Periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation

Abstract

The invention relates to the technical field of foam forming, in particular to a periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation, which is composed of a continuous phase structure made of foamed polyurethane and hollow structures uniformly arranged and distributed; the continuous phase structure comprises a base and bumps which are uniformly arranged and distributed on the surface of the base; the hollowed-out structure is located in the center of the protruding block. The structure has a shear thickening effect, shows efficient and stable impact energy absorption efficiency in a wide impact energy range, and has good impact resistance; and the composite material has a double-peak cell structure, and has higher mechanical strength than other cell structures under the same aperture ratio.

Description

Technical Field

[0001] This invention relates to the field of foam molding technology, and more specifically, to a periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation. Background Technology

[0002] Existing periodic multiscale impact-resistant structures include triply periodic minimal surfaces (TPMS). TPMS are characterized by zero mean curvature everywhere, exhibiting periodicity and non-self-intersecting structural features along the three principal axes of x, y, and z in three-dimensional space. TPMS structures are characterized by smoothness, full connectivity, and high specific surface area, and are widely found in nature, such as butterfly wings, sea urchin exoskeletons, and beetle shells (Yan Xin, Tian Lihao, Peng Hao, et al. A review of the design and application of triply periodic minimal surfaces[J]. Journal of Computer-Aided Design & Graphics, 2023, 35(3): 329-340.). In contrast, honeycomb-shaped open-pore structures have hexagonal single-pore shapes, which maximize the use of the material's internal space while providing lightweight and stable support, and have continuous pore walls and a small specific surface area. The pore size, pore wall thickness, and porosity of honeycomb open-cell structures can be adjusted within a wide range through formulation and process (Kurańska M, Malewska E, Polaczek K, et al. A pathway toward a newera of open-cell polyurethane foams-Influence of bio-polyols derived from used cooking oil on foams properties[J]. Materials, 2020, 13, 5161.). Topology-optimized periodic multi-scale structures can effectively reduce redundant mass and improve the effective load and utilization rate of materials by calculating and optimizing the periodic unit cell and pore structure of materials at the micro- and macro-levels, resulting in high-performance structures with both lightweight and high-strength characteristics (Chen Xiaoqian, Zhao Yong, Huo Senlin, et al. A review of multi-scale structure topology optimization design methods[J]. Acta Aeronautica Sinica, 2023, 44(15): 528863.). Compared to honeycomb structures, elastotropic structures with negative Poisson's ratios have higher structural stiffness and exhibit higher plateau stress and Young's modulus when subjected to normal compression; however, due to their lower densification strain, the overall energy absorption efficiency of the structure is lower than that of honeycomb structures.When subjected to in-plane compression, the negative Poisson's ratio induced auxetic structure exhibits extremely high energy absorption efficiency in the Y-axis direction (Alomarah A, Masood SH, Ruan D. Out-of-plane and in-plane compression of additively manufactured auxetic structures[J]. Aerosp. Sci. Technol., 2020, 106, 106-107.). Non-woven fabrics made of high-strength, high-modulus fibers such as aramid and ultra-high molecular weight polyethylene can form a high-strength, high-toughness 3D fabric structure by layering them at fixed angles, providing excellent protection against high-speed, high-penetration impacts from bullets and fragments (Zhang Hongwei, Tang Jianlan, Zhu Mankang. Research on the impact resistance of high-performance fiber laminates against fragments[J]. Journal of Ordnance Equipment Engineering, 2024, 45(10): 75-82.). (Morphology, Topology, Structure) The biomimetic gradient structure draws inspiration from the high-strength and tough biological structures widely found in nature, such as cuttlefish bones and ammonite shells. By simulating the micro- and macro-morphological and hierarchical structure of biological structures through calculation, a high-performance impact-resistant protective structure can be achieved (Helical impact-resistant structure with biomimetic gradient sinusoidal wave wall and its preparation method, 202411085636.0 [P], 2024-11-22; Impact-resistant structure based on ammonite hierarchical interlocking interface and its preparation method, 202411149670.X [P], 2024-11-29.).

[0003] Currently, the construction of TPMS structures is limited by modeling methods and additive manufacturing processes, and cannot systematically and comprehensively achieve its performance design goals. The generation of TPMS structural models relies on finite element analysis (FEM), but the limitations of FEM mesh generation lead to overall consistency loss and splicing distortion in the generated TPMS structures. FEM optimization consumes significant computational power and generates large amounts of model data, making direct transmission and 3D printing difficult. On the other hand, additive manufacturing technology, primarily 3D printing, is limited by printing accuracy and speed, hindering the industrial production of TPMS. The forming of honeycomb open-cell structures is significantly influenced by formulation, process, and mold. High porosity results in low density, wide pore size distribution, and numerous pore wall defects, thus affecting compressive strength and dimensional stability. Topology optimization of periodic multi-scale structures sacrifices structural accuracy to improve computational efficiency, leading to significant differences in the calculated structures obtained by different optimization methods. The periodic transmission of structures at the micro- and macro-levels further restricts the design space of multi-scale structures, resulting in limited improvement in structural performance from optimization results. The formation of topology-optimized periodic multi-scale structures relies on additive manufacturing, further limiting their structural accuracy and production efficiency. Expansion structures with negative Poisson's ratios exhibit significant anisotropy during compression, resulting in differentiated compressive properties in different stress directions. This hinders the formation of isotropic, impact-resistant structures with uniform energy absorption efficiency. Three-dimensional laminated fabric structures, due to their low compressibility and anisotropic microstructure, struggle to provide significant and uniform energy absorption. Biomimetic gradient structures cannot accurately replicate the composition, microstructure, and connectivity of biological structures, making it difficult to establish algorithms linking micro and macro structures. The imitation of biological structures further limits the design space, resulting in limited actual performance improvements. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation. This structure, employing the principle of minimum specific surface area and the discontinuous transformation method, designs an impact-resistant structure with micro- and macro-periodic periodic multi-scale characteristics, achieving both high mechanical strength and energy absorption efficiency while fully realizing structural lightweighting. Through the synergistic effect of the periodic micro-circular bubble structure and the macro-perforated structure, the periodic multi-scale structure exhibits rapid, uniform, and stable high impact response and protective performance. By using a rapid foaming process and high-precision molds, mass production and industrialization of the periodic multi-scale structure are achieved, thus solving the problems mentioned in the background art. To achieve the above objectives, the present invention provides the following technical solution: Based on the minimum specific surface area and discontinuous transformation, the periodic multi-scale impact-resistant structure is composed of a continuous phase structure made of foamed polyurethane and a uniformly distributed hollow structure.

[0005] Furthermore, the continuous phase structure comprises a base and protrusions evenly distributed on its surface; the hollow structure is located at the center of the protrusions.

[0006] Furthermore, the protrusion is triangular or hexagonal in shape.

[0007] Furthermore, the hollow structure is triangular or circular in shape.

[0008] Furthermore, the foamed polyurethane is specifically made from the following substances in corresponding parts by weight: 90-100 parts of bio-based polyether polyol, 55-65 parts of diphenylmethane diisocyanate, 2-5 parts of foaming agent, 1-8 parts of crosslinking agent, 1-4 parts of chain extender, 0.05-0.10 parts of catalyst, and 0.5-1 parts of hydrolysis stabilizer.

[0009] Furthermore, the foaming agent is one or more of water, cyclopentane, n-pentane, and isopentane.

[0010] Furthermore, the crosslinking agent is one or more of ethylenediamine, N,N'-dimethylhexadecylamine, and isophorone diamine.

[0011] Furthermore, the chain extender is one or more of trimethylenediamine, trimethylhydroxyethyl ethylenediamine, and pentamethyldipropylenetriamine.

[0012] Furthermore, the catalyst is one or more of bismuth isooctanoate, stannous octanoate, and dibutyltin dilaurate.

[0013] Furthermore, the hydrolysis stabilizer is one or more of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, polycarbodiimide, N,N'-dicyclohexylcarbodiimide, and bis(2,6-diisopropylphenyl)carbodiimide.

[0014] The technical effects and advantages of this invention based on a periodic multi-scale impact-resistant structure with minimum specific surface area and discontinuous transformation are as follows: This invention employs an equilateral triangular or hexagonal surface unit structure, maximizing the utilization of the material's surface space. Through discontinuous transformations using openings, grooves, and hollowing, the weight of the structure is effectively reduced macroscopically. By designing the materials and processes used, a foamed polyurethane material with an isotropic periodic circular microporous structure was obtained. This structure, while possessing high compressive strength, fully fills the internal space of the material through its circular cell morphology, minimizing the surface energy of the system and thus exhibiting higher stability, durability, and lighter weight. This structure exhibits a shear thickening effect, demonstrating high and stable impact energy absorption efficiency over a wide impact energy range, resulting in excellent impact resistance. Furthermore, its bimodal cell structure provides higher mechanical strength than other cell structures at the same open area ratio. Attached Figure Description

[0015] Figure 1 This is an overall schematic diagram of the periodic multi-scale impact-resistant structure with a triangular hollow structure of the present invention.

[0016] Figure 2 This is a schematic diagram of some triangular protrusions in the periodic multi-scale impact-resistant structure with triangular hollow structure of the present invention.

[0017] Figure 3 This is a topographical diagram of the circular microbubble pores with a periodic multi-scale impact-resistant structure featuring a triangular hollow structure, as described in this invention.

[0018] Figure 4 This is a pore size distribution diagram of the microbubble structure with a triangular hollow structure and a periodic multi-scale impact-resistant structure according to the present invention.

[0019] Figure 5 This is a morphological diagram of the nanopores of the periodic multi-scale impact-resistant structure with triangular hollow structure of the present invention.

[0020] Figure 6 This is a pore size distribution diagram of the periodic multi-scale impact-resistant nanopore structure with triangular hollow structure of the present invention.

[0021] Figure 7 This is a diagram showing the impact energy absorption performance of the periodic multi-scale impact-resistant structure with a triangular hollow structure of the present invention.

[0022] Figure 8 This is an overall schematic diagram of the periodic multi-scale impact-resistant structure with a circular hollow structure of the present invention.

[0023] Figure 9 This is a schematic diagram of a portion of the hexagonal protrusions in the periodic multi-scale impact-resistant structure with a circular hollow structure of the present invention.

[0024] Figure 10This is a diagram showing the impact energy absorption performance of the periodic multi-scale impact-resistant structure with a circular hollow structure of the present invention.

[0025] In the image above: 1. Base; 2. Protrusion; 3. Hollowed-out structure. Detailed Implementation

[0026] 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.

[0027] The minimum specific surface area mentioned in this invention refers to the maximum coverage of a flat surface by a polygon with a specific number of vertices such as 3, 4, or 6, so that the newly formed surface has the minimum specific surface area.

[0028] Discontinuous transformation structure: refers to engineering materials or structures that use bubbles, cavities, hollows, etc. as functional structures.

[0029] Periodic multiscale structure: refers to engineering materials that have periodic structures at both the micro and macro scales.

[0030] Based on the minimum specific surface area and discontinuous transformation periodic multi-scale impact-resistant structure, the structure is composed of a continuous phase structure made of foamed polyurethane and a uniformly arranged hollow structure 3.

[0031] The continuous phase structure comprises a base 1 and protrusions 2 evenly distributed on its surface; a hollow structure 3 is located at the center of the protrusions 2. The protrusions 2 are triangular or hexagonal in shape. The hollow structure 3 is triangular or circular in shape.

[0032] This discontinuously transformed hollow structure, by applying a periodic topological structure with the smallest specific surface area, effectively achieves lightweighting while ensuring optimal overall impact resistance of the macroscopic structure. The continuous phase of the foamed polyurethane possesses an isotropic periodic circular microporous structure with the smallest mathematical surface area, effectively achieving lightweighting while ensuring optimal overall impact resistance of the microstructure. The periodic circular microporous structure is a bimodal cell structure, meaning the pore size distribution is concentrated in two peak ranges, one high and one low, specifically manifested as a distribution of 1-2 orders of magnitude smaller pores on the surface of large pores. Compared to a unimodal cell structure, the bimodal cell structure has a smoother compressive stress-strain curve, resulting in higher impact energy absorption efficiency for the same volume and weight.

[0033] Polyurethane foam is specifically made from the following substances in the corresponding parts by weight: 90-100 parts of bio-based polyether polyol, 55-65 parts of diphenylmethane diisocyanate, 2-5 parts of foaming agent, 1-8 parts of crosslinking agent, 1-4 parts of chain extender, 0.05-0.10 parts of catalyst, and 0.5-1 parts of hydrolysis stabilizer.

[0034] The foaming agent is one or more of water, cyclopentane, n-pentane, and isopentane.

[0035] The crosslinking agent is one or more of ethylenediamine, N,N'-dimethylhexadecylamine, and isophorone diamine.

[0036] The chain extender is one or more of the following: trimethylenediamine, trimethylhydroxyethyl ethylenediamine, and pentamethyldipropylenetriamine.

[0037] The catalyst is one or more of bismuth isooctanoate, stannous octanoate, and dibutyltin dilaurate.

[0038] The hydrolysis stabilizer is one or more of the following: β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, polycarbodiimide, N,N'-dicyclohexylcarbodiimide, and bis(2,6-diisopropylphenyl)carbodiimide.

[0039] In addition, the specific preparation method of the above structure also includes the following steps: First, the above structure is designed and molded, and the mold is machined with high precision using CNC machining technology. The CNC mold is fixed in a high-pressure foaming machine and a release agent is sprayed on it. Bio-based polyether polyol, diphenylmethane diisocyanate, foaming agent, crosslinking agent, chain extender, catalyst and anti-hydrolysis stabilizer in the foaming machine's storage tank are uniformly mixed in the machine head, and then delivered to the nozzle through a precision metering pump, and poured into the mold through the nozzle. The mold is closed and reacted in a high-temperature sealed environment of 80℃-95℃ for 3-5 minutes. The mold is then opened to obtain a periodic multi-scale impact-resistant structure.

[0040] More specifically, the following tests were conducted on structures composed of different shapes.

[0041] Example 1: The structure is designed using Creo or ProE software in three dimensions, such as... Figure 1As shown; the periodic multi-scale impact-resistant structure of this design has triangular protrusions 2 and triangular hollow structure 3; the base 1 has a total length of 446 mm, a total width of 220 mm, and a total thickness of 16 mm. The diameter of the circular markings in the bottom marking area of ​​the base 1 is 8 mm, the height of the text inside the markings is 5 mm, the distance between the two circular markings is 29 mm, and the gap between the bottom trapezoidal area and the protective area where the triangular protrusions are arranged is 3 mm. The side length of the equilateral triangular protrusion 2 is 24.5 mm, and the height is 8 mm; the side length of the equilateral triangular hollow structure 3 inside the protrusion 2 is 10.73 mm, and the wall thickness of the equilateral triangle is 5 mm; the total length of the upper and lower pairs of equilateral triangular protrusions 2 is 54.65 mm, and the gap between the equilateral triangular protrusions 2 is 1-1.2 mm, as shown. Figure 2 As shown.

[0042] In the specific preparation process, a CNC mold is fixed in a high-pressure foaming machine, and a release agent is sprayed onto its surface. 100 parts of bio-based polyether polyol, 60 parts of diphenylmethane diisocyanate, 4 parts of cyclopentane, 7 parts of ethylenediamine, 2 parts of trimethylenediamine, 0.05 parts of stannous octoate, and 0.8 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester are transported from the storage tank to the machine head for uniform mixing. The mixture is then delivered to the nozzle via a precision metering pump and cast into the mold. The mold is closed and reacted at 95°C for 3 minutes in a high-temperature, sealed environment. Opening the mold yields a triangular, hollow, periodic, multi-scale impact-resistant structure.

[0043] The aforementioned periodic multi-scale impact-resistant polyurethane foam continuous phase has an isotropic circular microporous structure, such as... Figure 3 As shown, the pore size distribution of this circular microporous structure exhibits a bimodal characteristic, with the first peak in the pore size distribution being a diameter of 100-140 μm. Figure 4 As shown. It can be clearly observed from the scanning electron microscope images, such as... Figure 5 As shown, the surface of the larger microbubbles is distributed with nanopores two orders of magnitude smaller, and the pore diameters of these nanopores are concentrated in the range of 400-1000 nm. Figure 6 As shown, this is the second peak of the bimodal bubble structure.

[0044] According to the EN1621 standard, the impact resistance of periodic multiscale structures is tested using a drop hammer test. The test method involves using a 5 kg hammer to perform a vertical free-fall impact on the surface of the periodic multiscale structure within a height range of 1 m, and collecting and recording the residual impact force transmitted to the back of the structure.

[0045] The periodic multi-scale structure obtained in Example 1 exhibits a shear thickening effect, and its energy absorption efficiency increases non-linearly with increasing impact energy. In drop hammer impact tests, the periodic multi-scale impact-resistant structure showed an average absorption rate of 88.9 ± 0.4% of the impact energy generated when subjected to a 5 kg hammer dropped vertically from heights of 0.25 m, 0.5 m, and 1.0 m, demonstrating excellent impact resistance. Figure 7 As shown.

[0046] Example 2: Using Creo or ProE software to design a 3D model, a periodic multi-scale impact-resistant structure with a circular hollow structure is obtained, such as... Figure 8 As shown. This structure consists of a base 1 and hexagonal protrusions 2 evenly arranged on its surface. The base has a total length of 297 mm, a total width of 210 mm, and a total thickness of 22 mm. The hexagonal protrusions 2 have a side length of 15 mm, a height of 22 mm, a diameter of 10 mm for the circular hollow structure 3 at the center of the protrusions 2, a distance of 30 mm between the parallel sides of the hexagonal protrusions 2, and a gap of 2 mm between the hexagonal protrusions 2. Figure 9 As shown.

[0047] A CNC mold is fixed in a high-pressure foaming machine, and a release agent is sprayed onto its surface. 90 parts of bio-based polyether polyol, 55 parts of diphenylmethane diisocyanate, 5 parts of water, 6 parts of N,N'-dimethylhexadecanylamine, 2 parts of trimethylenediamine, 0.07 parts of bismuth isooctanoate, and 1 part of polycarbodiimide from a storage tank are transported to the machine head and mixed evenly. The mixture is then delivered to the nozzle via a precision metering pump and cast into the mold. The mold is closed and reacted at 95°C for 5 minutes in a high-temperature, sealed environment. Opening the mold yields a periodic, multi-scale impact-resistant structure with a circular hollow structure.

[0048] The described periodic multi-scale structure exhibits a shear thickening effect, and its energy absorption efficiency increases non-linearly with increasing impact energy. In drop hammer impact tests, the average absorption rate of the impact energy generated by the periodic multi-scale impact-resistant structure when subjected to a 5 kg hammer dropped vertically from heights of 0.25 m, 0.5 m, and 1.0 m was 89.04 ± 1.1%, demonstrating good impact resistance. Figure 10 As shown.

[0049] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0050] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A periodic multi-scale shock-resistant structure based on minimum specific surface area and discontinuous transformation, characterized in that, The structure consists of a continuous phase structure made of foamed polyurethane and a uniformly distributed hollow structure (3).

2. The periodic multi-scale shock-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 1, characterized in that, The continuous phase structure comprises a base (1) and protrusions (2) evenly distributed on its surface; the hollow structure (3) is located at the center of the protrusions (2).

3. The periodic multi-scale shock-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 2, characterized in that, The protrusion (2) is triangular or hexagonal in shape.

4. The periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 3, characterized in that, The hollow structure (3) is triangular or circular in shape.

5. The periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 1, characterized in that, The foamed polyurethane is specifically made from the following substances in corresponding parts by weight: 90-100 parts of bio-based polyether polyol, 55-65 parts of diphenylmethane diisocyanate, 2-5 parts of foaming agent, 1-8 parts of crosslinking agent, 1-4 parts of chain extender, 0.05-0.10 parts of catalyst, and 0.5-1 parts of hydrolysis stabilizer.

6. The periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 5, characterized in that, The foaming agent is one or more of water, cyclopentane, n-pentane, and isopentane.

7. The periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 5, characterized in that, The crosslinking agent is one or more of ethylenediamine, N,N'-dimethylhexadecylamine, and isophorone diamine.

8. The periodic multi-scale shock-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 5, characterized in that, The chain extender is one or more of trimethylenediamine, trimethylhydroxyethyl ethylenediamine, and pentamethyldipropylenetriamine.

9. The periodic multi-scale shock-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 5, characterized in that, The catalyst is one or more of bismuth isooctanoate, stannous octanoate, and dibutyltin dilaurate.

10. The periodic multi-scale impact-resistant structure based on minimum specific surface area and discontinuous transformation according to claim 5, characterized in that, The hydrolysis stabilizer is one or more of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, polycarbodiimide, N,N'-dicyclohexylcarbodiimide, and bis(2,6-diisopropylphenyl)carbodiimide.

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