IDENTIFICATION OF NONLINEAR FRACTURE PROPERTIES FROM SIZE EFFECT TESTS AND STRUCTURAL-ANALYSIS BASED ON GEOMETRY-DEPENDENT R-CURVES

The size effect method, previously developed for concrete and mortar, is demonstrated for rock. Geometrically similar fracture specimens of limestone are tested and the measured maximum load values are used to obtain fracture energy, fracture toughness and effective size of the fracture process zone. Further, it is shown how to determine, from these results, other nonlinear fracture parameters including the critical effective crack-tip opening displacement. R-curves, dependent on specimen geometry, are calculated and used to predict load-deflection curves, which are found to agree very well with measurements. A modification of the R-curves for post-peak response is proposed.