Crack propagation study in concrete and rock using discrete element method, digital image correlation and ultrasonic test.

The failure of concrete and rock is primarily governed by the initiation and propagation of cracks under different loading conditions. Despite extensive studies, the failure mechanisms remain partially understood. This paper presents an integrated numerical and experimental investigation into concrete and rock failure mechanisms using the Discrete Element Method (DEM), Digital Image Correlation (DIC), and ultrasonic compressional wave velocity (UCWV) test. Uniaxial compressive strength (UCS) and Brazilian disk splitting (BDS) tests were first conducted on concrete and rock samples. The obtained stress–strain curves and the observed failure patterns were used to validate the DEM-based numerical models. Moreover, compressional wave velocity (Vp) was measured by some UCWV tests before and after performing each UCS test to support the DEM results. Additionally, BDS tests were performed on both concrete and rock samples while high-speed imaging captured the fracture process. The results of numerical modeling indicate that the DEM model effectively reproduces the mechanical behavior and failure pattern of the samples. Microcrack initiation typically occurred near the loading boundaries and propagated toward the specimen center, eventually forming a major macrocrack along the loading axis. The BDS results also showed that crack propagation was predominantly aligned with the loading direction. Additionally, high-speed imaging captured the fracture process, revealing tensile and shear mode.