Study on Laser Surface Enhancement of Marine Propellers
Examensarbete för masterexamen
Patil Bellary, Pradeep
Due to the effects of global warming reducing the extent of the sea ice, more and more merchant ships enter ice-infested waters. Ice damages on ships are frequently reported. Propeller is among the most vulnerable parts of a ship subject to ice damages. Propeller damages lead to efficiency loss, deterioration of cavitation and noise, and even malfunction of the propulsion system. Reparation of damaged propellers are costly. In this study, we aimed at enhancing a propeller’s ice strength while keeping its open-water profile. This was achieved by implementing cladding material on the bronze propeller blades through laser treatment. In this thesis work, numerical analyses of laser cladding process was carried out using finite element (FE) method to investigate if the laser cladding improves the resistance of the marine propeller materials against repeated ice impact loads. A Co-Cr alloy was cladded on two different substrate materials. The laser cladded surfaces were grounded where the effect of a grinding wheel was derived using a combination of rectangular distribution of heat source and grinding forces instead of the presence of actual grinding wheel. Repeated ice impact loads were applied on both the non-cladded substrate and the cladded substrates after grinding for a certain period of time. The efficiency of the cladding and grinding processes was estimated using the impact load simulations. It was observed that after the application of every impact load on the non-cladded substrate, the longitudinal residual stresses and the equivalent plastic strain were increased. But, after grinding the cladded substrate, there was an improvement in the equivalent plastic strain. The inference obtained after multiple simulations were that the grinding process improves the equivalent plastic strain on the cladded substrate. It thus concludes that the laser cladding and grinding processes improve the performance of the propellers against repeated ice impact loads considerably.
finite element analysis, ice-propeller interaction, laser cladding, residual stresses, surface grinding