Abstract: Theoretically, direct tensile test is the most simple and effective method for determining the tensile strength of rocks, which is both theoretically and practically meaningful. However, clamping the specimens is a major difficult problem, which leads to the difficulties in preparing the specimens and the complicated test equipment. Double concentric annular core tension test is an innovative approach to laboratory determination of tensile strength of rocks, which could overcome the above-mentioned loading disadvantages of the conventional direct tension tests. Firstly, the mechanics of the double concentric annular core tension test is discussed; and then the specimen size effect and optimal size range are investigated experimentally and numerically to obtain more reliable tensile strengths. The results show that the maximum stress near the inner and outer bottom are close to each other and reliable tensile strength could be obtained when the ratio of outer ring diameter to specimen diameter r1/R is 0.62±0.08; the ratio of inner ring diameter to specimen diameter r2/R is 0.45±0.12; and the ratio of inner ring diameter to outer ring diameter r2/r1 is 0.64±0.06. Tensile strength results obtained from these tests could achieve the optimum least standard error and coefficient of variation compared with Brazilian test and hollow cylinder test.

Key words: tensile strength, double concentric annular core direct tensile test, size effect, optimal size range