混流式转轮焊接工艺优化与局部压应力化的实现

Welding process optimization and local compressive stress realization of francis runner

焊接残余拉应力的存在是引起混流式转轮疲劳断裂的重要原因之一,焊接残余压应力的存在能够有效提高焊接结构的抗疲劳性能.采用数值模拟方法对混流式转轮焊接残余应力场进行了模拟,转轮出水边焊缝区域存在较高的残余拉应力,适当减小出水边焊段长度,可有效降低残余拉应力峰值.对转轮原有及优化焊接工艺下的焊接残余应力场进行了测试分析.结果表明,通过优化分段焊接工艺可以对转轮的残余应力场分布进行调控,叶片出水边焊缝区域的残余拉应力明显降低,并转化为压应力,实现了转轮易开裂区域焊接残余应力的局部压应力化,从而有效提高转轮的抗疲劳性能.

The welding residual tension stress is one of the main reasons which lead to the fatigue failure of francis turbine runners.The residual compressive stress improves the fatigue resistance of welding structures.The welding residual stress of runner was simulated in this paper.The result shows that there is higher residual tensile stress region in the blade outlet near the welding region.The peak value of residual tensile stress could be reduced by decreasing the length of weld bead in the outlet.The welding residual stress of runner under original and optimized welding process has been measured and analyzed.The results indicated that the residual stress could be modified and controlled by optimizing welding process.The residual tensile stress in the blade outlet near the welding region sharply decreased and turned into compressive stress.The local compressive stress of welding residual stress on francis turbine runner's easily fracturing region was realized.So the fatigue resistance of the runner efficiently increased.