PFC Simulation of Brazilian Tensile Strength Test in Geomaterials’ Specimens with T-shaped Non-persistent Joints

The tensile strengths of geomaterials such as rocks, ceramics, concretes, gypsum, and mortars are obtained based on the direct and indirect tensile strength tests. In this research work, the Brazilian tensile strength tests are used to study the effects of length and inclination angle of T-shaped non-persistent joints on the mechanical and tensile behaviors of the geomaterial specimens prepared from concrete. These specimens have a thickness of ۴۰ mm and a diameter of ۱۰۰ mm, and are prepared in the laboratory. Two T-shaped non-persistent joints are made within each Brazilian disc specimen. The Brazilian disc specimens with T-shaped non-persistent joints are tested experimentally in the laboratory under axial compression. Then these tests are simulated in the two-dimensional particle flow code (PFC۲D) considering various notch lengths of ۶, ۴, ۳, ۲, and ۱ cm. However, different notch inclination angles of ۰, ۳۰, ۶۰, ۹۰, ۱۲۰, and ۱۵۰ degrees are also considered. In this research work, ۱۲ specimens with different configurations are provided for the experimental tests, and ۱۸ PFC۲D models are made for the numerical studies of these tests. The loading rate is ۰.۰۱۶ mm/s. The results obtained from these experiments and their simulated models are compared, and it is concluded that the mechanical behavior and failure process of these geomaterial specimens are mainly governed by the inclination angles and lengths of the T-shape non-persistent joints presented in the samples. The fracture mechanism and failure behavior of the specimens are governed by the discontinuities, and the number of induced cracks when the joint inclination angles and joint lengths are increased.  For larger joints when the inclination angle of the T-shaped non-persistent joint is around ۶۰ degrees, the tensile strength is minimum but as it is closed to ۹۰ degrees, the compressive strengths are maximum. However, an increase in the notch length increase the overall tensile strength of the specimens. The strength of samples decreases by increasing the joint length. The strain at the failure point decreases by increasing the joint length. It is also observed that the strength and failure process of the two sets of specimens and the corresponding numerical simulations are consistence.

Keywords:

T-shaped non-persistent joint , joint angle , joint length , PFC۲D