In the past half-century, fiber-reinforced composites have been widely used because of their excellent properties, and the important role of fiber-reinforced composites is self-evident. Since the emergence of composite materials, reinforced fibers have undergone a transformation from natural fibers to synthetic fibers.
At present, the most common reinforcement fibers include glass fiber, aramid fiber, carbon fiber, etc. This paper will first briefly introduce the common reinforcement fiber types.
In composite materials, the main role of the resin matrix is to bond the fibers together and transfer external loads from one fiber to the next. Most reinforced fibers are bent and floppy, and if tension is applied to them, they will have sufficient tensile strength and stiffness.
Reinforcement fibers are usually bundles, and individual fibers tend to be very fine, such as glass fibers and carbon fibers with a typical diameter range of 5 to 25 microns. For comparison, human hair is usually between 50 and 200 microns in diameter. All fiber-reinforced "structures" can be derived from filament fibers, including tow, yarn, chopped fiber, milled fiber, etc.
Common reinforcement fibers include glass fiber and carbon fiber.
1. glass fiber
There are many different varieties of fiberglass, but for composites, two are the most common. E-glass fiber is the standard type in almost all fiberglass-reinforced products, while S-glass fiber (also known as R-glass or T-glass fiber) has significantly better tensile strength.
S-glass fiber is usually smaller than E-glass fiber, has better adhesion in the resin matrix, and the impact performance is improved. But it costs a lot more. S-2 glass fiber is a higher-strength commercial S-glass fiber, which has twice the tensile strength of typical E-glass fiber and also has about 10-20% higher stiffness. But for almost all applications, E-glass fiber is sufficient.
Fiberglass is made by extruding molten (1700℃) mineral products (silica, aluminum and calcium oxide, etc.) through small diameter holes. Typically, E-glass fibers are about 10-25 microns in diameter, making them larger than carbon fibers.
2. carbon fiber
Carbon fibers come in many varieties, with varying mechanical properties and costs. The carbon fiber is not extruded directly from the molten material but is made by heat treatment of the precursor fiber, including pre-oxidation in an air atmosphere and carbonization in an inert atmosphere. Under tension, the carbon structure within the fiber aligns, helping to maximize tensile strength and stiffness.
The most common precursor used for carbon fiber is polyacrylonitrile (PAN) fiber. At present, the most common standard and medium modulus carbon fiber are based on PAN precursor. The modulus of carbon fiber prepared by the asphalt precursor system is usually higher. Depending on the properties of the precursor, the diameter of the fiber, and the details of the heat treatment (oxidation, carbonization, graphitization) process, the resulting carbon fiber has a wide range of mechanical properties.
A single carbon fiber is typically smaller than a glass fiber, just 5 microns in diameter. modulus modulus modulus Carbon fiber is often classified with Standard modulus and Intermediate modulus, especially with modulus. IM), High modulus (HM), and Ultra-high modulus carbon fiber.
3. Other commonly used reinforcing fibers
Kevlar Aramid Fiber:
A synthetic aramid fiber developed by DuPont. Other commercial aramid fibers include Twaron, Technora, and Nomex. As a reinforcement fiber for composite materials, aramid fiber is mainly used for applications with high tensile strength and puncture, wear, and breakage resistance. Aramid fibers are often difficult to bond, cut, and handle, and are often used in combination with carbon fiber or glass fiber.
Basalt fiber:
made by using a melting and extrusion process similar to glass fiber. Its tensile strength and modulus are slightly higher than E-glass fiber but less than carbon fiber. The density is similar to that of E-glass fiber. The price is between E-glass fiber and carbon fiber. There is a limited supply of composite-grade basalt, which is usually brown in color.
Ultra-high Molecular weight Polyethylene:
Both Dyneema and Spectra are fibers made from ultra-high molecular weight polyethylene (UHMWPE) or high modulus polyethylene "(HMPE) extruded filament. UHMWPE is used for tug cable, bowstring, fishing line, and vehicle armor and is rugged and durable. These fibers can be used in composite applications, often mixed with carbon fiber. Dyneema/ carbon fiber hybrid reinforcement can improve the toughness of laminates, energy absorption, and impact resistance of carbon fibers. Spectra fabrics can be applied topically to increase wear resistance.
High Molecular weight polypropylene:
Innegra is a fiber made by Innegra Technologies from high molecular weight polypropylene (HMPP). While not as strong as Kevlar or Dyneema, Innegra is tough and resistant to impact and breakage at a lower cost. Often Innegra is used as a component of hybrid reinforcement material, mixed with carbon fiber or glass fiber to increase the toughness of laminate.
Plant fibers:
While fiberglass and carbon fiber is the most common reinforcing fibers, the oldest structural reinforcing fibers are wood and plant fibers. In the past decade, there has been a resurgence of interest in laminate plant fibers, especially flax and jute, which offer useful mechanical properties and offer similar processing to standard fiber types. One challenge plant fibers face is a much wider range of mechanical properties than traditional engineered materials, and they are not as strong as regular E-glass fibers. Moisture absorption is a problem for all bio-based composite reinforcement materials, which can cause problems for many composite processes.
Ceramic fibers:
Ceramic matrix composites (CMC) have similar mechanical properties to carbon fiber composites but have extremely high-temperature resistance. They are usually broken down by oxide and non-oxide fibers, depending on their chemical composition. On the non-oxide side, boron is one of the best-known ceramic reinforcing materials, with incredible compressive strength. Silicon carbide (SiC) fibers have high strength and stiffness and are very hard. Oxide-based fiber has higher oxidation resistance but lower mechanical properties.
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