Determination of Strain-Softening Curve and Fracture Toughness of Granite

The J-integral-based technique for measuring strain-softening curves is applied to determine the fracture toughness of granite. The measuring method has been recently proposed by Li for concrete. This method provides information on the fracture process zone formation and can be used for fracture toughness determination in strain-softening materials. CT specimens of three different sizes, 1.5 inch, 2.5 inch and 6 inch CT were tested to examine the specimen size effect of measured strain-softening curves. Strain-softening curves measured on 2.5 inch CT specimens are shown to be in good agreement with that determined from 6 inch CT specimens, indicating the possibility of determining the valid fracture toughness value by means of the J-integral-based technique. The test results for 1.5 inch CT specimens, however, yield a lower fracture toughness value than that obtained on the other specimen sizes, suggesting the need of detailed investigations on specimen size requirements for the reliable use of subsized specimens. Finally, the strain-softening curves obtained by the J-based technique are compared with existing data determined by uniaxial tensile tests on several types of granite.