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Published March 1, 1996 | public
Journal Article

On loading rate effects in toughening processes

Abstract

Environmental crack tip reactions are a known source of premature fracture in oxides. These rate-dependent phenomena commonly are studied in strength tests where loading rate serves as the major experimental variable. A material susceptible to environmentally-assisted crack growth is stronger at fast testing rates. A topic which has received far less attention is the influence of stressing rate or loading rate on the shielding processes which occur at some distance from the crack tip, although the inverse has been studied by Deuerler et al. In their work, the crack velocity-stress intensity, v-K, curve was measured as a function of crack length in alumina. The v-K curve shifted to higher stress intensities for longer cracks, indicative of greater shielding as the crack grew progressively up the K_R (resistance) curve. In this paper, we explore the influence of loading rate on the fracture toughness of two aluminum oxides, one which fails in a brittle fashion (i.e., where toughness is independent of crack length), and a second which demonstrates significant resistance curve behavior due to grain bridging behind the crack tip. We present here the first known documentation of a loading rate effect on shielding phenomena in ceramic materials.

Additional Information

Copyright © 1996 Acta Materialia Inc. Published by Elsevier. (Received September 13, 1995). This work was supported by the National Science Foundation Center for Advanced Cement Based Materials at Northwestern University.

Additional details

Created:
August 20, 2023
Modified:
October 17, 2023