A negative poisson's ratio based energy absorbing cushion honeycomb structure helmet and a method of manufacturing the same

Abstract

The application relates to the technical field of personal protective equipment, in particular to an energy-absorbing cushion honeycomb structure helmet based on a negative Poisson's ratio and a preparation method thereof; a helmet shell is located at the outermost layer; a stabilizing layer, a honeycomb layer and a cushion layer are sequentially arranged from outside to inside in the helmet shell; the honeycomb layer comprises a plurality of reentry hexagonal honeycomb units; the honeycomb units are in the shape of hourglasses with the middle part being concave inward and being centrally symmetrical; and the honeycomb units are arranged in a honeycomb array mode; the helmet structure and the preparation method are designed, the problems of unreliable connection of the honeycomb structure, uncomfortable wearing and insufficient energy absorption in the prior art are solved, a more comprehensive and reliable head protection scheme is provided, the application is based on systematic reconstruction after deep understanding of the negative Poisson's ratio mechanical mechanism, the logical paradox of direct contact in the prior art is overcome, and the interface failure problem of the combination of the porous structure and the homogeneous layer is solved.

Description

Technical Field

[0001] This invention relates to the field of personal protective equipment technology, and more specifically, to a helmet with a negative Poisson's ratio-based energy-absorbing padding honeycomb structure and its preparation method. Background Technology

[0002] In the fields of road traffic and sports safety, head injuries are a leading cause of serious injury and death. Helmets, as effective tools for reducing the risk of injury, directly impact wearer safety through the performance of their energy-absorbing padding. Traditional helmets commonly use polystyrene foam (EPS) as the energy-absorbing padding, which absorbs impact energy through material compression and rupture. However, EPS material exhibits significant performance degradation under repeated impacts and struggles to balance lightweight design with high energy absorption frequency. In recent years, biomimetic structures and materials with a negative Poisson's ratio have been increasingly incorporated into helmet cushioning layer design due to their superior impact resistance, energy dissipation capacity, and deformation stability.

[0003] In recent years, negative Poisson's ratio structures based on metamaterials have attracted attention due to their unique "tensile expansion" effect (lateral contraction under compression and lateral expansion under tension). When subjected to impact compression, negative Poisson's ratio structures accumulate at the impact center, leading to an increase in local density (enhanced indentation drag), thus exhibiting excellent energy dissipation capabilities. Existing negative Poisson's ratio helmet pad designs, such as the invention patent application CN115868706A entitled "A Lattice Structure Helmet Cushion Layer," although attempting to introduce lattice structures, mostly suffer from problems such as overly complex structures, weak interlayer connections, and poor comfort due to direct contact between pure lattice structures and the head, even posing a possibility of secondary puncture wounds.

[0004] Furthermore, existing technologies include a utility model patent (CN220369544U) entitled "A Protective Helmet Based on a Negative Poisson's Ratio Structure," which designs both the shell and the buffer layer as a negative Poisson's ratio honeycomb structure. While this design achieves weight reduction to some extent, its uniform honeycomb structure still presents the following problems:

[0005] (1) The connection strength between the complex honeycomb structure and the rigid outer shell is difficult to guarantee; (2) The honeycomb structure comes into direct contact with the head, which can easily cause local pressure and affect the comfort of wearing it; (3) Impact energy is transmitted in a single honeycomb structure, lacking a gradient absorption mechanism, and the protective performance needs to be further improved.

[0006] Therefore, developing a new type of energy-absorbing pad that combines structural stability, high energy absorption efficiency, and good wearing comfort is a technical challenge that urgently needs to be solved in the energy field. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, the present invention aims to provide a helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure, which combines structural stability, high energy absorption efficiency, and good wearing comfort, as well as its preparation method.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: A helmet with a negative Poisson's ratio-based energy-absorbing padding honeycomb structure includes an outermost helmet shell, and inside the helmet shell, a stabilizing layer, a honeycomb layer, and a padding layer are arranged sequentially from the outside to the inside. The padding layer is in contact with the wearer's head. The honeycomb layer includes several reentrant hexagonal honeycomb units, which are hourglass-shaped with an inwardly concave center and central symmetry, thereby forming a top edge, a bottom edge, and upper and lower sloping edges that are symmetrical and of equal length. The cellular units are arranged in a cellular array, and the upper / lower diagonal sides of two adjacent cellular units on the left and right coincide with the lower / upper diagonal sides, and the top / bottom sides of two adjacent cellular units on the top and bottom coincide with the bottom / top sides. The liner layer is an unstructured solid layer or a microporous flexible layer; The stabilizing layer, honeycomb layer, and padding layer are integrally formed using polymer powder or wire by laser sintering or fused deposition modeling.

[0009] Furthermore, the thickness of the stabilizing layer is 4mm to 6mm.

[0010] Furthermore, the thickness of the padding layer is 18mm~22mm.

[0011] Furthermore, the angle between the upper / lower inclined side and the top / bottom side is 45°~60°.

[0012] Furthermore, the thickness of each side of the cellular unit is 0.8mm to 1.2mm.

[0013] Furthermore, the thickness of the honeycomb layer is 24 mm.

[0014] Furthermore, the material of the liner layer is one of polydodecyl lactam, thermoplastic polyurethane, or acrylonitrile-butadiene-styrene copolymer.

[0015] A method for fabricating a helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure, the method comprising the following steps: (1) Collect multiple sets of human head engineering data and construct a macroscopic curved surface model of the helmet pad that fits the contour of the human head; (2) Design the micro-topology of the reentrant hexagonal cellular cell, set the angle between the upper inclined side and the top side, the lower inclined side and the bottom side, and the wall thickness parameters, and fill the micro-topology into the middle layer of the macro-surface model, while generating the stable layer on the outside and the padding layer on the inside to obtain a complete three-dimensional digital model. (3) Selective laser sintering or fused deposition modeling additive manufacturing technology is used to import the three-dimensional digital model and select polymer powder or wire for integrated printing molding; (4) The formed padding layer is cleaned, the support is removed and the surface is smoothed.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The helmet structure and manufacturing method designed in this invention have excellent protective performance. Compared with traditional EPS foam helmets, the head injury standard (HIC), peak acceleration (PLA), intracranial pressure (ICP) and maximum principal strain of the brain (MPS) are significantly reduced. (2) The helmet structure and manufacturing method designed in this invention achieve densification based on the negative Poisson's ratio effect under impact through the layered hybrid design of the stabilizing layer, honeycomb layer and padding layer and the re-entry hexagonal honeycomb structure, which greatly improves the energy absorption efficiency. (3) The helmet structure and manufacturing method designed in this invention creatively solve the contradiction of "soft and weak" or "hard and piercing" of pure dot matrix structure. The outer layer provides stable support, the middle layer provides strong energy absorption, and the inner layer protects the head. While ensuring structural stability, it also improves wearing comfort. (4) The helmet structure and manufacturing method designed in this invention solve the problems of unreliable honeycomb structure connection, uncomfortable wearing, and insufficient energy absorption in the prior art, and provide a more comprehensive and reliable head protection solution. This invention is not a simple patchwork of prior art and common knowledge, but a systematic reconstruction based on a deep understanding of the mechanical mechanism of negative Poisson's ratio. It overcomes the logical paradox of direct contact in the prior art, solves the interface failure problem of the combination of porous structure and homogeneous layer, and achieves the synergistic effect of "1+1+1>3" through integrated process and parametric design. Attached Figure Description

[0017] Figure 1 This is a schematic cross-sectional view of the helmet described in this invention; Figure 2 This is a schematic diagram of the overall structure of the helmet described in this invention; Figure 3 This is a schematic diagram of the structure of the cellular unit described in this invention; Figure 4This is a finite element model diagram of the forehead partial padding in this embodiment; Figure 5 This is a schematic diagram of the finite element simulation model of head impact while wearing a helmet in this embodiment; Figure 6 This is a comparison curve of the head's center of mass acceleration under the impact simulation conditions in this embodiment; Figure 7 This example shows a comparison of ICP contour plots under impact simulation conditions. Figure 8 This example shows a comparison of the brain strain cloud diagrams under impact simulation conditions in this embodiment. In the diagram: 1-Helmet shell; 2-Energy-absorbing pad; 21-Stabilizing layer; 22-Honeycomb layer; 23-Padding layer; 24-Honeycomb unit; 241-Top edge; 242-Bottom edge; 243-Upper bevel edge; 244-Lower bevel edge; 3-Strap. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments.

[0019] like Figure 1 and Figure 2 As shown, the helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to the present invention includes a helmet shell 1 located at the outermost layer, and an energy-absorbing pad 2 provided on the inner side of the helmet shell 1. The energy-absorbing pad 2 includes a stabilizing layer 21, a honeycomb layer 22 and a padding layer 23 from the outside to the inside. The padding layer 23 is in contact with the wearer's head, and a strap 3 for fixing is provided at the bottom of the helmet shell 1.

[0020] The honeycomb layer 22 includes a number of re-entry hexagonal honeycomb units 24. The honeycomb unit 24 is generally in the shape of an hourglass with the center concave inward and centrally symmetrical, thereby forming a top edge 241, a bottom edge 242, and upper and lower inclined edges 243 and 244 that are symmetrical and of equal length.

[0021] like Figure 3 As shown, the six vertices of the honeycomb cell 24 are defined as ABCDEF, where points B and E are inwardly concave points. This unique concave design is key to achieving the negative Poisson's ratio effect. When subjected to an impact perpendicular to the plane of the honeycomb cell 24, the upper inclined sides AB and EF, and the lower inclined sides BC and DE rotate inward, causing the concave points B and E to contract towards the center. At the same time, the top edge AF and the bottom edge CD also move inward accordingly. This causes the entire honeycomb cell 24 to become denser in the direction of pressure, while its lateral dimensions also shrink, exhibiting negative Poisson's ratio characteristics.

[0022] In the cellular unit 24, the angle between the upper inclined side AB and the top side AF, and the lower inclined side BC and the bottom side CD are defined as the cellular wall angle. The angle range of the cellular wall angle is 45°~60°, and the wall thickness is 0.8mm~1.2mm. This ensures that the overall structure can achieve lightweight while also having sufficient load-bearing capacity.

[0023] The cellular cells 24 are arranged in a cellular array, and the upper diagonal side 243 / lower diagonal side 244 of two adjacent cellular cells 24 on the left and right coincides with the lower diagonal side 244 / upper diagonal side 243, and the top edge 241 / bottom edge 242 of two adjacent cellular cells 24 on the top and bottom coincides with the bottom edge 242 / top edge 241.

[0024] Upon impact, the impact force first acts on the outer shell and is rapidly transferred to the stabilizing layer 21. The stabilizing layer 21, with its high rigidity, can initially disperse the concentrated impact force over a larger area and evenly transfer it to the central negative Poisson's ratio honeycomb structure layer. When subjected to force, the re-entry hexagonal honeycomb cells 24 of the honeycomb layer 22 generate a negative Poisson's ratio effect, contracting and densifying inwards, efficiently dissipating most of the impact energy through plastic deformation. Finally, the remaining smaller amount of energy is transferred to the inner unstructured padding layer 23. This layer further absorbs energy through its own elastic deformation, and its smooth surface avoids direct pressure from the honeycomb structure on the head, ensuring wearing comfort and ultimate safety. This gradient energy management path of "dispersion-dissipation-absorption" fully leverages the advantages of the overall structure, achieving a synergistic protective effect that a single structure cannot achieve, significantly improving the helmet's overall protective performance.

[0025] In addition, the thickness of the stabilizing layer 21 is controlled between 4mm and 6mm, the thickness of the padding layer 23 is controlled between 18mm and 22mm, and the thickness of the honeycomb layer 22 is controlled at 24mm. Under these parameter designs, the best effect can be achieved.

[0026] The method for preparing a helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to the present invention includes the following steps: (1) Collect multiple sets of human head engineering data and construct a macroscopic curved surface model of the helmet pad that fits the contour of the human head; (2) Design the micro-topology of the re-entry hexagonal cellular cell 24, set the angle between the upper inclined side 243 and the top side 241, the lower inclined side 244 and the bottom side 242 and the wall thickness parameters, and fill the micro-topology into the middle layer of the macro-surface model, while generating the stable layer 21 on the outside and the padding layer 23 on the inside to obtain a complete three-dimensional digital model. (3) Selective laser sintering or fused deposition modeling additive manufacturing technology is adopted, a three-dimensional digital model is imported, and polymer powder or wire is selected for integrated printing and molding; (4) The formed padding layer 23 is cleaned, the support is removed and the surface is smoothed.

[0027] like Figure 4 and Figure 5 As shown, this embodiment uses 3D modeling to perform detailed parameter design and performance verification on the forehead area. The structure has a thickness of 24mm, a width of 75mm, and a surrounding angle of 36°.

[0028] To verify the protective performance of the helmet designed in this embodiment, a system was established as follows: Figure 5 The model shown is a finite element simulation of head impact under helmet use. This model simulates a forehead impact, comparing the biomechanical response of the original helmet with traditional EPS padding with that of the helmet designed in this embodiment. Simulation results are as follows... Figure 6 , 7 As shown in Figure 8, a quantitative evaluation was conducted using four key indicators: HIC, ICP, PLA, and MPS. Specific data are shown in the table below.

[0029] Therefore, the results clearly demonstrate that the helmet designed in this embodiment is significantly superior to traditional EPS-padded helmets in all key indicators. Based on the excellent performance of the forehead area, by extending the re-entry hexagonal honeycomb structure described in this invention to the entire outer layer of the helmet liner, and optimizing the parameters of the honeycomb unit size, wall thickness, and arrangement direction according to the protection requirements and impact angles of different parts (such as the head and neck, temples, and occiput), all-round head protection is achieved.

[0030] The utility model patent CN221099507U, entitled "A Bulletproof Helmet with Negative Poisson's Ratio Effect," also employs a similar negative Poisson's ratio honeycomb structure to improve the helmet's performance. Superficially, the only difference between this embodiment and the helmet structure is the outer stabilizing layer and the inner unstructured padding layer. However, a deeper analysis reveals significant differences between the two solutions in terms of physical implementation mechanisms, mechanical response logic, and system synergy. For those skilled in the art, it is impossible to derive this solution based on this utility model patent and common knowledge.

[0031] In the prior art CN221099507U, the beneficial effect is stated as "through the unidirectional curvature, it can better fit the inner surface of the helmet and the wearer's head." This indicates that direct contact and fit are the prerequisites and design intentions for the solution described in the prior art. Based on this, forcibly inserting an unstructured padding layer between the honeycomb structure and the head would completely block the deformation transmission path claimed by the prior art, rendering its core advantage meaningless. Therefore, based solely on this prior art, those skilled in the art would have absolutely no motivation to add a stabilizing layer or padding layer; on the contrary, they would deliberately avoid placing any intermediate layer that hinders fit between the negative Poisson's ratio structure and the head, based on this guidance.

[0032] In addition, the negative Poisson's ratio honeycomb structure is a typical porous topology structure. Its connection interface with the external homogeneous material is composed of discrete cell wall end faces, with limited contact area and a large number of sharp edges. If conventional physical stacking or adhesive bonding processes are used, unavoidable physical obstacles will be encountered: (1) stress concentration and puncture risk: under high-speed impact load, the local stress peak of the sharp edge of the honeycomb unit is very likely to puncture the stable layer or cause the bonding interface to peel off instantly; (2) disordered stress transmission path: the stress will undergo abrupt changes, reflection and attenuation every time it passes through a physical interface, and a smooth gradient transmission cannot be achieved.

[0033] The key difference lies in the fact that this solution fundamentally eliminates the physical interface between layers through additive manufacturing integrated molding technology, enabling the three-layer structure to achieve continuous molecular-level connection at the microscale. A smooth transition is formed between the cell wall root and the mean layer, completely avoiding stress concentration points. This "deep coupling of structural design and manufacturing process" is something that cannot be achieved by any separate combination method.

[0034] The gradient energy management path of "dispersion-dissipation-absorption" constructed in this scheme relies on precise matching and coordinated design of the structural parameters of each layer. Specifically, the stabilizing layer applies in-plane constraints to the honeycomb layer with a specific stiffness, forcing the honeycomb cells to orderly contract inward and densify during compression, avoiding disordered buckling. The honeycomb layer then triggers stable concave deformation under a precise load threshold, efficiently dissipating core kinetic energy. The thickness and stiffness of the unstructured padding layer ensure that the honeycomb layer can preferentially deform and densify fully in the initial stage of impact, providing secondary buffering only after the honeycomb layer has compacted and then compresses itself again.

[0035] This temporal synergistic response (constraint → densification → secondary buffering) constitutes a closed-loop dynamic system. If the honeycomb layers in the comparison document are simply mechanically sandwiched between traditional materials, the complexity of interlayer stiffness matching and deformation temporal coupling will lead to the outer layer being too thick and rigid, which may inhibit honeycomb shrinkage, and the inner layer being too soft, which may be crushed before the honeycomb layers are densified. This will not only fail to improve performance, but may also weaken the overall protection efficiency.

[0036] Finally, the experimental simulation data described above strongly demonstrates the non-obviousness of this design. Compared to traditional single structures or simple structural combinations, this design achieves significant optimizations, including a 25.7% reduction in intracranial pressure (ICP), a 27.7% reduction in maximum principal strain (MPS) of the brain, and an 11.8% reduction in head injury index (HIC).

[0037] Therefore, if the three-layer structure of this solution were merely a simple combination of existing honeycomb layers with traditional stabilizing and comfort layers, such a technical solution would already be within the capabilities of those skilled in the art. However, prior to this application, no related technical solution had ever disclosed such a three-layer integrated structural design, nor had it provided any technical insights into significantly reducing biomechanical damage indicators. Therefore, it can be reasonably inferred that if a simple, modular assembly method were used, due to issues such as interlayer interface failure, stiffness mismatch, and disordered deformation timing, its protective performance would be far lower than that of this solution, and even lower than that of existing single-structure technologies or traditional EPS pads.

Claims

1. A helmet with a negative Poisson's ratio-based energy-absorbing padding honeycomb structure, comprising an outermost helmet shell, characterized in that, Inside the helmet shell, from the outside in, there are a stabilizing layer, a honeycomb layer, and a padding layer, with the padding layer in direct contact with the wearer's head. The honeycomb layer includes several reentrant hexagonal honeycomb units, which are hourglass-shaped with an inwardly concave center and central symmetry, thereby forming a top edge, a bottom edge, and upper and lower sloping edges that are symmetrical and of equal length. The cellular units are arranged in a cellular array, and the upper / lower diagonal sides of two adjacent cellular units on the left and right coincide with the lower / upper diagonal sides, and the top / bottom sides of two adjacent cellular units on the top and bottom coincide with the bottom / top sides. The liner layer is an unstructured solid layer or a microporous flexible layer; The stabilizing layer, honeycomb layer, and padding layer are integrally formed using polymer powder or wire by laser sintering or fused deposition modeling.

2. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The thickness of the stabilizing layer is 4mm to 6mm.

3. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The thickness of the padding layer is 18mm~22mm.

4. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The angle between the upper / lower inclined side and the top / bottom side is 45°~60°.

5. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The thickness of each side of the cellular unit is 0.8mm to 1.2mm.

6. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The thickness of the honeycomb layer is 24 mm.

7. The helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to claim 1, characterized in that, The material of the liner layer is one of polydodecanoic acid, thermoplastic polyurethane, or acrylonitrile-butadiene-styrene copolymer.

8. A method for preparing a helmet with a negative Poisson's ratio-based energy-absorbing pad honeycomb structure according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) Collect multiple sets of human head engineering data and construct a macroscopic curved surface model of the helmet pad that fits the contour of the human head; (2) Design the micro-topology of the reentrant hexagonal cellular cell, set the angle between the upper inclined side and the top side, the lower inclined side and the bottom side, and the wall thickness parameters, and fill the micro-topology into the middle layer of the macro-surface model, while generating the stable layer on the outside and the padding layer on the inside to obtain a complete three-dimensional digital model. (3) Selective laser sintering or fused deposition modeling additive manufacturing technology is used to import the three-dimensional digital model and select polymer powder or wire for integrated printing molding; (4) The formed padding layer is cleaned, the support is removed and the surface is smoothed.

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