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SELECTION OF DEFORMATION MEASUREMENT DATA OF ROCK UNDER MTS COMPRESSION TESTS
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摘要: 变形测量数据的选取对认识岩石力学性质及变形参数的计算有着重要影响。MTS试验机已被广泛应用于岩石力学试验中，其中岩石的变形测量常用方式有引伸计、LVDT和压板位移，这3种测量方法得到的轴向应变的准确性和适用性有待深入研究。本研究采用MTS试验机进行岩石的单轴和三轴压缩试验，对比引伸计、压板位移和LVDT 3种方式测量得到的应力-应变曲线，分析3种不同测量方法的结果对岩样应力-应变曲线形态、强度和变形参数的影响。结果表明：峰值强度前，压板位移和LVDT测量得到的变形数据、计算的应力门槛值和变形参数存在较大误差，轴向应变应采用引伸计测量得到的变形数据；采用引伸计测量得到的变形数据在达到峰值强度后会出现轴向应变减小的现象，该曲线容易被误认为属于Ⅱ类曲线；建议在MTS试验机固定压头端安装LVDT传感器，采用LVDT测量得到的轴向变形计算峰值强度后的轴向应变；条件不允许安装LVDT传感器时，采用压板位移测量的数据来表示岩样在峰值强度后的变形。研究结果对于正确选用岩石变形测量数据、计算强度和变形参数以及认识岩石力学性质具有一定参考价值。Abstract: This paper investigates the accuracy and applicability of axial strain obtained by axial extensometer, LVDT and press-plate displacement. We carried out the uniaxial and triaxial compression tests of rock with MTS testing machine, and compared the stress-strain curves obtained with the axial extensometer, press-plate displacement and LVDT. Furthermore, we analyzed the effects of the results under three different measurement methods on the shape, strength and deformation parameters of the stress-strain curves of rock samples. The results show that in the pre-peak strength stage, the deformation data measured by the plate displacement and LVDT, the stress threshold value and deformation parameters have large differences. So axial strain should adopt the axial extensometer to obtain the deformation data. In addition, when the deformation data measured by the axial extensometer reaches the peak strength, the axial strain can decrease, and this curve can be easily mistaken as a class Ⅱ curve. It is recommended to install a LVDT sensor at the fixed head of the MTS testing machine, and calculate the axial strain after peak strength with the axial deformation measured by LVDT. When the LVDT sensor is not allowed to be installed, we should adopt the pressure plate displacement measurement to represent the deformation of the sample after the peak strength.
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Key words:
- Rock /
- Compression test /
- Deformation measurement /
- Obtaining value method /
- MTS testing machine
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图 4 大理岩轴向引伸计和压板位移应力-应变曲线的比较
Figure 4. Comparison of stress-strain curves between axial extensometer and plate-displacement of marble
图 5 花岗岩轴向引伸计和压板位移应力-应变曲线的比较
Figure 5. Comparison of stress-strain curves between axial extensometer and plate displacement of granite
图 6 玄武岩轴向引伸计和压板位移应力-应变曲线的比较
Figure 6. Comparison of stress-strain curves between axial extensometer and plate displacement of basalt
图 7 页岩三轴压缩试验的全应力-应变曲线的对比
Figure 7. Comparison of total stress-strain curves of triaxial compression test of shale
图 8 轴向引伸计A、B的应力-应变曲线的比较
Figure 8. Comparison of stress-strain curves of axial extensometer A and B
图 9 岩样破坏及LVDT安装示意图
Figure 9. Schematic diagram of sample failure and LVDT installation
表 1 页岩三轴压缩试验3种测量方法下的强度及变形参数统计表
Table 1. Statistical table of strength and deformation parameters under three measurement methods of shale triaxial compression test
测量方法 起裂强度σci /MPa 损伤强度σcd /MPa 弹性模量E /GPa 泊松比ν 压板位移 113.37 193.76 14.391 0.1381 引伸计 73.35 189.07 23.581 0.1927 LVDT 99.97 191.12 14.929 0.1221 
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