| Summary: | Fracture toughness is used to characterize rock resistance to fracturing and it is important in theoretical research and engineering applications. Mode-I fracture toughness can be predicted on the basis of an empirical relationship between fracture toughness (<i>K<sub>IC</sub></i>) and tensile strength (<i>σ<sub>t</sub></i>). In underground engineering, rocks are often subjected to different temperatures. Therefore, this paper explores the effect of temperature on the relationship between mode-I fracture toughness and tensile strength. The results show that the change trends in the <i>K<sub>IC</sub></i> and <i>σ<sub>t</sub></i> values of rocks at temperatures from 20 °C to 600 °C are broadly consistent with each other. For rocks heat-treated to the same temperature, the <i>K<sub>IC</sub></i> of the rock increases with an increase in <i>σ<sub>t</sub></i>. This positive correlation between <i>K<sub>IC</sub></i> and <i>σ<sub>t</sub></i> is different in rocks heat-treated to different temperatures. Critical crack propagation radius (<i>r<sub>IC</sub></i>) is an important factor in the relationship between <i>K<sub>IC</sub></i> and <i>σ<sub>t</sub></i> and is related to the type of rock and the conditions under which it is tested. For the same rock, <i>r<sub>IC</sub></i> is quite different after it has been exposed to different temperatures. The positive correlation between <i>K<sub>IC</sub></i> and <i>σ<sub>t</sub></i> results from a similarity in the fracture morphology and properties of failure when rock is destroyed in fracture and tensile tests.
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