Fracture toughness testing of brittle materials using semi-circular bend (SCB) specimen Mahinda D. Kuruppu a,⇑,1 , Ken P. Chong b,c,1 a Curtin University, Western Australian School of Mines, Kalgoorlie, WA 6430, Australia b George Washington University, Engineering, MAE, Washington, DC 20052, USA c National Institute of Standards and Technology, Engineering Lab., Stop 8615, Gaithersburg, MD 20899, USA article info Article history: Received 17 September 2011 Received in revised form 1 January 2012 Accepted 2 January 2012 Keywords: Fracture mechanics Brittle fracture Toughness testing Stress intensity factor J-integral Finite element analysis Mixed mode fracture Dynamic fracture abstract The semi-circular bend (SCB) specimen was suggested in 1984 for testing mode I fracture toughness of rock and other geo or brittle materials. Since then SCB has been used world- wide, extended and improved for many other applications by various researchers. Formu- lations for mode I and mixed mode fracture of this specimen proposed by a number of researchers are presented. Methods to determine fracture toughness using both straight- notched and chevron-notched specimens have been proposed although the general con- sensus is that a specimen having a sharp straight notch should yield accurate fracture toughness. Other applications of SCB specimen include testing of rock subjected to in situ conditions such as elevated temperature, confining pressure and pore water pres- sure. Furthermore it has been proven that it is a suitable specimen to test fracture tough- ness of rock at very high strain rates. Areas requiring further research to improve the accuracy of formulations are identified. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Fundamental research in deterioration and durability of structures and materials has shown great potential for increasing the life span of our infrastructure systems, as well as enhancing their functionality and serviceability. Brittle fracture mechanics is one of the main areas of research in deterioration of materials [1]. It is well known that linear elastic fracture mechanics is not strictly applicable for brittle materials like rock and other geomaterials due to the occurrence of relatively large fracture process zones as well as tension-softening behavior. In these materials, the process zone is made up of a region of microcracks that may be pre-existing and crack bridging may also occur in the process zone. Macrocrack initiation and propagation are associated with the activation of many microcracks in opening and/or shear modes, and in some cases, over- coming the resistance created by interlocking of relatively large and stiff grains of material. The sliding cracks that occur in compressive stress regimes, and the resulting wing cracks that occur due to local tensile stresses causing mode I microcrack- ing, have been very helpful in explaining the initiation and growth of cracks in brittle materials subjected to global compres- sive stresses [2]. In order to account for these variations in material behavior, brittle or rock fracture mechanics uses 0013-7944/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engfracmech.2012.01.013 Abbreviations: BD, Brazilian disk specimen; BEM, boundary element method; CB, chevron bend specimen; CCNBD, cracked chevron notched Brazilian disk; COD, crack opening displacement; CMOD, crack mouth opening displacement; FEM, finite element method; GMTS, generalized maximum tangential stress fracture criterion; SCB, semi-circular bend specimen; SIF, stress intensity factor; SR, short rod specimen. ⇑ Corresponding author. Tel.: +1 618 9088 6173; fax: +1 618 9088 6151. E-mail address: m.kuruppu@curtin.edu.au (M.D. Kuruppu). 1 Both authors Kuruppu and Chong are first authors. Engineering Fracture Mechanics 91 (2012) 133–150 Contents lists available at SciVerse ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech