Research on the Applicability of Metal Foam Based Sandwich Materials for Friction Stir Welded Ship Structures with Sufficient Fatigue Life Time
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Abstract
Research to analyse and/or develop novel materials and techniques is necessary to address competition and safeguard craftmanship in shipbuilding. In this master thesis, two new approaches to reduce the production and maintenance costs are studied: {metal foam core, metal face sheet} sandwich materials and corner adstir fillet stationary shoulder friction stir welding (FSW). The current project is a preparatory analysis for the research in which the two components will be combined. It is anticipated that their combination may generate more added value due to mutual reinforcement.
The study of metal foam based sandwich materials showed that looking at the material level, the {aluminium foam core, steel face sheet} sandwich material is theoretically promising with respect to the conventional steel solid plate in specific situations and applications. When the sandwich material is implemented as part of the stiffened panel, the expected benefit could not be realised. This confirms the search for a more selective use, such in naval vessels when one needs a high resistance to impacts and blasting, and when one wants to conserve the limited internal space.
Compared with the currently existing arc welding technique of double sided T-joints, the corner adstir fillet stationary shoulder FSW scores better on hardness and fatigue resistance of the weld. Since the properties of the weld material correspond to those of the parent material, the weld can no longer be seen as the weakest link of the structure. The fatigue experiment occasionally revealed a new failure type at the undercut, being a sharp corner created by the modified FSW shoulder. This second failure type did not impact on the overall expected failure resistance; however, the limited occurrence does not allow a final statistical interpretation.
Based upon our analyses, there is not yet a place for widespread use of {aluminium foam core, steel face sheet} sandwich materials, but there is an added value for the corner adstir fillet stationary shoulder FSW.