Measurements of the Strength of Grain Boundaries in Rock.
Internat J Rock Mech Min Sci and Geomech Abs 1974 May; 11(5):173-180
A method has been developed for evaluating the strength of adhesion between materials at grain boundaries in rock. This method involves selectively extracting a small (4.5-Mm-diam., 1.7-Mm-thick disk), two-phase sample from a rock and determining the tensile strength of the boundary between the minerals by pulling normal to the grain boundary. This technique has been successfully applied to the study of quartz-feldspar interfaces separated from graphic granite and the Rockville granite and to the study of pebble-matrix interface selectively extracted from the calumet conglomerate. Indirect tensile tests of these grain boundaries have also been performed, and their results have been compared with those of the direct pull tests. Examination of bicrystals broken at their grain boundary reveals that the bonds responsible for this adhesion operate over only a portion of the interfacial area. The significance of this work is that it demonstrates that strength tests can be conducted on small areas, for example, grain boundaries in rocks. This permits a determination of small-scale zones of strength or weakness, which may be related to the overall strength of the rock.
Internat. J. Rock Mech. Min. Sci. and Geomech. Abs., V. 11, No. 5, May 1974, PP. 173-180