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

A new test, referred to as axially double-edge notched Brazilian disk (ANBD), is proposed to measure true mode III fracture toughness (K-IIIc) 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 pointwise 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 K-IIIc are also investigated. A comparison study shows that K-IIIc values are similar to K-IIc but almost 2.5 times greater than K-Ic. 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. Highlights A new test named ANBD is introduced to measure true mode III fracture toughness. The test performance was evaluated by conducting experiments on granite samples. The effects of loading angle and ligament length were investigated. Measured values of KIIIc were compared to the ones of KIc and KIIc. Fracture surfaces of true and apparent mode III experiments were analysed.

Automated summary

This paper proposes a new test called ANBD to measure true mode III fracture toughness of rock materials. The test performance was evaluated through experiments on granite samples and the effects of test parameters were investigated. The results demonstrate the effectiveness of the ANBD test and provide insights into the fracture behavior of rock materials.