Bonded Repairs to RAN FFG Superstructure-Strain Gauge Data Analysis,
DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)
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Two adhesively bonded carbon fibre patches have been applied to the upper deck of HMAS SYDNEY, an FFG7 Class Frigate, to determine their effectiveness in overcoming fatigue cracking problems in the aluminium superstructure. Strain measurement trials were conducted before and after the patch application to determine their effect on stress levels in the superstructure. An analysis procedure based upon the relative normalised RMS strain value is proposed and validated, and is then used to assess the effects of the patches. A reduction in strain levels is observed along the sides of the patches and in other areas in the necked region of the superstructure, while there is an increase next to either end of the patches. The patches are seen as an effective means of reducing stresses at areas of higher stress and of transferring the load to the ends of the patches where stresses are lower. The effect of a weld repair to a crack on the starboard side of 02 deck, which was affected between the two strain measurement trials, is seen to cause much larger changes in relative strain levels on that side of the ship. Recommendations in relation to the conduct of further trials are provided, including the need to conduct in high sea states to ensure suitably strain high levels, a dedicated trials period, the need to obtain directional wave height spectra and enhancements to the data analysis software. Further analysis using the Finite Element Method is also recommended.
- Marine Engineering