李江腾 张琰 马刚 赵远

摘   要：利用WHY-200/10微機控制万能试验机，对红砂岩人字形切槽圆盘试样（CCNBD）进行静态与循环加卸载试验，研究在循环加卸载下红砂岩的Ι型断裂力学特性及变形特征;并基于红砂岩的宏观力学参数进行PFC3D数值模拟试验，探究微裂纹扩展规律. 试验结果表明：循环荷载的作用会使砂岩的Ι型断裂韧度值KΙC减小;且随着循环次数的增加，砂岩的Ι型断裂韧度逐渐减小，直至达到某一下限值;砂岩CCNBD循环加载曲线受到其静态加载曲线的严格控制，循环加载破坏点变形量与静载曲线中同荷载水平下峰后变形量相近;循环加载下试样的径向位移变形过程和微裂纹扩展规律与上限荷载比相关，主要有3个阶段：初期加载阶段、中期稳定阶段、后期加速阶段;当上限比为0.95时，试样的径向位移变形过程和微裂纹扩展只有初期和加速阶段;当上限比为0.75时，其位移变形和微裂纹扩展只有初期和稳定阶段，且不发生断裂破坏;循环加载下试样韧带两端断裂过程区（FPZ）的微裂纹发生充分衍生和扩展，最终的微裂纹数目明显多于静态加载.

关键词：循环加载;断裂韧度;亚临界裂纹;人字形切槽;PFC3D

中图分类号：TU45                                  文献标志码：A

Abstract：The WHY-200/10 microcomputer-controlled universal testing machine was used to perform static and cyclic loading and unloading tests on cracked chevron notched Brazilian disc （CCNBD） of red sandstone， and the type I fracture mechanical characteristics and deformation feature of red sandstone under cyclic loading and unloading were studied. Based on the macro-mechanical parameters of red sandstone， PFC3D numerical simulation experiment was conducted to explore the law of microcrack propagation. The experimental results show as follows. Cyclic loading reduces the type Ι fracture toughness（KΙC） of sandstone， and with the increase of cycling times， the type Ι fracture toughness of sandstone decreases gradually until it reaches a certain threshold. The cyclic loading curve of CCNBD is strictly controlled by the static loading curve. The deformation at the failure point of the cyclic loading curve is similar to the post-peak deformation at the same load level as the static load curve. The process of radial displacement and deformation of the specimens under cyclic loading is related to the upper limit load ratio. There are mainly three stages： initial loading stage， middle stabilization stage and late acceleration stage. When the upper limit ratio is 0.95， the radial displacement deformation process and microcrack propagation of the sample occurred only in the initial and acceleration stages. When the upper limit ratio is 0.75， the displacement deformation process and microcrack propagation happen only in the initial and stable stages， and there is not fracture failure occurring. Under cyclic loading， the micro-cracks in the fracture process zone （FPZ） at both ends of the ligament of the sample were fully derived and expanded， and the number of final micro-cracks is significantly more than that under static loading.

Key words：cyclic loading;fracture toughness;subcritical crack;cracked chevron notched;PFC3D

对于工程中常见的Ⅰ型断裂破坏，国际岩石力学学会（ISRM）提出了人字形切槽短棒（SR）、三点弯曲圆梁（CB）、人字形切槽圆盘（CCNBD）等多种测试方法[1-2]. 崔振东等[3]通过CCNBD室内试验发现了其试样直径对试验结果的影响较大，并探究了CCNBD断裂破坏模式和裂纹……