Study On Mechanical Properties Of Coal Rock Under Multiple Dynamic Impact Load

The rock burst occurs in the mine suddenly,and mine is often subjected to multiple impact because of rock burst.The mechanical characteristics of single impact and multiple impact must be different.Coal rock is as the action object of rock burst,it is necessary to study the mechanical properties of coal rock under multiple impact.This paper takes coal rock as the research object,the research is carried out from the optimization of the multiple impact equipment,the two impact test and the engineering simulation.Two kinds of SHPB impact loading system are designed,that is the inner and external bullet loading system and the front and back bullet loading system,the SHPB correlation check formula for variable cross-section impact is derived,good waveform calibration is obtained,Finally,the internal and external bullet loading system is selected for double impact experiment considering the experimental feasibility,cost,processing difficulty and so on.The static loading test and the single impact loading test is operated for comparing with double impact experiment,and two types of coal samples were chosen to do the experiments of low strain rate and high strain rate,Experimental results show,at the single impact,when the strain rate is low,Strain rate hardening effect of coal rock is obtained,when the strain rate is high,the strength is approximately constant with strain rate increasing;At the double impact,when the strain rate is low,the strength will increase at the second impact,When the strain rate is high,the strength will be reduced at the second impact,which has great difference with the mechanical characteristics of single impact.At the same time,based on ABAQUS,the double impact numerical simulation on coal rock is performed,the variation rule of stress-strain curves is consistent with the experiment,the reliability of the double impact experiment on coal rock SHPB is verified.The numerical simulation of "rock-coal-rock" structure with multiple impact is established,The single impact,double impact and four impact simulation of low strength and high strength were carried out.The simulation results show:the impulse is kept the same,at low impact strength,the damage of "coal-coal-rock" structure grows with the number of impact increasing;at high impact strength,with the impact number increasing,the structure damage roughly maintained the same.At the view of the stress history,at the low strength,the stress strengthen phenomenon appears in the stress time curve;At the high strength,the strength weaken phenomenon appears,which is consistent with the results of the double impact test of SHPB.Thus,the correctness of the conclusion is verified by experiment and numerical simulation.