The Tribological Adaptability for Ventral Scales of Dinodon rufozonatum in Dry/Wet/Rough Environments

The ventral scales of Dinodon rufozonatum were investigated to understand the outstanding tribological adaptability in various environments. The coefficient of friction (COF) of ventral scales was measured and changed with the contact conditions. It was discovered that the COF of scales under water-lubrication conditions (WLC) was larger than that under dry conditions (DC). More interestingly, the COF increased first and then decreased as the substrate roughness reduced. The abrasion marks on scales were then observed. The results indicated that the scales in DC wore more gently than that in WLC. Moreover, the degree of wear reduced with the decrease of substrate roughness. The frictional performance of ventral scales enabled the snakes to move more efficiently, quickly, and flexibly in multiple environments.

The analyses of frictional losses and thermal stresses in a diesel engine piston coated with different thicknesses of thermal barrier films using co-simulation method

This study comparatively presents the thermal and mechanical effects of different Thermal Barrier Coatings (TBCs) and their thicknesses on the performance of aluminum diesel engine piston by combining Finite Element Analyses (FEA) and Artificial Neural Network (ANN) methods. The piston structure of MWM TbRHS 518S indirect injection six-cylinder diesel engine was modeled. The clustered TBCs (NiCrAlY–Gd2Zr2O7, NiCrAlY–MgO-ZrO2, NiCrAl–Yttria Partially Stabilized Zirconia (YPSZ), and NiCrAlY–La2Zr2O7) were implemented to the related surface of aluminum alloy piston and then static, thermal, and transient structural FEA were conducted for each model. Based on both of the temperature and equivalent stress distributions, NiCrAlY–Gd2Zr2O7 coated model displayed the best performance. Additionally, the effects of top coating thicknesses of TBCs were investigated in the range of 0.1–1.0 mm with 0.1 mm increments in FEAs. The thermally effective top coating thickness was predicted as 0.95 mm for the selected TBC using ANN method. Then the effects of coating thickness on frictional performance were revealed by generating transient structural FE models and utilizing stribeck diagram. The uncoated and 0.95 mm NiCrAlY–Gd2Zr2O7 coated models were adjusted as transient and the related crank angle – dependent in-cylinder combustion pressure data was implemented. The friction force was reduced by at least 15% in NiCrAlY–Gd2Zr2O7 coated model.

High Performance Accelerated Tests to Evaluate Hard Cr Replacements for Hydraulic Cylinders

To prolong the lifetime of hydraulic cylinders, a wear-resistant low-friction surface is required. Until now, hard Cr coatings were the best materials for this. However, in recent years, there has been an increasing pressure on the manufacturing of hard Cr plating and plated products, because of environmental and health hazards. The replacement of these coatings by alternatives has not been highly successful yet, because it requires extensive component testing, which is costly and time-consuming and thus not appropriate for material development. For this reason, there is a high need to develop tribological methods that simulate hydraulic cylinders’ component-testing closely. In addition, these new methods should also provide additional information (e.g., friction evolution) that can assist in the further development and optimization of alternative coatings. Having the above in mind and building on an existing method from the American Society for Testing and Materials (ASTM G133), a new test method that allows users to test directly on hydraulic cylinders was developed. This method can provide a relative ranking of both the wear resistance and frictional performance of alternative coatings in direct comparison to state-of-the-art hard Cr. Importantly, the method is repeatable and has a much shorter test duration than full-scale component tests, thereby accelerating material development significantly.

Frictional Performance of an Ionic Liquid/Graphene Composite Additive in Lubricating Oil

In this study, we used a four-ball friction and wear testing machine to test the tribological properties of [HPy]BF4 ionic liquids (ILs), low-layer graphene (G), and IL and G compounds (IL/G) as lubricant additives at variousconcentrations, loads, and speeds. The morphology of the wear scar was characterized by a white-light interferometer and a scanning electron microscope (SEM). The results showed that the optimal concentrations of IL and G were 0.10[Formula: see text]wt.% and 0.05[Formula: see text]wt.%, respectively. When the IL concentration was 0.10[Formula: see text]wt.%, the friction coefficient and the wear scar diameter (WSD) reduced by approximately 18% and 8%, respectively, compared to the base oil. When the concentration of G was 0.05[Formula: see text]wt.%, the friction coefficient and WSD reduced by approximately 23% and 12%, respectively, compared to the base oil. After adding the optimal concentration of the IL/G composite additive under the same test conditions, the average friction coefficient of the steel ball reduced by approximately 30%, and the average WSD reduced by approximately 18%. IL/G nanoadditives could be easily attached to the pit area on the friction surface of the steel ball, which made the contact surface of the friction pair smoother and the area of the oil film bearing the load larger, compared to those using the base oil. These two combined phenomena promoted synergistic antifriction and antiwear effects, which significantly improved the frictional performance of the base oil.

Improving frictional performance of ring-liner system under cylinder deactivation conditions by surface texturing

In this study, a method of surface texture is considered to improve the frictional performance of the ring-liner system (i.e. RLS) under the conditions of cylinder deactivation (i.e. CDA). To assess the effectiveness of the method, a lubrication model is developed with considerations of the liner deformation, the actual rheological properties of lubricant, and the lubricant transport. By solving the model numerically, the friction reduction effect of surface texture for the RLS under the CDA is investigated. The results show that the surface texture can improve the friction properties significantly. For a six-cylinder gasoline engine, 7.57% and 7.28% decreases in the total average friction loss and power loss are observed when the RLS under the CDA is surface textured.

Synergistic Behavior of Graphene and Ionic Liquid as Bio-Based Lubricant Additive

The constant utilization of petroleum-based products has prompted concerns about the environment, hence a replacement for these products must be explored. Biolubricants are a suitable replacement for petroleum-based lubricants as they provide better lubricity. Biolubricant performance can be improved by the addition of graphene. However, there are reports that graphene is unable to form a stable suspension for a long period. This study used a graphene-ionic liquid additive combination to stabilize the dispersion in a biolubricant. Graphene and ionic liquid were dispersed into the biolubricant via a magnetic stirrer. The samples were tested using a high frequency reciprocating rig. The cast iron sample was then further observed using various techniques to determine the lubricating mechanism of the lubricant. Different dispersion stability of graphene was observed for different biolubricants, which can be improved with ionic liquids. All ionic liquid samples maintained an absorbance value of three for one month. The utilization of ionic liquid was also able to decrease the frictional performance by 33%. Further study showed that by using the ionic liquid alone, the frictional could only reduce the friction coefficient by 13% and graphene could only reduce the friction by 7%. A smooth worn surface scar can be seen on the graphene-IL sample compared to the prominent corrosive spot on the IL samples and abrasive scars on graphene samples. This indicates synergistic behavior between the two additives. It was found that the ionic liquid does not only improve the dispersion stability, but also plays a role in forming the tribolayer.

Fabrication and Testing of Bioinspired Surface Designs for Friction Reduction at the Piston Ring and Liner Interface

The piston ring and liner interface is a major source of friction loss in automotive combustion engines. This loss can be mitigated by learning from surfaces from nature that manipulate friction. In this study, novel fabrication and testing methods were developed and used to efficiently compare 3D bioinspired surface designs to existing piston liner surface topographies. Surface designs inspired by frog toes were fabricated using two-photon lithography, and their frictional performance is compared to that of typical piston liner topography. These designs reduce surface friction by an average of 18%, and up to 39%, compared to a flat control. The developed fabrication and testing methods allow comparison with existing topographies without needing to transfer the designs to the original materials and provide an efficient approach for designing surfaces to meet the frictional challenges of the future.