Influence of Microstructure on Fracture Propagation in Rock
Semiannual rept. 17 Dec 1970-30 Jun 1971
BATTELLE MEMORIAL INST COLUMBUS OH COLUMBUS LABS
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The report describes the results of research in progress to correlate the fracture resistance with microstructural features of Salem limestone and Berea sandstone. These tests are being conducted on wedge-loaded double-cantilever-beam specimens. The fracture resistance of Salem limestone measured in terms of R, the energy dissipation rate, was found to be strongly dependent on the crack orientation with respect to the bedding plane and ranges from about 40 joulessq. m. During these tests, acoustic emission from the rock specimens are monitored to detect the onset of cracking. The value of R for the sandstone is approximately the same as for the fracture path in both materials has been identified by fractography over a broad range of magnifications. A comparison of the R values and their meaning in terms of strength predictions is made with data obtained by other means. Consideration of these results leads to a model of fracture in these two materials involving the development of extensive microcracking in the region surrounding the main crack tip.
- Geology, Geochemistry and Mineralogy