Material response on the cavitation bubble collapses

Edmund Ofei Aidoo

Master's thesis

Abstract:

Research on cavitation bubble-wall interaction and its impact on material properties has been discussed. The experiment was designed and realized with pitting test carried out during the incubation period on an aluminum alloy in a modified vibratory cavitation device. The amplitude of the device was kept at constant maximum and the polished surface of the sample was exposed to cavitation pressure pulses. The test was conducted at three different exposure times to ascertain the effect of exposure time on pit formation. The surface was analyzed using a Scanning Electron Microscope and a contact profilometer. The selection of appropriate cutoff depth for the analysis of the pits was discussed as well as the correction of the signal from the surface profile. These techniques allowed us to characterize the parameters of the pits such as diameter, depth, volume and pit numbers. The frequency distribution of the pit diameters was analyzed for both the SEM images and the surface profile of the profilometer. The effect of the exposure time on the distribution of pits was analyzed. It was determined that the exposure time significantly affects the number of pits formed as well as the distribution of pit diameters. The relationship between pit volume and diameter was analyzed. The distribution of pit volumes by pitting rate for different exposure times were also discussed. The surface deformation (pit depth) is seen to increase with increasing impact forces. The jet diameter, however, does not determine the extent of deformation since this phenomenon depends on other variables such as material properties, test conditions, and the magnitude of the impact force. The discussion given at the end attempts to explain the observations made in the study.

Abstract:

Research on cavitation bubble-wall interaction and its impact on material properties has been discussed. The experiment was designed and realized with pitting test carried out during the incubation period on an aluminum alloy in a modified vibratory cavitation device. The amplitude of the device was kept at constant maximum and the polished surface of the sample was exposed to cavitation pressure pulses. The test was conducted at three different exposure times to ascertain the effect of exposure time on pit formation. The surface was analyzed using a Scanning Electron Microscope and a contact profilometer. The selection of appropriate cutoff depth for the analysis of the pits was discussed as well as the correction of the signal from the surface profile. These techniques allowed us to characterize the parameters of the pits such as diameter, depth, volume and pit numbers. The frequency distribution of the pit diameters was analyzed for both the SEM images and the surface profile of the profilometer. The effect of the exposure time on the distribution of pits was analyzed. It was determined that the exposure time significantly affects the number of pits formed as well as the distribution of pit diameters. The relationship between pit volume and diameter was analyzed. The distribution of pit volumes by pitting rate for different exposure times were also discussed. The surface deformation (pit depth) is seen to increase with increasing impact forces. The jet diameter, however, does not determine the extent of deformation since this phenomenon depends on other variables such as material properties, test conditions, and the magnitude of the impact force. The discussion given at the end attempts to explain the observations made in the study.

Keywords

Cavitation, Piting rate, Exposure time, Material response

Language used: English

Date on which the thesis was submitted / produced: 21. 5. 2018

Thesis defence

• Supervisor: Ing. Miloš Müller, Ph.D.

Technical University of Liberec

Faculty of Mechanical Engineering

Master programme / field:
Mechanical Engineering / Machines and Equipment Design