Unveiling the rotation of the maximum principal strain in concrete discs under Brazilian tensile tests

This study experimentally investigates the rotational characteristics of the maximum principal strain orientation at the center of concrete discs under Brazilian tensile test (BTT) based on strain gauge rosette measurements. It correlates the rotation of the maximum principal strain orientation with the evolution of P-wave velocity as well as the ratio of horizontal to vertical strains at the center. The experimental results reveal that under both monotonic and cyclic stress paths, the disc specimen experiences two significant rotation in the maximum principal strain orientation, occurring at the initial loading and at the final failure, respectively. The mechanisms behind these two strain rotations are fundamentally different: the earlier rotation is caused by disc-loading jaws contact induced uneven stresses, while the later one is due to the redistribution of stress caused by the cracks at failure. In predicting failure, the attenuation of P-wave velocity can issue an earlier precursory signal compared to the maximum principal strain orientation and the ratio of horizontal to vertical strain. The crack patterns at failure indicate that in the BTT, the crack path's normal direction aligns with the maximum principal strain orientation, suggesting that the crack propagation is governed by the orientation of maximum principal strain.