Influence of initial crack length on fracture properties of limestone using DIC technique

Due to limitations in equipment and testing methods, there is currently little literature studying the effect of initial crack length (a(0)) on fracture parameters. Considering that limestone is often associated with the construction of cultural heritage buildings, monuments, tunnels, subways and power stations, so limestone beams were used as the experimental objects, and were used to conduct three-point bending (3-p-b) tests based on digital image correlation (DIC) technique to study the influence of a(0) on fracture parameters, including critical crack tip opening displacement (CTODc), nominal strength without considering the crack (sigma(N)), nominal strength considering the crack (sigma(n)), critical mid-span deflection (delta(c)), critical crack mouth opening displacement (CMODc), unstable fracture toughness (K-Ic(un)), fracture energy (G(f)) and fully developed fracture process zone length (l(mFPZ)). In addition, based on the boundary effect model (BEM), the relationships between the crack-to-depth ratio (alpha(0) = a(0)/D) with K-Ic(un) and G(f) were analyzed. The findings indicate that, as a(0) increases, sigma(N), K-Ic(un), G(f), and l(mFPZ) decrease gradually, while CMODc, CTODc, and delta(c) increase gradually; as two important parameters of the BEM, the boundary influence length (A(1)) and size-independent fracture energy (G(F)) are 27.08 mm and 74.67 N/m, respectively.