Research On Grinding Mechanism And Process Optimization Of Carbon Fiber Reinforced Silicon Carbide Ceramic Matrix Composites(C_f/SiC)

Carbon fiber reinforced silicon carbide ceramic matrix composite(Cf/SiC)has excellent properties such as high hardness,wear resistance,low density and high strength.As a new high temperature material.Cf/SiC materials have been widely used in aerospace,transportation and other fields.However,the research on Cf/SiC material processing technology is still in its infancy,and the processing quality of Cf/SiC materials cannot be guaranteed,which seriously hinders its application and development.The anisotropy of Cf/SiC material,the different strength and stiffness of the matrix and fiber,and the weak interfacial layer make the material easy to be debonded between layers.The traditional grinding mechanism cannot be fully applied to the grinding of composite materials.It is necessary to combine the traditional grinding theory to build a new theory for the grinding mechanism of ceramic matrix composites.Its complex multi-material hybrid structure causes some defects in the process of processing removal,such as fiber pull-out,fiber outcrop,matrix crack,interfacial debonding,and subsurface cracking,etc.In order to control the surface processing quality,it is necessary to find out the effect and Mechanism of different processing parameters on the surface integrity and grinding force of grinding ceramic matrix composite,This thesis conducts exploratory research on the processing mechanism and process optimization.The main research contents include:(1)According to the material properties of carbon fiber and silicon carbide brittle materials,combined with brittle solid indentation mechanics and grinding mechanism,the formation mechanism of three typical fiber oriented 1D Cf/SiC materials was studied.The material removal was introduced from the perspective of crack propagation.The process of layer delamination and fiber toughening is additionally introduced;A supplementary introduction to the difference in the removal mechanism caused by the difference in fiber position during the grinding process(2)A systematic research of the grinding force was carried out.Through the single factor experiment of 2.5D Cf/SiC and SiC materials,the effects of different processing parameters and fiber angles on the grinding force and the evolution trend were discussed.In addition,the correlation between the factors affecting the grinding force was analyzed by orthogonal test,and the grinding force of the grinding process was optimized.(3)The surface integrity of the test specimens was studied.The influences and evolution trends of different processing parameters and fiber angles on the surface roughness Sa were analyzed.The correlation between the surface quality factors and the grinding factors were analyzed.The process parameters of grinding surface quality are optimized and relevant conclusions are drawn.By observing the surface topography characteristics,wear debris and subsurface damage,the causes of the formation and the influence of these topographic features on the surface quality were analyzed.Some relevant conclusions were drawn.(4)A three-dimensional mesoscopic model of 1D Cf/SiC material was established using Abaqus software,and the grinding process was simulated.The constitutive and damage criteria of carbon fiber materials were defined by the vumat subroutine.The grinding force and experimental results were contrast for verifying the accuracy of the model.The removal mechanism of materials at different fiber angles was studied by simulation results.