三轴循环加卸载下煤岩损伤的能量机制分析

由于煤岩的变形破坏是一个十分复杂的损伤演化过程,因此有必要深入研究各种加载模式下煤岩损伤演化过程的能量转化机制。通过岩石三轴循环加卸载试验,分析了不同围压作用下煤岩的损伤演化行为。实验研究表明,在循环加卸载情况下,煤岩表现出明显的循环滞后环,且随应力的增大煤岩的损伤耗散能增大。在低围压下及单轴压缩下,煤岩的弹性模量随循环应力增大而下降,但在高围压下煤岩的弹性模量没有随循环应力增大而下降。这表明围压的作用引起了煤岩损伤机制的变化。为此给出了基于能量分析的损伤变量定义及其演化规律,克服了传统的基于弹性模量定义的损伤变量的不足,可以较好地描述不同围压作用下的煤岩损伤演化程度。

Energy analysis on damage of coal under cyclical triaxial loading and unloading conditions

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.