Carbon fiber is a super-hard material with a hardness 10 times higher than ordinary steel and second only to diamond.
Carbon fiber is made of organic polymer fibers with extremely high carbon content stacked along the fiber bundle direction. However, the currently recognized high hardness and super shear resistance are not entirely due to material properties. One of the decisive factors is the critical gap. When there is a build-up of elements between fibers, that is the critical void.
When the stacking between fibers is below a certain critical value, the fiber porosity index between them will determine the hardness, shear resistance and tensile resistance of the fibers. The critical porosity that causes the mechanical properties of materials to decrease is 1%-4%.
When the pore volume content is in the range of 0-4%, for every 1% increase in pore volume content, the interlaminar shear strength decreases by approximately 7%. 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.