A novel compression-to-tension conversion device for direct tensile strength determination of rock-like materials using rotated H-shaped specimens: Experimental and numerical investigation

Understanding rock behavior under tension and quantifying tensile strength is of great importance, since rocks possess considerably greater strength under compressive forces than tensile ones. This paper presents a new approach for quantifying the tensile strength of synthetic rock specimens through direct testing. Seven types of rock-like materials composed of gypsum, cement, silica, sand, and water were prepared as specimens with a rotated H-shaped geometry, in which the vertical arms are aligned and interconnected while the horizontal arms are parallel but rotated 90° relative to one another. Specimens were installed in a stress-conversion testing rig and tested to failure. Concurrent with the laboratory tests, numerical modeling was carried out using PFC3D software, which was first calibrated for all seven material types. By conducting Brazilian tests and UCS tests, the micro-parameters of the numerical model were tuned until the computational predictions reproduced the observed mechanical response of the cast specimens. Following completion of the numerical modeling on H-shaped specimens, numerical and experimental results were compared, and the direct tension results were additionally benchmarked against indirect tension test outcomes. The results demonstrated strong agreement between numerical simulations and laboratory measurements. Tensile cracks were observed to nucleate at the vertical arm of the specimens, advance perpendicular to the loading axis, and ultimately bring about total fracture of the H-shaped specimen. Moreover, the tensile strength measured through the H-shaped specimen was approximately 30% inferior to that obtained from the Brazilian test.