| With the combination of the advantages of silicon carbide ceramics and carbon fiber,carbon fiber-reinforced silicon carbide matrix(C/SiC)composites show excellent properties of high specific strength,high specific modulus,wear resistance,corrosion resistance and fatigue resistance,which enables C/SiC composites to be widely used in aerospace,automobile industry,military industry,and energy industry.Featuring anisotropism and robustness,C/SiC composites have been classified as difficult-to-machine materials.Grinding with a diamond abrasive wheel is currently the predominant process for the C/SiC composites.However,because the damage and failure modes of fiber,interface,and matrix,and material removal mechanisms under the action of abrasive particles are still unclear,it is difficult to control the damage of the machined surface and subsurface,which severely restricts the development and application of C/SiC composites.Consequently,this paper makes a systematic study on the above key problems.In order to reveal the material damage process during the tensile test of C/SiC composites,this paper carries out real-time monitoring of the transverse tensile test against unidirectional C/SiC composites by introducing acoustic emission technique,which monitors the large-scale debonding failure of C/SiC composites,measures the interfacial transverse debonding strength,grasps the law of interface debonding behavior,and obtains the frequency component distribution of interfacial debonding behavior and brittle fracture of the matrix.On this basis,the relationship between damage behavior of materials and signal feature is established,and the interfacial failure mechanism and crack deflection law of C/SiC composites under loading are revealed,which theoretically supports the further study of the removal mechanism of C/SiC composites.Since it is difficult to observe the failure of each phase of ceramic matrix composites(CMCs)and distinguish the cut-in and cut-out states of the scratch in the existing scratch tests,this paper designs a high-speed single-abrasive scratch test:horizontal spiral scratch test,which combines the arrangement of a small inclination angle of the specimen and the horizontal spiral relative motion of the single-abrasive to realize the decoupling of scratching depth and scratching length and theoretically obtain comparatively longer scratches with a small scratching depth at any scratching speed.Based on the test plan,this paper conducts a single-diamond abrasive scratch test for unidirectional C/SiC composites.Through the analysis of the scratching force,scratch-induced surface and subsurface morphologies,it reveals the interfacial failure mechanisms and material removal modes under the action of single-abrasive particles,and masters the material removal mechanisms of the single-abrasive grinding for C/SiC composites.Based on the single-abrasive scratch test,this paper designs a surface grinding test by diamond grinding wheels with different fiber angles to study the effect of continuous filament on the material removal mechanism.Based on the experimental results,this paper analyzes the influence of grinding parameters and fiber angles on the grinding force,surface roughness and surface morphology during the grinding process.Through the research results of the single-abrasive scratch test and grinding experiment,this paper jointly investigates the effects of fiber orientation on the interfacial shear,interfacial debonding and matrix fracture behavior and explores material removal mechanisms based on the interfacial micromechanical behavior in the grinding of C/SiC composites.The results in this paper provide a useful theoretical basis for analyzing the interfacial mechanical behavior,crack extension and material damage evolution mechanism of C/SiC composites and upgrade the theoretical system of CMCs’ grinding,thereby providing key theoretical and technical support for obtaining high-quality grinding surface of CMCs. |
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