基于3D-DIC系统的白砂岩单轴压缩应变率效应的力学性能试验研究

Experimental Study on Mechanical Properties of White Sandstone Under Uniaxial Compression with Different Strain Rate Based on 3D-DIC System

通过选取典型岩样,研究了白砂岩在10^(-5)~10^(-3)s^(-1)应变率范围内的单轴压缩性能,采用3D-DIC系统观测和采集岩样表面位移云图,并分析不同应变率下岩样变形破坏特征差异。结果表明,岩样表面位移场变化反映了破坏面演化规律,剪切破坏面与位移场集中存在对应关系。全局轴向应变差异主要发生在微裂隙压密到弹性变形期间;加载初期,全局径向应变存在差异,在峰值强度时下端部区域径向位移最大,岩样上端部变形受到端部效应影响,径向向外膨胀受端面与垫片间摩擦限制;此外,下端部局部轴向应变大于上端部区域。随着加载速率增大,岩样从延性特征向脆性特征转变。加载速率较低时,岩样破坏过程中孔隙坍塌使得部分裂隙再次闭合、滑移而产生摩擦效应,从而使峰值强度附近的应力-应变曲线出现波动。白砂岩峰值强度、弹性模量、泊松比等力学参数随加载速率增大而增加。

Some typical rock was taken as the sample in an experiment to study the mechanical properties of white sandstone under uniaxial compression with strain rates ranging from 10^(-5)s^(-1) to 10^(-3)s^(-1). The surface displacement contours of the samples were observed and collected by using 3D-DIC system, and the difference in the deformation and failure characteristics of samples under the effect of different strain rate was also analyzed. The results show that the variation of displacement field on the surface of rock sample reflects an evolution law of failure surface, and there is a corresponding relationship between shear failure plane and concentrated displacement field. The difference in the overall axial strain mainly occurs during the period from micro-crack compaction to elastic deformation. At an initial stage of loading, there is difference in the overall radial strain. The lower end part of the sample has the largest radial displacement when the strength reaches the peak, while the upper end part is deformed under the impact of the end effect. The radial outward expansion is limited by the friction between the end face and the gasket. In addition, the local axial strain at the lower end is greater than that at the upper end. With an increase in the loading rate, rock sample has its mechanical characteristics converted from ductility to fragility. During the failure process of rock sample under the uniaxial compression with a lower loading rate, the occurred pore collapse results in friction effect due to the closure again and slippage of some cracks, thus there appears fluctuation in the stress-strain curve near the peak strength. It is shown that the mechanical parameters(peak strength, elastic modulus and Poisson′s ratio) of white sandstone increase as the loading rate increases.