The fracture toughness testing of ceramics and acoustic emission

Abstract

Measurements of the fracture toughness of commercial sintered alumina were monitored using acoustic emission to detect subcritical crack growth. Double-cantilever-beam specimens gave higher values of toughness than single-edge-notched bend (SENB) or double-torsion specimens did, even after correction for slow crack growth. The SENB test with a sharp crack appears to give the most reliable results, requires the easiest specimens to prepare and suffers the least slow crack growth. In view of this, detailed studies of the damage made by sawing notches, of the effects of the a/W ratio and of the cross-head displacement rate were made for SENB specimens. Sharp cracks with small a/W ratios and high cross-head speeds minimize the effects of slow crack growth.