Thesis
Structural integrity assessment of wire arc additively manufactured low carbon steel components for marine applications
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2023
- Thesis identifier
- T16680
- Person Identifier (Local)
- 202284853
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- In order to increase manufacturing efficiency of large engineering structures, wire arc additive manufacturing (WAAM), that belongs to direct energy deposition (DED) family of additive manufacturing (AM) processes, has been developed. This manufacturing method has significant potential to improve material design and efficiency of structural components, subsequently reducing production cost and lead times. Some industries, such as aerospace and automotive, have already employed WAAM technology into their manufacturing processes. However, insufficient testing data on WAAM components performance for various materials and operational conditions is one of the main barriers to rapid adoption of WAAM technology in the wider range of industrial applications. Particularly, the sensitivity of mechanical and fatigue properties of WAAM materials to corrosive environment needs to be understood to adopt WAAM technique in marine applications, for instance, in offshore wind structures. Moreover, the WAAM method involves repetitive welding, resulting in high stress concentration between adjacent welded layers and residual stress fields in WAAM components. Since welded joints in offshore constructions are known to be weak points for fatigue failures and crack initiation, it is necessary to conduct the structural integrity assessment of WAAM built steel components and compare their performance with the currently used wrought materials, to investigate the suitability of the WAAM technique for offshore applications. This thesis investigates the structural integrity of WAAM built ER70S-6 and ER100S-1 steel specimens, defining the hardness, tensile, fracture toughness, fatigue crack growth, uniaxial, torsion and multiaxial fatigue properties. Aiming to make a contribution for marine applications, corrosion-fatigue crack growth assessment has been also conducted, along with investigation of fracture characteristics of components previously exposed to corrosive environment. Due to heterogeneity of WAAM built components, the results from this study were analysed with respect to the extraction location and orientation from the WAAM walls. Different load levels were examined for fatigue crack growth tests, confirming the sensitivity of specimen behaviour. The obtained trends were compared with the corresponding recommended lines from the standards and with variety of data sets available in the literature on performance of wrought carbon steels which are widely used in offshore structures, to draw conclusions on suitability of WAAM steel components for the offshore industry. Furthermore, recognising the limitations of the welding based WAAM technique, life enhancement methods were considered, introducing rolling and laser shock peening as post-manufacturing surface treatments techniques. The efficiency of these methods was analysed by examining the fatigue crack growth and corrosion-fatigue crack growth performance of the treated specimens. The residual stress trends were measured by means of neutron diffraction and X-ray scattering to quantify the introduced changes after surface treatment application. Throughout the research, comprehensive microstructural investigations were conducted, including fractography analysis, evaluating the fracture and fatigue mechanisms, using optical and scanning electron microscope. The conclusions from this research have resulted in several journal publications, also presented in the thesis, that contribute to the overall understanding of WAAM steel components behaviour and extending the application of WAAM technology to the marine environments in the future.
- Advisor / supervisor
- Mehmanparast, Ali
- Resource Type
- DOI
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PDF of thesis T16680 | 2023-08-28 | Public | Download |