Dynamic fracture processes of L-shaped beam-column specimens with prefabricated cracks
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摘要: 针对含预制裂纹L形梁柱试件，为研究预制裂纹动态扩展的力学特征及其对梁柱试件破坏模式的影响，采用数字动态焦散线实验系统，对距节点核心区不同距离l处含有预制裂纹的试件进行落锤冲击实验，得到预制裂纹的扩展轨迹、速度、动态应力强度因子的变化规律。结果表明，l值增大，扩展裂纹在梁下边缘的贯通点与预制裂纹的夹角逐渐增大，曲裂程度变大。裂纹扩展速度随着l的增大振荡性增强，裂纹扩展平均速度逐渐降低。l值为2 mm时，裂尖表现为Ⅰ型断裂，l值增大，裂尖受到剪应力作用增强，Ⅰ型动态应力强度因子减小，Ⅱ型动态应力强度因子增大，断裂逐渐转变为Ⅰ-Ⅱ复合型。Abstract: The dynamic propagation mechanics of prefabricated crack and its effect on joint were studied for the impact fracture process of L-shaped beam-column specimens with prefabricated cracks. The drop testing was carried out on the specimens with cracks at different distances l far from node core area by using the digital dynamic caustic system and the variations of crack propagation trajectory, velocity and dynamic stress-intensity factor were obtained. The results show that the increase of l leads to the angle between the penetration point of the extended crack at the edge of the beam and the prefabricated crack increases gradually and the degree of crack curving becomes larger. With the increase of l, the oscillation of crack propagation velocity increases, the average velocity decreases and the crack propagation time is gradually prolonged. When the value of l is 2 mm, the fracture pattern is mode Ⅰ. As the value of l increases, the crack tip is increased by the shear stress, the dynamic stress intensity factor of mode Ⅰ decreases and the dynamic stress intensity factor of mode Ⅱ gradually increases. The fracture pattern gradually becomes Ⅰ-Ⅱ complex mode.
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Key words:
- beam-column specimen /
- impact /
- caustic /
- dynamic fracture /
- prefabricated crack /
- stress intensity factor
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图 2 Ⅰ型和Ⅰ-Ⅱ复合型裂纹尖端焦散斑形状
Figure 2. Caustic shapes at crack tip under mode Ⅰand mixed mode
图 8 裂纹扩展水平位移和竖向位移时程曲线
Figure 8. Horizontal and vertical displacements ofcrack propagation varying with time
图 9 裂纹扩展方向与竖直方向夹角的时程曲线
Figure 9. Angle between crack propagation direction and vertical direction varying with time
图 13 动态应力强度因子时程曲线
Figure 13. The curves of dynamic intensity stress factor versus time
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