Search

Deformation and failure of coal is a complex process with damage evolution, so it's important to study the energy mechanism during coal damage process under all kinds of loading conditions. A serial of cyclical loading and unloading tests of coal were conducted under different confining pressures by means of an advanced conventional triaxial compression testing system. The damage process of coal under confining pressure was discussed carefully. Experimental results show that hysteresis loops of coal occurs under cyclical loading and unloading conditions and correspondingly damage dissipation energy increase with increasing stress. Elastic modulus of coal would decrease with increasing cyclical stress under low confining pressure or uniaxial compression, but it would not decrease with increasing cyclical stress under high confining pressure. It indicates that damage mechanism changes due to the effect of confining pressure. So a new definition of coal damage variable was suggested based on energy analysis and the corresponding damage evolution regular was given. Such definition avoids the default of traditional definition of damage variable based on elastic modulus and can well describe the damage content of coal under different confining pressures. [ABSTRACT FROM AUTHOR]