Abstract: In order to accurately measure the tensile strength and deformation characteristics of rock specimens under different confining pressures, a series of technological modifications are carried out with material testing machine MTS815, which is mainly used for rock triaxial compression test, on the one hand, a set of test machine piston and three-axis chamber with the interlocking device, so that the original can only provide compression load testing machine MTS815 can also provide accurate axial tensile load; the other hand, the design and development of a multi The degree of freedom of rock specimen triaxial tension fixture, to solve the rock and other brittle materials in the stretching process is difficult to always maintain the technical problems. On this basis, a complete set of test techniques is proposed to realize the complex triaxial direct tensile test of various rock specimens in the range of 0-140 MPa confining pressures. The results show that the test apparatus and the test method can fully carry out the rock triaxial tensile test under different confining pressure conditions; and the corresponding test results are obtained. The results show that the test specimen and the test method can carry out the triaxial tensile test on the shale specimen with the supporting equipment and test method, also triaxial tensile test curve is obtained. The results show that the shale has different failure characteristics and failure modes under low confining pressure and high confining pressure. Under the low confining pressure, the shale is still characterized by brittleness.

Key words: material testing machine MTS815, rock triaxial tension, follow chain device, three-axis tensile fixture, triaxial tensile test curve