The overall response of sandstone specimens under direct tension is discussed. A closed-loop, electro-mechanical testing machine with strain control was used to obtain the complete load-displacement record. In particular, the effects of the kinematic constraints applied to the specimen to induce localization and fracture were examined from tests with imposed uniform displacement (fixed platens) and from tests with free rotation (hinged platens). An optical method, electronic speckle pattern interferometry, was used to monitor surface deformation of the specimen with very high resolution. It is shown that the boundary conditions have an influence on fracture evolution and overall response. In addition, traditional tensile tests, which allow rotations, usually underestimate the strength of rock.
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