High-effect coconut shell bionic structure composite armor and preparation method thereof

Abstract

The invention firstly provides a fiber preform with a negative Poisson's ratio effect. The fiber preform is formed by winding auxiliary fibers on core fibers, the core fibers are polypropylene fibers, and the auxiliary fibers are aramid fibers coated with epoxy resin. In the tensile test process, the inventor accidentally finds that the fracture energy of the aramid fiber and the PP fiber is obviously higher than the expected fracture energy in the helical structure expansion stage in which the negative Poisson's ratio is exerted, and the negative Poisson's ratio also has excellent performance compared with the expected fracture energy, so that the unexpected technical effect is realized. In addition, compared with carbon fibers which are mostly used in the prior art, the aramid fibers are low in later maintenance cost and have important practical application value. On the basis, the invention also provides an auxetic fabric prepared from the fiber preform, and modified reinforced polyurea prepared from the auxetic fabric. Finally, the invention further provides a high-effect coconut shell bionic structure composite armor, the concept of gradient and negative Poisson's ratio is introduced into a functional gradient armor in the field of anti-explosion materials, and through hardness-toughness gradient and porosity gradient transition design, the composite armor has remarkable advantages in the aspects of penetration resistance, light weight and repeated impact resistance.

Description

Technical Field

[0001] The present invention belongs to the field of materials, relates to the technical field of protective armor, and specifically relates to a high-performance coconut shell bionic structure composite armor, which is applied to engineering fields such as armored vehicle protection. Background Art

[0002] An armored vehicle is a military or special vehicle with armored protection, mainly used for tasks such as battlefield transportation, fire support, reconnaissance, or personnel protection. As a vehicle providing armored protection for combat supplies, armored vehicles need to be protected against explosion and penetration. Currently, the anti-explosion technologies adopted by existing armored vehicles in China generally only involve local decompression, pressure relief area, and anti-explosion design of the frame structure, and still have the following defects.

[0003] (1) The overall strength of the armor is insufficient. Armored vehicles need to withstand high-energy attacks such as explosion shock waves and explosive fragments, so high-strength materials and energy-absorbing materials are required. The currently adopted armor materials have insufficient energy absorption, and under large-scale explosions or high-speed impacts, they will crack or break, thus reducing the anti-explosion performance.

[0004] (2) The anti-explosion and anti-penetration capabilities are limited. Explosion shock waves have characteristics such as high pressure and high temperature, and can cause serious damage to armor materials. Currently commonly used metal armor materials have the problem of low explosion resistance, and are prone to deformation, cracking, or reduction in the strength of welded joints.

[0005] (3) The density of the armor structure is too large. In order to improve the strength and protection ability of armor materials, it is often necessary to increase the density of the materials. This leads to an increase in the overall weight of the armored vehicle, thus affecting its mobility and handling performance. Excessive weight will also increase fuel consumption and reduce the driving range, having a negative impact on combat effectiveness.

[0006] Based on the above defects, the anti-explosion means of directly releasing explosion energy in the prior art are extremely likely to cause secondary damage to armored vehicles and personal property. This is because, during the explosion process, substances change the pressure state of the environmental medium in a very short time, do work on the outside world to release energy, and have the characteristics of high speed and self-propagation. The explosion can propagate by itself without external energy support and is very rapid. Moreover, during the high-speed impact process, the material will deform and break, and the corresponding organizational structure and performance will undergo permanent changes.

[0007] To solve the aforementioned problems, conducting research on new anti-explosion and anti-penetration materials is an effective way to improve the performance of armored vehicles. Patent Application 202311512183.0 discloses "Method and System for Manufacturing Protective Armor, Protective Armor, and Vehicle". This application prepares the protective armor by splitting the ceramic armor into multiple prefabricated parts for separate preparation and then assembling them. However, this application only solves the technical problems of low preparation efficiency and poor quality in the one-piece forming process, and does not fundamentally improve the anti-explosion and anti-penetration capabilities of the protective armor of armored vehicles. Summary of the Invention

[0008] Aiming at the problems existing in the protective materials of armored vehicles in the prior art, the present invention provides a high-performance anti-explosion and anti-penetration composite armor based on the bionic design concept of coconut shell structure. The composite armor conducts three-layer stepped compounding on the "laminated composite material", which not only significantly enhances the anti-impact performance, but also can reduce the rigid transmission effect of the impact load through an efficient energy absorption mechanism, thereby effectively buffering the direct impact on the crew and minimizing the risk of human injury to the greatest extent, and has important military application value and social significance.

[0009] Technical solution of the present invention:

[0010] The present invention first provides a fiber preform with a negative Poisson's ratio effect. The fiber preform is formed by winding auxiliary fibers around a core fiber. The core fiber uses polypropylene fiber, and the auxiliary fiber uses aramid fiber; wherein, the winding angle is 5° - 30°, the diameter ratio of the core fiber to the auxiliary fiber is (1 - 10):1, and the diameter of the fiber preform is 2 - 2.2 mm. Polypropylene fiber (PP fiber) is widely used in the fields of agriculture, medical care, and environmental protection. In this application, PP fiber is introduced into the material with a negative Poisson's ratio, and high-modulus aramid fiber is selected as the auxiliary fiber, intending to achieve the negative Poisson's ratio effect through the modulus difference. The inventor unexpectedly found during the tensile test that the fracture energy of aramid fiber and PP fiber is significantly higher than expected during the stage of the spiral structure expansion of the negative Poisson's ratio, and the negative Poisson's ratio also has an excellent performance compared with the expectation, achieving an unexpected technical effect. Moreover, compared with carbon fiber widely used in the prior art, the fatigue life of aramid fiber is 3 - 5 times that of carbon fiber, reducing the later maintenance cost by about 30 - 50%, and has important practical application value.

[0011] Preferably, the periphery of the aramid fiber is coated with a bonding material; the bonding material is prepared by mixing epoxy resin and polyamide curing agent in a mass ratio of 1:1. In this application, the purpose of using the bonding material is to bond the aramid fiber filaments so that it is easy to prepare a material with a negative Poisson's ratio. However, it was found during the test that there is a good bonding ability between the aramid fiber and the epoxy resin, which increases the deformation ability during the stretching of the fiber preform and improves the negative Poisson's ratio value. This is contrary to the prior art where the epoxy resin is wrapped around the periphery of the fiber preform, resulting in a decrease in the negative Poisson's ratio compared to the expectation and hindering the exertion of the negative Poisson's ratio effect. Similarly, an unexpected technical effect is also produced.

[0012] This application provides a stretchable fabric with a negative Poisson's ratio effect. The stretchable fabric is woven from the fiber preform as described above. Preferably, the weaving method is plain weave. The stretchable fabric obtained by plain weave has a large number of interlacing points and short floating lengths. When subjected to impact loads, the binding force between the warp and weft fibers is large, and the fabric structure is stable.

[0013] This application also provides a stretchable fabric modified reinforced polyurea, which is prepared from the stretchable fabric described in claim 3. The specific method is as follows: Pour polyurea into a mold, lay the aforementioned stretchable fabric, then pour polyurea for the second time, and demold after curing to obtain the modified reinforced polyurea.

[0014] This application also provides a high-performance coconut shell bionic structure composite armor. The high-performance coconut shell bionic structure composite armor includes a functional gradient protection layer, a porous gradient buffer layer, and a composite elastic energy absorption layer arranged in sequence from outside to inside. In this invention, the concepts of "gradient" and "negative Poisson's ratio" are introduced into the field of anti-explosion materials, functional gradient armor. Through the design of hardness-toughness gradient and pore gradient transition, it has significant advantages in anti-penetration, lightweight, and anti-multiple impact. First of all, the functional gradient protection layer ensures that the object with high-speed penetration does not directly contact the internal structure. The high hardness of the ceramic layer breaks the projectile and disperses the shock wave; the gradient transition can relieve the thermal stress and interface stress; the toughness of the metal layer can support the whole and prevent the overall brittle fracture. Furthermore, the porous gradient buffer layer effectively slows down the impact and absorbs most of the energy guided by the outer layer through the design of the pore gradient; finally, the composite elastic energy absorption layer uses a negative Poisson's ratio material to enhance the modified polyurea, and utilizes its high energy absorption characteristics to store the remaining energy of the whole composite armor and protect the safety of the internal personnel.

[0015] The functional gradient protection layer is obtained by hot pressing and sintering a protection material and an interface material. Among them, the protection material is composed of TC4 alloy powder and Al 2 O 3 powder, and the interface material is B powder. In the functional gradient protection layer, Al 2 O 3The volume fraction decreases from the outside to the inside, while the volume fraction of TC4 increases from the outside to the inside. The particle size of the TC4 alloy powder is 15 - 53 μm, and the 2 O 3 powder has an average particle size of 1 μm, and the average particle size of the B powder is 50 - 100 nm. In the prior art, Al 2 O 3 is mainly used to manufacture high-temperature resistant and corrosion-resistant ceramics, refractory bricks, etc., and is used as a catalyst carrier in the petrochemical and pharmaceutical industries; while the TC4 alloy is mostly used in the manufacture of medical devices such as artificial joints and dental implants, and the manufacture of engine components in the aerospace field, etc. In this step, by combining Al 2 O 3 with the TC4 alloy and applying it as a protective layer on the armor in the military field, a composite material that can not only effectively resist impact but also prevent overall brittle fracture is formed. At the same time, by functionally grading ceramics and metals, the stress transfer path is optimized, the impact energy is effectively dispersed, and the overall protection efficiency is improved.

[0016] In addition, boron (B) and its compounds are fluxing agents in the metallurgical industry and raw materials for smelting ferroboron and boron steel, which can reduce the melting point, reduce expansion, and increase strength and hardness. In this step, by adding B powder, not only can the coating of ceramic particles by liquid titanium be promoted, the strength and hardness be improved, but also TiB 2 can be formed through reaction during sintering to achieve a nanoscale uniform distribution, and the agglomeration problem of directly adding TiB 2 is avoided, which is not recorded in the prior art. At the same time, TiB 2 forms a chemically inert barrier between Al 2 O 3 and the titanium matrix, preventing the reaction between Al 2 O 3 and titanium at high temperature to form brittle TiAl 3 or TiO 2 phases, achieving an unexpected technical effect.

[0017] Preferably, the gradient protective layer is composed of a surface layer, an intermediate layer, and a backplate layer. Among them, the volume fraction of Al 2 O 3 in the surface layer is 90%; the volume fractions of Al 2 O 3 in the intermediate layer are 70 - 80%, 50 - 60%, 30 - 40%, and 10 - 20% in sequence; the backplate layer is 0%; the dosage of the interface material is 2 - 4 wt% of the protective material.

[0018] In the functional gradient protective layer, first of all, Al 2 O 3The hardness of the ceramic surface layer reaches 1600 - 2100 HV, which can effectively blunt the head of the armor-piercing projectile, reduce its kinetic energy penetration efficiency, significantly improve the kinetic energy absorption rate of the projectile body compared with homogeneous composite materials, and enhance the anti-fracture performance. Secondly, the ceramic and metal contents change stepwise along the thickness direction, dispersing the impact stress wave through the continuously changing material ratio and reducing stress concentration. Thirdly, the TiB 2 transition layer forms a continuous interface layer, improving the bonding strength, reducing the residual stress at the interface, and thus reducing the risk of interface cracking.

[0019] The porous gradient buffer layer is obtained by hot pressing and sintering a buffer material and an interface material; the buffer material is composed of TC4 alloy powder and Al 2 O 3 powder, and the interface material is B powder; in the porous gradient buffer layer, the volume fraction of TC4 decreases from the outside to the inside, and the volume fraction of Al 2 O 3 increases from the outside to the inside. The particle size of the TC4 alloy powder is 15 - 53 μm, the particle size of the Al 2 O 3 powder is 106 - 180 μm, and the average particle size of the B powder is 50 - 100 nm. In this step, the Al 2 O 3 powder used as a sintering aid not only improves the hardness of the porous gradient buffer layer, but also forms micron-sized pores, unexpectedly realizing the optimization of the pore structure. The inventor speculates that this is because during the preparation process, alumina does not completely melt, hindering the flow and densification of the molten metal, resulting in occupancy during solidification and forming micron-sized pores.

[0020] Preferably, the porous gradient buffer layer is composed of a dense layer, a transition layer and a porous layer; the volume fraction of TC4 in the dense layer is 100%, the porosity of the transition layer is 15% - 20%, and the volume fraction of TC4 therein is 60 - 80%; the porosity of the porous layer is 30% - 35%, and the volume fraction of TC4 therein is 40 - 60%; the dosage of the interface material is 2 - 4 wt% of the protective material.

[0021] The structure of the porous gradient buffer layer is a gradient design from a dense layer, a transition layer to a porous layer. On the one hand, compared with pure titanium alloy, while the weight is reduced, the energy absorption capacity is improved; on the other hand, compared with pure porous titanium alloy, the strength can be enhanced, and at the same time, the problem of structural failure caused by insufficient strength of pure porous titanium alloy is avoided. This is because alumina is a high-hardness ceramic material. Its addition not only predictably increases the compressive strength and hardness of the titanium alloy, but also unpredictably optimizes the pore structure, making the energy absorption more uniform and slowing down the transmission of impact. On this basis, by changing the proportion of alumina, by adjusting the particle size, shape and distribution of alumina particles, a smooth transition from the dense layer to the porous layer is achieved, and the structure and properties of the porous layer are controlled.

[0022] The composite elastic energy absorption layer is a negative Poisson's ratio fabric modified and reinforced polyurea; the modified and reinforced polyurea is prepared by using the aforementioned negative Poisson's ratio fabric as the skeleton. The specific method is: pour polyurea into a mold, lay the aforementioned negative Poisson's ratio fabric, and then pour polyurea again. After curing, demold to obtain the modified and reinforced polyurea.

[0023] By regulating the spiral wrap angle between the auxiliary fiber and the core fiber in the heterogeneous fiber preform, the weaving method and grid size of the negative Poisson's ratio fabric, the structural parameters with the best energy absorption capacity can be achieved. After being impacted, the negative Poisson's ratio effect of the negative Poisson's ratio fabric plays a role, enhancing the energy dissipation capacity. After the matrix is impacted, due to the closer distance between the molecular components, the strong attractive bonds and large spatial entanglement enable the armor to resist further impacts, thereby improving the overall anti-explosion ability of the composite armor.

[0024] The preparation method of the high-performance coconut shell bionic structure composite armor as described above includes the following steps:

[0025] (1) Preparation of the functional gradient protection layer: Mix TC4, Al 2 O 3 and B powders in a planetary ball mill according to the gradient ratio, and lay the mixed powders in the mold in the order of the surface layer, the intermediate layer and the back panel layer; after cold isostatic pressing and vacuum hot pressing and sintering, obtain the protection layer through post-treatment;

[0026] (2) Preparation of the porous gradient buffer layer: Put the powders of each layer into a ball mill tank and ball mill for 10 - 15 hours, and fill the powders in the mold in the order of the dense layer, the transition layer and the porous layer; after cold isostatic pressing and vacuum hot pressing and sintering, obtain the buffer through post-treatment; use the vacuum hot pressing diffusion bonding method to bond the dense layer side of the buffer layer with the back panel layer side of step (1) to obtain the protection buffer outer layer;

[0027] (3) Preparation of the composite elastic energy-absorbing layer: Pour polyurea on one side of the porous layer of the protective buffer outer layer prepared in step (2), lay the fiber preform described in claim 1 or 2 and plain weave it into a auxetic fabric, and then pour polyurea for the second time. After curing, a coconut shell bionic structure composite armor is obtained.

[0028] Advantages of the present invention:

[0029] (1) Based on the bionic design concept of the coconut shell structure, the present invention conducts a three-layer ladder composite on the "layered composite material", changing the anti-explosion means of the traditional armor to release explosion energy. By dissipating the explosion shock energy layer by layer, the purpose of high anti-explosion and anti-penetration performance is achieved; the risk of human injury is minimized to the greatest extent, and it has important military application value and social significance.

[0030] (2) The present invention introduces an auxetic fabric with a negative Poisson's ratio effect into the coconut shell bionic structure composite armor, and prepares a modified reinforced polyurea with the auxetic fabric as the skeleton, so that the fracture energy of the modified reinforced polyurea is increased to 41.01 MJ / m 3 , which is 49.3% higher than that of carbon-polyvinyl alcohol fabric-reinforced polyurea, and the impact strength is increased by 486.9 kJ / m 2 , which is 43.4% higher than that of carbon-polyvinyl alcohol fabric-reinforced polyurea. Overall, a large attenuation of the shock wave energy is achieved, and the ability of multiple anti-explosions is possessed.

[0031] (3) For the coconut shell bionic structure composite armor described in the present invention, under the same design volume, the weight is 32.2% lighter than that of the traditional steel armor and 12.1% lighter than that of the layered structure protective armor; at the same time, the dynamic compressive strength, fracture failure strain and impact absorption work under high-speed impact have all been significantly improved to varying degrees, indicating that the anti-explosion and anti-penetration performance has been optimized on the premise of light weight, and unexpected technical effects have been produced. Description of the Drawings

[0032] Att Figure 1 is a schematic diagram of the bionic structure of the coconut shell bionic structure composite armor described in this application;

[0033] Att Figure 2 is a schematic diagram of the formation mechanism of the composite material structure and the negative Poisson's ratio effect of the auxetic fabric in the coconut shell bionic structure composite armor described in this application;

[0034] Att Figure 3 is a comparison chart of the negative Poisson's ratio of the auxetic fabric in Example 1 and Comparative Example 2;

[0035] Att Figure 4 is a comparison chart of the stress-strain curves of the fabric stretching process in Example 1 and Comparative Example 1;

[0036] Att Figure 5Comparison diagrams of the photos (a, b) taken by a high-speed camera and the Y-direction strain nephograms (c, d) at the end of the elastic stage during the tensile process of the fabric-reinforced polyurea in Example 1 and Comparative Example 3;

[0037] Appendix Figure 6 SEM images of the titanium alloy before (a) and after (b) optimization in Example 8. Detailed implementation manners

[0038] The present invention will be further described below with reference to the examples. The materials or reagents used are all purchased commercially.

[0039] Example 1: Preparation of a fiber preform, a auxetic fabric, and a modified reinforced polyurea having a negative Poisson's ratio effect

[0040] The fiber preform is formed by winding auxiliary fibers around a core fiber. The core fiber is made of polypropylene fiber, and the auxiliary fiber is made of aramid fiber. Among them, the winding angle is 10°, the diameter ratio of the core fiber to the auxiliary fiber is 5:1, and the diameter of the fiber preform is 2 - 2.2 mm. The periphery of the aramid fiber is coated with a bonding material. The bonding material is prepared by mixing epoxy resin and polyamide curing agent in a mass ratio of 1:1.

[0041] The specific preparation method is as follows: (1) Twisting the aramid fiber and the polypropylene fiber respectively until there are no obvious gaps inside the fibers; (2) Heating E-44 (6101) epoxy resin and low-molecular-weight -650 - polyamide resin to 80°C and holding for 5 min, then preparing a bonding material according to a mass ratio of 1:1 and wrapping the aramid fiber, followed by curing; (3) Fixing the core fiber and the auxiliary fiber treated in step (2) on a fiber winding machine, and winding the auxiliary fiber around the core fiber to obtain a heterogeneous fiber preform.

[0042] Weaving the aforementioned fiber preform into a plain weave to obtain an auxetic fabric. The size of the auxetic fabric is 15 mm × 15 mm.

[0043] Pouring polyurea into a mold, laying the aforementioned auxetic fabric, then pouring polyurea again, and demolding after curing to obtain a modified reinforced polyurea.

[0044] Example 2: Preparation of a fiber preform, an auxetic fabric, and a modified reinforced polyurea having a negative Poisson's ratio effect

[0045] Different from Example 1, the fiber preform is formed by winding auxiliary fibers around a core fiber. The core fiber is made of polypropylene fiber, and the auxiliary fiber is made of aramid fiber. Among them, the winding angle is 18°, and the diameter ratio of the core fiber to the auxiliary fiber is 1:1.

[0046] Example 3: Preparation of a fiber preform with a negative Poisson's ratio effect, a auxetic fabric, and a modified reinforced polyurea

[0047] Different from Example 1, the fiber preform is formed by winding auxiliary fibers around a core fiber. The core fiber is made of polypropylene fiber, and the auxiliary fiber is made of aramid fiber. Among them, the winding angle is 5°, and the diameter ratio of the core fiber to the auxiliary fiber is 10:1.

[0048] Example 4: Preparation of a fiber preform with a negative Poisson's ratio effect, a auxetic fabric, and a modified reinforced polyurea

[0049] Different from Example 1, the fiber preform is formed by winding auxiliary fibers around a core fiber. The core fiber is made of polypropylene fiber, and the auxiliary fiber is made of aramid fiber. Among them, the winding angle is 30°, the diameter of the fiber preform is 2 - 2.2 mm, and the diameter ratio of the core fiber to the auxiliary fiber is 7:1.

[0050] Comparative Example 1:

[0051] Different from Example 1, the auxiliary fiber is made of carbon fiber. Att Figure 4 is the stress-strain curve during the stretching process of the fabric. Among them, the area under the curve is the fracture energy, which is the energy absorbed by the material per unit volume during the deformation process. From Figure 4 it can be seen that the fracture energy of Example 1 obtained by integration increased by 51% compared with that of Comparative Example 1. It shows that the fabric prepared with the fiber preform of aramid fiber in this application has excellent energy absorption ability, achieving unexpected technical effects.

[0052] Comparative Example 2:

[0053] Different from Example 1, the periphery of the aramid fiber is not coated with a bonding material (epoxy resin). Att Figure 3 shows the influence of the combination of epoxy resin and aramid fiber on the negative Poisson's ratio of the fabric. From Figure 3 it can be seen that the extreme values of the negative Poisson's ratio of Example 1 and Comparative Example 2 are -2.62 and -1.63 respectively; the duration of the negative Poisson's ratio of Example 1 is significantly extended, increasing by about 1 times compared with Comparative Example 2. This shows that the combination of epoxy resin and aramid fiber is beneficial to the unfolding of the helical yarn structure in the fabric, enabling it to make full use of the structural advantages, exert the negative Poisson's ratio effect, and improve the energy absorption ability.

[0054] Comparative Example 3:

[0055] Different from Example 1, the fabric uses a carbon-polyvinyl alcohol fabric to prepare a modified reinforced polyurea. Att Figure 5During the tensile process of the fabric-reinforced polyurea in Example 1 and Comparative Example 3, photos taken using a high-speed camera and the Y-direction strain nephogram at the end of the elastic stage are shown. Figure 5 a and Figure 5 b are images at the same moment in the elastic deformation stage of Example 1 and Comparative Example 3 respectively; in Example 1, a relatively uniform elastic deformation is presented and the specimen morphology is intact, while in Comparative Example 3, the deformation is more concentrated and local damage occurs. Figure 5 c and Figure 5 d are the vertical-direction strain nephograms 1 s before the plastic stage of Example 1 and Comparative Example 3 respectively; the strain in Example 1 is relatively uniform and the absolute value of the strain is 0.15 - 0.35, while the strain in Comparative Example 3 is more concentrated and the absolute value of the strain is 0.02 - 0.16, indicating that Example 1 can give full play to the advantages of aramid fibers and the auxetic structure to fully absorb energy, making the specimen in the elastic stage last longer and not easily causing plastic failure.

[0056] Example 5: High-performance coconut shell bionic structure composite armor and its preparation

[0057] The high-performance coconut shell bionic structure composite armor includes a functionally graded protective layer, a porous graded buffer layer, and a composite elastic energy-absorbing layer arranged in sequence from outside to inside. Attached Figure 1 is the bionic structure schematic diagram of the coconut shell bionic structure composite armor described in this application; Attached Figure 2 is the schematic diagram of the formation mechanism of the composite material structure and the negative Poisson's ratio effect of the auxetic fabric in the coconut shell bionic structure composite armor described in this application.

[0058] The functionally graded protective layer is obtained by hot pressing and sintering a protective material and an interface material. Among them, the protective material is composed of TC4 alloy powder and Al 2 O 3 powder, and the interface material is B powder. The gradient protective layer consists of a surface layer, an intermediate layer, and a back plate layer. Among them, the volume fraction of Al 2 O 3 in the surface layer is 90%; the volume fractions of Al 2 O 3 in the intermediate layer are 70%, 50%, 30%, and 10% in sequence; the back plate layer is 0%. The particle size of the TC4 alloy powder is 15 - 53 μm, and the average particle size of the Al 2 O 3 powder is 1 μm. The dosage of the interface material B powder is 3 wt% of the protective material; the average particle size of the B powder is 50 nm.

[0059] The porous graded buffer layer is obtained by hot pressing and sintering a buffer material and an interface material; the buffer material is composed of TC4 alloy powder and Al 2 O 3Powder composition, and the interfacial material is B powder. The porous gradient buffer layer is composed of a dense layer, a transition layer and a porous layer; among them, the volume fraction of TC4 in the dense layer is 100%; the porosity of the transition layer is 18%, and the volume fraction of TC4 therein is 75%; the porosity of the porous layer is 32%, and the volume fraction of TC4 therein is 50%. The particle size of the TC4 alloy powder is 15 - 53 μm, and the Al 2 O 3 powder has a particle size of 106 - 180 μm. The dosage of the interfacial material B powder is 2 wt% of the protective material; the average particle size of the B powder is 50 nm.

[0060] The composite elastic energy-absorbing layer is a negative Poisson's ratio material-modified reinforced polyurea; the auxetic fabric obtained by the preparation method of Example 1 of the negative Poisson's ratio material. The reinforced polyurea uses the auxetic fabric as the skeleton.

[0061] Preparation method of high-performance coconut shell bionic structure composite armor, comprising the following steps:

[0062] (1) Preparation of the functional gradient protective layer: Mix TC4, Al 2 O 3 and B powder in a planetary ball mill according to the gradient ratio, and lay the mixed powder in the mold in the order of the surface layer, the intermediate layer and the back plate layer; after cold isostatic pressing and vacuum hot pressing sintering, the protective layer is obtained through post-treatment. Among them, the cold isostatic pressing is specifically: after preliminary forming by uniaxial cold pressing (pressure 100 MPa), cold isostatic pressing is carried out with a pressure of 300 MPa and a holding time of 30 min. The temperature of the vacuum hot pressing sintering is 1550 - 1660 °C, the pressure is 30 - 40 Mpa, and the time is 2 hours. The post-treatment is specifically: hot isostatic pressing at 920 °C and 120 MPa for 2 h, and after eliminating the residual pores, surface finishing can be carried out.

[0063] (2) Preparation of the porous gradient buffer layer: Put the powders of each layer into the ball milling tank, ball mill for 10 - 15 hours under argon protection, and fill the powders in the mold in the order of the dense layer, the transition layer and the porous layer; after cold isostatic pressing and vacuum hot pressing sintering, the buffer layer is obtained through post-treatment; use the vacuum hot pressing diffusion bonding method to bond the dense layer side of the buffer layer with the back plate layer side of step (1) to obtain the protective buffer outer layer. Among them, the cold isostatic pressing is specifically: the pressure is 360 MPa and the holding time is 300 seconds. During the vacuum sintering, the temperature and atmosphere are controlled in stages; in the degassing stage, the temperature is raised to 250 °C and held for 2 hours; in the dehydrogenation stage, the temperature is raised to 800 °C and held for 6 hours; in the pre-sintering stage, the temperature is raised to 1000 °C and held for 2.5 hours; in the final sintering stage, the temperature is raised to 1200 - 1250 °C and held for 3 hours. The post-treatment is soaking and washing with 5% H 2 SO 4 acid solution to wash away Al 2 O 3After that, simply wash away the acid solution.

[0064] (3) Preparation of the composite elastic energy-absorbing layer: Pour polyurea on one side of the porous layer of the protective buffer outer layer prepared in step (2). Lay the fiber preform described in claim 1 or 2 with plain weave to form a auxetic fabric, and then pour polyurea again. After curing, a coconut shell bionic structure composite armor is obtained. The curing conditions are curing at 25°C for 24 hours, and the polyurea is obtained through commercial channels.

[0065] Example 6: High-performance coconut shell bionic structure composite armor and its preparation

[0066] Different from Example 4, the high-performance coconut shell bionic structure composite armor includes a functionally graded protective layer, a porous graded buffer layer, and a composite elastic energy-absorbing layer arranged in sequence from outside to inside.

[0067] The functionally graded protective layer consists of a surface layer, an intermediate layer, and a back panel layer. Among them, the volume fraction of Al 2 O 3 in the surface layer is 90%; the volume fractions of Al 2 O 3 in the intermediate layer are 80%, 60%, 40%, and 20% in sequence; the back panel layer is 0%. The particle size of the TC4 alloy powder is 15 - 53μm, and the average particle size of the Al 2 O 3 powder is 1μm. The dosage of the interface material B powder is 2wt% of the protective material; the average particle size of the B powder is 100nm.

[0068] The porous graded buffer layer consists of a dense layer, a transition layer, and a porous layer; among them, the volume fraction of TC4 in the dense layer is 100%; the porosity of the transition layer is 15%, and the volume fraction of TC4 in it is 60%; the porosity of the porous layer is 30%, and the volume fraction of TC4 in it is 40%. The particle size of the TC4 alloy powder is 15 - 53μm, and the particle size of the Al 2 O 3 powder is 106 - 180μm. The dosage of the interface material B powder is 3wt% of the protective material; the average particle size of the B powder is 100nm.

[0069] The composite elastic energy-absorbing layer is auxetic material-modified reinforced polyurea; the auxetic material is the auxetic fabric prepared in Example 2. The reinforced polyurea uses the auxetic fabric as the framework.

[0070] The preparation method of the high-performance coconut shell bionic structure composite armor is the same as that of Example 4.

[0071] Example 7: High-performance coconut shell bionic structure composite armor and its preparation

[0072] Different from Example 4, the high-performance coconut shell bionic structure composite armor comprises a functionally graded protective layer, a porous graded buffer layer, and a composite elastic energy-absorbing layer arranged in sequence from outside to inside.

[0073] The functionally graded protective layer consists of a surface layer, an intermediate layer, and a back panel layer. Among them, the volume fraction of Al 2 O 3 in the surface layer is 90%; the volume fractions of Al 2 O 3 in the intermediate layer are 75%, 60%, 45%, and 30% in sequence; the back panel layer is 0%. The particle size of the TC4 alloy powder is 15 - 53 μm, and the average particle size of the Al 2 O 3 powder is 1 μm. The dosage of the interface material B powder is 4 wt% of the protective material; the average particle size of the B powder is 100 nm.

[0074] The porous graded buffer layer consists of a dense layer, a transition layer, and a porous layer; among them, the volume fraction of TC4 in the dense layer is 100%; the porosity of the transition layer is 20%, and the volume fraction of TC4 in it is 80%; the porosity of the porous layer is 35%, and the volume fraction of TC4 in it is 60%. The particle size of the TC4 alloy powder is 15 - 53 μm, and the particle size of the Al 2 O 3 powder is 106 - 180 μm. The dosage of the interface material B powder is 4 wt% of the protective material; the average particle size of the B powder is 100 nm.

[0075] The composite elastic energy-absorbing layer is a negative Poisson's ratio material-modified reinforced polyurea; the negative Poisson's ratio material is the auxetic fabric prepared in Example 2. The reinforced polyurea uses the auxetic fabric as the framework.

[0076] The preparation method of the high-performance coconut shell bionic structure composite armor is the same as that in Example 4.

[0077] Comparative Example 4:

[0078] Select the common armor steel 4340 steel and process it to the same thickness as the composite armor.

[0079] Comparative Example 5:

[0080] Prepare a ceramic-alloy-polyurea laminated structure composite armor. The specific preparation method is as follows: Use Al 2 O 3Powder, adding 1-2 wt% of MgO as a sintering aid, ball milling and mixing evenly, loading the powder into a mold, using vacuum hot pressing sintering, heating to 1600-1650 °C, pressure 20-30 MPa, holding for 1-2 hours to obtain a ceramic layer. Using TC4 powder, heating to 900-1000 °C in stages, gradually pressurizing to 30-50 MPa, holding for 30-60 minutes to obtain an alloy layer. Stack the ceramic layer and the alloy layer, spray a titanium-based active brazing filler metal in the middle, and place it in a vacuum hot pressing furnace. Temperature 900-950 °C, pressure 10-15 MPa, holding for 30-60 minutes. Pour polyurea, and after curing, obtain a ceramic-alloy-polyurea laminated structure composite armor.

[0081] Example 8: Comparison of the morphology of titanium alloy before and after optimization

[0082] The porous gradient buffer layers in Examples 5-7 were characterized by scanning electron microscopy. At the same time, the TC4 alloy powder without adding Al 2 O 3 powder was characterized by scanning electron microscopy as a control. The results are shown in detail in Figure 6 .

[0083] As can be seen from Figure 6 a, the morphology of the titanium alloy before optimization is relatively complete on the surface and there are no obvious pores. As can be seen from Figure 6 b, the morphology of the titanium alloy after optimization shows that there are a large number of pores with irregular shapes and pore diameters mainly in the range of 100-300 μm distributed on the alloy matrix; this indicates that the buffer layers prepared in Examples 5-7 of the present application are titanium alloys with a porous structure after optimization.

[0084] Example 9: Performance characterization

[0085] (1) The auxetic fabrics and modified reinforced polyurea prepared in Examples 1-4 were characterized for performance (Table 1), specifically including the following contents:

[0086] 1. Mechanical property test: The tensile experiment was carried out using an electronic tensile tester according to GB / T3923.1-2013 "Textiles - Tensile properties of fabrics - Part 1: Determination of maximum force and elongation at maximum force (strip method)", and the loading speed was 5 mm / min. The impact experiment was carried out on a simply supported beam impact tester according to ISO 179-1:2000.

[0087] 2. Poisson's ratio measurement: For the fabric, the digital speckle correlation method was used to collect images during the tensile process, and the Poisson's ratio was calculated.

[0088] Table 1. List of results of performance characterization of fabrics and modified reinforced polyurea prepared in Examples 1-4

[0089]

[0090] As can be seen from Table 1, for the auxetic fabrics prepared in Examples 1-4, the negative Poisson's ratio is from -1.73 to -2.62, and the elongation at break is from 36.59% to 45.25%. For the modified reinforced polyurea prepared using the auxetic fabric, the fracture energy is from 30.27 to 41.01 MJ / m 3 , and the impact strength is from 359.8 to 486.9 kJ / m 2 .

[0091] For Comparative Example 1 using carbon fiber as the auxiliary fiber, the negative Poisson's ratio of the fabric prepared is -1.47, and its absolute value is 44% lower than that of the fabric prepared in Example 1; the elongation at break is 31.89%, which is 30% lower than that of the fabric prepared in Example 1. For the modified reinforced polyurea prepared using the auxetic fabric, the fracture energy is 28.95 MJ / m 3 , which is 29% lower than that in Example 1, and the impact strength is 351.6 kJ / m 2 , which is 28% lower than that in Example 1. This shows that for the fabric prepared using carbon fiber as the auxiliary fiber, both the absolute value of the negative Poisson's ratio and the elongation at break are lower than those of the fabric prepared using aramid fiber as the auxiliary fiber, achieving unexpected technical effects. This Figure 4 mutually corroborates. On this basis, the performance of the modified reinforced polyurea is also significantly improved. In addition, compared with carbon fiber, the maintenance cost of aramid fiber is also lower, which is of great significance for industrial applications.

[0092] In addition, for Comparative Example 2 without using epoxy resin coating, the negative Poisson's ratio of the fabric prepared is -1.63, which is 38% lower than that of the fabric prepared in Example 1; the elongation at break is 36.03%, which is 20% lower than that of the fabric prepared in Example 1. For the modified reinforced polyurea prepared using the auxetic fabric, the fracture energy is 33.86 MJ / m 3 , which is 17% lower than that in Example 1, and the impact strength is 406.2 kJ / m 2 , which is 16% lower than that in Example 1. This shows that for the fabric prepared using aramid fiber as the auxiliary fiber without using epoxy resin treatment, both the absolute value of the negative Poisson's ratio and the elongation at break are lower than those of the fabric prepared using aramid fiber as the auxiliary fiber with epoxy resin treatment. This Figure 3 mutually corroborates. Different from the fact that using epoxy resin usually has negative effects in the prior art, in this application, the aramid fiber treated with epoxy resin instead plays a positive technical effect, overcomes the technical prejudice, and achieves unexpected technical effects. On this basis, the performance of the modified reinforced polyurea is also significantly improved.

[0093] Moreover, in Comparative Example 3 using a carbon-polyvinyl alcohol auxetic fabric, the negative Poisson's ratio of the prepared fabric was -1.32, which was 24%-50% lower than that of the fabrics prepared in Examples 1-3; the elongation at break was 29.63%, which was 19%-35% lower than that of the fabrics prepared in Examples 1-3. The fracture energy of the modified reinforced polyurea prepared using the auxetic fabric was 27.45 MJ / m 3 , which was 33% lower than that of Example 1, and the impact strength was 339.6 kJ / m 2 , which was 30% lower than that of Example 1. This Figure 5 mutually corroborates. This shows that the absolute value of the negative Poisson's ratio and the elongation at break of the fabric prepared using carbon fiber and polyvinyl alcohol fiber are both lower than those of the fabric prepared using aramid fiber and polypropylene fiber. This also once again corroborates that the fiber preform prepared using aramid fiber and polypropylene fiber in this application not only has excellent performance in terms of negative Poisson's ratio, but also significantly improves the fracture energy during the stage of the helical structure expansion where the negative Poisson's ratio plays a role. On this basis, the performance of the modified reinforced polyurea is also significantly improved.

[0094] (2) Density tests were carried out on the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7, and the results are shown in Table 2 in detail.

[0095] Table 2. List of density characterization results of the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7

[0096] Example 5 Example 6 Example 7 Reduction rate of density compared with Comparative Example 4 / % 32.2 30.7 28.5 Reduction rate of density compared with Comparative Example 5 / % 12.1 10.1 7.3

[0097] As can be seen from Table 2, compared with the armor steel 4340 steel of Comparative Example 4, the density of the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7 was reduced by 28.5%-32.2%. This fully shows that, under the same volume, compared with the armor steel 4340 steel used in the prior art, it is lighter in weight, improving the vehicle's mobility and endurance. Moreover, compared with the ceramic-alloy-polyurea laminated structure composite armor of Comparative Example 5, the density of the bionic structure composite armor prepared in Examples 5-7 was reduced by 7.3%-12.1%. This shows that although the laminated structure composite armor can achieve a certain degree of lightweight compared with the armor steel 4340 steel; through gradient design in this application, further lightweighting of the high-performance coconut shell bionic structure composite armor is achieved.

[0098] (3) Mechanical property tests were carried out on the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7. The specific method: a split Hopkinson pressure bar (SHPB) system was used for high-speed impact tests, and the loading strain rate was 2600 s -1 . The results are shown in Table 3 in detail.

[0099] Table 3. List of performance characterization results of the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7

[0100]

[0101] As can be seen from Table 3, the high-performance coconut shell bionic structure composite armor prepared in Examples 5-7 has a dynamic compressive strength of 2630-3080 Mpa under high-speed impact, a fracture failure strain of 0.167-0.207, and an impact absorption work of 221-285 MJ / m 3 。

[0102] For the armor steel 4340 steel in Comparative Example 4, the dynamic compressive strength under high-speed impact is 1853 Mpa, which is 29%-40% lower than that of the bionic structure composite armor prepared in this application; the fracture failure strain is 0.118, which is 29%-43% lower than that of the bionic structure composite armor prepared in this application; the impact absorption work is 168 MJ / m 3 , which is 31%-41% lower than that of the bionic structure composite armor prepared in this application. This fully demonstrates that the bionic structure composite armor prepared in this application has achieved significant improvement in various performances compared with the armor steel 4340 steel used in the prior art.

[0103] For the ceramic-alloy-polyurea laminated structure composite armor prepared in Comparative Example 5, the dynamic compressive strength under high-speed impact is 2604 Mpa, which is 1%-15% lower than that of the bionic structure composite armor prepared in this application; the fracture failure strain is 0.122, which is 27%-40% lower than that of the bionic structure composite armor prepared in this application; the impact absorption work is 187 MJ / m 3 , which is 15%-34% lower than that of the bionic structure composite armor prepared in this application. This fully demonstrates that the bionic structure composite armor prepared in this application has achieved significant improvement in various performances compared with the simple laminated structure composite armor. This shows that although the performance of the simple laminated structure composite armor has been improved compared with that of Example 1, it is still lower than that of the bionic structure composite armor prepared in this application.

[0104] In summary, the bionic structure composite armor prepared in this application: (1) First, it innovatively conducts a three-layer ladder composite of "laminated composites", and through the gradual dissipation of explosive shock energy layer by layer, the purpose of high anti-explosion and anti-penetration performance is achieved; (2) Second, a stretch fabric with a negative Poisson's ratio effect is introduced into the coconut shell bionic structure composite armor, and a modified reinforced polyurea is prepared with the stretch fabric as the skeleton, significantly improving the fracture energy and impact strength, and having the ability of multiple anti-explosions. (3) Under the same designed volume, the weight can be reduced by 32.2% compared with traditional steel armor and by 12.1% compared with the laminated structure protective armor; on the premise of lightweight, the anti-explosion and anti-penetration performance is optimized, producing unexpected technical effects.

Claims

1. A fiber preform with negative Poisson's ratio effect, characterized in that: The fiber preform is formed by winding auxiliary fibers on core fibers, the core fibers are polypropylene fibers, and the auxiliary fibers are aramid fibers; wherein the winding angle is 5°-30°, the diameter ratio of the core fibers to the auxiliary fibers is (1-10):1, and the diameter of the fiber preform is 2-2.2 mm.

2. The fiber preform with negative Poisson's ratio effect according to claim 1, characterized in that: The periphery of the aramid fiber is coated with a bonding material; the bonding material is prepared from epoxy resin and polyamide curing agent.

3. A tensile fabric with negative Poisson's ratio effect, characterized in that: The traction fabric is woven by using the fiber preform according to claim 1 or 2; the weaving method is plain weave.

4. Auxiliary fabric modified reinforced polyurea, characterized by: The modified reinforced polyurea is prepared by using the auxetic fabric described in claim 3.

5. A high-performance coconut shell bionic structure composite armor, characterized by: It includes a functional gradient protection layer, a porous gradient buffer layer and a composite elastic energy absorbing layer arranged in sequence from the outside to the inside; The functional gradient protective layer is obtained by hot pressing and sintering a protective material and an interface material; the protective material is composed of TC4 alloy powder and Al2O3 powder, and the interface material is B powder; in the functional gradient protective layer, the volume fraction of Al2O3 decreases from the outside to the inside, and the volume fraction of TC4 increases from the outside to the inside; The porous gradient buffer layer is obtained by hot pressing and sintering a buffer material and an interface material; the buffer material is composed of TC4 alloy powder and Al2O3 powder, and the interface material is B powder; in the porous gradient buffer layer, the volume fraction of TC4 decreases from the outside to the inside, and the volume fraction of Al2O3 increases from the outside to the inside; The composite elastic energy-absorbing layer is the tensile fabric-modified reinforced polyurea as described in claim 4.

6. The high-performance coconut shell bionic structure composite armor according to claim 5 is characterized by: The gradient protective layer consists of a surface layer, an intermediate layer and a back plate layer, wherein the volume fraction of Al2O3 in the surface layer is 90%; the volume fractions of Al2O3 in the intermediate layer are 70-80%, 50-60%, 30-40%, and 10-20% respectively; the back plate layer is 0%; and the amount of the interface material used is 2-4wt% of the protective material.

7. The high-performance coconut shell bionic structure composite armor according to claim 6 is characterized by: The particle size of the TC4 alloy powder is 15-53 μm, the average particle size of the Al2O3 powder is 1 μm, and the average particle size of the B powder is 50-100 nm.

8. The high-performance coconut shell bionic structure composite armor according to claim 5 is characterized by: The porous gradient buffer layer consists of a dense layer, a transition layer and a porous layer; the volume fraction of TC4 in the dense layer is 100%, the porosity of the transition layer is 15%-20%, and the volume fraction of TC4 is 60-80%; the porosity of the porous layer is 30%-35%, and the volume fraction of TC4 is 40-60%; the amount of the interface material used is 2-4wt% of the protective material.

9. The high-performance coconut shell bionic structure composite armor according to claim 8 is characterized by: The particle size of the TC4 alloy powder is 15-53 μm, the particle size of the Al2O3 powder is 106-180 μm, and the particle size of the B powder is 50-100 nm.

10. The method for preparing the high-performance coconut shell bionic structure composite armor according to any one of claims 1 to 9, characterized in that: The steps include: (1) Preparation of functional gradient protective layer: TC4, Al2O3 and B powders are mixed in a planetary ball mill according to a gradient ratio, and the mixed powders are laid layer by layer in a mold in the order of surface layer, middle layer and back plate layer; cold isostatic pressing is performed, vacuum hot pressing sintering is performed, and the protective layer is obtained after post-treatment; (2) Preparation of porous gradient buffer layer: Powders of each layer are placed in a ball mill and ball milled for 10-15 hours, and the powders are filled in a mold in the order of dense layer, transition layer, and porous layer; cold isostatic pressing is performed and vacuum hot pressing is performed to sinter, and a buffer is obtained after post-treatment; the dense layer side of the buffer layer is combined with the back plate layer side of the protective layer by a vacuum hot pressing diffusion bonding method to obtain a protective buffer outer layer; (3) Preparation of composite elastic energy-absorbing layer: Cast polyurea on one side of the porous layer of the protective buffer outer layer prepared in step (2), lay the tensile fabric described in claim 3, and then cast polyurea for a second time to obtain coconut shell bionic structure composite armor after curing.

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