Observation of Stable Crack Growth in AL2O3-Ceramics by Acoustic Microscopy and Acoustic Emission
When cracks propagate upon loading in certain ceramics, one observes an increase in crack-resistance with increasing crack length (R-curve behavior). This phenomenon is controversially discussed presently [1,2]. The dissipation of energy, in one class of models, is explained by the assumption that microcracks are present at the crack tip having certain extension (process-zone) . In the other models, the increase in crack-resistance is explained by the interaction of the crack interfaces due to friction between serrated crack walls . From practical point of view, it is necessary to understand these phenomena because they may possibly enable one to improve the fracture toughness of high-strength ceramics. In this paper we report on measurements of the elastic properties at the crack-tip of a stably extended crack using Scanning Acoustic Microscopy (SAM). Acoustic Emission (AE) was also monitored during crack-growth. We also discuss phenomena observed at the crack-walls.
KeywordsNickel Attenuation Acoustics
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