Effects of non-symmetric non-uniformly distributed welding residual stress on fatigue failure initiation and propagation in a hydropower generator shaft

IF 1.7 4区 材料科学 Q3 MATERIALS SCIENCE, MULTIDISCIPLINARY Multidiscipline Modeling in Materials and Structures Pub Date : 2023-06-30 DOI:10.1108/mmms-01-2023-0023
A. K. Abdul Jawwad, M. Mahdi
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Abstract

PurposeThis article aims to investigate and model the effects of welding-generated thermal cycle on the resulting residual stress distribution and its role in the initiation and propagation of fatigue failure in thick shaft sections.Design/methodology/approachExperimental and numerical techniques were applied in the present study to explore the relationship(s) between welding residual-stress distribution and fatigue failure characteristics in a hydropower generator shaft. Experimental techniques included stereomicroscopy, optical and scanning electron microscopy (SEM), chemical analysis and mechanical testing. Finite element modelling (FEM) was used to model the shaft welding cycle in terms of thermal (temperature) history and the associated development of residual stresses within the weld joint.FindingsExperimental analyses have confirmed the suitability of the used material for the intended application and confirmed the failure mode to be low cycle fatigue. The observed failure characteristics, however, did not match with the applied loading in terms of design stress levels, directionality and expected crack imitation site(s). FEM results have revealed the presence of a sharp stress peak in excess of 630 MPa (about 74% of material's yield strength) around weld start point and a non-uniform residual stress distribution in both the circumferential and through-thickness directions. The present results have shown very close matching between FEM results and observed failure characteristics.Practical implicationsThe present article considers an actual industrial case of a hydropower generator shaft failure. Present results are valuable in providing insight information regarding such failures as well as some preventive design and fabrication measures for the hydropower and other power generation and transmission sector.Originality/valueThe presence of the aforementioned stress peak around welding start/end location and the non-uniform distribution of residual-stress field are in contrast to almost all published results based on some uniformity assumptions. The present FEM results were, however, the only stress distribution scenario capable of explaining the failure considered in the present research.
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非对称非均匀分布焊接残余应力对水轮发电机轴疲劳失效萌生和扩展的影响
目的研究和模拟焊接产生的热循环对厚轴截面残余应力分布的影响及其在疲劳破坏萌生和扩展中的作用。设计/方法/方法本研究采用实验和数值方法探讨了水轮发电机轴的焊接残余应力分布与疲劳破坏特性之间的关系。实验技术包括立体显微镜,光学和扫描电子显微镜(SEM),化学分析和力学测试。采用有限元模型(FEM)对轴焊接周期的热(温度)历史和焊接接头内残余应力的相关发展进行建模。实验分析证实了所用材料对预期应用的适用性,并证实了失效模式为低周疲劳。然而,观察到的破坏特征在设计应力水平、方向性和预期的裂纹模仿位置方面与实际载荷不匹配。有限元分析结果表明,在焊缝起始点附近存在一个超过630 MPa的尖锐应力峰值(约占材料屈服强度的74%),并且在周向和全厚方向上存在不均匀的残余应力分布。结果表明,有限元计算结果与实测破坏特征吻合非常密切。实际意义本文考虑了一个水力发电机轴故障的实际工业案例。目前的研究结果在为水电和其他发电和输电部门提供有关此类故障的深入信息以及一些预防性设计和制造措施方面具有重要价值。上述应力峰在焊接开始/结束位置附近的存在以及残余应力场的非均匀分布与几乎所有发表的基于某些均匀性假设的结果相反。然而,目前的有限元结果是唯一能够解释本研究中所考虑的破坏的应力分布情景。
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来源期刊
CiteScore
3.70
自引率
5.00%
发文量
60
期刊介绍: Multidiscipline Modeling in Materials and Structures is published by Emerald Group Publishing Limited from 2010
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