Double-platform energy-absorbing buffer material with negative Poisson's ratio characteristic

Abstract

The invention belongs to the technical field of impact protection and energy absorption, and particularly relates to a double-platform energy-absorbing buffer material with a negative Poisson's ratio characteristic, which comprises a top layer, an energy-absorbing layer group and a bottom layer which are fixedly arranged in sequence, the energy absorption layer set is composed of a plurality of stacked energy absorption layers, and each energy absorption layer comprises a plurality of energy absorption units arranged in a rectangular array. Each energy absorption unit comprises two orthogonally-arranged energy absorption unit cell structures, each energy absorption unit cell structure forms a first energy absorption cavity through a connecting face and a first inwards-concave structure, and a transverse rod and a second inwards-concave structure are arranged on the outer side of each first inwards-concave structure to form a second energy absorption cavity. The adjacent energy absorption units in the layers are connected through transverse rods, and the energy absorption layers are fixed through connecting faces. By means of various step-by-step buckling deformations of the two-stage concave structure, the first stress platform and the second stress platform which are independently adjustable are sequentially generated in the compression process, and efficient two-stage energy absorption is achieved; the three-dimensional structure has the negative Poisson's ratio effect and multidirectional bearing capacity, and can effectively avoid transverse expansion due to compression.

Description

Technical Field

[0001] This invention belongs to the field of impact protection and energy absorption technology, and particularly relates to a dual-plateau energy-absorbing buffer material with negative Poisson bit properties. Background Technology

[0002] With the rapid development of new energy vehicles, aerospace, and rail transportation, higher demands are being placed on the lightweight, high energy absorption efficiency, and multi-level buffering capabilities of impact protection structures. Currently, traditional energy-absorbing elements such as honeycomb structures, foam materials, and thin-walled tubes are widely used in scenarios such as bottom protection of vehicle battery packs and landing cushioning for aircraft. These structures absorb impact energy through plastic deformation or crushing, meeting protection requirements to a certain extent. However, with the increasing complexity of application conditions, the performance of traditional energy-absorbing structures is gradually revealing significant shortcomings.

[0003] Traditional honeycomb or foam materials possess only a single yield plateau with fixed plateau stress, making them unable to simultaneously meet the multi-level energy absorption requirements of both low-energy everyday impacts and high-energy severe impacts. This presents a contradiction of "excessive stiffness at low energy levels and failure at high energy levels." Furthermore, positive Poisson's ratio materials exhibit lateral expansion under axial compression, easily compressing surrounding cells or connectors within confined spaces, inducing structural instability or shear failure. While existing negative Poisson's ratio structures can achieve lateral contraction, they are mostly two-dimensional configurations, degenerating into ordinary thin-walled tubes in the out-of-plane direction. This results in insufficient lateral stiffness, making them prone to Euler buckling or shear collapse, with uncontrollable deformation modes and significantly reduced energy absorption efficiency. In addition, traditional structures have relatively low specific energy absorption, making it difficult to achieve high energy absorption under limited space and weight constraints.

[0004] Therefore, there is an urgent need for a dual-plateau energy-absorbing buffer material with negative Poisson bit properties to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-plateau energy-absorbing buffer material with negative Poisson bit properties to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present invention provides the following solution: A dual-platform energy-absorbing buffer material with negative Poisson bit properties includes: a top layer, an energy-absorbing layer group, and a bottom layer, which are fixedly arranged in sequence; The energy-absorbing layer group includes multiple stacked energy-absorbing layers, and each energy-absorbing layer includes multiple energy-absorbing units arranged in a rectangular array. The energy-absorbing unit includes two orthogonally arranged energy-absorbing unit cell structures. Each energy-absorbing unit cell structure includes a connecting surface located at the top and bottom, respectively. The two connecting surfaces are connected by two symmetrically arranged first concave structures. The connecting surface and the first concave structure together form the first energy-absorbing cavity; One end of a crossbar is fixed at the recess of the first concave structure, and the other end of the crossbar is fixed to one end of a second concave structure. The other end of the second concave structure is fixed to one of the connecting surfaces. The crossbar and the second concave structure are both located outside the first energy absorption cavity. The outer wall of the first concave structure, the second concave structure and the crossbar together form the second energy absorption cavity. Two adjacent energy-absorbing units located on the same horizontal plane are fixed together by the crossbar; The connecting surfaces of multiple energy-absorbing units located on the same horizontal plane form the mounting plane of the energy-absorbing layer; The mounting planes of two adjacent energy-absorbing layers are fixed, and the mounting plane of the energy-absorbing layer located at the edge is fixed to the corresponding top or bottom layer.

[0007] Optionally, the cross-section of the second concave structure is triangular.

[0008] Optionally, the third concave structure includes horizontal segments on the left and right sides and a second bent segment in the middle, wherein the cross-section of the second bent segment is trapezoidal or triangular, and the horizontal segments constitute the connecting surface.

[0009] Optionally, the energy-absorbing unit is a semi-crystalline polymer material.

[0010] Optionally, when both the first bent segment and the second bent segment have trapezoidal cross-sections, the angle between the hypotenuse of the trapezoidal cross-section of the first bent segment and the adjacent vertical segment is greater than the angle between the short side and the hypotenuse of the trapezoidal cross-section of the second bent segment.

[0011] Optionally, when the cross-section of the second bent segment is trapezoidal, the length of the horizontal segment is less than the length of the shorter side of the trapezoidal cross-section of the second bent segment.

[0012] Compared with the prior art, the present invention has the following advantages and technical effects: This invention effectively solves the problems of traditional energy-absorbing unit cell structures' inability to adapt to multi-level impacts due to the single-platform stress of the material, the spatial instability caused by the lateral expansion of positive Poisson's ratio materials, and the insufficient out-of-plane stiffness of two-dimensional negative Poisson's ratio structures by utilizing the dual-platform energy absorption mechanism of a three-dimensional negative Poisson's ratio energy-absorbing material. Under axial compression, the first concave structure undergoes plastic buckling to form the first-level energy-absorbing platform, followed by the second concave structure triggering the formation of the second-level platform, achieving graded buffering. The negative Poisson's ratio characteristic causes the structure to contract laterally, preventing compression of surrounding components. The three-dimensionally orthogonally arranged energy-absorbing units possess load-bearing capacity in multiple directions, with controllable deformation modes and improved energy absorption efficiency. This material is suitable for applications requiring lightweight construction, high energy absorption efficiency, and multi-level buffering, such as battery pack protection for new energy vehicles and landing cushioning in aerospace. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram of the energy absorption unit structure of the present invention; Figure 2 This is a front view of the energy-absorbing layer assembly structure of the present invention; Figure 3 This is a top view of the energy-absorbing layer structure of the present invention; Figure 4 This is an isometric view of the energy-absorbing layer structure of the present invention; Figure 5 This is a schematic diagram of the energy-absorbing unit cell structure of the present invention; Figure 6 This is a schematic diagram of the simulation environment for the finite element model of the energy-absorbing structure of the present invention; Figure 7 This is a graph showing the convergence and divergence analysis of the mesh in this invention. Figure 8 This is a dynamic deformation and equivalent stress cloud diagram of the present invention; Figure 9 The diagram shows the nominal stress-strain curves of this invention and existing energy-absorbing structures. Figure 10 This is a comparison chart of the total energy absorption (EA) values ​​of the present invention and existing energy-absorbing structures; Figure 11 This is a comparison chart of the specific energy absorption (SEA) values ​​of the present invention and existing energy-absorbing structures; Among them, 1. Horizontal section; 2. Third concave structure; 3. Vertical section; 4. First concave structure; 5. Horizontal bar; 6. Second concave structure. Detailed Implementation

[0014] The technical solutions of 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.

[0015] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Reference Figures 1 to 11This invention discloses a dual-platform energy-absorbing buffer material with negative Poisson bit properties, comprising: a top layer, an energy-absorbing layer group, and a bottom layer that are fixedly disposed in sequence; The energy-absorbing layer group includes multiple stacked energy-absorbing layers, and each energy-absorbing layer includes multiple energy-absorbing units arranged in a rectangular array. The energy-absorbing unit includes two orthogonally arranged energy-absorbing unit cell structures. Each energy-absorbing unit cell structure includes connecting surfaces located at the top and bottom, respectively. The two connecting surfaces are connected by two symmetrically arranged first concave structures 4. The connecting surface and the first concave structure 4 together form the first energy-absorbing cavity; One end of a crossbar 5 is fixed in the recess of the first concave structure 4, and the other end of the crossbar 5 is fixed to one end of the second concave structure 6. The other end of the second concave structure 6 is fixed to one of the connecting surfaces. The crossbar 5 and the second concave structure 6 are both located outside the first energy absorption cavity. The outer wall of the first concave structure 4, the second concave structure 6 and the crossbar 5 together form the second energy absorption cavity. Two adjacent energy-absorbing units located on the same horizontal plane are fixed together by a crossbar 5; The connecting surfaces of multiple energy-absorbing units located on the same horizontal plane form the mounting plane of the energy-absorbing layer; The mounting planes of two adjacent energy-absorbing layers are fixed, and the mounting plane of the energy-absorbing layer located at the edge is fixed to the corresponding top or bottom layer.

[0017] The application process of this three-dimensional negative Poisson's ratio energy-absorbing material is as follows: When an impact load is applied to the top layer, the force is transmitted through the energy-absorbing layer group. The first concave structure 4 in the energy-absorbing unit first undergoes elastic deformation, and then enters the plastic buckling stage, forming a first-level stress plateau to absorb low-energy impacts. As the compressive strain increases, the second concave structure 6 drives the crossbar 5 to bend upward, triggering the second-level stress plateau to cope with high-energy impacts. Throughout the process, the first and second energy-absorbing cavities deform collaboratively, and the structure exhibits a negative Poisson's ratio effect, avoiding lateral expansion instability. This invention achieves graded buffering through the dual-level energy absorption mechanism of the first concave structure 4 and the second concave structure 6; the three-dimensional orthogonally arranged energy-absorbing unit cell structure has load-bearing capacity in multiple directions; the negative Poisson's ratio characteristic ensures stable deformation in confined spaces; and the specific energy absorption is significantly higher than that of traditional honeycomb materials, making it suitable for scenarios such as vehicle battery pack protection and aerospace landing cushioning.

[0018] As an optional implementation, the first concave structure 4 includes vertical segments 3 located on the upper and lower sides and a first bent segment located in the middle, wherein the cross-section of the first bent segment is trapezoidal or triangular.

[0019] The vertical section 3 and the first bent section of the first concave structure 4 deform together during compression. The trapezoidal or triangular cross-section design of the first bent section optimizes the stress distribution, avoids stress concentration, makes the first-stage energy absorption platform more stable, and improves the buffering effect of low-energy impact.

[0020] As an alternative implementation, the cross-section of the second concave structure 6 is triangular.

[0021] The second concave structure 6 adopts a triangular cross section. When triggered in the second stage of energy absorption, its sharp corner design promotes upward bending and folding, forming a stable second stress platform and enhancing the energy absorption efficiency of high-energy impacts.

[0022] As an optional implementation, a third concave structure 2 is provided in the middle of the connecting surface.

[0023] The third concave structure 2 is located in the middle of the connecting surface. It provides additional deformation space during compression and assists the first concave structure 4 in coordinating deformation, making the first-stage energy absorption platform smoother and more stable.

[0024] As an optional implementation, the third concave structure 2 includes horizontal segments 1 located on the left and right sides and a second bent segment located in the middle, wherein the cross-section of the second bent segment is trapezoidal or triangular, and the horizontal segments 1 form a connecting surface.

[0025] The horizontal segment 1 of the third concave structure 2 forms the connecting surface. The second bending segment adopts a trapezoidal or triangular cross section, which deforms together with the first concave structure 4 during compression. The horizontal segment 1 provides stable support, and the second bending segment optimizes the stress distribution, making the first-stage energy-absorbing platform smoother and improving the low-energy impact buffering effect.

[0026] As an optional implementation, the thicknesses of the connecting surface, the first concave structure 4, the second concave structure 6, and the crossbar 5 are equal.

[0027] The connecting surfaces, the first concave structure 4, the second concave structure 6, and the crossbar 5 are of equal thickness, ensuring that the deformation of each component is coordinated during compression, the stress distribution is uniform, local stress concentration is avoided, and the overall structure's energy absorption stability and service life are improved.

[0028] As an optional implementation, the energy-absorbing unit is a semi-crystalline polymer material.

[0029] As an optional implementation, when both the first and second bent segments have trapezoidal cross-sections, the shorter side of the trapezoidal cross-section of the first bent segment is shorter than the shorter side of the trapezoidal cross-section of the second bent segment.

[0030] As an optional implementation, when both the first and second bent segments have trapezoidal cross-sections, the angle between the hypotenuse of the trapezoidal cross-section of the first bent segment and the adjacent vertical segment 3 is greater than the angle between the short side and the hypotenuse of the trapezoidal cross-section of the second bent segment.

[0031] As an optional implementation, when the cross-section of the second bent segment is trapezoidal, the length of the horizontal segment 1 is less than the length of the short side of the trapezoidal cross-section of the second bent segment.

[0032] The unit cell structure of this invention is based on a basic star-shaped structure with smoothed sharp corners, and the unit cell structure is orthogonally fixed to form an energy-absorbing unit. The energy-absorbing layer is composed of multiple energy-absorbing units arranged periodically, each unit containing multiple inwardly inclined bent ribs, which are connected by three-dimensional cross nodes to form a porous structure. During compression, the ribs can undergo synergistic inward deformation along a preset buckling direction, so that the entire honeycomb structure maintains a significant negative Poisson's ratio lateral contraction effect during compression and does not experience structural instability.

[0033] The honeycomb structure of this invention undergoes two stages of structural deformation during axial compression: The first stage undergoes gradual folding to form the first stress plateau, which is used to absorb low-energy impacts. Secondary high-density folding → forms a second stress plateau for absorbing high-energy impacts.

[0034] Through the above structural design, the present invention can achieve: graded energy absorption function, which reduces the peak load under low-energy impact and enhances the energy absorption capacity under high-energy impact; lateral contraction and stable folding, which improves the stability of working in narrow spaces or guide cavities; and improved specific energy absorption efficiency, achieving lightweight and high-performance protection.

[0035] The thickness t of the unit cell structure can be adjusted, so the wall thickness of each transverse rib and diagonal rib that makes up the energy-absorbing unit is consistent.

[0036] Unlike traditional star-shaped structures that can only rely on adjusting the concave angle, this invention allows all geometric design parameters to affect the mechanical properties of the negative Poisson's ratio structure. It is more flexible in design and maintains the high negative Poisson's ratio value of the star-shaped structure while improving its strength, thus ensuring the deformation stability of the structure under impact.

[0037] Multiple energy-absorbing layers are stacked to form an energy-absorbing metamaterial. Two adjacent energy-absorbing units are connected by a reinforced crossbar 5, which not only helps to form more plastic hinges to generate plastic deformation and absorb more energy, but also drives the crossbar 5 to bend and deform upward to form a new load-bearing structure.

[0038] This invention features a simple and easy-to-manufacture structure, which can be prepared via 3D printing and offers highly flexible control to meet various needs. The invention uses polyamide powder PA11 as the substrate. PA11 is derived from bio-based castor oil and belongs to the long-chain nylon family. Compared to conventional PA12, PA11 exhibits higher elongation at break (typically between 45% and 55%) and impact strength. This allows the plastic hinges at the internal connecting nodes of the energy-absorbing unit cell described in this invention to withstand severe rotational deformation without premature fracture failure when subjected to impact compression and undergoing a transition from the first to the second plateau. PA11 exhibits significant viscoelastic characteristics. Under quasi-static to medium-high speed impact conditions, the material modulus increases with increasing strain rate, thereby endowing the energy-absorbing structure with dynamically adjustable stiffness characteristics, which is beneficial for dissipating more kinetic energy in high-speed impacts.

[0039] This invention employs SLS (Selective Laser Sintering) technology as an additive manufacturing solution, primarily using a high-power laser to fuse polyamide powder together. The three-dimensional star-shaped negative Poisson's ratio structure described in this invention contains numerous overhangs, hollow areas, and concave features, with a small internal space within the energy-absorbing units. If additive manufacturing processes such as Fused Deposition Modeling (FDM) or Solidification Laser Lamination (SLA / DLP), which require the addition of physical support structures, are used, it becomes extremely difficult to completely remove the support structures from the complex lattice gaps, and the removal process easily damages the delicate rod-like structures. However, SLS technology, based on the principle of powder bed melting, allows the un-laser-sintered PA11 powder to directly act as a self-supporting material within the printing chamber, providing stable physical support for the suspended star-shaped framework. After printing, only compressed air sandblasting is needed to remove the interstitial powder, thus achieving high-precision, damage-free, and integrated molding of this complex topology. These characteristics are beneficial for improving the surface molding quality and load-bearing capacity of the three-dimensional negative Poisson's ratio structure. The load-bearing performance of metamaterials is highly dependent on a two-way balance between "compressive strength" and "plastic deformation capacity," neither of which can be lacking. Among them, compressive strength is the basic guarantee for a material to resist external loads and maintain structural stability: it must ensure that the metamaterial can resist buckling, that is, the unstable deformation of the structure after being subjected to force, and avoid failure problems such as premature fracture and breakage due to insufficient strength, so as to meet the core load-bearing function requirements. Therefore, the best manufacturing material for this negative Poisson's ratio porous material should be polyamide material PA11.

[0040] In this invention, the energy-absorbing material comprises several unit cell structures. Each energy-absorbing unit cell structure is formed by two orthogonally arranged single-cell structures to create a three-dimensional structure.

[0041] The energy-absorbing material is formed by a periodic arrangement of multiple energy-absorbing units, each unit containing several bent ribs that tilt inwards along the space. Each rib consists of two or more bend segments, with the bends forming local buckling induction points. Multiple ribs converge three-dimensionally at the nodes, forming a closed and stable spatial frame.

[0042] To verify the performance of the invention, a quasi-static compression simulation was performed on the lattice model using finite element simulation software. The model involved in the simulation consists of three unit cell structures in the X, Y, and Z directions, with the structures symmetrically distributed.

[0043] The deformation process is as follows: First, during the quasi-static compression simulation of the energy-absorbing layer group, the structure needs to be in contact with the top and bottom plates distributed above and below. Both the top and bottom plates are rigid plates. During the simulation, the bottom rigid plate is fixed, and the top rigid plate moves at a speed of 1 mm / min along the negative Y-axis.

[0044] In the initial stage of compression, the structure is in the initial elastic response phase, and no macroscopic Euler buckling occurs. Due to the concave geometry of the energy-absorbing units, vertical compression leads to significant inward contraction in the horizontal direction. This typical negative Poisson's ratio effect causes the structural material to concentrate towards the impact center, thereby increasing the local density and dynamic stiffness of the impacted area. This means that the structure rapidly establishes resistance through geometric hardening in the early stages of deformation, corresponding to the higher initial yield peak in the aforementioned stress-strain curve.

[0045] As compression continues, the structure enters the main energy-absorbing plateau region. At this point, the diagonal ribs of the energy-absorbing units begin to rotate and bend significantly, with all deformation highly concentrated at the node connections. This deformation mode indicates the formation of numerous plastic hinges in the structure. Unlike the shear band failure that is prone to occur in traditional honeycomb structures, the structure of this invention exhibits an extremely stable hierarchical collapse mode. The orderly folding of the ribs converts the external impact energy into the plastic deformation energy of the material. This stable folding process maintains a long and smooth stress plateau, which is the source of high total energy absorption.

[0046] As the compression stroke increases, the internal space of the first energy-absorbing cavity is almost completely compressed. Notably, the previously relatively independent upper and lower cell walls begin to self-contact, and the small folds in the inner layers are compacted. This self-contact phenomenon is not structural failure, but rather triggers a secondary stiffening mechanism. The flattened cell walls stack together, providing additional support and reaction force. This explains why the stress-strain curve shows a second rise in the later stages of the plateau, exhibiting a second stage of double-plateau characteristics. This stage ensures that the structure can still provide a final "safety line" of protection when facing extreme large deformations, preventing buffer failure.

[0047] In summary, this invention dissipates energy through a controllable deformation path of "inward contraction and aggregation, orderly folding, and contact reinforcement." This predictable and repeatable deformation mode is the core technical feature of this invention as a highly reliable buffer device.

[0048] To ensure simulation accuracy and improve computational efficiency, a mesh sensitivity analysis was performed on the finite element model of this invention under quasi-static loading. Mesh sizes were 2 mm, 1.5 mm, 1 mm, 0.8 mm, 0.7 mm, 0.6 mm, and 0.5 mm. Stress-strain curves for different mesh sizes are shown below. Figure 7 As the element size decreases, the equivalent stress decreases significantly and tends to converge at a mesh size of 0.6 mm, resulting in a relatively long computation time. Therefore, solid elements with a mesh size of 0.6 mm are used to mesh the honeycomb structure.

[0049] To verify the superiority of this invention in the field of buffering and energy absorption, it was compared with two other typical honeycomb structures—a traditional regular hexagonal positive Poisson's ratio structure and a conventional concave hexagonal negative Poisson's ratio structure—using the ANSYS-DYNA module for simulation. The test conditions for all three were kept consistent, all under quasi-static compression conditions.

[0050] By comparing the three dynamic response curves, it can be concluded that the present invention has the following significant structural buffering and energy absorption advantages.

[0051] 1. Significantly improved initial yield strength and load-bearing capacity.

[0052] from Figure 9 As can be seen, in the elastic stage with strain <0.05, the red line of the origami star structure of this invention exhibits the highest initial stiffness and yield stress, with its initial peak stress reaching approximately 0.47 MPa to 0.50 MPa. In contrast, the yield stress of the green line of the regular hexagonal structure is only about 0.2 MPa, and that of the blue line of the concave hexagonal structure is about 0.37 MPa. This indicates that the unique three-dimensional origami construction and star-shaped topology design of this invention provide stronger resistance to external impacts at the outset, thereby significantly improving the load-bearing threshold of the buffer device and preventing premature structural collapse under low-energy loads.

[0053] 2. Excellent platform stress level and high-efficiency energy dissipation.

[0054] The stress plateau region is the core area for energy absorption in a buffer structure. The hexagonal structure (green line): The stress level in the plateau region is extremely low (approximately 0.2 MPa) and excessively flat, indicating that it provides relatively little load-bearing capacity during impact and has limited energy dissipation ability. The concave hexagonal structure (green line): Although it exhibits some negative Poisson's ratio characteristics, its overall plateau stress level is lower than that of the example in this invention. The buffer structure of this invention (red line): Maintains a relatively high plateau stress value across a wide strain range of 0.05 to 0.6, gradually increasing from 0.48 MPa to approximately 0.8 MPa. According to the principle of energy absorption, the area enclosed under the stress-strain curve represents the energy absorption capacity per unit mass of the structure, i.e., the specific energy absorption area (SEA). Visually, the area under the curve of the structure of this invention is significantly larger than that of the other two comparative structures. This means that within the same compression stroke, this invention can dissipate more impact kinetic energy, demonstrating excellent buffer energy absorption efficiency, and is particularly suitable for aerospace or automotive protection fields with high crashworthiness requirements.

[0055] 3. The present invention has unique two-stage stress strengthening characteristics and controllable deformation mechanism.

[0056] Unlike the single stress plateau characteristic of traditional structures, the stress-strain curve of this invention exhibits a significant secondary hardening phenomenon in the strain range of 0.2 to 0.3, and then maintains a stable high-stress plateau characteristic in the strain range of 0.32 to 0.62.

[0057] This unique mechanical response is attributed to the interaction of the folded ribs of the origami structure below the transverse connecting rods between the cells of the three-dimensional origami star structure, as well as the spatial geometric hardening mechanism. This "reinforcement-stabilization" wave characteristic gives the structure multi-level protection capabilities when facing complex impacts: when subjected to a large impact, the structure can resist deformation through stiffness enhancement, thereby preventing the protected object from directly hitting the bottom.

[0058] 4. An ideal densification process.

[0059] After strain exceeds 0.78 and enters the densification stage, the stress increase trend of the structure of this invention is similar to that of the concave hexagonal structure, but the starting point of load-bearing capacity is higher. This indicates that the present invention retains the typical material shrinkage and density increase characteristics of negative Poisson's ratio structures, ensuring the integrity of the structure and the effective transmission of force under extreme compression conditions. In summary, compared with existing regular hexagonal and concave hexagonal honeycomb structures, the origami star structure of the present invention, by introducing a three-dimensional folding configuration, has achieved unexpected technical effects in terms of improving platform stress, increasing total energy absorption, and optimizing buffer stability.

[0060] It is important to note that, unlike the flat but low-strength plateau characteristic of traditional hexagonal structures, the stress plateau stage of this invention exhibits a unique double-step and reinforced feature. This non-constant plateau characteristic is not instability, but rather a design advantage of this invention: it allows the nominal stress to adaptively increase with the nominal strain. This means that during the buffering process, the resistance provided by the structure gradually increases with the impact depth, thereby achieving more efficient energy absorption within a limited deformation space, i.e., a larger area under the curve.

[0061] To further verify the technical advantages of this invention in terms of material utilization, this embodiment calculates the specific energy absorption (SEA) of the three structures based on the aforementioned quasi-static compression test results.

[0062] The data vividly reveals the significant differences in energy absorption efficiency among different topological configurations: the regular hexagonal structure, being a positive Poisson's ratio structure, suffers from lateral expansion upon impact due to its deformation mode primarily relying on simple rib bending, resulting in underutilization of the material and an SEA of only 6.86 J / g. While the concave hexagonal structure introduces a negative Poisson's ratio effect, its improvement is limited by the constraints of its two-dimensional configuration, resulting in an SEA value of 8.94 J / g. The origami star structure presented in this invention, benefiting from the enhanced spatial stiffness and dual-platform energy absorption characteristics brought about by its three-dimensional folding configuration, achieves an SEA value as high as 12.21 J / g. It can be observed that the origami star structure proposed in this invention significantly outperforms existing technologies in energy absorption efficiency, representing a 77.9% improvement compared to the traditional regular hexagonal structure and a 36.5% improvement compared to the concave hexagonal structure. This substantial performance improvement demonstrates that this invention is not a simple patchwork of existing shapes, but rather a qualitative leap achieved through structural improvement. This indicates that, under the same protection level, the design scheme of the present invention can significantly reduce the weight of the buffer protection device.

[0063] This extremely high specific energy absorption is primarily attributed to the unique all-material rib participation mechanism of this invention. During the deformation process of the origami star structure, not only are local hinges at work, but its three-dimensional star-shaped ribs undergo complex coordinated torsion and multi-level folding in space. This mechanism greatly reduces the "dead zones" in the structure—that is, redundant material that does not participate in load-bearing—thus maximizing the effectiveness of every gram of material in energy dissipation. In summary, this invention achieves the optimal balance between "high protective performance" and "extreme lightweight," solving the technical challenge of traditional porous structures that struggle to balance strength and weight.

[0064] To verify the protective reliability of the present invention against high-energy impacts, this embodiment statistically analyzed the total energy absorption (EA) values ​​of the three structures described above under the same geometric dimensions and the same compression displacement conditions.

[0065] Among them, the EA value of the regular hexagonal structure is only 48.53J, indicating that its ability to absorb impact kinetic energy is relatively weak. The EA value of the concave hexagonal structure is 81.76J, which is an improvement but still at a low level. The EA value of the origami star-shaped structure proposed in this invention is as high as 138.35J, which is unmatched by the other two structures. After quantitative calculation and comparison, the total energy absorption capacity of this invention is 2.85 times that of the regular hexagonal structure, and the energy absorption effect is improved by 185%.

[0066] The total energy absorption capacity of this invention is 1.69 times that of the concave hexagonal structure, representing a 69% improvement in energy absorption efficiency. This near-doubling of performance demonstrates that this invention is not merely a simple shape adjustment, but rather achieves a qualitative leap in structural load-bearing capacity through the synergistic effect of a dual-stress platform and a three-dimensional spatial folding mechanism. Figure 9 Stress-strain curve analysis reveals that the extremely high EA value of this invention stems from the large enclosing area beneath its stress-strain curve. Within the same compression distance, the structure of this invention can maintain a higher reaction force, i.e., a higher platform stress. This means that the structure is constantly performing work and absorbing energy under a "high load" state. This implies that in practical engineering applications such as automotive energy-absorbing boxes or landing gear, the device of this invention can successfully withstand impacts from faster, more massive objects without bottoming out, thus providing a safety redundancy for occupants or precision instruments far exceeding that of existing technologies.

[0067] The three-dimensional negative Poisson's ratio origami star-shaped buffer structure proposed in this invention can exhibit the negative Poisson's ratio effect, expanding the three-dimensional design field of star-shaped structures. At the same time, compared with the traditional star-shaped structure, this array structure can still exhibit negative Poisson's ratio performance when the thickness-to-length ratio is large.

[0068] Under axial compression, the oblique ribs first undergo local buckling at the bends, generating a coordinated inward movement through nodal geometric constraints, forming the first stage of slow compression, corresponding to the first stress plateau. As the compression increases, the ribs gradually come together and undergo dense folding. Simultaneously, the origami structure below the transverse connecting rod causes the crossbar 5 to bend vertically upward, forming another load-bearing structure. The overall structure becomes more compact, thus forming the second stress plateau. Throughout the process, the ribs fold inward, causing the transverse dimension of the structure to decrease with compression, exhibiting a negative Poisson's ratio characteristic.

[0069] This invention also provides a method for preparing a dual-plateau energy-absorbing buffer material with negative Poisson bit properties. The raw material used is polyamide material PA11 powder. This material has low density, high specific strength, and good corrosion resistance, which perfectly meets the requirements of this invention for lightweight buffering and energy absorption.

[0070] The specific preparation steps include the following: Step 1: 3D Digital Modeling and Data Processing. A geometric model of the negative Poisson's ratio structure, as in the invention example, is constructed using the 3D modeling software SolidWorks. The model is exported as an STL file and imported into the additive manufacturing preprocessing software MaterialiseMagics. The model is inspected and mesh repaired in the software to ensure that the model surface is closed and the normal vector is correct. Unlike metal printing, the selective laser sintering (SLS) process of this invention does not require the addition of internal physical support structures; the self-supporting characteristics of the powder bed are used to achieve the forming of the cantilever arm and concave corner. This avoids damage to the delicate star-shaped skeleton of this invention caused by subsequent support removal. The model is directly 3D positioned and sliced, with the slice layer thickness set to 0.10 mm (100 oz), and the slice data is exported as a processing path file recognizable by the printing equipment.

[0071] Step 2: Powder preparation and equipment debugging. High-performance polyamide (PA11) powder is selected, with a particle size distribution range controlled between 45 μm and 60 μm. To balance cost and mechanical properties, it is preferable to mix new powder and recycled powder in a 1:1 (or 50%:50%) ratio and then sieve the mixture to remove agglomerated impurities, ensuring that the powder has good flowability.

[0072] Start the SLS molding equipment and fill the molding chamber with nitrogen (N2) as a protective atmosphere. Circulate and purify until the oxygen content in the molding chamber drops below 1.0% to prevent the PA11 powder from oxidizing and degrading at high temperatures, which could cause the material to yellow or become brittle. Start the heating system to preheat the molding chamber and powder chamber to approximately the process window temperature (185℃-192℃). This temperature is controlled below the melting point of PA11 material but above its recrystallization temperature to prevent warping and deformation during the molding process.

[0073] Step 3: Selective Laser Sintering. The dried powder is poured into the powder chamber, and layer-by-layer printing begins. For the PA11 substrate material and the origami star structure of this invention, the preferred printing process parameters are as follows: laser power 25W-45W, scanning speed 2500mm / s-3500mm / s, scanning spacing 0.20mm-0.30mm, and powder layer thickness 0.10mm. During printing, the laser beam selectively melts the powder according to the slicing path, and the unmelted areas are retained as support material. An optimized checkerboard scanning strategy is adopted to homogenize the thermal field distribution and reduce the accumulation of residual thermal stress in the long cantilever of the structure of this invention.

[0074] Step 4: Post-processing. After printing, the following post-processing steps are performed in sequence to obtain the final performance part. Natural cooling: The part cannot be removed immediately. It needs to be allowed to cool naturally in situ within the equipment chamber for at least 10-12 hours, allowing the temperature inside the molding chamber to drop below 60°C. This step releases residual thermal stress inside the structure through slow cooling, preventing the three-dimensional star-shaped structure from twisting and deforming upon removal. Powder removal: The molding chamber is removed, and the molded component of this invention is separated. Due to the presence of numerous interconnected energy-absorbing cavities inside the structure of this invention, a glass microsphere sandblasting machine is required to thoroughly clean the structure from all directions, completely removing unmelted powder adhering to the concave corners and gaps of the star shape, to prevent residual powder from hardening and affecting the mechanical response of subsequent crushing tests.

[0075] The PA11 star structure prepared using the above process parameters has a relative density of over 99.5%, no obvious microcracks, accurately reproduces the complex topological details of the design model, and ensures the stable realization of the dual-stress platform.

[0076] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0077] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties, characterized in that, include: The top layer, energy-absorbing layer group, and bottom layer are fixedly installed in sequence; The energy-absorbing layer group includes multiple stacked energy-absorbing layers, and each energy-absorbing layer includes multiple energy-absorbing units arranged in a rectangular array. The energy-absorbing unit includes two orthogonally arranged energy-absorbing unit cell structures. Each energy-absorbing unit cell structure includes a connecting surface located at the top and bottom respectively. The two connecting surfaces are connected by two symmetrically arranged first concave structures (4). The connecting surface and the first concave structure (4) together form the first energy-absorbing cavity; One end of a crossbar (5) is fixed in the recess of the first concave structure (4), and the other end of the crossbar (5) is fixed to one end of a second concave structure (6). The other end of the second concave structure (6) is fixed to one of the connecting surfaces. The crossbar (5) and the second concave structure (6) are both located outside the first energy absorption cavity. The outer wall of the first concave structure (4), the second concave structure (6) and the crossbar (5) together form the second energy absorption cavity. Two adjacent energy-absorbing units located on the same horizontal plane are fixed together by the crossbar (5); The connecting surfaces of multiple energy-absorbing units located on the same horizontal plane form the mounting plane of the energy-absorbing layer; The mounting planes of two adjacent energy-absorbing layers are fixed, and the mounting plane of the energy-absorbing layer located at the edge is fixed to the corresponding top or bottom layer.

2. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 1, characterized in that, The first concave structure (4) includes vertical segments (3) located on the upper and lower sides and a first bent segment located in the middle, wherein the cross section of the first bent segment is trapezoidal or triangular.

3. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 1, characterized in that, The cross-section of the second concave structure (6) is triangular.

4. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 2, characterized in that, A third concave structure (2) is provided in the middle of the connecting surface.

5. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 4, characterized in that, The third concave structure (2) includes horizontal segments (1) on the left and right sides and a second bent segment in the middle, wherein the cross-section of the second bent segment is trapezoidal or triangular, and the horizontal segments (1) constitute the connecting surface.

6. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 1, characterized in that, The thicknesses of the connecting surface, the first concave structure (4), the second concave structure (6), and the crossbar (5) are equal.

7. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 1, characterized in that, The energy-absorbing unit is a semi-crystalline polymer material.

8. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 5, characterized in that, When both the first and second bent segments have trapezoidal cross-sections, the shorter side of the trapezoidal cross-section of the first bent segment is shorter than the shorter side of the trapezoidal cross-section of the second bent segment.

9. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 5, characterized in that, When both the first bent segment and the second bent segment have trapezoidal cross sections, the angle between the hypotenuse of the trapezoidal cross section of the first bent segment and the adjacent vertical segment (3) is greater than the angle between the short side and the hypotenuse of the trapezoidal cross section of the second bent segment.

10. A dual-plateau energy-absorbing buffer material with negative Poisson bit properties according to claim 5, characterized in that, When the cross-section of the second bent segment is trapezoidal, the length of the horizontal segment (1) is less than the length of the short side of the trapezoidal cross-section of the second bent segment.

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