PSI - Issue 27

Muhammad Yusvika et al. / Procedia Structural Integrity 27 (2020) 109–116 Yusvika et al. / Structural Integrity Procedia 00 (2019) 000 – 000

115

7

experimental observation. The overall results agreement was a good pattern, and the cavitation erosion area coincided reasonably well. a b

F ig. 4. Erosion prediction from simulation (left) and experimental (right) with propeller P1225 ( D = 0.24 m) (Peters et al., 2018). 6. Coating application method to detect cavitation erosion This part will discuss a technique used in the marine propeller to investigate the cavitation erosion with the coating method. Hammit supposed that cavitation structures carry a significant amount of potential energy, and the aggressiveness of cavitation could be assessed through conservation of energy conversion (Hammit, 1963). They stated that there is an impact threshold value, in which the bubble collapse contributes to the fatigue fracture of the material surface. Knapp noted that the pitting rate on a soft aluminum test specimen is only one in 30,000 of traveling bubble cavities that exceed energy levels that cause erosion damage (Knapp, 1955). Aktas et al. have performed experimental research to observe cavitation erosion by the coating method. The experimental investigation was conducted at Emerson Cavitation Tunnel (ETC) of Newcastle University (Aktas et al., 2020). A model scale propeller KC-193 with a diameter of 0.305 m was used for this experiment. The previous investigation shows that the cavitation bubble collapse may cause erosion of propeller material. This study aims to capture the pitting pattern area that may serve as an indicator of probable erosion causes. From the experiment was performed by Aktas et al., a schematic investigation of different paint coating was applied. The blades were exposed to cavitation in a cavitation tunnel, and erosion patterns were macroscopically recorded using a high-speed camera. Fig. 5 shows the experimental setup and measuring instruments used.

Fig. 5. Cavitation observation using stroboscopic lightning (Aktas et al., 2020).

Among the results that have been tested, the acrylic paint diluted with freshwater showed an unambiguous indication of the pitting damage. Amongst the tested alternatives of the soft coating application techniques, dipping appeared to be the most promising technique providing a uniform soft surface over the blades. Perhaps the only The weakness of the dipping technique appeared to be rather a soft surface thickness at the edges of the blades, which can be thicker or thinner depending on the solution substances and post-coating handling requiring care. Fig. 6 shows the indicated area as the erosion is by cavitation on the blade surface.