The influences of sintering temperature on the microstructure and giant dielectric properties of ... more The influences of sintering temperature on the microstructure and giant dielectric properties of a new co-doped TiO 2 system, i.e., V and Ta co-doped TiO 2 , were investigated. The grain size of (V 1/2 Ta 1/ 2) 0.01 Ti 0.99 O 2 ceramics was enlarged with increasing sintering temperature. Dense microstructure and homogeneous dispersion of dopants were achieved in the ceramics sintered at 1400e1500 C for 5 h. The dielectric permittivity in the frequency range 40e10 6 Hz of the (V 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 ceramics significantly increased with the mean grain size, while the dielectric loss tangent was reduced to 0.033 at 10 2 Hz. Furthermore, the high-temperature stability of the dielectric permittivity was improved with increasing mean grain size. The electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries and/or surface layers was confirmed using impedance spectroscopy. The conduction inside the semiconducting grains was attributed to electron hopping between Ti 4þ and Ti 3þ , which was confirmed by X-ray photoelectron spectroscopy. Very high resistivity with a large conduction activation energy of the insulating parts was suggested as the primary cause of the giant dielectric permittivity with low loss tangent.
The introduction of computational modelling during alloy development has significantly reduced th... more The introduction of computational modelling during alloy development has significantly reduced the cost of production and the prolonged time spent by researchers doing trials and errors in the laboratory. In this study, computational software (JMat Pro) was used to simulate the effect of the addition of Zr and Co, on the material properties of NiAl-Mo(Cr) alloy such as the elastic modulus, hardness, thermal conductivity, bulk modulus and specific heat capacity. A significant improvement in the mechanical properties was observed in the developed alloys as compared to those without Zr and Co. Also, the addition of as low as 0.5 at. % Zr and 1.0 at. % Co to NiAl-Cr(Mo) resulted in improved compressive strength and plasticity of the alloy.
The accurate prediction of the thermomechanical properties of newly developed polymer composites ... more The accurate prediction of the thermomechanical properties of newly developed polymer composites is important in the determination of their possible areas of application. In this study, a 3D model of representative volume element (RVE) with different wood flour weight ratios (5, 10, 15, 20, 25 and 30 %) was used to develop wood flour polymer composites. Micromechanical material modelling software (Digimat) was used in conjunction with finite element analysis software (Abaqus) to develop the polymer composites and to determine their thermomechanical properties (modulus of elasticity, Poisson’s ratio, thermal conductivity, density, and hardness). The hardness, tensile strength and modulus of elasticity increase with an increase in the wt.% of wood flour, while the Poisson ratio, thermal conductivity and density decrease with an increase in the wt.% of wood flour. Also, the predicted thermomechanical properties using the micromechanical material modelling software (RVE) follow the same...
Ni-Cr-ZrO2 composites with varying amounts of ZrO2 additive (5 wt%, 7.5 wt%, 10 wt% and 12.5 wt%)... more Ni-Cr-ZrO2 composites with varying amounts of ZrO2 additive (5 wt%, 7.5 wt%, 10 wt% and 12.5 wt%) were fabricated using spark plasma sintering method at a sintering temperature of 1000°C, heating rate of 100°C/min, holding time of 5 min, and a pressure of 50 MPa. The effect of ZrO2 addition on the microstructure, tribological and mechanical properties of the developed composites were studied. The results showed that maximum densification was attained at 10 wt% ZrO2. Further increase in the fractions of ZrO2 within the composites results in a decrease in the relative density of the sintered composite. A significant increase in hardness from 433.24 HV to 510.11 HV and elastic modulus from 252.67 GPa to 294.6 GPa was observed in the fabricated samples as the ZrO2 content increase from 5 to 12.5 wt%. An appreciable improvement in the wear performance of the sintered samples was obtained with increasing ZrO2 content. The observed improvement in the properties of the sintered composites w...
This study investigates the influence of residual stresses induced by the manufacturing process, ... more This study investigates the influence of residual stresses induced by the manufacturing process, on the fatigue life prediction of micro gas turbine blades manufactured by laser metal deposition additive manufacturing technique and heat-treated at different heat-treatment parameters. Finite element modelling, using commercial software Abaqus CAE ® and FE-Safe ®, was used to simulate the turbine blade and disk assembly’s operations and analyze induced stresses, as well as estimate the life cycle of the assembly. Results show internal stress build-ups, up to 400 MPa in magnitude can be induced in engineered components right from the point of additive manufacture, the effects of which can become amplified to as much as double that scale or more by the time the component is in operation. As much as between 75% to 300% fatigue life prediction error reduction can hence be attained by simply accounting for induced stress contribution of the process of its manufacture, rendering cost-saving...
The possibility of creep–fatigue interaction occurring in steam pipes of power generation plants ... more The possibility of creep–fatigue interaction occurring in steam pipes of power generation plants during operation has been on the front burner for years. Often, failure of the pipes during operation is attributed to either creep alone or fatigue alone. Of recent, some failures are speculated to be due to simultaneously coupled interaction between creep and fatigue, especially when the failure occurs earlier than anticipated. The literature shows that such studies are very limited and indeed under-researched. Thus, there is a dire need to systematically investigate this coupled creep–fatigue phenomenon and provide clarity as the failure of high-pressure steam piping has consequential and very significant effects on the suppliers and end users. In this work, a special Fortran user subroutine script of a phenomenological modified hyperbolic sine creep model was developed and implemented in Abaqus CAE/2019 finite element code to initially determine the creep behavior of a P91 steam piping network subjected to a typical daily start-up and shutdown cycle. Subsequently, fe-safe/TURBOlife software was employed to investigate whether the failure induced by the start-up and shutdown cycles was due to fatigue alone, creep alone or due to creep–fatigue interaction. Interestingly, the study showed that the failure of the piping network under the specified operating conditions is specifically due to creep alone. Furthermore, the intrados of the elbow in the piping network was identified as the region most prone to failure, and the piping network will only survive a total of 7.1 and 7.7 years under these operating conditions for both machined and fine-machined surfaces, respectively. These results were thereafter analytically validated, and it showed a strong correlation with the numerically determined creep rate.
Creep behaviour of X20 (12Cr-1MoVNi) steam piping subjected to a typical operating pressure of 18... more Creep behaviour of X20 (12Cr-1MoVNi) steam piping subjected to a typical operating pressure of 18 MPa and temperature of 550°C have been investigated using finite element analysis code, Abaqus and fe-safe/ Turbolife software. User subroutine script for the modified hyperbolic sine creep model used was developed in Fortran and implemented in Abaqus. The maximum creep stress and strain were developed on the intrados of the elbows in the piping network. The maximum creep stress and minimum creep rate were obtained after an hour of operation and the stress was observed to relax with increase in operational time while the creep strain increases with time. Under the specified operating conditions, the steam pipe is expected to survive a useful creep life of 15.3 and 16.9 years with corresponding maximum creep damage of 7:479 Â 10 À6 and 7:479 Â 10 À6 for machine-finished and fine machine-finished steam pipe surfaces respectively. Lastly, strong correlation exists between the numerically simulated and analytically computed creep strain rate at the straight region of the piping.
The International Journal of Advanced Manufacturing Technology, 2020
The geometrical increase in the demand for electrical energy has posed serious pressure on the po... more The geometrical increase in the demand for electrical energy has posed serious pressure on the power generation components such as the steam pipes due to the consequential increase in the operating parameters such as temperature and pressure. This increment in operating parameters tends to limit the useful life of these pipes. Thus, high creep resistant materials such as X20 CrMoV12-1 and P91 (9Cr-1Mo) are used to manufacture steam pipes. In this paper, the creep behaviour of X20 CrMoV12-1 and P91 (9Cr-1Mo) steam piping network subjected to typical operating condition was determined via a finite element analysis code, Abaqus CAE/2017 alongside fe-safe/Turbolife software, and their results were compared. The maximum creep stress, strain rate, creep damage and worst creep life in both piping materials were developed on the intrados of the elbow, with P91 steam pipe having higher useful creep life. Furthermore, a good correlation was achieved between the result of the analytically calculated and numerically simulated creep rate at the straight section of the piping networks.
The thermo-mechanical stress, strain and temperature distribution across the thickness of X20 ste... more The thermo-mechanical stress, strain and temperature distribution across the thickness of X20 steam pipe at region less susceptible to thermo-mechanical failure was simulated using finite element analysis software, Abaqus. The mesh convergence studies conducted showed that 10 mm mesh size was suitable for the simulation. The temperature distribution profile across the thickness of Pyrogel showed that pyrogel is an excellent insulation jacket for steam pipes. The maximum stress value obtained from the simulation shows that the pipe is operating below the yield strength of X20 steel at the region under study. Hence, the pipe's failure at this region due to thermo-mechanical stress or strain only is practically impossible over a long period of time. A deviation of 0.5% was found to exist between the analytical and simulated stress value obtained. This indicates a strong correlation between the simulated and analytical stress results.
Flanges are vital component used in power generation plants for linking, closing and connecting o... more Flanges are vital component used in power generation plants for linking, closing and connecting of pipes to the boiler and turbine compartments. The linking of piping networks via this approach has limited the use of welding in the industry. High temperature, pressure and thermal transitions are presumed to influence the behaviour of bolted flange assemblies in service. Sadly, the behaviour of bolted steam pipeflange assembly under these conditions have not been sufficiently studied. Thus, the usage, maintenance and replacement of the steam pipe flanges are based on assumptions which can have detrimental consequences. In order to investigate this under-researched area, the thermo-mechanical behaviour of a bolted X20 (12Cr-1MoVNi) steam pipe-flange assembly subjected to a typical power generation plant operational condition was determined using finite element analysis code, Abaqus CAE/2019. The stress and strain distribution across the assembly were computed and the maximum stress in the assembly was developed on the low temperature, high compressive stress side of the bolt's shank while the maximum strain was developed on the interior surface of the pipe. Also, the value of the maximum stress (331.8 MPa) developed on the bolts is below the operational limiting stress of the assembly material, thus, indicating that the assembly is operating within the acceptable stress, but with the bolts being identified as the component most prone to failure.
Environmental conservation and waste control have informed and encouraged the use of biodegradabl... more Environmental conservation and waste control have informed and encouraged the use of biodegradable polymeric materials over synthetic non-biodegradable materials. It has been recognized that nano-sized biodegradable materials possess relatively good properties as compared to conventional micron-sized materials. However, the strength characteristics of these materials are inferior to fossil-based non-biodegradable materials. In this study, biodegradable polylactide (PLA), reinforced with treated coconut husk particulates (CCP) for improved mechanical properties, was fabricated using an electrospinning process and representative volume element (RVE) technique, and some of the obtained mechanical properties were compared. It was observed that the electrospun CCP-PLA nanofibre composites show improved mechanical properties, and some of these mechanical properties using both techniques compared favourably well. The electrospun fibres demonstrate superior properties, mostly at 4 wt.% rein...
IOP Conference Series: Materials Science and Engineering, 2019
The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in or... more The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in order to fabricate NiCrCoAlTiW-Ta superalloy. Nickel which is the key element that formed the matrix powder particle size was varied in the range of 3-44, 45-106 and 106-150 μm. The effect of varying the starting powder particle size, on the formation of intermetallic phases was investigated. Also, important thermophysical properties in the development of superalloys for high temperature applications were investigated by using laser flash machine, in the range of 100-800 °C. The constituents of the microstructure for the sintered alloy includes, the gamma (γ) matrix phase (Ni), precipitated intermetallic gamma prime (γ’) phase Ni3(Al, Ti) and the precipitated solid solution strengthening elements (Cr and W). There was an increase in the density with decreasing powder particle size. Also, the averave grain size increased with increasing powder particle size. The thermophysical properties ob...
International Journal of Engineering Research in Africa
This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni bina... more This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni binary alloys produced at varying nickel content with alloy steel ball as the counterface material, at room temperature under varied applied normal loads. Finite element modeling was used to investigate the high-velocity impact response of the sintered alloys due to the dimensional constraint associated with SPSed samples. Microstructural analysis results revealed the presence of intermetallic phases of Ti-Ni with increasing nickel content. The best wear resistance ranging from 0.25 x 10-3 mm3/Nm to 0.22 x 10-3 mm3/Nm across all applied loads was obtained in Ti-6Ni alloy. This was attributed to the compaction of the protective triboxide and carbide layers on the surface of the sample. Oxidative and wear by adhesion were observed at low applied normal load while at high loads the prevalent wear mechanism was abrasive with reduced influence of oxidative and adhesive wear. Finite element analys...
International Journal of Engineering Research in Africa
The creep response and stress relaxation of X20 CrMoV12-1 steam piping under diverse operating co... more The creep response and stress relaxation of X20 CrMoV12-1 steam piping under diverse operating conditions were simulated using finite element analysis (FEA) code, Abaqus alongside fe-safe/Turbolife software. In the study, steady-state creep and creep analysis characterized by 24 hours daily cycle consisting of a total of 6 hours peak, 4 hours transient and 14 hours off-peak period was considered. Modified hyperbolic sine creep model used in the analysis was implemented in Abaqus via a special creep user-subroutine to compute the stress relaxation and creep behaviour, while the useful service life and creep damage was estimated using fe-safe/Turbolife. The optimum creep strain, stress, damage, and worst life were found at the intrados of the piping, with the steady-state analysis having a higher useful creep life and slower creep damage accumulation. Furthermore, slower stress relaxation with faster damage accumulation was observed in the analysis involving cycles. Finally, a good ag...
In service, steam pipes are subjected to high temperature close to 0.4 Tm (melting temperature) o... more In service, steam pipes are subjected to high temperature close to 0.4 Tm (melting temperature) or higher and pressure; thus, making them prone to failure due to creep. Often, the design methods for these steam pipes usually do not provide their specific in-service life; hence, some type of service fitness tests are performed, and data obtained from the tests are used to inform the routine inspections. Choosing a creep model that favorably describe the creep behavior of components in service is paramount to engineers as well as the plant operators. Reports have shown that there are several creep models available and they all behave differently with different materials, and operating conditions. In this study, the creep behavior of X20 (12Cr-1MoVNi) steam piping network subjected to three phenomenological creep models (conventional hyperbolic sine creep, modified hyperbolic sine creep and constitutive creep model) was investigated. Fortran user subroutine scripts were developed for the three models and implemented in finite element (FE) code, Abaqus to determine the creep stress and strain rate, while the useful creep life and creep damage was determined using fe-safe/TURBOlife software. The results show that the modified hyperbolic sine creep model is more suitable for estimating the creep behavior of X20 steam piping under the specified operating conditions because of its more conservative prediction.
IOP Conference Series: Materials Science and Engineering
The exponential increase in the demand for energy has placed tremendous pressure on the power gen... more The exponential increase in the demand for energy has placed tremendous pressure on the power generation companies and the components used for the power supply. The efficiency of such supply is dependent on the operating parameters of the plants but at the expense of the useful life of the components. Turbine blade is one of the components that contribute immensely to such efficiency and it should be made of high-strength material with an exceptional ability to withstand the harsh operation environment. The properties of spark plasma sintering technique produced Inconel 738 low carbon (IN738LC) superalloy was used in finite element analysis software, Abaqus CAE/2017 to simulate the thermo-mechanical behaviour of steam turbine blade. The maximum thermomechanical stress and strain were developed on the root of the turbine blade (along the tailing edge) and the value of the maximum stress developed is far below the yield stress of the superalloy. Hence, spark plasma sintered Inconel 738LC is suitable for turbine blade production as such blade will survive several thermo-mechanical stress and strain cycles prior to failure.
The influences of sintering temperature on the microstructure and giant dielectric properties of ... more The influences of sintering temperature on the microstructure and giant dielectric properties of a new co-doped TiO 2 system, i.e., V and Ta co-doped TiO 2 , were investigated. The grain size of (V 1/2 Ta 1/ 2) 0.01 Ti 0.99 O 2 ceramics was enlarged with increasing sintering temperature. Dense microstructure and homogeneous dispersion of dopants were achieved in the ceramics sintered at 1400e1500 C for 5 h. The dielectric permittivity in the frequency range 40e10 6 Hz of the (V 1/2 Ta 1/2) 0.01 Ti 0.99 O 2 ceramics significantly increased with the mean grain size, while the dielectric loss tangent was reduced to 0.033 at 10 2 Hz. Furthermore, the high-temperature stability of the dielectric permittivity was improved with increasing mean grain size. The electrically heterogeneous microstructure consisting of semiconducting grains and insulating grain boundaries and/or surface layers was confirmed using impedance spectroscopy. The conduction inside the semiconducting grains was attributed to electron hopping between Ti 4þ and Ti 3þ , which was confirmed by X-ray photoelectron spectroscopy. Very high resistivity with a large conduction activation energy of the insulating parts was suggested as the primary cause of the giant dielectric permittivity with low loss tangent.
The introduction of computational modelling during alloy development has significantly reduced th... more The introduction of computational modelling during alloy development has significantly reduced the cost of production and the prolonged time spent by researchers doing trials and errors in the laboratory. In this study, computational software (JMat Pro) was used to simulate the effect of the addition of Zr and Co, on the material properties of NiAl-Mo(Cr) alloy such as the elastic modulus, hardness, thermal conductivity, bulk modulus and specific heat capacity. A significant improvement in the mechanical properties was observed in the developed alloys as compared to those without Zr and Co. Also, the addition of as low as 0.5 at. % Zr and 1.0 at. % Co to NiAl-Cr(Mo) resulted in improved compressive strength and plasticity of the alloy.
The accurate prediction of the thermomechanical properties of newly developed polymer composites ... more The accurate prediction of the thermomechanical properties of newly developed polymer composites is important in the determination of their possible areas of application. In this study, a 3D model of representative volume element (RVE) with different wood flour weight ratios (5, 10, 15, 20, 25 and 30 %) was used to develop wood flour polymer composites. Micromechanical material modelling software (Digimat) was used in conjunction with finite element analysis software (Abaqus) to develop the polymer composites and to determine their thermomechanical properties (modulus of elasticity, Poisson’s ratio, thermal conductivity, density, and hardness). The hardness, tensile strength and modulus of elasticity increase with an increase in the wt.% of wood flour, while the Poisson ratio, thermal conductivity and density decrease with an increase in the wt.% of wood flour. Also, the predicted thermomechanical properties using the micromechanical material modelling software (RVE) follow the same...
Ni-Cr-ZrO2 composites with varying amounts of ZrO2 additive (5 wt%, 7.5 wt%, 10 wt% and 12.5 wt%)... more Ni-Cr-ZrO2 composites with varying amounts of ZrO2 additive (5 wt%, 7.5 wt%, 10 wt% and 12.5 wt%) were fabricated using spark plasma sintering method at a sintering temperature of 1000°C, heating rate of 100°C/min, holding time of 5 min, and a pressure of 50 MPa. The effect of ZrO2 addition on the microstructure, tribological and mechanical properties of the developed composites were studied. The results showed that maximum densification was attained at 10 wt% ZrO2. Further increase in the fractions of ZrO2 within the composites results in a decrease in the relative density of the sintered composite. A significant increase in hardness from 433.24 HV to 510.11 HV and elastic modulus from 252.67 GPa to 294.6 GPa was observed in the fabricated samples as the ZrO2 content increase from 5 to 12.5 wt%. An appreciable improvement in the wear performance of the sintered samples was obtained with increasing ZrO2 content. The observed improvement in the properties of the sintered composites w...
This study investigates the influence of residual stresses induced by the manufacturing process, ... more This study investigates the influence of residual stresses induced by the manufacturing process, on the fatigue life prediction of micro gas turbine blades manufactured by laser metal deposition additive manufacturing technique and heat-treated at different heat-treatment parameters. Finite element modelling, using commercial software Abaqus CAE ® and FE-Safe ®, was used to simulate the turbine blade and disk assembly’s operations and analyze induced stresses, as well as estimate the life cycle of the assembly. Results show internal stress build-ups, up to 400 MPa in magnitude can be induced in engineered components right from the point of additive manufacture, the effects of which can become amplified to as much as double that scale or more by the time the component is in operation. As much as between 75% to 300% fatigue life prediction error reduction can hence be attained by simply accounting for induced stress contribution of the process of its manufacture, rendering cost-saving...
The possibility of creep–fatigue interaction occurring in steam pipes of power generation plants ... more The possibility of creep–fatigue interaction occurring in steam pipes of power generation plants during operation has been on the front burner for years. Often, failure of the pipes during operation is attributed to either creep alone or fatigue alone. Of recent, some failures are speculated to be due to simultaneously coupled interaction between creep and fatigue, especially when the failure occurs earlier than anticipated. The literature shows that such studies are very limited and indeed under-researched. Thus, there is a dire need to systematically investigate this coupled creep–fatigue phenomenon and provide clarity as the failure of high-pressure steam piping has consequential and very significant effects on the suppliers and end users. In this work, a special Fortran user subroutine script of a phenomenological modified hyperbolic sine creep model was developed and implemented in Abaqus CAE/2019 finite element code to initially determine the creep behavior of a P91 steam piping network subjected to a typical daily start-up and shutdown cycle. Subsequently, fe-safe/TURBOlife software was employed to investigate whether the failure induced by the start-up and shutdown cycles was due to fatigue alone, creep alone or due to creep–fatigue interaction. Interestingly, the study showed that the failure of the piping network under the specified operating conditions is specifically due to creep alone. Furthermore, the intrados of the elbow in the piping network was identified as the region most prone to failure, and the piping network will only survive a total of 7.1 and 7.7 years under these operating conditions for both machined and fine-machined surfaces, respectively. These results were thereafter analytically validated, and it showed a strong correlation with the numerically determined creep rate.
Creep behaviour of X20 (12Cr-1MoVNi) steam piping subjected to a typical operating pressure of 18... more Creep behaviour of X20 (12Cr-1MoVNi) steam piping subjected to a typical operating pressure of 18 MPa and temperature of 550°C have been investigated using finite element analysis code, Abaqus and fe-safe/ Turbolife software. User subroutine script for the modified hyperbolic sine creep model used was developed in Fortran and implemented in Abaqus. The maximum creep stress and strain were developed on the intrados of the elbows in the piping network. The maximum creep stress and minimum creep rate were obtained after an hour of operation and the stress was observed to relax with increase in operational time while the creep strain increases with time. Under the specified operating conditions, the steam pipe is expected to survive a useful creep life of 15.3 and 16.9 years with corresponding maximum creep damage of 7:479 Â 10 À6 and 7:479 Â 10 À6 for machine-finished and fine machine-finished steam pipe surfaces respectively. Lastly, strong correlation exists between the numerically simulated and analytically computed creep strain rate at the straight region of the piping.
The International Journal of Advanced Manufacturing Technology, 2020
The geometrical increase in the demand for electrical energy has posed serious pressure on the po... more The geometrical increase in the demand for electrical energy has posed serious pressure on the power generation components such as the steam pipes due to the consequential increase in the operating parameters such as temperature and pressure. This increment in operating parameters tends to limit the useful life of these pipes. Thus, high creep resistant materials such as X20 CrMoV12-1 and P91 (9Cr-1Mo) are used to manufacture steam pipes. In this paper, the creep behaviour of X20 CrMoV12-1 and P91 (9Cr-1Mo) steam piping network subjected to typical operating condition was determined via a finite element analysis code, Abaqus CAE/2017 alongside fe-safe/Turbolife software, and their results were compared. The maximum creep stress, strain rate, creep damage and worst creep life in both piping materials were developed on the intrados of the elbow, with P91 steam pipe having higher useful creep life. Furthermore, a good correlation was achieved between the result of the analytically calculated and numerically simulated creep rate at the straight section of the piping networks.
The thermo-mechanical stress, strain and temperature distribution across the thickness of X20 ste... more The thermo-mechanical stress, strain and temperature distribution across the thickness of X20 steam pipe at region less susceptible to thermo-mechanical failure was simulated using finite element analysis software, Abaqus. The mesh convergence studies conducted showed that 10 mm mesh size was suitable for the simulation. The temperature distribution profile across the thickness of Pyrogel showed that pyrogel is an excellent insulation jacket for steam pipes. The maximum stress value obtained from the simulation shows that the pipe is operating below the yield strength of X20 steel at the region under study. Hence, the pipe's failure at this region due to thermo-mechanical stress or strain only is practically impossible over a long period of time. A deviation of 0.5% was found to exist between the analytical and simulated stress value obtained. This indicates a strong correlation between the simulated and analytical stress results.
Flanges are vital component used in power generation plants for linking, closing and connecting o... more Flanges are vital component used in power generation plants for linking, closing and connecting of pipes to the boiler and turbine compartments. The linking of piping networks via this approach has limited the use of welding in the industry. High temperature, pressure and thermal transitions are presumed to influence the behaviour of bolted flange assemblies in service. Sadly, the behaviour of bolted steam pipeflange assembly under these conditions have not been sufficiently studied. Thus, the usage, maintenance and replacement of the steam pipe flanges are based on assumptions which can have detrimental consequences. In order to investigate this under-researched area, the thermo-mechanical behaviour of a bolted X20 (12Cr-1MoVNi) steam pipe-flange assembly subjected to a typical power generation plant operational condition was determined using finite element analysis code, Abaqus CAE/2019. The stress and strain distribution across the assembly were computed and the maximum stress in the assembly was developed on the low temperature, high compressive stress side of the bolt's shank while the maximum strain was developed on the interior surface of the pipe. Also, the value of the maximum stress (331.8 MPa) developed on the bolts is below the operational limiting stress of the assembly material, thus, indicating that the assembly is operating within the acceptable stress, but with the bolts being identified as the component most prone to failure.
Environmental conservation and waste control have informed and encouraged the use of biodegradabl... more Environmental conservation and waste control have informed and encouraged the use of biodegradable polymeric materials over synthetic non-biodegradable materials. It has been recognized that nano-sized biodegradable materials possess relatively good properties as compared to conventional micron-sized materials. However, the strength characteristics of these materials are inferior to fossil-based non-biodegradable materials. In this study, biodegradable polylactide (PLA), reinforced with treated coconut husk particulates (CCP) for improved mechanical properties, was fabricated using an electrospinning process and representative volume element (RVE) technique, and some of the obtained mechanical properties were compared. It was observed that the electrospun CCP-PLA nanofibre composites show improved mechanical properties, and some of these mechanical properties using both techniques compared favourably well. The electrospun fibres demonstrate superior properties, mostly at 4 wt.% rein...
IOP Conference Series: Materials Science and Engineering, 2019
The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in or... more The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in order to fabricate NiCrCoAlTiW-Ta superalloy. Nickel which is the key element that formed the matrix powder particle size was varied in the range of 3-44, 45-106 and 106-150 μm. The effect of varying the starting powder particle size, on the formation of intermetallic phases was investigated. Also, important thermophysical properties in the development of superalloys for high temperature applications were investigated by using laser flash machine, in the range of 100-800 °C. The constituents of the microstructure for the sintered alloy includes, the gamma (γ) matrix phase (Ni), precipitated intermetallic gamma prime (γ’) phase Ni3(Al, Ti) and the precipitated solid solution strengthening elements (Cr and W). There was an increase in the density with decreasing powder particle size. Also, the averave grain size increased with increasing powder particle size. The thermophysical properties ob...
International Journal of Engineering Research in Africa
This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni bina... more This work investigated the dry sliding wear behaviour of spark plasma sintered (SPSed) Ti-Ni binary alloys produced at varying nickel content with alloy steel ball as the counterface material, at room temperature under varied applied normal loads. Finite element modeling was used to investigate the high-velocity impact response of the sintered alloys due to the dimensional constraint associated with SPSed samples. Microstructural analysis results revealed the presence of intermetallic phases of Ti-Ni with increasing nickel content. The best wear resistance ranging from 0.25 x 10-3 mm3/Nm to 0.22 x 10-3 mm3/Nm across all applied loads was obtained in Ti-6Ni alloy. This was attributed to the compaction of the protective triboxide and carbide layers on the surface of the sample. Oxidative and wear by adhesion were observed at low applied normal load while at high loads the prevalent wear mechanism was abrasive with reduced influence of oxidative and adhesive wear. Finite element analys...
International Journal of Engineering Research in Africa
The creep response and stress relaxation of X20 CrMoV12-1 steam piping under diverse operating co... more The creep response and stress relaxation of X20 CrMoV12-1 steam piping under diverse operating conditions were simulated using finite element analysis (FEA) code, Abaqus alongside fe-safe/Turbolife software. In the study, steady-state creep and creep analysis characterized by 24 hours daily cycle consisting of a total of 6 hours peak, 4 hours transient and 14 hours off-peak period was considered. Modified hyperbolic sine creep model used in the analysis was implemented in Abaqus via a special creep user-subroutine to compute the stress relaxation and creep behaviour, while the useful service life and creep damage was estimated using fe-safe/Turbolife. The optimum creep strain, stress, damage, and worst life were found at the intrados of the piping, with the steady-state analysis having a higher useful creep life and slower creep damage accumulation. Furthermore, slower stress relaxation with faster damage accumulation was observed in the analysis involving cycles. Finally, a good ag...
In service, steam pipes are subjected to high temperature close to 0.4 Tm (melting temperature) o... more In service, steam pipes are subjected to high temperature close to 0.4 Tm (melting temperature) or higher and pressure; thus, making them prone to failure due to creep. Often, the design methods for these steam pipes usually do not provide their specific in-service life; hence, some type of service fitness tests are performed, and data obtained from the tests are used to inform the routine inspections. Choosing a creep model that favorably describe the creep behavior of components in service is paramount to engineers as well as the plant operators. Reports have shown that there are several creep models available and they all behave differently with different materials, and operating conditions. In this study, the creep behavior of X20 (12Cr-1MoVNi) steam piping network subjected to three phenomenological creep models (conventional hyperbolic sine creep, modified hyperbolic sine creep and constitutive creep model) was investigated. Fortran user subroutine scripts were developed for the three models and implemented in finite element (FE) code, Abaqus to determine the creep stress and strain rate, while the useful creep life and creep damage was determined using fe-safe/TURBOlife software. The results show that the modified hyperbolic sine creep model is more suitable for estimating the creep behavior of X20 steam piping under the specified operating conditions because of its more conservative prediction.
IOP Conference Series: Materials Science and Engineering
The exponential increase in the demand for energy has placed tremendous pressure on the power gen... more The exponential increase in the demand for energy has placed tremendous pressure on the power generation companies and the components used for the power supply. The efficiency of such supply is dependent on the operating parameters of the plants but at the expense of the useful life of the components. Turbine blade is one of the components that contribute immensely to such efficiency and it should be made of high-strength material with an exceptional ability to withstand the harsh operation environment. The properties of spark plasma sintering technique produced Inconel 738 low carbon (IN738LC) superalloy was used in finite element analysis software, Abaqus CAE/2017 to simulate the thermo-mechanical behaviour of steam turbine blade. The maximum thermomechanical stress and strain were developed on the root of the turbine blade (along the tailing edge) and the value of the maximum stress developed is far below the yield stress of the superalloy. Hence, spark plasma sintered Inconel 738LC is suitable for turbine blade production as such blade will survive several thermo-mechanical stress and strain cycles prior to failure.
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Papers by Smith Salifu