Investigation On Delamination Defects In Drilling Of CFRP And Their Effects On Load Carrying Properties

Carbon Fiber Reinforced Polymer/Plastic(CFRP)has the advantages of high specific strength,high specific stiffness,and designable performance.It has become the preferred material for weight reduction and efficiency enhancement in aerospace and medical equipment.In order to meet the assembly requirements,CFRP often needs a lot of hole-making after molding,but the quality of the hole-making is very demanding in application.Hole-making damage has always been the main factor restricting the application of CFRP.However,the CFRP presents multiple interfaces and multi-phases at micro level and anisotropy at macro level,which makes CFRP prone to delamination damage during the hole making process.The damage affects the mechanical properties of the composite.Moreover,when the composite component is thin,bending deformation is likely to occur during the hole-making process,which aggravates the generation of delamination defects.In this paper,the influence of drilling parameters on the thrust force in CFRP drilling is studied and the influence of the clamping diameter on the thrust force of CFRP drilling is explored.A prediction model of critical thrust force for drilling delamination considering the overall bending deformation of CFRP is established and verified by experiment and simulation.Finally,the influence of CFRP drilling delamination defects on the mechanical properties of the material is investigated by finite element method.The main research contents of this present thesis are summarized as follows:(1)The effects of feed rates and tool speeds on the thrust force of CFRP drilling and the influence of the clamping hole diameter on the thrust force of CFRP drilling were studied by drilling experiments,respectively.(2)By considering the thrust force of the chisel edge and the main cutting edge on the CFRP during the drilling process,and considering the influence of CFRP bending deformation on the thrust force,the prediction model of delamination critical thrust force in drilling CFRP is established and deduced.(3)The finite element simulation model is established to obtain the numerical value of the critical thrust force in drilling.The experimental value of the critical thrust force in CFRP drilling is obtained by drilling blind holes before punching.The theoretical critical thrust force prediction model is validated by comparing the theoretical value,simulation value and experimental value.(4)The finite element simulation model is established to analyze the tensile and bending mechanical properties of the CFRP sample with prefabricated delamination defects of different sizes and positions.The influence of drilling delamination defects on the mechanical properties of the material is analyzed.