An ultralight mechanical metamaterial and a preparation method and application thereof

Abstract

The present application relates to the technical field of mechanical metamaterial preparation, in particular to a super-light mechanical metamaterial, a preparation method and application thereof. The super-light mechanical metamaterial is a layered composite structure, comprising an inner structure layer and an outer structure layer arranged in turn along the thickness direction. The inner structure layer comprises a first foaming layer and a second foaming layer, and a plurality of through-flow channels parallel to each other and arranged at equal intervals are arranged between the two layers. The flow channels and the adjacent interval structures are repeatedly arranged along the width direction to form a periodic structure unit. The preparation method comprises the following steps: preparing an inner foaming material mixture and an outer foaming material mixture respectively, pressing to form unfoamed materials, constructing linear positioning grooves on the surface of the first inner unfoamed material, preparing polyvinyl alcohol filaments and embedding them into the positioning grooves, laminating and assembling the blanks, and then integrally forming through mold crosslinking foaming, and finally obtaining the super-light mechanical metamaterial through elution hole forming and drying shaping.

Description

Technical Field

[0001] This invention relates to the field of mechanical metamaterials preparation technology, specifically to an ultralight mechanical metamaterial, its preparation method, and its application. Background Technology

[0002] Dance ankle braces, a common type of sports protective gear, are primarily used to reduce the impact load on the ankle joint during jumping, landing, rotation, and repetitive flexion and extension, thereby lowering the risk of soft tissue strains and sprains. Currently, the cushioning layer materials in dance ankle braces mostly use ordinary foam, EVA foam, rubber elastomers, or fabric composite padding. While these materials offer some cushioning, they generally suffer from problems such as random internal pore structure, insufficient breathability, poor structural controllability, and difficulty in balancing lightweight design with support. These issues make it difficult to meet the comprehensive requirements of dance-specific ankle brace cushioning layer materials in terms of fit, lightweight, cushioning, and air exchange capacity.

[0003] Most existing foamed cushioning materials rely on natural foaming to form a disordered pore structure. The internal pore size, connectivity, and arrangement are difficult to control precisely, resulting in poor structural consistency in the thickness and in-plane directions, which in turn affects the cushioning stability and comfort during use. Especially under conditions of prolonged wear or high-frequency movement, traditional cushioning layer materials are prone to problems such as stuffiness, uneven local pressure, or reduced cushioning effect.

[0004] On the other hand, mechanical metamaterials, as a novel material system that uses artificially designed internal structural units to regulate overall mechanical properties, have attracted widespread attention in recent years. However, most existing mechanical metamaterials rely on complex lattice designs or additive manufacturing processes, resulting in high preparation costs, low processing efficiency, and limited engineering applications in the field of flexible wearable protective gear. For dance ankle brace cushioning layer materials, there is still a lack of a clear, feasible, and widely applicable technical solution for constructing ultralight mechanical metamaterials with periodic structural units, directional flow channels, and layered differentiated pore structures, based on relatively mature and feasible processes.

[0005] Therefore, it is necessary to provide an ultralight mechanical metamaterial and its preparation method to solve the technical problems of existing dance ankle brace cushioning layer materials, such as structural disorder, insufficient breathability, and difficulty in balancing lightweight and support. Summary of the Invention

[0006] To address the aforementioned problems, this invention designs an ultralight mechanical metamaterial, which is a layered composite structure comprising an inner structural layer and an outer structural layer arranged sequentially along the thickness direction, wherein: The inner structural layer includes a first foam layer and a second foam layer arranged sequentially along the thickness direction; Multiple parallel and equally spaced through-flow channels are provided between the first foam layer and the second foam layer; The flow channel extends along the length of the ultralight mechanical metamaterial; Adjacent flow channels are separated by a spacer structure formed of foamed material; The flow channels and spacing structures are repeatedly arranged along the width direction to form periodic structural units; The average pore size of the inner structural layer is 150~300 μm, and the average pore size of the outer structural layer is 50~150 μm; The equivalent diameter of the flow guiding channel is 0.1~0.8 mm, and the center-to-center distance between adjacent flow guiding channels is 2~8 mm; The total thickness of the ultralight mechanical metamaterial is 3~8 mm, of which the thickness of the inner structural layer is 1~3 mm and the thickness of the outer structural layer is 2~5 mm; the thickness ratio of the first foaming layer and the second foaming layer is (0.8~1.2):1.

[0007] Explanation: The aforementioned ultralight mechanical metamaterial employs a layered composite structure. The side in contact with the human body is designated as the inner structural layer, and the side away from the human body is designated as the outer structural layer. The inner structural layer is composed of a first foam layer and a second foam layer, with multiple parallel and equally spaced through-flow channels forming between them. This structure allows the flow channels to be distributed in a regular array within the material, repeating along the width direction with adjacent foam material spacers, thus forming well-defined and controllable periodic structural units. These periodic structural units are not disordered pores formed by random foaming, but rather a regular internal configuration formed through a predetermined arrangement. Therefore, the resulting material meets the requirements for lightweighting while also possessing structural designability and configuration controllability.

[0008] The average pore size of the inner structural layer is larger than that of the corresponding porous region of the outer structural layer. This makes the structure closer to the body more conducive to fit, cushioning, and ventilation, while the structure further away from the body is better at maintaining overall shape stability. A through-flow channel is positioned between the first and second foam layers, avoiding the formation of large pores or hard edges directly on the skin-contact surface, thus improving wearing comfort and reducing localized pressure. By limiting the equivalent diameter, center-to-center spacing, and overall thickness range of the flow channel, this ultralight mechanical metamaterial can meet the comprehensive requirements of lightweight, fit, and support for the cushioning layer of dance ankle braces, while also facilitating stable mass production through subsequent processes.

[0009] As another aspect of the present invention, a method for preparing the above-mentioned ultralight mechanical metamaterial is also provided, wherein n is a multiplier coefficient of the amount of each component added in each of the following steps, and n is a positive number that can satisfy the operating system of this method, and the method includes the following steps: S1. Preparation of foam material mixture: The inner foaming material mixture and the outer foaming material mixture were prepared separately by a intensive mixing process. S2, tableting preforming: The inner foamed material mixture is milled on a two-roll mill for 2-5 minutes at a roll temperature of 75-90℃ and then pressed into a first inner unfoamed material and a second inner unfoamed material; the outer foamed material mixture is milled on a two-roll mill for 2-5 minutes at a roll temperature of 75-90℃ and then pressed into an outer unfoamed material. S3. Construct a linear positioning groove: Multiple parallel linear positioning grooves are formed on the surface of the first inner unfoamed material using a grooving mold. The linear positioning grooves extend along the length of the sheet, with a groove depth of 0.05~0.40 mm, a groove width of 0.12~1.00 mm, and a groove center-to-center distance of 2~8 mm. S4. Preparation of polyvinyl alcohol monofilaments: Polyvinyl alcohol monofilaments were prepared by a spinning process. S5. Preparation of the inner layer preform: The polyvinyl alcohol monofilament is embedded between the first inner unfoamed material and the second inner unfoamed material by a monofilament embedding method, and then pressed to obtain the inner layer preform. S6, Stacking preforms: The inner preforms obtained in S5 and the outer unfoamed material obtained in S2 are stacked sequentially in the thickness direction, so that the inner preforms are located on the side closer to the human body and the outer unfoamed material is located on the side farther away from the human body, to obtain the preform to be foamed. S7. Compression molding with cross-linking foaming: The blank to be foamed is placed in a mold and hot-pressed at 155~175℃ and 6~15 MPa for 8~20 min to obtain a foamed composite. S8. Elution, pore formation, and drying / setting: The foamed composite obtained from S7 was immersed in a water bath at 50-85℃ for 1-8 hours to dissolve and remove the polyvinyl alcohol monofilaments, thus obtaining a through-flow channel. The water was changed every 0.5-2 hours during the immersion process. After immersion, it was dried at 50-70℃ for 4-12 hours to obtain an ultralight mechanical metamaterial.

[0010] Explanation: The above preparation route constructs the through-flow channel and periodic structural units using a "configuration first, molding second, and washing third" approach. First, inner and outer foamed material mixtures are prepared separately, and the corresponding unfoamed materials are obtained through sheet preforming, ensuring that the subsequent structural layout is based on a continuous and stable sheet matrix. Then, a grooving die forms linear positioning grooves on the surface of the first inner unfoamed material, pre-defining the arrangement, direction, and spacing of the sacrificial templates, thus providing a foundation for the regularity and periodicity of the flow channel. Polyvinyl alcohol monofilaments are prepared through a spinning process, and then embedded within the linear positioning grooves, allowing the polyvinyl alcohol monofilaments to be arranged in a parallel, equidistant, and oriented manner within the material.

[0011] During the integrated molding process of laminated preforms and compression molding cross-linking foaming, polyvinyl alcohol (PVA) monofilaments are stably sandwiched between two layers of inner unfoamed material and integrally molded with the overall structure. In the subsequent water bath washing process, the PVA monofilaments are dissolved and removed, thus forming through-flow channels in their original positions. Because the position, direction, and spacing of the flow channels are predetermined in the early stages, the final structure exhibits good repeatability and consistency. This preparation method avoids the problems of direct mechanical drilling and post-cutting grooving that easily cause local damage and structural instability. It can construct an internally ordered channel structure while ensuring overall integrity, and is easily integrated with the integrated molding process of foamed materials, making it suitable for engineering implementation.

[0012] Furthermore, the method for preparing the foamed material mixture in S1 is as follows: S1-1, Preparation of the inner foaming material mixture: First, 1000n g of ethylene-vinyl acetate copolymer and [120n, 300n] g of polyolefin elastomer are added to a mixer and mixed at 85-95℃ for 3-6 min. Then, [40n, 120n] g of light calcium carbonate, [4n, 12n] g of zinc oxide and [3n, 8n] g of stearic acid are added and mixed at 90-100℃ for 2-4 min. Subsequently, [90n, 150n] g of modified azodicarbonamide foaming agent is added and mixed for 1-2 min. Finally, [8n, 16n] g of dicumyl peroxide crosslinking agent is added and mixed for 0.5-1.5 min before discharging to obtain the inner foam material mixture. S1-2, Preparation of the outer foaming material mixture: First, add 1000n g of ethylene-vinyl acetate copolymer and [80n, 220n] g of polyolefin elastomer to a mixer and mix at 85~95℃ for 3~6 min; then add [60n, 180n] g of light calcium carbonate, [4n, 12n] g of zinc oxide and [3n, 8n] g of stearic acid, and continue mixing at 90~100℃ for 2~4 min; then add [50n, 110n] g of modified azodicarbonamide foaming agent and mix for 1~2 min; finally add [10n, 18n] g of dicumyl peroxide crosslinking agent, mix for 0.5~1.5 min and discharge to obtain the outer foaming material mixture.

[0013] Furthermore, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 18-28 wt%, and the melt flow rate is 2-15 g / 10 min; the polyolefin elastomer is an ethylene-octene copolymer with a density of 0.860-0.890 g / cm³. 3 .

[0014] Explanation: The above method uses ethylene-vinyl acetate copolymer and polyolefin elastomer as the main foaming matrix. The ethylene-vinyl acetate copolymer imparts good foaming and molding properties and flexibility to the material, while the polyolefin elastomer improves the material's elastic recovery and stability under repeated pressure. Light calcium carbonate is used to adjust the material's bulk density and molding stability. Zinc oxide and stearic acid are used as co-components to improve stability during foaming and processing. Modified azodicarbonamide foaming agent is used to form a porous structure during hot pressing. Dicumyl peroxide crosslinking agent is used to establish a stable crosslinking network during foaming. By setting different amounts of polyolefin elastomer, light calcium carbonate, foaming agent, and crosslinking agent in the inner and outer foaming material mixtures respectively, different pore structure characteristics can be formed in the subsequent hot pressing foaming process.

[0015] The inner foaming material mixture uses a higher amount of foaming agent and a lower amount of crosslinking agent, along with a higher proportion of polyolefin elastomer and a lower proportion of lightweight calcium carbonate, which is beneficial for forming a relatively large pore structure in the inner structural layer. Conversely, the outer foaming material mixture uses a lower amount of foaming agent and a higher amount of crosslinking agent, along with a relatively higher proportion of lightweight calcium carbonate, which is beneficial for forming a relatively smaller and more stable pore structure in the outer structural layer. This differentiated formulation design not only creates a structural gradient along the thickness direction of the final material but also clearly distinguishes the structure between the side closer to and farther from the body, thus better meeting the comprehensive requirements of fit, lightweight, and overall support for the cushioning layer of dance ankle braces.

[0016] Furthermore, the method for preparing polyvinyl alcohol monofilaments in S4 is as follows: S4-1. Add polyvinyl alcohol to deionized water and stir to dissolve at 90~98℃ for 1.5~4 h to prepare a polyvinyl alcohol solution with a mass fraction of 8~18 wt%. S4-2. Degas the obtained polyvinyl alcohol solution at -0.06~-0.09 MPa for 10~30 min, and filter it through a 100~300 mesh filter; then extrude it through a spinneret to obtain polyvinyl alcohol monofilaments, and dry them at 40~80℃ for 2~8 h. S4-3. Subsequently, the polyvinyl alcohol monofilament is stretched and shaped, with a stretch ratio of 2 to 6 times, a shaping temperature of 120 to 160°C, and a shaping time of 10 to 120 seconds, to obtain stretched and shaped polyvinyl alcohol monofilament. The degree of polymerization of polyvinyl alcohol is 1700~2400, the degree of alcoholysis is 97~99 mol%, and the diameter of polyvinyl alcohol monofilament is 0.10~0.80 mm.

[0017] Note: The above-mentioned polyvinyl alcohol monofilament is used as a sacrificial template, and its preparation process follows the route of "dissolving—defoaming and filtering—spinning—drying—stretching and setting". By preparing polyvinyl alcohol into a solution of appropriate concentration and subjecting it to defoaming and filtering, the stability and uniformity of the subsequent spinning process can be improved. By controlling the spinning and drying conditions, polyvinyl alcohol monofilaments with relatively stable diameters can be obtained. Through subsequent stretching and setting, the polyvinyl alcohol monofilaments can have good linearity retention and operational stability, thus meeting the requirements of embedding in linear positioning grooves and subsequent compression molding processes.

[0018] The diameter of the polyvinyl alcohol (PVA) monofilaments is matched with the width, depth, and center-to-center spacing of the linear positioning grooves, ensuring that the PVA monofilaments can be stably embedded in the linear positioning grooves and maintain their predetermined arrangement during subsequent lamination and molding foaming processes. PVA itself has good water solubility; therefore, after the foamed composite is formed, it can be removed by water bath immersion without introducing additional organic solvents or high-energy machining steps. This improves process simplicity and reduces secondary damage to the foaming substrate.

[0019] Furthermore, the method for preparing the inner layer preform in S5 is as follows: S5-1. Embed the polyvinyl alcohol monofilament obtained in S4 into the linear positioning groove in S3, so that they are arranged in parallel in the same direction; then cover the second inner unfoamed material onto the first inner unfoamed material, so that the polyvinyl alcohol monofilament is located between the two layers of inner unfoamed material. S5-2. Pre-compress at 60~95℃ and 2~8 MPa for 0.5~3 min to embed polyvinyl alcohol monofilaments between the two inner layers of unfoamed material to obtain the inner layer preform.

[0020] Explanation: The preparation process of the aforementioned inner preform first utilizes linear positioning grooves to individually limit and orient polyvinyl alcohol (PVA) monofilaments. Then, a second inner unfoamed material is used to cover and embed the first inner unfoamed material, positioning the PVA monofilaments between the two layers. Following this, pre-compression treatment is applied at appropriate temperature and pressure to ensure a stable bond between the two inner unfoamed materials, while reliably clamping the PVA monofilaments in their predetermined positions. This pre-fabrication method allows for the pre-fixing of the sacrificial template's position and orientation before the compression molding and cross-linking foaming integral molding step, preventing displacement, twisting, or aggregation during subsequent heating and pressurization.

[0021] Using two layers of inner unfoamed material to clamp polyvinyl alcohol monofilaments not only facilitates the placement of the flow channels in the middle region within the inner structural layer, but also prevents the channels from being directly exposed to the skin surface after molding, resulting in a more continuous surface structure of the material. This process also makes it easier to control the arrangement, location, and thickness direction of the flow channels, providing a direct technological basis for ultimately forming regular, repeatable periodic structural units.

[0022] As another aspect of the present invention, the present invention also provides the application of the above-mentioned ultralight mechanical metamaterial, applying it to the cushioning layer material in a dance ankle brace.

[0023] Note: When the aforementioned ultralight mechanical metamaterial is used as a cushioning layer in dance ankle braces, it can be integrated with the main body of the ankle brace and positioned in the human contact area near the ankle or in its adjacent cushioning area. Because this ultralight mechanical metamaterial possesses a layered composite structure, an inner layer of airflow channels, and differentiated porous structures on both the inner and outer sides, it is suitable for use in areas of dance ankle braces that require a combination of lightweight, snug fit, cushioning, and internal air exchange. Especially in dance movements involving frequent flexion, extension, jumping, and changes in impact loads, this material can be used as a functional cushioning layer within the ankle brace.

[0024] Applying the aforementioned ultralight mechanical metamaterials to the cushioning layer material of dance ankle braces facilitates the transformation of the integrated configuration advantages of channel structures, layered structures, and foamed matrices into structural adaptation advantages in actual protective gear. This avoids the shortcomings in breathability, structural regularity, and local conformability when using traditional single foam materials. Since the ultralight mechanical metamaterials of this invention can achieve relatively clear structural control through a specific preparation method, they have significant application value in the design and manufacturing of ankle brace cushioning layer materials.

[0025] Compared with existing dance ankle brace cushioning layer foam materials, the advantages of this invention are: (1) The present invention constructs through-flow channels that are parallel to each other and equally spaced inside the inner structural layer, so that the flow channels and adjacent spaced structures are repeatedly arranged along the width direction to form regular periodic structural units, thereby improving the controllability and consistency of the internal structure of the material.

[0026] (2) The present invention adopts a layered composite structure of inner and outer structural layers, and through differentiated foaming material formulation and integrated molding foaming process, different pore structure features are formed on the side close to the human body and the side far from the human body, thereby taking into account both the needs of fit and cushioning and overall support.

[0027] (3) The present invention uses a linear positioning groove in conjunction with a polyvinyl alcohol monofilament sacrificial template to construct a through-flow channel, and then forms an internal ordered channel structure through water bath washing. The process route is clear and easy to combine with existing foaming molding processes, and has good feasibility and engineering application value. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of the present invention; Figure 2 This is a test diagram of the impact buffer and compression support performance in Experiment Example 1; Figure 3 This is the dynamic air permeability and heat dissipation performance test diagram in Experiment Example 2; Figure 4 This is the cyclic compression durability test diagram from Experiment Example 3. Detailed Implementation

[0029] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0030] Example 1: The content of this example describes a method for preparing an ultralight mechanical metamaterial, namely, the preparation method of preferred product 1, as follows.

[0031] S1. Preparation of foam material mixture: S1-1. Preparation of the inner foam material mixture: First, add 1000 g of ethylene-vinyl acetate copolymer and 220 g of polyolefin elastomer to a mixer and mix at 90°C for 4 min; then add 70 g of light calcium carbonate, 8 g of zinc oxide and 5 g of stearic acid, and continue mixing at 95°C for 3 min; then add 130 g of modified azodicarbonamide foaming agent and mix for 1.5 min; finally add 11 g of dicumyl peroxide crosslinking agent, mix for 1 min and discharge to obtain the inner foam material mixture.

[0032] S1-2. Preparation of the outer foaming material mixture: First, add 1000 g of ethylene-vinyl acetate copolymer and 140 g of polyolefin elastomer to a mixer and mix at 90°C for 4 min; then add 120 g of light calcium carbonate, 8 g of zinc oxide and 5 g of stearic acid, and continue mixing at 95°C for 3 min; then add 80 g of modified azodicarbonamide foaming agent and mix for 1.5 min; finally add 16 g of dicumyl peroxide crosslinking agent, mix for 1 min and discharge to obtain the outer foaming material mixture.

[0033] The ethylene-vinyl acetate copolymer contains 24 wt% vinyl acetate and has a melt flow rate of 5.2 g / 10 min; the polyolefin elastomer is an ethylene-octene copolymer with a density of 0.868 g / cm³. 3 .

[0034] S2. Pre-forming of the sheet: The inner foamed material mixture is milled on a two-roll mill for 3 minutes at a roller temperature of 80°C, and then pressed into a first inner unfoamed material with a thickness of 0.9 mm and a second inner unfoamed material with a thickness of 0.9 mm. The outer foamed material mixture is milled on a two-roll mill for 3 minutes at a roller temperature of 80°C, and then pressed into an outer unfoamed material with a thickness of 2.0 mm.

[0035] S3. Constructing linear positioning grooves: Using a grooving mold, multiple parallel linear positioning grooves are formed on the surface of the first inner unfoamed material. The linear positioning grooves extend along the length of the sheet, with a groove depth of 0.20 mm, a groove width of 0.40 mm, and a groove center-to-center distance of 4.0 mm.

[0036] S4. Preparation of Polyvinyl Alcohol Monofilaments: 120 g of polyvinyl alcohol was added to 880 mL of deionized water and stirred at 95°C for 2.5 h to prepare a 12 wt% polyvinyl alcohol solution. The resulting polyvinyl alcohol solution was degassed at -0.08 MPa for 20 min and filtered through a 200-mesh filter. The solution was then extruded through a spinneret with a 0.30 mm pore size to obtain polyvinyl alcohol monofilaments, which were dried at 60°C for 4 h. Subsequently, the polyvinyl alcohol monofilaments were stretched and shaped 4 times at 140°C for 60 s to obtain stretched and shaped polyvinyl alcohol monofilaments with a diameter of 0.30 mm. The degree of polymerization of the polyvinyl alcohol used was 2000, and the degree of alcoholysis was 98.5 mol%.

[0037] S5. Preparation of the inner layer preform: The polyvinyl alcohol monofilaments obtained in S4 are embedded in the linear positioning grooves in S3, so that they are arranged in parallel along the same direction; then the second inner unfoamed material is laminated onto the first inner unfoamed material, so that the polyvinyl alcohol monofilaments are located between the two inner unfoamed materials; pre-compressed at 80℃ and 4 MPa for 1.5 min, so that the polyvinyl alcohol monofilaments are embedded between the two inner unfoamed materials, and the inner layer preform is obtained.

[0038] S6. Stacking preforms: The inner preforms obtained in S5 and the outer unfoamed material obtained in S2 are stacked sequentially in the thickness direction, so that the inner preforms are located on the side closer to the human body and the outer unfoamed material is located on the side farther away from the human body, thus obtaining the preform to be foamed.

[0039] S7. Compression Crosslinking Foaming Integrated Molding: Place the blank to be foamed in a mold and hot press it at 165℃ and 10 MPa for 12 min to obtain a foamed composite.

[0040] S8. Washing and Pore Formation and Drying: The foamed composite obtained in S7 was immersed in a 70℃ water bath for 3 hours to dissolve and remove the polyvinyl alcohol monofilaments, thus obtaining a through-flow channel; the water was changed every 1 hour during the immersion process; after immersion, it was dried at 60℃ for 8 hours to obtain an ultralight mechanical metamaterial.

[0041] The resulting product has a total thickness of 5.1 mm, an inner structural layer thickness of 2.2 mm with an average pore size of 200 μm, and an outer structural layer thickness of 2.9 mm with an average pore size of 100 μm. Among these, the thickness of the first foaming layer in the inner structural layer is 1.1 mm, and the thickness of the second foaming layer is 1.1 mm.

[0042] Example 2: Product 2 with modified inner foaming agent / crosslinking agent.

[0043] The preparation method of the ultralight mechanical metamaterial according to Example 1 was adopted, except that the amount of modified azodicarbonamide foaming agent in the inner foaming material mixture was adjusted to 100 g and the amount of dicumyl peroxide crosslinking agent was adjusted to 14 g. The remaining steps and parameters were the same as in Example 1.

[0044] Example 3: Product 3 with modified inner foaming agent / crosslinking agent.

[0045] The preparation method of the ultralight mechanical metamaterial according to Example 1 was adopted, except that the amount of modified azodicarbonamide foaming agent in the inner foaming material mixture was adjusted to 150 g and the amount of dicumyl peroxide crosslinking agent was adjusted to 9 g. The remaining steps and parameters were the same as in Example 1.

[0046] Example 4: Product 4 with modified outer foaming agent / crosslinking agent.

[0047] The preparation method of the ultralight mechanical metamaterial according to Example 1 was adopted, except that the amount of modified azodicarbonamide foaming agent in the outer foaming material mixture was adjusted to 60 g and the amount of dicumyl peroxide crosslinking agent was adjusted to 20 g. The remaining steps and parameters were the same as in Example 1.

[0048] Example 5: Product 5 with modified outer foaming agent / crosslinking agent.

[0049] The preparation method of the ultralight mechanical metamaterial according to Example 1 was adopted, except that the amount of modified azodicarbonamide foaming agent in the outer foaming material mixture was adjusted to 100 g and the amount of dicumyl peroxide crosslinking agent was adjusted to 12 g. The remaining steps and parameters were the same as in Example 1.

[0050] Example 6: Product 6 with reduced flow channel diameter.

[0051] The ultralight mechanical metamaterial was prepared according to the preparation method of Example 1, with the only difference being: in S3, the width of the linear positioning groove was adjusted to 0.20 mm, the groove depth was adjusted to 0.10 mm, and the center-to-center distance of the groove was maintained at 4.0 mm; in S4, the diameter of the polyvinyl alcohol monofilament was adjusted to 0.15 mm, and the remaining steps and parameters were the same as in Example 1.

[0052] Example 7: Product 7 with increased center spacing of the flow guide channel.

[0053] The ultralight mechanical metamaterial was prepared according to the preparation method of Example 1, with the only difference being: in S3, the width of the linear positioning groove is 0.40 mm, the groove depth is 0.20 mm, and the center-to-center distance of the groove is adjusted to 6.0 mm; in S4, the diameter of the polyvinyl alcohol monofilament is 0.30 mm, and the remaining steps and parameters are the same as in Example 1.

[0054] Example 8: Product 8 with increased flow channel diameter.

[0055] The ultralight mechanical metamaterial was prepared according to the preparation method of Example 1, with the only difference being: in S3, the width of the linear positioning groove was adjusted to 0.60 mm, the groove depth was adjusted to 0.30 mm, and the center-to-center distance of the groove was maintained at 4.0 mm; in S4, the diameter of the polyvinyl alcohol monofilament was adjusted to 0.50 mm, and the remaining steps and parameters were the same as in Example 1.

[0056] Example 9: Product 9 with large channel dense arrangement.

[0057] The ultralight mechanical metamaterial was prepared according to the preparation method of Example 1, with the only difference being: in S3, the width of the linear positioning groove was adjusted to 0.85 mm, the groove depth was adjusted to 0.35 mm, and the center-to-center distance of the groove was adjusted to 3.0 mm; in S4, the diameter of the polyvinyl alcohol monofilament was adjusted to 0.70 mm, and the remaining steps and parameters were the same as in Example 1.

[0058] Example 10: Product 10 with low pre-compression / low molding process.

[0059] The preparation method of the ultralight mechanical metamaterial in Example 1 was followed, except that the pre-compression conditions in S5 were adjusted to 65°C, 2 MPa, and 0.5 min; and the molding conditions for cross-linking foaming in S7 were adjusted to 160°C, 8 MPa, and 10 min. The remaining steps and parameters were the same as in Example 1.

[0060] Example 11: Product 11 of high molding process.

[0061] The ultralight mechanical metamaterial was prepared according to the preparation method of Example 1, except that the molding cross-linking foaming integral molding conditions in S7 were adjusted to 172°C, 14 MPa, and 18 min, while the other steps and parameters were the same as in Example 1.

[0062] Example 12: Product 12 of high pre-compression process.

[0063] The preparation method of the ultralight mechanical metamaterial according to Example 1 was carried out, with the only difference being that: the pre-compression conditions in S5 were adjusted to 92°C, 7 MPa, and 3 min; and the molding cross-linking foaming integral molding conditions in S7 were kept at 165°C, 10 MPa, and 12 min. The remaining steps and parameters were the same as in Example 1.

[0064] Example 13: Product 13 without constructing linear positioning grooves.

[0065] The preparation method of the ultralight mechanical metamaterial according to Example 1 was carried out, except that: in S3, the linear positioning groove was not constructed; in S5, polyvinyl alcohol monofilaments were manually arranged in parallel at a spacing of 4.0 mm on the surface of the first inner unfoamed material, and then the second inner unfoamed material was covered and pre-pressed. The remaining steps and parameters were the same as in Example 1.

[0066] Example 14: Product 14 without polyvinyl alcohol monofilament.

[0067] The preparation method of the ultralight mechanical metamaterial according to Example 1 is carried out, except that: in S4, polyvinyl alcohol monofilaments are not prepared, and in S5, the polyvinyl alcohol monofilament embedding step is omitted. The second inner unfoamed material is directly laminated onto the first inner unfoamed material and pre-pressed. The remaining steps and parameters are the same as in Example 1.

[0068] Example 15: Parameter Lower Bound Support Example The material is prepared according to a method for preparing ultralight mechanical metamaterials, and all process and formulation parameters are taken at the lower limit of the scope permitted by the claims. Specifically: The inner foaming material mixture contains 1000 g of ethylene-vinyl acetate copolymer, 120 g of polyolefin elastomer, 40 g of light calcium carbonate, 4 g of zinc oxide, 3 g of stearic acid, 90 g of modified azodicarbonamide foaming agent, and 8 g of dicumyl peroxide; the outer foaming material mixture contains 1000 g of ethylene-vinyl acetate copolymer, 80 g of polyolefin elastomer, 60 g of light calcium carbonate, 4 g of zinc oxide, 3 g of stearic acid, 50 g of modified azodicarbonamide foaming agent, and 10 g of dicumyl peroxide; the initial mixing time is 2 min, and the roller temperature is 75℃; the linear positioning groove depth is 0.05 mm, the groove width is 0.12 mm, and the groove center-to-center distance is 8 mm; the polyvinyl alcohol solution has a mass fraction of 8 wt% and a polyvinyl alcohol monofilament diameter of 0.10 mm; the pre-compression conditions are 60℃, 2 MPa, and 0.5 min; the molding cross-linking foaming integrated molding conditions are 155℃, 6 MPa, and 8 min. The washing conditions were: immersion temperature 50℃ for 1 hour; drying conditions were: 50℃ for 4 hours. This example is only for supporting parameter ranges and is not used for performance comparisons in subsequent experimental cases.

[0069] Example 16: Parameter upper limit support example.

[0070] The material is prepared according to a method for preparing ultralight mechanical metamaterials, and all process and formulation parameters are taken at the upper limit of the allowable range of the claims. Specifically: The inner foaming material mixture contains 1000 g of ethylene-vinyl acetate copolymer, 300 g of polyolefin elastomer, 120 g of light calcium carbonate, 12 g of zinc oxide, 8 g of stearic acid, 150 g of modified azodicarbonamide foaming agent, and 16 g of dicumyl peroxide; the outer foaming material mixture contains 1000 g of ethylene-vinyl acetate copolymer, 220 g of polyolefin elastomer, 180 g of light calcium carbonate, 12 g of zinc oxide, 8 g of stearic acid, 110 g of modified azodicarbonamide foaming agent, and 18 g of dicumyl peroxide; the initial mixing time is 5 min, and the roller temperature is 90℃; the linear positioning groove depth is 0.40 mm, the groove width is 1.00 mm, and the groove center-to-center distance is 2 mm; the polyvinyl alcohol solution mass fraction is 18 wt%, and the polyvinyl alcohol monofilament diameter is 0.80 mm; the pre-compression conditions are 95℃, 8 MPa, and 3 min; the molding cross-linking foaming integrated molding conditions are 175℃, 15 MPa, and 20 min. The washing conditions were: immersion temperature 85℃ for 8 hours; drying conditions were: 70℃ for 12 hours. This example is only for supporting parameter ranges and is not used for performance comparisons in subsequent experimental cases.

[0071] Comparative Example 1: Commercially available EVA ankle support cushioning sheet.

[0072] The EVA cushioning sheet used in commercially available dance ankle braces was selected as a commercially available control material. It had a thickness of 5.0 mm and an apparent density of 0.18 g / cm³. 3 It does not have a flow channel structure or a layered differentiated structure.

[0073] Experimental Example 1: Impact buffering and compression support performance test.

[0074] Test subjects: Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1.

[0075] Sample conditions: 50 mm diameter discs were punched from each sample, with the thickness maintained at the original thickness of the finished product. Before testing, the discs were placed at (23±2)℃ and (50±5)% relative humidity for 24 h.

[0076] Test environment: room temperature (23±2)℃.

[0077] Test method: (1) 50% compressive stress: Using an electronic universal testing machine, the compression speed is 100 mm / min, and the sample is compressed to 50% of its original thickness. The compressive stress is recorded. (2) Peak transmitted force: A drop hammer impactor was used with an impact head mass of 2.0 kg, an impact height of 250 mm, and an impact energy of about 4.9 J. The peak transmitted force measured by the sensor below the sample was recorded.

[0078] See the table above and Figure 2 Example 1 achieves a better balance between compressive support and impact cushioning performance. Examples 2 and 4 show significantly increased 50% compressive stress, indicating that the material is generally too stiff. While providing some support, this is detrimental to wearer comfort, and the peak load is also correspondingly increased. Example 3 shows a decrease in 50% compressive stress to 148 kPa, indicating that the material is too soft. Although the peak load is low, the support is insufficient, making it prone to local collapse under repeated ankle loading. Example 5 shows weakened lateral support, leading to decreased cushioning stability. In contrast, Example 1 has a 50% compressive stress of 188 kPa, still within the moderate support range suitable for elastic ankle brace cushioning layers. It also has the lowest peak load at 1415 N, indicating that it provides better attenuation of impact loads while ensuring a comfortable fit and stable support. Compared to commercially available EVA cushioning layers, Example 1 does not significantly increase stiffness but significantly reduces peak load, better meeting the requirements of wearable ankle brace cushioning layers that are "not too soft, not too stiff, and balance cushioning and support."

[0079] Experimental Example 2: Dynamic air permeability and heat dissipation performance test.

[0080] Test subjects: Example 1, Example 6, Example 7, Example 8, Example 9, Example 13, Example 14 and Comparative Example 1.

[0081] Sample conditions: Cut 50 mm × 50 mm test pieces from each sample, with the thickness being the original thickness of the finished product. Before testing, place them in an environment of (23±2)℃ and (50±5)% relative humidity for 24 h.

[0082] Test environment: ambient temperature (25±1)℃, relative humidity (50±5)%.

[0083] Test method: (1) Dynamic air permeability: The specimen was fixed in a sealed fixture and compressed for 30 minutes at 30% compressive strain and 1 Hz. The average air exchange was recorded by a flow meter. (2) Simulated wearing temperature rise: The test piece was placed between a 34℃ constant temperature heating platform and a breathable fabric, and compressed at 30% compression strain and 1 Hz for 30 min. The temperature rise of the test piece on the skin-contact side was recorded.

[0084] See the table above and Figure 3The formation method, size, and arrangement regularity of the flow channels have a significant impact on dynamic air permeability and heat dissipation performance. Example 14, lacking polyvinyl alcohol monofilaments, did not form a continuous flow channel within the material, resulting in lower dynamic air permeability. Example 13, while incorporating polyvinyl alcohol monofilaments, lacked linear positioning grooves, leading to poor consistency in the flow channel arrangement and significantly lower air permeability and heat dissipation performance compared to Example 1. Examples 6 and 7 demonstrate insufficient air exchange capacity when the channel diameter is too small or the center-to-center spacing is too large. While Examples 8 and 9 further improved dynamic air permeability, larger channels or overly dense arrangements weakened the continuity of the local foamed material, requiring comprehensive evaluation in conjunction with subsequent durability assessments. Overall, Example 1 demonstrated stable performance in terms of dynamic air permeability and temperature rise control, indicating that a method for preparing ultralight mechanical metamaterials, through the directional construction of flow channels using linear positioning grooves and polyvinyl alcohol monofilaments, can significantly improve the air exchange conditions of the cushioning layer material in dance ankle braces.

[0085] Experiment Example 3: Cyclic Compression Durability Test.

[0086] Test subjects: Example 1, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13 and Comparative Example 1.

[0087] Sample conditions: Cut 50 mm × 50 mm test pieces from each sample, with the thickness being the original thickness of the finished product. Before testing, place them in an environment of (23±2)℃ and (50±5)% relative humidity for 24 h.

[0088] Test environment: room temperature (23±2)℃.

[0089] Test method: (1) Cyclic compression conditions: Apply 30% compressive strain on a dynamic compression tester at a frequency of 2 Hz for 5000 cycles; (2) Permanent deformation rate: After the cycle is completed, let it stand for 30 minutes and record the thickness recovery; (3) Rebound rate: calculated using compression recovery test; (4) Retention rate of flow channels: Cut a cross section of the sample and observe the ratio of the number of complete flow channels to the initial number using a stereomicroscope.

[0090] See the table above and Figure 4Example 1 showed the best performance in cyclic compression durability, indicating that the preferred pre-compression conditions, compression-crosslinked foaming integral molding conditions, and regular flow channel array play an important role in the long-term service stability of the material. Example 10 shows that when the pre-compression and molding conditions are too low, the inner preform is not sufficiently bonded, and the flow channel retention rate decreases significantly. Examples 11 and 12 show that although excessively high molding or pre-compression conditions can improve local density, they can also cause structural stress concentration, resulting in limited improvement in durability. Examples 8 and 9 show that as the diameter of the flow channels increases and the channels are densely packed, the continuity of the local foamed material weakens, leading to an increase in permanent deformation rate and a decrease in the flow channel retention rate. Example 13 further illustrates that if linear positioning grooves are not used for limiting, both channel regularity and structural retention will significantly deteriorate. Compared with commercially available EVA ankle support cushioning sheets, Example 1 is superior in terms of permanent deformation rate, resilience, and structural retention, indicating that a method for preparing an ultralight mechanical metamaterial has better structural stability under long-term cyclic loading conditions.

Claims

1. An ultralight mechanical metamaterial, characterized in that, The ultralight mechanical metamaterial is a layered composite structure, comprising an inner structural layer and an outer structural layer arranged sequentially along the thickness direction, wherein: The inner structural layer includes a first foam layer and a second foam layer arranged sequentially along the thickness direction; Multiple parallel and equally spaced through-flow channels are provided between the first foam layer and the second foam layer; The flow channel extends along the length direction of the ultralight mechanical metamaterial; Adjacent flow channels are separated by a spacer structure formed of foamed material; The flow guiding channels and the spacing structure are repeatedly arranged along the width direction to form a periodic structural unit; The average pore size of the inner structural layer is 150~300 μm, and the average pore size of the outer structural layer is 50~150 μm; The equivalent diameter of the flow guiding channel is 0.1~0.8 mm, and the center-to-center distance between adjacent flow guiding channels is 2~8 mm; The total thickness of the ultralight mechanical metamaterial is 3~8 mm, wherein the thickness of the inner structural layer is 1~3 mm and the thickness of the outer structural layer is 2~5 mm; wherein the thickness ratio of the first foaming layer and the second foaming layer in the inner structural layer is (0.8~1.2):

1.

2. The method for preparing an ultralight mechanical metamaterial as described in claim 1, characterized in that, Let n be the multiplier coefficient for the amount of each component added in each of the following steps, and let n be a positive number that satisfies the operating system requirements of this method. Then the preparation method includes the following steps: S1. Preparation of foam material mixture: The inner foaming material mixture and the outer foaming material mixture were prepared separately by a intensive mixing process. S2, tableting preforming: The inner foamed material mixture is milled on a two-roll mill for 2-5 minutes at a roll temperature of 75-90°C, and then pressed into a first inner unfoamed material and a second inner unfoamed material; the outer foamed material mixture is milled on a two-roll mill for 2-5 minutes at a roll temperature of 75-90°C, and then pressed into an outer unfoamed material. S3. Construct a linear positioning groove: Multiple parallel linear positioning grooves are formed on the surface of the first inner unfoamed material using a grooving mold. The linear positioning grooves extend along the length of the sheet, with a groove depth of 0.05~0.40 mm, a groove width of 0.12~1.00 mm, and a groove center-to-center distance of 2~8 mm. S4. Preparation of polyvinyl alcohol monofilaments: Polyvinyl alcohol monofilaments were prepared by a spinning process. S5. Preparation of the inner layer preform: The polyvinyl alcohol monofilament is embedded between the first inner unfoamed material and the second inner unfoamed material by a monofilament embedding method, and then pressed to obtain the inner layer preform. S6, Laminated billet assembly: The inner preform obtained in S5 and the outer unfoamed material obtained in S2 are stacked sequentially in the thickness direction, with the inner preform located closer to the human body and the outer unfoamed material located further away from the human body, to obtain the blank to be foamed. S7. Compression molding with cross-linking foaming: The blank to be foamed is placed in a mold and hot-pressed at 155~175℃ and 6~15 MPa for 8~20 min to obtain a foamed composite. S8. Elution, pore formation, and drying / setting: The foamed composite obtained in S7 was immersed in a water bath at 50-85℃ for 1-8 hours to dissolve and remove the polyvinyl alcohol monofilaments, thus obtaining a through-flow channel. The water was changed every 0.5-2 hours during the immersion process. After immersion, it was dried at 50-70℃ for 4-12 hours to obtain an ultralight mechanical metamaterial.

3. The method for preparing an ultralight mechanical metamaterial as described in claim 2, characterized in that, The method for preparing the foamed material mixture described in S1 is as follows: S1-1, Preparation of the inner foaming material mixture: First, 1000n g of ethylene-vinyl acetate copolymer and [120n, 300n] g of polyolefin elastomer are added to a mixer and mixed at 85-95℃ for 3-6 min. Then, [40n, 120n] g of light calcium carbonate, [4n, 12n] g of zinc oxide and [3n, 8n] g of stearic acid are added and mixed at 90-100℃ for 2-4 min. Subsequently, [90n, 150n] g of modified azodicarbonamide foaming agent is added and mixed for 1-2 min. Finally, [8n, 16n] g of dicumyl peroxide crosslinking agent is added and mixed for 0.5-1.5 min before discharging to obtain the inner foam material mixture. S1-2, Preparation of the outer foaming material mixture: First, add 1000n g of ethylene-vinyl acetate copolymer and [80n, 220n] g of polyolefin elastomer to a mixer and mix at 85~95℃ for 3~6 min; then add [60n, 180n] g of light calcium carbonate, [4n, 12n] g of zinc oxide and [3n, 8n] g of stearic acid, and continue mixing at 90~100℃ for 2~4 min; then add [50n, 110n] g of modified azodicarbonamide foaming agent and mix for 1~2 min; finally add [10n, 18n] g of dicumyl peroxide crosslinking agent, mix for 0.5~1.5 min and discharge to obtain the outer foaming material mixture.

4. The method for preparing an ultralight mechanical metamaterial as described in claim 3, characterized in that, The ethylene-vinyl acetate copolymer has a vinyl acetate content of 18-28 wt% and a melt flow rate of 2-15 g / 10 min; the polyolefin elastomer is an ethylene-octene copolymer with a density of 0.860-0.890 g / cm³. 3 .

5. The method for preparing an ultralight mechanical metamaterial as described in claim 2, characterized in that, The method for preparing polyvinyl alcohol monofilaments in S4 is as follows: S4-1. Add polyvinyl alcohol to deionized water and stir to dissolve at 90~98℃ for 1.5~4 h to prepare a polyvinyl alcohol solution with a mass fraction of 8~18 wt%. S4-2. Degas the obtained polyvinyl alcohol solution at -0.06~-0.09 MPa for 10~30 min, and filter it through a 100~300 mesh filter; then extrude it through a spinneret to obtain polyvinyl alcohol monofilaments, and dry them at 40~80℃ for 2~8 h. S4-3. Subsequently, the polyvinyl alcohol monofilament is stretched and shaped, with a stretching ratio of 2 to 6 times, a sizing temperature of 120 to 160°C, and a sizing time of 10 to 120 seconds, to obtain stretched and shaped polyvinyl alcohol monofilament. The polyvinyl alcohol has a degree of polymerization of 1700-2400 and a degree of alcoholysis of 97-99 mol%, and the polyvinyl alcohol monofilament diameter is 0.10-0.80 mm.

6. The method for preparing an ultralight mechanical metamaterial as described in claim 2, characterized in that, The method for preparing the inner layer preform in S5 is as follows: S5-1. Embed the polyvinyl alcohol monofilament obtained in S4 into the linear positioning groove constructed in S3, so that they are arranged in parallel along the same direction; then cover the first inner unfoamed material with the second inner unfoamed material, so that the polyvinyl alcohol monofilament is located between the two layers of inner unfoamed material. S5-2. Pre-compress for 0.5-3 min at 60-95℃ and 2-8 MPa to embed the polyvinyl alcohol monofilament between the two inner layers of unfoamed material to obtain the inner layer preform.

7. The application of an ultralight mechanical metamaterial as described in claim 1, characterized in that, It is used as a cushioning layer material in dance ankle braces.

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