Numerical modelling of power law constants established through impression and micro-Uniaxial creep methods for service exposed A234WPB steel
- Authors: Tembo, Blessed
- Date: 2024-04
- Subjects: Number theory , Numerical analysis , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64852 , vital:73931
- Description: Continuous monitoring of creep life in materials operating at high temperatures and pressures is imperative to prevent catastrophic failures and ensure timely replacement of worn-out components in industrial plants. Small-scale creep testing methodologies offer a valuable means of assessing material creep life while preserving structural integrity. Motivated by the need for reliable methods in creep life assessment, this study aimed to investigate the creep properties of A234WPB material subjected to service conditions using Impression creep and micro-uniaxial creep testing techniques. The research questions focused on establishing power law constants through small-scale creep testing, validating these constants using numerical modelling, and assessing their practical implementation in predicting material creep life. Samples extracted from service-exposed A234WPB steel alloy underwent step-load impression creep tests and step-temperature micro-uniaxial creep tests to derive the power law creep equation. The determined stress exponent of 3.967 indicated that dislocation creep was the dominant creep-controlling mechanism at 520 °C. A numerical model, utilizing the established power law constants, demonstrated a strong correlation with experimental findings in steady-state creep rates. Furthermore, the conventional Monkman-Grant approach was employed to predict the remaining life of the service-exposed material using impression creep data. The predicted remaining life aligned with the scatter band of uniaxial rupture life on a Larson-Miller plot, highlighting the practical utility of impression creep and micro-uniaxial creep testing techniques in assessing creep life. This study contributes to the advancement of small-scale creep testing methods and underscores their potential for practical implementation in industrial settings, thereby enhancing the reliability and safety of high-temperature and high-pressure operations. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Tembo, Blessed
- Date: 2024-04
- Subjects: Number theory , Numerical analysis , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64852 , vital:73931
- Description: Continuous monitoring of creep life in materials operating at high temperatures and pressures is imperative to prevent catastrophic failures and ensure timely replacement of worn-out components in industrial plants. Small-scale creep testing methodologies offer a valuable means of assessing material creep life while preserving structural integrity. Motivated by the need for reliable methods in creep life assessment, this study aimed to investigate the creep properties of A234WPB material subjected to service conditions using Impression creep and micro-uniaxial creep testing techniques. The research questions focused on establishing power law constants through small-scale creep testing, validating these constants using numerical modelling, and assessing their practical implementation in predicting material creep life. Samples extracted from service-exposed A234WPB steel alloy underwent step-load impression creep tests and step-temperature micro-uniaxial creep tests to derive the power law creep equation. The determined stress exponent of 3.967 indicated that dislocation creep was the dominant creep-controlling mechanism at 520 °C. A numerical model, utilizing the established power law constants, demonstrated a strong correlation with experimental findings in steady-state creep rates. Furthermore, the conventional Monkman-Grant approach was employed to predict the remaining life of the service-exposed material using impression creep data. The predicted remaining life aligned with the scatter band of uniaxial rupture life on a Larson-Miller plot, highlighting the practical utility of impression creep and micro-uniaxial creep testing techniques in assessing creep life. This study contributes to the advancement of small-scale creep testing methods and underscores their potential for practical implementation in industrial settings, thereby enhancing the reliability and safety of high-temperature and high-pressure operations. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
Optimisation of laser welding for thin-walled Ti6Al4V glider pressure hull
- Authors: Nel, Matthew Ryan
- Date: 2024-04
- Subjects: Laser welding , Welding , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64739 , vital:73882
- Description: Laser welding is a type of fusion welding process characterised by deep penetration, low heat input and high welding speed. This dissertation investigates the suitability of this process for the fabrication of an underwater glider buoyancy engine from thin Ti6Al4V alloy sheet. Areas of interest include the effect of process parameters on weld microstructure, static properties (microhardness, tensile and bend tests) and dynamic properties (fatigue tests). The effect of welding speed and laser defocusing were evaluated considering experimental matrices consisting of four different travel speeds and three defocus distances. These were narrowed down to three travel speeds and a single defocus distance, resulting in a final test matrix delivering three different heat inputs. Thereafter, the effect of heat input on static and dynamic properties was investigated. Vickers microhardness tests were carried out to predict weld response during tensile testing, with the expectation being that harder welds would offload more strain. This was confirmed using digital image correlation, which allowed for virtual measurement and visualisation of strain offloading. Bend tests were carried out on parent and welded samples to confirm whether Ti6Al4V could be formed to the correct geometry. Forming Ti6Al4V into a U-shape was the first consideration, since dynamic testing required samples of this geometry with longitudinal weld orientation. A two-stage forming methodology was developed from these experiments. Formed samples were subjected to fatigue tests in a custom designed fatigue platform for testing weld orientation as it would appear in the final component. Prediction of the welded buoyancy engine life was the goal behind these tests. Fracture surfaces were analysed to gain understanding of where crack initiation and final fracture occurred. Porosity served as the primary cause for crack initiation in failed samples. Pore distribution was heaviest in low-heat weldments and decreased with increasing heat input, while pore size increased with increasing heat input. This resulted in medium-heat weldments exhibiting superior performance to that of low- and high-heat ones. It was concluded that the laser welding process is able to produce weldments of sufficient integrity in thin Ti6Al4V sheet-formed components intended for use in glider buoyancy engines. , Thesis (MEng) -- Faculty of Engineering, the Built Environment and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Nel, Matthew Ryan
- Date: 2024-04
- Subjects: Laser welding , Welding , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64739 , vital:73882
- Description: Laser welding is a type of fusion welding process characterised by deep penetration, low heat input and high welding speed. This dissertation investigates the suitability of this process for the fabrication of an underwater glider buoyancy engine from thin Ti6Al4V alloy sheet. Areas of interest include the effect of process parameters on weld microstructure, static properties (microhardness, tensile and bend tests) and dynamic properties (fatigue tests). The effect of welding speed and laser defocusing were evaluated considering experimental matrices consisting of four different travel speeds and three defocus distances. These were narrowed down to three travel speeds and a single defocus distance, resulting in a final test matrix delivering three different heat inputs. Thereafter, the effect of heat input on static and dynamic properties was investigated. Vickers microhardness tests were carried out to predict weld response during tensile testing, with the expectation being that harder welds would offload more strain. This was confirmed using digital image correlation, which allowed for virtual measurement and visualisation of strain offloading. Bend tests were carried out on parent and welded samples to confirm whether Ti6Al4V could be formed to the correct geometry. Forming Ti6Al4V into a U-shape was the first consideration, since dynamic testing required samples of this geometry with longitudinal weld orientation. A two-stage forming methodology was developed from these experiments. Formed samples were subjected to fatigue tests in a custom designed fatigue platform for testing weld orientation as it would appear in the final component. Prediction of the welded buoyancy engine life was the goal behind these tests. Fracture surfaces were analysed to gain understanding of where crack initiation and final fracture occurred. Porosity served as the primary cause for crack initiation in failed samples. Pore distribution was heaviest in low-heat weldments and decreased with increasing heat input, while pore size increased with increasing heat input. This resulted in medium-heat weldments exhibiting superior performance to that of low- and high-heat ones. It was concluded that the laser welding process is able to produce weldments of sufficient integrity in thin Ti6Al4V sheet-formed components intended for use in glider buoyancy engines. , Thesis (MEng) -- Faculty of Engineering, the Built Environment and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
Quantify the shift in critical strain energy density for a dynamic loaded S355J2 weld section by small punch testing
- Authors: Snyman, Ross
- Date: 2024-04
- Subjects: Materials -- Testing , Materials -- Microscopy , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64830 , vital:73927
- Description: The potential of using “critical strain energy density” as an indicator to detect material degradation on fatigue-loaded components, where the stress amplitude was gradually increased, was investigated by applying the small punch test methodology. Small punch discs were extracted from four fatigue specimens. Discs were extracted from two zones within the fatigue specimens: the heat-affected zone of a shield metal arc welded butt joint, as well as from parent metal plate area. Each fatigue specimen having been exposed to a different stress amplitude but equal number of fatigue cycles of 20 million. This allowed the development of a Small Punch Test results database, permitting the calculation of material properties by using a Finite Element Analysis inverse method. Critical strain energy values did not reveal any conclusive shift or correlation for discs extracted from the HAZ. This is mainly attributed to variance in the grain structure for HAZ samples. For discs extracted from parent metal, a decreasing trend in strain energy density value was noted in relation to an increase in the fatigue test stress amplitude. This observed change was a clear indication of the potential for using “Strain Energy Density”, as extracted from this test methodology, as a ranking tool for quantifying the extent of degradation of in-service components. The application of this study demonstrated the ability to monitor and predict material degradation for a given stress range over the expected life of a cyclically loaded component utilizing strain energy density results. This is useful, particularly in heavy industries where structures and large-scale components are used beyond their original design life. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Snyman, Ross
- Date: 2024-04
- Subjects: Materials -- Testing , Materials -- Microscopy , Mechanical engineering
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64830 , vital:73927
- Description: The potential of using “critical strain energy density” as an indicator to detect material degradation on fatigue-loaded components, where the stress amplitude was gradually increased, was investigated by applying the small punch test methodology. Small punch discs were extracted from four fatigue specimens. Discs were extracted from two zones within the fatigue specimens: the heat-affected zone of a shield metal arc welded butt joint, as well as from parent metal plate area. Each fatigue specimen having been exposed to a different stress amplitude but equal number of fatigue cycles of 20 million. This allowed the development of a Small Punch Test results database, permitting the calculation of material properties by using a Finite Element Analysis inverse method. Critical strain energy values did not reveal any conclusive shift or correlation for discs extracted from the HAZ. This is mainly attributed to variance in the grain structure for HAZ samples. For discs extracted from parent metal, a decreasing trend in strain energy density value was noted in relation to an increase in the fatigue test stress amplitude. This observed change was a clear indication of the potential for using “Strain Energy Density”, as extracted from this test methodology, as a ranking tool for quantifying the extent of degradation of in-service components. The application of this study demonstrated the ability to monitor and predict material degradation for a given stress range over the expected life of a cyclically loaded component utilizing strain energy density results. This is useful, particularly in heavy industries where structures and large-scale components are used beyond their original design life. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
- Full Text:
- Date Issued: 2024-04
- «
- ‹
- 1
- ›
- »