Propagation characteristics and failure behaviors of crack in tunnel under impact loads
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摘要: 为了开展含预制裂纹的巷道模型试样在冲击载荷下的动态断裂响应实验，选用青砂岩作为模型材料制作巷道模型试样，以可调速落锤冲击实验机作为冲击加载装置进行试样的动态断裂实验，分析冲击载荷作用下的巷道内裂纹的扩展规律。采用裂纹扩展计及应变片测试系统监测裂纹的起裂时间、扩展速度及止裂时间，并借助于AUTODYN、ABAQUS有限元数值分析软件对实验模型进行数值模拟，计算裂纹的动态起裂韧度、动态扩展韧度、动态止裂韧度等断裂参数。结果表明：巷道内裂纹在扩展路径过程中存在着明显的止裂现象；采用实验-数值方法能够较好地得出裂纹的起裂韧度、扩展韧度和止裂韧度等参数。另外，对止裂现象进行了初步的分析，讨论了试样内应力反射波与透射波对止裂问题的影响。Abstract: In order to obtain the dynamic response of the pre-cracked tunnel under impact loads, we investigated the crack propagation characteristics in the tunnel using the green sandstone as the model material of the tunnel, and the self-developed adjustable speed-drop hammer impact tester that can realize low- and medium-impact loading speed as the loading device. We determined the crack's initiation time, propagation velocity and arrest time, using a measuring system consisting of a crack propagation gauge and a strain gauge, and successfully obtained the crack's initiation toughness, propagation toughness and arrest toughness using the finite element software AUTODYN and ABAQUS based on the test data. The results showed that crack arrest occurred in the process of crack propagation; and that the experimental-numerical method can be successfully used to calculate the crack initiation toughness, propagation toughness and arrest toughness. Further, we conducted a preliminary analysis of crack arrest, and examined the influence of internal stress reflection wave and transmission wave on crack arrest.
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Key words:
- tunnel /
- crack /
- initiation toughness /
- propagation toughness /
- arrest toughness /
- propagation velocity
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图 4 入射杆及透射杆上记录的应变-时间曲线
Figure 4. Curves of strain-time recorded from incident and transmitted bars
图 5 监测点应变片断裂时间确定方式
Figure 5. Method for determining fracture time of the strain gauges
图 6 试样中CPG记录的两种不同电压信号及测试的裂纹扩展速度
Figure 6. Two different voltage signals recorded and the crack propagation velocity by CPG in the tunnel specimen
图 8 数值分析结果与实验破坏结果对比
Figure 8. Comparison between numerical results and experimental results
图 9 裂纹尖端坐标及1/4节点奇异单元
Figure 9. Coordinates and 6 nodes triangular element displacement
表 1 采用实验-数值方法得到的动态断裂韧度
Table 1. Dynamic fracture toughness obtained by experimental-numerical method
试样编号 tf/μs va/(m·s-1) KⅠCD/(MPa·m1/2) $ \dot{K} $/(kPa·m1/2·s-1) 29 468.2 578.47 5.55 11.85 30 458.4 584.93 6.12 13.35 35 460.8 438.49 4.45 9.66 40 457.2 596.05 6.96 15.22 47 462.0 511.11 5.07 10.97 
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