Experimental Research On Grinding Performance Of Unidirectional C_f/SiC Composites

C_f/SiC composite materials are widely used in key components in the aerospace field because of their outstanding heat resistance,high specific stiffness and specific strength.However,due to the typical brittle and hard characteristics of SiC ceramic materials and the heterogeneous heterogeneity of composite materials,it is difficult to obtain ideal size and shape accuracy requirements for parts.At present,for the processing of such materials,milling and turning processes usually remove materials with a depth of cut of tens of microns,which easily leads to the overall peeling and delamination of the6.9μm diameter carbon fiber bundle.At the same time,the low conductivity and chemical inertness of materials make it difficult for special processing methods to remove materials efficiently and with high quality.The current grinding method is the main method for precise and controllable removal of such materials.In this paper,basic experiments and theoretical analysis are carried out for key and difficult issues such as the removal behavior,mechanical modeling and quality improvement of unidirectional carbon fiber materials.The main research work is summarized as follows:(1)According to the material characteristics,a single diamond abrasive grain scratch test was carried out.According to the analysis of surface scratches,acoustic emission and force signals,it can be known that the size and signal value of scratches increase with the increase of indentation load.Under the same parameters,the scratch size and signal value are larger of the SB direction,and the acoustic emission signal fluctuates more violently.Combining surface scratches with acoustic emission and force signal analysis,the material grinding and removal mechanism of unidirectional fiber composites is revealed;and based on the SEM morphology analysis,the removal mechanism of scratched materials in different directions is obtained as the material is brittle removal.The main and SA direction fibers are mainly tensile fracture and fiber pull-out,and the main fracture modes of SB direction fibers are bending fracture and shear fracture;(2)Based on the material parameters and Hertz’s contact law,considering factors such as material heterogeneity and fiber orientation,the grinding force model of the material-abrasive scratching,plowing and chipping stages was constructed,combined with the grinding force experiment Validate model accuracy with coefficients.The results show that the average errors of the normal and tangential grinding force models in the SA direction are 12.81%and 12.44%,and the average errors of the normal and cutting grinding force models in the SB direction are 11.44%and 11.65%.(3)Carry out the orthogonal grinding test method based on different fiber orientation and test morphology analysis,combined with the surface morphology and grinding force analysis after processing,explain the change mechanism of the surface morphology of the material affected by the process load,fiber orientation.The results show that the surface roughness values fluctuate around the fiber radius scale,and the average values of surface roughness Ra in the SA and SB directions are in the range of 4.21-5.00μm and 4.42-5.26μm,respectively.Combined with the SEM surface morphology of the specimen and the scratch removal mechanism of a single diamond abrasive grain,it can be known that the material is mainly brittle removal,and the main defects of the fiber in the SA direction are tensile fracture and extrusion fracture;the main defect of the fiber in the SB direction is bending Fracture and shear fracture.