Correlation between crack propagation and toughness in rocks and concretes

In this study, laboratory scale samples obtained from massive rock samples (Meram Andesite, Ankara Andesite, Afyon Grey Marble, Evliyatekke Tuff, Sille Andesite, Karaman Travertine), and massive artificial rock samples (moulded from gypsum powder mixtures) were used to examine relations between their toughness and crack propagation issues. Through laboratory tests, crack formation and propagation were observed in notched standard semi-circular bend (SCB) toughness test specimens and square-prismatic specimens resembling building columns, under vertical loading conditions. During the experiments, data suitable for digital image correlation (DIC) and gray level co-occurrence matrix (GLCM) image processing systems were generated, and the moments of crack initiation and propagation directions were analyzed post-experiment based on the experimental images. Standard rock mechanics tests, including uniaxial compressive strength, indirect tensile strength, water content, density, porosity, Schmidt hardness, and point load strength tests, were performed on the specimens. Furthermore, brittleness tests were conducted to determine the brittleness of the samples. Mode-I fracture toughness values were determined using notched semi-circular bend (SCB) specimens. To investigate toughness and crack propagation characteristics, prismatic specimens with square cross-sections made from a mixture of gypsum powder were prepared, and the deformation behavior of both solid specimens and those with circular perforations was monitored under vertical loading conditions. Crack formation and propagation behavior were observed in these specimens. In the field of civil engineering, similar load bearing tests for reinforced concrete building columns have been investigated at laboratory scale within the scope of the durability of structures. A comparative evaluation of these experiences with the results of the toughness tests performed in this study was made. To observe crack propagation, both notched and intact plate specimens were subjected to vertical loading and examined for their crack propagation behavior. Displacements on the specimens were recorded using high-speed, multi-shot equipment to analyze crack propagation behaviors through image processing techniques. The data from these recordings were analyzed using DIC and GLCM methods, providing insights into fracture toughness and crack propagation behavior. Column-like specimens, both solid and those with horizontally cored cylindrical holes at their centers, were subjected to strength tests. The toughness values of these specimens, along with the micro-level progression of cracks, were evaluated using DIC and GLCM methods.