honeycomb structures suffer from interface failure. In traditional honeycomb sandwich structures, the upper and lower panels are typically connected to the honeycomb core layer by adhesive bonding or brazing. Under repeated impacts or severe vibrations, the adhesive interface is prone to debonding, leading to a decrease in the overall structural stiffness and energy absorption performance, making it difficult to meet the requirements for long-term service.

[0005] Secondly, the reliability of the infilled reinforcement structure is insufficient. To improve energy absorption performance, existing technologies often fill the honeycomb cells with polyurethane foam, ceramic, or metal porous materials to form an "infilled reinforcement structure." However, under repeated impact loads, the filler material is prone to pulverization and detachment from the pores, making it difficult for the buffer layer to recover, increasing the structural mass and significantly reducing the repeatable energy absorption performance.

[0006] Secondly, the secondary implantation structure has manufacturing defects. Some improvements involve "implanting" reinforcing components such as thin-walled metal tubes into the honeycomb or foam core layer to improve local compressive and bending stiffness. However, this type of "secondary implantation" process is usually a point bonding or local interference fit, with limited interfacial bonding force. Furthermore, there are assembly gaps and axial deviations between the reinforcing tube and the panel and core layer, which can easily lead to eccentric stress and bending instability during the initial loading stage, making it difficult to fully utilize the energy absorption function of the reinforcing components.

[0007] Biological research has shown that the elytra of the pine weevil (Sipalus gigas) possess a composite load-bearing system consisting of a transverse annular shell and longitudinal struts, enabling it to withstand external pressure far exceeding its own weight without overall collapse. However, existing biomimetic structures mostly focus on local imitation of single configurations, lacking systematic parameter design and multi-layered synergistic optimization for this type of "annular shell-strut" load-bearing mechanism. Furthermore, research on using selective laser melting (SLM) and other metal additive manufacturing technologies to achieve one-piece molding of such biomimetic structures while balancing structural performance and manufacturing constraints is also limited.

[0008] Based on this, an integrated biomimetic sandwich structure of "elliptical cavity - vertical cylindrical support - upper and lower panels" is proposed to provide a new lightweight and high damage tolerance structural solution for key parts such as the wing-fuselage transition section, belly compartment and landing gear of UAVs. Summary of the Invention

[0009] The technical problem this invention aims to solve is: addressing the issues of low energy absorption efficiency caused by interfacial debonding, filler material pulverization failure, and local buckling instability in existing lightweight sandwich structures for UAV fuselages under complex impact loads. This invention provides a high-energy-absorbing lightweight sandwich structure inspired by the elytra of a pine weevil and its preparation method. This invention aims to obtain a biomimetic structure that combines lightweight design, load-bearing capacity, and energy absorption performance through a bio-inspired load-bearing configuration and integrated metal additive manufacturing technology.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine weevil includes an upper panel and a lower panel, and a core layer structure disposed between the upper and lower panels. The core layer structure is composed of several structural units arrayed and spliced ​​in a plane. Each structural unit includes an elliptical cavity in the middle and hollow support columns on both sides of the elliptical cavity. The axis of the elliptical cavity is parallel to the upper and lower panels, and the top and bottom of the elliptical cavity are connected to the upper and lower panels respectively, providing lateral deformation space when subjected to out-of-plane compressive loads. The axis of the hollow support column is perpendicular to the upper and lower panels, passes through and supports between the upper and lower panels, and its outer wall is tangential or coplanarly connected to the end outer wall of the elliptical cavity, thereby forming a multi-level coupled load-bearing system composed of an elliptical ring shell and vertical hollow support columns inside the core layer.

[0012] The geometric parameters of the structural unit include the major axis, minor axis, wall thickness of the elliptical cavity, and the diameter of the hollow support. Some geometric parameters are determined through parametric reverse design methods to obtain the target design parameters based on the performance requirements and constraints of the application scenario.

[0013] In a preferred embodiment, the core layer structure includes one or more structural unit arrays along a direction perpendicular to the upper and lower panels; when the core layer structure includes multiple structural unit arrays, adjacent structural unit arrays share a common intermediate panel.

[0014] In another preferred embodiment, when the core structure includes a three-layer structural unit array, the middle layer structural unit array is offset relative to the upper and lower layer structural unit arrays along the elliptical cavity axis, with an offset distance of p. x This is used to adjust the interlayer force transmission path of a three-layer structure and satisfy the following:

[0015] .

[0016] Where R is the length of the structural unit along the axis of the elliptic cavity; l c The outer major axis dimension of the elliptic cavity.

[0017] Preferably, on the middle panel shared by two adjacent structural unit arrays, a process communication hole is provided at the intersection of the projection area of ​​the bottom end of the upper hollow support column and the projection area of ​​the top end of the lower elliptical cavity, for forming a powder discharge communication channel during powder bed fusion additive manufacturing. Further, the equivalent diameter of the process communication hole is D. h and satisfy

[0018] ;

[0019] Where, d c The inner diameter of the hollow support column, l c The outer major axis dimension of the elliptic cavity.

[0020] This invention also provides a parametric reverse design method based on sandwich structures, comprising: establishing a parametric geometric model of the structural unit and selecting several geometric parameters as design variables; constructing an objective function and constraints according to the performance requirements of the application scenario; generating sample points based on the design variables and obtaining response data through experiments and / or numerical simulations; establishing a mapping model between the design variables and the objective function based on the sample points and response data, and solving the mapping model to obtain a set of candidate design solutions; and selecting the target solution from the set of candidate design solutions according to a preset criterion as the final design parameters.

[0021] Preferably, let the design variable vector be...

[0022] ;

[0023] The target response variable is

[0024] ;

[0025] The mapping relationship between design variables and target response can be expressed as follows:

[0026] ;

[0027] Where Φ is the mapping model.

[0028] Furthermore, the parametric reverse engineering process can be represented as the following optimization problem:

[0029] ;

[0030] ;

[0031] Where F(X) is the objective function, and Ω is the feasible region composed of performance requirements, structural dimensions, and manufacturing conditions; after obtaining the candidate design solution set from the feasible region, the objective solution X that satisfies the preset criteria is selected. * As the final design parameters.

[0032] This invention also provides a method for preparing the above-mentioned high-energy-absorbing lightweight sandwich structure imitating the elytra of a pine nodule weevil. The structure is integrally formed using a powder bed melting additive manufacturing process, preferably selective laser melting technology. The three-dimensional model data of the structure is imported into slicing software, metal powder is selected as the forming raw material, and the structure is printed layer by layer along the axis of the hollow support. After printing, the part is subjected to stress-relieving heat treatment.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) A multi-stage energy absorption mechanism of "buckling-folding-stretching" is formed, which significantly improves the energy absorption efficiency. By combining the elliptical ring shell and the hollow support, a multi-stage coordinated deformation process is achieved, from the local buckling of the elliptical shell, to the folding and collapse of the shell and the gradual buckling of the hollow support, and then to the local stretching in the later stage. This helps to delay the instability and collapse of the overall structure, obtain a relatively smooth and continuous bearing platform, and improve the energy absorption capacity under the same mass.

[0035] (2) Integrated molding significantly reduces the risk of interface debonding and material pulverization. The elliptical ring shell, hollow support column and panel are integrated by using additive manufacturing processes such as SLM, which eliminates the bonding interface between different components and fundamentally avoids the problems of interface debonding and pulverization of filler material during impact.

[0036] (3) A design method based on multi-objective optimization is provided. By establishing a response surface model between geometric parameters and energy absorption performance, representative size combinations that meet the target equivalent density and energy absorption per unit mass can be quickly selected according to the density constraints and energy absorption requirements of different parts of the UAV.

[0037] (4) The structure has optimized self-supporting characteristics, which reduces manufacturing difficulty and cost. The elliptical cavity and hollow support are both self-supporting geometric features. During the SLM forming process, no additional support structure needs to be arranged inside to complete the printing.

[0038] (5) The coordinated design of the three-layer staggered stack and the process connection hole not only ensures the formation of the powder discharge path, but also further improves the interlayer force transmission path of the multi-layer structure, suppresses the multi-layer synchronous shear failure trend that is prone to occur in the conventional three-layer aligned stack structure during the compression process, makes the failure process more likely to start and expand layer by layer, and achieves structural lightweighting.

[0039] (6) By comparing the conventional three-layer alignment structure and the three-layer misalignment structure under out-of-plane compression conditions, it can be seen that the three-layer misalignment design changes the transmission path of the interlayer load, transforming the original through shear failure that was easy to develop synchronously along similar cross sections into a local failure mode that evolves in stages and regions, thereby improving the stability and damage tolerance of the three-layer structure during compression. Attached Figure Description

[0040] Figure 1 A three-dimensional schematic diagram of the pine-shaped weevil elytra structural unit provided in an embodiment of the present invention;

[0041] Figure 2 This is a geometric schematic diagram of the structural unit of the present invention, wherein, Figure 2 (a) is a schematic diagram of the two-dimensional cross-section and geometric parameters of the element. Figure 2 (b) is a schematic diagram of the sandwich panel structure formed by splicing two units;

[0042] Figure 3 This is a schematic diagram of the overall structure of the sandwich panel formed by splicing multiple units in an embodiment of the present invention, wherein, Figure 3 (a) is a schematic diagram of a single-layer core structure. Figure 3 (b) is a schematic diagram of the double-core structure. Figure 3 (c) is a schematic diagram of a three-layer conventional aligned stacked core layer structure;

[0043] Figure 4 This is a schematic diagram of a three-layer staggered stacked sandwich structure in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram showing the misalignment direction and distance of the middle layer of the three-layer staggered stacking structure in an embodiment of the present invention;

[0045] Figure 6 This is a comparison diagram of the finite element simulation results of a conventional three-layer alignment structure and a three-layer misalignment structure under compression conditions in an embodiment of the present invention.

[0046] Figure 7This is a finite element simulation evolution diagram of the three-layer misaligned structure under different compression stages in an embodiment of the present invention;

[0047] Figure 8 These are photographs of samples with different core layer heights prepared using selective laser melting (SLM) in this embodiment of the invention.

[0048] Figure 9 This is a schematic diagram of the design results obtained based on the multi-objective optimization method in an embodiment of the present invention, wherein, Figure 9 (a) is a schematic diagram of the Pareto optimal solution set with the objectives of energy absorption per unit mass and equivalent density. Figure 9 (b) is a comparison diagram of the unit mass energy absorption of three representative solution structures with different numbers of layers;

[0049] Figure 10 This is a load-displacement curve of a representative sandwich sample under quasi-static compression conditions in an embodiment of the present invention.

[0050] Figure 11 This is a schematic diagram of a typical deformation stage of a representative sandwich sample during compression in an embodiment of the present invention.

[0051] The meanings of the labels in the diagram are as follows: 1—Top panel; 2—Bottom panel; 3—Elliptical cavity; 4—Hollow cylindrical support; 5—Core structure; R—Length of the structural unit along the axial direction; l c —Outer major axis dimension of the ellipsoid cavity; l0 —Inner major axis dimension of the ellipsoid cavity; h e —Outer minor axis dimension of the elliptic cavity (core height); w c —Wall thickness of the elliptical cavity and hollow support; d0—Outer diameter of the hollow cylindrical support; d c —Inner diameter of the hollow cylindrical support; t s —Thickness of upper and lower panels; h—Total height of sandwich panel; F—Compressive load; x—Compressive displacement; F p1 —First peak load; F v1 —First valley load; F mean —Platform average force; x d — Compacting displacement; EA— Absorbed energy; SEA— Energy absorbed per unit mass; D h —Equivalent diameter of the process connection hole; p x —The misalignment distance of the intermediate layer structural unit array relative to the upper and lower layers along the axis of the ellipsoidal cavity. Detailed Implementation

[0052] To facilitate a better understanding of the technical solution of this invention by those skilled in the art, the high-energy-absorbing lightweight sandwich structure mimicking the elytra of the pine weevil and its preparation method are further described below with reference to the accompanying drawings and specific embodiments. It should be noted that, without departing from the spirit and scope of the invention and the claims, the specific dimensional parameters, process conditions, and experimental conditions in the following embodiments can be appropriately adjusted according to actual application needs, and do not constitute a limitation on the scope of protection of this invention.

[0053] like Figure 1 and Figure 2 As shown in (a), the structural unit of the present invention includes an upper panel 1, a lower panel 2, an elliptical cavity 3 located in the middle, and hollow cylindrical support columns 4 distributed on both sides of the elliptical cavity 3. The elliptical cavity 3 forms an annular shell with an outer ellipse and an inner ellipse nested within each other on a section perpendicular to its axis. The minimum distance between the inner and outer ellipses is the wall thickness w. c The axis of the elliptical cavity 3 is parallel to the upper panel 1 and the lower panel 2. The top and bottom are rigidly connected to the upper panel 1 and the lower panel 2 respectively, providing space for lateral deformation and shell folding under compressive loads.

[0054] like Figure 2 As shown in (a), the outer major axis dimension of the ellipsoidal cavity 3 is l. c The outer minor axis dimension is h e The element length along the ellipse axis is R. Furthermore, l c with h e The relationship between them satisfies a major-minor axis ratio of 1.3 to 2.5, and R and l c The wall thickness w should maintain a relationship of 3 to 3.5 to achieve a reasonable shell slenderness ratio, balancing formability and buckling energy absorption capacity. c With outer long axis l c The ratio is preferably 0.05 to 0.15 to ensure that the elliptical shell has sufficient local stability while also being able to undergo controllable buckling and folding under compressive loads. The thickness t of the upper panel 1 and the lower panel 2... s For practical applications, a thickness of 0.8–2.0 mm can be used to achieve coordination between panel buckling and core buckling. Furthermore, the wall thickness of the hollow cylindrical support 4 and the wall thickness w of the elliptical cavity 3 are... c same.

[0055] In this specification, "the outer wall region at the end of the ellipsoidal cavity" refers to the outer surface of the two ends along the axial direction of the ellipsoidal cavity, including the outer surface section that transitions to the hollow support column; the outer wall region at the end can be tangentially connected, coplanarly connected, or continuously connected through transition structures such as fillets / chamfers.

[0056] In another preferred embodiment, such as Figure 4 and Figure 5 As shown, when the core structure adopts a three-layer structural unit array, the middle layer structural unit array is staggered relative to the upper and lower structural unit arrays along the elliptical cavity axis. Preferably, the upper and lower structural unit arrays are aligned, while the middle layer structural unit array is translated along the elliptical cavity axis, thus forming a stacking configuration of "three-layer symmetry, single-layer stagger".

[0057] In the square front view configuration of this embodiment, the structure satisfies the following along this direction.

[0058] ;

[0059] Among them, l c Let d0 be the outer major axis dimension of the elliptic cavity, d0 be the outer diameter of the hollow cylindrical support, and R be the length of the structural element along the axis of the elliptic cavity. The distance between the centers of two adjacent elliptic cavities is l. c + d0. The intermediate layer structural unit array is arranged in a half-period staggered manner relative to the upper and lower layer structural unit arrays, with a stagger distance p. x satisfy

[0060] ;

[0061] The purpose of adopting the above staggered arrangement is to address the problem that conventional three-layer aligned stacked structures are prone to synchronous shear failure at multiple closely spaced locations under out-of-plane compression conditions (e.g., Figure 6 (Diagonal shear fracture zone), by adjusting the force coupling relationship and interlayer force transmission path within the three-layer structure through intermediate layer misalignment, the load transmission position between different layers is redistributed, thereby reducing the tendency to form a continuous failure zone along the same through section.

[0062] To meet the powder removal requirements in powder bed fusion additive manufacturing, a process communication hole is provided on the shared intermediate panel of two adjacent structural unit arrays, at the intersection of the projection area of ​​the bottom end of the upper hollow support column and the projection area of ​​the top end of the elliptical cavity of the lower layer. The process communication hole penetrates the intermediate panel, connecting the internal cavities of adjacent layers and forming a powder removal channel. Preferably, the equivalent diameter of the process communication hole is D. h And satisfy:

[0063] ;

[0064] Where, d c The inner diameter of the hollow support column, l c This refers to the outer major axis dimension of the elliptical cavity. By constraining these dimensions, we can ensure smooth powder discharge while preventing excessive local weakening of the intermediate panel, which could affect the interlayer bonding strength.

[0065] In one specific embodiment, a conventional three-layer aligned structure and a three-layer misaligned structure were compared under the same external dimensions and material system. The results showed that the total mass of the three-layer misaligned structure was 67.94 g, while the total mass of the conventional three-layer aligned structure of the same size was 73.05 g, resulting in a mass reduction of 5.11 g. The weight reduction rate can be expressed as:

[0066] ;

[0067] Where m0 is the mass of a conventional three-layer aligned structure of the same size, and m1 is the mass of a three-layer misaligned structure. According to this embodiment, η... m ≈ 6.995%.

[0068] To further illustrate the impact of the three-story staggered arrangement on the structural failure mode, the finite element method was used to analyze the stress and deformation processes of a conventional three-story aligned structure and a three-story staggered structure under out-of-plane compressive loads, respectively. Figure 6 As shown in the figure. Simulation results show that conventional three-layer aligned structures are more prone to forming through-type, multi-layer synchronous shear failure zones at similar locations during compression; while the three-layer misaligned structure, due to the misalignment of the middle layer structural unit array along the elliptical cavity axis, redistributes the interlayer force transmission path, shifts the stress concentration area and the local failure initiation location, thereby suppressing the original trend of multi-layer synchronous shear failure.

[0069] like Figure 7 As shown, the three-layer misaligned structure exhibits a phased failure pattern during compression. In the initial loading stage, the load is mainly borne by the upper elliptical cavity and hollow columns, with local high-stress areas first appearing at the ends of the elliptical cavity and near adjacent columns. In the plateau energy absorption stage, the misaligned configuration of the middle layer guides the transfer of interlayer loads, causing the local buckling and shear deformation of the middle and lower layers to no longer unfold synchronously along the same continuous cross section. As the structure approaches the densification stage, a multi-regional, progressive collapse mode gradually forms inside the structure, and the failure process exhibits a layer-by-layer initiation and gradual expansion characteristic.

[0070] Therefore, the synergistic design of the three-layer staggered stack and the process connection hole not only meets the powder removal requirements in the metal powder bed molten additive manufacturing process, but also improves the problem of synchronous shear failure that is prone to occur in conventional three-layer aligned stacked structures under pressure by changing the interlayer load transfer mode in the three-layer structure, thereby improving the compressive stability, damage tolerance and lightweight level of the structure.

[0071] like Figure 2 (b) and Figure 3As shown, several structural units can be arrayed and spliced ​​along the l direction in a plane. Adjacent units are joined and closed by semi-cylindrical supports to form hollow cylindrical supports 4, thus forming a continuous sandwich structure, which may consist of only one layer of structural unit array ( Figure 3 (a) can also stack two or three layers of structural unit arrays along the direction perpendicular to the top and bottom panels. Figure 3 (b) Figure 3 (c) The intermediate panel is shared between adjacent structural unit arrays. s and core layer height h e The design can be tailored to the thickness requirements of the drone's wing or fuselage skin.

[0072] In a preferred embodiment, to balance structural performance and lightweight requirements, the present invention employs a parametric reverse design method to design the sandwich structure. First, a parametric reverse design method is established based on manufacturing constraints and installation space. Figure 2 (b) shows the parametric geometric model of the structural unit, and selects the elliptic cavity wall thickness w. c Panel thickness t s and core layer height h e As design variables, energy absorption per unit mass and structural equivalent density are used as target responses based on application requirements, and sample points are generated within a pre-defined range of variables.

[0073] In this embodiment, the Box-Behnken experimental design method is preferably used to generate sample points, and the response data of the corresponding sample points is obtained through a quasi-static compression experiment. Furthermore, a response surface model is used to establish the design variable w. c t s h e The mapping relationship between the target response and the target response. In this embodiment, the mapping relationship can be represented as follows:

[0074] ;

[0075] Where Y represents the target response vector, and Φ is the mapping model.

[0076] After obtaining the mapping model, multi-objective optimization is performed on it to obtain a set of candidate design solutions. The optimization problem in this embodiment can be expressed as:

[0077] ;

[0078] ;

[0079] Where F represents the objective function, and Ω represents the feasible region comprised of performance requirements, structural dimensions, and manufacturing conditions. In the candidate design solution set, the representative solution of minimum density, knee point, and maximum energy absorption can be selected as typical design solutions based on the specific application focus, such as... Figure 9 As shown in (a).

[0080] like Figure 9 As shown in (b), under the same core material and manufacturing process, single-layer, double-layer, and triple-layer sandwich structure models were constructed for three representative solutions, and the trend of their energy absorption per unit mass (SEA) as a function of the number of layers was calculated. The results show that in the structural system of this invention, the multi-layer knee representative solution achieves a better trade-off between energy absorption per unit mass and platform stability, making it suitable as the preferred solution for parts such as UAV wing skin that have high requirements for repeatable energy absorption performance.

[0081] Example 3: Additive Manufacturing Process and Physical Preparation

[0082] Based on the three representative solution parameters determined in Example 2, this example uses selected area laser melting (SLM) technology to prepare titanium alloy (Ti-6Al-4V) sandwich samples. Figure 8 As shown, sandwich samples with single-layer, double-layer, and triple-layer structures were prepared to investigate the layer effect.

[0083] The printing equipment can employ a metal powder bed melting device. Preferred process parameters are: laser power P approximately 250–300 W, scanning speed v approximately 800–1200 mm / s, powder layer thickness t approximately 20–40 μm, scanning spacing h approximately 0.08–0.12 mm, protective gas argon, and oxygen content within the chamber controlled below 100 ppm. It should be noted that the above parameters can be appropriately adjusted within the range known in the art to adapt to different equipment and sample sizes.

[0084] During the modeling and slicing stages, the upper panel 1, lower panel 2, ellipsoidal cavity 3, and hollow cylindrical support 4 are modeled and sliced ​​using an integrated 3D model. The inner cavity of the ellipsoidal cavity 3 is continuous along its axial direction, with openings at both ends of the axial direction to facilitate powder discharge after additive manufacturing. Alternatively, the ellipsoidal cavity has at least one powder discharge hole / channel on its shell to achieve powder discharge. In addition, the upper surface, sidewalls, and lower surface of the ellipsoidal cavity are all designed with self-supporting shape features. During the printing process, when the laser scans to the top area of ​​the ellipsoidal cavity 3, no additional support structure needs to be added to the inner cavity. The stability of the molten pool can be ensured without collapse by optimizing the scanning path and scanning sequence. After printing, the sample is de-powdered and cleaned, and then subjected to stress-relief annealing in a vacuum or protective atmosphere environment at approximately 800 ℃ for 1–2 hours to reduce residual stress and improve mechanical properties.

[0085] The single-layer, double-layer, and triple-layer sandwich samples prepared by the above process are as follows: Figure 8 As shown, the geometric contours of the elliptical cavity 3 and the hollow cylindrical support 4 can be clearly observed, and no obvious defects such as poor fusion or internal cavity collapse are observed, which verifies that the structure of the present invention is suitable for integral molding using SLM process.

[0086] Example 4: Analysis of Mechanical Properties and Energy Absorption Mechanism

[0087] The sandwich sample prepared in Example 3 was subjected to a quasi-static planar compression test. The loading direction was perpendicular to the upper panel 1 and the lower panel 2, and the loading speed was preferably 1 mm / min. Figure 10 The typical load-displacement curve F-x is shown, taking a three-layer knee-point representative solution structure as an example. Figure 11 The deformation morphology of the corresponding sample at different deformation stages.

[0088] Combination Figure 10 and Figure 11 The deformation failure process of this structure can be divided into three typical stages. The first stage is the linear elastic stage: in the initial stage of compression, the load increases approximately linearly with the displacement, and the structure as a whole exhibits high compressive stiffness until the first peak load F is reached. p1 At this point, local buckling and stress concentration begin to occur at both ends of the major axis of the elliptic cavity 3. The second stage is the platform energy absorption stage: as the load exceeds F... p1 The structure enters the plastic collapse process, and the load rapidly decreases to the first valley load F. v1Subsequently, the elliptical cavity 3 underwent significant shell-folding deformation. Simultaneously, the hollow cylindrical supports 4 on both sides developed multi-wave wrinkles and buckled progressively under compressive loads. The elliptical shell and the hollow supports were coupled through an "arch-brace" coupling, ensuring that the load-displacement curve maintained a nearly constant average platform force F over a relatively long displacement range. mean The fluctuations are relatively small, forming a stable energy absorption platform. The third stage is the densification stage: when the compression displacement approaches the densification displacement x... d At this point, the inner walls of the ellipsoidal cavity 3 tend to fit together, the hollow cylindrical support 4 is gradually compacted, the internal voids are significantly reduced, and the load F rapidly increases, entering the compaction stage. During this stage, local cracking or local failure may occur in the structure, and the energy absorption process ends.

[0089] according to Figure 10 The area of ​​the shaded region within the densification displacement xd in front of the central platform can be used to calculate the total absorbed energy EA of the structure during compression, defined as follows:

[0090] ;

[0091] Where F(x) is the instantaneous load at displacement x. The compaction displacement x d The following method can be used to determine the slope: After smoothing the load-displacement curve obtained from the experiment, search backwards from the end of the curve for the inflection point where the instantaneous slope increases rapidly. When the slope of the curve increases to the average slope F of the plateau... mean When the displacement ratio is a preset multiple (e.g., 2 to 4 times), the displacement corresponding to the inflection point is defined as the densification displacement x. d Furthermore, to measure the energy absorption efficiency of a structure under lightweight constraints, the energy absorption per unit mass (SEA) is defined as follows:

[0092] ;

[0093] Where m is the total mass of the sandwich sample. The EA and SEA values ​​can be obtained by integrating the F-x curves of different representative solutions and sandwich structures with different numbers of layers. Experimental results show that, under the same material and similar equivalent density conditions, the SEA of the multi-layer knee representative solution structure is significantly higher than that of the minimum density representative solution structure, and it exhibits a longer displacement range and smaller load fluctuations during the plateau phase.

[0094] From the perspective of deformation mechanism, the present invention, through the coupling design of ellipsoidal cavity 3 and hollow cylindrical support 4, enables the energy absorption process to unfold in a multi-stage deformation process of "local buckling of shell, shell folding, progressive buckling of support, and local stretching". Compared with the traditional honeycomb sandwich structure, which mainly relies on the buckling of a single pore wall to absorb energy, the structure of the present invention can make full use of the plastic deformation of metal materials without the debonding of the face and core, thus exhibiting higher energy absorption density and better energy absorption stability.

[0095] It should be noted that the test conditions in the above embodiments are only a typical application scenario of the present invention. For different types of UAVs or other lightweight protective structures, the wall thickness w of the ellipsoidal cavity and hollow cylindrical support can be adjusted according to the actual load spectrum. c Core height h e Panel thickness t s The number of structural layers and the types of materials are determined to obtain biomimetic sandwich solutions that can adapt to different protection levels and weight constraints.

[0096] After reading this specification, those skilled in the art can make various equivalent substitutions or modifications to the structural details and test schemes without creative effort, and all such modifications should fall within the protection scope of this invention.

Claims

1. A high-energy-absorbing, lightweight sandwich structure mimicking the elytra of a pine weevil, characterized in that, include: Top panel and bottom panel; And a core layer structure disposed between the upper panel and the lower panel; The core structure is composed of several structural units arranged in a plane. The structural unit includes an elliptical cavity at the center and hollow support columns distributed on both sides of the elliptical cavity; The major axis of the elliptical cavity is parallel to the upper and lower panels, and the top and bottom of the elliptical cavity are connected to the upper and lower panels respectively, so as to provide lateral deformation space when subjected to out-of-plane compressive loads. The axis of the hollow support column is perpendicular to the upper and lower panels. The hollow support column passes through and supports the upper and lower panels. The outer wall of the hollow support column is tangent to or coplanar with the outer wall region of the end of the elliptical cavity along its axial direction, thereby forming a load-bearing system of elliptical ring shell and vertical hollow support column inside the core structure.

2. The high-energy-absorbing lightweight sandwich structure of the elytra of the pine weevil according to claim 1, characterized in that: In the core structure, two adjacent structural units share a support structure at the splicing boundary; Specifically, each of the structural units has a hollow semi-circular support column on each of its two sides. When multiple structural units are spliced ​​together in the horizontal direction, the semi-circular shells on the docking sides of adjacent units close to form the hollow support column.

3. The high-energy-absorbing lightweight sandwich structure of the elytra of the pine weevil according to claim 1, characterized in that: The elliptical cavity has an inner elliptical profile and an outer elliptical profile on a cross section perpendicular to its axis. The minimum distance between the inner and outer elliptical profiles is defined as the wall thickness w of the elliptical cavity. c The wall thickness of the hollow cylindrical supports on both sides is equal to the wall thickness w of the ellipsoidal cavity. c ; The outer major axis l of the elliptic cavity c With the outer minor axis h e The ratio range is: 1.3 ≤ l c / h e ≤ 2.5; The wall thickness w c With the outer long axis l c The ratio range is: 0.05 ≤ w c / l c ≤ 0.15; The length R of the structural unit along the axis of the elliptic cavity is related to the outer major axis l. c The ratio range is: 3 ≤ R / l c ≤ 3.5; The upper panel, lower panel, elliptical cavity, and hollow support column are integrally formed structures, and their materials are one or more of titanium alloy, aluminum alloy, stainless steel, or high-strength steel.

4. The high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine-burl weevil according to any one of claims 1 to 3, characterized in that: The core structure includes one or more structural unit arrays along a direction perpendicular to the upper and lower panels; When the core structure includes multiple layers of the structural unit array, adjacent layers of the structural unit array share a common intermediate panel.

5. The high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine-burl weevil according to claim 4, characterized in that: When the core structure comprises three layers of structural unit arrays, the middle layer structural unit array is offset relative to the upper and lower layer structural unit arrays along the elliptical cavity axis, and the offset distance is p. x And satisfy: 。 6. The high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine-burl weevil according to claim 5, characterized in that: A process communication hole is provided on the middle panel shared by two adjacent structural unit arrays. The process communication hole is located at the intersection of the bottom projection area of ​​the upper hollow support column and the top projection area of ​​the lower elliptical cavity, and is used to form a powder discharge communication channel.

7. The high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine-burl weevil according to claim 6, characterized in that: The equivalent diameter of the process communication hole is D. h And satisfy: ； Where, d c The inner diameter of the hollow support column, l c The outer major axis dimension of the elliptic cavity.

8. A parametric reverse design method based on the sandwich structure described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Establish a parameterized geometric model of the structural unit and select several geometric parameters as design variables; (2) Construct a multi-objective optimization function and constraints according to the energy absorption requirements and lightweight requirements of the application scenario; (3) Generate sample points based on the design variables and obtain the response data of each sample point through experiments or numerical simulations; (4) Establish a mapping model between the design variables and the multi-objective optimization function based on the sample points and response data, and use an optimization algorithm to solve the mapping model to obtain a candidate design solution set; (5) Select the target solution that meets the preset criteria from the candidate design solution set according to the load requirements and constraints of the application scenario, and use it as the final design parameter.

9. A method for preparing a high-energy-absorbing lightweight sandwich structure mimicking the elytra of a pine knot weevil, characterized in that, The structure as described in any one of claims 1 to 7 is prepared by additive manufacturing, comprising: Import the 3D model data of the structure into the slicing software; Metal powder is selected as raw material and formed by powder bed melting additive manufacturing process, preferably selective laser melting (SLM) technology. The printing process involves layering and stacking the layers along the axis of the hollow support column, eliminating the need to add a support structure inside the elliptical cavity during the printing process. After printing, the part undergoes stress-relieving heat treatment.

10. A drone airframe, characterized in that: A high-energy-absorbing lightweight sandwich structure resembling a pine burl elytra, as described in any one of claims 1 to 7, is provided at the wing skin, fuselage load-bearing structure, or landing gear connection. Alternatively, the skin structure of the drone body may be integrally printed using the preparation method described in claim 10.

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