STUDY OF R-CURVE BEHAVIOUR IN ALUMINA BY IN SITU OBSERVATION OF STABLE INDENTATION CRACK GROWTH

摘要

Bend, alumina bars were mirror polished on the prospective tensile surface and next were precracked using Vickers pyramid. The indented samples were loaded stepwize in a 4 point bending apparatus. After unloading the microscopic observations of crack growth were made. The test allowed to obtain simultaneously the fracture toughness K_(IC) and the residual stress parameters χ by linear interpolation of the data. Obtained values of K_(IC) increased from 3.67 MPam~(1/2) for Vickers load P = 9.8 N to 5.11 MPam~(-2) for P = 100 N. They were comparable with data given in indentation strength in bending test.