## 1 Introduction
[37] conducted three sets of experiments considering different load contact configurations to study crack development in transverse isotropic sandstone discs subjected to the Brazilian test. This study confirmed that the anisotropy angles and load configurations have strong effects on crack development. [PERSON] et al. [42] performed an evaluation on the indirect tensile strength of various rocks using different types of jaws, and concluded that the determination of the indirect tensile strength of rocks was dependent on the loading geometry and the rock material. The major drawbacks of their work are that they focused only on the tensile strength of rock specimens and the failure patterns of failed discs. In addition, it can be found from the existing literature that most studies were carried out on a specific type of rock or rock-like material, and some of their conclusions are different and even contradictory. To summarize, the different findings in the above studies prove  
Figure 1: Typical Brazilian tensile test loading configurations: (**a**) flat loading platens; (**b**) flat loading platens with two small diameter steel rods and (**c**) curved loading jaws. that no current uniform understanding exists as regards the Brazilian test, and the failure mechanisms of the Brazilian discs subjected to different loading methods have not been fully recognized. Therefore, this study intends to thoroughly investigate this knowledge gap by considering various rock types and loading conditions. In order to detect possible crack initiation locations in the experiment and to study the development of surface deformations of rock specimens, traditional measuring instruments including strain gauges, linear variable differential transformers (LVDTs) and extensometers can be employed. However, these instruments are not capable of providing detailed information about the fracture behavior of the specimen. In addition, strain measurements of these instruments are highly localized, and will be affected by many factors such as temperature, adhesives, etc. [37; 41]. To overcome these limitations, the digital image correlation (DIC) method has been proposed as a non-contact optical measurement technique to investigate the damage evolution and crack development of rock specimens. It also has many other advantages, such as operating in real-time, and being full-field and non-destructive [43; 44]. The theoretical basis of the DIC technique was first proposed by [PERSON] et al. [45], and has been used in many fields of material testing. [PERSON] et al. [46] evaluated the fracture behavior of ductile and brittle specimens subjected to a uniaxial compression test using DIC. [PERSON] et al. [6] analyzed the deformation and failure processes of marble containing a single hole under uniaxial compression using DIC technology. [PERSON] et al. [41] studied the failure mechanism of sandstone disc specimens under three different testing conditions via DIC. [PERSON] et al. [47] used DIC to study the deformation and failure behavior of a rock specimen in the indentation test. [PERSON] et al. [37] applied DIC to investigate the crack development of a sandstone disc in the Brazilian test. All these works highlighted that DIC technology is applicable and reliable for characterizing the mechanical deformation behavior and failure patterns of various rock types. In this paper, three different load contact configurations were considered, including two international standard methods (Type I test and Type III test) as well as the Chinese standard (Type II test). Additionally, five different rock types with diverse brittleness indexes were tested. Finally, the effect of the load contact configurations on indirect tensile strength and the crack patterns (including crack initiation and propagation) with respect to various rocks were investigated in the Brazilian disc tests by combining DIC technology. The key findings of this work are essential in accurately using the Brazilian test to obtain the tensile strength and other information of a rock specimen.