This study explores explore the failure characteristics of high temperature granite under different numbers of heating–cooling cycles. Combining a series of laboratory uniaxial compression tests with acoustic emission (AE) monitoring, it reveals the AE characteristics and damage behavior of high temperature granite in different damage stages. Increasing the number of heating–cooling cycles exponentially raised the mass-loss and volume-increase rates of the granite and exponentially decreased the P-wave velocity. These results indicate that multiple heating–cooling cycles irreversibly damaged the high temperature rock mass. Moreover, the variations in both the P-wave velocity and the stress threshold at each stage gradually plateaued after three thermal cycles. Under uniaxial compression, the evolution mechanism of microcracks in the rock was successfully described by the AE characteristic parameters and real-time spatial AE position. The cumulative AE counts and AE energy rates were consistent in different damage stages of the rock specimen. Both quantities began increasing after entering the unstable crack growth stage. As the number of heating–cooling cycles increased, the main fracture mechanism of rock rupture transitioned from mixed mode to shear mode, as evidenced by the distributions of rise angle and average frequency. Meanwhile, the gradually increasing b-value indicated that small-scale fracture events gradually dominated the rock damage. The present results can assist the design of deep geothermal-resource mining schemes and safe mining constructions.

Understanding the brittle fracture behavior of rock is crucial for engineering and Earth science. In this paper, based on acoustic emission (AE) and laser Doppler vibration (LDV) monitoring technology, the staged damage behaviors of rock-like materials with different brittleness degrees under uniaxial compression are studied via multiple parameters. The results show that the brittleness degree determines the fracture mode. As the specimen’s brittleness degree increases, the tensile failure increases and shear failure decreases. AE activity is enhanced at the crack damage point. With an increasing specimen brittleness degree, different instability precursor information is shown during the unstable crack growth stage: the AE b value changes from the fluctuating to continuously decreasing state, and the natural frequency changes from the stable fluctuation to upward fluctuation state. The AE b value near the stress drop is the smallest, and it decreases with an increasing brittleness degree. The natural frequency reduction indicates the rock-like fracture. The natural frequency is a symbolic index that reflects staged damage characteristics and predicts the amount of energy released by brittle failure. These findings provide guidelines for rock stability monitoring and provide support for better responses to stability evaluations of rock slopes, rock collapses, and tunnel surrounding rock in engineering.

Cracks in rock mass have adverse effects on its mechanical characteristics and the stability of rock mass engineering. In this paper, cement mortar is used to make specimens with prefabricated cracks with different dip angles, and uniaxial compression, true triaxial compression and true triaxial unloading tests are carried out. The stress-strain curves under uniaxial compression and true triaxial compression have 4 and 5 stages, respectively. The strength of the specimen is the lowest as the dip angle of the crack is 45 °. Under uniaxial compression, the failure mode is mainly tensile failure, accompanied by a few shear cracks. With the increase of the crack dip angle of the specimen, the types of cracks generated at the tip of the prefabricated crack increase and change from shear crack to tensile crack. The distance between the crack tip and the loading end affects the failure degree of the specimen. Under true triaxial compression, the confining pressure significantly improves the strength and deformation characteristics of the specimen, and weakens the influence of the crack dip angle on the strength. The failure mode as a crack dip angle of 15 ° is mainly tensile, accompanied by tensile-shear composite and shear. The failure mode as crack dip angles of 45 ° and 75 ° is mainly tensile-shear composite, accompanied by tensile failure and shear failure. With the increase of the crack dip angle, the surface spalling of the specimen is more obvious, and the damage degree of the specimen is more severe. Under the triaxial unloading confining, the failure mode is mainly shear, accompanied by tensile and tensile-shear composite, more than two shear cracks through the top and bottom of the specimen lead to the failure. Compared with uniaxial compression, the damage degree of specimen is more severe under true triaxial compression and true triaxial unloading.

Locked segment of rock-like material specimens with different brittleness index were prepared by combining materials in different ratios. Compression-shear tests of rock-like material specimens with different brittleness degree were carried out by acoustic emission and Laser Doppler Vibrometer measurement. The fracture evolution process of the specimen was divided into three stages through the displacement-time curve: compaction stage and elastic deformation stage, constant deformation stage and accelerated deformation stage. The natural frequency responded obviously at the boundary point of the constant deformation stage and accelerated deformation stage, the point of natural frequency steeply dropped corresponds to the starting point of constant deformation stage, which is defined as the damage point. The point of substantial increase in the natural frequency corresponds to the starting point of accelerated deformation stage, which is defined as expansion point. There were obvious critical instability information before the failure of specimens: The natural frequency showed rise, steep drop and stable jitter; The ringing count rate and energy rate increased near the critical instability point; The b-value continued to decrease at a low level before the peak strength. Tensile failure was the main failure mode of the three specimens with different brittleness degree, the tensile failure degree increased with the increase of brittleness degree. The energy released by the specimen at failure moment increased with the increase of brittleness degree, and the b-value decreased with the increase of brittleness degree. The degree of brittleness is one of the important indexes to study the locked segment.

A series of mechanical experiments and penetration tests, for investigating the effects of additives, on DNAN-based explosives were carried out. At various strain rates, the data result that the stress-strain curves range 10−5s−1-102s−1, were obtained in mechanical experiments by the application of quasi-static and dynamic apparatus. Utilizing the visco-elastic Maxwell model which is calibrated with the experiment data,the dynamic behavior of the explosives could be simulated in penetration process. The results show that the peak stress and displacement of the explosive with binder 1# is smaller than those of the explosive with plasticizer 2# at the same positions. It indicates that the explosive with binder 1# undertake a less severe stress condition than the other, and the explosive with binder 1# may perform more stable. The conclusion of penetration tests which show that both of the additives stabilize the explosive are more effective, coincides with the simulation results.