单轴压类岩石试件应变局部化位置、方向及预警应用研究

Position, direction of strain localization of rock-like specimens under uniaxial compression and its application to early-warning

应变局部化是岩石破坏的先兆,为揭示单轴压缩条件下控制变形局部化带出现时间、位置和生长方向的主要因素。以白光数字散斑相关方法作为观测手段,获取实验过程中变形局部化的时间演变全过程数据,计算最大主应变场、最小主应变场、位移场,并结合轴力-位移关系曲线对多个试件的局部化演变特征进行了综合对比分析,发现类岩石脆性材料在单轴压受力条件下局部化带的发展沿最大主应变(最大压应变)方向,并随着最大主应变方向的偏转而发生偏转;局部化带的出现位置受最小主应变控制;短时位移场显示脆性类岩石材料局部化带内以张拉破坏为主,并非剪切破坏;局部化带不仅可在接近峰值载荷的高荷载条件下出现,还可能出现在荷载值较低的变形加速拐点处;局部化启动、局部化带两侧观测点水平位移分量反向是较好的构件破坏预警指标。

Strain localization is the warning sign of rock damage. In order to reveal the key mechanical factors that control its occurrence time, position and growth direction, digital image correlation method is used to obtain the whole deformation process of specimens under uniaxial compression tests. The maximum and minimum principal strain field, displacement field are then calculated. Combining with the axial load-displacement curve, the strain localization evolution characteristics of different specimens are compared and analyzed comprehensively. It is found that for brittle rock-like material under uniaxial compression the strain localization belt grows at the direction of maximum principal strain(maximum compressive strain) and deflects with the direction change of maximum principal strain;the position of the strain localization belt is controlled by minimum principal strain;the transient displacement field indicates that damage of brittle rock-like material in the strain localization belt is mainly caused by tensile deformation not shear deformation;strain localization not only occurs at the point close to peak load, but also at the inflection point where deformation accelerates but the load is low;the appearance of localization belt and opposite horizontal displacement vector along the belt are two proper failure prediction indices.