Aramid fiber has the characteristics of high specific strength and high elongation at break, and can completely replace glass fiber/resin composite materials in many fields.
At present, countries all over the world are constantly developing and optimizing various new ballistic materials to enhance the ballistic protection performance of vehicles and individual soldiers. High-performance fiber composite materials have the characteristics of light weight, high strength, and excellent ballistic resistance. They are the most researched, fastest-growing and most promising ballistic materials. The military developed countries represented by the United States pay special attention to the development of high-performance anti-ballistic fibers and their composite materials. National defense scientific research institutions such as the US Army Research Laboratory and universities funded by the Ministry of Defense have carried out a lot of research work in recent years. This article mainly introduces the research and development, application status and performance level of aramid fiber, carbon fiber and PBO fiber abroad.
1. Aramid fiber
Aramid fibers have the characteristics of high specific strength and high elongation at break. Under the same surface density, the ballistic resistance of aramid/resin composites is 2 to 3 times that of glass fiber/resin composites. It can be used in many fields. Comprehensive replacement of glass fiber/resin composites.
Institutions such as the Joint Army Research Laboratory of Clemson University in the United States use the traditional finite element method to conduct numerical analysis of the anti-ballistic fiber mat to determine the penetration resistance of the material and the overall deflection, deformation, and damage response to impact. The researchers of the team have further optimized and upgraded the ballistic impact/explosion protection calculation and analysis model of flat-woven fiber-reinforced polymer matrix composites. In 2014, the relationship between the microstructure and performance of PPTA (poly-p-phenylene terephthalamide)-based materials was studied, and a multi-length scale calculation method was developed to determine the impact of various microstructural features on different scales on the PPTA-based felt. Effect of cloth or PPTA fiber reinforced polymer matrix composites on macroscopic ballistic penetration resistance.
Cassino in Italy and the University of Southern Lazio combined plain weave felt with thermosetting resin to make laminates, and conducted Walker numerical model prediction and ballistic performance tests on the prepared composite armor. U.S. Army Research Laboratory et al. used flat strip-shaped transparent nylon monofilament as reinforcement, and prepared a composite material with a light transmittance of about 40% with a transparent epoxy resin matching its refractive index as a matrix. The ballistic test of the material shows that the V50 value of the obtained material is greater than 305m/s, which is much higher than that of epoxy resin and polycarbonate.
The Sandia National Laboratory of the United States studied the influence of twisting on the transverse impact properties of elastic fiber yarns, and measured the Euler shear wave velocity induced by the impact with a high-speed camera. The results show that the Euler shear wave velocity increases with the number of twists in the fiber yarn, implying higher ballistic performance. Therefore, the use of twisted fiber yarns in ballistic fiber mats can improve the ballistic properties of the material. The effect of magnetic field on the ballistic properties of aramid fiber and ultra-high molecular weight polyethylene fiber was studied. The researchers sandwiched aramid fibers and ultra-high-molecular-weight polyethylene fibers between two sets of opposite rare-earth magnets to test the effect of magnetic field repulsion on the ballistic properties of the materials. The results show that magnetic repulsion can inhibit bullets from entering the front panel of aramid fibers.
Nanomodification of aramid fibers or nanofilling of their composites will also improve ballistic properties. The researchers enhanced the interfacial strength by growing vertical ZnO nanowires on the fiber surface. The interface strength of the fiber is 96.9% higher than that of the bare fiber, and the peak load of the pull-out test is increased by 6.5 times. The ZnO nanowires enhance the pull-out performance of the fibers, which in turn also increases the ballistic impact protection level of the material.
The researchers studied the effect of nanoparticle fillers on impact-resistant composites, and conducted V50 ballistic tests on fiber composites filled with ground carbon fibers and nanoparticles (carbon nanotubes and core-shell rubber particles). The results show that the nano-core-shell rubber particle filler is effective for energy absorption during impact due to the cavitation effect, and also significantly improves the ballistic performance. Carbon nanotube fillers can improve the matrix-fiber interface performance, and also significantly improve the ballistic performance. The two can enhance the V50 anti-ballistic performance of the composite material. Adding 1% mass fraction of milled carbon fibers and adding 1% nanoparticles to the composite material can increase V50 by 7.3% (carbon nanotubes) and 8% (core-shell rubber particles) relative to the reference sample, respectively.
2. Carbon fiber
The Young's modulus of carbon fiber is usually more than three times that of traditional glass fiber, and it has important application potential in lightening military equipment and improving survivability. In 2015, the Georgia Institute of Technology in the United States developed a new process for the preparation of gel-spun continuous carbon fibers based on polyacrylonitrile (PAN) spinning technology. The average tensile strength of the prepared PAN-based carbon fibers is between 5.5 and 5.8 GPa. , the tensile modulus is between 354 and 375GPa, and the tensile modulus is 25% to 36% higher than that of the IM7 type PAN-based carbon fiber widely used in aerospace. highest value combination. In the future, by optimizing materials and processes, the strength and modulus of PAN-based carbon fibers will be improved simultaneously.
3. PBO fiber
PBO fiber was originally developed by the U.S. Air Force, and later products were manufactured by Japanese companies. PBO fiber is known as a future ultra-high performance fiber that can replace aramid fiber. This fiber has a lower density than aramid fiber, but its mechanical properties and environmental resistance Far superior to other aramid fibers.
In 2006, the University of California signed a contract with the US Army to conduct ballistic tests to determine the ballistic performance of Zylon fibers. The results show that Zylon fiber has better performance than Kevlar29, and when used in armor, it will effectively enhance protection performance and mobility. Although PBO fibers have the advantages of light weight, high strength and high modulus, they are limited by the degradation of mechanical properties during use in protective applications. In order to solve this problem, the researchers developed a post-treatment process of supercritical CO2 chemical reagent diffusion to treat PBO fibers, so as to reduce the decline rate of its mechanical properties and prolong its service life. Researchers from the University of Massachusetts Amherst studied the stabilization of PBO fibers after supercritical CO2 post-treatment, using supercritical CO2 as the extractant to extract the residual phosphoric acid and water on the PBO fibers, and using it as a medium to introduce a variety of The substance neutralizes phosphoric acid and weakens the degradation effect of water and acid on PBO fiber.
Lamination of ballistic fibers can be a factor in performance degradation. The researchers investigated the effect of folding on the performance degradation of ballistic PBO fibers, and determined experimentally the impact of this failure mechanism on armor protection performance. They also further investigated the effect of folding on the internal structure of the elastic fibers. Japanese researchers have done a lot of research on PBO fibers. For example, they have studied heat treatment to improve the tensile and fatigue strength of high-modulus PBO fibers, and studied the influence of shear rate on the tensile strength of high-modulus PBO fibers.
