直接埋藏法修补疲劳裂纹缺陷的研究  

Repair of Fatigue Crack Defects by Direct Burial Method

作　　者：程方杰 孔康骞 欧阳忠宇 Cheng Fangjie;Kong Kangqian;Ouyang Zhongyu(School of Materials Science and Engineering,Tianjin University,Tianjin 300350,China;Tianjin Key Laboratory of Advanced Joining Technology,Tianjin 300350,China)

机构地区：[1]天津大学材料科学与工程学院,天津300350 [2]天津市现代连接技术重点实验室,天津300350

出　　处：《天津大学学报（自然科学与工程技术版）》2020年第5期502-507,共6页Journal of Tianjin University：Science and Technology

摘　　要：在海洋平台的安全维护中,挖除原始疲劳裂纹缺陷并准备坡口是水下焊接修复工程中一项十分困难的作业步骤.为此,提出一种不挖除原始裂纹缺陷的直接埋藏法来修复疲劳裂纹缺陷.为了探索该技术的可行性,在陆地上制备了模拟补焊试样,通过对试样补焊前后的疲劳性能进行测试,分析研究了直接埋藏法修复后疲劳裂纹出现的位置、试样的疲劳循环周次以及打磨对补焊后试样疲劳循环周次的影响规律.使用Abaqus软件模拟计算了补焊所产生的残余应力和补焊后试样在不同外部载荷作用下原始裂纹尖端的应力情况.试验结果表明,新的疲劳裂纹主要出现在补焊焊趾处和补焊焊道上;补焊后接头的平均疲劳循环周次比原始试样并没有下降,反而提高了36%;对补焊焊趾进行打磨处理,接头的平均疲劳循环周次比补焊焊趾未打磨的接头提升了16%.数值模拟结果显示,补焊焊道收缩在裂纹最深处产生了-157 MPa的残余应力.三点弯曲加载时,裂纹最深处的应力由补焊前的508 MPa降为补焊后的94 MPa;单轴拉伸时,裂纹最深处的应力由补焊前的480 MPa降为补焊后的320 MPa.该结果表明直接埋藏法补焊所产生的残余压应力是延缓或阻止原始裂纹继续向母材扩展的主要原因.综合试验和模拟结果,可以认为直接埋藏法修补疲劳裂纹在水下焊接修复工程中有着很强的可行性.The removal of an original fatigue crack defect and preparation of a groove are difficult steps in underwater welding repair projects during the safety maintenance of offshore platforms.Therefore,a direct burial method without direct removal of the original crack defects is proposed to repair fatigue crack defects.To explore the feasibility of this method,simulated welding repair specimens were prepared on land.The fatigue tests of the repaired specimens were adopted to analyze the initial positions of the fatigue cracks after direct burial method repair,fatigue cycles of specimens before and after welding repair and the effect of grinding them.Abaqus was used to calculate the residual stress generated by welding repair and the repaired specimens’stress at the crack tip under different external loads.Results revealed that the new fatigue crack mainly initiates at the weld toe of a repaired weld and the repaired weld bead.The average fatigue cycles after welding repair did not decrease,and instead increased by 36%.The fatigue cycles of the repaired weld joint with polished toe improved by 16%.The numerical simulation results show that the shrinkage of the welding repair produced a residual stress of-157 MPa at the deepest point of the crack.In the case of a three-point bending load,the stress at the deepest point of the crack was reduced from 508MPa before the welding repair to 94 MPa after.When uniaxial tension was applied,the stress at the deepest point of the crack was reduced from 480MPa before welding repair to 320 MPa after welding repair.The results indicate that residual compressive stress caused by welding repair using the direct burial method accounts for the delay or prevention of the original crack expanding to the base metal.Therefore,the direct burial method can repair a fatigue crack in underwater welding repair projects.

关 键 词：疲劳裂纹 埋藏法 补焊 有限元法 

分 类 号：TG405[金属学及工艺—焊接]