The Suppression Strategy Of Hole Exit Delamination Based On Drilling Carbon Fiber Reinforced Silicon Carbide Ceramic Matrix Composite

Carbon fiber reinforced silicon carbide ceramic matrix composites(C/SIC)have the characteristics of anisotropy,inhomogeneity,high hardness and high brittleness,which are typical difficult to process materials.The delamination defect of hole exit in drilling carbon fiber reinforced silicon carbide ceramic matrix composites seriously affects its application in aerosPace and other fields.In this thesis,carbon fiber reinforced silicon carbide ceramic matrix composites as the research object,suppress the carbon fiber reinforced silicon carbide ceramic matrix composites hole exit delamination defects as the goal of research,with the help of theoretical analysis and experimental research,and CAD,CATIA,MATLAB,SPSS,ORIGRIN and other computer aided software.The formation process and causes of hole exit delamination were studied,and the suppression strategies of hole exit delamination defects were put forward,thus providing theoretical basis for drilling carbon fiber reinforced silicon carbide ceramic matrix composites in aerosPace field.Firstly,the hole exit delamination of carbon fiber reinforced silicon carbide ceramic matrix composites is analyzed theoretically.The drilling process was analyzed by force analysis,the cutting force model was established,the formation process of hole exit delamination defect and hole exit delamination mechanism were analyzed,and the hole exit delamination model was established.The conclusions are as follows:the formation process of delamination defects at hole exit is revealed,and the sequence is as follows:①under the action of axial thrust,the undrilled Part deforms;② as the drilling process continues,the deformation of the undrilled Part increases gradually;③the interlaminar bonding strength of C/SIC ceramic matrix composites can not resist deformation,crack proPagation and interpenetration,and hole exit delamination defects appear.After qualitative analysis of the related variables to the hole exit delamination model,it is considered that optimizing the processing technology,reducing the axial drilling force and increasing the crack strain energy release rate are the basic ways to suppress the hole exit delamination.Secondly,the hole exit delamination of carbon fiber reinforced silicon carbide ceramic matrix composites is studied experimentally.By using carbide coating cutter,CBN welding cutter,PCD welding cutter and brazing diamond abrasive drill for drilling experiment,the delamination damage degree of hole exit and corresponding tool wear after drilling with different tools were observed and analyzed.The effect of different processing Parameters on the delamination factor of hole exit during drilling was studied.The conclusions are as follows:brazing diamond abrasive drill is a kind of tool suitable for drilling C/SIC ceramic matrix composites;Increasing the spindle speed and decreasing the feed speed can restrain the hole exit delamination defects.Chip has significant influence on axial drilling force and hole machining quality.Reducing the influence of chip on drilling process can restrain hole exit delamination.Thirdly,based on the axial drilling force,this thesis carries out the related research of hole exit delamination defect suppression.The empirical formula prediction model of axial drilling force was established,and the significance test was carried out.The statistical variables of axial drilling force and hole exit delamination were analyzed.Finally.based on axial drilling force,relevant strategies to suppress hole exit delamination were proposed.The conclusions are as follows:The empirical formula of axial drilling force shows that there is a significant relationship between axial drilling force and tool diameter,spindle speed and feed speed.The feed speed has the greatest influence on axial drilling force,followed by spindle speed and tool diameter.The Pearson coefficient between the axial drilling force and delamination defects at the hole outlet is 0.945,indicating a significant positive correlation between the two,which means that reducing the axial drilling force can suppress delamination defects at the hole exit.The optimization of machining Parameters can effectively reduce the axial drilling force and suppress the delamination defect at the hole exit.Optimizing the numerical control program and controlling the drilling Path and corresponding Parameters can effectively reduce the axial drilling force and restrain the delamination defect of hole exit.Finally,based on the strain energy release rate of the crack,the thesis carried out a study on the delamination defect suppression at the hole exit.The strain energy release rate of crack and the hole exit delamination further analysis,the strain energy release rate of crack and fracture toughness of the relationship between the theoretical research,puts forward the material preParation method to enhance work-piece fracture toughness and mechanical method to enhance fracture toughness,finally by conducting experiments,and the reliability of the theoretical analysis is verified,Some strategies to restrain delamination defects at hole outlet are proposed.The conclusions are as follows:one of the effective ways to increase the crack strain energy release rate of ceramic matrix composites is to increase its fracture toughness.Two effective ways to improve the fracture toughness of materials are material preParation method and mechanical method.The methods of material preParation to enhance the fracture toughness of work-piece mainly include three basic approaches:optimizing the layer structure,modifying the fiber reinforcement and optimizing the preParation process.The theoretical analysis and experimental data of mechanical fracture toughness enhancement of work-piece show that the fracture toughness and crack strain energy release rate can be enhanced by artificially applying compressive stress to the work-piece,and the hole exit delamination can be effectively suppressed.