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压剪荷载作用下红砂岩裂纹尖端应变分布特征及起裂机理研究
Study on strain distribution characteristics and fracture initiation mechanism at crack tip of red sandstone under compressive shear load
投稿时间:2023-07-10  修订日期:2023-11-06
DOI:
中文关键词:  剪切盒试验  压剪断裂  数字图像相关技术  断裂机理
英文关键词:shear box test  compressive shear fracture  digital image correlation technique  fracture mechanism
基金项目:中国博士后科学基金,国家自然科学基金项目(面上项目,重点项目,重大项目)
作者单位邮编
左金涛 四川大学 水利水电学院 610065
卓莉* 四川大学 水利水电学院 610065
刘怀忠 四川大学 水利水电学院 610065
谢红强 四川大学 水利水电学院 610065
何江达 四川大学 水利水电学院 610065
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中文摘要:
      岩石在纯剪切荷载作用下,产生的裂纹都为Ⅰ型或者复合型断裂,为了研究Ⅱ型断裂,有必要研究压剪荷载共同作用下的断裂机理。本文利用剪切盒装置对双边切口的红砂岩试样进行加载,并通过数字图像相关(DIC)技术对试样切口尖端及岩桥上的应变状态进行分析,最后对裂纹起裂机理做出判断。试验结果显示,剪切角为30°至60°时试样均从切口尖端起裂,并且起裂裂纹沿岩桥所在平面有不同程度偏转;剪切角为70°时试样从岩桥中部起裂,起裂裂纹沿着岩桥所在平面。分析得到的主要结论如下:随着剪切角的增大,起裂平面张拉位移最大值和滑移位移最大值之比逐渐增大,起裂机理逐渐由剪切转变为张拉断裂;当剪切角为30°、40°时,试样岩桥在初始裂缝平面上的应力状态始终处于压剪状态,起裂机理为剪切主导的拉剪复合型断裂;当剪切角为50°、60°时,在加载前期,试样岩桥在初始裂缝平面上的应力状态处于压剪状态,但随着荷载进一步增大,岩桥应力状态逐渐转变为拉剪状态,起裂机理为拉剪复合型断裂;当剪切角为70°时,试样岩桥上的应力状态在加载过程中始终存在拉应力,并且随着荷载增大,切口尖端沿初始裂缝平面上也出现拉应力,不能达到压剪状态,裂纹起裂机理为张拉断裂。
英文摘要:
      In the pure shear state of rock, the fractures are all mode I or mixed mode. In order to study the mode II fracture, it is necessary to study the fracture mechanism under the combined action of compressive shear load. In this paper, the shear box device is used to load the doubled-edge notched red sandstone samples, and the strain state on the sample's notch tip and rock ligament is analyzed by digital image correlation (DIC) technique. Finally, the crack initiation mechanism is determined. The test results show that when the shear angle is 30° to 60°, all the samples crack from the notch tip, and the fracture deflection degrees along the rock bridge plane is different. When the shear angle is 70°, the sample cracks from the middle of the rock bridge, and the fracture grows along the rock bridge plane. The main conclusions of the analysis are as follows: with the increase of shear angle, the ratio of maximum tensile displacement and maximum sliding displacement increases gradually, and the fracture mechanism changes from shear fracture to tensile fracture; when the shear angle is 30° and 40°, the stress state of the sample rock bridge at the initial fracture plane is always in the compressive shear state, and the fracture mechanism is tensile shear mode fracture dominated by shear. When the shear angle is 50° and 60°, in the early stage of loading, the stress state of the rock bridge at the initial crack plane is in the compressive shear state, but with the further increase of the load, the stress state of the rock bridge gradually changes to the tensile shear state, and the cracking mechanism is the tensile shear mixed fracture. When the shear angle is 70°, tensile stress always exists in the loading process of the specimen rock bridge, and with the increase of the load, tensile stress also appears along the initial crack plane of the notch tip, which cannot reach the compression shear state, and the crack initiation mechanism is tensile fracture.
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