Characterizing the mechanical tensile behavior of Beishan granite with different experimental methods

Highlight
• The tensile behavior of granite is studied with different testing methods.
• Differences between the direct and two types of indirect tensile tests are studied.
• The macrobehavior of rock sample is well explained by the recorded AE events.
• The indirect tensile test is sensitive to the test set-up.
• It is indicated that the strength obtained by the direct tensile test is more reliable.

This work investigates with different test methods the mechanical tensile behavior of Beishan granite, especially the damage evolution process. The granite is taken from the Beishan site, a potential Chinese area for high-level radioactive waste repository. In the work, three widely used tensile testing methods are employed, namely the Brazilian test with simplified ISRM standard (Type I), the Brazilian test with the China standard (Type II), and the direct tensile test. An acoustic emission test system is also used to capture the microcracking process under different loading conditions. Even though the tensile strength obtained by the three testing methods is similar, some difference can still be noticed. The highest value of average tensile strength (11.24 MPa) is obtained by the indirect method proposed by IRSM, which is about 22% higher than the indirect method with China standard (9.15 MPa) and about 18% higher than the direct tensile test (9.53 MPa). The damage evolution process is further analyzed based on the recorded AE events. It is revealed that in direct tensile testing, the AE events accumulated mainly along the failure surface, whereas in indirect tests the location and variation of AE events are much more complex. Moreover, due to the stress concentration induced by the steel bars placed between the flat plate and the specimen, the accumulation of AE events around the loading surface is more significant in the indirect test with the China standard than the accumulation recorded in the IRSM method. The recorded AE events give rise to a reasonable explanation of the macroscopic mechanical behavior of granite, and are also valuable for understanding the damage evolution process of granite induced by tensile stress.