Master of Science in Materials Science

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Browsing Master of Science in Materials Science by Author "Guluwita, SP"

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    Analysis of fast attack craft rudder failure
    Gunarathna, AHGPN; Guluwita, SP
    It is observed that frequent rudder failures of Sri Lanka Navy’s fast attack craft which are equipped with conventional propulsion system. Therefore, it was unable to effectively utilize these craft for operational requirements in the Navy. In this research it was analyzed both recently failed fast attack craft rudder and existing rudder fabrication process in order to minimize this type of rudder failures in future. Analysis of failed rudder and the existing rudder fabrication process was done through macro/micro level inspection, chemical composition analysis and micro hardness testing of relevant materials. Analysis revealed that rudder failed from the welded joint where rudder blade connected to rudderstock and weakening of the weld joint during fabrication. The weld joint was weakened due to formation of intermetallic phases, carbide precipitation, porosities and hot cracks in the heat affected zone of the weld. Therefore, finally rudder was failed as a result of fatigue failure. Use of similar low carbon stainless steel with suitable welding electrodes to ensure final weld lies in austenite region with containing 4% to 12% ferrite in the weld could overcome this issue.
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    Variation in yield strength and elongation of re-bars manufactured using local ingots
    Perera, KPAS; Guluwita, SP
    Recycling of scrap steel to produce ribbed steel bars is a common practice followed in many countries. Selection of the best composition of ingredients for the melt is a huge challenge faced by the manufacturers in the scrap recycling industry. A major problem faced by them during the recycling process is the difficulty they have in controlling the levels of undesirable residual elements such as Cu, Ni, Sn, As, Cr, Mo, Pb, etc., that come with scraps. In SLS 375:2009 and BS 4449 Standards, the ‘maximum percentage by mass’ of residual elements is represented by the “Carbon Equivalent Value”. Carbon Equivalent (CE) value is used to understand how different alloys and residual elements affect the strength of steel. In ingot casting, a good control of ladle treatment is required for the proper control of de-oxidation and de-sulphurisation chemicals and residuals. An extensive study was carried out by referring to the literature and benchmarking the best practices of several steel makers to improve the ingot casting process. In this dissertation, the results of the experimental investigation on the effects of alloying and residual elements on yield strength and elongation of TMT bars is presented. The experimental study was focused on identifying the most suitable mixed proportion of ferro-silicon to ferro-silico-manganese, and the best controllable range of CE values to be used during melting to ensure that the products manufactured are consistent in quality. The quantities of the main alloying chemicals mixed together are changed to make the diluted percentage of manganese content in the bath solution to be 0.8% by mass. The ingots and TMT bar samples prepared were tested to see how the Carbon Equivalent value and the mixed proportion of alloying chemicals affect the yield strength and elongation of the finished bars. It was revealed that a consistent yield strength and elongation of each TMT bar of a set can be achieved by having the Carbon Equivalent value in the range 0.37