Fatigue of welded aluminium structures in high speed marine vessels

Kecsmar, John Peter (2003) Fatigue of welded aluminium structures in high speed marine vessels. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis seeks to explore Important Issues underpinning the fatigue design of high speed marine vessels made from aluminium. Understanding of fatigue mechanisms requires a study of the microstructure of the material to Include slip planes and systems and the manner In which these form cracks. Such cracks In a material or a structure lead to stress concentrations, which can be modelled using fracture mechanics concepts. The principal characteristics of both the principal grades of aluminium used In shipbuilding, namely the 5000 and 6000 series, are discussed. The critical influence of sea water and welding on the mechanical properties of the alloys, particularly on the fatigue behaviour, Is highlighted. The effects of various other forming, shaping and joining operations In a shipyard are also explored. The thesis addresses the manner In which choice of design details, such as shapes of cutouts, affects both the mechanical performance and the production costs. The proper use of finite element analysis to model stress concentration factors of shipyard joints and around cutouts is discussed in depth. Finally, the fatigue design concepts are applied to assess the efficacy of structure in the water jet ducting system of a high speed Tricat vessel made from aluminium alloys.

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