Dynamic failure mechanism of gas pipeline with flange joint under blasting seismic wave
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摘要: 基于典型城市燃气管道直埋地层特点，通过全尺寸直埋燃气管道爆破地震实验，并结合LS-DYNA动力有限元数值计算软件建立不同爆源距离的无接口和法兰接口的燃气管道模型，分析研究了爆破地震波作用下法兰接口燃气管道动力响应特征及其失效机制。研究结果表明：管道截面应变以轴向拉伸应变为主，环向应变为辅；不同爆破工况下，无接口管道和法兰接口管道及地表峰值振动速度随爆源距离减小而增大；沿管道轴线方向，无接口管道、地表峰值振动速度以管道中心截面为对称面沿两端不断减小，法兰接口管道峰值振速由两侧向中间逐渐增大，在法兰接口处突然减小；法兰接口处出现明显的应力集中现象；管道法兰接口处是爆破地震作用下研究的关键点，螺栓的峰值有效应力、垫片轴向压力、法兰峰值有效应力、法兰偏转角随爆源距离增大而减小；法兰管道偏转角与地表峰值振动速度具有对应关系，法兰接口燃气管道中心正上方地表的控制振速（13.82 cm/s）可作为邻近燃气管道爆破工程地表的安全控制值。Abstract: In the process of blasting and excavation of urban subways, controlling the impact of blasting vibration on adjacent pipelines is critical. Based on the characteristics of directly buried gas pipelines in Wuhan and the full-scale direct-buried gas pipeline blasting seismicexperiment, the dynamic finite element numerical calculation software LS-DYNA was used to establish gas pipeline without joints and flange gas pipeline models under different blasting source distances. The effects of blasting seismic wave’s dynamic response characteristics of flanged gas pipeline were analyzed. The research results show that the strain of pipeline section is mainly axial tensile strain, supplemented by circumferential strain. The peak particle velocity of pipeline without joints and flange pipes and the ground surface increase with the decrease of the distance from the blasting source under different blasting conditions. Along the pipeline axis, the peak vibration velocity of the pipeline without joints and the ground surface decreases along the two ends with the central section of the pipe as the symmetry plane. The peak particle velocity of the flange pipeline gradually increases from two sides to the middle but suddenly decreases at the flange joint. There is an obvious stress concentration at the flange interface. The flange joint is the key point of pipeline under blasting earthquake. The peak effective stress of the bolt, the axial pressure of the gasket, the peak effective stress of the flange, and the flange deflection angle decrease with the increase of the explosion source distance. The deflection angle of the flanged pipeline has a corresponding relationship with the peak vibration velocity of the ground surface. The control vibration speed of 13.82 cm/s on the surface directly above the center of the flanged gas pipeline is used as the safety control value of the adjacent gas pipeline under blasting engineering.
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Key words:
- blasting vibration /
- dynamic response /
- vibration speed /
- flange interface /
- control vibration speed
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1. 麻省理工学院研究人员发现金属在极端冲击下愈热愈强的反常规现象[1]
材料的强度依赖于加载测试时的速率，这是因为位错等缺陷的变形移动具有内在的动力学限制。随着变形应变率的增加，更多的强化机制被激发以增加其强度。麻省理工学院研究人员发现，在应变率大于 106 s−1 的微弹道冲击测试中，当温度升高至157 ℃时，铜的强度会增加约30%，纯钛和金中也观察到了这种效应。这种现象是违反直觉的，因为几乎所有材料在正常条件下加热时都会变软。纯金属的这种异常热强化是由于控制变形机制从热激活强化转变为位错的类弹道传输引起的，位错通过声子相互作用受到阻力。这些认识为从高速加工操作到高超音速运输中更准确地模拟和预测材料在各种极端应变率条件下的性能提供了新的思路。
2. 耶路撒冷希伯来大学研究人员实验证实拉伸裂纹速度可突破经典速度限制[2-3]
脆性材料会因快速裂纹而失效。经典断裂力学描述了拉伸裂纹的运动，这些裂纹在尖端的点状区域内将耗散掉被释放的弹性能。在这一框架内，“经典”拉伸裂纹并不能超过瑞利波速度。耶路撒冷希伯来大学研究人员实验利用水凝胶材料，通过实验证明了“超剪切”拉伸裂纹的存在。虽然水凝胶是一种柔性材料，但它的裂纹扩展特性完全遵循脆性材料断裂理论的预测。当水凝胶的拉伸状态超过极限时，拉伸裂纹的扩展速度明显地超过了瑞利波波速。超剪切动力学遵循的原理与指导“经典”裂纹的原理不同；这种断裂模式在临界（与材料相关）施加应变下被激发。这种非经典的拉伸断裂模式颠覆了对断裂力学的传统认知，亟需从理论层面揭示其存在的物理机制。
3. 北京大学等研究人员开发了一种动态强度高达14 GPa的碳纳米管纤维[4]
北京大学、北京石墨烯研究院、中国科学院力学研究所、武汉大学、中国科学院苏州纳米技术与纳米仿生研究所等研究人员提出了一种高强碳纳米管纤维的多尺度结构优化策略，系统提高了碳纳米管管间作用、纤维取向性、致密性和动态强度。在动态冲击性能的研究中，研究人员利用微尺度高速冲击拉伸实验装置，发现纤维随着拉伸速度的提高发生韧脆失效模式的转变，具有显著的应变率强化效应。当应变率约
1400 s−1时，纤维的动态强度达到14 GPa，突破了现有高性能纤维强度。运用强激光诱导的高速横向冲击实验方法，揭示了微米直径纤维单丝在模拟弹道冲击加载下的动力学响应规律，发现由于冲击能量的快速非局域耗散而展现出优异的防护性能，纤维比能量耗散功率远高于凯夫拉等传统防弹纤维。这些发现表明碳纳米管纤维在冲击防护领域具有巨大的应用潜力。 -
图 5 实验和数值模拟的波形和频谱图
Figure 5. Waveform and spectrogram of experiment and numerical simulation
图 7 法兰接口管道数值模型示意图
Figure 7. Schematic diagram of numerical model of flange interface pipe
图 13 各个工况的螺栓的有效应力分布图
Figure 13. Effective stress distribution diagram of bolts in various working conditions
图 19 法兰偏转角与地表振速关系
Figure 19. Relationship between flange deflection angle and ground surface vibration velocity
表 1 模型材料参数
Table 1. Model material parameters
材料 密度/(g·cm−3) 弹性模量/GPa 剪切模量/GPa 泊松比 黏聚力/MPa 内摩擦角/（°） 抗拉强度/MPa 管道、法兰 7.85 205.000 1.2 0.33 420.000 螺栓 7.82 210.000 1.0 0.30 660.000 粉质黏土 1.98 0.012 4.3 0.28 0.035 15 0.028 砂岩 2.40 3.000 11.2 0.28 5.500 43 2.580 
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表 2 爆轰产物状态方程参数
Table 2. Detonation product state equation parameters
ρ/（g·cm−3） A/GPa B/GPa R1 R2 ω E0/GPa V/cm3 1.25 214 18.2 4.2 0.9 0.1 4.19 1
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表 3 数值模拟结果与实测数据对比分析
Table 3. Comparative analysis of numerical simulation results and measured data
工况 监测点 合振动速度、应变 误差率/% 现场实验 数值模拟 Ⅰ D3 1.65 cm/s 1.72 cm/s 4.2 D4 1.17 cm/s 1.26 cm/s 7.6 D6 0.76 cm/s 0.72 cm/s 5.3 D7 1.45 cm/s 1.54 cm/s 6.2 S1 28.65×10−6 34.23×10−6 19.4 S2 13.54×10−6 8.56×10−6 3.7 Ⅱ D3 2.84 cm/s 2.76 cm/s 8.0 D4 1.99 cm/s 2.06 cm/s 3.5 D6 2.64 cm/s 2.73 cm/s 9.0 D7 1.32 cm/s 1.46 cm/s 10.6 S1 36.71×10−6 41.23×10−6 12.3 S2 16.12×10−6 13.15×10−6 18.4 Ⅲ D3 6.57 cm/s 6.98 cm/s 6.2 D4 4.18 cm/s 4.45 cm/s 6.4 D6 5.47 cm/s 5.78 cm/s 5.6 D7 3.98 cm/s 4.15 cm/s 4.3 S1 37.15×10−6 43.23×10−6 16.3 S2 15.96×10−6 18.56×10−6 16.2 Ⅳ D3 15.19 cm/s 15.32 cm/s 0.8 D4 11.21 cm/s 12.54 cm/s 1.3 D6 13.18 cm/s 14.25 cm/s 8.1 D7 7.34 cm/s 8.32 cm/s 13.4 S1 187.06×10−6 198.09×10−6 5.9 S2 19.23×10−6 22.63×10−6 17.7 Ⅴ D3 30.45 cm/s 31.56 cm/s 3.6 D4 21.19 cm/s 23.23 cm/s 9.6 D6 28.45 cm/s 29.56 cm/s 3.9 D7 12.15 cm/s 13.21 cm/s 8.7 S1 209.50×10−6 225.61×10−6 7.6 S2 35.62×10−6 42.66×10−6 19.8
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表 4 垫片的各项参数
Table 4. The parameters of the gasket
密度/（g·cm−3） Ex/MPa Ey/MPa Ez/MPa μxy μyz μxz Gxy/MPa Gyz/MPa Gxz/MPa 7.85 232.17 434.51 19089.64 0.44 0.008 0.005 115.88 32770.11 103.59
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