三维内置裂隙倾角对类岩石材料拉伸力学性能和断裂特征的影响

INFLUENCES OF 3D INTERNAL CRACK DIP ANGLE ON TENSILE MECHANICAL PROPERTIES AND FRACTURE FEATURES OF ROCK-LIKE MATERIAL

采用试验手段研究单轴拉伸条件下内置三维裂隙倾角对类岩石砂浆材料力学特性及断裂特征的影响。试验中配制物理力学性能与砂岩接近的砂浆材料,研制三维裂隙空间定位装置,同时改进传统岩石材料直接拉伸试验方法,研制黏结轴拉试验装置。试验结果发现,含裂隙砂浆试件的单轴拉伸受力变形过程分为4个阶段:缺陷张开阶段、弹性变形阶段、弹塑性变形阶段和破坏阶段,其中弹性阶段所占比例最高,突发性破坏阶段是拉伸破坏和压缩破坏最明显的区别。裂隙倾角α的改变对砂浆材料力学性能影响很大,随着α增大(0°<α<90)°,试件峰值强度σP逐渐降低,α=45°左右时,σP变化幅度最大。在拉伸荷载作用下,内置裂隙长轴前缘附近先后产生包裹状翼裂纹和次生裂纹,在短轴附近产生扭结区,裂隙的张拉扩展导致试件最终断裂。裂隙倾角α的改变影响裂隙扩展的轨迹和试件破坏后的形态。

Uniaxial tensile experiments are conducted to study the influence of 3D internal crack dip angle on tensile mechanical properties and fracture features of rock-like material. Special mortar sample of which physical and mechanical parameters are closed to those of sandstone is prepared; and spatial location device for 3D crack is designed. Some improvements are performed for direct tensile experimental methods with rocks; and location equipment for rock-like material bonding tensile experiment is also presented. Experimental results indicate that the tensile loading and deforming process of mortar samples with preexisting crack can be divided into four stages： flaws opening stage, elastic deformation stage, elastoplastic deformation stage, and failure stage, among which elastic stage takes up the most proportion; and the abrupt failure stage is obviously different between tensile and compressive failure. Change of crack dip angleα has much influence on mortar mechanical properties. As α grows （0° 〈α〈90°）, the peak strength, σp, of sample reduces gradually, and when αis around 45° , the σp change amplitude is the largest. Under uniaxial tensile stress, the wrapping wing crack and secondary crack initiate sequentially near the long axis front of internal crack; and the kink region also initiates near the short axis front of internal crack. Finally, the tensile propagation of cracks leads to sample fracture. The change of dip angle has great effects on crack propagation track and sample failure mode.