# Shape Effect and Accuracy Analysis of Rock Tensile Strength Test
###### Abstract  
To investigate the influence of shape effects on the tensile strength of rocks, splitting tests were conducted on disc specimens with the same thickness-to-diameter ratio but different diameters using physical similarity simulation and numerical simulation experiments. Additionally, finite element analysis software was employed to perform numerical simulation tests on two types of dumbbell-shaped specimens involved in direct tensile tests of rocks. This study revealed that when the thickness-to-diameter ratio is fixed at 0.5, the splitting tensile strength decreases gradually as the specimen diameter increases from 30 mm to 110 mm. This trend can be well fitted using a power function. The tensile strength measured from direct tensile tests on the two types of dumbbell-shaped specimens shows a slight decreasing trend as the diameter of the central effective test area decreases. Moreover, the measured tensile strength is lower than the actual tensile strength. The test results for disc specimens are the closest to the actual tensile strength, followed by arc-transition dumbbell-shaped specimens, and lastly, straight-transition dumbbell-shaped specimens. The correlation coefficients between the test results and the actual tensile strength for the three types of specimens are also provided. t 29 January 202020 February 20202 February 20202 February 20202 February 20202 February 2020202 February 2  
method is widely used in engineering to determine the tensile strength of rocks because of its convenient specimen preparation and strong operability of the test [9; 10]. A significant number of studies conducted (both domestically and internationally) have focused on accurately measuring the tensile strength of rocks, as well as comparing various measurement methods. These studies have yielded many valuable results. In terms of measuring rock tensile strength, researchers [PERSON] and [PERSON] [11] proposed a conceptual model based on brittle spalling. They determined the tensile strength of rocks using the damage initiation threshold method. Their findings indicated that the results obtained from the Brazilian splitting test (BTS) often overestimate the true tensile strength (DTS). To address this, they proposed correction factors specific to different rock types: 0.9 for metamorphic rocks, 0.8 for igneous rocks, and 0.7 for sedimentary rocks. Furthermore, [PERSON] [12] introduced an innovative idea for measuring tensile strength by using three-dimensional images of the rock fracture surface. This indirect measurement method represents a new direction in testing technology. In the realm of direct tensile tests, [PERSON] [13] designed a new loading apparatus that incorporates an insertable disc drill hole rod to measure the direct tensile strength of rocks. He investigated the ideal contact angle between the rock and the loading rod, recommending a contact angle of 50\({}^{\circ}\) as optimal. Additionally, he examined how specimen shape affects test results and offered suggestions for optimization. Regarding the Brazilian splitting test method, [PERSON], [PERSON], and their colleagues [14; 15; 16] conducted indoor experiments and theoretical analyses to assess the impact of loading angles on test results. They concluded that a platform loading angle between 20\({}^{\circ}\) and 30\({}^{\circ}\) could yield more accurate measurements of tensile strength. In summary, the existing research has provided substantial theoretical and technical support for improving the measurement methods of rock tensile strength across various aspects. Through comparative analyses of direct tensile tests and Brazilian splitting tests, scholars have proposed correlation coefficients and correction factors between different methods, as well as optimized specimen designs and loading techniques. These findings lay crucial groundwork for further enhancing the accuracy and practicality of rock tensile strength testing.