A multiphase shear thickening liquid-Kevlar fiber composite material, its preparation method and application

Abstract

This invention discloses a multiphase shear thickening fluid-Kevlar fiber composite material, its preparation method, and its application, belonging to the field of novel composite material technology. This invention modifies the shear thickening fluid by adding CNC and SiC modifiers, and then impregnates Kevlar high-performance fiber cloth in the modified multiphase shear thickening fluid to prepare the multiphase shear thickening fluid-Kevlar fiber composite material. The multiphase shear thickening fluid in this invention can be uniformly dispersed on the surface of Kevlar fibers, with ideal adhesion and structure; moreover, it can change the particle cluster form and increase particle stiffness, effectively expanding the temperature range of the shear thickening interval, and significantly enhancing the Kevlar fiber cloth's resistance to impact deformation and absorption of impact energy. This provides theoretical support and experimental basis for the development of high-performance protective soft armor using MSTF-Kevlar fiber composite materials in the field of impact protection.

Description

Technical Field

[0001] This invention relates to the field of novel composite materials technology, and in particular to a multiphase shear thickening liquid-Kevlar fiber composite material, its preparation method, and its application. Background Technology

[0002] In today's era of rapid technological advancement, the research and application of protective materials has become a key research area in composite materials. The development of safe and reliable new protective materials and the improvement of the performance of existing protective structures profoundly impact safety assurance in numerous fields. Currently, in industrial safety, sports, and especially military protection, there is an urgent need to research and develop protective materials, structures, and equipment with high impact resistance. For practical application scenarios such as explosions and impacts, characterized by high instantaneous loads, high energy release, and high dynamic response, protective materials used in these scenarios need to have excellent energy absorption properties. High-strength, high-toughness, and lightweight high-performance fiber fabrics, such as aramid fibers, ultra-high molecular weight polyethylene fibers (UHMWPE), carbon fibers, and glass fibers, are commonly used as base materials for the development of soft armor. Among these, the high-performance synthetic Kevlar fiber, invented by DuPont in 1965, is the most widely used. This type of soft armor overcomes the disadvantages of traditional hard armor, such as being bulky, inconvenient to wear, and restricting the wearer's body movement. While ensuring flexibility and convenience, it still possesses excellent energy absorption properties and impact resistance, providing protection against energy impact threats. Extensive research on high-performance fabric materials has shown that while pure fabric materials possess enormous potential for impact protection, maximizing the protection against impact energy requires stacking multiple layers of Kevlar fabric. This results in traditional soft armor being quite thick and cumbersome in practical use. To address the shortcomings of pure fabric soft armor while maintaining lightweight flexibility, it is necessary to enhance the impact resistance of single-layer Kevlar fabric.

[0003] Impregnating high-performance fabrics with shear-thickening fluids (STFs) has become a potential method and key research direction for enhancing the impact resistance of single-layer fabrics. Shear-thickening fluids, as special concentrated suspensions with intelligent response, exhibit unique rheological characteristics where viscosity changes with shear rate. At low shear rates, their viscosity decreases, demonstrating good fluidity. As the shear rate gradually increases beyond the critical shear rate, their flow viscosity surges, even exhibiting solid-state characteristics at high dispersed phase mass fractions. With continued increases in shear rate, STFs ultimately exhibit shear-thinning rheological characteristics, resulting in an "S-shaped" rheological performance curve. The mainstream microscopic explanations for the viscosity change characteristics of STFs are currently the "order-disorder transition theory," "particle cluster theory," and "fluid lubrication-friction contact theory." Based on these microscopic thickening principles and the viscosity increase rate during the thickening stage, STF thickening behavior is divided into continuous shear thickening (CST) and discontinuous shear thickening (DST). In particular, the several-order-of-magnitude increase in viscosity exhibited by discontinuous shear thickening will play a significant role in reinforcing Kevlar fiber fabrics. The method of impregnating Kevlar fibers with STF dispersion in ethylene glycol solution was first proposed by Wagner et al. Ballistic experiments showed that the composite material had significantly enhanced ballistic penetration resistance with almost no loss of flexibility. Subsequent research on STF-impregnated fiber fabrics has mainly focused on modifying the STF, replacing it with high-performance fiber fabrics, and developing special thin-layer structures. Qin (cpb) et al. changed the STF dispersion medium to ionic liquids (ILs), which transformed the STF rheological properties from the traditional unimodal shear thickening behavior to bicontinuous shear thickening behavior. At the same time, the puncture resistance, mechanical properties, and electromagnetic interference shielding ability of the impregnated fabric were significantly enhanced. Sheng (tws) et al. replaced the traditional SiO2 particles with polystyrene microspheres to prepare a novel STKF-impregnated Kevlar fabric. Puncture experiments showed that the tensile strength of this soft composite material increased by more than 55%, and the maximum pull-out force increased by more than 6 times. Pan(cej) et al. impregnated fabrics with STF using a SiO2 / ethanol system. Besides mechanical property testing, they focused on the flame retardant properties of the composite material, concluding that the STF-Kevlar composite exhibits excellent flame retardant properties and retains good toughness and mechanical properties even after high-temperature treatment at 400℃. Xie(md) et al., using the finite element numerical analysis software LS-DYNA, analyzed the impact resistance mechanism of the STF-Kevlar composite material using a fluid-structure interaction method. Their results showed that the impact resistance of the composite material is much greater than that of pure fabric, and that the STF is the main energy-absorbing component when the impact velocity is high.

[0004] While current research has extensively studied the various mechanical, electrical, and thermal properties of STF-Kevlar composites, STF remains primarily a traditional single-dispersed-phase shear-thickening system, and research on STF modification is still insufficient. Furthermore, current studies on the rheological properties of STF are not comprehensive enough; some rheological studies have overlooked the fact that STF absorbs energy and heats up during impact, and the response of STF to temperature changes has not been systematically described. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a multiphase shear thickening liquid-Kevlar fiber composite material, its preparation method, and its application. This composite material is prepared by adding a modifying additive, CNC or SiC, to the shear thickening liquid to prepare the multiphase shear thickening liquid, and then impregnating Kevlar fibers in the multiphase shear thickening liquid. The multiphase shear thickening liquid can significantly enhance the Kevlar fiber cloth's resistance to impact deformation and its ability to absorb impact energy.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material includes the following steps:

[0008] S1: Add modified additives to the shear thickening fluid to prepare a multiphase shear thickening fluid;

[0009] S2: Impregnate Kevlar fibers with the multiphase shear thickening liquid prepared in step S1 to obtain a multiphase shear thickening liquid-Kevlar fiber composite material.

[0010] Furthermore, the modifying additives mentioned in step S1 include CNC or SiC.

[0011] Furthermore, the specific operation of step S1 includes the following steps:

[0012] S101: Add nano-SiO2 to the dispersion medium PEG200 in portions and stir until a uniform suspension is obtained to obtain a shear thickening liquid without the reinforcing phase;

[0013] S102: Add the modified additive CNC or SiC powder to the shear thickening liquid and stir evenly to obtain a multiphase shear thickening liquid sample containing the reinforcing phase.

[0014] S103: Curing the multiphase shear thickening liquid sample at constant temperature and humidity for 12 hours to remove air bubbles and obtain the finished multiphase shear thickening liquid.

[0015] Furthermore, the mass ratio of nano-SiO2 to PEG200 is 5-7:3-5; the mass ratio of nano-SiO2 to modified additives is 5-7:1-3.

[0016] Furthermore, the constant temperature and humidity curing conditions in step S103 are: 30℃ and 95% humidity.

[0017] Furthermore, the specific operation of step S2 includes the following steps:

[0018] S201: The multiphase shear thickening liquid prepared in step S1 is diluted with anhydrous ethanol and then ultrasonically dispersed and mixed evenly.

[0019] S202: Impregnate Kevlar fiber cloth with the mixture from step S201 and stir, then remove and dry to obtain the multiphase shear thickening liquid-Kevlar fiber composite material.

[0020] Furthermore, in step S202, the Kevlar fiber cloth is impregnated for 5 minutes, the drying temperature is 40°C, and the drying time is 6 hours.

[0021] In addition, the present invention also provides a multiphase shear thickening liquid-Kevlar fiber composite material prepared by the preparation method described above.

[0022] Furthermore, this invention also provides the application of the multiphase shear thickening liquid-Kevlar fiber composite material as described above in impact-resistant protective materials.

[0023] Furthermore, this invention also provides a performance testing method for the multiphase shear thickening liquid-Kevlar fiber composite material as described above, comprising the following steps:

[0024] Step a: Electron microscopy experiments were performed on the multiphase shear thickening fluid-Kevlar fiber composite material;

[0025] Step b: The multiphase shear thickening liquid was tested using room temperature rheological experiments and variable temperature rheological experiments;

[0026] Step c: Perform quasi-static tensile mechanical tests on single yarns of the multiphase shear thickening liquid-Kevlar fiber composite material;

[0027] Step d: Pull-out test of multiphase shear thickener-Kevlar fiber composite material under impact load;

[0028] Step e: Perform a drop hammer impact test on the multiphase shear thickening fluid-Kevlar fiber composite material. The beneficial effects of this invention are:

[0029] 1. This invention innovatively modifies STF by adding CNC and SiC modifying additives to shear thickening fluid. Kevlar high-performance fiber cloth is impregnated in MSTF to prepare composite material. The performance of the prepared multiphase shear thickening fluid-Kevlar fiber composite material is tested by electron microscopy, room temperature rheology, variable temperature rheology, single yarn quasi-static tensile testing, yarn pull-out, and drop hammer impact testing. The results show that the addition of CNC and SiC can significantly improve the protective performance of the composite material. This provides theoretical support and experimental basis for the development of high-performance protective soft armor of MSTF-Kevlar fiber composite material in the field of impact protection.

[0030] 2. In this invention, Kevlar fibers are impregnated in modified MSTF. Due to the good microstructure of the modified MSTF, the modifying additives have a significant modifying effect on the agglomeration of MSTF particles, so that MSTF can be uniformly dispersed on the surface of Kevlar fibers, and the degree of adhesion and adhesion structure are both ideal. Moreover, it can change the form of particle clusters and increase particle stiffness. Under varying temperature conditions, the modifying additives can effectively increase the temperature range of the shear thickening zone, thereby enhancing the temperature applicability of the MSTF system.

[0031] 3. The multiphase shear thickening liquid-Kevlar fiber composite material prepared in this invention exhibits a significant upward trend in stress. At the same time, the ultimate load of the MSTF-Kevlar composite material in the elastic stage is also significantly greater than that of pure Kevlar fiber cloth. The shear thickening effect increases the energy absorption value in both the elastic and oscillating stages, resulting in a significant impact energy absorption effect of the MSTF-Kevlar composite material. Attached Figure Description

[0032] Figure 1 The diagram shows the preparation process of the multiphase shear thickening liquid-Kevlar fiber composite material in this invention, as well as the corresponding performance testing diagrams. Among them, (a) is the preparation process of the multiphase shear thickening liquid-Kevlar fiber composite material; (b) is a microscopic schematic diagram of the MSTF-Kevlar fiber composite material; (c) is a rheological experiment diagram; (d) is a quasi-static tensile test diagram of a single yarn and a yarn pull-out test diagram; and (e) is a drop weight impact test diagram.

[0033] Figure 2 These are electron microscope images of nano-SiO2, CNC, and SiC used in this invention.

[0034] Figure 3 Electron micrographs of four types of MSTF (STF) prepared in this invention using 30wt% SiO2, 68wt% SiO2, 65wt% SiO2+3% CNC, and 65wt% SiO2+3% SiC.

[0035] Figure 4The image shows an electron microscope image of STF-Kevlar fiber composite materials prepared by MSTF (STF) of pure Kevlar fiber cloth, 60wt% SiO2, 57wt% SiO2+3% CNC and 57wt% SiO2+3% SiC in this invention.

[0036] Figure 5 The results are from the MSTF (STF) rheological experiments of the formulations of 30wt% SiO2, 28.5wt% SiO2 + 1.5wt% CNC, and 28.5wt% SiO2 + 1.5wt% SiC in this invention.

[0037] Figure 6 The results are the MSTF rheological properties experimental results with a fixed total dispersed phase (SiO2 and modified additives) mass fraction of 60 wt% in this invention.

[0038] Figure 7 The results show the effects of different mass fractions of modified additives on the room temperature rheological properties of MSTF when the mass fraction of SiO2 dispersed phase is fixed at 65 wt% and 68 wt% in this invention.

[0039] Figure 8 These are the results of the variable-temperature rheological experiment in this invention.

[0040] Figure 9 This describes the quasi-static tensile mechanical experiment process and results of a single yarn in this invention.

[0041] Figure 10 These are experimental photographs of the stretching of single yarns of four groups of MSTF(STF)-Kevlar composite materials in this invention.

[0042] Figure 11 This document describes the yarn pull-out experiment process and results in the MSTF-Kevlar composite material of this invention.

[0043] Figure 12 These are experimental images of the pull-out of four groups of MSTF(STF)-Kevlar composite yarns in this invention.

[0044] Figure 13 This is the fiber cloth force-displacement curve from the three drop hammer impact tests in this invention.

[0045] Figure 14 This is the energy-displacement curve of the first repeated drop hammer impact test of MSTF-impregnated Kevlar fiber cloth and pure Kevlar fiber cloth in this invention.

[0046] Figure 15 This is the energy-displacement curve of the second repeated drop hammer impact test of MSTF-impregnated Kevlar fiber cloth and pure Kevlar fiber cloth in this invention.

[0047] Figure 16 This is the energy-displacement curve of the third repeated drop hammer impact test of MSTF-impregnated Kevlar fiber cloth and pure Kevlar fiber cloth in this invention. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0049] Example 1:

[0050] Example 1 provides a method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material. The preparation process is shown in the attached figure. Figure 1 As shown in (a), the steps include:

[0051] S1: Prepare multiphase shear thickening fluid using modified additives CNC or SiC;

[0052] Nano-sized SiO2 spherical particles (particle diameter 300-400nm, spherical particle content above 60%) were added in small amounts and repeatedly to the dispersion medium polyethylene glycol solution (PEG200), and stirred with a planetary ball mill until a uniform suspension was obtained to obtain a shear thickening fluid (STF) without reinforcing phase.

[0053] The modified additive was added to the STF multiple times and mechanically stirred again to obtain a multiphase shear thickening liquid (MSTF) sample containing the reinforcing phase; the modified additive was nanocellulose CNC (nanodiameter of 5-10nm) or nano silicon carbide SiC (particle diameter of 20-30nm).

[0054] The prepared MSTF sample was placed into a plastic cryogenic tube and sealed. It was then placed in a constant temperature and humidity curing chamber (30℃, 95% humidity) for 12 hours to remove air bubbles and obtain the finished MSTF.

[0055] Specifically, the mass ratio of nano-SiO2 to polyethylene glycol (the mass of polyethylene glycol in the polyethylene glycol solution)

[0056] To compare the modification effects of different CNC and SiC, various finished MSTFs with different CNC and SiC mass fractions were prepared in this embodiment. The specific material ratio results are shown in Table 1 below.

[0057] Table 1 Material proportioning parameters for different finished MSTF (STF) products

[0058]

[0059]

[0060] Further, in step S2: Kevlar fibers are impregnated with the finished MSTF prepared in step S1 to obtain a multiphase shear thickening liquid-Kevlar fiber composite material.

[0061] Specifically, this invention uses a "dilution-impregnation-drying" method to prepare a multiphase shear thickening liquid-Kevlar fiber composite material. Pure Kevlar fiber is selected from 100g of 400D plain weave fiber cloth (0.17mm thickness) from Lotte Carbon Fiber Co., Ltd. Considering the good volatility, low toxicity, and economic and safe characteristics of ethanol solvent, the prepared MSTF is diluted with anhydrous ethanol. The mixture is then treated with ultrasonic dispersion for 30 minutes to ensure uniform mixing of the MSTF and anhydrous ethanol. The Kevlar fiber cloth is then cut into squares and impregnated in the mixture with thorough stirring. After impregnation for 5 minutes, the impregnated fabric is removed and dried in a 40°C oven for 6 hours to obtain the MSTF-Kevlar fiber composite material, which is then sealed in a bag.

[0062] For comparison, in this embodiment, Kevlar fibers were impregnated with finished MSTF (STF) prepared with 60wt% SiO2, 57wt% SiO2+3% CNC and 57wt% SiO2+3% SiC respectively.

[0063] A microscopic schematic diagram of the MSTF-Kevlar fiber composite material prepared in this embodiment is attached. Figure 1 As shown in (b), from the appendix Figure 1 As can be seen in (b), the dilution impregnation method makes MSTF more evenly covered on the surface of the fiber cloth, and the ethanol solvent is not introduced into the composite material. The hydrogen bonds mainly exist between the hydroxyl groups on the surface of the shear thickening liquid particles and the dispersion medium, and hardly form chemical bonds with the diluent.

[0064] Example 2:

[0065] Example 2 involves electron microscopy experiments on the raw materials nano-SiO2, CNC, SiC, and their corresponding MSTF(STF) and MSTF(STF)-Kevlar from Example 1.

[0066] The microstructure of MSTF (STF) with SiO2 powder, two modified additives (CNC and SiC), and mass fractions of 30 wt% SiO2, 68 wt% SiO2, 65 wt% SiO2 + 3% CNC, and 65 wt% SiO2 + 3% SiC were characterized using a scanning electron microscope (SEM) (ZEISS SIGMA 300). The microstructure of the original materials and the morphology of MSTF particle clusters were observed at magnifications ranging from 2 μm to 200 nm. Simultaneously, the microstructure of the three types of MSTF (STF)-Kevlar fiber composites prepared in Example 1 was observed using a scanning electron microscope at magnifications ranging from 10 μm to 500 nm, focusing on the interfacial contact between MSTF cluster particles and Kevlar fibers. This provides a microscopic theoretical basis for explaining the specific role of MSTF-Kevlar composites in impact resistance.

[0067] The microstructure characterization results of nano-SiO2, CNC, and SiC are attached. Figure 2 As shown, (a) represents the microscopic characterization results of SiO2, (b) represents the microscopic characterization results of SiC, and (c) represents the microscopic characterization results of CNC. (See attached image.) Figure 2 As shown in (a), the nano-SiO2 particles exhibit good dispersibility. The particles are spherical in shape, consisting of a large silicon atom sphere and two small oxygen atom spheres, with a particle size between 200 and 250 nm. The particles are relatively regular and smooth, agglomerated in a stacked manner. This stacking is not dense, with large gaps between particles and no binding material; no cluster structure exists. This indicates that before being formulated into a shear-thickening liquid, the chemical bonding and agglomeration between particles are not significant. (From the attached...) Figure 2 As shown in (b), the nano-SiC particles are irregularly shaped flaky with a rough surface. Due to their irregular and rough surface morphology, the stacking of pure SiC particles can form a mechanically interlocking structure, and the groups formed by this stacking have a certain structural framework that resists deformation. This appearance structure also provides a physical attachment structure for SiO2 particle clusters around SiC particles in multiphase shear thickening liquids containing modified additives. Simultaneously, at a magnification of 200 nm, it can be seen that there are fine, irregular micro-dust particles between the SiC block particles. These dust particles fill the gaps between the stacked structures formed by the SiC block particles, making the structure more compact. From the attached... Figure 2As shown in (c), the nanocellulose CNC is generally fibrous rod-shaped with a rough surface and some cracks. Observing its higher magnification SEM image, it can be seen that its interior is also composed of interconnected fibrous filaments, with good integrity. Due to the special arrangement of its filaments, the nanocellulose structure exhibits anisotropy, large specific surface area, and high crystallinity. This allows CNC to act as a "bridging" agent in STF, entangled and linked multiple SiO2 clusters to form larger cluster structures, thereby changing the rheological properties of the shear thickening fluid.

[0068] Furthermore, the microscopic characterization results of the four types of MSTFs (STFs) prepared with 30wt% SiO2, 68wt% SiO2, 65wt% SiO2+3% CNC, and 65wt% SiO2+3% SiC are attached. Figure 3 As shown. From the appendix Figure 3 As can be seen, the STF prepared with 30wt% SiO2 has a low mass fraction, resulting in a dispersed distribution of SiO2 particles within the dispersant. The particle surfaces are coated with the dispersant PEG200, and a few particles exhibit flocculation. However, the dispersion distance between the flocs is relatively large, and the overall structure remains in a drifting, free state with minimal agglomeration. Simultaneously, a large number of unflocculated, free SiO2 particles are present. In contrast, the STF prepared with 68wt% SiO2 shows that with increasing mass fraction of dispersed SiO2 particles, the particles are densely packed, in contact with each other, forming particle clusters. Multiple clusters are interconnected or closely spaced. This cluster structure plays a role in shear thickening. As the shear rate increases, the number of clusters increases, leading to blockage and a sharp increase in the viscosity of the STF.

[0069] The addition of modified additives CNC and SiC affects the structure of SiO2 cluster particles at high mass fractions. MSTF with added CNC exhibits a thinner layer of dispersant coating, resulting in a denser particle cluster structure. In contrast, MSTF with added SiC shows more complete coating of the dispersed SiO2 particles by the dispersant, with significant SiO2 particle agglomeration and a certain degree of interparticle cross-linking. SiC particles also act as fillers in the MSTF; at higher shear rates, SiC particles may alter interfacial adhesion, promoting particle aggregation and changing the shear thickening effect.

[0070] Furthermore, electron microscopy was performed on the three types of MSTF(STF)-Kevlar fiber composites prepared in Example 1, as well as pure Kevlar fibers. The results are shown in the attached figure. Figure 4As shown, (a) is the microstructure of pure Kevlar fiber cloth; (b) is the microstructure of STF-Kevlar fiber composite material prepared with 60 wt% SiO2 STF; (c) is the microstructure of MSTF-Kevlar fiber composite material prepared with 57 wt% SiO2 + 3% CNC MSTF; and (d) is the microstructure of MSTF-Kevlar fiber composite material prepared with 57 wt% SiO2 + 3% SiC MSTF. (See attached image.) Figure 4 As can be seen, the surface of pure Kevlar fibers is smooth, with large gaps between fibers and only a small amount of dust. After Kevlar fibers are impregnated with 60wt% SiO2, a large number of silica particles adhere to the fiber surface. However, this adhesion is uneven, with large areas of the fiber surface remaining unattached and only a single layer of SiO2 particles adhering, without forming multilayer particle adhesion or clusters. When two types of additives, CNC and SiC, are added, the particle adhesion rate is significantly improved, and the fiber surface is almost completely covered by MSTF particles. The particle adhesion rate of CNC additive is greater than that of SiC additive. The introduction of these two types of modified additives results in significant cluster and layered structures of the attached SiO2, and the gaps between fibers are significantly reduced. This indicates that the multiphase shear thickening liquid containing modified additives was successfully introduced into Kevlar fibers, and the degree and structure of adhesion are both ideal.

[0071] Example 3:

[0072] Example 3: Rheological experiments were conducted on MSTF (STF) with different ratios from Example 1 using a rheometer (Anton Paar MCR302), as shown in the attached figure. Figure 1 As shown in (c), the rheometer is a rotational rheometer, consisting of a base plate and a rotor. A sensor at the circumference is used to measure the torque frequency, which is then converted into viscosity to obtain a shear rate-viscosity rheological curve. The viscosity change behavior of MSTF (STF) at low mass fractions is studied through the rheological curve.

[0073] 1. MSTF (STF) room temperature rheological experiment

[0074] Rheological experiments were conducted on MSTF (STF) with formulations of 30 wt% SiO2, 28.5 wt% SiO2 + 1.5 wt% CNC, and 28.5 wt% SiO2 + 1.5 wt% SiC at room temperature (30℃). The results are attached. Figure 5 As shown, (a) are the rheological property curves of the three types of MSTF (STF); (b) are the shear rate-shear stress curves of the three types of MSTF (STF). (See attached diagram.) Figure 5As can be seen, under low mass fraction conditions, the MSTF shear thickening process is not obvious; instead, it exhibits a significant shear thinning phenomenon. When the shear rate is 200... -1 It exhibits stable viscosity, with both maximum and minimum viscosities being relatively low. This is because the SiO2 content in the dispersed phase is too small; after the initial structure is destroyed under shearing, the particles cannot form clusters, resulting in a shear rate of 500. -1 Afterwards, the thickening effect was almost negligible, the shear stress was low, and the total energy absorbed was low, which proves that MSTF with a low mass fraction does not have good impact resistance.

[0075] Furthermore, this invention also employs MSTF with a fixed total dispersed phase (SiO2 and modified additives) mass fraction of 60 wt% for room temperature rheological experiments. Specifically, rheological experiments were conducted using 57 wt% SiO2 + 3 wt% CNC, 57 wt% SiO2 + 3 wt% SiC, 58 wt% SiO2 + 2 wt% CNC, 58 wt% SiO2 + 2 wt% SiC, 59 wt% SiO2 + 1 wt% CNC, and 59 wt% SiO2 + 1 wt% SiC. The results are shown in the appendix. Figure 6 As shown, (a) is the rheological property curve, and (b) is the shear rate-shear stress curve. (From the attached...) Figure 6 As can be seen, in the low strain rate range, all MSTFs exhibited significant shear-thinning behavior, and the addition of high-quality modifiers (3wt% CNC, 3wt% SiC) had a certain inhibitory effect on the unfavorable shear-thinning behavior. After exceeding the critical shear rate, all MSTFs entered the shear-thickening range (10–100%). -1 The viscosity of MSTF increased significantly in all formulations. The MSTF system with 3 wt% CNC showed the highest shear viscosity peak, indicating that a high mass fraction of CNC additive effectively enhanced the shear thickening effect. The MSTF system with 1 wt% SiC showed the lowest shear viscosity peak, indicating that the improvement in shear thickening effect by SiC additive at lower mass fractions is limited. Comparing the MSTF formulations with 58 wt% SiO2 + 2 wt% CNC and 57 wt% SiO2 + 3 wt% SiC, the shear thinning regions of the two formulations were basically similar. However, in the shear thickening region, the MSTF system with 2 wt% CNC showed a stronger shear thickening effect and a higher shear viscosity peak than the MSTF system with 3 wt% SiC. This indicates that the CNC additive has a stronger shear thickening effect on MSTF than the SiC additive.

[0076] From the perspective of shear stress (attached) Figure 6In (b) of the formulation, the MSTF with 3 wt% CNC showed higher initial stress and peak shear stress than other formulations, indicating that the addition of CNC effectively enhanced the interaction force between MSTF particles. In contrast, the MSTF system with added SiC (e.g., 3 wt% CNC) exhibited a flatter shear stress curve, suggesting that SiC particles are more rigid and prone to slippage during shear thickening. The shear thickening index ηs reflects the shear thickening ability of the MSTF system. The MSTF with 57 wt% SiO2 + 3 wt% CNC had the highest ηs of 2.96, indicating that this formulation exhibited the best shear thickening performance.

[0077] Furthermore, this invention also adds 1 wt% to 3 wt% CNC and SiC modifying additives while keeping the mass fraction of the SiO2 dispersed phase constant at 65 wt% and 68 wt%, respectively. The effect of different modifying additive mass fractions on the room-temperature rheological properties of MSTF under a fixed SiO2 dispersed phase mass fraction was analyzed. The rheological experimental results are attached. Figure 7 As shown, (a) are the rheological property curves of 65wt% + CNC and 65wt% + SiC; (b) are the shear rate-shear stress curves of 65wt% + CNC and 65wt% + SiC; (c) are the rheological property curves of 68wt% + CNC and 68wt% + SiC; and (d) are the shear rate-shear stress curves of 68wt% + CNC and 68wt% + SiC. (See attached...) Figure 7 As can be seen, at the same SiO2 mass fraction, the peak viscosity and shear thickening amplitude of the MSTF with added CNC are greater than those of the MSTF with added SiC. This indicates that the "bridging" effect of the CNC fiber structure has a greater impact on the shear thickening effect than that of the SiC additive, thus the energy absorption capacity of the MSTF containing CNC is more prominent. Comparing the rheological curves of the same additive with different SiO2 mass fractions, it can be seen that the initial viscosity, critical thickening viscosity, peak viscosity, and shear thickening amplitude of the MSTF with 68wt% SiO2 are much greater than those with 65wt% SiO2. In contrast, the MSTF curves with different additive contents at the same SiO2 mass fraction are more similar, with smaller changes in peak viscosity, critical shear rate, and shear thickening amplitude. This suggests that in the modified MSTF containing additives, the influence of additives on the shear thickening effect is relatively limited, and the rheological properties are more determined by the mass fraction of the dispersed phase SiO2. The additives mainly improve some of the rheological properties of the MSTF with a fixed dispersed phase content.

[0078] 2. MSTF (STF) variable-temperature rheological experiment

[0079] To investigate the effect of temperature on the rheological properties of MSTF, this experiment also designed MSTF formulations with proportions of 65wt% SiO2 + 3wt% CNC, 66wt% SiO2 + 2wt% CNC, 67wt% SiO2 + 1wt% CNC, 65wt% SiO2 + 3wt% SiC, 66wt% SiO2 + 2wt% SiC, and 67wt% SiO2 + 1wt% SiC. An STF with 68wt% SiO2 was prepared as a control group for variable-temperature rheological experiments, using a fixed shear rate of 100 s⁻¹. -1 (This shear rate is based on experimental data under normal temperature rheological conditions, 100 s) -1 The STF shear thickening effect is more obvious under shear rate conditions. Using the shear environment temperature as the independent variable, with a temperature range of 0–120℃, the results of the variable-temperature rheological experiments are attached. Figure 8 As shown, (a) is the temperature-viscosity curve of each MSTF formulation; (b) is the temperature / viscosity characteristic curve of each MSTF formulation.

[0080] From the appendix Figure 8As can be seen, the shear viscosity of all formulations exhibits a three-stage trend with increasing temperature. At lower temperatures, the MSTF viscosity is almost zero. This is because, under low-temperature conditions, the intermolecular forces and molecular thermal motion between the dispersion medium PEG200 and the dispersed phase particles are severely suppressed, resulting in a low viscosity in the initial stage of the MSTF temperature-dependent rheological curve. When the lower critical temperature is exceeded (approximately 10℃~20℃), the Brownian motion of the particles intensifies, and the interaction forces between dispersed phase particles (such as van der Waals forces and electrostatic interactions) and the fluidity of the base liquid reach equilibrium. The particles can form strong mutual aggregation, leading to a significant shear thickening effect in the system. When the ambient temperature exceeds the upper critical temperature (approximately 40℃~65℃) and enters the high-temperature region, the molecular thermal motion intensifies significantly, the interfacial interactions between particles weaken, and the particle cluster structure generated during shear thickening is destroyed, causing the MSTF viscosity to decrease rapidly and the system fluidity to increase. Comparing MSTF containing CNC / SiC additives with STF containing 68wt% SiO2, we can see that both the upper and lower critical temperatures (especially the upper critical temperature) are increased, and the shear thickening temperature range of MSTF containing CNC is slightly larger than that of MSTF containing SiC. This indicates that the additives can effectively increase the temperature range of the shear thickening interval, enhancing the temperature adaptability of the MSTF system. This ensures that MSTF, when used in protective materials to absorb kinetic energy as internal energy, still retains good shear thickening energy absorption properties, preventing the shear thickener from failing due to temperature changes caused by internal energy absorption. Furthermore, it is noteworthy that under varying temperature conditions, the peak viscosity of MSTF containing additives is greater than that of STF containing 68wt% SiO2. This indicates that the conclusion that the addition of CNC and SiC additives can effectively improve the peak viscosity of the MSTF system under varying temperature conditions remains applicable. Moreover, the addition of CNC slows down the viscosity decrease trend of MSTF at high temperatures, ensuring that MSTF maintains good stability at high temperatures.

[0081] Example 4:

[0082] Example 4 investigates the stress variation characteristics of a single yarn in the MSTF-Kevlar composite material prepared in Example 1 under impact, and the effects of two types of modifying additives (CNC, SiC) on the tensile mechanical response of the single yarn and internal fibers. A quasi-static tensile mechanical test was conducted on the tensile strength of the single yarn using a general-purpose materials testing machine (Instron 5982, force range 0–100 kN, measurement accuracy ±0.5% of the indicated value), as shown in the attached figure. Figure 1As shown in (d). Single yarns were taken from three types of square MSTF (STF)-Kevlar composite materials (STF-Kevlar composite material obtained by impregnating Kevlar fibers with 60wt% SiO2, MSTF-Kevlar composite material obtained by impregnating Kevlar fibers with 57wt% SiO2 + 3wt% CNC, and MSTF-Kevlar composite material obtained by impregnating Kevlar fibers with 57wt% SiO2 + 3wt% SiC). Pure Kevlar fiber fabric yarn was also used as a control. After each single yarn was wound twice around two pairs of 5mm × 5mm square aluminum plates, it was fixed to the loading head of a material testing machine without transverse prestress. The loading rate of the material testing machine was set to 0.5mm / min, and the loading temperature was room temperature. The force and displacement of the loading head were recorded during the loading process. Each group of samples was tested four times, as shown in the attached diagram. Figure 9 As shown in Figure (a), the experimental results are attached. Figure 9 As shown in (b).

[0083] From the appendix Figure 9 As shown in (b), in the initial stage, the dispersed phase and dispersion medium of MSTF adhere and fill between the fibers. When the loading rate of the material testing machine is low, the shear rate between the yarns also responds to a small value. At this time, MSTF exhibits shear thinning characteristics, the viscosity decreases, the system fluidity increases, and shear thinning reduces the friction between fibers while avoiding the mechanical coupling phenomenon between STF and fibers. This has a negative impact on the tensile properties of a single yarn. However, when the loading rate of the material testing machine is high, MSTF exhibits shear thickening, the dispersed phase particles form a cluster structure, and a direct mechanical coupling is formed between them and the yarn. The fluidity of MSTF is greatly reduced, the friction between fibers increases, which reduces the tensile load on the fibers and increases the tensile properties of the yarn.

[0084] The stress-strain curves from the four repeated experiments are attached. Figure 9 As shown in (c). From the appendix Figure 9 As can be seen in (c), the tensile stress-strain curves of the four groups of materials have basically the same trend, mainly divided into the elastic stage where stress increases with strain. In this stage, the material is in the elastic region, and the fiber bundles of the yarn maintain good stress-bearing performance. After the peak stress, the tensile stress of the four groups of materials drops irregularly and rapidly to zero. In this stage, the structure of the intertwined fibers of the yarn is completely destroyed, and it loses its ability to bear stress. This stage can be called the failure stage. There is a smooth transition section between the two stages, which is the yield stage. The stress reaches its peak in the yield stage.

[0085] This invention compares the elastic modulus of four groups of materials in four experiments. The elastic modulus of the four groups of materials is shown in Table 2. Table 2 shows that under low tensile loading rates in this experiment, MSTF has a relatively small effect on improving the tensile modulus of single yarns; the mechanical properties of the fiber itself play a dominant role. Even the 57wt%SiO2+3wt%CNC and 57wt%SiO2+3wt%SiC materials have a weakening effect. However, this still indicates that MSTF plays an important role in the tensile properties of the yarn, and it can be predicted that this effect will significantly improve the tensile strength of the yarn under high shear rates. From the stress-strain curve trends of the four groups of materials, the yield strain of the three modified materials is smaller than that of pure Kevlar fiber cloth. The yield strain of pure Kevlar fiber cloth yarn can reach over 4%, while the yield strain of SiC-added materials is the lowest, averaging around 2.5%. This is because SiC particles are embedded between the fiber filaments, and their rough surfaces cause mechanical wear on the fibers during stretching, thus causing the yarn to enter the failure stage prematurely. The general reduction in yield strain reflects, to some extent, the decrease in yarn extensibility and toughness caused by MSTF particles, which is a defect in modified MSTF-impregnated Kevlar fiber composites.

[0086] Experimental photographs of single yarn stretching of four groups of materials are shown below. Figure 10 As shown, from the appendix Figure 10 As can be seen, the fracture phenomenon of pure Kevlar single fibers is obvious, and the fibers fracture brittlely at the yarn break. The single yarn impregnated with MSTF shows obvious tensile resistance at the break. The MSTF yarn modified with CNC has a neater break and a stable break point position, and the sample shows more uniform tensile behavior. The MSTF yarn modified with SiC shows smaller deformation, which indicates that SiC has a significant stiffness enhancement effect.

[0087] Table 2 Comparison of Elastic Modulus of Four Groups of Materials

[0088]

[0089] Example 5:

[0090] To investigate the yarn pull-out behavior and partial yarn slippage of MSTF-Kevlar composites under impact loading, this study employed a general-purpose materials testing machine (Instron 5982, force range 0–100 kN, measurement accuracy ±0.5% of indicated value) to conduct yarn pull-out experiments on the MSTF-Kevlar composite fiber cloth. This was done to evaluate the yarn pull-out behavior of the composite material under impact. (See attached figure.) Figure 1As shown in (d) in the figure. The pull-out experiment used three types of 10cm × 40cm regular rectangular fiber fabrics (60wt% SiO2 impregnated Kevlar fiber fabric, 57wt% SiO2 + 3wt% CNC impregnated Kevlar fiber fabric, and 57wt% SiO2 + 3wt% SiC impregnated Kevlar fiber fabric), with pure Kevlar fiber fabric as the control group. The warp threads of the composite fiber fabric were parallel to the long side of the rectangle, and the weft threads were parallel to the short side of the rectangle, ensuring that there was no excessive stress concentration in any part of the material when clamped on the universal testing machine. Since there was no yarn weaving constraint on the long and short sides of the rectangle, the edge yarns were heated by a flame to cause them to curl due to heat, minimizing the loosening of the edge yarns. Take adjacent warp threads parallel to the long side at the midpoint of one short side, wrap them around a square aluminum plate, and then fix them to the loading head of the universal testing machine. Make a recess at the corresponding position on the other short side so that this recess is not fixed during loading. The remaining protruding parts are fixed by the loading head of the testing machine so that the five fixed yarns on one side can be pulled out during the loading process of the material testing machine. Set the fixed loading rate of the material testing machine to 5 mm / min and the loading temperature to room temperature. Record the force and displacement of the loading head during the loading process. Repeat the experiment three times for each group of samples.

[0091] The specific procedures and results of the pull-out experiment are attached. Figure 11 As shown, (a) is a photograph of the pull-out experiment; (b) is the pull-out experiment method; and (c) is the pull-out force-displacement curve of the pull-out experiment. Pull-out experiments were conducted on five yarns. The yarn to be pulled out was extracted from the middle of the sample and fixed to the upper loading head. The fiber cloth on both sides of the sample, excluding the yarn to be pulled, was clamped to the lower loading head. The loading rate was 5 mm / min. This loading rate corresponds to the lower shear rate in the shear thickening liquid rheological experiment, as shown in the attached figure. Figure 11 As shown in (a) above. In this yarn pull-out experiment, the elastic characteristics of the yarn itself, the structural characteristics of the plain weave of the fiber cloth, and the STF filling the gaps between the yarns will have the main influence on the macroscopic pull-out behavior of the yarn. Figure 11As shown in (b), in the initial stage of the tensile test, the yarn structure exhibits a sinusoidal curl, with significant gaps between the warp and weft yarns. Friction is generated solely through lateral contact friction, forming a sufficient number of interlaced weaving units to tightly bind the entire fabric. As the pull-out displacement gradually increases, the curled structure of the yarn straightens from top to bottom, and the weaving units become more compact, forming an interlocking structure between the warp and weft yarns to resist the pull-out action. STF contributes little at this stage. When the warp and weft yarns are in full contact, the shear thickening liquid undergoes shearing thickening or shear thinning behavior under shear force, altering the magnitude of the friction between the yarns. At this stage, the yarn is not pulled out and remains in the static friction stage. As the pull-out displacement reaches the critical value, the pull-out force reaches its peak, and the warp yarns begin to slide in and out from the interlacing points of the weft yarn's weaving structure, converting the friction between the yarns into dynamic friction. The pull-out force-displacement curves for the four sets of yarn pull-out experiments are shown below. Figure 11 As shown in (c1)-(c3) of (c), in the static friction stage, the pulling force gradually increases with the increase of displacement. The yarn mainly exhibits elastic deformation. The trend of the curve in the static friction stage is similar to the force-deformation curve in the elastic stage of the quasi-static tensile mechanical experiment of a single yarn. This is because the yarn itself produces a certain elastic deformation. Although the five yarns have relative displacement, they are not pulled out. The weaving structure of the composite fiber cloth is not destroyed. After the external force is removed, the elastic deformation of the yarn can be restored, and the composite material can also be restored to the state before the force is applied. Once the peak pull-out force is exceeded, the yarn is gradually pulled out, entering the dynamic friction stage. The pull-out force-displacement curve exhibits a "slippage-viscosity" phenomenon, meaning the pull-out force oscillates periodically with increasing displacement, but the overall curve still shows an upward trend. This periodic oscillation is mainly due to the fact that the warp yarn is pulled out from the weft yarn interlacing point. The pull-out force disrupts the tight interlocking structure between the warp and weft yarns in the previous stage, reducing the frictional force generated by yarn misalignment. This continues until the warp yarn is pulled out again, forming the next interlocking structure, causing the pull-out force to continue to rise. This process repeats, exhibiting a periodic oscillation trend. The curve shows an overall upward trend unaffected by the reduction in the warp and weft yarn interlacing points. This is because, although the contact area between the warp and weft yarns decreases with the pull-out of the warp yarn, the shear rate between the yarns increases. The MSTF viscosity increases with the shear rate, resulting in increased friction between the yarns. Macroscopically, this manifests as an overall upward trend in the pull-out force.

[0092] contrast Figure 11The effects of modified additives on the pull-out behavior of MSTF-Kevlar composites were evaluated using (c1), (c2), and (c3). It can be seen that the Kevlar fiber cloth impregnated with 57wt% SiO2 + 3wt% CNC and the 57wt% SiO2 + 3wt% SiC maintained relatively stable friction during the dynamic friction stage, and the amplitude of the periodic oscillation was less than that of the fiber cloth impregnated with 60wt% SiO2. This indicates that the addition of modified additives helps to maintain the stability of friction during yarn pull-out and avoids large fluctuations.

[0093] Appendix Figure 12 The images show experimental pull-out images of four groups of MSTF(STF)-Kevlar composite yarns. It can be seen that the yarns pulled out of pure Kevlar fiber fabric exhibit a smaller pull-out influence area (the area showing significant tensile displacement excluding the five yarns under tension). This indicates that when the pure Kevlar fiber fabric yarns are stretched, the five yarns under tension independently resist the pull-out action, with minimal impact on the surrounding yarns. However, after impregnation with MSTF, the yarn pull-out influence area significantly increases. This suggests that the addition of MSTF transfers the pull-out action borne by the five yarns to the surrounding yarns, allowing more yarns to participate in resisting the pull-out action.

[0094] Example 6:

[0095] This study employed a drop hammer testing machine (CEAST 935, energy range 0.59–757 J, impact velocity 0.77–4.65 m / s) to conduct drop hammer impact tests on single-layer MSTF-Kevlar fiber cloth to characterize the mechanical response characteristics of MSTF-Kevlar composite materials under high strain rate impact. The drop hammer impact simulation aimed to observe the structural changes and energy absorption characteristics of MSTF-Kevlar composite materials when applied in impact protection. The medium strain rate characteristics of the drop hammer impact test ensured that MSTF exhibited good shear thickening properties under impact, thereby enhancing the impact resistance of the Kevlar fiber cloth. Figure 1As shown in (e) in the experiment, three types of MSTF(STF)-Kevlar composite materials were used (60wt% SiO2 impregnated Kevlar fiber cloth, 57wt% SiO2 + 3wt% CNC impregnated Kevlar fiber cloth, and 57wt% SiO2 + 3wt% SiC impregnated Kevlar fiber cloth). Pure Kevlar fiber cloth was set as a control group. Each group of samples was a rectangle with a size of 300×300mm. The drop hammer tester had a punch diameter of 16mm, a mass of 0.63kg, a hemispherical head, and a drop hammer counterweight of 5kg. The initial height of the drop hammer punch was controlled so that the impact energy carried by the drop hammer when it contacts the sample was 100J, and the impact point was the center of the rectangular sample. A rectangular single-layer MSTF(STF)-Kevlar fiber cloth is subjected to a ring-shaped fixed constraint by a ring clamp and is provided with radial pretension during clamping to ensure that the surface of the fiber cloth is taut and flat. It is then placed on the support under the testing machine. The ambient temperature during impact is room temperature. During the impact process, the instrument synchronously records the changes in force with displacement and the changes in energy absorbed by the sample. Each group of samples is tested three times.

[0096] The fiber force-displacement curves for the three experiments are shown in the attached figures. Figure 13 As shown in (a), (b), and (c) of the appendix. Figure 13As can be seen, the force-displacement curves of the four materials show a generally similar trend, which can be divided into three stages. The first stage is the elastic stage, where the force increases linearly with displacement. This corresponds to the elastic tensile deformation of the fiber cloth yarn after the impact head contacts the fiber cloth sample. The overall weave structure becomes tighter due to the impact load at the center, and the resistance of the yarn to the impact head, i.e., the total force on the yarn, gradually increases. The second stage is the falling stage. In this stage, under the action of the impact head, most of the yarn in the impact contact area of ​​the composite fiber cloth is squeezed to both sides of the impact head, causing lateral displacement and torsion. The weave structure of the fiber fabric is destroyed by the impact head, resulting in a sharp decrease in the resistance of the composite fiber cloth to the impact head. However, some yarns are still under the impact load directly below the impact head and begin to be pulled out under its action. Therefore, the force quickly rises back to the level before the fall after the sharp decrease. The third stage is the oscillation stage. In this stage, the yarn gradually slips, and the friction between the yarns becomes dominated by kinetic friction. The periodic oscillation trend corresponds to the oscillation phenomenon observed in the yarn pull-out experiment. Since MSTF is already under a high strain rate, as the amount of yarn slippage gradually increases, the contact area and friction between the warp and weft yarns decrease, so the force generally decreases during the oscillation. In the elastic stage, it can be seen that the force on the pure Kevlar fiber cloth increases gradually with displacement, while the force on the MSTF-impregnated fiber cloth shows a significant upward trend. At the same time, the ultimate load of the MSTF(STF)-Kevlar composite material in the elastic stage is also significantly greater than that of the pure Kevlar fiber cloth. This proves that under a high strain rate, the addition of MSTF(STF) can significantly improve the stiffness and ultimate impact resistance of Kevlar fiber cloth in the elastic stage under impact load conditions. For the force-displacement curves of four groups of MSTF(STF)-Kevlar composite fiber fabrics, the curve integrals for each of the three stages were calculated. The absolute area integral value can measure the amount of energy absorbed by the composite material during the impact process. It can be seen that the energy absorbed is the most in the oscillation stage (accounting for about 50%), followed by the elastic stage (accounting for about 30%). Compared with pure Kevalr fiber fabric, the introduction of MSTF can significantly increase the energy absorption value in the elastic and oscillation stages, making the impact energy absorption effect of MSTF-Kevlar composite material significant. Considering that the weave structure of the fiber fabric has been damaged and become loose when entering the descent stage, if subjected to a secondary impact, there is no intact structure to produce elastic deformation, and the displacement of the fiber fabric yarn in the third stage has exceeded the protection requirements, the peak force at the end of the first stage is defined as the critical force at which the composite fiber fabric loses its protective function under impact. It is used as an important indicator to evaluate the protective performance of the composite fiber fabric. The peak force of each experimental curve was statistically analyzed, and the mean, variance, and standard deviation were calculated. The results are shown in Table 3 below.

[0097] Table 3 Peak force curves from the drop hammer impact test

[0098]

[0099] Table 3 shows that the average peak force of the 57wt% SiO2 + 3wt% CNC impregnated Kevlar fiber cloth is the highest (10 times higher than pure Kevlar fiber cloth). The average peak force of the 60wt% SiO2 impregnated Kevlar fiber cloth is slightly lower than that of the CNC-added composite material, while the average peak force of the 57wt% SiO2 + 3wt% SiC impregnated Kevlar fiber cloth is significantly lower than the former two, indicating that the MSTF-Kevlar composite material with CNC additive has the best protective performance. Discrete analysis of the variance and standard deviation of the four groups of materials shows that the variance and standard deviation of the 57wt% SiO2 + 3wt% SiC impregnated Kevlar fiber cloth are the lowest among the three MSTF-Kevlar composite materials, indicating that the addition of SiC can significantly enhance the stability of the composite material under impact.

[0100] The drop hammer impact test also needs to evaluate the impact protection performance of MSTF-Kevlar composite material from an energy perspective. During the impact process, the velocity of the drop hammer begins to decrease after contacting the composite fiber cloth. According to the principle of energy conservation, this part of the kinetic energy will be absorbed by the composite fiber cloth. Therefore, considering the protective ability of protective equipment from the perspective of the maximum energy that the human body can withstand, the absorption value of the protective material to impact energy is an important indicator for judging the performance of the protective material. The energy absorption-displacement curves of repeated drop hammer impact tests on MSTF impregnated Kevlar fiber cloth and pure Kevlar fiber cloth are attached. Figure 14-16 As shown, from the appendix Figure 14-16 As can be seen, the impact energy absorption curve of pure Kevlar fiber cloth can be divided into three stages. In the first stage, the displacement increases rapidly, and energy absorption is relatively slow. In the second stage, the displacement continues to increase, and energy absorption rises until the highest point. In the third stage, after passing the highest energy point, the displacement increases slightly, and the energy rapidly decreases to zero. At this point, the fiber cloth is punctured, the fiber filaments break, and energy absorption drops rapidly. The overall trends of the three MSTF(STF)-Kevlar composite materials are similar, and can be divided into three segments: Stage I, Stage II, and the intermediate plateau stage. The appearance of the plateau stage may be due to the lateral displacement and twisting of the yarn near the punch, which also corresponds to the attached... Figure 13 The decline phase in Stage II. Overall, energy absorption shows an upward trend, but compared to Stage I, the upward trend in Stage II is slower (see appendix). Figure 14-16The pie charts represent the slopes of each curve in two stages. In the second and third repeated experiments, the Stage II curves of the 60wt% SiO2-impregnated Kevlar fiber cloth and the 57wt% SiO2 + 3wt% SiC-impregnated Kevlar fiber cloth remained flat, indicating that the energy absorption efficiency of Stage II had decreased significantly. Only the 57wt% SiO2 + 3wt% CNC material maintained a high upward trend in the Stage II curves in all three experiments, with high energy absorption efficiency and the highest energy absorption value at the end of the second stage. This indicates that the CNC additive effectively improved the energy absorption efficiency and the total energy absorption value. However, from the overall energy absorption curves, the energy absorption capacity of the three types of Kevlar fiber cloths with added MSTF was significantly improved. Considering that excessive deformation of the fiber cloth would lead to a weakening or even loss of protective ability, the energy at a displacement of 80mm was taken as the maximum absorbed energy. The energy absorption rate and average energy absorption value of Stage I in the three experiments are shown in Table 4 below.

[0101] Table 4. Energy absorption rate and average energy absorption in three experiments, Stage I.

[0102]

[0103] As shown in Table 4, the maximum energy absorption value of 57wt% SiO2 + 3wt% CNC is the highest (average value is 51.3), and the energy absorption rate of Stage I is the highest (1.22 J / mm). At the same time, the maximum energy absorption value and energy absorption efficiency of the composite material with added SiC and 60% SiO2 are significantly improved compared with pure Kevlar fiber cloth. This indicates that MSTF has a significant effect on enhancing the energy absorption performance of fiber cloth, and the modification of CNC additive makes the energy absorption effect the strongest.

[0104] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material, characterized in that, Includes the following steps: S1: A multiphase shear thickening liquid is prepared by adding the modified additive CNC to the shear thickening liquid; the ratio of SiO2 to CNC in the multiphase shear thickening liquid is 57%SiO2 + 3%CNC. S2: Impregnate Kevlar fibers with the multiphase shear thickening liquid prepared in step S1 to obtain a multiphase shear thickening liquid-Kevlar fiber composite material. The specific operation of step S2 includes the following steps: S201: The multiphase shear thickening liquid prepared in step S1 is diluted with anhydrous ethanol and then ultrasonically dispersed and mixed evenly. S202: Impregnate Kevlar fiber cloth with the mixture from step S201 and stir, then remove and dry to obtain the multiphase shear thickening liquid-Kevlar fiber composite material; the impregnation time is 5 min, the drying temperature is 40℃, and the drying time is 6 h.

2. The method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material according to claim 1, characterized in that, The modified additive mentioned in step S1 is SiC, and the mass ratio of nano-SiO2 to SiC in the corresponding multiphase shear thickening liquid is 5~7:1~3.

3. The method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material according to claim 2, characterized in that, Step S1 includes the following steps: S101: Add nano-SiO2 to the dispersion medium PEG200 in portions and stir until a uniform suspension is obtained to obtain a shear thickening liquid without the reinforcing phase; S102: Add the modified additive CNC or SiC powder to the shear thickening liquid and stir evenly to obtain a multiphase shear thickening liquid sample containing the reinforcing phase. S103: Curing the multiphase shear thickening liquid sample at constant temperature and humidity for 12 hours to remove air bubbles and obtain the finished multiphase shear thickening liquid.

4. The method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material according to claim 3, characterized in that, The mass ratio of nano-SiO2 to PEG200 is 5~7:3~5.

5. The method for preparing a multiphase shear thickening liquid-Kevlar fiber composite material according to claim 3, characterized in that, The conditions for constant temperature and humidity curing in step S103 are: 30℃ and 95% humidity.

6. A multiphase shear thickening liquid-Kevlar fiber composite material prepared by the preparation method according to any one of claims 1-5.

7. The application of the multiphase shear thickening liquid-Kevlar fiber composite material as described in claim 6 in impact-resistant protective materials.

8. The performance testing method for the multiphase shear thickening liquid-Kevlar fiber composite material as described in claim 6, characterized in that, Includes the following steps, Step a: Electron microscopy experiments were performed on the multiphase shear thickening fluid-Kevlar fiber composite material; Step b: The multiphase shear thickening liquid was tested using room temperature rheological experiments and variable temperature rheological experiments; Step c: Perform quasi-static tensile mechanical tests on single yarns of the multiphase shear thickening liquid-Kevlar fiber composite material; Step d: Pull-out test of multiphase shear thickener-Kevlar fiber composite material under impact load; Step e: Perform drop hammer impact tests on the multiphase shear thickening liquid-Kevlar fiber composite material.

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