Search

As an important basic energy and industrial raw material in China, the safe mining of coal is the key to ensuring the national energy security and supporting the stable development of economy and society. With the gradual depletion of shallow coal resources, deep mining has gradually become the new normal of coal resource development in China, and the risk of coal- rock dynamic disasters has risen, which seriously restricts the safety and efficiency of coal mining, and has caused adverse effects on the sustainable development of coal industry. Accurate and reliable monitoring methods are considered as the prerequisite for the prevention and control of coal-rock dynamic disasters. Geophysical methods are widely used in the early warning of coal and rock dynamic disasters by sensing the acoustic, electrical, magnetic and other physical signals released during the deformation and failure process to retrieve the damage and failure state of coal and rock mass. Among those methods, the electromagnetic radiation method is a non-invasive, non-destructive, real-time and strong precursory technique suitable for the development requirements of mine informatization and intellectualization. Therefore, the development of electromagnetic radiation monitoring technology is of great significance for the prevention and control of coal and rock dynamic disasters and can provide important technical support for the construction of intelligent mines. The research achievements of electromagnetic radiation theory and technology are summarized in three aspects: experimental phenomena, mechanism models and technical methods. The discovery process of electromagnetic radiation phenomenon is reviewed. The signal characteristics, influencing factors, electromechanical coupling effects and other electromagnetic radiation characteristics of coal-rock are analyzed. According to the correlation between typical electromagnetic radiation mechanism models, stress action and crack propagation process, a classified review is made. The existing coal and rock electromagnetic radiation monitoring and early warning equipment and technical methods are then briefly introduced. On this basis, the new progress made in recent years is described in detail, including the research on vector characteristics of electromagnetic radiation, micro-scale verification of electromagnetic radiation mechanism, and electromagnetic positioning technology of coal-rock fracture. It summarizes the two current theoretical and technical research bottlenecks that the mechanism is not fully revealed and the location of disaster-prone areas cannot be achieved. Finally, a new target for the future development of electromagnetic radiation theory and technology is proposed.

The existing research only analyzes the rock burst appearance characteristics under specific conditions, lacks research on the rock burst appearance induced by coal pillar under the condition of thick and hard roof. In order to solve this problem, taking I010203 working face of a mine in Xinjiang as the research object, the paper analyzes the characteristics and causes of working face rock burst under the condition of thick and hard roof multi-seam mining by means of field monitoring and numerical simulation. By analyzing the spatial distribution law of microseismic and large energy events monitored on site, the distribution characteristics of support pressure, and the distribution characteristics of surrounding rock stress during the mining of the working face simulated by numerical simulation, this paper obtained the following results. The stress concentration and the microseismic event density in the transport roadway area of the working face are higher than those in the return air roadway area. And the stress concentration and microseismic event density in the roof and coal seam area are higher than those in the floor area. Based on the above results, the causes of coal pillar rock burst appearance in the mining process of I010203 working face are analyzed by using rock burst caused by dynamic and static combined load theory. ① It is easy to produce lateral overhanging roof above the coal pillar in the transport roadway section. The sudden breaking of the long overhanging roof generates a large amount of dynamic loads. At the same time, a large amount of static loads accumulate on the coal pillars and the roof during the mining process. When the superposition of the two exceeds the critical load, it may cause the rock burst appearance of the working face or a large energy event. The mining process of the I010203 working face mainly includes the main controlling factors such as coal pillar concentrated stress, overlying roof and surrounding rock supporting stress. Therefore, it is easy to produce coal pillar type and thick hard roof caving type rock burst appearance. ② When the mining position of the working face gradually approaches the boundary of the ‘knife shape’ goaf, the boundary stress is transferred downward to the I010203 working face, which leads to the further increase of the rock burst risk of the I010203 working face.

This paper aims to determine the relationship between thermodynamic entropy generation and fatigue crack propagation life of superalloy GH4169 at 300–650°C. The entire specimen was considered as the thermodynamic system. The plastic energy dissipation in the crack tip was obtained by finite element simulation utilizing the Chaboche nonlinear hardening model. Then the cyclic entropy generation rate (CEGR) and the accumulated entropy generation are calculated by combining simulation and experimental methods. Results show that the CEGR is a power function of the stress intensity factor range, and it is almost a constant at fatigue failure. The fatigue fracture entropy (FFE) increases as fatigue cycles at failure increase at constant temperature, but it first decreases and then increases when temperature increases from 300 to 650°C. A fatigue life prediction model based on the thermodynamic damage parameter is established and verified by comparison with experimental results and available data in the literature. Highlights: Thermodynamics provides a new thought to the study of elevated temperature crack growth.The Chaboche nonlinear hardening model is considered in entropy generation calculation.An entropy‐based damage parameter can represent the damage of a thermodynamic system.Entropy‐based life prediction model can acceptably predict the crack propagation life. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of RA-AF of coal failure in different coal bedding, uniaxial compression failure experiments of coal with 0°, 30°, 60° and 90° bedding angles were carried out. The mechanical and AE data of coal body were collected synchronously. The relationship between the characteristics of RA-AF and crack propagation mode was analyzed. The results show that: in the Ⅰ and Ⅱ stages, the AE count level is low, in the Ⅲ stage, the AE count is gradually increased, in the Ⅳ stage, when α=0° and 60°, AE counts are more and the peak value is higher; when α=0° and 90°, the tensile failure ratio is 58.44% and 58.06%, respectively, and the tensile failure is the main crack; when α=30°, tensile failure and shear failure are the same, and the crack appears as tensile shear composite failure; when α=60°, the shear failure ratio of the sample is 68.14%, and the shear failure is the main crack.