Application of fiber reinforced materials
Applications of fiber reinforced materials
Composed of reinforcing fibers and matrix. The diameter of the fiber (or whisker) is very small, generally below 10 μm. The defects are few and small, and the fracture strain is no more than 3%. It is a brittle material. Susceptible to damage, breakage and corrosion. Compared with the fiber, the matrix has much lower strength and modulus, but it can withstand larger strains, often has viscoelasticity and elastic plasticity, and is a tough material. Fiber reinforced composite materials can be divided into short fiber reinforced composite materials, long fiber composite materials and complex short fiber reinforced composite materials according to the length of the fiber. Due to the difference in fiber and matrix, there are many varieties of fiber reinforced composite materials, such as carbon fiber reinforced epoxy, boron fiber reinforced epoxy, Kevlar fiber reinforced epoxy, Kevlar fiber reinforced rubber, glass fiber reinforced plastic, boron fiber reinforced aluminum, graphite fiber reinforced Aluminum, carbon fiber reinforced ceramics, carbon fiber reinforced carbon and glass fiber reinforced cement, etc.
Fiber reinforced materials must first explain a concept, which is “composite materials”. Broadly speaking, composite materials refer to materials composed of two or more components (units) with different properties or different organizations. From an engineering concept, composite materials refer to new materials made by artificially combining two or more materials with different properties but complementary properties. The components of composite materials are divided into two parts: matrix and reinforcement. The continuously distributed components are usually called matrix, such as polymer (resin) matrix, metal matrix, ceramic matrix; substances such as fibers, particles, whiskers, etc. dispersed in the matrix are called reinforcements. As the name suggests, composite materials whose reinforcements are fiber substances are fiber reinforcements.
Common fiber reinforced composite materials [1~3] (Fibre Reinforced Plastics, referred to as FRP) include glass fiber reinforced composite materials (Glass Fiber Reinforced Plastics, referred to as GFRP), carbon fiber reinforced composite materials (Carbon Fiber Reinforced Plastics, referred to as CFRP), aromatic composite materials. Aramid Fiber Reinforced Plastics (AFRP for short). At present, CFRP and AFRP have been maturely researched and developed and widely used in civil engineering. Among them, CFRP is the earliest, mature technology and a high-performance fiber composite material used in the field of civil engineering so far. The application of AFRP in building materials is mainly for reinforcing concrete, which has a good reinforcing effect. It has been successfully used in bridges, docks, chemical plants and other facilities. The application forms of FRP mainly include fiber cloth (one-way and two-way), sheets (impregnated with adhesive), continuous fiber bars, fiber shells, various shapes of profiles, chopped fibers and combined structural systems. Because FRP reinforcing materials have: light weight; high specific strength and specific stiffness; good fatigue resistance; good vibration damping performance; Received date: 2004-03-31 The thermal expansion coefficient is similar to that of concrete and steel; (6) Resistance It has the advantages of corrosion, non-electromagnetic properties, designability and good processability, so it has received widespread attention in structural reinforcement and renovation projects. The application in the field of civil construction engineering is one of the important directions for the future development of FRP. FRP reinforcement and repair technology FRP reinforcement methods usually include two methods: pasting and winding, with pasting being the more commonly used method. The pasting method uses resin bonding materials as the matrix to paste the fibers on the surface of the structure or component to form a composite FRP body. Through its collaborative work with the structure or component, it can reinforce the structural component and improve the stress performance. Reinforcement method [9]. There are several bonding and reinforcement methods for FRP. The process route of the OBAYASHI-MITSUBISHI pasting method is as follows: Surface cleaning (polishing) Primer, putty, brush primer (resin), REPLARK (CFRP sheet), brush surface coating (resin), surface painting or finishing SIKA pasting method.
Grind the pasting area, apply a base layer of resin, level it, apply impregnated resin, paste CF, and then apply an impregnated coating cloth. Compared with traditional reinforcement and repair methods, pasting FRP reinforcement and repair of concrete structures has obvious technical advantages, which are mainly reflected in: convenient construction and high work efficiency. , has good operability, does not require large construction machinery and important equipment, and does not require a large working space. It takes up less space for construction and has a wide range of applications; the fiber cloth is light and thin, and the cross-section and load of the original structural components after reinforcement are The increase is not large and does not affect the function of the original building; the reinforcement construction will cause little disturbance to the existing structure, which can significantly improve the mechanical properties, durability and corrosion resistance of the existing structure without affecting the overall structure of the existing structure. Sex etc. There are two ways to apply FRP reinforcement and repair technology. One is directly applied to new structures, and the other is used for repair and reinforcement of old structures to achieve good architectural effects. FRP is mainly used in the repair and reinforcement of old structures in beams, slabs, columns and masonry structures. The application fields of FRP are mainly reflected in bridge structures, civil building structures and other fields. Current status of FRP application research In the 1960s, the United States began to develop FRP, and its research mainly focused on GFRP. However, research on GFRP was interrupted for nearly 20 years due to its low elastic modulus. Later, due to the degradation of building structures and bridge structures caused by salt corrosion of steel bars, the research on FRP was put back on the agenda. The South Dakota University of Mines and Technology developed a CFRP strand similar to steel strand (composed of 7 strands), and now other universities and research institutions are working on the research and application of FRP bars [11]. A project jointly conducted by California Polytechnic State University and Oregon State University not only conducted on-site research on a 3-span bridgeProcess methods such as plastic injection molding (RRIM) and structural reaction injection molding (SRIM). The types of reinforcement materials used include fiberglass mats, preformed materials, combined reinforcement materials, etc.
The ground fibers used in the RIM molding process are pre-mixed with resin before being injected into the mold. Preformed materials are mostly sprayed on a screen composed of directional fibers, chopped fibers and binders, or heated to form felt sheets, or a combination of methods is used to make preformed materials.
High-pressure closed-mold molding process: This type of process mainly includes injection molding, high-pressure compression molding and other processes. The reinforcement materials used are often pre-mixed with resin and then press-molded. Its production cost is relatively low.
BMC is a typical example. Thermosetting resin and chopped strands are premixed into a mass, and then pressed into fiberglass products. If chopped strands are mixed with thermoplastic resin, they can be made into granular materials, fed into a pultruder, and made into hot products. Plastic fiberglass products. If long fiber prepreg is used, the prepreg continuous untwisted roving can be pultruded to make thermoplastic pultruded fiberglass products.
SMC and GMT are two types of molding processes that use mixed-direction chopped untwisted roving and continuous raw yarns to perform a continuous impregnation process and then press into shape. In some cases, continuous roving is mechanically oriented to achieve higher mechanical strength and modulus.
Pre-impregnated tape: This is made by pre-impregnating continuous roving or two-way fabric with resin. For thermosetting resin, the prepreg is heated to reach the B-stage state. For thermoplastic resins, the B-stage state can be reached by cooling to room temperature. Regardless of thermoset prepreg or thermoplastic prepreg, they can be made into fiberglass products after being placed in a press and heated and pressurized.
4. Special properties of glass fiber
Due to the reinforcement of glass fiber, FRP materials have excellent properties that cannot be matched by matrix resins, such as the integrity of the material, which can reduce the weight of the material, high mechanical properties, impact resistance, corrosion resistance, and good dielectric properties. Performance and dimensional stability as well as material durability, etc., have made fiberglass materials widely used in various fields.
It should be noted that while making full use of the properties of glass fiber, it also has some important properties that have not been fully understood by people.
First, glass fiber has certain elastic properties. Glass fiber can be stretched under tension until it breaks, but there is no yield point. If the applied tensile force is released before reaching the breaking point, the glass fiber will return to its original length.
Second, glass fiber has no hysteresis. This is where glass fiber is completely different from metal fiber and organic fiber. Glass fiber, due to its high strength, can store or release large amounts of energy without losing this energy.
Third, glass fiber has dynamic fatigue resistance properties. Therefore, if a certain amount of anti-wear protection is added to the surface of glass fiber, its fiberglass products can become ideal materials for spring parts of cars and trucks, as well as household appliances.
However, since glass fiber has no yield point, it will suddenly break while its load-bearing capacity gradually weakens. For example, commonly used E-glass fiber unidirectionally reinforced composite materials often undergo stress fracture after a certain amount of time under a certain load. After testing, its tensile strength will decay over time. It decays very quickly initially and will lose 1/3 of its initial value. But then, it will take 50 years to decay to 1/2 of the original value.
What is the difference between fiber-reinforced and particle-reinforced composites
A general term for metal matrix composite materials that reinforce a metal or alloy matrix with particles such as carbides, nitrides, and graphite.
A metal matrix composite material that is easier to mass manufacture, process, form and has lower cost. It is also a relatively mature composite material in research and development.
This type of composite material has a wide composition range, and the base metal and reinforcing particles can be selected according to the working conditions. The commonly used particles include silicon carbide, titanium carbide, boron carbide, tungsten carbide, aluminum oxide, silicon nitride, and titanium boride. , boron nitride and graphite, etc., the particle size is generally 3.5~10μm, and some are also selected
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