The behavior of a specimen under uniaxial tension and the process of microfracture in such a specimen are phenomena of considerable interest from the point of view of understanding strength charaterization of rock. We present numerical results, based on A simulator named Rock Failure Process Analysis code (RFPA), that show the nucleation and growth of macrocracks in relatively homogeneous and heterogeneous specimens under uniaxial tension. In this simulator, the heterogeneity of rock is considered by assuming that the material Properties of elements conform to Weibull distribution, an elastic damage-based law that considered the strainrate dependency is used to describe the constitutive law at mesoscopic scale, and finite element program is employed as a basic stress analysis tool. The failure process of Brazilian disk of rock is numerically simulated, and the numerical results are compared with the available experimental results.
While the details of macrocrack formation varied from specimen to specimen, a number of features were Consistently obtained in the numerical simulations. In all relatively homogeneous specimens, the macrocrack nucleated abruptly at a point in the specimen soon after reaching peak stress. Prior to macrocrack nucleation, AE events or microfractures were distributed diffusely throughout the specimen. It is very difficult to predicate Where the macrocrack will initiate. The failure of the specimen is completely brittle and no residual strength is Observed. Relatively heterogeneous specimens showed somewhat different response. In these simulations, the same diffused AE events or microfractures but with higher count number appeared in the early stage of loading. For the specimens with the same property of heterogeneity, however, the numerical simulations show that the failure modes depend greatly on the crack initiation location that is found to be sensitive to the local disorder features within the specimen.
Tension failure is one of the most important failure l1lodes in brittle materials such as rock. Even in the Situation of compression, it is found that, at a smaller size Scale, i.e., the micro- and meso-level, fracture of rock is essentially a tension phenomenon. In addition, Since the tensile strength of rock is much lower than its compressive strength, the direct consideration at analyzing the tensile behavior of rock under direct tensile loading conditions is particularly required in designs of underground structures. However, as pointed out by Okubo and Fukui (1996), the current design process fails in this regard and only limited data are available on rock tensile characteristics, especially complete stress-strain curves in uniaxial tension (Okubo and Fukui, 1996; Peng, 1975; Nova and Zaninetti, 1990).
Better understanding the dynamic fracture processes of rocks promises benefits in many area form rock mechanics to mining engineering and earthquake prediction. For example, it is essential to understand how fracture initiate and propagate under different loading conditions in order to provide suggestions for understanding real rock fracture process. During the past several years researchers have carried out many dynamic tests of quasi-brittle materials such as rock and concrete.
