At certain grain sizes, alumina R curves have been shown to increase with crack growth. This phenomenon is in contrast to R curves for metals, which exhibit a steady-state plateau effect with increasing crack growth. Recent results show R curves for calcium silicate geomaterials also increase. The specimen geometry employed for both alumina and geomaterials is a generalized plane stress double cantilever beam (DCB). The specimens are under direct pin loading with fixed displacement. This note will discuss the common mechanisms of increasing R curve behavior of these quasi brittle materials. Finally, a hypothesis on the discrepancy between the fracture toughness of single crack rock samples and in large seismic events is presented.

Date Published: 1 December 1991
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Proc. SPIE 1554, Second International Conference on Photomechanics and Speckle Metrology, (1 December 1991); doi: 10.1117/12.49497

Published in SPIE Proceedings Vol. 1554:
Second International Conference on Photomechanics and Speckle Metrology
Fu-Pen Chiang; Fu-Pen Chiang, Editor(s)