The main aim of the present work is to investigate, through the strain energy density method, the fatigue behaviour of high strength welded joints realised employed in hydraulic runner blades. The geometries, found in literature, present the welding bead machined in order to have no geometrical discontinuities in the specimen realising a wide fitting radius between the two welded plates; the only critical geometrical discontinuity in the specimen is given by the lack of penetration that leads to an internal crack‐like defect. The specimens presented failure both from the weld toe and from the weld root depending on the amount of welding penetration. The results, summarised in this work with the strain energy density method, show clearly the possibility to consider a unique master curve for this kind of joints regardless of the failure initiation point. Acquiring, through a finite element model, the strain energy density value both at the weld toe and at the weld root and comparing them, the method is proved to be adequate to detect the most critical area of the joint. A first fatigue master curve in terms of cyclic averaged strain energy density value is provided for the fatigue design of high strength welded joints.

中文翻译：

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用应变能密度法评估高强度焊接接头的疲劳

本工作的主要目的是通过应变能密度法研究液压流道叶片中采用的高强度焊接接头的疲劳性能。在文献中发现的几何形状呈现了加工的焊道，以便在试样中没有几何上的不连续性，从而在两个焊接板之间实现了宽的装配半径。样品中唯一的关键几何不连续性是由于缺乏穿透性而导致内部裂纹状缺陷。根据焊接熔深的多少，试样从焊趾和焊根处均显示出破坏。用应变能密度法总结了这项工作的结果，清楚地表明，不管失效起始点如何，都可以考虑为此类接头考虑唯一的主曲线。通过有限元模型获取焊趾和焊缝根部的应变能密度值并进行比较，证明该方法足以检测接头的最关键区域。提供了根据循环平均应变能密度值的第一疲劳主曲线，用于高强度焊接接头的疲劳设计。