With the rapid development of cycling in China, many cyclists intend to buy or already own carbon fiber bicycles, but there are still many cyclists who do not have a detailed and systematic understanding of the performance of carbon fiber materials. We often encounter cyclists asking me, How long can the carbon fiber frame and wheel set last? Is intensity feasible? Will your frame break when I weigh 120 pounds? So what exactly is carbon fiber? How good is his intensity? Today I will lead you riders to know about carbon fiber.
What we usually call a carbon fiber frame is actually more accurately called a carbon fiber composite frame, which is a type of fiber reinforced composite materials. It is composed of carbon fiber and epoxy resin. In CFRP, we call carbon fiber a reinforcing material, which is the dispersed phase, and the resin as a matrix material, which is the continuous phase. Therefore, becoming one of the first-choice materials for high-end bicycles is determined by its own mechanical and chemical properties.
1. The specific strength (strength-density ratio) and specific modulus (modulus-density ratio) are high. This results in a frame of the same strength that can be made very light by using CFRP (carbon fiber composite material). The following compare the mechanical properties of several common structural materials
Material Density (g/cm3) Tensile strength (Gpa) Elastic modulus (Gpa) Specific strength Specific modulus
steel 7.8 1.010 206 0.13 26
Aluminum 2.8 0.461 74 0.17 26
Titanium 4.5 0.942 112 0.21 25
CFRP two 1.45 1.472 137 1.02 95
CFRP-1.6 1.050 235 0.66 147
2. Good fatigue resistance
The fatigue failure of general metal materials is sudden failure without obvious signs, while CFRP has good fatigue resistance, and there are obvious signs before failure. Several CFRP cars of the Hebei Mountain Team showed visible cracks, but still retained most of their strength, which greatly improved the safety of riding. Reason: The reinforcing fiber is finer and there are fewer defects. The matrix has good plasticity and can inhibit the development of cracks. Of course, because it belongs to cutting-edge materials, technology and quality control, it is still immature and has yet to be tested by practice.
3. Good damage safety
There are thousands of independent fibers in the cross section of CFRP. Even if some of the fibers are broken due to overload, the load will be quickly redistributed to the undamaged fibers, so as not to cause the component to lose its load-bearing capacity and break in an instant.
4. Strong shock absorption
(1) CFRP has a large specific modulus, high natural frequency, and it is not easy to resonate
(2) CFRP is a heterogeneous multiphase system. There are a large number of interfaces between the fiber and the matrix. Because the interface can reflect and absorb vibration, CFRP has strong vibration damping and can quickly attenuate the vibration.
5. Good high temperature performance
Carbon fiber can withstand a high temperature of about 2000 degrees Celsius without changing its strength. Therefore, the overall temperature resistance of CFRP depends on the epoxy resin as the matrix. The heat resistance of various grades of epoxy resin is different, and additives will also be produced. influences. The CFRP frame will have no problems in this respect
6. Good aging resistance
Once when shopping in Beijing, a shop assistant asked this question. The carbon fiber in CFRP will be oxidized by oxygen in the air when it is above 500 degrees Celsius, and it is completely protected by the matrix. The aging resistance of the base material epoxy resin with appropriate additives is also very good, and the general service life is 20 years. So the CFRP frame will be mechanically damaged first, so don’t worry about its chemical aging
7. Strong designability
Everyone knows, let’s not say much
Well, my wrist is sore. Originally, my typing was slow and it was very hard. This time I will stop here. Next time I will introduce the two components of CFRP and the composite process.
Fiber composite material is a combination of two or more materials with different properties. Its structure includes fiber, matrix and interface. These three aspects will affect the performance of CFRP. The fiber in CFRP is carbon fiber, which is used to bear the load, and the matrix is used to protect the fiber laying form, allow the fiber to bear compression and shear load, distribute the load, and protect the fiber.
Let’s briefly introduce carbon fiber, epoxy resin, and composite process.
Carbon fiber is usually made by firing raw silk, and most of the carbon fiber in the CFRP of the frame is made by firing polyacrylonitrile (PAN).
PAN precursor (air pre-oxidation at 200-300 degrees Celsius) becomes flame-resistant fiber (under the protection of 800-1500 degrees inert gas) and becomes carbon fiber (2000-300 degrees inert gas). Graphite carbon fiber contains up to 98% carbon and is similar to graphite. Layered crystalline structure
"EPOXY RESIN" refers to a linear organic polymer compound containing two or more epoxy groups in the molecule. CFRP matrix is an insoluble and infusible three-dimensional network polymer formed by cross-linking and curing of epoxy resin and curing agent, or self-curing. There are many types and grades of epoxy resins, so I won’t introduce them here.
The composite method mainly includes prepreg method, injection molding method, compression molding method and so on. Zhengzhou Institute of Light Industry used the compression molding method to make CFRP bicycle frames, and Juhan Technology, a subsidiary of Taiwan Giant Machinery (Giant), used the prepreg coiled tube method.
A brief introduction to the huge craft
The semi-finished products that the continuous fiber or fabric is pre-impregnated with resin after a certain treatment are called prepregs. One-way, two-way or three-way braid (other fibers such as KEVLAR or titanium wire can be added at this time to improve performance), transported to the resin tank through the wire feeder to impregnate the solution-like resin, and then dry the solution in the resin through the drying box , And then wound into rolls for later use. What is used is not resin solution, but molten resin, which becomes the dry method. The resin content of the prepreg made by the dry method is relatively uniform, and the hidden dangers that affect the interlayer shear strength of CFRP are reduced, but the equipment is more complicated and the investment is relatively large.
After the prepreg is completed, it enters the solid molding. After the prepreg is cut, divided and weighed, (a GIANT TCR is about 500 slices of different shapes and paste) The staff responsible for the plasticity of each part of the frame will slice and paste the soft prepreg by hand To the mold. Then the parts are spliced and sent to a heating furnace for heating and curing. After curing, after polishing, drilling, painting and other post-processing, a CFRP frame was born.
Taiwan began to study T carbon fiber as early as the late 1970s. The private Feng Chia University and the Catalyst Research Center of Taiwan China Technical Service Corporation are more representative units. There are also many supporting manufacturers. For example, carbon fiber and epoxy resin have formed a certain production capacity. The output of carbon fiber is second only to Japan in Asia, but there is still a gap in quality. The huge carbon fiber raw materials are imported from Japan's Toray Company. Taiwan’s CFRP bicycles were first made of aluminum alloy joint CFRP frames developed by Huge Machinery in 1987. Later, with the cooperation of the Industrial Technology Research Institute, the second-generation one-piece CFRP frame was completed in 1993, and then the third-generation design was developed successively. Gradually establish its own brand, the highest peak annual output is 80,000, occupying 70% of the international market. Due to the unstable process and price, the market is not easy to develop. It fell to 50,000 in 1997 and continued to decline in 1998.
In 2016, Toray developed a technology to improve the surface smoothness of thermosetting CFRP (carbon fiber reinforced resin matrix composite material). The CFRP sunroof (roof) using this technology is equipped on the new concept car "TEEWAVE AC1", which has been unveiled at the internal exhibition "Toray Advanced Materials Exhibition 2016" which opened on October 6, 2016. In the new technology, after infiltrating the epoxy resin as the base material, before pressing, the epoxy resin is injected into the mold again to increase the thickness of the surface resin, and then it is hardened. After demolding, the surface is painted and polished. It can be seen that the arrival of new technologies and materials has gradually changed our way of life. At the same time, with the advancement of technology and the maturity of the craft, the price gradually drops. Carbon fiber bicycles have withstood the test of actual use and the market and are gradually approaching our life circle.