Crack Propagation During Single Diamond Abrasive-grain Cutting Zirconia Ceramics

As a kind of typical engineering ceramics,zirconia ceramic has been widely applied in aerospace,national defense and military industry owing to its superior physical and mechanical properties.At present,grinding with super-hard fine abrasive is the main processing method of ceramic materials.However,zirconia ceramics are easy to generate subsurface damage such as cracks and residual stress during grinding process due to their hard brittleness,resulting in the heavily decline of parts service performance and life.Hence,it is of great significance to study the materials removal mechanism and cracks nucleation for zirconia ceramics to improve the surface quality and machining efficiency.This research regard single diamond abrasive-grain cut zirconia ceramic as the object,and take the coupling methods of theory-simulation-experiment to discuss the cutting cracks nucleation process at the condition of static and dynamic loading.Based on the results,the grinding crack layer suppression measures are proposed to achieve efficient and precise manufacturing process of zirconia ceramics.Below is the specific research work:(1)Based on the indentation regional stress and crack nucleation theory,a finite element model of zirconia ceramic Vickers indentation is established and the experiments are carried out.The mechanical properties of zirconia ceramic,such as hardness and fracture toughness,are obtained by measuring the characteristic parameters of indentation.Then the critical load for generating macro cracks under static loading is calculated,and the crack nucleation as well as propagation process of zirconia ceramics during the loading/unloading process of Vickers indenter are analyzed on the basis of indentation stress field.(2)Substitute the static mechanical performance parameters of zirconia ceramic into empirical formula to calculate the ductile-brittle transition depth of material removal.Based on the Johnson-Holmquist-Ceramic constitutive equation,a finite element-smooth particle hydrodynamics coupling model and a finite element model of single abrasive-grain cutting zirconia ceramic are established to simulate the chip formation and material ductility removal process at different scales.Then the discussion upon crack propagation and effect of process parameters on cutting force are carried out.(3)Establish the experimental platform,and successively develop single factor experiments and response surface experiments on single abrasive-grain cut zirconia ceramic.After analyzing the cutting force and acoustic emission signal as well as observing the surface topography of zirconia ceramic,the process of material removal,crack nucleation and propagation evolution of zirconia ceramics under abrasive-grain impact is obtained,which provides an important guarantee for obtaining good surface processing quality.