With the application of advanced technology in military warfare, the situation of personnel and property losses is becoming more and more complex. Therefore, in-depth research and application of bulletproof materials should also be conducted. Ceramic armor and fiber-reinforced composite materials are important research and application directions. An overview of the new composite bulletproof ceramic plate and aramid bulletproof composite materials is given, a comparison between the new composite bulletproof ceramic plate and the traditional bulletproof plate is carried out, and its characteristics and some problems that still exist in current research and application are analyzed; the bulletproof mechanism of the aramid bulletproof composite material is carried out. Describe in detail and point out the main factors affecting the performance of aramid ballistic composite materials.
01
New composite ceramic bulletproof plate
Research on ceramic armor is an important part of the development and application of bulletproof composite materials. The ballistic protection effect of ceramic armor is superior to that of ordinary armor steel. Currently, passive armor and reactive armor are the most widely researched and applied. In terms of bulletproof mechanism, the armor material in reactive armor will generate kinetic energy after being excited by the bullet, and the kinetic energy reacts on the bullet, while passive armor resists the impact of the bullet through its own characteristics. Today, the United States, Russia and other countries have used ceramics and composite materials to develop armor systems with better weight efficiency, and developed ceramic panel armor, which has been widely used.
1.1 Bulletproof mechanism
When a bullet hits the composite ceramic bulletproof plate at high speed, the principle of action force and reaction force is used to cause it to enter the bulletproof plate at high speed and then bounce out at high speed with the opposite force inside, forming an approximately circular bullet hole on the surface. It achieves the purpose of destroying only the surface of the bulletproof plate without causing fatal damage to the overall composite bulletproof plate, thereby achieving bulletproofing.
1.2 Performance parameters of new composite ceramic bulletproof plates
The main characteristics of ceramic materials are shown in Table 1.
Ceramic materials have high specific stiffness, high specific strength and chemical inertness in many environments. At the same time, their low density, high hardness and high compressive strength compared to metals make them more widely used. High-purity aluminum has higher density, lower hardness and fracture toughness, so its elastic resistance is lower; the structure of silicon carbide ceramics makes it have high strength, high hardness, wear resistance, corrosion resistance, high thermal conductivity and other properties; Titanium diboride has a high elastic modulus; boron carbide has a high melting point, excellent hardness and mechanical properties, and its density is the lowest among several commonly used ceramic materials. In addition, the elastic modulus is high, making it an ideal choice for military armor. and a good choice of materials in the space field.
The main characteristics of composite materials are shown in Table 2.
In addition to having a certain modulus, bulletproof composite materials must also have good elongation, fracture toughness, high specific strength and be able to maintain good performance under strain rates. E-glass has high tensile strength but poor toughness, while Kevlar material has low density, high strength, good toughness, high temperature resistance, and is easy to process and form. Boron has the characteristics of low density, high specific strength and high elastic modulus.
1.3 Characteristics of new composite ceramic bulletproof plate materials
New composite ceramic bulletproof panels have incomparable advantages over traditional bulletproof panels. See Table 3 for specific comparisons.
(1) Can withstand multiple bullet strikes. This material can withstand the continuous impact of multiple bullets on the same surface at the same time without the whole being broken. It will only form approximately circular bullet holes on the surface without affecting the bulletproof effect of other parts of the material.
(2) It has good structural designability. Composite ceramic plates can produce bending deformation at corresponding angles, and can return to their original shape after deformation. They can be designed into composite ceramic bulletproof materials in various shapes such as flat, curved and inclined surfaces.
(3) Can be repaired and reused. After being hit by a bullet, the circular bullet holes on the surface can be filled with ceramic bulletproof bodies and recombined with bulletproof glue to regain the performance of the original material.
(4) High reliability in use. This material comprehensively uses the ballistic properties of high-performance ceramic plates, UHWMPE plates and TC4 plates, making the ballistic resistance better than that of single materials, and can effectively block various specifications of pistols and related small and medium-caliber penetrating bombs.
(5) The technology has high maturity and strong designability. This material already has a fairly mature production process and can be designed according to individual needs according to actual needs to meet different bulletproof needs.
1.4 Problems with current bulletproof composite materials
Since bulletproof composite materials are composed of a variety of materials, the inhomogeneity, anisotropy, complex constitutive relationships, complex failure mechanisms, and complex strength criteria of composite materials are the main mechanics of composite materials and their structures. characteristics, thereby increasing the complexity and difficulty of analysis, calculation, testing and design of composite materials, their structures and protection mechanisms. Up to now, bulletproof composite materials still have the following problems.
(1) Insufficient energy absorption. The unabsorbed energy of bulletproof materials during use will cause losses to personnel and property, and the destructive power of weapons will also increase with the upgrade of weapons. Therefore, future research and application should focus on improving the bulletproof performance and safety of materials in this aspect. .
(2) The weight is not light enough. The weight of bulletproof composite materials is an important factor in whether they can be promoted and used. Therefore, the weight of bulletproof composite materials should be reduced as much as possible while ensuring good bulletproof resistance.
(3) Strengthening and toughening contradictions. Especially for bulletproof ceramic composite materials, this contradiction is often difficult to overcome. Adding certain toughening materials to ballistic-proof composite materials may reduce the strength of the material. However, if the strength of the material is increased, the toughness of the material may be reduced. Therefore, many tests are required to find the most suitable strength and toughness of the ballistic-proof material. .
(4) Regarding the compatibility of composite materials, including physical, chemical, mechanical and other material characteristics, composite materials can integrate various characteristics to provide better protection.
In addition, there are also issues such as interface and price, which have not been completely resolved.
02
Aramid bulletproof composite material
2.1 Bulletproof mechanism
When the fiber bulletproof material is subjected to impact energy, it will stretch and deform. The energy absorbed by the fiber will become the work required for its deformation. The work required for its tensile deformation and fracture is the fracture energy, also known as the work of fracture. , the fracture energy of the fiber is related to the number of fibers participating in tensile deformation fracture. The parameter that measures the anti-ballistic properties of fibers is the fiber's energy absorption rate (breaking energy per unit mass of fiber).
When fiber bulletproof materials are impacted by an external impact, the longitudinal stress generated by the impact will rapidly propagate in all directions in the fiber material, forming a "shock wave" (i.e., sound wave). The speed of sound in fiber bulletproof materials will affect the instantaneous diffusion of energy, which determines the amount of fibers involved in energy absorption, thereby affecting the bulletproof effect of the material. Therefore, the speed of sound in the fiber is another important parameter that affects the ballistic performance of the fiber.
The shapes of fibers in bulletproof materials include straight and curved. If the fiber shape of the material is straight, the energy will propagate along the axial direction of the fiber without reflection, and the energy will therefore spread far and fast; if the fiber shape is curved, or the fiber If there are breaks in the fiber, the bending points or breaks in the fiber will reflect part of the energy, reducing the instantaneous diffusion range, and the bulletproof effect of the material will also be reduced. It can be seen that the bulletproof effect of fiber two-dimensional two-dimensional cloth will be better than that of plain weave cloth.
The transfer of energy is often accompanied by contact between fibers within the same layer or between layers. During the transmission of impact energy, energy reflection occurs within the interfaces of all materials, and the situations are diverse and complex. Therefore, the most effective propagation path of impact energy is diffusion along the fiber axis.
2.2 Main factors affecting the performance of aramid bulletproof composite materials
The performance of bulletproof composite materials is mainly affected by the modulus and content of the matrix material, the properties of the fiber material, the weaving method and process of the fiber.
2.2.1 Effect of matrix resin modulus on ballistic properties of composite materials
Because low-modulus matrix resin has good damping properties and is conducive to energy absorption, laminates made of low-modulus matrix resin have better bulletproof effects than high-modulus matrix resin.
2.2.2 Effect of matrix resin content on ballistic properties of composite materials
The matrix resin content has a very important impact on the ballistic properties of composite materials. Increasing the fiber volume content in composite materials will improve the ballistic properties, but if the fiber volume content is too high, the ballistic properties will decrease. Because the matrix resin in the composite material can transmit stress in the structural unit, but if the fiber volume content is too high, the matrix content in the composite material will be too small, resulting in a reduction in the bonding performance between the resin and the fiber and between the fiber and the fiber, thus Affecting the integrity of the laminate, the elastic properties of the composite material will also decrease. Fiber volume content refers to the percentage of fiber volume in the fabric to the entire volume of the fabric, which can be converted into area density. Area density is an important factor in measuring the actual applicability of bulletproof panels. If it can meet the protection requirements, the area density should be as small as possible during design and application, so that the cost and weight can be greatly reduced.
2.2.3 Effect of laminate area density on laminate ballistic performance
There will be a tendency for fibers to slip when projectiles penetrate the laminate, and some fibers will not be able to reduce projectile penetration. If the areal density increases, the absorbed energy of the laminate will increase, indicating that its ballistic resistance increases with the increase in areal density. The ballistic performance of the weft-free laminate is better than that of the plain weave laminate.
2.2.4 Effect of fiber fabric structure on ballistic properties of laminates
Compared with satin and plain weave fabrics, two-dimensional two-dimensional fabrics have the lowest degree of processing and the smallest loss of fiber strength. The fibers of the fabric will be arranged in parallel in straight lines, with the largest strength retention value. Since there are no direct overlapping points between fibers, the shrinkage rate is basically zero, which effectively reduces the reflection of strain waves and avoids stress concentration at local points when projectiles impact. Therefore, the rupture absorption energy of the two-dimensional two-dimensional cloth is high. Because the fabric structure of the two-dimensional two-dimensional fabric is loose, it is conducive to energy absorption, making it the best bulletproof performance.
2.2.5 Effect of the number of fabric layers on the ballistic properties of laminates
Low surface density fabrics have better ballistic properties. The ballistic resistance of composite materials is determined by the braided threads used for the fibers in the material, the fabric weave, the number of layers in each layer, and the arrangement of the fibers. Under a given weight, the thinner and tighter the braid and the more layers the material has, the better the material's ballistic properties will be. When the surface density of the ballistic material is constant, fabrics with more layers and smaller single-surface density should be considered. At the same time, improving the performance of the fiber itself will also improve the ballistic resistance of the material.
03
Applications and Development Trends
Advanced ballistic-resistant composite materials have high specific strength, specific modulus, design and versatility, and are indispensable in many military applications. They are basic factors in design and key technologies for personal protection and advanced weapons and armaments. Therefore, for an organization, if it can enter this research and application field and become a qualified supplier of a certain type of product, it will be of great strategic significance in terms of both social and economic benefits.
Composite materials have good performance because they combine the respective advantages of reinforcement materials and matrices. They are also the fastest growing and most promising bulletproof materials. Bulletproof materials are gradually developing into diversification and compounding, and various new bulletproof materials with high hardness and high toughness have emerged to deal with more complex protection problems. With the development of lightweight and efficient armor systems, the advantages of bulletproof ceramics and fiber-reinforced bulletproof composite materials have become increasingly prominent. New composite ceramic bulletproof panels have incomparable advantages with traditional bulletproof panels, but the existing problems cannot be ignored, so we focus on In order to solve the problems existing in bulletproof composite materials, continuous optimization of material properties is the current research focus.
