Effect of fiber bending induced matrix shear behavior on machined surface quality in carbon fiber reinforced plastic milling

Fiber bending by the cutting tool is one of the dominant causes of fiber pull-out on machined surfaces during CFRP milling. During the bending, the polymer matrix between the fibers is subjected to shear stress resulting in fiber-matrix debonding. The increase in the debonding length causes an increase in the fiber pull-out length. In milling, not all the new surfaces created by tool-workpiece engagement become the machined surface. However, during this process, the strain energy absorbed by the deformed matrix is released into fiber-matrix debonding along the fibers which can cause fiber pull-out on the machined surface. In this study, shear strain energy of polymer matrix due to fiber bending during milling tool-workpiece engagement was calculated with the geometrical relationship between fibers and a cutting edge. We found that the increase in R_a and R_z of the machined surface had clear tendencies to the increase in the calculated energy.