Studies On Dynamic Tensile Properties Of Granite Under Confining Pressure

In the thesis, comprehensive studies on mechanical properties of granite under indirect and direct dynamic tensile loads are conducted with the apparatus to conduct direct dynamic tension tests. A series of trial experiments are conducted by gypsum samples firstly. Furthermore, the rate dependence of dynamic tensile strength and deformation properties of granite are investigated through laboratory tests. It is demonstrated that the indirect tensile strength, Young's moduli and critical tensile strain of granite increases with the increasing strain rate. And under dynamic uniaxial tensile loads, the direct tensile strength and the Young's moduli increases with the increasing strain rate, while Young's moduli's rising rate with the increasing strain rate is less than the tensile strength's. Under dynamic tensile loads with confining pressure, the tensile strength increases with the increasing strain rate, the rising rate decreases with the increasing confining pressure. While the tensile strength decreases with the increasing confining pressure, the decreasing rates tend to increase with the increasing strain rate. It is also investigated that the Young's moduli increases with the increasing strain rate and decreases with the increasing confining pressure likewise, but the changing rate can't be conducted.Theoretical analyses have been simultaneously done to study the mechanical properties of granite under dynamic tensile loads by using penny-shaped crack model. It is stated that the tensile strength of granite increases with the increasing strain rate and the rising rate decreases with the increasing confining pressure. The tensile strength decreases with the increasing confining pressure and decreasing rates tend to increase with the increasing strain rate. It is indicated that the theoretical result agree well with experimental results. It is also suggested that, the nonlinear strain's percentage increases slightly with the increasing strain rate and the increasing confining pressure. And the axial and transverse compliance tensor increase with the increasing tensile stress after its exceeding the critical stress, while the axial compliance tensor's rising rate decreases with the increasing tensile stress and the transverse compliance tensor's rising rate increases with the increasing tensile stress. It is also indicated that, the varieties of theoretical strength and stress train relation with strain rate and confining pressure agree with experimental results.