Novel fiber fracture criteria for revealing forming mechanisms of burrs and cracking at hole-exit in drilling Carbon Fiber Reinforced Plastic

Abstract

Abstract In the machining process of Carbon Fiber Reinforced Plastic (CFRP), fibers fracture in two modes, including shearing fracture and bending fracture. Studies show that both fractures originate from the combined action of normal and shear stresses, while specific stress states are different. In the present study, novel fiber fracture criteria are proposed, which are closely correlated with the specific stress state corresponding to each fracture mode. Obtained results demonstrate that in the proposed criteria, calculation accuracy of the main cutting force improves by over 30 % when the comparison is made with the conventional criteria. Moreover, the removal processes of fibers at the hole-exit during drilling CFRP are simulated to analyze the forming mechanisms of burrs and cracking. Results suggest that although all burrs and cracking are induced by the out-of-plane deformation of fibers, the main causes of such deformations at the hole-exit in different regions are not the same. In the region corresponding to the fiber cutting angle of 90°, deformation originates from the squeezing action among fibers fracturing at different times, while in the region corresponding to the fiber cutting angle of 0°, deformation is directly caused by the squeezing action of the cylindrical surface on the main cutting edge.