Development of specimen geometries for mode i fracture toughness testing with disc type rock specimens

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2010
Alkılıçgil, Çiğdem
Flattened Brazilian disc and modified ring test methods are attractive methods being simpler compared to the other mode I fracture toughness testing methods on rock cores. The aim of this study is to improve these simple methods to yield fracture toughness values that are close to the ones determined by the suggested methods. ABAQUS finite element program was used to determine stress intensity factors of models with various dimensions. Comparing fracture toughness to the results obtained by semicircular bending method tests (0.94 MPa√m for andesite and 0.56 MPa√m for marble) and the cracked chevron notched Brazilian disc method tests (1.45 MPa√m for andesite and 1.08 MPa√m for marble), proper geometrical parameters were investigated by changing diameter, central-hole diameter, and loading angle of Ankara andesite and Afyon marble specimens. Semicircular bending method results were lower than the cracked chevron notched Brazilian disc method results. With flattened Brazilian disc method, the closest results (1.45 MPa√m for andesite and 1.12 MPa√m for marble) to the suggested method was obtained by 54 mm diameter discs with loading angles between 32.5° and 38.0° and with thicknesses between 19 mm and 34 mm. With modified ring test on andesite, the closest results to the suggested method was obtained by 75 mm diameter discs with 8 mm central-hole diameter and 25° loading angle (1.47 MPa√m for andesite and 1.07 MPa√m for marble), and with 14 mm central-hole diameter and 16° loading angle (1.50 MPa√m for andesite and 1.05 MPa√m for marble).