زهرا شيرازي تيراني

Rock fracturing plays a decisive role in many branches of engineering, including mining, tunnelling, dam construction an‎d the exploitation of oil an‎d gas reservoirs. Understan‎ding its mechanism is essential for designing safe an‎d optimal structures. A review of previous research shows that most past studies have focused on rock specimens under compressive loading an‎d that only a limited number of investigations have been conducted on ring-shaped rock specimens under tensile loading. Furthermore, the application of strain-based criteria to analyse the failure process of these specimens has yet to be investigated. Unlike stress-based criteria, strain-based criteria depend on material properties an‎d produce different results for different Poissonʹs ratio values. Therefore, they can provide a more accurate an‎d practical analysis when designing rock structures. This study investigated the failure behaviour of ring-shaped rock specimens using base strain criteria to examine fracture toughness an‎d crack propagation trends under different loading conditions. The specimens were tested at different crack angles under pure Mode I, mixed Mode I/II an‎d pure Mode II loading, an‎d the finite element method was employed to determine fracture parameters. The performance of two criteria, Maximum Tangential Strain (MTSN) an‎d Generalised Maximum Tangential Strain (GMTSN), in predicting fracture behaviour was investigated. The results showed that the GMTSN criterion agreed better with the experimental data than the MTSN criterion, particularly under composite loading conditions an‎d in pure Mode II loading. This improvement in performance is mainly due to the GMTSN formulation considering the T-stress component, which increases the accuracy of predictions an‎d reduces analytical error. Furthermore, analysing the effect of specimen geometry showed that, for specimens with a smaller inner radius, the difference between the predictions of the two criteria is more pronounced, whereas in specimens with a larger inner radius, the performance of both criteria is approximately similar an‎d acceptable. Furthermore, the T-stress component also influences the crack initiation angle; an increase in the magnitude of this stress leads to an increase in the crack angle, while its decrease leads to a decrease in the same angle. Overall, the findings of this research indicate that in cases where the role of the T-stress component is prominent, the GMTSN base strain criterion can provide more accurate predictions an‎d more reliable analyses than the MTSN criterion an‎d can be used as an effective tool in the design an‎d analysis of rock structures.

شكست سنگ , نمونه رينگي‌شكل , بارگذاري مركبI/II , مؤلفه تنش T

Rock fracture , Ring-shaped specimen , mixed mode I/II loading , T-stress

Zahra Shirazitirani

Majid Reza Ayatollahi