Synthèse
Volume 12, Numéro 1, Pages 8-12
2006-06-30
Characterization Of Alumina By Hertzian Indentation And R-curve
Authors : Bouras S. . Zerizer I. . Gheldane F. . Bouazza M.t. . Berriche Y. .
Abstract
We followed the resistance to crack propagation using the acoustic emission and the Hertzian indentation: the acoustic emission count rate decreases before the critical propagation is reached. At a critical load Pc in Hertzian indentation tests, the crack propagates at the surface as an entire circle around the ball and also in depth as a cone. The circular crack occurs progressively, step by step, in several stages according to the loading. Critical load Pc is determined by an acoustic emission peak of higher amplitude. The loads below Pc provoke weak acoustic emission translating a sub-critical crack extension related to the resistance to crack propagation. In three points bending, the increase of the stress intensity factor versus crack extension is shown clearly. In spite of the pre-existent micro-cracks presence, alumina shows a crack growth resistance that translates stable crack propagation before the fracture : the toughness increases. The bridging by grains and the crack ramification are responsible of the crack propagation resistance.
Keywords
Alumina, R-curve, resistance to crack propagation, hertzian indentation, acoustic emission
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