Three-point bending test investigation of the fracture behavior of siltstone after thermal treatment

•The paper analyses the influence of temperature on fracture behavior of siltstone.•Failure mechanism greatly changes from 25 to 600 °C.•FEM analyses indicate that random crack initiation occurs in heterogeneous material.

The influence of temperature on the fracture behavior of siltstone is investigated in detail by mode I fracture toughness tests under three-point bending in situ SEM observations. A total of 27 specimens subjected to thermal pre-treatment have been tested. Experimental results indicate that effects of temperature on siltstone fracture behavior are obvious, not only on failure mechanism, but also on mechanical parameters like peak failure loads, fracture toughness and modulus of elasticity. The failure mechanism changes from intergranular fracture to mixed intergranular and transgranular fractures, and finally to intergranular fracture and thermal cracking with temperature from 25 to 60 °C. Fracture toughness KIC decreases slightly from room temperature 25 to 100 °C, and then increases significantly from 100 to 125 °C, and then gradually declines from 125 to 600 °C. A new numerical elastic modulus estimation method is proposed, considering a series of fluctuated experimental data. The variation of the elastic modulus with the temperature is similar with that of fracture toughness.