Knowledge

Welcome to our knowledge centre. Here you can find a selection of resources and articles on our products and industries we are involved with.

Paper

Simulation and Prediction of Wear Using Finite Element Analysis with Experimental Validation

Recently, developments in automotive industries have increased competition. So, the design and development of new products have become more time …

Recently, developments in automotive industries have increased competition. So, the design and development of new products have become more time sensitive. But an equally important aspect is the durability and reliability of new products. Currently, the reliability of products is tested and examined using traditional laboratory methods. In this traditional approach, the products are tested until failure, which is usually a costly and time consuming process. Additionally, this approach increases the time from design to market. Reducing the testing duration of new products will reduce the product development cost and time to market. Therefore there is an increase in employing Accelerate Life Test (ALT) methods by many companies. ALT is the method of testing a product sample by applying more severe environmental conditions than normal conditions. Although cost and time can be reduced by this method, the method is insufficient in many cases because it often does not accurately determine the root cause of potential failures. Consequently, this need has given rise to the development of prediction models to enable a better understanding of product reliability. According to many studies, the main reason for the failure of mechanical components is the loss of material on the surfaces, in other words, wear. Previous research efforts have created a platform for wear simulation by combining Finite Element Analysis (FEA) with mathematical wear equations. This research is focused on reducing the wear simulation time by using an axisymmetric model and developing a mathematical equation in which the wear on the contacting surfaces in relative motion can be calculated by simulating the wear on only one surface in contact. This approach should make the FEA model more time and cost efficient. In this research, a critical factor (wear rate) is determined from experimental data, i.e., wear tests. Based on these results, the local wear is firstly calculated and then integrated over the sliding distance. Then, a series of FEA simulations are done in a loop by updating the wear coefficient and load conditions. Finally, the simulation results and mathematically calculated results from a derived equation are compared with experimental results. The simulation results show a reasonably good agreement with the experimental results. Moreover, the simulation model gives more details like the distribution of contact pressure and the spreading of stress at the contact surfaces.

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Paper

Marine Engine Lubrication

A low S marine fuel trunk piston diesel engine lubricant includes an overbased metal detergent; a zinc dihydrocarbyl dithiophosphate; optionally …

A low S marine fuel trunk piston diesel engine lubricant includes an overbased metal detergent; a zinc dihydrocarbyl dithiophosphate; optionally an aminic antioxidant; and a borated ashless dispersant. The lubricant exhibits improved thermal and oxidative stability and improved high temperature detergency.

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Paper

Lubricating Composition Containing an Antiwear Agent

The invention provides a lubricating composition containing an antiwear agent and an oil of lubricating viscosity. The invention further relates …

The invention provides a lubricating composition containing an antiwear agent and an oil of lubricating viscosity. The invention further relates to the use of the lubricating composition in an internal combustion engine, or a driveline device.

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Paper

Influence of Dispersant and ZDDP on Soot Wear

Diesel engines and gasoline direct injection (GDI) engines both produce soot due to incomplete combustion of the fuel and some …

Diesel engines and gasoline direct injection (GDI) engines both produce soot due to incomplete combustion of the fuel and some enters the lubricant where it accumulates between drain intervals, promoting wear of rubbing engine components. Currently the most favoured mechanism for this wear is that the anti-wear additives present in engine oils, primarily zinc dialkyldithiophosphates (ZDDPs), react very rapidly with rubbing surfaces to form relatively soft reaction products. These are easily abraded by soot, resulting in a corrosive-abrasive wear mechanism. This study has explored the impact of engine oil dispersant additives on this type of wear using combinations of dispersant, ZDDP and carbon black, a soot surrogate. It has been found that both the concentration and type of dispersant are critical in influencing wear. With most dispersants studied, wear becomes very high over an intermediate dispersant concentration range of ca 0.1–0.4 wt% N, with both lower and higher dispersant levels showing much less wear. However a few dispersants appear able to suppress high wear by ZDDP and carbon black over the whole concentration range. A series of experiments have been carried out to determine the origin of this behaviour and it is believed that high levels of dispersant, and, for a few dispersants, all concentration levels, protect the iron sulphide tribofilm initially formed by ZDDP from abrasion by carbon black.

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Paper

Lubricant Composition Containing an Antiwear Agent

The invention provides a lubricant composition comprising an oil of lubricating viscosity and a (thio)phosphoric acid salt of an N-hydrocarbyl-substituted …

The invention provides a lubricant composition comprising an oil of lubricating viscosity and a (thio)phosphoric acid salt of an N-hydrocarbyl-substituted gamma- (γ-) or delta- (δ-)amino(thio)ester. The invention further relates to a method of lubricating a mechanical device with the lubricant composition.

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Paper

Adsorption of Stearic Acid at the Iron Oxide/Oil Interface: Theory, Experiments, and Modeling

Improved friction performance is an important objective of equipment manufacturers for meeting improved energy efficiency demands. The addition of friction-reducing …

Improved friction performance is an important objective of equipment manufacturers for meeting improved energy efficiency demands. The addition of friction-reducing additives, or friction modifiers (FMs), to lubricants is a key part of the strategy. The performance of these additives is related to their surface activity and their ability to form adsorbed layers on the metal surface. However, the extent of surface coverage (mass per unit area) required for effective friction reduction is currently unknown. In this article, we show that full coverage is not necessary for significant friction reduction. We first highlight various features of surface adsorption that can influence the surface coverage, packing, and free energy of adsorption of organic FMs on iron oxide surfaces. Using stearic acid in heptane and hexadecane as model lubricant formulations, we employ a combination of experiments and molecular dynamics (MD) simulations to show how the dimerization of acid molecules in the bulk solvent and the crystallographic orientation of the surface modifies surface adsorption. In addition, we show that the solvent can strongly influence the adsorption kinetics, and MD simulations reveal that hexadecane tends to align on the surface, increasing the energy barrier for the adsorption of stearic acid to the surface. Furthermore, we present a combined approach using MD and molecular thermodynamic theory to calculate adsorption isotherms for stearic acid on iron oxide surfaces, which agrees well with experimental data obtained with a quartz crystal microbalance (QCM). Our results suggest that while the friction of systems lubricated with organic FMs decreases with increasing coverage, complete coverage of the surface is neither practically achievable nor necessary for effective friction reduction for the systems and conditions studied here.

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Paper

Motorcycle Lubricant

It has been found that the balance between friction reduction in the engine crankcase and the maintenance of sufficient friction …

It has been found that the balance between friction reduction in the engine crankcase and the maintenance of sufficient friction in the clutch assembly of a 4T motorcycle, where the engine crankcase and the clutch assembly are lubricating by the same lubricating oil composition from a common sump, can be achieved by use of a lubricating oil composition comprising a combination of molybdenum containing additive and ashless organic friction modifier.

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Paper

Using Acoustic Emission to Characterize Friction and Wear in Dry Sliding Steel Contacts

Acoustic emission (AE) was recorded during tribological tests on 52,100 steel specimens under different loads. AE signals were transformed to the …

Acoustic emission (AE) was recorded during tribological tests on 52,100 steel specimens under different loads. AE signals were transformed to the frequency domain using a Fast Fourier Transform and parameters such as power, RMS amplitude, mean frequency, and energy were analyzed and compared with friction coefficient and wear volume measurements. Results show that certain acoustic frequencies reflect friction while others reflect wear. If frequencies are chosen optimally, AE and friction signals are highly correlated (Pearson coefficients >0.8). SEM and Raman analysis reveal how plastic deformation and oxide formation affect friction, wear and AE simultaneously. AE recordings contains more information than conventional friction and wear volume measurements and are more sensitive to changes in mechanism. This all demonstrates AE's potential as a tool to monitor tribological behavior.

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Paper

The Role of Denatured Synovial Fluid Proteins in the Lubrication of Artificial Joints

CoCrMo ball-on-flat wear tests were carried out with 25 wt% bovine calf serum (25BCS) and human synovial fluid (HSF) to investigate …

CoCrMo ball-on-flat wear tests were carried out with 25 wt% bovine calf serum (25BCS) and human synovial fluid (HSF) to investigate artificial joint lubricating mechanisms. Post-test the wear scar on the disc was measured and surface deposits in and around the rubbed region were analysed by Micro InfraRed Reflection Absorption Spectroscopy (Micro-IRRAS). In most tests the HSF samples gave higher wear than the 25BCS solution; in some cases, up to 77%. After rinsing a similar pattern of surface deposits was observed in and around the wear scar for both the model and HSF. Micro-IRRAS showed the deposits were primarily denatured proteins with an increased β-sheet content. In some cases, trans-alkyl chain/carbonyl components were also present and these were assigned to lipids. Thioflavin T fluorescent imaging also indicated aggregated non-native β-sheet fibrils were present in the deposits and their presence was associated with lower wear. The formation of insoluble, denatured protein films is thought to be the primary lubrication mechanism contributing to surface protection during rubbing. From this and earlier work we suggest inlet shear induces denaturing of proteins resulting in the formation of non-native β-sheet aggregates. This material is entrained into the contact region where it forms the lubricating film. Patient synovial fluid chemistry appears to influence wear, at least in the bench test, and thus could contributes to increased risk of failure, or success, with metal-metal hips. Finally using 25BCS as a reference screening fluid gives an overly optimistic view of wear in these systems.

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