Tribologia-lehti 40 vuotta, Still Going Strong

TRIBOLOGIA - Finnish Journal of Tribology -lehden ensimmäisen päätoimittajan juhlakirjoitus

Tribological studies of different bioimplant materials for orthopedic application using Taguchi experimental design

In this research ball on disc wear tests have been carried out with ASTM G-99 standard at room temperature in simulated body fluid. The tribological property such as the coefficient of friction and wear weight loss was studied by using the Taguchi design of experiments. The design of the experiment was done using L8 orthogonal array to determine the collective contribution of the wear parameters. An analysis of variance demonstrated that the individual contribution of type of material factor was 97.15% and 66.66% for the coefficient of friction and wear weight loss respectively, which is the highest individual contribution as compared to other factors. It was concluded that the coefficient of friction and wear weight loss is mainly influenced by type of material factor. The analysis of the signal-to-noise ratio shows that the optimal coefficient of friction and wear weight loss was obtained with CoCrMo material at an applied normal load of 5 N with a sliding velocity of 0.05 m/s for a track diameter of 30 mm. To check the accuracy of results a confirmation test was carried out which indicates that predicted values are very close to the experimental values and the model is significant to predict the coefficient of friction. The results showed that the coefficient of friction and wear weight loss increases with increasing the applied load and sliding velocity. The microstructure of all substrates materials was analyzed using a scanning electron microscope. Wear track study showed that adhesive dominant wear mechanism for all four different substrate materials

Mechanical and the effect of oil absorption on tribological properties of carbon-based brake pad material

This research focuses on the mechanical and effect of oil absorption on the tribological properties of carbon-based brake pad material (CBP).  Carbon-based materials, including those at a nanosize, are combined for developed brake pad material. The mechanical properties related to wear properties such as compression strength, stiffness, hardness, and absorption properties were determined. The effect of oil absorption on the tribological properties of carbon-based materials was investigated. The obtained properties are compared with that of a ceramic-made brake pad (commercial). The experimental results show that the mechanical and absorption properties of the developed brake pad material varied with the combination and quantity of additives used to develop each brake pad material. CBP material offered higher performance than ceramic-made brake pads. The CBP material showed a higher shear strength of about 110%, 51% enhanced compressive strength, 35% greater modulus, comparative statistical hardness, 98% lesser water intake, and 97% oil absorption rate than ceramic made brake pad. The tribological properties of friction material after soaked in oil proved that absorption properties affect tribological properties of brake pads, which can be attributed to the oil content in the material system. The effect of oil uptakes on wear rate and friction of the commercial brake pad was higher than CBP materials, implying that the loading of carbon-based materials is a viable way to reduce absorption rate, which helps in increasing brake pad performance. The improved properties are suggestive of materials combinations that may be used to develop brake pad materials

Examination of particulate contamination contents in commercial diesel fuel

The purity of diesel fuel is a crucial issue, in particular in the face of modern injection systems operating under very high pressures with very precisely fitted mating parts. At such pressures and in high temperatures, injectors are particularly exposed to abrasive wear due to the presence of fine, hard abrasive particles in diesel fuel. This article presents the results of diesel fuel contamination with abrasive particles in various size ranges (above 1, 2, 3, 4, 6 and 14 µm) determined in accordance with ASTM D7619 and EN 12662. Fuel samples came from leading manufacturers and were collected at filling stations which are the last links of the distribution chain. Furthermore, all diesel fuels were tested for compliance with all the requirements of EN 590. Analysing the results obtained, the problem of contamination with abrasive particles was found to be present in Poland. Around 37% of the samples tested did not meet the requirements of the Worldwide Fuel Charter (WWFC) in terms of purity class (ISO code 18/16/13 for particles in the range above 4, 6 and 14 µm according to ISO 4406). Violations of the purity class were found mainly for particles in the range over 4 µm. A very large number of particles from the lowest ranges, which are not included in the Worldwide Fuel Charter (above 1, 2 and 3 µm), were also found, and these may cause damage to fuel injection systems. The number of particles in the range above 1 μm in majority of samples exceeded the class 22, and that of those in the range above 2 and 3 μm was mainly between classes 19 and 21. Moreover, no correlation was found between the results of the particulate matter determination (ASTM D 7619) and the total impurity content (EN 12662). Based on the results of the tests carried out, it can be concluded that exceeded number of particles in individual size ranges are not always related to the content of impurities in a form of metallic pulp, impurities from outside the system or the precipitation of enriching additives. Nevertheless, they may be one of the factors contributing to damage to precision fuel injection systems

Disquisition on material parameters and their influence on wear rates at high temperatures

The aim of this work is to find correlations of hard phase content and matrix type with hot hardness and wear rates in the cyclic impact abrasion test at high testing temperatures. Several materials with different matrix types and varying hard phase content have been investigated regarding their wear behaviour as well as their hot hardness up to 800°C. The hot hardness and hard phase content then was correlated to the wear rates using statistical methods. Materials with comparable matrix properties and higher hard phase content always have higher hot hardness and these parameters are statistically dependent so correlation of wear rate with hot hardness is statistically sufficient. It was found, that within the same material the wear rate is correlated to the hot hardness as long as there is no significant change in the wear mechanism. When the matrix of the material changes the hot hardness can not be directly correlated to the wear rate any more. It was also found that among all materials tested those with an austenitic matrix generally have higher wear resistance even if they have the same hot hardness

Survey of damage mechanisms on PVD coated HSS hobs used in Swedish gear manufacturing industry

Gear hobbing is widely used for production of cylindrical gears in the Swedish transmission industry. The hob, usually consisting of a homogenous HSS (High Speed Steel) body coated with a ceramic PVD (Physical Vapour Deposition) coating, is designed for regrinding and recoating several times without affecting its cutting geometries. Efficient usage of the tool, considering production costs and gear quality, requires reconditioning before wear starts to affect the gear quality negatively and certainly before tool wear renders reconditioning impossible. Hobs of today generally lack in reliability, making it difficult to judge when they have to be taken out for reconditioning. This work presents a survey of wear as observed on today’s state of the art hobs used by Swedish gear manufactures. It aims to identify damage mechanisms and the common problems in order to enable future production of more reliable hobs. The tools were temporarily borrowed from the production and the analyses were made non-destructively using optical microscopes. This was complemented by destructive cross- sectional analysis on two of the hobs.  Wear was most commonly located on the rake faces and the cutting edges of the cutting teeth. It mainly propagates by discrete fractures which appear to originate at local defects in the coating or at the interface. High intrinsic stress in the coating likely promotes coating spallation and accelerates the wear of the cutting edge

Frictorq, tribómetro para avaliação objectiva de superfícies texteis

Muitos materiais têxteis, senão mesmo a sua grande maioria, são usados ou então em contacto com o ser humano. são inumeras as aplicações em que os materiais estão em contacto com o corpo e as mãos, como é o caso do vestuário e dos têxteis lar, e mesmo os têxtais técnicos em algumas aplicações especiais, entre outras. O conceito de vestuário, assim visto como a nossa segunda pele, está intimamente relacionado com enorme variedade de tecidos, que surgem, naturalmente, em função das exigencias e das voluções da moda. neste sentido, e com especial ênfase no vestuário, existem vários parâmetros que permitem avaliar a qualidade e a aplicabilidade de tecidos. o coeficiente de atrito é um desses parâmetros, sendo um dos principais indicadores para avaliação objectiva de um conceito vulgarmente conhecido por toque. Este artigo pretende rever os principais desenvolvimentos que conduziram à concepção, construção e aperfeiçoamento de um aparelho para a medição do coeficiente de atrito de tecidos, que fosse de utilização simples, preciso e com um custo aceitável. de acordo com os ultimos desenvolvimentos, também aqui analisados e discutidos, é possivel concluir que o protótipo concebido é preciso e fiável, mostrando os resultados obtidos um comportamento comparável com outro instrumento com reconhecimento mundial, o sistema japonês Kes(Kawabata Evaluation System

Influence of the Bowtie Shaped Dimples on the Performance of Sliding Surfaces under Hydrodynamic Lubrication

It covers the tribological behaviour of sliding surfaces, one of which has bowtie-shaped micro-dimples. Against the other fixed, textured wall, one wall is smooth and moving at a constant speed. For the formation of hydrodynamic pressure and tribological behaviour, the effects of bowtie-shaped dimples and orientated bowtie-shaped dimples have been compared with circular-shaped dimples. Additionally, the impact of sliding speed, dimple area density, and dimple depth on tribological behaviour was examined. The findings show that compared to a circular-shaped dimple, an atypical bowtie-shaped and orientated bowtie-shaped dimple generates a higher net hydrodynamic pressure in the fluid domain and offers improved stability between the sliding surfaces. It has been demonstrated that geometrical factors like dimple depth and area density as well as operational factors like sliding speed have a substantial impact on the hydrodynamic average pressure and tribological behaviour of sliding surfaces. The experimental results support the conclusions from the analysis and CFD

Effects of reinforcement grain size and concentration on the physicomechanical properties of green automotive brakepads from waste cowhorns and rockshells

This study presents the development and characterization of green automotive brakepads using cowhorn (CH) and Rockshell (Thias Coronata L.) (R) as reinforcement material in full factorial experiments. The brakepads were produced by compression moulding at 220.73N using epoxy resin binder, CaCO3 fillers, Diethylenetriamine hardener, colourless methyl-ethyl ketone peroxide (MEKP) catalyst, carbon black friction modifier, with copper and iron fillings as thermal conductivity additives. Three levels of particle grain sizes 125, 250, 500µm were produced from each material. Hybrid CHR samples were also produced with same grain sizes. The density, hardness, and compressive strength properties were observed to reduce with increase in grain size while liquid absorption increased with increase in grain size. Impregnating the reinforcement materials with increasing concentration of R-particles improved the hardness, compressive strength and liquid absorption but decreased the friction coefficient. The R-samples performed best among all in liquid absorption, except for oil absorption where the commercial (control) sample surpassed it. EDX spectroscopy results showed presence of antimony and vanadium toxic heavy metals in the control sample unlike the developed brakepads. All properties measured exhibited multivariate quadratic regression models with good fitness of R2-values, 0.8438 ≤ R2 ≤ 0.9976, and significance-F values, 0.000398 ≤ significance F. ≤ 0.18101. All response surfaces showed best performance with R-concentration of 80 – 100% and 125 – 250µm grain size ranges. Hence, reinforcements of cowhorn and rockshell particles with concentration and grain sizes above can be used to develop brakepads with properties superior to the toxic control brakepads

Characterization on Specific Wear Rate of Al Composite Reinforced with nano-Al2O3 Using Taguchi’s Technique

The aim of the investigation was to study and predict wear properties of nano Al2O3 reinforced Al composite fabricated by a two-step stir casting method. A pin-on-disc wear device was used to study the wear characteristics. An L9 Orthogonal array was selected as per Taguchi's method to analyze the results and ANOVA was used to examine the impact of applied force, sliding speed, and duration on specific wear rates with "smaller the better" as selection criteria. As per the investigation, applied load significantly influences the particular specific wear rate. Sliding duration is the second most important factor, whereas sliding speed is the factor that has the lowest impact on a given specific wear rate. We created a regression equation with R2 and adj R2 of 99.85% and 99.76% respectively that can estimate the specific wear rate of nano Al2O3 reinforced Al composite. An apple-to-apple comparison between experimental and projected values was built using two confirmation tests, and it revealed an inaccuracy of 2.1% and 6.6%, using a scanning electron microscope. The worn-out surface of the samples with the lowest and greatest specific wear rates was examined and identified with unique oxidation layers and cracks