Abstract
The new emerging Wire and Arc Additive Manufacturing (WAAM) technology has significant potential to improve material design and efficiency for structural components as well as reducing manufacturing costs. Due to repeated and periodic melting, solidification and reheating of the layers, the WAAM deposition technique results in some elastic, plastic and viscous deformations that can affect material degradation and crack propagation behaviour in additively manufactured components. Therefore, it is crucial to characterise the cracking behaviour in WAAM built components for structural design and integrity assessment purposes. In this work, fatigue crack growth tests have been conducted on compact tension specimens extracted from ER70S-6 steel WAAM built components. The crack propagation behaviour of the specimens extracted with different orientations (i.e. horizontal and vertical with respect to the deposition direction) has been characterised under two different cyclic load levels. The obtained fatigue crack growth rate data have been correlated with the linear elastic fracture mechanics parameter varDelta K and the results are compared with the literature data available for corresponding wrought structural steels and the recommended fatigue crack growth trends in the BS7910 standard. The obtained results have been found to fall below the recommended trends in the BS7910 standard and above the data points obtained from S355 wrought material. The obtained fatigue growth trends and Paris law constants from this study contribute to the overall understanding of the design requirements for the new optimised functionally graded structures fabricated using the WAAM technique.
Highlights
The wire and arc additive manufacturing (WAAM) method creates multi-layer components by melting a wire at a controlled rate using an electric or plasma arc (Williams et al 2015; Martina et al 2012)
Knowing that S355G8+M and S355G+10M are widely used in the fabrication of offshore structures, which are subjected to severe cyclic loading conditions during their lifespan (Igwemezie et al 2019; Jacob et al 2019; Jacob and Mehmanparast 2021), the comparison of results in Fig. 7 shows that the WAAM technology can be potentially employed in the fabrication of less critical components and parts of offshore structures using low carbon steel wires, though the fatigue crack growth rates are expected to be higher than the S355 weldments but still lower than the recommended FCG trends provided in the BS7910 standard
Fatigue crack growth tests were conducted in air on standard tension C(T) specimens extracted from ER70S-6 WAAM built walls
Summary
The wire and arc additive manufacturing (WAAM) method creates multi-layer components by melting a wire at a controlled rate using an electric or plasma arc (Williams et al 2015; Martina et al 2012). The majority of the published work on WAAM built components reported in the literature is on the parts made of titanium and stainless steel alloys, for application in the aerospace industry; there is an essential need to examine the fatigue and fracture behaviour of other WAAM built materials, e.g. ferritic steel, to explore the suitability of this AM technology for other high production rate industries such as offshore wind. The preliminary test results reported in the literature on titanium and stainless steel WAAM components show that relatively lower FCG rates were observed in the multi-layer deposited specimens compared to the conventional parts made from the wrought material. 0.05 tance observed in fatigue crack growth tests To fill this gap in the knowledge, the present study examines the FCG behaviour of WAAM built specimens made with ER70S-6 mild steel wire. The results presented in this study provide an insight into the extension of the application of WAAM technology to other industries, such as offshore wind, where a significant number of large scale components must be fabricated within limited timeframes
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