Subsurface Damage Analysis And Experimental Study Of Carbon Fiber Composite Milling

Carbon fiber reinforced resin matrix composites(CFRP)have the advantages of light weight,high strength,strong designability and fatigue resistance,and are widely used in machinery,medical,aerospace and other fields.However,due to the anisotropy of CFRP and the large differences between different phase materials,it becomes a typical difficult-to-machine material.In the milling process,subsurface damage often occurs,such as fracture and pull-out under the fiber surface,interface debonding,etc.,which seriously affects the usability of the material and causes potential safety hazards in the later stage.Therefore,in order to suppress the defects in the machining process,the formation and expansion mechanism of subsurface damage in CFRP milling has been analyzed from the macro and micro scales.Finite element simulation methods are used to effectively capture the generation and expansion of damage during cutting,and the correctness of the simulation is verified through experiments.The research in this paper has theoretical and engineering significance for the processing of CFRP materials.Currently,research on sub-surface damage of CFRP has been mainly focused on single-pass milling.However,multi-pass milling strategies have been widely applied in industry,and the impact of defects generated during previous milling passes on subsequent passes cannot be disregarded.In this study,the subsurface damage behavior of CFRP in side milling was studied based on multiple milling strategies.First,a macro-milling model for CFRP was established by considering it as an equivalent homogeneous material.An explicit user-defined material subroutine was programmed based on the Hashin failure criteria,which is used to describe the stress-strain and damage behavior of CFRP during milling.The variations in cutting force,stress,and subsurface damage were investigated for different fiber orientations.Compared to single-pass milling,the use of a multi-pass milling strategy reduced subsurface damage depth by 33.8%～48.6%.Secondly,a micro-scale cutting model including the fiber,matrix,and interface phases has been established to account for the performance differences among different phases in CFRP.The cutting deformation process and fiber fracture process of CFRP under different fiber orientations have been analyzed.Based on the material removal mechanism,the causes of sub-surface damage in CFRP and the degree of influence of different milling strategies on the sub-surface damage at the micro-scale have been analyzed.The results show that using multi-pass milling can reduce the interface debonding depth by 34% to 56%,and decrease the fiber sub-surface fracture depth by53% to 67%,effectively suppressing the damage degree of fiber sub-surface fractures and interface cracking defects.Finally,experimental tests of CFRP side milling have been conducted.The cutting force signals during cutting process with different fiber orientations of CFRP have been collected by a three-dimensional force sensor,and the cutting forces obtained from experiments have been compared with those from simulations.The analysis results indicate that the maximum error between simulations and experiments is 14%,which validates the accuracy of the model.The microscopic surface morphology of the machined surface has been observed using a scanning electron microscope and compared with the simulation results,which confirms the effectiveness of the simulation prediction.