Carbon fiber can be divided into standard modulus (200-280GPa), intermediate modulus (280-350GPa), high modulus (350-600GPa) and ultra-high modulus (600+GPa) carbon fiber according to the level of tensile modulus. In carbon fiber bicycles, the four grades of carbon fiber have specific applications. Due to the large price difference between the four types of carbon fiber, the price of carbon fiber bicycles is very different.
For engineers, building a carbon fiber frame is like assembling a complex 3D puzzle together. Bicycles can have hundreds of parts, assembled into 40 or more layers. To make it correct, designers need to rely on finite element analysis (FEA) software to help them determine where to use which grade of carbon fiber, and how to configure these modules in the best way to achieve strength, stiffness, and flexibility The ideal combination of sex.
Common misunderstandings about carbon fiber bicycles
Before understanding the specific application parts of the four types of carbon fiber in bicycles, let's discuss several common misunderstandings about carbon fiber bicycles.
Myth 1: Carbon fiber frames will not last as long as metal frames.
Reality: As long as the user doesn't need to crash the car or hit the frame with a hammer, the carbon fiber bicycle can theoretically be used forever. In fact, the use time of steel and aluminum bicycles is largely limited by the fatigue life of metals. Once fatigue damage occurs, the bicycle cannot be used safely, but the fatigue resistance of carbon fiber can ensure that it remains stable indefinitely.
Misunderstanding 2: The damaged carbon fiber frame cannot be repaired.
Reality: Shawn Small, head of Ruckus Composites points out: "In many cases, carbon fiber is easier to repair than aluminum bicycles." His shop repairs 1,500 bicycles every year. In order to repair the damaged frame, Ruckus removed the damaged part, laid a layer of carbon fiber prepreg on the gap, and then repainted the bike.
Myth 3: Carbon bicycles are more fragile than aluminum or steel bicycles.
Reality: The carbon fiber frame is relatively strong and can withstand considerable forces, but the premise is that it must be applied in the direction expected by the engineer (such as road vibration caused by potholes). However, if the force comes from an unexpected direction, such as hitting a tree or stepping on an accelerator pedal, the material is very fragile and may break.
Myth 4: The carbon fiber bike frame will be damaged under the scorching sun.
Reality: Actually, this is very safe. Bicycle manufacturers use UV-resistant paint or wax to protect the frame from potentially harmful rays.
Different grades of carbon fiber used in bicycles
1. Standard modulus carbon fiber
The tensile modulus is 200-280 GPa; the tensile strength is 2500 MPa or higher.
Relatively rigid, this is the cheapest form of carbon fiber, almost only used in entry-level frames.
Mainly used for full pipes, pipe joints, high stress areas around the head pipe, down pipes and chains.
2. Intermediate modulus carbon fiber
The tensile modulus is 280-350 GPa; the tensile strength is 3500 MPa or higher.
The carbon fiber with the highest strength among all carbon fibers is mainly used in high-end frames.
It is mainly used in high-strength areas, such as bendable support frames, and areas with strict requirements on strength, such as parts of the upper tube, down tube, and head tube.
3. High modulus carbon fiber
The tensile modulus is 350-600 GPa; the tensile strength is 2500 MPa or higher.
The hardness of this carbon fiber is 62% higher than the standard modulus on average, but it is more fragile. In general, high-end bicycles may contain 25% of high-modulus fibers.
Mainly used in areas that require additional lateral stiffness, such as downtubes, seat tubes or rear forks.
4. Ultra-high modulus carbon fiber
The tensile modulus is 600+ GPa; the tensile strength is 2500 MPa or higher.
The hardest type of carbon fiber. It is brittle and very expensive. It is selectively used for top bikes. Although top bikes usually use higher-strength mid-model carbon fiber, even so, ultra-high modulus carbon fiber sometimes even reaches 15%.
Mainly used in low impact areas, such as the center of the top tube.