Connecting modes of two cracks under impact loads
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摘要: 脆性材料内部含有大量裂纹，当某一裂纹扩展时，其他裂纹会对扩展裂纹产生影响。为了研究冲击载荷下，脆性材料内两裂纹的相互影响、连通规律及裂纹尖端应力强度因子的变化规律，利用有机玻璃板制作了含非平行双裂纹的实验试件，利用落板冲击设备进行了中低速冲击实验，结合有限元分析软件ABAQUS计算出裂纹尖端应力强度因子，利用有限差分软件AUTODYN进行了动态数值模拟研究，并将其模拟结果与实验结果进行对比分析。实验及模拟结果表明：裂纹破坏形态与AUTODYN数值模拟破坏形态基本一致；试件的断裂形态随着两裂纹间距不同而不同；裂纹间的相互影响程度随着裂纹间间距增大而减小；裂纹尖端应力强度因子KI随着裂纹间距的增大而减小，而KII随着裂纹间距增大而增大。Abstract: A multitude of flaws always exists in brittle material and the influence will be exerted on by other flaws when one flaw is propagating. To investigate the propagation, coalition behavior and stress intensity factors of two cracks in brittle materials under impact loading, Polymethyl methacrylate (PMMA) was selected to manufacture the double cracked specimens. By using the medium-low speed impact system, impact experiments were conducted, and the crack tip SIFs were calculated by using finite element code ABAQUS. The finite difference code AUTODYN was used in the simulation crack propagation behavior, and the simulation results were compared with the test results. The results of experiment and simulation show that the simulation results generally agree with the experimental results in crack propagation paths; the crack propagation behavior varies with the change of the distance between the two cracks; the effect between the two cracks decreases with the increase of the distance between the two cracks; the stress intensity factors KI decrease with the increase of the distance between the two cracks while KII is the opposite.
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图 4 入射板和透射板上的应变片测得的电压信号
Figure 4. Voltage signals recorded from incident and transmit plate
图 7 不同D值（D表示竖直裂纹尖端到倾斜裂纹中心距离）裂纹扩展路径的实验和模拟对比图（θ=45°）
Figure 7. Comparison test results with simulation results for the specimens with different D the distance between vertical crack tip to the center of incline crack (θ=45°)
图 8 裂纹扩展过程中的第一主应力云图
Figure 8. Contour plots of first principal stress during crack propagation.
图 9 裂纹扩展路径上特殊点处的周向应力分布图
Figure 9. Circumferential stress on the ahead of propagation crack tip
图 11 竖直裂纹尖端应力强度因子随时间变化曲线
Figure 11. The curve of stress intensity factor at crack1 tip with time
图 12 倾斜裂纹的两个尖端的应力强度因子随时间变化曲线
Figure 12. The curves of stress intensity factors at the two tips of incline crack versus time
图 13 CPG示意图及其所测信号
Figure 13. The sketch of CPG and voltage signal recorded in experiment
图 14 极限应力强度因子确定方法
Figure 14. Determination of propagation critical stress intensity factors
表 1 试件样本和实验时落板高度及冲击速度
Table 1. Height of drop weight plate and impact velocity for each specimen
试件编号 D/mm H/mm v/(m·s−1) D100−A45 100 1.840 6.005 D75−A45 75 1.865 6.046 D50−A45 50 1.827 5.984 D25−A45 25 1.834 6.000 D20−A45 20 1.854 6.028 D15−A45 15 1.847 6.017 D10−A45 10 1.828 5.986 
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表 2 落板冲击设备部件参数
Table 2. Parameters of impacting test system
部件名称 高度/mm 宽度/mm 厚度/mm 弹性模量/GPa 泊松比 落板 150 480 30 − − 入射板 3 000 300 30 72 0.33 透射板 2 000 300 30 72 0.33
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表 3 各对照组起裂时刻及起裂韧度
Table 3. Initiation time and initiation toughness for each specimen
试件编号 起裂时刻tf /μs 起裂韧度 D10−A45 272 4.99 D15−A45 267 4.85 D20−A45 275 4.53 D25−A45 259 4.36 D20−A45 264 4.24 D15−A45 260 4.19 D10−A45 263 4.22
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