Trimethylolpropane (TMP) esters possess good frictional properties, portraying good potential as ... more Trimethylolpropane (TMP) esters possess good frictional properties, portraying good potential as alternative bio-lubricants. However, the most common TMP ester, which is TMP oleate, is found to be widely used only for hydraulics application. Therefore, to explore its potential usage in automotive applications, the present study determines the frictional behaviour of TMP oleate at different operating lubrication regimes. Friction forces for TMP oleate lubricated conjunction, consisting of cast iron pin being rotated against a stainless-steel disk, are measured using a pin-on-disk type tribometer. The applied normal load is 3 kg while the disk rotational speed is varied between 20 rpm and 2000 rpm. Along fluid film and boundary lubrication regimes, the average coefficients of friction for TMP oleate lubricated conjunction are measured to be 0.074 and 0.101, respectively. Along fluid film lubrication regime, with the maximum Hertzian pressure being calculated to be 1.1 GPa, the contact is expected to be elastohydrodynamic in nature. Transitions of lubrication regimes, similar to the classical Stribeck curve, are also observed between sliding velocities of 1.8 m.s-1 and 2.7 m.s-1. Hence, the measured Stribeck curve demonstrates the potential use of TMP oleate for automotive applications, where a large range of operating lubrication regimes is required
A better fuel-efficient automotive engine is more sought-after to promote greener environment in ... more A better fuel-efficient automotive engine is more sought-after to promote greener environment in the era of global warming. One of the factors to cause the increase of fuel consumption in vehicles is the frictional loss within an internal combustion engine. In this study, the focus is to determine the tribological behaviour between the piston top compression ring and the engine cylinder liner for a full engine cycle. Mathematical models are derived from a 1-D Reynolds equation, assuming Half-Sommerfeld and Reynolds boundary conditions. Greenwood and Tripp rough surface contact model is applied to predict frictional properties along the ring-liner contact, considering viscous and boundary friction. It is found that the Half-Sommerfeld boundary condition predicts minimum lubricant film thickness that correlates well with literature data. However, the friction force predicted by the Reynolds boundary condition along dead centres correlates better with literature data. With friction alo...
IOP Conference Series: Materials Science and Engineering, 2020
Fatty acid methyl ester (FAME) possesses good lubricity properties, prompting numerous research w... more Fatty acid methyl ester (FAME) possesses good lubricity properties, prompting numerous research work to explore their potential as lubricant additives. However, fully formulated lubricants consist of additive packages, which includes essential anti-wear agents, such as zinc dialkyldithiophosphate (ZDDP). Adding FAME into a lubricant could lead to adverse tribological effects if the competitive molecular interaction between different additives are not well understood. Therefore, the present study determines the tribological impact of molecular interaction between ZDDP and methyl oleate along boundary lubrication regime. Lateral force microscopy, coupled with fluid imaging approach, is adopted, allowing for the analysis to focus on asperity level interaction. A silicon nitride tip is used to slide against a mirror-polished steel substrate while being fully submerged in the tested fluids. The tested fluids are mixtures of ZDDP and methyl oleate, blended at different volumetric percenta...
Journal of Mechanical Engineering and Sciences, 2019
Fundamental understanding of piston ring-pack lubrication is essential in reducing engine frictio... more Fundamental understanding of piston ring-pack lubrication is essential in reducing engine friction. This is because a substantial portion of engine frictional losses come from piston-ring assembly. Hence, this study investigates the tribological impact of different piston ring profiles towards engine in-cylinder friction. Mathematical models are derived from Reynolds equation by using Reynolds’ boundary conditions to generate the contact pressure distribution along the complete piston ring-pack/liner conjunction. The predicted minimum film thickness is then used to predict the friction generated between the piston ring-pack and the engine cylinder liner. The engine in-cylinder friction is predicted using Greenwood and Williamson’s rough surface contact model. The model considers both the boundary friction and the viscous friction components. These mathematical models are integrated to simulate the total engine in-cylinder friction originating from the studied piston ring-pack for a ...
To isolate shearing of boundary film from direct surface-to-surface asperity interactions, the st... more To isolate shearing of boundary film from direct surface-to-surface asperity interactions, the study determines boundary lubrication properties of palm oil-based TMPE (PTMPE) using Lateral Force Microscopy coupled with fluid imaging. PTMPE is produced through a series of 3-step transesterification processes, converting palm oil (PO) into palm methyl ester (PME) and finally into PTMPE. It is shown that PME generates the lowest friction. However, using Eyring thermal activation energy approach, PME is shown to possess less desirable load bearing property, portraying a form of stiction or adhesive nature. Even though friction is higher, PTMPE exhibits better load bearing ability, demonstrating the onset of lubricant laminar flow due to increased hydrodynamic effect, which is not observed for the PO and PME measurements.
The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raise... more The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raised tribological performance concerns among major automobile manufacturers. Biodiesel dilution on engine lubricants could have adverse long-term effects on the engine efficiency, which will reduce the fuel economy, thus, leading to higher greenhouse gas emissions. Therefore, this study investigates the tribological impact of palm methyl ester (PME) diluted in SAE5W40 and SAE10W40 engine lubricants along different lubrication regimes under engine cold start condition. Through lubrication Stribeck curve analysis conducted using a pin-on-disc tribometer, coefficient of friction (CoF) for both engine lubricants showed parabolic maximum behaviour with increasing PME dilution. The CoF reduction beyond these peak values is attributed to the improved friction modifier effect from the nowdominant PME but with reduced load carrying capacity. An effective lubricant should possess both reasonable friction modifier effect and highest load carrying capacity in mitigating boundary friction. Hence, through the study, it could be deduced that the acceptable PME dilution threshold level for SAE5W40 is up to 17.5-vol%, while for SAE10W40 is between 28.0-vol% and 34.5-vol%. PME dilution levels beyond these thresholds could easily cause lubrication film rupture under high load, high shear rate conditions during application along the mixed to boundary lubrication regimes, inducing material wear.
IOP Conference Series: Materials Science and Engineering, 2020
The study simulates the lubricant Stribeck curve for Palm Methyl Ester (PME) by coupling modified... more The study simulates the lubricant Stribeck curve for Palm Methyl Ester (PME) by coupling modified Reynolds solution with Greenwood and Tripp’s rough surface contact model. The predicted lubricant Stribeck curves for PME is validated with measured data from a pin-on-disc tribometer. The Reynolds equation is modified to accommodate for the lubricant properties of PME (e.g. viscosity and density), which is mathematically described using Gibbs energy additivity approach. Solving the modified Reynolds equation would then provide the fluid film formation behaviour of PME, such as the contact pressure and film thickness. These fluid film parameters are then used as the input to determine the boundary and viscous friction of the investigated lubricated contact using Greenwood and Tripp’s rough surface contact model. The proposed mathematical solution correlates well with experimental data and is shown to be capable of predicting lubricant Stribeck, capturing the frictional behavior for the ...
IOP Conference Series: Earth and Environmental Science, 2021
This paper aims to investigate the tribological friction using the Stribeck curve lubrication reg... more This paper aims to investigate the tribological friction using the Stribeck curve lubrication regime using an alternative source of biodiesel. Replacement of current usage of fossil fuels is essential, therefore, it is important to develop a proper recycling, renewable and sustainable product that reduces global warming. Biodiesel also known as Fatty Acid Methyl Ester (FAME), is biodegradable, produced from a renewable source, non-toxic, and produces a minimum greenhouse gas emissions. To reduce raw material cost, waste cooking oil is one of the most suitable replacements of vegetable oil for biodiesel synthesis. Rheological behavior of Waste Palm Methyl Ester (WPME), such as kinematic viscosity, density, and acid value, was measured based on EN14214 and compared with Palm Methyl Ester (PME). The friction performance of WPME was evaluated using a pin on the disc tribometer machine. The influence of different operating conditions such as loads at 1kg, 2kg, 3kg and 4kg and sliding vel...
IOP Conference Series: Earth and Environmental Science, 2021
This paper aims to investigate the tribological friction using the Stribeck curve lubrication reg... more This paper aims to investigate the tribological friction using the Stribeck curve lubrication regime using an alternative source of biodiesel. Replacement of current usage of fossil fuels is essential, therefore, it is important to develop a proper recycling, renewable and sustainable product that reduces global warming. Biodiesel also known as Fatty Acid Methyl Ester (FAME), is biodegradable, produced from a renewable source, non-toxic, and produces a minimum greenhouse gas emissions. To reduce raw material cost, waste cooking oil is one of the most suitable replacements of vegetable oil for biodiesel synthesis. Rheological behavior of Waste Palm Methyl Ester (WPME), such as kinematic viscosity, density, and acid value, was measured based on EN14214 and compared with Palm Methyl Ester (PME). The friction performance of WPME was evaluated using a pin on the disc tribometer machine. The influence of different operating conditions such as loads at 1kg, 2kg, 3kg and 4kg and sliding vel...
This paper discusses the quality of surface finish when threading titanium-based alloy under dry ... more This paper discusses the quality of surface finish when threading titanium-based alloy under dry condition. The quality of surface finish was studied at various cutting parameters and at the two extreme stages of the machining process, i.e. at the beginning and end of the process. The objective is to evaluate the effect of a worn-out tool on the quality of surface finish. PVD-coated carbide tools were used in this study. Experiments were conducted at two cutting speeds, 35 and 55 m/min, two depths of cut, 0.2 and 0.25 mm, and a constant pitch of 2.0 mm. The tool wear and the quality of surface finish were inspected visually by microscope. The tool’s flank wear was measured gradually and machining was stopped when the flank wear reached the rejection criterion of0.3 mm. The microstructure beneath the machined surface was also evaluated. It was found that, at the beginning of machining, there was only a feed mark on the surface finish. When the machining was prolonged until the tools ...
Intensive research on the performance of coated carbide tools in machining titanium alloy is bein... more Intensive research on the performance of coated carbide tools in machining titanium alloy is being conducted worldwide. Titanium alloy has special characteristics such as high strength at elevated temperature and high mechanical resistance that makes carbide tools suitable to cut this material. This is because carbide tools are classified as hard and highly resistant to wear even at high temperature. This paper discusses the failure mode of a coated carbide cutting edge that is caused by the loading and unloading effect during milling. Tool failure adversely affects tool life, the quality of the machined surface and the surface's dimensional accuracy, and consequently the economics of cutting operations. The milling parameters that were observed to affect the failure of coated carbide tools were cutting speed, feed rate, depth of cut, and the application of a cutting fluid. Wear occurred along the flank and rake faces, which then propagated into the substrate material after the removal of the coating material. Wear along the flank and rake faces led to the concentration of stress over a certain area of the cutting edge, which was initiated by a microcrack and then propagated due to the loading and unloading effect during the intermittent milling process until significant brittle fracture occurred in the substrate material. Cutting speed and depth of cut were identified as the main factors responsible for the failure and fatigue of the coated carbide tools during the milling of titanium alloy.
The study emphasises on the fundamental understanding of the tribological behaviour for a lubrica... more The study emphasises on the fundamental understanding of the tribological behaviour for a lubrication system. In a dynamic system (e.g. piston ring/liner contact), the opposing sliding surfaces are separated by a layer of lubrication �lm, preventing direct metal-to-metal contact. Under critical operating conditions (e.g. high applied load), the �lm thickness might reduce to similar order of magnitude of the surface roughness, leading to boundary friction. A multi-scale approach is required to better predict the lubrication performance in a dynamic system. The �rst part of this study focuses on the development of a numerical algorithm using Reynolds equation to predict �uid �lm formation in a lubrication system. A rough surface contact model using the Greenwood and Tripp assumption is applied to predict the frictional properties along a lubricated conjunction using a three types of commercially available SAE grade lubricant namely, SAE5W40, SAE10W40 and SAE15W40. The simulated friction force is compared to the values measured using a pin-on-disc tribometer, showing good correlation between both data sets. With acceptable level of con�dence on the mathematical model, the second part of the study attempts to simulate a tribological properties of lubrication system considering biodiesel as the lubricant in the engine lubrication system. As the rough surface contact parameters are considered to be consistent in both case study, Reynolds solution is modi�ed in order to considers the �uid �lm formation of biodiesel with relation to their Fatty Acid Methyl Ester (FAME) compositions. Two parameters, namely 1) average number of carbon atom (zave) and 2) average number of double bonds (ndave) for biodiesels are included when introducing the e�ect of FAME compositions to the classical Reynolds equation. The term � has been introduced to the modi�ed Reynolds equation to correlate these two parameters. The value for the term � is determined by �tting the simulated lubrication Stribeck curve to the measured data for each of the selected biodiesels. Through this, a polynomial correlation is then obtained for the term � as a function of the product of average number of carbon atoms and average number of double bonds for the biodiesels. The coupling of Reynolds solution and rough surface contact model give a good correlation between measured data and predicted value in determining lubrication Stribeck curve regime for typical lubricants and biodiesel
In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been fo... more In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been found to have adverse effects on the boundary lubrication properties of additives in fully formulated engine lubricants. Such dilution of engine lubricants could be even more pronounced for CI engines running on higher blend concentrations of biodiesel. Given the nanoscopic nature of the interaction, this study seeks to determine the nano-tribological properties of an engine lubricant additive (e.g., zinc dialkyldithiophosphate (ZDDP)) when diluted with a fatty acid methyl ester (e.g., methyl oleate). Using lateral force microscopy (LFM) together with a fluid imaging technique, the lowest nanoscopic friction forces and coefficient of friction values (0.068–0.085) were measured for ZDDP when diluted with 70 vol% of methyl oleate. These values are also observed to be lower than those measured for neat ZDDP and neat methyl oleate, respectively, under similar conditions. Subsequently, interpre...
The paper simulates lubricant Stribeck curve for SAE grade engine lubricants by coupling Reynolds... more The paper simulates lubricant Stribeck curve for SAE grade engine lubricants by coupling Reynolds solution with Greenwood and Tripp's rough surface contact model. The predicted lubricant Stribeck curves for SAE5W40 and SAE15W40 engine lubricants are validated with measured data from a pin-on-disc tribometer. The proposed mathematical solution is shown to be capable of predicting lubricant Stribeck curves that correlate well with experimental data for both engine lubricants, capturing frictional behavior for the whole range of lubrication regimes. Such predictive tool could prove to be beneficial to automotive manufacturers in selecting suitable engine lubricants for their vehicles
Accurately predicting frictional performance of lubrication systems requires mathematical predict... more Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubri...
Trimethylolpropane (TMP) esters possess good frictional properties, portraying good potential as ... more Trimethylolpropane (TMP) esters possess good frictional properties, portraying good potential as alternative bio-lubricants. However, the most common TMP ester, which is TMP oleate, is found to be widely used only for hydraulics application. Therefore, to explore its potential usage in automotive applications, the present study determines the frictional behaviour of TMP oleate at different operating lubrication regimes. Friction forces for TMP oleate lubricated conjunction, consisting of cast iron pin being rotated against a stainless-steel disk, are measured using a pin-on-disk type tribometer. The applied normal load is 3 kg while the disk rotational speed is varied between 20 rpm and 2000 rpm. Along fluid film and boundary lubrication regimes, the average coefficients of friction for TMP oleate lubricated conjunction are measured to be 0.074 and 0.101, respectively. Along fluid film lubrication regime, with the maximum Hertzian pressure being calculated to be 1.1 GPa, the contact is expected to be elastohydrodynamic in nature. Transitions of lubrication regimes, similar to the classical Stribeck curve, are also observed between sliding velocities of 1.8 m.s-1 and 2.7 m.s-1. Hence, the measured Stribeck curve demonstrates the potential use of TMP oleate for automotive applications, where a large range of operating lubrication regimes is required
A better fuel-efficient automotive engine is more sought-after to promote greener environment in ... more A better fuel-efficient automotive engine is more sought-after to promote greener environment in the era of global warming. One of the factors to cause the increase of fuel consumption in vehicles is the frictional loss within an internal combustion engine. In this study, the focus is to determine the tribological behaviour between the piston top compression ring and the engine cylinder liner for a full engine cycle. Mathematical models are derived from a 1-D Reynolds equation, assuming Half-Sommerfeld and Reynolds boundary conditions. Greenwood and Tripp rough surface contact model is applied to predict frictional properties along the ring-liner contact, considering viscous and boundary friction. It is found that the Half-Sommerfeld boundary condition predicts minimum lubricant film thickness that correlates well with literature data. However, the friction force predicted by the Reynolds boundary condition along dead centres correlates better with literature data. With friction alo...
IOP Conference Series: Materials Science and Engineering, 2020
Fatty acid methyl ester (FAME) possesses good lubricity properties, prompting numerous research w... more Fatty acid methyl ester (FAME) possesses good lubricity properties, prompting numerous research work to explore their potential as lubricant additives. However, fully formulated lubricants consist of additive packages, which includes essential anti-wear agents, such as zinc dialkyldithiophosphate (ZDDP). Adding FAME into a lubricant could lead to adverse tribological effects if the competitive molecular interaction between different additives are not well understood. Therefore, the present study determines the tribological impact of molecular interaction between ZDDP and methyl oleate along boundary lubrication regime. Lateral force microscopy, coupled with fluid imaging approach, is adopted, allowing for the analysis to focus on asperity level interaction. A silicon nitride tip is used to slide against a mirror-polished steel substrate while being fully submerged in the tested fluids. The tested fluids are mixtures of ZDDP and methyl oleate, blended at different volumetric percenta...
Journal of Mechanical Engineering and Sciences, 2019
Fundamental understanding of piston ring-pack lubrication is essential in reducing engine frictio... more Fundamental understanding of piston ring-pack lubrication is essential in reducing engine friction. This is because a substantial portion of engine frictional losses come from piston-ring assembly. Hence, this study investigates the tribological impact of different piston ring profiles towards engine in-cylinder friction. Mathematical models are derived from Reynolds equation by using Reynolds’ boundary conditions to generate the contact pressure distribution along the complete piston ring-pack/liner conjunction. The predicted minimum film thickness is then used to predict the friction generated between the piston ring-pack and the engine cylinder liner. The engine in-cylinder friction is predicted using Greenwood and Williamson’s rough surface contact model. The model considers both the boundary friction and the viscous friction components. These mathematical models are integrated to simulate the total engine in-cylinder friction originating from the studied piston ring-pack for a ...
To isolate shearing of boundary film from direct surface-to-surface asperity interactions, the st... more To isolate shearing of boundary film from direct surface-to-surface asperity interactions, the study determines boundary lubrication properties of palm oil-based TMPE (PTMPE) using Lateral Force Microscopy coupled with fluid imaging. PTMPE is produced through a series of 3-step transesterification processes, converting palm oil (PO) into palm methyl ester (PME) and finally into PTMPE. It is shown that PME generates the lowest friction. However, using Eyring thermal activation energy approach, PME is shown to possess less desirable load bearing property, portraying a form of stiction or adhesive nature. Even though friction is higher, PTMPE exhibits better load bearing ability, demonstrating the onset of lubricant laminar flow due to increased hydrodynamic effect, which is not observed for the PO and PME measurements.
The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raise... more The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raised tribological performance concerns among major automobile manufacturers. Biodiesel dilution on engine lubricants could have adverse long-term effects on the engine efficiency, which will reduce the fuel economy, thus, leading to higher greenhouse gas emissions. Therefore, this study investigates the tribological impact of palm methyl ester (PME) diluted in SAE5W40 and SAE10W40 engine lubricants along different lubrication regimes under engine cold start condition. Through lubrication Stribeck curve analysis conducted using a pin-on-disc tribometer, coefficient of friction (CoF) for both engine lubricants showed parabolic maximum behaviour with increasing PME dilution. The CoF reduction beyond these peak values is attributed to the improved friction modifier effect from the nowdominant PME but with reduced load carrying capacity. An effective lubricant should possess both reasonable friction modifier effect and highest load carrying capacity in mitigating boundary friction. Hence, through the study, it could be deduced that the acceptable PME dilution threshold level for SAE5W40 is up to 17.5-vol%, while for SAE10W40 is between 28.0-vol% and 34.5-vol%. PME dilution levels beyond these thresholds could easily cause lubrication film rupture under high load, high shear rate conditions during application along the mixed to boundary lubrication regimes, inducing material wear.
IOP Conference Series: Materials Science and Engineering, 2020
The study simulates the lubricant Stribeck curve for Palm Methyl Ester (PME) by coupling modified... more The study simulates the lubricant Stribeck curve for Palm Methyl Ester (PME) by coupling modified Reynolds solution with Greenwood and Tripp’s rough surface contact model. The predicted lubricant Stribeck curves for PME is validated with measured data from a pin-on-disc tribometer. The Reynolds equation is modified to accommodate for the lubricant properties of PME (e.g. viscosity and density), which is mathematically described using Gibbs energy additivity approach. Solving the modified Reynolds equation would then provide the fluid film formation behaviour of PME, such as the contact pressure and film thickness. These fluid film parameters are then used as the input to determine the boundary and viscous friction of the investigated lubricated contact using Greenwood and Tripp’s rough surface contact model. The proposed mathematical solution correlates well with experimental data and is shown to be capable of predicting lubricant Stribeck, capturing the frictional behavior for the ...
IOP Conference Series: Earth and Environmental Science, 2021
This paper aims to investigate the tribological friction using the Stribeck curve lubrication reg... more This paper aims to investigate the tribological friction using the Stribeck curve lubrication regime using an alternative source of biodiesel. Replacement of current usage of fossil fuels is essential, therefore, it is important to develop a proper recycling, renewable and sustainable product that reduces global warming. Biodiesel also known as Fatty Acid Methyl Ester (FAME), is biodegradable, produced from a renewable source, non-toxic, and produces a minimum greenhouse gas emissions. To reduce raw material cost, waste cooking oil is one of the most suitable replacements of vegetable oil for biodiesel synthesis. Rheological behavior of Waste Palm Methyl Ester (WPME), such as kinematic viscosity, density, and acid value, was measured based on EN14214 and compared with Palm Methyl Ester (PME). The friction performance of WPME was evaluated using a pin on the disc tribometer machine. The influence of different operating conditions such as loads at 1kg, 2kg, 3kg and 4kg and sliding vel...
IOP Conference Series: Earth and Environmental Science, 2021
This paper aims to investigate the tribological friction using the Stribeck curve lubrication reg... more This paper aims to investigate the tribological friction using the Stribeck curve lubrication regime using an alternative source of biodiesel. Replacement of current usage of fossil fuels is essential, therefore, it is important to develop a proper recycling, renewable and sustainable product that reduces global warming. Biodiesel also known as Fatty Acid Methyl Ester (FAME), is biodegradable, produced from a renewable source, non-toxic, and produces a minimum greenhouse gas emissions. To reduce raw material cost, waste cooking oil is one of the most suitable replacements of vegetable oil for biodiesel synthesis. Rheological behavior of Waste Palm Methyl Ester (WPME), such as kinematic viscosity, density, and acid value, was measured based on EN14214 and compared with Palm Methyl Ester (PME). The friction performance of WPME was evaluated using a pin on the disc tribometer machine. The influence of different operating conditions such as loads at 1kg, 2kg, 3kg and 4kg and sliding vel...
This paper discusses the quality of surface finish when threading titanium-based alloy under dry ... more This paper discusses the quality of surface finish when threading titanium-based alloy under dry condition. The quality of surface finish was studied at various cutting parameters and at the two extreme stages of the machining process, i.e. at the beginning and end of the process. The objective is to evaluate the effect of a worn-out tool on the quality of surface finish. PVD-coated carbide tools were used in this study. Experiments were conducted at two cutting speeds, 35 and 55 m/min, two depths of cut, 0.2 and 0.25 mm, and a constant pitch of 2.0 mm. The tool wear and the quality of surface finish were inspected visually by microscope. The tool’s flank wear was measured gradually and machining was stopped when the flank wear reached the rejection criterion of0.3 mm. The microstructure beneath the machined surface was also evaluated. It was found that, at the beginning of machining, there was only a feed mark on the surface finish. When the machining was prolonged until the tools ...
Intensive research on the performance of coated carbide tools in machining titanium alloy is bein... more Intensive research on the performance of coated carbide tools in machining titanium alloy is being conducted worldwide. Titanium alloy has special characteristics such as high strength at elevated temperature and high mechanical resistance that makes carbide tools suitable to cut this material. This is because carbide tools are classified as hard and highly resistant to wear even at high temperature. This paper discusses the failure mode of a coated carbide cutting edge that is caused by the loading and unloading effect during milling. Tool failure adversely affects tool life, the quality of the machined surface and the surface's dimensional accuracy, and consequently the economics of cutting operations. The milling parameters that were observed to affect the failure of coated carbide tools were cutting speed, feed rate, depth of cut, and the application of a cutting fluid. Wear occurred along the flank and rake faces, which then propagated into the substrate material after the removal of the coating material. Wear along the flank and rake faces led to the concentration of stress over a certain area of the cutting edge, which was initiated by a microcrack and then propagated due to the loading and unloading effect during the intermittent milling process until significant brittle fracture occurred in the substrate material. Cutting speed and depth of cut were identified as the main factors responsible for the failure and fatigue of the coated carbide tools during the milling of titanium alloy.
The study emphasises on the fundamental understanding of the tribological behaviour for a lubrica... more The study emphasises on the fundamental understanding of the tribological behaviour for a lubrication system. In a dynamic system (e.g. piston ring/liner contact), the opposing sliding surfaces are separated by a layer of lubrication �lm, preventing direct metal-to-metal contact. Under critical operating conditions (e.g. high applied load), the �lm thickness might reduce to similar order of magnitude of the surface roughness, leading to boundary friction. A multi-scale approach is required to better predict the lubrication performance in a dynamic system. The �rst part of this study focuses on the development of a numerical algorithm using Reynolds equation to predict �uid �lm formation in a lubrication system. A rough surface contact model using the Greenwood and Tripp assumption is applied to predict the frictional properties along a lubricated conjunction using a three types of commercially available SAE grade lubricant namely, SAE5W40, SAE10W40 and SAE15W40. The simulated friction force is compared to the values measured using a pin-on-disc tribometer, showing good correlation between both data sets. With acceptable level of con�dence on the mathematical model, the second part of the study attempts to simulate a tribological properties of lubrication system considering biodiesel as the lubricant in the engine lubrication system. As the rough surface contact parameters are considered to be consistent in both case study, Reynolds solution is modi�ed in order to considers the �uid �lm formation of biodiesel with relation to their Fatty Acid Methyl Ester (FAME) compositions. Two parameters, namely 1) average number of carbon atom (zave) and 2) average number of double bonds (ndave) for biodiesels are included when introducing the e�ect of FAME compositions to the classical Reynolds equation. The term � has been introduced to the modi�ed Reynolds equation to correlate these two parameters. The value for the term � is determined by �tting the simulated lubrication Stribeck curve to the measured data for each of the selected biodiesels. Through this, a polynomial correlation is then obtained for the term � as a function of the product of average number of carbon atoms and average number of double bonds for the biodiesels. The coupling of Reynolds solution and rough surface contact model give a good correlation between measured data and predicted value in determining lubrication Stribeck curve regime for typical lubricants and biodiesel
In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been fo... more In biodiesel-fueled compression-ignition (CI) engines, dilution by unburned biodiesel has been found to have adverse effects on the boundary lubrication properties of additives in fully formulated engine lubricants. Such dilution of engine lubricants could be even more pronounced for CI engines running on higher blend concentrations of biodiesel. Given the nanoscopic nature of the interaction, this study seeks to determine the nano-tribological properties of an engine lubricant additive (e.g., zinc dialkyldithiophosphate (ZDDP)) when diluted with a fatty acid methyl ester (e.g., methyl oleate). Using lateral force microscopy (LFM) together with a fluid imaging technique, the lowest nanoscopic friction forces and coefficient of friction values (0.068–0.085) were measured for ZDDP when diluted with 70 vol% of methyl oleate. These values are also observed to be lower than those measured for neat ZDDP and neat methyl oleate, respectively, under similar conditions. Subsequently, interpre...
The paper simulates lubricant Stribeck curve for SAE grade engine lubricants by coupling Reynolds... more The paper simulates lubricant Stribeck curve for SAE grade engine lubricants by coupling Reynolds solution with Greenwood and Tripp's rough surface contact model. The predicted lubricant Stribeck curves for SAE5W40 and SAE15W40 engine lubricants are validated with measured data from a pin-on-disc tribometer. The proposed mathematical solution is shown to be capable of predicting lubricant Stribeck curves that correlate well with experimental data for both engine lubricants, capturing frictional behavior for the whole range of lubrication regimes. Such predictive tool could prove to be beneficial to automotive manufacturers in selecting suitable engine lubricants for their vehicles
Accurately predicting frictional performance of lubrication systems requires mathematical predict... more Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubri...
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