Fatigue Crack Repair Mechanism and Effect by Pneumatic Impact Treatment
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摘要:
为探明气动冲击技术对钢桥面板疲劳裂纹的维修机理及修复效果，首先基于动力学理论，研究气动冲击过程中靶材的塑性变形规律，分析在塑性变形作用下的裂纹表面闭合过程；随后，采用数值模拟，探讨裂纹表面闭合部位的局部应力场及其在受载作用下的应力响应和变形规律；最后，通过疲劳试验对气动冲击的维修效果进行对比验证. 结果表明：所提出的数学模型可对冲击深度进行预测，气动冲击过程中材料表面将产生显著的塑性变形，其冲击深度与横向变形近似相等；当裂纹断面横向相对变形量大于裂纹宽度时，会产生接触闭合及相互挤压行为，从而在接触闭合部位形成局部压应力区；该压应力能够一定程度上抵抗外荷载对裂纹表面的张拉作用，降低裂纹尖端应力强度因子，从而延缓或阻碍疲劳裂纹扩展.
Abstract:To explore the repair mechanism and effect of pneumatic impact treatment on fatigue cracks of the steel bridge deck, the plastic deformation of the target material during the pneumatic impact treatment was studied based on kinetic theory, and the behaviors of crack surface closure under such plastic deformation were analyzed. Then, the local stress field in the closure part was investigated, and the stress response and its deformation under the applied load were discussed by numerical method. Fatigue tests were carried out to verify the repair effect of pneumatic impact treatment at last. The results show that the mathematical model proposed here is able to predict the impact depth. Large plastic deformation is observed on the material surface during the pneumatic impact treatment process, and the impact depth and transverse deformation are similar. When the relative transverse deformation of the crack fracture surface becomes larger than the crack width, the contact closure and compressional deformation can be found, which will introduce the contact stress at the closure part. This contact stress can resist the tension effect of the crack surface under applied load, reduce the stress intensity factor at the crack tip, and restrain the propagation of fatigue cracks, which is also proved by the tests.
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Key words:
- bridge engineering /
- pneumatic impact /
- numerical simulation /
- crack closure /
- stress intensity factor
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图 5 裂纹表面闭合水平方向变形过程
Figure 5. Deformation of crack surface closure in horizontal direction
图 6 裂纹断面接触应力分布
Figure 6. Distribution of contact stress through crack fracture surface
表 1 气动冲击设备参数
Table 1. Parameters of device for pneumatic impact
参数 f/Hz l/mm m/kg Ao/mm2 取值 90 6 0.367 25 25 
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表 2 Q345qD材料系数
Table 2. Material constant of Q345qD
参数 q λ β c
/（N·mm−1.5）γ 取值 0.999 745 4.736 × 10−8 0.367 25 8.0 × 109 0.6
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表 3 疲劳试验结果
Table 3. Fatigue test results
试件编号 预制长度/mm 最终长度/mm 循环次数/万次 SP1 67.2 79.1 463 SP2 58.5 60.0 647 SP3 66.5 未变化 581 SP4 68.5 未变化 601 SP5 70.6 未变化 505 SP6 70.2 未变化 540
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