DSpace Repository :: Browsing by Author "Ajiboye, J.S."

Browsing by Author "Ajiboye, J.S."

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Atomistic Simulations of Interfacial deformation and bonding mechanism of Pd-Cu Composite Metal Membrane using Cold Gas Dynamic Spray Process.
(Vacuum, 2020-12-01) Oyinbo, S.T.; Jen, T.C.; Zhu, Y.; Ajiboye, J.S.; Ismail, S.O.
Abstract The creation of atomic structures and the study of the deformation processes through molecular dynamics simulations have shown many advantages. However, gaps associated with the development and evolution of microstructure in the coating zone and dynamic processes that take place during cold gas dynamic sprayed materials still exist. The focus of this study was to investigate the interfacial deformation behaviours and the mechanism of bonding between atoms of palladium (Pd) and copper (Cu) composite metal membrane (CMM) using molecular dynamic simulations. The results confirmed that asymmetric deformation occurred during cold gas dynamic spray at the Pd-Cu interfacial region. As the impact time increases, the layer thickness at the interface also increases. The concentrations of Pd-Cu CMM at the interfacial zone showed the presence of phase transitions at relatively long impact time. Furthermore, CGDS deformation was found to be an unsteady and dynamic process. Explicit bond analysis in this study also has shown that breaking of atomic bonds is not the key mechanism for the initial Pd-Cu plastic deformation occurrence. The higher interfacial bonding energy and interfacial shearing strength at the Pd-Cu CMM interface expressed the bonding strength and compatibility of Pd and Cu.
Characterization of Frictional Behavior in Cold Forging
(Tribology Letter, 2010-10-15) Jung, K.H.; Lee, H.C.; Ajiboye, J.S.; Im, Y.T.
In the present investigation, tip test was utilized to characterize the effects of surface roughness of the specimen and forming tools, rate of deformation, and type of lubricants on friction in solid and solid contact under high contact pressure at room temperature. For the test, a cylindrical specimen made of aluminum alloy of 6061-O was used and grease, corn oil, VG100, and VG32 were applied as lubricants. Single punch and two counter punch sets with different surface roughness of Ra = 0.08 and 0.63 lm were manufactured in order to investigate a frictional behavior during the test. In addition, two different deformation speeds of 0.1 and 5.0 mm/s were used for the test to check their effect on friction as well. Load levels and tip distances obtained from the test were compared to find out any correlation between the two. The change of surface topology of the specimen was monitored by optical measurement technique to better understand a frictional behavior at the punch and counter punch interfaces. Present investigation clearly shows that tip test is easy to apply to experimentally characterize the frictional behavior in cold forging under various processing conditions considered.
The effect of selected parameters on temperature distributions in axisymmetric extrusion process
(Journal of Mechanical Science and Technology, 2007-09-30) Ajiboye, J.S.; Adeyemi, M.B.
A numerical method was developed to simulate the transient temperature distributions during forward extrusion process. The computer program simulates the extrusion process and takes into account some extrusion variables such as extrusion velocity, extrusion ratio, die preheat temperature, and percentage reduction in area. It can be seen that the higher the percentages reduction in areas, the higher the temperature rises during the extrusion process. Also, increasing speed of deformation shows an increasing dead zone temperature rise than a more gradual die land temperature rise. It is further seen that extrusion temperature increase is a function of the container temperature.
The Effect of Surface Conditions on Friction by Tip Test
(Journal of Tribology, 2009-11-09) Jung, K.H; Lee, H.C.; Ajiboye, J.S.; Kang, S. H.; Im, Y
In the present investigation, a tip test based on upsetting and backward extrusion was utilized to characterize the effect of surface roughness of the billet and forming tools, and the type of lubricants on friction. For the test, cylindrical specimens made of aluminum alloys of 6061-O and 2024-O, and single punch and two die sets with different surface topologies, were used with four lubricants such as VG32, VG100, corn oil, and grease. The load levels and tip distances were measured for both materials, and compared with each other to determine shear friction factors at the punch and counter punch interfaces separately, depending on the variation in surface topologies and lubrications using finite element simulations. As a result, a linear relationship among the dimensionless load, tip distance, and shear friction factors at the punch and counter punch interfaces was derived for the experimental conditions investigated. The slope change of this linear relationship from negative to positive clearly depends on the variation in surface conditions at the billet/punch and billet/counter punch interfaces. Also, it was demonstrated that the dimensionless tip distance for the frictionless case can be extrapolated from the experimental data. This value can be used for characterizing the relative effect on friction due to surface conditions at the punch and counter punch, and lubrication quality of the lubricant for the given processing conditions.
Effects of extrusion variables on temperature distribution in axisymmetric extrusion process
(International Journal of Mechanical Sciences, 2007-09-01) Ajiboye, J.S.; Adeyemi, M.B.
A numerical method was developed to simulate the non-steady-state temperature distributions during forward extrusion process. The velocity, strain rates, and strain fields within the deformation zones during extrusion were obtained, using upper bound method of analysis to obtain internal heat generations coupled to the necessary heat transfer conduction equations. The computer program written in C++ language essentially simulates the extrusion process and takes into account extrusion variables such as material properties, friction conditions, extrusion velocity, extrusion ratio, die preheat temperature, billet height, percentage reduction in area, and die land length. The effects of billet height and percentage reduction in area on the temperature distributions within the dead metal zone give good agreements with experimental results. It is found that the higher the billet’s heights and higher the percentages reduction in areas, the higher the temperature rises during the extrusion process. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no effect on the dead zone temperature. Also, increasing speed of deformation shows an increasing dead zone temperature rise than a more gradual die land temperature rise. It can be stated that the extrusion temperature increases proportionally to the increase of the container temperature.
Effects of Lubricant on the Mechanical properties of Aluminium 6063 alloy after ECAE
(Industrial Lubrication and Tribology, 2014-04-08) Ajiboye, J.S.; Adebayo, S.A.; Azeez, T.M.
The purpose of this paper is to investigate the degree of improvement in mechanical properties of aluminum alloy (AA6063) after processing with equal channel angular extrusion (ECAE) using four environmentally benign lubricants. Aluminum (Al) 6063 bar was annealed at 350°C for 1 hour, machined and cut to billets measuring 14 × 14 × 44 mm3. These specimens for extrusions were machined to the specified dimension to a visibly good finish. The billets were extruded through ECAE die of 14 × 14 mm2 channel cross-section area; the channel angle was 120°; and the angle of the outer arc of the channels was 30°. The punch and container used for the experiment were made of tool steel alloy AISI D2, and were chromium-coated and polished. Four lubricants such as palm, olive, coconut and groundnut oils were used in this study. The yield, ultimate tensile strengths (UTS) and the ductility of the material ECAEed with palm oil as lubricant, which gave the least extrusion pressure, produces the maximum yield, UTS and ductility, followed by groundnut oil and coconut oil, while olive oil gave the least yield strength, (UTS) and ductility. However, palm oil and olive oil have better load reduction than other lubricants. Furthermore, from the hardness results, though scattered, all of the points at the tensile strained side of the extrudate lie within a reasonably narrow band, suggesting a high degree of homogeneity and greater hardness value within the rod than the compressive side after being ECAEed.
Experimental study on the effect of deforming material and speed on friction and lubrication by tip test
(ASME Transaction Journal of Tribology, 2012-04-01) Ajiboye, J.S.
Choosing the proper metal forming lubricant for nonferrous metals such as aluminum, copper, and brass has become a difficult and complicated decision. The effects of deformation velocity and the influence of deforming material were determined in the two sets of experiments carried out using a single punch with a roughness magnitude Ra of 0.17 lm and four lubricants such as grease, corn oil, VG100, and VG32. In the first set, two different deformation speeds of 0.1 and 1mm/s were used for cylindrical specimens made of aluminum alloys of 6061-O, 1050-O, and copper alloys tests using a counterpunch die of roughness magnitude Ra of 0.08 lm. In the second set of experiments, cylindrical specimens made of aluminum alloys of AA2024-O and AA6061-O and three deformation speeds of 0.1, 1, and 5mm/s were used to evaluate the performance of each lubricant under increasing ram speed, but with a roughness magnitude Ra of 0.63 lm. All the lubricants show reduction in maximum load with increasing deformation speed except grease which shows a rise in the maximum load from zero to a maximum at a deformation speed of 1mm/s and then descends gradually to a minimum load at a speed of 5mm/s for AA2024-O and AA6061-O. This load reduction seen with grease as lubricant is probably due to thermal softening; therefore grease will not be considered a desirable lubricant under increasing deformation speed because of the adverse effects on the tooling. The present findings show that tip test can be utilized to select an appropriate lubricant for a particular alloy. It reveals that none of the tested lubricants can be used for copper alloy as all the lubricants show increasing measured load for increasing speed magnitude. However, of the liquid lubricants (corn oil, VG100, and VG32) considered, corn oil shows as the best lubricant for cold forging operations of aluminium 6061-O, 1050-O, and 2024-0 under increasing speed magnitude. Also, the tip test has been able to differentiate among materials.
Load Prediction for the Extrusion from Circular Billet to Symmetric and Asymmetric Polygons using Linearly converging die profiles
(Key Engineering Materials, 2014-09-01) Ajiboye, J.S.; Oyinbo, S.T.
The deformation load is the most important parameter in the press design as it affects the structure and the general integrity of the final product. Therefore, every other parameter such as die shape, friction, type of process (hot or cold), and speed considered in modeling is optimized to cut back on the metal forming load. The flow of metal is largely influenced by the geometry of the die and hence the geometric shape of the tools is the main factor by which an optimum load can be evaluated. In extrusion process the strain distribution, resulting from deformation load, and other important variables that influence material structure, such as a hydrostatic stress, are strongly dependent on the geometry of the die. In the present investigation using linearly converging die profiles, the extrusion of symmetric and asymmetric polygons such as circular, square, triangular, hexagonal, heptagonal, octagonal, and L-, T- and H-, respectively sections from round billet have been numerically simulated. Mathematical equations describing the die profiles were derived, and then using MATLAB R2009b the co-ordinate of the die profiles was evaluated. A solid CAD model for the linearly converging die profile was made using Autodesk Inventor 2013 software and numerical analysis using DEFORM software for extrusion of the above sections from round billet was then performed to predict, for dry and lubricated condition, the extrusion load during deformation. It is found that the predictive loads for asymmetric shapes are found to be higher than that of the symmetric shapes. While there is no marked difference between the predictive loads for symmetric shapes that of the asymmetric shapes is significant where L-section has the highest extrusion load, followed by T-section and the H-section given the least pressure.
Mathematical modelling of die pressure of a screw briquetting machine
(Journal of King Saud University - Engineering Sciences, 2020-12-01) Orisaleye, J.I.; Ojolo, S.J.; Ajiboye, J.S.
The screw briquetting machine has problems which have been attributed to poor design. There are limited theoretical studies targeted at solving problems of biomass briquetting machines. The briquetting die determines the final shape and quality of the biomass briquettes. The performance of the screw briquet- ting machine is also dependent on the design of the briquetting die. In this paper, mathematical models were developed to study the die pressure using a plug flow theory. Effects of die entry angle, die reduction ratio, length of briquetting die, biomass compact yield strength and friction on the die pressure were investigated using the models. Increasing the die entry angle, reduction ratio, compact yield strength and friction coefficient resulted in increase in the die pressure. Increase in length of briquetting die and friction coefficient also resulted in increase in the die pressure. Optimum die entry angle was dependent on the yield strength of compacted material and the friction coefficient at the interface between the die and the compacted material. This study is useful in developing improved screw briquetting machines.
Numerical Simulation of Axisymmetric and Asymmetric Extrusion Process Using Finite Element Method
(International Journal of Scientific & Engineering Research, 2015-06-01) Oyinbo, S.T.; Ikumapayi, O.M.; Ajiboye, J.S.; Afolalu, S.A.
The deformation load is the most important parameter in the press design. The flow of metal, consequently load, is largely influenced by the geometry of the die and hence the geometric shape of the tools is the main factor by which an optimum load can be developed. In extrusion process the strain distribution, resulting from deformation load, and other important variables that influence material structure, such as a hydrostatic stress, are strongly dependent on the geometry of the die. In the present investigation using linearly converging die profiles, the extrusion of simple and advanced polygons such as circular, square, triangular, hexagonal, heptagonal, octagonal, L-, T-, and H- sections from round billet have been numerically simulated. Mathematical equations describing the die profiles were evaluated. A solid CAD model for the linearly converging die profile was made using Autodesk Inventor 2013 software and numerical analysis using DEFORM 3D software for extrusion of the above sections from round billet was then performed to determined, for dry and lubricated condition, the load prediction, effective stress, effective strain, strain rate, velocity and temperature distribution during the deformation. It is found that the predictive loads for advance (asymmetric) shapes are found to be higher than that of the simple shapes. While there is no marked difference between the predictive load for simple (axisymmetric) shapes, the L-section has the highest extrusion load, followed by T-section and the H-section given the least pressure.
Plug flow analysis for the design of the compaction region of a tapered screw extruder biomas briquetting machine
(Agricultural Engineering International: CIGR Journal, 2015-09-01) Ojolo, S.J.; Ajiboye, J.S.; Orisaleye, J.I.
The study of compaction or solids conveying in a screw extruder has been carried out majorly on the straight screws using the plug flow analysis. Despite this, the analysis of the straight screw appears to be complex as contained in existing literatures based on the force and torque balance. The tapered screw, which is considered to be an effective option for biomass compaction, introduces greater complications because the geometry is constantly changing. In this study, a method based on the traction and retardation mechanism of friction is developed for a fully unwound screw channel utilizing only the force balances. The procedure has been used to carry out a parametric analysis of the tapered screw extruder for a screw press biomass briquetting machine. The taper angle was considered to significantly increase the pressure developed in the extruder depending on the length of the compaction zone. The optimum taper angle has also been found to be dependent on the frictional coefficient of the biomass material with enclosing surfaces and ranges between 2 and 4.
Pressure build-up and wear analysis of tapered screw extruder biomass briquetting machines
(CIGR Journal Open access, 2019-01-01) Orisaleye, J.I; Ojolo, S.J.; Ajiboye, J.S.
The design of efficient screw extruder biomass briquetting machines is important for the utilization of loose biomass materials from wood and agricultura l wastes for the production of solid fuel. In this study, the effects of geometrical parameters (channel depth and helix angle) and operational parameters (friction coefficient, mass flow rate and speed) on the performance and design of the briquetting machine were investigated using a pressure model based on the plug flow theory. An analytical model, which utilizes the pressure model, was also developed from Archard’s wear law to investigate screw wear of biomass briquetting machines. The study on the pressure model showed that a shallow screw channel and small helix angle resulted in rapid pressure build-up along the screw extruder biomass briquetting machine. High friction at the barrel-material interface, low friction at the screw-material interface, high screw speed and high mass flow rate also resulted in rapid pressure build-up along the screw extruder biomass briquetting machine. The geometrical and operational parameters which resulted in rapid pressure build-up required shorter screw length for the briquetting machine. The wear model developed predicted the screw wear satisfactorily and showed that the screw speed and the choice of material for screw affected the screw wear. The wear volume increased exponentially towards the end of the screw where pressure is the highest. Redesigning the screw to select optimum geometry and speed with appropriate choice of material could improve the screw life and performance of the biomass briquetting machine.
Temperature changes with die profiles in axisymmetric forward extrusion process
(Journal of Applied Scence, Engineering and Technology, 2008) Ajiboye, J.S.; Adeyemi, M.B.
Transient heat transfer and temperature change due to varying die opening shapes in a direct extrusion of lead have been numerically investigated and presented. Upper bound method of analysis was used to evaluate the internal heat generation due to plastic deformation and frictional heat at various stages of the extrusion process. At the extrusion die land region, temperature rises with increasing complexity of die openings geometry with I-shaped section, giving the highest temperature rise, followed by T-shaped section, rectangular, circular shaped die openings with square section die opening, giving the least temperature rise for any given extrusion parameter. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no overall effect on the dead metal zone temperature rise. Increasing die land length leads to increasing contact area between the extrudate and the die resulting in increasing frictional power. It is, therefore, seen that die land is one of the critical factors to consider avoiding surface cracking or hot-shortness in extrusion.
Upper bound analysis for extrusion at various die land lengths and shaped profiles
(International Journal of Mechanical Sciences, 2006-10-06) Ajiboye, J.S.; Adeyemi, M.B.
The effects of die land lengths, a rarely investigated die extrusion parameter on the die-shaped profiles, on the extrusion pressures are investigated and presented. The analyses of the extrusion pressures by the upper bound method have been extended for the evaluations of the extrusion pressures to complex extruded sections such as square, rectangular, I,- and T-shaped sections with power of deformation due to ironing effect at the die land taken into account. The extrusion pressure contributions due to the die land evaluated theoretically for shaped sections considered are found to increase with die land lengths for any given percentage reduction and also increase with increasing percentage die reductions at any given die land length. The effect of die land lengths on the extrusion pressure increases with increasing complexity of die openings geometry with I-shaped section giving the highest extrusion pressure followed by T-shaped section, rectangular, circular-shaped die openings with square section die opening, giving the least extrusion pressure for any given die reduction at any given die land lengths.

Browsing by Author "Ajiboye, J.S."

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