EXPERIMENTAL ANALYSIS OF PROCESS AND TENSILE STRENGTH FOR CONCRETE BRAZILIAN SPLITTING TEST WITH DIFFERENT LOADING BOUNDARIES BY DIC METHOD

Brazilian splitting test was widely used in the evaluation of tensile strength of brittle materials, but the results of strength are difference with different loading boundaries, such as flat plates, bearing strips, arc die, and flattened Brazilian disc,which has always been a research focus. In this paper, the splitting test was designed under different loading boundaries of direct flat plates and bearing strips, and analyzed theoretically, carried out experimentally as well. By the high-speed camera and digital image correlation (DIC) method, the process of the evolution of strain field, crack initiation and propagation on the surface of the specimen were studied in the splitting test. The influence of different loading boundaries on the tensile strength and the strain concentration evolution were further discussed. The results show that: (1) The evolution characteristics of strain concentration caused by the nonlinear tensile properties of concrete are sensitive to loading conditions, which lead to strain concentration earlier from the loading ends and evolves to the center of the specimen when loaded by flat plates . In this case, even the experimental condition of "center cracking" is satisfied, its strength still lower than that of bearing strips, the difference can reach 17.9%; (2) As long as the contact angles of bearing strips loading is designed properly, the stress field of the specimen can develop stably than that of direct flat plate loading, which is conductive to ensure strain concentration as well as fracture starting from the center. It is better to meet the requirements of the Brazilian splitting test; (3) It is not sufficient to only verify the validity condition of "center cracking", which must be carefully considered in the test design and analysis. The research results have important reference significance for the design and test analysis of the Brazilian splitting experiment of brittle materials.