Application of Asymmetric Notched Semi-Circular Bending Specimen to Evaluate Mixed-Mode I-II Fracture Behaviors of Sandstone

Abstract

In this paper, to investigate mixed-mode I-II fracture behaviors, three different asymmetric notched semi-circular bending specimens (ANSCB) were designed by adjusting the angle and the distance between supporting rollers to conduct asymmetric three-point bending tests. Several aid technologies, including acoustic emission (AE), digital image correlation (DIC), crack propagation gauge (CPG), and scanning electron microscopy (SEM), was utilized to monitor and assess the fracture characteristic. Meanwhile, the fractal dimension of the fracture surface was assessed based on the reconstructed digital fracture surface. The results show that mixed-mode I-II ANSCB three-point bending fracture is a brittle failure with the characteristics of the main crack being rapidly transfixed and the bearing capacity decreasing sharply. Based on the DIC method, the whole fracture process consists of a nonlinear elastic stage, fracture process zone, crack initiation stage and crack propagation stage. The crack initiation is mainly caused by the tension-shear strain concentration at the pre-existing crack tip. At the microscale, the crack propagation path is always along the grain boundary where the resultant stress is weakest. According to the monitoring of the AE, it can be found that micro-tensile cracks are mainly responsible for the asymmetric three-point bending fracture. The data obtained by CPG suggest that the subcritical crack growth rate is positively correlated to the ultimate load. In addition, asymmetric loading leads to a coarser fracture surface, and thus a higher fractal dimension of the fracture surface. The current study can provide a better understanding of the mixed-mode I-II fracture behaviors of rock.

The Counterbalance of the Adverse Effect of Abrasion on the Properties of Concrete Incorporating Nano-SiO2 and Polypropylene Fiber Based on Pore Structure Fractal Characteristics

“…Fractal geometry can be used to quantitatively characterize the irregularity, disorder, and complexity of shapes [20,21]. The pore network of eroded concrete exhibits significant fractal geometrical characteristics.…”

Influence of Carbon Nanofiber Content on the Fracture Mechanical Properties of Cement-Based Materials: Insights from Three-Point Bending and Nanoindentation Tests

“…Common macroscopic test methods for evaluating fracture mechanical properties include the TPB (three-point bending) test [16][17][18][19][20][21] and the wedge-splitting test [22][23][24][25][26]. Zhang et al [27] employed the TPB test to examine the impact of nano-SiO 2 and PVA fibers on the fracture characteristics of cementitious compounds.…”