Dynamic fracture mechanism and behaviour of V-notch white marble specimens with strain gauge and digital image correlation in three-point bending tests

Abstract

A three-point bending test was conducted on white marble specimens with V-shaped notches. The fracture mechanism of these specimens, including crack initiation toughness and propagation speed under different opening angles, was studied, and their special fracture behaviour was analysed. In this experiment, a falling weight loading device was used to impact the V-notch white marble specimens with different opening angles at the same impact speed. To measure the crack tip initiation toughness, a strain gauge theory is formulated in this study. The calculation results are in good agreement with the digital image correlation (DIC) calculation results. The error is approximately 10%, and the results obtained by the acute angle patching method are stable. The experimental results also show that when the opening angle is large, the specimens crack, and the energy dissipated by the crack initiation is considerable. Owing to the particularity of the white marble structure, the rock fracture behaviour during the dynamic fracture process is clearly observed in the experiment. All the specimens exhibited spreading crack branches at the crack tip under stress. The foregoing occurs because the original defects at the crack tip deform and grow after sustaining stress. Some of the cracks combine to form the main crack and produce branches. In this study, the microcrack areas on the crack tip and fracture path observed in the experiment are collectively referred to as the crack growth area. The expansion of the crack growth area precedes the expansion of the main crack. The expansion of the strain concentration area is calculated by DIC; it reflects the dynamic formation of cracks on the surface of the specimen. Scanning electron microscopy shows that microcracks mainly occur under the intergranular failure mode.