混流式转轮焊接残余应力局部压应力化的实现

Optimization of welding process and realization of local compressive stress of Francis runner

焊接残余拉应力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。文中对原有及优化焊接工艺下的转轮出水边易开裂区域的焊接残余应力分布进行了测试分析,并对局部加热及锤击处理对应力场分布的影响进行了研究。结果表明,通过优化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,而且转变为压应力,采用局部加热和锤击可以明显降低转轮易开裂区域的残余拉应力值,进一步促进高压应力区域的形成,实现转轮易开裂区域的压应力化,从而提高转轮的抗疲劳性能。

The welding residual tension stress is one of the main reasons caused the fatigue failure of Francis turbine runners.The residual compressive stress can increase the fatigue resistance of welded structures.The distribution of welding residual stress in the region easily to fail in runner outlt under original and optimized welding process was measured and analyzed.And the influence of local heating and peening on the stress field in the runner easily fracture region was studied.The results indicate that the residual stress can be modified and controlled by optimizing welding process.The residual tensile stress in the blade outlet near to the weld region is sharply decreased and turns into compressive stress.Local heating and peening can significantly reduce the residual stress and further promote the formation of high compressive stress region,and then the local compressive stress of welding residual stress in the region easily to fail in Francis turbine runner was realized.And the fatigue resistance of the runner was efficiently increased.