A Characterization Method Of Surface/Subsurface Damage And Its Application In Grinding Induced Damage Of Ceramics

Ceramics, with very excellent physical and chemical properties, are increasingly used in the fields of aerospace, communication, petrochemical engineering, power, metallurgy, mechanical and modern biomedical engineering. Grinding is the most efficient and effective technique to finish ceramics workpieces, especially precision and ultra-precision grinding. Grinding is a complex abrasive cutting process, involving a material removal by the contact between abrasives and the workpiece with certain damage. Ceramics, typical brittle materials with high hardness, strength and abrasive resistance, are difficult to be machined. The ground components are most likely to contain surface/subsurface damages, influencing strongly the performance and reliability of ceramic components. Therefore, it is essential to study and understand comprehensively the grinding induced damage in ceramic.The current research efforts related to the grinding induced damage of ceramics focus on the experimental, theoretical and numerical aspects including such damage as microcracks, residual stresses. A degraded elastic modulus based characterization method of surface/ subsurface damage for ceramic materials is presented based on continuum damage mechanics (CDM) and nanoindentation/ scrath techniques. An elastic brittle damage constitutive equation is developed according to the nanoindentation results under a conospherical tip. Then the FEM simulation of the indentation loading process is conducted. The nanoscratch tests are employed to simulate the single abrasive grinding to study the damage evolution. The proposed efforts will be a foundation for improving the precision grinding theories of the ceramics. Main research efforts are as follows:1. A degraded elastic modulus based damage variable is defined to describe the damage induced property degradation of the materials based on the traditional Kachanov CDM framework. A simple and feasible characterization method of surface/ subsurface damage is realized based on nanoindentation test.2. An elastic brittle damage constitutive equation of the alumina is developed according to the nanoindentation results under a conospherical tip, considering the elastic damage of brittle ceraics. And then the FEM simulation of the indentation loading process is conducted with conospherical and berkovich tip, to verify the developed constitutive equation.3. The effect of grinding parameters such as grinding depth, griniding wheel characteristics on the grinding induced surface/ subsurface damage is studied simulatively with alumina sample, through nanoscratch tests with controlled peak scratch force and the tip geometry. A series of indentation tests are employed on the points either with different distance from the scratch center under the constant load or the points with the similar distance under ramp force. The surface topography of the sratches and the indents is analyzed through piezo in-situ tip scanning method and the SEM method. The feasibility of applying the proposed damage characteraization method to the grinding induced damage is consequently studied.4. The elastic brittle damage constitutive equation and the characterization method of grinding induced damage for ceramics are studied based on CDM and nanoindentaion/ scratch technique. The research findings in the grinding induced damage of ceramics, CDM, nano testing techniques and simulation of the grinding process are referred as well as the damage mechanisms and constitutive models of brittle materials such as concrete, rock. A further research on extending the proposed characterization method to other materials should be carried out.