Research On Mechanical Property Of Coal Rock Under Tensile Impact Loading

Dynamic disasters,such as rock burst,coal and gas outburst,still occur frequently during mine exploitation all over the world.Although,coal rock is subject to compressive impact loading under common conditions,its tensile failure becomes the main concern owning to the effect of stress wave.This paper selected the coal rock as research object,and the research work was carried out from perspective of optimization of dynamic tension impacting equipment,experiments of coal's one-dimensional dynamic tension and engineering simulation of coal-rock structure separately.Considering the experimental demand of coal's dynamic tension,the dimension of parts in SHTB apparatus was designed and optimized,with correlation check formula for variable cross-section impact derived.Hence,the influences of parts dimension on waveform multiply,wave amplitude,generation of incident wave were studied.Therefore,one-dimensional dynamic tension experiments were conducted on coal specimen,and the quasi-static tension,dynamic compression experiments were carried out as well to serve as a comparison in the meantime.The experiment results show that there exists an obvious strain-rate hardening effect in coal dynamic tension at low strain-rates,and the failure strain is insensitive to strain-rate;while,the dynamic strength is insensitive to strain-rate and the failure strain increases with growth of strain-rate at low strain-rates.Besides,the dynamic strength and module of coal rock show an evident strengthening effect compared to the quasi-static one.Moreover,compared to the dynamic compression property of coal rock,the ultimate strength of dynamic tension is far lower than that of dynamic compression,with a gap of around an order of magnitude.Meanwhile,on basis of ABAQUS finite element simulation,the dynamic tension impacting numerical simulation on coal rock was performed,with the basic parameters in constitutive equation modified.The stress-strain curves obtained by simulation is consistent with the experimental one,which verifies the reliability of SHTB tensile impacting experiment on coal rock.Additionally,The engineering model of "rock-coal-rock" structure was established,and the dynamic tensile impacting at low strength and high strength were carried out respectively.The simulation results show that at low impact strength,the damage of "rock-coal-rock" structure appears at the free surface of working area at first;At high impact strength,the structure was damaged inside the model firstly,then it stretches to the free surface of working area,with a fracture form of "layered" failure.It is noted that this fracture form is similar to the failure form in dynamic tension experiments of coal specimen,which is a typical effecting result of reflected stress wave.Thus,the correctness of basic conclusions is verified by both experiment and numerical simulation.