| Composite materials,especially for the Carbon Fiber Reinforced Plastic(CFRP),are widely used in aviation,aerospace and other related fields because of its light weight,high strength,and good corrosion resistance etc.The machining quality is an important factor which influencing the work-piece assembly and service performance.Therefore,the study of cutting mechanism,cutting force,surface defects prediction and the characterization of surface quality in CFRP machining has great significance in improving the manufacturing level of aircraft industry and other related fields.Firstly,the cutting mechanism and energy consumption in CFRP orthogonal cutting was presented based on the energy method.The energy consumption in CFRP cutting was analyzed with the following four parts: energy consumed for formation of new surfaces,friction energy at the tool-chip interface,fracture energy for chip formation and energy consumption for subsurface damage.Based on the analysis of the four parts of energy and the principle of energy conservation,a new analytical method was developed to predict the cutting force in CFRP orthogonal cutting.Meanwhile,the CFRP orthogonal cutting experiments with different fiber angles were conducted to verify the correctness of the model.According to the Hertz contact stress distribution and the principle of minimum potential energy,the fiber deformation and failure process in CFRP cutting were analyzed,and the prediction model of fiber-matrix debonding was developed as well.The variation of subsurface debonding with fiber angle was obtained through the presented model before.The micro finite element model for the CFRP cutting was built by using energy based nonlinear failure criterion,and the simulation results showed good agreement with the theoretical results.The influence of fiber angle on chip formation mechanism in CFRP cutting was obtained by using high-speed video camera.Based on the connection between fracture toughness with the cutting process,a new approach is proposed for predicting fracture toughness of the newly machined surface in CFRP machining.On the basis of the above results,a new concept of surface energy increment was put forward to realize quantitative characterization of machined surface damage.The influences of tool wear and fiber angle on surface energy increment were also discussed.For the CFRP milling process,the surface integrity of milled surface was evaluated with three evaluation indicator: surface roughness,surface void proportion and affection layer.The influence of milling parameter on surface integrity of CFRP milling was investigated by using SEM and image segmentation technique.The generation mechanisms of surface defects were investigated with different degree of tool wear and fiber angle.The quasi-static load test(tensile and compression)were carried out for different surface quality test specimens,and the influence of surface roughness,surface void and affection layer on strength weakening was also presented.The above research results have a great contribution for improving the machining quality evaluation,assembly quality and service performance of CFRP. |
