Deformation intensity and acoustic emission characteristics of hard coal sample under uniaxial compression after high temperature

In order to explore the mechanism of high temperature effect on the mechanical properties and acoustic emission characteristics of coal samples, after natural cooling at 100, 200, 300, 400 and 500 degrees Celsius, the AE information of coal samples was detected synchronously during uniaxial compression, and then the fragments were scanned by JSM-6 390 LV electron microscopy.With the natural cooling after different temperatures heating, the micro-structure of coal samples and the deformation, strength and acoustic emission characteristics of coal samples during uniaxial compression were analyzed.The results show that ① the deformation of coal sample after the high temperature can be divided into four stages, i.e.compaction, elasticity, yield and damage in the process of uniaxial compression.The higher the temperatures experienced, the more obvious the compaction and yield stages.After peak, the stress drop is slowed; ② After high temperature heating, the elastic modulus, deformation modulus and compressive strength of hard coal samples decrease with temperature increases periodically.The 100℃ and 500℃ high temperatures have a significant influence on elastic modulus, deformation modulus and compressive strength.In 100-400℃ temperature range, the temperatures have the same influence of elastic modulus, deformation modulus and compressive strength of the coal samples.Compared with the coal samples at a normal 25℃, the average decreases of elastic modulus of coal samples after 100, 200, 300, 400 and 500℃ heating were 19.7%, 19.8%, 24.2%, 34.3% and 77.4% respectively, and the average decreases of compressive strength were 47.88%, 49.99%, 56.24%, 56.91% and 87.57% respectively; ③ The deformation and failure process under uniaxial compression are always accompanied by acoustic emission information.The acoustic emission amplitude, count, energy, and stress - time curve have better corresponding relationships during the loading on coal samples.The acoustic emission characteristics of coal sample after different high temperatures heating are different.The maximum amplitude, count and energy of acoustic emission does not occur at the same time.The acoustic emission total amplitude and time curve turning point is earlier than the cumulative count and energy curve turning point, and with the increase of temperature, the accumulative amplitude curve turning point and time curve turning point occur earlier, and the cumulative counts and energy curve turning point occurs later; ④ After high temperature, the acoustic emission parameters and temperature of coal samples have segmented characteristics, and their cumulative amplitude and count increase first then decreases with the increase of temperature, and the accumulative energy fluctuates with the change of temperature; ⑤ There is no definite relationship between the compressive strength of the coal sample and the cumulative amplitude, count and energy of the emission, and the compressive strength and acoustic emission parameters are the different properties of the coal samples.The structure of coal samples has changed after high temperature action at 100-500℃.The number and scale of cracks in coal samples increase with the increase of temperature.The change of internal structure of coal samples is the cause of deterioration of mechanical properties of coal samples. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.