Carbon fiber rims have a greater impact on mechanical properties in terms of pore ratio and pore aspect ratio, pore size and distribution. It was also found that large pores (area >0.03mm2) have a negative impact on mechanical properties, which is attributed to the impact of pores on crack propagation in the glue-rich area between layers.
The distance between the layers of a carbon fiber rim is about 3.39 to 3.42A. The arrangement of carbon atoms between the parallel layers is not as regular as that of graphite, and the layers are connected together by van der Waals forces.
The structure of carbon fiber rims is usually considered to be composed of two-dimensional ordered crystals and pores. The content, size and distribution of pores have a greater impact on the performance of carbon fiber rims. When the porosity is lower than a certain critical value, the pores The rate has no obvious effect on the interlaminar shear strength, flexural strength and tensile strength of carbon fiber rim composite materials.
Some studies have pointed out that the critical hole rate that causes the mechanical properties of materials to decline is 1%-4%. When the pore volume content is in the range of 0-4%, for every 1% increase in the total pore volume, the interlaminar shear strength decreases by approximately 7%. Through research on carbon fiber rim epoxy resin and carbon fiber rim dual maleimide resin laminates, it can be seen that when the porosity exceeds 0.9%, the interlaminar shear strength begins to decrease. It is known from experiments that pores are mainly distributed between fiber bundles and at the interface between layers. And the higher the pore content, the larger the size of the pores and significantly reduces the area of the interlayer interface in the laminate. When the material is stressed, it is easy to be damaged along the layers, which is why the interlayer shear strength is relatively sensitive to pores. In addition, the pores are stress concentration areas with weak load-bearing capacity. When stressed, the pores expand to form long cracks and are destroyed. Even if two laminates have the same porosity (using different prepreg methods and manufacturing methods during the same curing cycle), they exhibit completely different mechanical behaviors. The specific values for the decrease of mechanical properties with the increase of porosity are different, which shows that the influence of porosity on mechanical properties is highly discrete and has poor repeatability. The influence of pores on the mechanical properties of composite laminates is very complicated due to the inclusion of a large number of variable factors. question. These factors include: shape, size, and location of pores; mechanical properties of fibers, matrix, and interfaces; static or dynamic loads.
Bicycle carbon fiber rims are inorganic polymer fibers with a carbon content of more than 90%. Those with a carbon content of more than 99% are called graphite fibers. The microstructure of carbon fiber rims is similar to artificial graphite, which is a turbostratic graphite structure.