Experimental study on mechanical characteristics and damageevolution law of coal samples under cyclic load

In order to explore the mechanical characteristics and damage evolution of coal samples under cyclic load,using the TAW-2000 press machine and SH- II acoustic emission(AE)system was used.The cyclic load test results show that:with the increase of coal cycle peak stress,peak cyclic axial strain,radial strain and plastic deformation showed linear growth.The coal sample is broken into many blocks with different shapes.With the increase of cyclic stress,the curve shows obvious migration effect.With the increase of cyclic peak stress,the volume strain increases continuously,the curves are discrete-intensive-discrete.Through the elastic modulus and the peak value large change,the coal sample can be broken at one time and two times,and the coal sample can be broken at one time and two times by the Poisson ratio fluctuation and steady growth.With the increase of the cyclic stress,the AE count increases continuously,and the AE count increases rapidly after a certain point,and the coal sample reach the obvious plastic stage.In the early stage of cyclic loading and unloading,the damage degree is low,showing a slow growth trend.When the plastic boundary point is reached,the damage variable shows a stepwise growth.The loading stage of AE energy growth trend is first slow after fast speed again,the unloading stage of AE energy growth has been relatively slow and steady,the abnormal growth of the AE energy can also predict the coal sample to failure.The loading and unloading response score is typically four stages,showing a U type change overall.