Research On The Mechanical Characteristics Of Cyclic Impact Failure Of Gas-Containing Coal

In China’s energy production and consumption,coal has always played a leading role,and this situation will be difficult to change for a long time in the future.During the mining process of coal,frequent dynamic disturbances often occur,leading to energy accumulation and release within the coal seam,continuous development of micro cracks and fractures,and instability of the coal body leading to coal mine accidents.Cyclic impact load is a typical form of frequent dynamic disturbance.Studying the mechanical characteristics of cyclic impact failure of gas containing coal under cyclic load is of great significance for coal mine safety.This thesis mainly focuses on medium strength coal samples and analyzes the mechanical properties of gas containing coal under cyclic loading under different loading conditions using the SHPB test system.Orthogonal experiments and range analysis are used to analyze the sensitivity of mechanical factors to cyclic impact failure of gas containing coal.The main conclusions are as follows:(1)Conclusions of experimental study on the mechanical characteristics of gascontaining coal impact failure under cyclic dynamic load:(1)Under cyclic impact loading of coal samples,the basic shape of the stressstrain curve remains consistent,indicating that the constitutive characteristics of coal samples will not be changed under cyclic impact loading conditions.As the impact energy increases,the strain growth rate accelerates,leading to the occurrence of "strain softening" phenomenon.The fatigue life of coal samples is significantly affected by the impact speed,and as the impact speed increases,the fatigue life will decrease.At the same impact speed,the fatigue life corresponding to different gas pressures decreases with the increase of gas pressure,which is the result of the joint action of free gas and adsorbed gas.(2)As the number of cycles increases,the impact on the coal sample also increases,and the number of internal cracks gradually increases.The overall dynamic strength trend continues to decrease,and the strain rate of the coal sample shows a decreasing trend.The wave impedance of the coal sample gradually decreases,and the ability to resist external loads continuously weakens,leading to a decrease in dynamic strength with an increase in the number of cycles.The impact velocity under the same gradient gradually decreases with the increase of gas pressure,and the dynamic strength of the coal sample gradually decreases.The dynamic strength changes before and after coal sample failure fluctuate around 0.7～0.8.With the increase of gas pressure,the strain rate shows an increasing trend.The reason is that the influence of gas on the strength of coal makes it easier for the internal cracks to develop.(3)As the number of cycles increases,the strain rate presents a decreasing trend.The impact velocity under the same gradient,along with the increase in gas pressure,results in an increasing trend in the strain rate.The reason is that the impact of gas on the strength of coal bodies makes it easier for the internal fractures to develop.(2)Sensitivity analysis conclusion of mechanical factors for cyclic impact failure of gas containing coalThe sensitivity of peak strain influencing factors in cyclic impact of gas containing coal is in the order of impact speed,and gas pressure,cycle times;The sensitivity of peak strain influencing factors in cyclic impact of gas containing coal is in the order of impact speed,cycle times,and gas pressure;The sensitivity of the influencing factors of strain rate in cyclic impact of gas containing coal is in the order of impact velocity,gas pressure,and cycle times.This thesis includes 28 figures,10 tables,and 98 references.