A chopped fiber prestressed reinforced active core and its preparation method

Abstract

The present invention discloses a chopped fiber prestressed reinforced active core and its preparation method. By adding viscoelastic chopped fibers, stretched to the creep stage and then unloaded, to the active material, the active material significantly increases its strength under the continuous recovery stress of the chopped fibers. This effectively addresses the bottleneck problem of the active core being too easily broken and scattered after the stress release of the target shell fragmentation of the active explosive warhead, resulting in insufficient active core remaining after impacting subsequent targets, and the difficulty in unleashing the combined destructive power of the explosive warhead.

Description

Technical Field

[0001] The present invention relates to the technical field of explosive warheads, and in particular to a chopped fiber prestressed reinforced active core and a preparation method thereof. Background Art

[0002] The explosive warhead is the primary type of warhead used to strike multi-layered large ships and buildings. It primarily consists of a high-strength metal hull, a high-explosive charge, and a fuze. The basic operating principle is that the warhead relies on kinetic energy to penetrate the target. The fuze's layer counting / timing function detonates the high-explosive charge after the warhead has penetrated a certain number of target layers or reached a certain depth, damaging the target.

[0003] With the improvement of target protection performance, in order to achieve efficient destruction of multi-layered large ships and buildings, the terminal velocity of the explosive warhead must be continuously improved. During the process of impacting the target, the impact load and overload borne by the explosive warhead structure are continuously increased, which poses severe challenges to the reliable timing / layer / depth initiation of the fuze and the stability of the explosive charge, and significantly restricts the application of traditional explosive warheads and the technical development of explosive warheads with a basic fuze-explosive technical system.

[0004] Active materials are a new type of high-energy-density energetic material, characterized by "quasi-inert insensitivity, explosive-like energetics, micromillisecond activation delay, and non-self-sustaining explosive energy release." Under normal conditions, they are in an inert metastable state with excellent mechanical properties. However, under strong impact loads, they become activated and undergo chemical reactions, rapidly and violently releasing large amounts of chemical energy, producing shock waves, heat, and combustion. Leveraging the technical characteristics and advantages of active materials, the active material core replaces the explosive, creating an active explosive warhead. This eliminates the need for a fuse or explosive, adapts to the extreme speeds and load characteristics of projectile-target interactions, and leverages the combined destructive power of explosives.

[0005] From the perspective of the active explosive warhead's mechanism of action, during high-speed penetration of a target, a strong impact load is transmitted to the warhead structure, activating the active core material while also causing the warhead shell to fail. After the failed shell shatters and loses its restraint, the axial and radial stresses in the activated active core are released, causing it to fragment and scatter, triggering deflagration of the active core material and causing combined explosive damage to the target.

[0006] However, the high-energy fluoropolymer-based active core materials currently widely used are mainly composed of components such as fluoropolymer matrix, inert metal powder, active metal powder, and modified additives. Since they can only be prepared through mixing / pressing processes and cannot be sintered at high temperatures, there are significant problems with their low compressive strength (~130MPa) and tensile strength (~20MPa). Under the aforementioned axial and radial stress release, the active core is prone to fragmentation and scattering. In the scenario of acting on multi-layer targets, it is easy to result in too few remaining active cores acting on subsequent target structures, which significantly limits the destructive power of the active explosive warhead.

[0007] At present, the main means to improve the adaptability of high-energy fluoropolymer-based active cores in explosive warheads is to add a certain thickness of metal or non-metallic coating structure to the outside of the core, but this will directly lead to a reduction in the effective mass of the high-energy active core, affecting the improvement of the power of the explosive warhead.

[0008] Therefore, combining the typical target characteristics of active explosive warheads and the requirements for active cores, inventing new active core preparation processes and improving the strength of active cores are of great significance to the development and application of active explosive warhead technology. Summary of the Invention

[0009] In view of this, the present invention provides a short-fiber prestressed reinforced active core, in which viscoelastic short-fibers that are stretched to the creep stage and then unloaded are added to a fluoropolymer-based active material system. The prepared active material core will have significantly improved strength under the continuous recovery stress of the short-fibers, thereby solving the bottleneck problems of the active core being too easy to break and scatter after the stress of the target shell of the active explosive warhead is released, too few active cores remaining when acting on subsequent targets, and difficulty in exerting the combined destructive power of the explosive warhead.

[0010] The chopped fiber prestressed reinforced active core of the present invention comprises an active core body and a prestressed chopped fiber material, wherein the mass of the prestressed chopped fiber material accounts for 5% to 15% of the total mass, and the active core body accounts for 85% to 95% of the total mass;

[0011] The prestressed chopped fiber material is formed by stretching the fiber material into the creep stage and then chopping it. The length of the prestressed chopped fiber material is 50 to 100 times the particle size of the active metal powder in the active core body.

[0012] Preferably, the fiber material is nylon or has a density of 0.94-0.98 g / cm 3 , UHMW-PE with tensile strength>20MPa and elongation at break>250%.

[0013] Preferably, the fiber material is stretched by applying a constant tensile stress, the amplitude of the applied constant tensile stress is 30% to 40% of the fracture limit of the fiber material, and the tensile stress action time is 6 to 24 hours, so that the fiber material enters the creep stage, and after the tensile stress is unloaded, shrinkage prestress is generated, and the stretched fiber material is chopped to obtain prestressed chopped fiber material.

[0014] Preferably, a coupling agent is used to perform surface treatment on the prestressed chopped fibers.

[0015] Preferably, the coupling agent is a silane coupling agent, a titanate coupling agent or an aluminate coupling agent.

[0016] Preferably, the amount of coupling agent m is determined based on the mass of the chopped fibers:

[0017] m=m1*s1 / S

[0018] Where m1 is the mass of the chopped fiber, s1 is the specific surface area of ​​the chopped fiber, and S is the minimum wetting area of ​​the coupling agent.

[0019] Preferably, the active core body adopts polymer matrix / inert metal powder / active metal powder, including 20-80% matrix powder, 0-50% inert metal powder and 20-50% active metal powder by mass, or adopts an active core body containing TiH2, MgH2, ZrH2, MoO3, Fe2O3 or MnO2 modified additives.

[0020] The present invention also provides a method for preparing the above-mentioned chopped fiber prestressed reinforced active core, comprising:

[0021] S1, drying and sieving the component powders according to the active core body formula;

[0022] S2, heat treating the fiber material at 100-150° C. for 0.5-2 h to eliminate residual stress in the fiber material;

[0023] S3, stretching the fiber material to make it enter the creep stage;

[0024] S4, cutting the stretched fiber material into chopped fibers;

[0025] S5, according to the active core formula, weighing the processed active core body component powders and chopped fiber materials according to the ratio requirements, and mixing them to obtain a mixed powder;

[0026] S6, adding the mixed powder into the mold, maintaining the pressure under a certain molding pressure for a certain time, and pressing the mixed powder into an active core sample.

[0027] Preferably, in S6, when the aspect ratio of the prepared active core is not greater than 3, a unidirectional molding method is adopted; when the aspect ratio of the prepared active core is greater than 3, a bidirectional molding method is adopted; the molding pressure is determined according to the density requirement of the active core; and the holding time is 1 to 5 minutes.

[0028] Beneficial effects:

[0029] In response to the problem of insufficient strength of high-energy active cores prepared by traditional mixing / pressing processes, the present invention proposes adding viscoelastic chopped fibers that are stretched to the creep stage and then unloaded to the polymer-based active material system. The prepared active material core will have significantly improved compressive strength and tensile strength under the continuous recovery stress of the chopped fibers, thereby solving the bottleneck problems of the active core being too easy to break and scatter after the shell of the target being affected by the active explosive warhead is broken and the stress is released, too little active core remaining when affecting subsequent targets, and the energy released by the active core being unable to effectively destroy large multi-layered ship targets, making it difficult to exert the combined explosive damage power. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the active core structure reinforced with chopped fiber prestressing.

[0031] Among them, 1-prestressed chopped fibers, 2-matrix powder, 3-inert metal powder, and 4-active metal powder.

[0032] Figure 2 Schematic diagram of stress recovery behavior of chopped fibers.

[0033] Figure 3 Schematic diagram comparing the failure behaviors of a traditional active material core and a chopped fiber prestressed reinforced active material core under tensile load.

[0034] Figure 4 This is a tensile test specimen for the chopped fiber prestressed reinforced active material core in an embodiment of the present invention.

[0035] Figure 5 Comparison of tensile stress-strain curves of the chopped fiber prestressed reinforced active material core in the embodiment of the present invention and the traditional active material core.

[0036] Figure 6 These are the experimental results of penetrating the target plate using a traditional active material core and a short-cut fiber prestressed reinforced active material core of the present invention; (a) is the traditional active material core; (b) is the short-cut fiber prestressed reinforced active material core of the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0038] The present invention provides a chopped fiber prestressed reinforced active core, comprising an active core body and prestressed chopped fiber material, wherein the mass of the chopped fiber material is 5% to 15% of the total mass, and the mass of the active core body is 85% to 95% of the total mass.

[0039] The chopped fiber material is formed by stretching a fiber material into the creep stage and then chopping it. The fiber material is generally selected from polymer-based materials with viscoelastic mechanical properties, such as nylon, UHMW-PE (ultra-high molecular weight polyethylene) (density 0.94-0.98 g / cm3, tensile strength >20 MPa, elongation at break >250%), etc.

[0040] When the fiber material is stretched, a constant tensile stress is generally applied, with a tensile stress amplitude of 30-40% of the fiber material's fracture limit, and the tensile stress is applied for 6-24 hours, so that the fiber material enters the creep stage, and shrinkage prestress is generated after the tensile stress is unloaded;

[0041] Under tensile stress, the stress-strain in the fiber material satisfies the following relationship:

[0042]

[0043] Where σ is the tensile stress, ε(t) is the strain, and E v is the elastic constant of the fiber material, η v is the viscosity constant of the fiber material, and t is the stretching time.

[0044] After the tensile stress is unloaded, the relationship between the strain in the fiber and time is:

[0045]

[0046] Where ε0 is the strain generated in the fiber material at the moment of tensile stress unloading.

[0047] The length of the chopped fibers is generally selected according to the active core body to better play its role in restoring stress, and is generally 50 to 100 times the particle size of the active metal powder in the active core body;

[0048] Preferably, the chopped fibers are surface treated with a coupling agent to improve the processing properties of the chopped fibers, thereby enabling the active core material to obtain better mechanical properties. The coupling agent is selected from silane coupling agents, titanate coupling agents, or aluminate coupling agents, and is treated by mechanical mixing. The amount of coupling agent used, m, is determined based on the mass of the chopped fibers.

[0049] m=m1*s1 / S

[0050] Where m1 is the mass of the chopped fiber, s1 is the specific surface area of ​​the chopped fiber, and S is the minimum wetting area of ​​the coupling agent.

[0051] The active core body can adopt a polymer matrix / inert metal powder / active metal powder formula, which includes 20-80% matrix powder, 0-50% inert metal powder and 20-50% active metal powder by mass. It can also adopt an active core formula containing modifying additives such as TiH2, MgH2, ZrH2, MoO3, Fe2O3, MnO2, etc.

[0052] The matrix powder is generally made of materials such as PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), and THV (a polymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride).

[0053] The active metal powder is generally one or more materials such as aluminum, zirconium, aluminum-zirconium alloy, boron, titanium, hafnium, etc., and is selected according to the mechanical and chemical performance requirements of the active core material; the particle size of the active metal powder is selected according to the performance requirements such as the activation threshold and reaction rate of the active core material;

[0054] The inert metal powder is generally one or more materials such as tungsten, SiC, ceramics, etc., and is selected according to the mechanical performance requirements of the active core material; the particle size of the inert metal powder is selected according to the performance requirements such as the activation threshold and reaction rate of the active core material.

[0055] The working principle of the chopped fiber prestressed reinforced active core of the present invention is:

[0056] The present invention adds prestressed chopped fiber material to the active core body. During the process of the active core penetrating the target, the recovery stress of the chopped fiber material is utilized to enhance the compressive strength and tensile strength of the active core, so that the active core is less likely to break and scatter when penetrating multi-layer targets, thereby increasing the volume and mass of the remaining active core, and thus being able to continue to act on subsequent target plate structures, significantly enhancing the destructive power of the active explosive warhead.

[0057] The present invention also provides a method for preparing the above-mentioned chopped fiber prestressed reinforced active core. In the reinforced active core, the chopped fiber material accounts for 5% to 15% of the total mass, and the active core body accounts for 85% to 95% of the total mass. The active core body contains 20% to 80% by mass of matrix powder, 20% to 50% by mass of active metal powder, and 0% to 50% by mass of inert metal powder. The specific steps are as follows:

[0058] (1) Spread the matrix powder evenly on a shallow container and place it in a drying oven; preferably, the matrix powder should be spread evenly and flatly, with a thickness generally not greater than 1 cm;

[0059] (2) Vacuum the drying oven, set the drying oven temperature and drying time, and dry the base powder; preferably, the drying temperature range is 50-70°C, and the drying time is generally set to 3-8 hours according to the moisture absorption degree of the powder;

[0060] (3) The dried matrix powder is passed through a 300-mesh sieve to obtain a matrix powder material with a particle size of less than 50 μm for later use;

[0061] (4) Spread the active metal powder evenly in a shallow container and place it in a drying oven. After evacuating the drying oven or filling it with an inert atmosphere, dry the active metal powder at a temperature not exceeding 50° C. for 5 to 8 hours before use.

[0062] (5) Spread the inert metal powder evenly in a shallow container and place it in a drying oven. After evacuating the drying oven or filling it with an inert atmosphere, dry the inert metal powder for 3 to 5 hours at a temperature not exceeding 50° C. before use.

[0063] (6) heat treating the fiber material at 100-150° C. for 0.5-2 h to eliminate residual stress in the fiber material;

[0064] (7) Then, a universal material testing machine or other similar device is used to apply a constant tensile stress to the fiber material, with a stress amplitude of 30 to 40% of the fiber material's fracture limit, and the tensile stress is applied for 6 to 24 hours, so that the long fiber enters the creep stage, and a shrinkage prestress is generated after the tensile stress is unloaded;

[0065] (8) Cutting the stretched long fibers into short fibers; the length of the short fibers is determined according to the formulation of the active core body to better play its role in restoring stress, generally 50 to 100 times the particle size of the active metal powder;

[0066] (9) Surface treatment of chopped fibers with a coupling agent to improve the processing properties of the chopped fibers, thereby enabling the active core material to obtain better mechanical properties;

[0067] (10) Stir the chopped fibers for 5 to 30 minutes, which is adjusted according to equipment conditions and stirring speed.

[0068] (11) According to the formula of the enhanced active core, the processed matrix powder, active metal powder, inert metal powder, and chopped fiber material are weighed according to the ratio requirements, and added to the mixing equipment in sequence. The mixing time and mixing rate are set to mix the powders;

[0069] Preferably, the mixing equipment is a V-barrel mixer, and the mixing time and mixing rate are determined according to the total mass of the powder; the mixing environment should be dry and ventilated, and the humidity should not exceed 20% RH;

[0070] (12) Add the mixed powder into a cylindrical mold, use a unidirectional or bidirectional molding method, hold the pressure for a certain period of time under a certain molding pressure, and then press the mixed powder into a cylindrical active core sample;

[0071] Preferably, when the aspect ratio of the active core is not greater than 3, a one-way molding method is generally adopted; when the aspect ratio of the active core is greater than 3, a two-way molding method is generally adopted; the molding pressure is determined according to the density requirements of the active core, generally 40 to 150 MPa; the holding time is generally 1 to 5 minutes.

[0072] The following is an example to illustrate:

[0073] Polytetrafluoroethylene (PTFE) was selected as the fluoropolymer matrix material. An appropriate amount of PTFE powder was spread flat on a shallow aluminum tray to a thickness of 5 mm and placed in a drying oven. After evacuating the oven, the drying temperature was set to 50°C and the PTFE powder was dried for 3 hours. The dried PTFE powder was passed through a 300-mesh sieve to remove any agglomerated powder. This resulted in a dry fluoropolymer powder with a particle size of less than 50 microns and good flowability, which was then ready for use.

[0074] Air-atomized aluminum powder with a median particle size of 45 μm was selected as the active metal powder. An appropriate amount of aluminum powder was spread flat on an aluminum shallow tray with a thickness of 3 mm and placed in a drying oven. After the drying oven was filled with argon atmosphere, the drying temperature was set to 50°C. After drying the aluminum powder for 3 hours, it was temporarily stored under inert atmosphere protection for future use.

[0075] Ball-milled tungsten powder with a median particle size of 30 μm was selected as the inert metal powder. An appropriate amount of tungsten powder was spread on an aluminum shallow tray with a thickness of 3 mm and placed in a drying oven. After the drying oven was filled with argon atmosphere, the drying temperature was set to 50°C. The tungsten powder was dried for 3 hours and then temporarily stored under the protection of an inert atmosphere for future use.

[0076] The long fiber material was selected from polyamide nylon 66, which has viscoelastic mechanical properties and a tensile strength of approximately 50 MPa. The nylon fibers were heat-treated at 100°C for 1 hour to eliminate residual stress within the fibers. A universal material testing machine then applied a constant tensile stress of 30 MPa for 6 hours, causing the long fibers to enter a creep phase. After the tensile stress is unloaded, contraction prestress is generated. The long nylon fibers were then cut into short strands approximately 4 mm in length.

[0077] Epoxysilane was selected as the coupling agent, diluted with a mixed solution of ethanol and water (ratio 0.65:0.35), added to the chopped fibers by spraying, and stirred for about 30 minutes using a high-speed stirring device until the diluted solution was completely evaporated. The chopped fibers were then placed in a drying oven and vacuum-dried at 50 degrees to complete the coupling between the chopped nylon fibers and the coupling agent for later use.

[0078] Weigh polytetrafluoroethylene powder, aluminum powder, tungsten powder, and chopped fibers in a mass ratio of 53.68%, 21.23%, 17.99%, and 7.1%, respectively, and add them to a V-tube mixer. Mix at 120 rpm for 1 hour. During mixing, maintain the humidity in the operating room at no more than 20% RH using a dehumidifier.

[0079] The mixed powder was placed into a 40mm inner diameter steel cylindrical mold cavity and pressed using a unidirectional pressing method. The mold was pressed at 100 MPa and held for 3 minutes to complete the pressing. The resulting active core had an actual density of 99.98% of its theoretical density.

[0080] Based on the same process and parameters, without adding prestressed short fibers, an active material core material (PTFE 64.5wt.% / Al 25.51wt.% / W 9.99wt.%) with the same oxygen balance and density as the above materials was prepared for comparison.

[0081] The two active core materials were machined into rod-shaped tensile test specimens, and two groups of quasi-static tensile mechanical property tests were carried out on each of them. The loading strain rate was 0.001s -1 .

[0082] The experimental results show that the tensile strengths of the active core material without prestressed short fibers in two tensile tests were 22.04 MPa and 21.43 MPa, respectively, and the corresponding failure strains were 0.29 and 0.26, respectively.

[0083] The tensile strengths of the short fiber prestressed reinforced active material core prepared by the present invention were tested in two experiments and were respectively 38.57 MPa and 36.34 MPa, and the corresponding failure strains were respectively 0.51 and 0.48.

[0084] The two active core materials were machined into cylindrical fragments and the fragment penetration test was carried out. The experimental results are as follows: Figure 6 Among them, the traditional active core material without adding prestressed short fibers failed to penetrate the target plate, and the bulge was significant. The diameter of the bulge area was about Φ60, and the maximum bulge height was 16mm ( Figure 6 (a)); The short fiber prestressed reinforced active material core prepared by the present invention can penetrate the target plate, and the perforation area is 151.5mm 2 , the maximum ridge height is 9mm, and the perforation edge is a regular shear shape ( Figure 6(b)). It can be seen that the traditional active core material, due to its low compressive and tensile strength, is prone to fragmentation during the penetration process of the target plate, resulting in weak penetration ability and failure to penetrate the aluminum plate. Under the same projectile-target collision conditions, the short-cut fiber prestressed reinforced active core material prepared by the present invention has enhanced penetration ability compared to the traditional active core material due to its improved compressive and tensile strength, and can penetrate the aluminum plate and create a plug-shaped expansion hole.

[0085] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A chopped fiber prestressed reinforced active core, characterized in that: It comprises an active core body and a prestressed chopped fiber material, wherein the mass of the prestressed chopped fiber material is 5% to 15% of the total mass, and the active core body accounts for 85% to 95% of the total mass; The prestressed chopped fiber material is formed by stretching the fiber material into the creep stage and then chopping it. The length of the prestressed chopped fiber material is 50 to 100 times the particle size of the active metal powder in the active core body.

2. The chopped fiber prestressed reinforced active core according to claim 1, characterized in that: The fiber material is nylon or a fiber with a density of 0.94-0.98 g / cm 3 , UHMW-PE with tensile strength>20MPa and elongation at break>250%.

3. The chopped fiber prestressed reinforced active core according to claim 1 or 2, characterized in that: The fiber material is stretched by applying a constant tensile stress, wherein the amplitude of the applied constant tensile stress is 30% to 40% of the fracture limit of the fiber material and the tensile stress is applied for 6 to 24 hours, so that the fiber material enters a creep stage. After the tensile stress is unloaded, shrinkage prestress is generated, and the stretched fiber material is chopped to obtain a prestressed chopped fiber material.

4. The chopped fiber prestressed reinforced active core according to claim 1, characterized in that: The prestressed chopped fibers are surface treated with a coupling agent.

5. The chopped fiber prestressed reinforced active core according to claim 4, characterized in that: The coupling agent is a silane coupling agent, a titanate coupling agent or an aluminate coupling agent.

6. The chopped fiber prestressed reinforced active core according to claim 1 or 4, characterized in that: The amount of coupling agent, m, is determined based on the mass of the chopped fibers: m=m1*s1 / S Where m1 is the mass of the chopped fiber, s1 is the specific surface area of ​​the chopped fiber, and S is the minimum wetting area of ​​the coupling agent.

7. The chopped fiber prestressed reinforced active core according to claim 1, characterized in that: The active core body adopts polymer matrix / inert metal powder / active metal powder, including 20-80% matrix powder by mass, 0-50% inert metal powder and 20-50% active metal powder, or adopts an active core body containing TiH2, MgH2, ZrH2, MoO3, Fe2O3 or MnO2 modified additives.

8. A method for preparing a chopped fiber prestressed reinforced active core according to any one of claims 1 to 7, characterized in that: include: S1, drying and sieving the component powders according to the active core body formula; S2, heat treating the fiber material at 100-150° C. for 0.5-2 h to eliminate residual stress in the fiber material; S3, stretching the fiber material to make it enter the creep stage; S4, cutting the stretched fiber material into chopped fibers; S5, according to the active core formula, weighing the processed active core body component powders and chopped fiber materials according to the ratio requirements, and mixing them to obtain a mixed powder; S6, adding the mixed powder into the mold, maintaining the pressure under a certain molding pressure for a certain time, and pressing the mixed powder into an active core sample.

9. A preparation method according to claim 8, characterized in that: In said S6, when the aspect ratio of the prepared active core is not greater than 3, a unidirectional molding method is adopted; when the aspect ratio of the prepared active core is greater than 3, a bidirectional molding method is adopted; the molding pressure is determined according to the density requirement of the active core; and the holding time is 1 to 5 minutes.

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