The effect of loading contact angle on the tensile behavior of rock disks

Tensile strength is one of the most important characteristics of rock masses that could govern the stability of rock structures. Due to difficulties in its direct measurements, indirect methods such as the Brazilian test have been developed to assess the tensile strength of laboratory-scale rock material. This study considers the effect of loading contact angle on the indirect tensile strength of rock-like disks by adopting experimental and discrete element methods. Several experimental specimens made of synthetic materials were examined under diametrical loading, and consequently, a numerical model using PFC3D was calibrated accordingly. Then, the impacts of the loading contact angle (θ) on the tensile strength, failure pattern, and contact force chain were investigated in detail. The results indicated that as θ increases from 0°, suggested by ASTM, to 90°, the tensile state is dominated at the specimen center, whereas for angles greater than 90°, the dominant stress state changed to compression. Also, while σxx (tensile stress) at the center of the disk did not change for θ below 40°, the σyy (compressive stress) and σzz (out-of-plan normal stress) increased after θ =30°. The analysis of developed cracks suggested that when θ is lower than 30°, the percentage of tensile and shear cracks were constant (80% and 20%, respectively). As the loading contact angle increased, tensile cracks decreased, whereas the other increased. By analyzing the failed specimens, three categories of crack patterns and two categories of contact force chains were identified.