True Mode III Fracturing of Rocks: An Axially Double-Edge Notched Brazilian Disk Test

Abstract

A new test, referred to as axially double-edge notched Brazilian disk (ANBD), is proposed to measure true mode III fracture toughness (KIIIc) of rock materials. The term true denotes a shear-induced fracturing via self-planar crack extension as opposed to a twisted tension-based one commonly observed in many mode III experiments of rocks. The ANBD test follows a straightforward procedure thanks to its simple core-based geometry and diametrical compression loading setup. Finite element analyses are employed to evaluate the stress intensity variations along the crack front and to calculate the point-wise stress intensity factors (SIFs) for different geometry and loading configurations. The results of ANBD tests conducted on granitic samples demonstrate the good performance of this test in yielding true mode III fracturing. The influences of the test parameters of ligament length and loading angle on KIIIc are also investigated. A comparison study shows that KIIIc values are similar to KIIc but almost 2.5 times greater than KIc. This demonstrates that the true mode III test offers a similar shear-based fracturing mechanism to the true mode II, which is significantly more energy-consuming than the tension-based mode I failure type.