Modeling Of Cutting Force And Research On Cutting Mechanism Of Carbon Fiber Composites

Carbon fiber reinforced composite material(CFRP)has high strength and high modulus,and is widely used in aerospace,defense and military industry,and other fields.However,the complex multi-phase structure and high anisotropy of CFRP will produce delamination,fuzzing,tearing and other defects during drilling and milling,which will seriously reduce the mechanical properties and fatigue life of CFRP components.In order to achieve low-damage machining of CFRP,it is necessary to study the cutting mechanism of composite materials from a meso level.Therefore,the thesis first establishes the cutting force prediction model and the defect prediction model under variable uncut material thickness,and then establishes the fiber deformation equation and cutting force model of CFRP under full cutting fiber angle.Based on the above theoretical research,the orthogonal cutting experiment reveals the CFRP material removal mechanism and damage formation process.The main research contents are as follows:(1)Reveal the mechanism of delamination defects in the CFRP cutting process.Based on the two-parameter elastic foundation beam theory,considering the relationship between the thickness of the uncut material and the cutting time,the deflection curve equation of the cutting fiber with the uncut thickness is established.The stress distribution in the contact area between the tool and the fiber is analyzed by the Hertz contact theory,and the maximum tension is used.Stress theory judges fiber breakage.The cutting force prediction model was Established from shear zone,chip zone and rebound zone.Experimental results show that the cutting force prediction model can accurately predict the cutting force of CFRP under different working conditions.In addition,when the cutting depth is 0.025 mm,the debonding length is the longest;and when the cutting depth is 0.05 mm and 0.075 mm,the debonding length is almost unchanged.When the thickness of the uncut material is less than 0.1mm,the fiber cannot be cut.(2)Explore the formation mechanism of CFRP processing defects under different cutting fiber angles.The fiber force under different cutting fiber angles is analyzed,and the cutting force prediction model and fiber deformation equation of the full cutting angle are established.Experimental results show that the cutting force prediction model can accurately predict the cutting force under different cutting fiber angles.When the cutting fiber angle ?<90°+?,the fiber gradually bends with the feed of the tool,and finally reaches the ultimate strength fracture.When the cutting fiber angle ?>90°+?,at the first,the fiber of the free end of the cutting fiber is bended by the tool.At this time,the contact between the tool and the fiber is the point contact of the free end of the fiber;secondly,the bending slope of the free end of the fiber reaches the slope of the rake surface.When cutting the fiber,the cracking point moves down rapidly with the cutting time,and the contact between the fiber and the tool changes from point contact to line contact.(2)Research the cutting damage of CFRP under different cutting fiber angles through the orthogonal cutting experiment.When the cutting fiber angle ?<90°+?,there are a lot of broken resin matrix and broken carbon fiber residue on the cutting surface.With the increase of the cutting fiber angle,the smoother the cutting surface and the less fiber debonding and cracking.When the cutting fiber angle is120°/135°/150°,a large number of fibers are completely exposed on the cutting surface,without resin matrix wrapping,and broken resin remains on the cutting surface.The main form of fiber fracture is bending fracture.