Cavitation erosion of materials

 

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dc.contributor.advisor Ball, Anthony en_ZA
dc.contributor.author Heathcock, Christopher John en_ZA
dc.date.accessioned 2016-02-12T07:13:05Z
dc.date.available 2016-02-12T07:13:05Z
dc.date.issued 1980 en_ZA
dc.identifier.citation Heathcock, C. 1980. Cavitation erosion of materials. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/16975
dc.description Bilbiography: p. 141-148. en_ZA
dc.description.abstract This investigation was undertaken to find the optimum hydraulic fluids and materials for combating cavitation erosion in hydraulic mining machinery operating,on 5:95 oil-in-water emulsions, Controlled cavitation was generated in the laboratory in a vibratory cavitation apparatus employing the stationery specimen system. The influence of separation distance between the drill tip and specimen and of varying medium temperature on cavitation erosion were also investigated but were of secondary importance to the studies on materials and emulsions, The evaluation of the influence of a number of commercial metal cutting coolants and specific hydraulic emulsions oncavitation erosion,showed that those emulsions with a high mineral oil content suppress erosion the most, This phenomenon is considered to be either the result of a reduction in nucleation of highly damaging surface cavities due to the elimination of surface nuclei by an oil film, or to damping of cavity collapse due to the high dissolved gas content of oil-in-water emulsions, A large number of commercial grade alloys and polymers have been investigated, The alloys ranged from single phase, face centered cubic nickel alloys to complex, multi-phase, cobalt based alloys while the polymeric materials were all linear and crystalline. The modes of erosion and mechanisms of erosion resistance were studied in detail by optical microscopy, scanning and transmission electron microscopy and X-ray diffractometry. The fractographic studies on the alloys revealed, in particular, the role played by second phase particles and other surface features such as protruding grain boundaries and surface steps created by dislocation movement, twinning and phase transformations, Furthermore, X-ray diffractometry coupled with theoretical considerations and the findings of previous investigations indicated the fundamental importance of phase transitions in contributing towards the erosion resistance of alloys, Cobalt based Stellite alloys, nickel based cemented carbides and the intermetallic alloy NiTi have exceptionally high erosion resistance, The Stellites have a high yield stress and also undergo an awe phase transition which results in a high work hardening rate and high strain to fracture, NiTi similarly undergoes a phase transformation which allows absorption of seven per cent reversible strain and also results in a high work hardening rate. The erosion resistance of nickel based tungsten carbides is, in turn, attributable to the very high yield stress of these materials, Ultra high molecular weight polyethylene and nylons have relatively high erosion resistances, Their exceptional performances are due to a high strain to fracture and high yield strength respectively. On the other hand low tensile strength polytetrafluoroethylene has a very poor resistance to erosion. This work has identified various material properties which are required for erosion resistance, These are : (a) a high yield stress, (b) a high work hardening rate and (c) a high strain to fracture. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Mechanical Engineering en_ZA
dc.title Cavitation erosion of materials en_ZA
dc.type Doctoral Thesis
uct.type.publication Research en_ZA
uct.type.resource Thesis en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Engineering and the Built Environment
dc.publisher.department Department of Mechanical Engineering en_ZA
dc.type.qualificationlevel Doctoral
dc.type.qualificationname PhD en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Heathcock, C. J. (1980). <i>Cavitation erosion of materials</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering. Retrieved from http://hdl.handle.net/11427/16975 en_ZA
dc.identifier.chicagocitation Heathcock, Christopher John. <i>"Cavitation erosion of materials."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering, 1980. http://hdl.handle.net/11427/16975 en_ZA
dc.identifier.vancouvercitation Heathcock CJ. Cavitation erosion of materials. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Mechanical Engineering, 1980 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/16975 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Heathcock, Christopher John AB - This investigation was undertaken to find the optimum hydraulic fluids and materials for combating cavitation erosion in hydraulic mining machinery operating,on 5:95 oil-in-water emulsions, Controlled cavitation was generated in the laboratory in a vibratory cavitation apparatus employing the stationery specimen system. The influence of separation distance between the drill tip and specimen and of varying medium temperature on cavitation erosion were also investigated but were of secondary importance to the studies on materials and emulsions, The evaluation of the influence of a number of commercial metal cutting coolants and specific hydraulic emulsions oncavitation erosion,showed that those emulsions with a high mineral oil content suppress erosion the most, This phenomenon is considered to be either the result of a reduction in nucleation of highly damaging surface cavities due to the elimination of surface nuclei by an oil film, or to damping of cavity collapse due to the high dissolved gas content of oil-in-water emulsions, A large number of commercial grade alloys and polymers have been investigated, The alloys ranged from single phase, face centered cubic nickel alloys to complex, multi-phase, cobalt based alloys while the polymeric materials were all linear and crystalline. The modes of erosion and mechanisms of erosion resistance were studied in detail by optical microscopy, scanning and transmission electron microscopy and X-ray diffractometry. The fractographic studies on the alloys revealed, in particular, the role played by second phase particles and other surface features such as protruding grain boundaries and surface steps created by dislocation movement, twinning and phase transformations, Furthermore, X-ray diffractometry coupled with theoretical considerations and the findings of previous investigations indicated the fundamental importance of phase transitions in contributing towards the erosion resistance of alloys, Cobalt based Stellite alloys, nickel based cemented carbides and the intermetallic alloy NiTi have exceptionally high erosion resistance, The Stellites have a high yield stress and also undergo an awe phase transition which results in a high work hardening rate and high strain to fracture, NiTi similarly undergoes a phase transformation which allows absorption of seven per cent reversible strain and also results in a high work hardening rate. The erosion resistance of nickel based tungsten carbides is, in turn, attributable to the very high yield stress of these materials, Ultra high molecular weight polyethylene and nylons have relatively high erosion resistances, Their exceptional performances are due to a high strain to fracture and high yield strength respectively. On the other hand low tensile strength polytetrafluoroethylene has a very poor resistance to erosion. This work has identified various material properties which are required for erosion resistance, These are : (a) a high yield stress, (b) a high work hardening rate and (c) a high strain to fracture. DA - 1980 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1980 T1 - Cavitation erosion of materials TI - Cavitation erosion of materials UR - http://hdl.handle.net/11427/16975 ER - en_ZA


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