3D texture parameters for wear scars after severe regime

Purpose This paper aims to present an analysis of several 3 D texture parameters for the entire wear scars obtained in severe regime, on a four-ball tester. The aim of this analysis is to correlate the tribological parameter as wear scar diameter to texture parameters. Design/methodology/approach Tested lubricants were rapeseed oil, rapeseed oil additivated with 1% Wt nano TiO2 and rapeseed oil additivated with 1%Wt nano ZnO. The severe regime was applied for 1400 rpm and for loads increasing in steps of 50 N, from 500 to 900 N. Several analyzed roughness parameters (height parameters and functional ones) could be related to the evolution of a wear parameter, the wear scar diameter. Comparing the values for neat rapeseed oil and additivated variants, the texture parameters allow for evaluating if the additives protect or not the worn surfaces. Findings Measurements pointed out two groups of roughness parameters: one that has an evolution depending on wear scar diameter (WSD) and load (Sa, St, functional parameters) and one including Ssk that has shown no dependence on load and WSD. Also, the functional parameters Spk and Svk follow in a similar manner the wear parameter, WSD, but Sk is the least dependent on load. For the highest load, amplitude parameters such as Sa and St are following the tendency of WSD. Each lubricant has its particular correlation between wear parameters and texture quality, expressed by the help of a set of roughness parameters. Research limitations/implications Such studies help tribologists to rank lubricants based on a combined analysis with wear parameters and texture parameters. Practical implications The results allow for evaluating new formulated lubricants. Originality/value The study on the quality on worn surfaces introduces the original idea of analyzing the entire wear scar surface (approximated by an ellipse with the axes as those experimentally measured) by the help of a set of 3 D roughness parameters.

Investigation of Valve Tip End Wear Mechanism of a Four-Cylinder Automotive Engine Under High-Speed Application

This work investigates the causes of wear occurring at the engine valve tip end after 400 hours of engine operation. Fatigue wear was observed on the valve tip at the product development stage of the engine, which is going to be used in an automotive vehicle. Valves were assembled on a gasoline/CNG fuel-based four-cylinder IC engine. In this engine, tip end wear was prominent during high-speed testing conditions as compared to other types of engine tests. The chemical composition of worn surfaces was verified by spectroscopy. The microstructures, grain sizes and surface roughness were determined by optical microscopy and surface roughness tester. To evaluate the wear mechanism, valve tip end worn surfaces were analyzed using Scanning electron microscopy. The SEM analysis indicates the initiation of micropits and subsequent propagation of the fatigue wear during engine operating conditions. The residual stresses were measured at valve tip end surfaces and subsurfaces using X-ray diffraction techniques. Several investigations employing multiple techniques were carried out to identify the root cause of failure while comparing results against those of untested valves. Parameters that can affect valve tip end properties were identified in the study and countermeasures provided, and that lead to successful completion of the testing with the same operating condition.

Multi-scale modelling for adhesive wear in tribo-pairs of nano-hydroxyapatite reinforced UHMWPE bio-composite and Co-Cr alloy

The ultra-high molecular weight polyethylene (UHMWPE) is a popular biomaterial. Pre-clinical evaluation of UHMWPE in terms of wear resistance is extremely important to avoid the effect of implant loosening after implantation. This work proposed an efficient and accurate computational modelling approach to predict elasto-plastic properties at meso-scale, and further integrated at macro-scale to predict adhesive wear in dry tribo-pairs condition. The representative volume element (RVE) based finite element technique was used to predict elastoplastic behaviour of nano-hydroxyapatite (nHA) reinforced UHMWPE composite. The predicted values were validated experimentally and applied as a material property of pin during a numerical investigation of adhesive wear by a macro-scale modelling approach. The CoCr alloy was taken as the counter disc material. The integration of Archard's wear model and user-subroutine was done for numerical prediction of wear. The numerically obtained wear rate and friction coefficient results were validated experimentally by a pin on the disc wear setup under dry conditions. The fabrication of the specimen for validation was done by microwave-assisted compression moulding (MACM). The microstructural investigation of worn surfaces was done by scanning electron microscopy (SEM) to understand the mechanism of adhesive wear. The surface mapping of worn surfaces was done using an optical profilometer to observe the surface roughness after adhesive wear. Biocompatibility of the composite material was confirmed by In-vitro direct contact cytotoxicity test

On the Influence of Tribological Properties of AISI 4140 Annealed Steel against Ceramic Counterparts under Dry and Lubricated Conditions and Their Effect on Steel Microstructure

AISI 4140 steel is still one of the most distinguished steels employed in tribological applications because of its low cost, great mechanical properties, and appropriate wear resistance. In this contribution, the tribological performance of AISI 4140 annealed steel against engineering ceramic was analyzed to promote parameters for the application of this steel, especially in systems that are subjected to contact pressures between 490–1240 MPa. Dry and lubricated pin-on-disk experiments were completed at different normal loads. The worn surfaces were analyzed by contact profilometry, optical and scanning electron microscopies, energy dispersive spectroscopy, and microhardness examinations. In dry conditions, a better friction response was found on the steel tested with ZrO2. Friction coefficient and wear rate resulted in reductions up to 60% and 99% compared with those obtained with Al2O3 and Si3N4 counterparts. A strain-hardening phenomenon due to the friction process was observed on the samples tested with ZrO2 and Si3N4, which showed grain refinement and hardness increment on worn surfaces. Therefore, those systems exhibited better wear responses. In lubricated conditions, all counterparts exhibited low friction and wear, but the performance of Al2O3 and Si3N4 was highlighted. The results demonstrate that the performance of AISI 4140 annealed steel under the tested conditions is comparable with that of the same steel with other surface treatments.

Design and Evaluation the Anti-Wear Property of Inorganic Fullerene Tungsten Disulfide as Additive in PAO6 Oil

Inorganic fullerene-like tungsten disulfide particles have been proved to have good anti-friction and anti-wear properties as lubricating materials. As far as we know, however, when it is used as a lubricant additive, its behavior and action mechanism in the friction process are rarely studied. Herein, IF–WS2 particles were synthesized by a Chemical Vapor Deposition (CVD) method. The effect of IF–WS2 particle concentrations in the PAO6 oil on the tribological behaviors was investigated with a four-ball wear machine at both 75 and 100 °C. Additionally, the analyzed morphology and composition of nanomaterials and worn surfaces were analyzed by Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The friction behavior in actual working conditions was studied by a wear testing machine. The experimental results show that compared with the original PAO6 oil, at a dispersion of 0.25 wt% in PAO6 oil, the IF–WS2 particles showed the best performance in terms of coefficient of friction, wear scar diameter and wear mass, which significantly reduced by 27%, 43% and 87%, respectively. At the same time, in the process of friction, it was found that IF–WS2 particles accumulated in the depressions to fill the scratches, and adsorption films and chemical films, including FeS2, WS2 and WO3, were formed on the worn surfaces to avoid the direct contact among the friction pairs more effectively, resulting in the improved anti-wear performances. Additionally, the addition of IF–WS2 particles effectively delayed the rise of lubricating oil temperature. In addition, dispersant span 80 can effectively improve the dispersion and stability of IF–WS2 in PAO6. This work provides us for understanding the effective lubrication mechanism of IF–WS2 particles in more detail and having a new acknowledge of the comprehensive performance of IF–WS2/PAO6 oil.

Tribological Behavior of Steel Reinforced Glass/Epoxy Hybrid Composites

In this paper, the specific wear rate (SWR) and the coefficient of friction (CoF) of steel embedded glass/epoxy hybrid composites were examined and compared. Experiments were carried on the pin-on-disc machine on different types of composite materials like plain composite (steel volume 0%) and hybrid composites (steel volume 5% and 10%) pressed against a rotating steel disc (EN 31). Composites were fabricated using the hand-lay-up method. The volume percentage of steel pin/pipe varied from 0 to 10% and glass fiber from 50 to 60%, while the percentage of epoxy was kept 40% stable. The experiments were carried out on a group of samples for duration 20 minutes for different loads of 70N, 80N, 90N, 100N, and 110N with a varying sliding distance of 1000 m, 1250 m, 1500 m, 1750 m, and 2000 m. The results show that the SWR and CoF vary with different load and sliding distance. In general, CoF rises for some time of rubbing, and then it remains constant for the rest of the testing time. The results obtained show that the SWR and CoF increase with increasing sliding distance and load for all the composites. However, SWR and CoF decrease as an increase in the volume percentage of steel. An SWR of hybrid composite is observed to be reduced by 28.02% and 45.98% with an increasing percentage of steel by 5% and 10% respectively. CoF of hybrid composite is observed to be reduced by 14.11% and 24.02% with an increasing percentage of steel by 5% and 10% respectively. At last, the worn surfaces of the hybrid composites were studied through a Scanning Electron Microscope (SEM). Shallow and fine grooves appeared on the worn surfaces of hybrid composites at low loads and cracks were found in large quantities at high load which increased weight loss.

Investigation of the Tribological Behavior of Mineral Lubricant Using Copper Oxide Nano Additives

In this study, tribological properties of custom formulated and stabilized nano lubricant are investigated. Spherical CuO nanoparticles are suspended in 20W-50 mineral base lubricant using Oleic Acid (OA) as a surfactant. Three different nano lubricant concentrations with 0.2, 0.5, and 1 wt.% were analyzed through ASTM G-99 pin-on-disc tribometer standardized test under boundary/mixed lubrication regimes. The generated friction and wear analyses confirm a consolidation of tribological properties with a reduction in friction coefficient in the range of 14.59–42.92%, compared with the base lubricant. Analysis of worn surfaces (SEM/EDX) as well as (AFM) was conducted. Combined hypotheses were proposed from the analysis of worn surfaces; these hypotheses suggested that CuO nanoparticles exhibit an integrated effect of two phenomenal lubrication mechanisms. Additionally, dispersion stability evaluation of the suspended nanoparticles was performed through Zeta potential, (FTIR), and sedimentation analyses. Stability results showed that steric stabilization is the dominating effect of the repulsive forces between nanoparticles, surpassing the electrostatic repulsive forces.

Repair technologies using polyamides

A new method is proposed and equipment is developed for applying a polyamide antifriction coating to worn surfaces of parts. Its use with a machine tool with NC implements the principle of additive technology. The composition of the polyamide composition was selected for the restoration of permanent joints, which ensure their protection against fretting corrosion and the required strength. Keywords: polyamide coating, additive technology, fretting corrosion, inner surface, modification. [email protected]

Biotribology in Arthroplasty: Worn Surfaces Investigation on Ceramic Hip Femoral Heads Considering Wettability

Ceramic-on-ceramic bearings for total hip replacement are considered the best choice to avoid problems such as osteolysis and wear, mainly related to soft bearings. The aim of this work was to investigate in a comparative way different kinds of ceramic femoral heads for total hip replacements from a biotribological point of view, discussing the results obtained in terms of topographies, presence of metal transfer (MT) phenomena, and wettability on their worn surfaces in a tribological framework. Different ceramic femoral heads derived from in vitro wear tests, retrieved form patients, and brand new total hip replacements were investigated. The patients group had an average age of 60 years (ranging from 27 to 83). In most cases, the cause of failure was aseptic loosening of the acetabular component. Roughness analyses were performed to measure the tribological surface evolution of the material; an SEM and EDS investigation on the explanted heads proves and quantified MT, while the wettability was measured through a novel optical laboratory set-up with the aim to furnish useful data in the framework of synovial lubrication phenomena acting in the tribosystem. For the average roughness measurements on explanted specimens were considered three parameters (Ra = the average area between the roughness profile and its mean line; Rt = the vertical distance from the deepest valley to the highest peak of the roughness profile; and Rsk = it is the skewness and it is a measure of the asymmetry of the amplitude distribution function. In other words, the skewness indicates whether a surface is dominated by peaks or by valleys) and their values were: Ra 0.22 ± 0.12 μm, Rt 34.5 ± 13.5 μm and Rsk −0.01 ± 11.3; on the new specimens we measured Ra 0.01 ± 0.001 μm, Rt 0.12 ± 0.09 μm, and Rsk = 5.67 ± 8.7; for the in vitro specimens they were Ra 0.05 ± 0.12 μm, Rt 0.71 ± 1.4 μm and Rsk 7.73 ± 20.6. The wettability angle measurements showed hydrophilic surfaces for all femoral heads considered in this study with small differences between the three investigated categories, allowing to discuss their effects on the biobearings’ lubrication phenomena.