Experimental study on energy dissipation of mudstone in coal mine under im-pact loading

Rock crushing is essentially a process of energy absorption and dissipation. In the process of drilling and blasting during the excavation of rock roadway in coal mine,not only sufficient energy should be required to cause rock failure and rupture in the excavation zone, but also the damage caused by explosive energy to retained rock mass should be controlled. Especially the dynamic response characteristics of mudstone with lower strength under impact loading need to be studied emphatically. Taking the mudstone of typical roadway in Huainan mining area as the research object,a 50 mm diameter separated Hopkinson test device is used for the impact compression test on mudstone under different impact pressures to study the dynamic mechanical properties of mudstone and the characteristics of fracture and fragmentation of specimens under dynamic loading. The energy dissipation law of mudstone under dynamic loading was emphatically studied. To further reveal the relationship between the dynamic fracturing of mudstone with the main chemical composition and micro-structure of mudstone,the static physical and mechanical properties of mud- stone were tested,and the X-ray fluorescence spectroscopy ( XRF) and X-ray diffraction ( XRD) of mudstone were carried out to determine the main composition,chemical composition and particle composition of mudstone. The surface and fracture of mudstone specimens were magnified and observed with a 1 000-fold magnification electronic digital mi- croscope. Based on the meso-structure of rock,the damage and evolution of rock were studied through the analysis of the changes of meso-structure,physical and mechanical processes. The results show that the main chemical composition of mudstone is mainly SiO2 ,followed by Al2 O3 and Fe2 O3 ,which have low mechanical strength and poor physical prop- erties. The dynamic process of a large number of void defects ( such as voids,dislocations,micro-fissures,etc. ) in mudstone intensifies and results in damage under impact loading. Under the continuous action of stress wave,a large number of micro-damage and micro-inhomogeneity occur in the specimen and undergo complex evolution. A large number of microcracks will occur and develop in the internal structure of particles,along intergranular cracks and along grain boundaries,as well as in the stratification of fragments and inclusions at the structural boundaries. Under the action of the back-and-forth reflection of the stress wave,the mudstone specimens produce circumferential failure and axial splitting damage. The absorption energy of the specimen increases linearly with the increase of the incident energy. The transmission energy of the specimen increases logarithmically with the increase of the incident energy. The reflection energy of the specimen increases in the form of Quadratic function with the incident energy. The energy den- sity per unit volume,unit mass energy,and absorption impedance energy can be used to characterize the absorbed en- ergy of the sample,which increases linearly with the incident energy and quadratically with the strain rate.