Corrugation wavelength fixing mechanism and its relationship to train and track geometry parameters
- Authors: Balekwa, Bingo Masiza
- Date: 2017
- Subjects: Railroads - Maintenance and repair , Mechanical wear , Railroad engineering , Reliability (Engineering) , Electric railroads - Equipment and supplies - Management
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/262890 , uj:27786
- Description: M.Tech. , Abstract: The wavelength fixing mechanism is studied by correlating natural frequencies of a locomotive wheelset to rail corrugation frequency. The bending natural frequencies of a locomotive wheelset are found to be related to a corrugation frequency at the Belfast to Steelpoort track. Modal analysis was conducted to determine the natural frequencies of the wheelset, and a corrugation frequency was calculated using captured train speeds and measured wavelengths. Due to severe curving forces, corrugation is only on curved track, particularly on the inner (low) rail of the track with wavelengths of 58 mm - 90 mm. Corrugation is understood to have occurred due to wear because there is no discernible metal flow on it at all curves. Concrete sleepers have an influence on the formation and sustaining of corrugation on rails - given the fact that corrugation was only found on curved track supported on concrete sleepers. There is a strong discernible relationship between corrugation wavelengths and train speeds; this is true especially for loaded trains. The train speeds are directly proportional to the wavelengths, whereas the tractive efforts are inversely proportional. This makes sense given the fact that in general, tractive efforts are inversely proportional to train speeds. Reference [1] states that amongst most researches that have been conducted over a century, an increase in corrugation wavelength with increasing train speed is observed. The greater the curve radius, the longer the wavelengths. In order to avoid long-pitch corrugation, the track curve radius should be reduced to less than 400 m, this means smaller radius curves have mostly short-pitch corrugation (wavelength < 80 mm) and large radius curves have mostly long-pitch (wavelength > 80 mm) [2]. There seems to be no discernible relationship between the track gauge deviation and the degree of severity of corrugation. All corrugated curves were found on curves with track gauge deviation, either narrowed or widened. Track curves with corrugation were compared with those that have no corrugation present. Track gauge deviations for curves with no corrugation are significantly less than those of curves with corrugation. This research study also looked at answering some of the common questions, regarding corrugation and its relationship with the environment and terrain.
- Full Text:
- Authors: Balekwa, Bingo Masiza
- Date: 2017
- Subjects: Railroads - Maintenance and repair , Mechanical wear , Railroad engineering , Reliability (Engineering) , Electric railroads - Equipment and supplies - Management
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/262890 , uj:27786
- Description: M.Tech. , Abstract: The wavelength fixing mechanism is studied by correlating natural frequencies of a locomotive wheelset to rail corrugation frequency. The bending natural frequencies of a locomotive wheelset are found to be related to a corrugation frequency at the Belfast to Steelpoort track. Modal analysis was conducted to determine the natural frequencies of the wheelset, and a corrugation frequency was calculated using captured train speeds and measured wavelengths. Due to severe curving forces, corrugation is only on curved track, particularly on the inner (low) rail of the track with wavelengths of 58 mm - 90 mm. Corrugation is understood to have occurred due to wear because there is no discernible metal flow on it at all curves. Concrete sleepers have an influence on the formation and sustaining of corrugation on rails - given the fact that corrugation was only found on curved track supported on concrete sleepers. There is a strong discernible relationship between corrugation wavelengths and train speeds; this is true especially for loaded trains. The train speeds are directly proportional to the wavelengths, whereas the tractive efforts are inversely proportional. This makes sense given the fact that in general, tractive efforts are inversely proportional to train speeds. Reference [1] states that amongst most researches that have been conducted over a century, an increase in corrugation wavelength with increasing train speed is observed. The greater the curve radius, the longer the wavelengths. In order to avoid long-pitch corrugation, the track curve radius should be reduced to less than 400 m, this means smaller radius curves have mostly short-pitch corrugation (wavelength < 80 mm) and large radius curves have mostly long-pitch (wavelength > 80 mm) [2]. There seems to be no discernible relationship between the track gauge deviation and the degree of severity of corrugation. All corrugated curves were found on curves with track gauge deviation, either narrowed or widened. Track curves with corrugation were compared with those that have no corrugation present. Track gauge deviations for curves with no corrugation are significantly less than those of curves with corrugation. This research study also looked at answering some of the common questions, regarding corrugation and its relationship with the environment and terrain.
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Minimising wheel wear by optimising the primary suspension stiffness and centre plate friction of self-steering bogies
- Authors: Fergusson, Shelley Nadine
- Date: 2010-02-24T08:44:35Z
- Subjects: Railroad car wheels , Mechanical wear
- Type: Thesis
- Identifier: uj:6645 , http://hdl.handle.net/10210/3045
- Description: M.Ing. , This report documents the steps taken to gain insight into the dynamics of a HS MkVII self-steering three piece bogie. This was done by firstly studying the dynamics and stability of linear simplifications of the bogie and wagon and then by investigating the dynamics of the bogie by means of a non-linear model.With the necessary insight into the dynamics of the bogie, an optimised relationship between the primary suspension stiffness and the centre plate friction of a self-steering three-piece bogie was achieved. The optimised model’s wear is less than half that of the reference model and has a safe operating speed of 80km/h for an empty wagon and 140 km/h for a loaded wagon. It is recommended that the following be done before issuing a final technical recommendation; • A final optimisation of the lateral and longitudinal primary suspension stiffness arrangement; taking into consideration the physical vertical load bearing capacity of the rubber suspension elements. • A study in order to quantify the effects, on wear, of the increased misaligned position of the bogie on straight track following a curve. A verification of the ADAMS/Rail simulation results by conducting specific on-track tests. • A comprehensive cost-benefit analysis.
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- Authors: Fergusson, Shelley Nadine
- Date: 2010-02-24T08:44:35Z
- Subjects: Railroad car wheels , Mechanical wear
- Type: Thesis
- Identifier: uj:6645 , http://hdl.handle.net/10210/3045
- Description: M.Ing. , This report documents the steps taken to gain insight into the dynamics of a HS MkVII self-steering three piece bogie. This was done by firstly studying the dynamics and stability of linear simplifications of the bogie and wagon and then by investigating the dynamics of the bogie by means of a non-linear model.With the necessary insight into the dynamics of the bogie, an optimised relationship between the primary suspension stiffness and the centre plate friction of a self-steering three-piece bogie was achieved. The optimised model’s wear is less than half that of the reference model and has a safe operating speed of 80km/h for an empty wagon and 140 km/h for a loaded wagon. It is recommended that the following be done before issuing a final technical recommendation; • A final optimisation of the lateral and longitudinal primary suspension stiffness arrangement; taking into consideration the physical vertical load bearing capacity of the rubber suspension elements. • A study in order to quantify the effects, on wear, of the increased misaligned position of the bogie on straight track following a curve. A verification of the ADAMS/Rail simulation results by conducting specific on-track tests. • A comprehensive cost-benefit analysis.
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Mechanisms influencing railway wheel squeal excitation in large radius curves
- Authors: Fourie, Daniël Johannes
- Date: 2012-07-31
- Subjects: Railroad cars - Wheels , Railroad cars - Dynamics , Mechanical wear
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/375924 , uj:8867 , http://hdl.handle.net/10210/5334
- Description: M.Ing. , Sound pressure levels exceeding acceptable limits are being generated by trains travelling on the 1000 m radius curved railway line past the town of Elands Bay. Unacceptable sound levels are attributed mainly to top of rail wheel squeal. Top of rail wheel squeal belongs to the family of selfinduced vibrations and originates from frictional instability in curves between the wheel and the rail under predominantly saturated lateral creep conditions. In small radius curves, saturated lateral creep conditions occur due to the steering of railway wheelsets with large angles of attack. Given the large curve radius and the utilisation of self-steering bogies on the Sishen-Saldanha Iron Ore railway line, curve squeal is a highly unexpected result for the 1000 m radius curved railway line. This is because curving of bogies in large radius curves are achieved without high wheelset angles of attack leading to saturated creep conditions. An experimental and analytical investigation was carried out to identify the mechanisms influencing the generation of wheel squeal in large radius curves. Simultaneous measurement of sound pressure and lateral wheel-rail forces were made during regular train service in one of the two 1000 m radius curves at Elands Bay to characterise the bogie curving behaviour for tonal noise due to wheel squeal occurring in the large radius curve. The lateral force curving signature not only reveals the levels of lateral wheel-rail forces required for bogie curving, but also whether the bogie is curving by means of the creep forces generated at the wheel-rail interface only or if contact is necessitated between the wheel flange and rail gauge corner to help steer the bogie around the curve. The test set-up consisted of two free field microphones radially aligned at equivalent distances towards the in – and outside of the curve in line with a set a strain gauge bridges configured and calibrated to measure the lateral and vertical forces on the inner and outer rail of the curve. This test set-up allowed the squealing wheel to be identified from the magnitude difference of the sound pressures recorded by the inner and outer microphones in combination with comparing the point of frequency shift of the squeal event due to the Doppler Effect with the force signals of the radially aligned strain gauge bridges. From the experimental phase of the investigation, it was found that wheel squeal occurring in the 1000 m radius curve at Elands Bay is characteristic of empty wagons and is strongly related to the squealing wheel’s flange/flange throat being in contact with the gauge corner of the rail. Here high levels of spin creepage associated with high contact angles in the gauge corner lead to high levels of associated lateral creepage necessary for squeal generation. This is in contrast to lateral creepage due to high wheelset angles of attack being the key kinematic parameter influencing squeal generation in small radius curves. Furthermore, the amplitude of wheel squeal originating from the passing of empty wagons was found to be inversely proportional to the level of flange rubbing on the squealing wheel i.e. increased flange contact on the squealing wheel brings about a positive effect on squeal control. Contrary to the empty wagons which are characterised by tonal curve squeal, loaded 4 wagons requiring contact between the wheel flange and rail gauge corner in the 1000 m curve was characterised by broadband flanging noise. It was concluded from measurements that flange contact occurring under high lateral forces for steady state curving of loaded wagons provides the complete damping necessary for squeal control. The curve squeal noise that originated from the passing of empty wagons in the Elands Bay curve could further be classified according to the frequency at which the squeal event manifested itself in the curve, i.e. low frequency audible (0 – 10 kHz), high frequency audible (10 – 20 kHz) and ultrasonic squeal (> 20 kHz). The vast majority of low frequency audible squeal events recorded in the 1000 m Elands Bay curve occurred at approximately 4 kHz and originated from the low rail/trailing inner wheel interface, whilst the vast majority of high frequency audible squeal events occurred in the frequency range between 15 and 20 kHz and originated from both the high rail/leading outer wheel and low rail/trailing inner wheel interfaces.
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- Authors: Fourie, Daniël Johannes
- Date: 2012-07-31
- Subjects: Railroad cars - Wheels , Railroad cars - Dynamics , Mechanical wear
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/375924 , uj:8867 , http://hdl.handle.net/10210/5334
- Description: M.Ing. , Sound pressure levels exceeding acceptable limits are being generated by trains travelling on the 1000 m radius curved railway line past the town of Elands Bay. Unacceptable sound levels are attributed mainly to top of rail wheel squeal. Top of rail wheel squeal belongs to the family of selfinduced vibrations and originates from frictional instability in curves between the wheel and the rail under predominantly saturated lateral creep conditions. In small radius curves, saturated lateral creep conditions occur due to the steering of railway wheelsets with large angles of attack. Given the large curve radius and the utilisation of self-steering bogies on the Sishen-Saldanha Iron Ore railway line, curve squeal is a highly unexpected result for the 1000 m radius curved railway line. This is because curving of bogies in large radius curves are achieved without high wheelset angles of attack leading to saturated creep conditions. An experimental and analytical investigation was carried out to identify the mechanisms influencing the generation of wheel squeal in large radius curves. Simultaneous measurement of sound pressure and lateral wheel-rail forces were made during regular train service in one of the two 1000 m radius curves at Elands Bay to characterise the bogie curving behaviour for tonal noise due to wheel squeal occurring in the large radius curve. The lateral force curving signature not only reveals the levels of lateral wheel-rail forces required for bogie curving, but also whether the bogie is curving by means of the creep forces generated at the wheel-rail interface only or if contact is necessitated between the wheel flange and rail gauge corner to help steer the bogie around the curve. The test set-up consisted of two free field microphones radially aligned at equivalent distances towards the in – and outside of the curve in line with a set a strain gauge bridges configured and calibrated to measure the lateral and vertical forces on the inner and outer rail of the curve. This test set-up allowed the squealing wheel to be identified from the magnitude difference of the sound pressures recorded by the inner and outer microphones in combination with comparing the point of frequency shift of the squeal event due to the Doppler Effect with the force signals of the radially aligned strain gauge bridges. From the experimental phase of the investigation, it was found that wheel squeal occurring in the 1000 m radius curve at Elands Bay is characteristic of empty wagons and is strongly related to the squealing wheel’s flange/flange throat being in contact with the gauge corner of the rail. Here high levels of spin creepage associated with high contact angles in the gauge corner lead to high levels of associated lateral creepage necessary for squeal generation. This is in contrast to lateral creepage due to high wheelset angles of attack being the key kinematic parameter influencing squeal generation in small radius curves. Furthermore, the amplitude of wheel squeal originating from the passing of empty wagons was found to be inversely proportional to the level of flange rubbing on the squealing wheel i.e. increased flange contact on the squealing wheel brings about a positive effect on squeal control. Contrary to the empty wagons which are characterised by tonal curve squeal, loaded 4 wagons requiring contact between the wheel flange and rail gauge corner in the 1000 m curve was characterised by broadband flanging noise. It was concluded from measurements that flange contact occurring under high lateral forces for steady state curving of loaded wagons provides the complete damping necessary for squeal control. The curve squeal noise that originated from the passing of empty wagons in the Elands Bay curve could further be classified according to the frequency at which the squeal event manifested itself in the curve, i.e. low frequency audible (0 – 10 kHz), high frequency audible (10 – 20 kHz) and ultrasonic squeal (> 20 kHz). The vast majority of low frequency audible squeal events recorded in the 1000 m Elands Bay curve occurred at approximately 4 kHz and originated from the low rail/trailing inner wheel interface, whilst the vast majority of high frequency audible squeal events occurred in the frequency range between 15 and 20 kHz and originated from both the high rail/leading outer wheel and low rail/trailing inner wheel interfaces.
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Mechanical and tribological properties of nanoceramics dispersion strengthened 2205 duplex stainless steel
- Mphahlele, Mahlatse Ramaesele
- Authors: Mphahlele, Mahlatse Ramaesele
- Date: 2018
- Subjects: Ceramic materials - Mechanical properties , Ceramic materials - Fatigue , Nanostructured materials , Tribology , Mechanical wear
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269167 , uj:28590
- Description: M.Tech. (Chemical Engineering) , Abstract: Conventional Duplex Stainless Steel used in industrial applications suffers degradation in wear and mechanical properties. A good approach to solve these problems is the dispersion of second phase nanoparticles into duplex stainless steel matrix to improve its strength and properties. Taking the advantage of the high hardness and high chemical stability of titanium nitride (TiN), efforts were made to disperse varying amounts of TiN nanoparticles into the matrices of SAF 2205 to enhance its properties. Hence the mechanical properties and tribological behaviour of the duplex stainless steel (SAF 2205 DSS) strengthened with varied amounts of titanium-based ceramics using nanoindentation system and tribometers were studied. The elastic and plastic deformation properties of the DSS composite materials were determined with a nanoindenter together with the wear behavior of the DSS samples using the strain-to-break (H/Er) and the plastic deformation (H3/Er2) parameters. Also the wear characteristics were estimated with a Tribometer, and Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) was employed to evaluate the morphology and chemistry of the wear scar of the DSS composite. The TiN nanoceramics reinforced SAF 2205 composites were fabricated using spark plasma sintering using optimized process parameters: sintering pressure (50MPa), sintering temperature (1150 oC), heating rate (100 oC/min) and sintering holding time (15 minutes). The TiN dispersions into the SAF were varied between 0 - 8 wt% at an interval of 2 wt%. Nanoindentation technique was used to access the plastic (H) properties, elastic (E) properties, the strain-to-break parameter (H/Er) and the resistance to plastic deformation parameter (H3/Er2) behaviour of the composites under loading and unloading conditions. The wear properties of coefficient of friction, wear loss, wear and specific wear rates under dry sliding conditions and varying loads and worn surface were investigated. The microstructures and worn surfaces of the composites were then evaluated using JEOL Scanning Electron Microscopy (FESEM, JSM-7600F). The results show that the TiN is evenly dispersed in the duplex matrix with a general tendency to locate itself at the grain boundaries. The mechanical properties improved considerably as the TiN content increased, resulting from grain boundary refinements and better dispersion strengthening mechanisms. The grain boundaries have better hardness and reduced young modulus compared to the grains. Furthermore, the ratios H/Er and H3/Er2 increased as the TiN composition increases which demonstrates that the nanocomposites wear resistance is favourable and it was in good correlation with the wear test data. The worn mechanism was a mixed mode of adhesive-abrasive at lower TiN composition but at higher TiN content, the adhesive mechanism prevails. This study established that increasing the addition of nanosized titanium nitride confers better microstructural properties, nanoindentation properties and wear behaviour on spark plasma sintered SAF 2205. Nanocomposite with DSS–6 % TiN reinforcement is recommended for industrial applications.
- Full Text:
- Authors: Mphahlele, Mahlatse Ramaesele
- Date: 2018
- Subjects: Ceramic materials - Mechanical properties , Ceramic materials - Fatigue , Nanostructured materials , Tribology , Mechanical wear
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269167 , uj:28590
- Description: M.Tech. (Chemical Engineering) , Abstract: Conventional Duplex Stainless Steel used in industrial applications suffers degradation in wear and mechanical properties. A good approach to solve these problems is the dispersion of second phase nanoparticles into duplex stainless steel matrix to improve its strength and properties. Taking the advantage of the high hardness and high chemical stability of titanium nitride (TiN), efforts were made to disperse varying amounts of TiN nanoparticles into the matrices of SAF 2205 to enhance its properties. Hence the mechanical properties and tribological behaviour of the duplex stainless steel (SAF 2205 DSS) strengthened with varied amounts of titanium-based ceramics using nanoindentation system and tribometers were studied. The elastic and plastic deformation properties of the DSS composite materials were determined with a nanoindenter together with the wear behavior of the DSS samples using the strain-to-break (H/Er) and the plastic deformation (H3/Er2) parameters. Also the wear characteristics were estimated with a Tribometer, and Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) was employed to evaluate the morphology and chemistry of the wear scar of the DSS composite. The TiN nanoceramics reinforced SAF 2205 composites were fabricated using spark plasma sintering using optimized process parameters: sintering pressure (50MPa), sintering temperature (1150 oC), heating rate (100 oC/min) and sintering holding time (15 minutes). The TiN dispersions into the SAF were varied between 0 - 8 wt% at an interval of 2 wt%. Nanoindentation technique was used to access the plastic (H) properties, elastic (E) properties, the strain-to-break parameter (H/Er) and the resistance to plastic deformation parameter (H3/Er2) behaviour of the composites under loading and unloading conditions. The wear properties of coefficient of friction, wear loss, wear and specific wear rates under dry sliding conditions and varying loads and worn surface were investigated. The microstructures and worn surfaces of the composites were then evaluated using JEOL Scanning Electron Microscopy (FESEM, JSM-7600F). The results show that the TiN is evenly dispersed in the duplex matrix with a general tendency to locate itself at the grain boundaries. The mechanical properties improved considerably as the TiN content increased, resulting from grain boundary refinements and better dispersion strengthening mechanisms. The grain boundaries have better hardness and reduced young modulus compared to the grains. Furthermore, the ratios H/Er and H3/Er2 increased as the TiN composition increases which demonstrates that the nanocomposites wear resistance is favourable and it was in good correlation with the wear test data. The worn mechanism was a mixed mode of adhesive-abrasive at lower TiN composition but at higher TiN content, the adhesive mechanism prevails. This study established that increasing the addition of nanosized titanium nitride confers better microstructural properties, nanoindentation properties and wear behaviour on spark plasma sintered SAF 2205. Nanocomposite with DSS–6 % TiN reinforcement is recommended for industrial applications.
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Surface engineering : laser metal deposition of titanium alloy Grade 5 and tungsten
- Authors: Ndou, Ndivhuwo
- Date: 2017
- Subjects: Lasers - Industrial applications , Gas tungsten arc welding , Mechanical wear , Pulsed laser deposition , Titanium alloys - Fatigue
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/269875 , uj:28675
- Description: D.Phil. (Mechanical Engineering) , Abstract: Titanium alloy Grade 5 (Ti6Al4V) has attracted the interest of the engineering community, because of its excellent physical and mechanical properties. Due to its low density, superior quality at high temperature and good corrosion resistance, Ti6Al4V alloy is used in the aerospace industry. The alloy has also been applied in many areas, such as sport, marine, the chemical industry, the automotive industry and the biomedical field – due to its excellent corrosion resistance in a corrosive environment or medium. Because of the poor wear-resistance properties exhibited by the alloy, five weight percent of tungsten (W) was agglomerated with it, this percentage weight addition of tungsten was optimised, in order to improve its surface properties in this research study. The tungsten is selected due to its superior strength, creep resistance, and structural stability at elevated temperatures. Trial experiments were first conducted with the two powders, Ti6Al4V and W (Ti6Al4V+W). The parameters with good laser deposition process were selected for the preliminary studies. The relationships between the process parameters on the material characterizations were thoroughly investigated. Design Expert 9 software was used to validate the experimental results. In the design of the experiment, the Response Surface Methodology (RSM) was used to determine the required process parameters standard order and the leverage, as well as the response to the input factors. The model was validated to establish the variations between the predicted value and the actual value. The laser deposited Ti6Al4V+W specimens were characterized through the evolving microstructures, dry sliding wear, corrosion, microhardness and x-Ray diffraction.
- Full Text:
- Authors: Ndou, Ndivhuwo
- Date: 2017
- Subjects: Lasers - Industrial applications , Gas tungsten arc welding , Mechanical wear , Pulsed laser deposition , Titanium alloys - Fatigue
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/269875 , uj:28675
- Description: D.Phil. (Mechanical Engineering) , Abstract: Titanium alloy Grade 5 (Ti6Al4V) has attracted the interest of the engineering community, because of its excellent physical and mechanical properties. Due to its low density, superior quality at high temperature and good corrosion resistance, Ti6Al4V alloy is used in the aerospace industry. The alloy has also been applied in many areas, such as sport, marine, the chemical industry, the automotive industry and the biomedical field – due to its excellent corrosion resistance in a corrosive environment or medium. Because of the poor wear-resistance properties exhibited by the alloy, five weight percent of tungsten (W) was agglomerated with it, this percentage weight addition of tungsten was optimised, in order to improve its surface properties in this research study. The tungsten is selected due to its superior strength, creep resistance, and structural stability at elevated temperatures. Trial experiments were first conducted with the two powders, Ti6Al4V and W (Ti6Al4V+W). The parameters with good laser deposition process were selected for the preliminary studies. The relationships between the process parameters on the material characterizations were thoroughly investigated. Design Expert 9 software was used to validate the experimental results. In the design of the experiment, the Response Surface Methodology (RSM) was used to determine the required process parameters standard order and the leverage, as well as the response to the input factors. The model was validated to establish the variations between the predicted value and the actual value. The laser deposited Ti6Al4V+W specimens were characterized through the evolving microstructures, dry sliding wear, corrosion, microhardness and x-Ray diffraction.
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Surface friction behaviour of anodised commercially pure titanium screw assemblies
- Authors: Van Vuuren, Dirk Johan
- Date: 2016
- Subjects: Titanium alloys - Fatigue , Surfaces (Technology) , Surface hardening , Mechanical wear
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/367278 , http://hdl.handle.net/10210/242369 , uj:24996
- Description: M.Ing. (Mechanical Engineering) , Abstract: The document reports on research conducted on titanium bolt assemblies pertaining to the surface friction behaviour between the sliding surfaces of a screw and nut within a fastener assembly. The research was motivated by problems encountered in the dental implant industry whereby the prescribed preload after application of the fixation torque was not achieved. The insufficient preload in the abutment screw led to implant failure due to the dynamic nature of its maxillofacial function and resulting in tissue growth into micro-spaces because of joint separation between the abutment and implant. Commercially pure Grade 4 titanium screws were sulphurically anodised to various oxide layer thicknesses in an attempt to reduce the coefficient of friction within the implant assembly. Testing procedures involved the design and manufacturing of the experimental specimen and testing fixture, anodising of screws, friction coefficient measurement, oxide layer thickness measurement, surface hardness measurement, and surface typography investigation. The design process of the specimen and the testing fixture included various FEA (Finite element analysis) in optimising both of the aforementioned systems of the research and conclusively generate accurate results and findings to compare with each other. Oxide layer thickness measurement was conducted by wavelength reflectance theory and visual measurement of the oxide layer using a scanning electron microscope. The surface hardness of the material was measured using a Vickers hardness tester while surface typography investigation was performed using a scanning electron microscope. Findings of the experiments revealed that the coefficient of friction reduces by 10% to 40% as the anodising voltage is increased up to an oxide layer thickness of 0.4μm, where after the surface friction coefficient increases to eventually surpass the coefficient of friction for untreated fastener assemblies. Untightening examination exhibited similar behaviour to fixation, where the removal friction coefficient reduces to attain a minimum of 0.69 at an oxide thickness of 0.06μm. The untightening coefficient of friction was at a maximum at the increased oxide layer thicknesses of 0.97μm to 3.4μm. Oxide layer thickness investigation revealed that the thickness of the oxide layer increases exponentially as the anodising voltage is increased. The increase in anodising voltage also...
- Full Text:
- Authors: Van Vuuren, Dirk Johan
- Date: 2016
- Subjects: Titanium alloys - Fatigue , Surfaces (Technology) , Surface hardening , Mechanical wear
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/367278 , http://hdl.handle.net/10210/242369 , uj:24996
- Description: M.Ing. (Mechanical Engineering) , Abstract: The document reports on research conducted on titanium bolt assemblies pertaining to the surface friction behaviour between the sliding surfaces of a screw and nut within a fastener assembly. The research was motivated by problems encountered in the dental implant industry whereby the prescribed preload after application of the fixation torque was not achieved. The insufficient preload in the abutment screw led to implant failure due to the dynamic nature of its maxillofacial function and resulting in tissue growth into micro-spaces because of joint separation between the abutment and implant. Commercially pure Grade 4 titanium screws were sulphurically anodised to various oxide layer thicknesses in an attempt to reduce the coefficient of friction within the implant assembly. Testing procedures involved the design and manufacturing of the experimental specimen and testing fixture, anodising of screws, friction coefficient measurement, oxide layer thickness measurement, surface hardness measurement, and surface typography investigation. The design process of the specimen and the testing fixture included various FEA (Finite element analysis) in optimising both of the aforementioned systems of the research and conclusively generate accurate results and findings to compare with each other. Oxide layer thickness measurement was conducted by wavelength reflectance theory and visual measurement of the oxide layer using a scanning electron microscope. The surface hardness of the material was measured using a Vickers hardness tester while surface typography investigation was performed using a scanning electron microscope. Findings of the experiments revealed that the coefficient of friction reduces by 10% to 40% as the anodising voltage is increased up to an oxide layer thickness of 0.4μm, where after the surface friction coefficient increases to eventually surpass the coefficient of friction for untreated fastener assemblies. Untightening examination exhibited similar behaviour to fixation, where the removal friction coefficient reduces to attain a minimum of 0.69 at an oxide thickness of 0.06μm. The untightening coefficient of friction was at a maximum at the increased oxide layer thicknesses of 0.97μm to 3.4μm. Oxide layer thickness investigation revealed that the thickness of the oxide layer increases exponentially as the anodising voltage is increased. The increase in anodising voltage also...
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