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循环加载下砂岩断裂特性试验及模拟研究
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中南大学

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国家自然科学基金资助项目(51979293)


Experimental and Simulation Study on Fracture Characteristics of Randstone under Cyclic Loading
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central south universtiy

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National Natural Science Foundation of China(51979293)

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    摘要:

    利用WHY-200/10微机控制万能试验机,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,主要有三个阶段: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(PFZ)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。

    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, to study on the type I fracture mechanical characteristics and deformation of red sandstone under cyclic loading and unloading feature.Based on the macro-mechanical parameters of red sandstone, PFC3D numerical simulation experiment was conducted to investigate the law of microcrack propagation.The experimental results are as follows. The effect of cyclic loading will make the type Ι fracture toughness(KΙC) decreased,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 its static loading curve.The deformation at the cyclic loading failure point is similar to the post-peak deformation at the same load level in the static load curve.The process of radial displacement and deformation of the specimen 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 and microcrack propagation of the sample are only in the initial and acceleration stages.When the upper limit ratio is 0.75, the displacement deformation and microcrack propagation are only in the initial and stable stages, and no fracture failure occurs.Under cyclic loading, the micro-cracks in the fracture process zone (PFZ) at both ends of the ligament of the sample were fully derived and expanded, and the number of final micro-cracks was significantly more than that under static loading.

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  • 收稿日期: 2020-02-20
  • 最后修改日期: 2020-06-16
  • 录用日期: 2020-06-29
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