Fatigue and corrosion-fatigue crack growth behavior of wire arc additively manufactured parts

Crack initiation and propagation in welded joints are the main failure mechanisms in offshore structures, which operate in harsh marine environment under severe cyclic loading conditions. As an essential part of the design and structural integrity assessment of such joints, fatigue crack growth (FCG) and corrosion-fatigue crack growth (CFCG) mechanisms need to be characterized and accounted for. In recent years, significant efforts have been made to examine the suitability of additively manufactured parts, compared to traditional welded joints, for application in offshore structures. The wire arc additive manufacturing (WAAM) technology is a promising fabrication technique which has been proven to have many advantages for producing large structures; however, the fatigue and corrosion-fatigue performance of WAAM steel components for application in the marine environments is still unexplored. In this study, the WAAM technique was employed to fabricate 16 specimens made of ER70S-6 and ER100S-1 low carbon steel wires, which were then tested under cyclic loading conditions in air and seawater to assess the FCG and CFCG behavior and hence explore the suitability of this fabrication technology for marine applications. The test duration and FCG/CFCG rates were investigated for each material with respect to the extraction orientation and location of the specimens from the WAAM walls. Furthermore, the obtained results were compared with the BS7910 standard recommended trends and experimental data available in the literature for conventionally built steel weldments.