Bicycle carbon fiber is an inorganic polymer fiber with a carbon content of more than 90%. Which carbon content is higher than 99% of the graphite fiber. The microstructure of carbon fiber is similar to artificial graphite, which is a strabospheric graphite structure.

The spacing between carbon fiber layers is about 3.39 to 3.42A. The arrangement of carbon atoms between parallel layers is not as regular as that of graphite. The layers are connected by van der Waals force.

The structure of carbon fiber is usually considered to be composed of two-dimensional ordered crystals and pores, in which the content, size and distribution of pores have a great influence on the performance of carbon fiber.

When the porosity is lower than a certain critical value, the porosity has no obvious effect on the interlaminar shear strength, bending strength and tensile strength of carbon fiber composites. Some studies have pointed out that the critical porosity that causes the degradation of the mechanical properties of the material is 1%-4%. When the pore volume content is in the range of 0-4%, the interlaminar shear strength decreases by about 7% for every 1% increase in pore volume content. Through the study of carbon fiber epoxy resin and carbon fiber double maleimide resin laminates, it is found that when the porosity exceeds 0.9%, the interlaminar shear strength begins to decrease. It is known from the test that the pores are mainly distributed between the fiber bundles and at the interface between the layers. And the higher the pore content, the larger the pore size, and significantly reduce the area of the interlayer interface in the laminate. When the material is stressed, it is easy to break along the interlayer, which is also the reason why the interlayer shear strength is relatively sensitive to the pore. In addition, the pore is the stress concentration area, the bearing capacity is weak, when the force, the pore expands to form a long crack, which is destroyed.

Even if two laminates with the same porosity (using different prepreg methods and manufacturing methods in the same curing cycle), they show completely different mechanical behavior. The specific values of mechanical properties decrease with the increase of porosity are different, which shows that the effect of porosity on mechanical properties is large and the repeatability is poor. The effect of porosity on the mechanical properties of composite laminates is a complex issue due to the large number of variables involved. These factors include: the shape, size, and location of the pores; the mechanical properties of the fibers, matrix, and interfaces; and static or dynamic loads.

Compared with porosity and pore aspect ratio, pore size and distribution have a greater impact on mechanical properties. It is found that large pores (area> 0.03 mm2) have a negative effect on mechanical properties, which is attributed to the effect of pores on crack propagation in the glue-rich zone between layers.