单轴压缩下岩石声发射及其分形特征

Acoustic emission of rock and its fractal feature under uniaxial compression

利用MTS815程控伺服刚性试验机加载系统和AE210声发射检测系统,对灰岩进行单轴压缩试验,获得了岩石应力—应变—声发射事件数曲线。根据声发射特征,将曲线分为5个阶段,各阶段对应的声发射特征差异显著;利用分形理论得出声发射事件数序列分形维数在整个加载过程中呈先升后降的规律。在压密阶段至弹性阶段,声发射分形维数呈现上升特征,表明岩石破坏以小尺度的微破裂为主且在岩石试件中微破裂相对均匀分布;在稳定破裂扩展阶段至破坏阶段,分形维数呈现下降特征,表明岩石中大尺度微破裂增加且逐渐向主破裂面贯通。对声发射事件数据序列进行计算,参数点与拟合回归的直线的相关系数均在0.82以上,参数点与所拟合直线之间具有较好的相关性,也即岩石破裂过程的声发射参数序列具有分形特征。

The stress-strain-AE event count curve is obtained from the uniaxial compression test made on limestone with the load- ing system of MTS815 program-controlled servo rigidity testing machine and AE210 acoustic emission detection system. In accord- ance with acoustic emission feature, the curve can be divided into five stages and the differences among the acoustic emission fea- tures corresponded to all the stages are significant, thus it is obtained from the fractal theory that the fractal dimension of the a- coustic emission event count sequence presents a law of rising at first and then failing during the whole loading process. From the compacting stage to the elastic stage, the fractal dimension of the acoustic emission presents a rising feature, which indicates that the rock failure mainly consists of the small-scale micro-ruptures, while the micro-ruptures in rock sample are uniformly distribu- ted. From the stage of the stable rupture expansion to the failure stage, the fractal dimension presents a falling feature, which in- dicates that the large-scale micro-ruptures are increased and continuously passed through to the main ruptured plane. The calcula- tion made on theacoustic emission event count sequence shows that all the correlation coefficients between the parametric points and the fitted straight lines of regression are above 0. 82 with better correlation between parametric point and fitted straight line, that is to say, the acoustic emission parameter sequence has the fractal feature during the fracture of rock.