This paper aims to study the effects of surface topography on the fatigue strength of wire-arc additive manufacturing (WAAM) components, paying particular attention to the interaction of roughness, waviness, and microstructure. For this purpose, first, a novel surface topography characterization approach is proposed to separate waviness and roughness without distorting the surface features, as smaller-scale irregularities, called secondary crack-like defects, have been confirmed to exist at notch-like valleys of WAAM specimens. This novel approach can practically be employed for any surface data obtained by different measuring methods, and it is not limited to WAAM specimens. Then, Murakami’s area model with a corrected stress intensity factor is introduced to evaluate the fatigue strength of WAAM specimens by considering the interaction between surface features (roughness and waviness) and their simultaneous effect. This approach can also particularly predict the fatigue strength of other engineering components once a small secondary crack or defect exists at the notch tip without entailing fatigue tests or intricate analysis. Moreover, microstructure changes due to the back-and-forth transformations in the microstructure and the formation of a soft phase in the interlayer area at the notches during the manufacturing process with lower hardness values have been considered using this model.

中文翻译：

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电弧增材制造的高强度钢试样的表面不规则性表征和疲劳强度评估


本文旨在研究表面形貌对线弧增材制造 （WAAM） 组件疲劳强度的影响，特别关注粗糙度、波纹度和微观结构的相互作用。为此，首先，提出了一种新的表面形貌表征方法，在不扭曲表面特征的情况下分离波纹度和粗糙度，因为已证实较小尺度的不规则性（称为次生裂纹状缺陷）存在于 WAAM 样品的缺口状谷中。这种新颖的方法实际上可以用于通过不同测量方法获得的任何表面数据，并且不仅限于 WAAM 样品。然后，引入具有校正应力强度因子的村上隆面积模型，通过考虑表面特征（粗糙度和波纹度）之间的相互作用及其同时效应来评估WAAM试件的疲劳强度。一旦缺口尖端存在小的二次裂纹或缺陷，这种方法还可以特别预测其他工程部件的疲劳强度，而无需进行疲劳测试或复杂的分析。此外，使用该模型还考虑了在制造过程中由于微观结构的来回转变而导致的微观结构变化，以及在硬度值较低的缺口处在层间区域形成软相。