13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Rock fracture toughness testing using SCB specimen M. R. Ayatollahi1,*, M. J. Alborzi1 1 Fatigue and Fracture Lab., School of Mechanical Engineering, Iran University of Science and Technology, Narmak, 16846 Tehran, Iran * Corresponding author: m.ayat@iust.ac.ir Abstract There are various testing methods for measuring fracture toughness of rocks. The semi-circular bend (SCB) specimen has recently received much attention by researchers for testing mode I fracture toughness of rocks and other geo-materials. While the SCB specimen is often prepared by a straight crack, chevron notched semi-circular bend specimen (CCNSCB) has been rarely utilized. In this paper, using the analytical methods for evaluating the minimum dimensionless stress intensity factor ( * min Y ) of chevron notched specimens, the slice synthesis method is employed to obtain the dimensionless critical stress intensity factor of the specimen. Then, fracture tests are performed on a white crystalline rock under mode I loading using the CCNSCB specimen. The experimental results show very little scatter in the measured values of fracture toughness. Keywords Rock, CCNSCB, Experiments, Finite element modeling 1. Introduction Fracture mechanics provides an engineering description for the transformation of an intact structural component into a broken one through crack extension [1]. Physical operations like blasting and crushing which are used in practical applications such as tunneling, drilling and mining projects are often considered as a process of formation and growth of cracks in rock masses. Fracture toughness is a major parameter in fracture mechanics which represents the energy required to initiate brittle failure around the crack tip. Fracture experiments on full scale rock masses are difficult and expensive. Thus, researchers prefer to perform their fracture analyses utilizing various laboratory-scale cracked specimens. Three testing methods have been suggested by the International Society for Rock Mechanics (ISRM) for measuring rock fracture toughness: (i) Chevron Bend specimen method (CB) (ii) Short Rod specimen method (SR) [2], and (iii) Cracked Chevron Notched Brazilian Disc (CCNBD) specimen method [3]. The semi-circular bend (SCB) specimen proposed by Chong and Kuruppu [5] has also recently received much attention by researchers. Some advantages of the SCB specimen are its simplicity, minimal requirement of machining and ability of preparation from rock cores. The SCB specimen can also be used as an alternative to the ISRM standard specimens in determining fracture toughness in orthogonal directions of transversely isotropic materials or sedimentary rock, such as sandstone or oil shale [6]. In addition to the rocks, the SCB method has been applied to other core-based brittle materials, such as concrete and asphalt. Furthermore, SCB is a suitable specimen to rock fracture toughness test at high strain rates [6]. Figure 1. a) Schematic view of SCB specimen b) Straight crack c) Chevron notched
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