A review on recent advances on improving polyimide matrix nanocomposites for mechanical, thermal, and tribological applications: Challenges and recommendations for future improvement

In recent years, advancements on improving the mechanical and tribological properties of polyimide nanocomposites have remarkably increased, owing to the fact that polyimide nanocomposites exhibits lightweight, high strength, thermal stability as well as anti-wear and solvent resistance. The polyimide nanocomposites are described as material of polyimide matrix reinforced with certain volume or weight percent concentration of nanofillers. Researchers have demonstrated the importance of thermoplastic polyimide nanocomposites in mechanical, thermal, and tribological applications. However, the nanocomposites are reportedly facing interfacial adhesion issues and surface properties degradation, which have affected their mechanical, friction, and abrasive wear resistance for tribological applications. Although, much advancements on improving the mechanical, thermal, and wear resistance properties of polyimide nanocomposites has been reported. However, this review summarizes the effects of nanofillers, such as carbon nanotubes (CNTs), graphene (GN), graphene oxide (GO), boron nitride (BN), molybdenum disulfide (MoS2), silica (SiO2), titania (TiO2), alumina (Al2O3), carbon fibres (CF), aramid fibre (AF), glass fibre (GF), zinc dioxide (ZnO2), zirconium dioxide (ZrO2), silicon nitride (Si2N4), and carbon nitride (C3N4) on the mechanical, thermal, and wear properties of polyimide nanocomposites for tribological applications. The authors concluded the review study with advancement, challenges and suggestions for future improvement of polyimide nanocomposites as friction component material. Thus, the review offers an insight into the improvement and selection of polyimide nanocomposites material for mechanical, thermal, and tribological applications. More so, the review will also give away for further research.

THE EXPERIMENTAL METHOD AND CFD STUDY OF THE BARE HULL FORM OF UNDERWATER VEHICLE AT NEAR SURFACE CONDITION

Hull form selection, resistance and powering are important in designing underwater vehicle. An underwater vehicle bare hull form is based on the five parameters due to the interaction between the propeller and the hull. When they are running on the surface condition, there will be problems likely as surface vessel, but the main hull of the underwater vehicle is below the waterline with low freeboard. The underwater vehicles are operating with high speed at a high Froude Number. Therefore, the wave making component becomes important in surface resistance. The wave making resistance of the underwater vehicle model at surface condition is analyzed by using CFD tools. Friction component of resistance is calculated by using ITTC’57 correlation line. The flow around the ship’s hull is complicated, so that model experiments are still the most reliable data source on ship resistance determination. The bare hull form of underwater vehicle resistance is based on the model experiments and CFD results. The towing mechanism arrangement should be considered at model. Therefore, towing mechanism is designed for model testing. This paper discusses the towing method and result between model test and CFD. This paper also makes comparison of wave formation Towing tank test and CFD at various speeds. The model was tested with bare hull form of underwater vehicle in the Ship Model Towing Tank at Marine Hydrodynamics Centre, Myanmar Maritime University. CFD analysis is also carried out and the results are compared for surface condition. The three software packages XFLOW, XMESH and XPAN are used for CFD simulations. The comparison of results shows that the coefficient differences are less staggered based on the speed.

Mesoscale modelling of bond failure behaviour of ribbed steel bar and concrete interface

To explore the nonlinear bond behaviour between ribbed bar and concrete, combined with the characteristics of concrete meso-structure and ribbed bar surface characteristics and considering frictional resistance and the mechanical interlocking between rebar and concrete, a meso-scale model is established. Based on the good agreement between the simulation results and experimental results, the failure mechanism of bond between rebar and concrete is discussed, and the distribution characteristics of bond stress of steel bar are analysed. Furthermore, based on the meso numerical analysis method, the influence of friction coefficient between rebar and concrete on the failure mode of concrete and bond stress-slip curve was discussed, and the proportion of friction component in bond strength is obtained.

Optimisation of a chuck for cardboard can seaming – part 1: surface engineering and tribological evaluation

Purpose During the production of cardboard food cans, the packaging bottom and the cylindrical wall are joined in the seaming process. In order to achieve a high-quality, crack-free surface of the cardboard seam, low friction between the seaming chuck and the cardboard must be ensured. The goal of this study was to minimise the friction between the seaming chuck and the cardboard can surface. Design/methodology/approach Tribological properties of the seaming chuck were optimised by adjusting its material properties, surface topography and surface energy followed by measurements of the resulting friction response in sliding contact with a representative paper sample. Findings A strong correlation between the surface free energies of the tribological samples and their measured coefficients of friction was observed, indicating that in tribological tests, adhesion was the dominating friction mechanism. Furthermore, the fact that the smoother samples yielded higher friction values than the rougher ones is most likely also correlated with the higher adhesion of the smoother samples originating from their larger contact area. Research limitations/implications The existing results indicate that for tribological optimisation of paper and cardboard contacts primarily the adhesive friction component should be considered – by either reducing the surface free energy of the counter-body or optimising its surface topography. Practical implications By applying the selected solution concept, a friction reduction of more than 50% as compared to the benchmark was achieved. Originality/value The present study provides a guideline for tribological optimisation of paper and cardboard contacts. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0064/

Reduction of Friction and Soil Adhesion of Medium Carbon Steel via Hard Coating and Surface Texture

Rapid development of mechanical cultivation demands satisfactory wear performance and lower soil adhesion on the soil-engaging components of terrain machinery. A thick 2Cr13 hard coating was used in conjunction with surface textures in this sector. The results showed that 2Cr13 coating and surface texture decreased the friction coefficient and wear rate enormously. The surface wettability of the coating was reduced by a dimpled-surface texture. The adhesion test suggested that dimples greatly decreased the adhesion force by decreasing the friction component and the decrement increased with the increase of dimple size. The adhesion force increased with the soil moisture and then decreased when exceeding the moisture content threshold.

Estimation of Friction and States for Robust Control of Position Servo

Friction is an inherent nonlinearity in electromechanical systems. It adversely affects the system performance. The key challenge is to get its accurate information as it is not measurable. This paper proposes a two-observer concept for friction and state estimation. Novelty of proposal includes finite time convergent estimations of the friction component and the system states. These estimations are used to design a robust control for accurate position tracking in servosystem. It is shown that accurate friction and state estimations are obtained, and control efforts are reduced while achieving precise performance. Tracking performance is improved using proposed control. The outcome of the proposed methodology is validated through computer simulations and experimentations.

Experimental study of carbon nanotubes in high viscosity lubricants

Carbon nanotubes (CNTs) beneficial tribological properties were reported in numerous studies performed mostly in idealized tribometer conditions, previously described full engine tests confirmed that CNTs added to the lubricating oil reduced friction significantly. Apparently the engine application requires low CNT concentration in oil, otherwise when increasing the CNT concentration beyond a certain level oil viscosity increases, rapidly forming a greasy substance not suitable for engine lubrication. In this paper we report a study of tribological properties of such a high viscosity lubricant performed in Amsler tribometer in comparison to high quality commercially available lithium grease. The CNT based high viscosity lubricant in its current formulation turned out as not reliable for general application due to its low adhesion to the metal surface. In contrary to some samples made of a polymer widely used in industry as a friction component, we observed wear reduction reaching nearly 50% when replacing the best suitable lithium grease by a CNT based lubricant. This effect was first observed after 30 min into a friction test, suggesting a CNT related mechanism of anti-wear protection which still need to be explained.

Tribological Performance of PVD Film Systems Against Plastic Counterparts for Adhesion-Reducing Application in Injection Molds

The deposition of physical vapor deposition (PVD) hard films is a promising approach to enhance the tribological properties of injection molds in plastic processing. However, the adhesion is influenced by the pairing of PVD film and processed plastic. For this reason, the friction behavior of different PVD films against polyamide, polypropylene, and polystyrene was investigated in tribometer tests by correlating the relation between the roughness and the adhesion. It was shown that the dispersive and polar surface energy have an impact on the work of adhesion. In particular, Cr-based nitrides with a low polar component exhibit the lowest values ranging from 65.5 to 69.4 mN/m when paired with the polar polyamide. An increased roughness leads to a lower friction due to a reduction of the adhesive friction component, whereas a higher work of adhesion results in higher friction for polyamide and polypropylene. Within this context, most Cr-based nitrides exhibited coefficients of friction below 0.4. In contrast, polystyrene leads to a friction-reducing material transfer. Therefore, a customized deposition of the injection molds with an appropriated PVD film system should be carried out according to the processed plastic.

Experimental Investigation on Physical and Mechanical Behavior of Kathmandu Clay

Deformation due to load from the construction of infrastructure in soft ground is high and sometimes also becomes problematic. There are various techniques to strengthen the ground among which, the most suitable and commonly used method is chemical stabilization using cement. This method is fast and cement is relatively cheap, abundant and efficient. This research is focused on the study of improvement on physical and mechanical properties of cement mixed clay. Soil sample from Kathmandu, Nepal is taken for the laboratory investigations. The soil is reconstituted by using Ordinary Portland Cement of 5%, 10%, and 15% by its mass. The study revealed that physical and mechanical characteristics of cemented clay are greatly improved for engineering purposes. The specific gravity of all samples are linearly vary with cement content. Similarly, the liquid limit and plastic limit of clay are increased with increased cement content. However, hydraulic conductivity of the soils is decreased with the increase in cement content i.e. reduction is almost 7.5 times when cement increases from 5% to 15%. Finally, cohesion is increased from 3.23 kPa to 67.89 kPa in contrast to friction component which is decreased from 19.58° to 18.56°. Therefore, shear strength of clay is improved due to improvement on cohesion property of clay because of the reduction in the thickness of the diffused doubled-layer of adsorbed water.