Tribologia - Finnish Journal of Tribology

Overview of recent dissertations in the field in Finland

Christopher Kuugna Dawari — 2022-12-31

Overview of recent dissertations in the field in Finland

Foreword No 3−4 (2022)

Vuokko Heino — 2022-12-31

Dear Readers,

Year 2022 is at it’s end and it has been, once again, an extraordinary year. Energy and energy savings has been on the focus which is strengthening the demand for better tribological solutions. Material performance can be improved with sophisticated tribological solutions, not to mention the lower energy consumption due to the lower friction for example. These themes and their importance are widely recognized. However, they are rarely understand as tribological issues – while the term is not that familiar to the most of us. This is one of the key issues for the existence of Tribologia-journal – to spread the joyful message of tribology and to increase the common knowledge of the field in the society.

In this issue, we have been fortunate to receive journal articles from the recent studies related to tribology. Also, we received publications which were presented in the previous Nordtrib conference, held in Norway (Ålesund). We would like to thank our authors for contributing our journal.

Next year, we as a journal, will start our journey towards our fifth decade. Officially we have received the middle age. Current editorial team would like kindly thank the previous editorial teams for all their efforts. At the very beginning of the journey of this journal, the amount of work required to publish an issue has been quite high. Thanks to our previous editorial teams and their contributions, we have already a long history in publishing which we are proudly continuing.

Thank you for reading and wish you have prosperous New Year 2023!

Vuokko Heino
Editor-in-Chief

Influence of micro boron carbide particles on microstructure, mechanical properties, and dry sliding wear properties of an aluminium Al2214-B4C metal matrix composite

Revanna K — 2022-12-31

In this experimental research, an attempt is made to develop Al2214-B₄C composite materials with reinforcement of micro boron carbide (B₄C) (viz. 0, 1.5, 3, 4.5, and 6 wt.%) by using a novel liquid metallurgical stir casting technique with modified bottom pouring facilities and studying the microstructure, physical, mechanical, and dry sliding wear resistance responses. The microstructure of Al2214-B₄C composite samples with varied boron carbide weight percentages was examined under an electronic scanning microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDX) device. The physical characteristics like density and porosity, mechanical strength, such as micro and macro hardness, yield and ultimate tensile strength, and sliding wear response were examined under variable experimental conditions. The experimental results of the Al2214-B₄C composite revealed a decreased specific density with an increased weight percentage of boron carbide particles in the matrix and a homogeneous distribution of reinforced micro boron carbide particles in the Al2214 matrix. There was an appreciable improvement in mechanical properties and wear properties in composite materials as compared to an unreinforced aluminium alloy.

Role of silicon on the tribological performance of Al-based automotive alloys and the effect of used motor oil

Salim Kaiser — 2022-12-31

A wear test in a used motor oil sliding environment was performed on Al-based automotive alloys with Silicon doped in various levels. Where a pin-on-disc wear testing equipment was used at a normal pressure of 1.53 MPa and a sliding speed of 0.51 m/s, kept constant. For comparison of the wear performance, dry and fresh motor oil sliding environments were also considered. The results showed that as silicon content was increased in the alloys, the wear rate decreased up to the eutectic composition, followed by an increase for all the environments. It was mainly for higher levels of Si-rich intermetallic Mg₂Si precipitates in the α-aluminum matrix and made the alloys’ strength superior, in addition to increased wear resistance. In the post eutectic composition, primary silicon particles which are coarse and polyhedral appeared weakening the matrix. The coefficient of friction also decreased because of the higher hardness and the Si particles' employment as solid lubricants. In a dry environment, the wear rate and friction coefficient were much greater for their direct contact but lower under motor oil due to the reduced roughness caused by the sealing effects of the contact surfaces. Conversely, in oil environment, the opposite phenomenon was observed where coefficient of friction was incased with Si level to the alloy because the oil formed a thin film working as a lubricant between the contact surfaces which controlled the wear properties. Used oil demonstrates some degree of higher wear rate along with friction coefficient due to heavy and harmful chemical compounds in it. Examined by optical microscopy and SEM analysis, worn surfaces have shown that Si added alloy improved wear resistance through mild and smooth abrasive grooves filled with oxides in dry sliding conditions. In case of oil sliding environment smooth surfaces are created by the resistance of the oil film to the direct contact between the surfaces.

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

Chinwuba OSSIA — 2022-12-31

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.

High-stress abrasive wear characteristics of ultra-high strength press-hardening steel

Oskari Haiko — 2022-12-31

Ultra-high strength steels are widely utilized in many applications operating in harsh abrasive wear conditions. For instance, the machineries used in mining and mineral handling or in agricultural sector require robust, but cost-effective wear-resistant materials. Steels provide excellent combination of mechanical properties and usability. This study encompasses mechanical and wear testing of an experimental medium-carbon press-hardening steel. The as-received material was austenitized at two different temperatures and quenched in water. Additionally, low-temperature tempering was applied for one variant. In total, three variants of the press-hardening steel were produced. Microstructural characterization and mechanical testing were conducted for the steel samples. The wear testing was carried out with high-stress abrasive method, in which the samples were rotated inside a crushed granite bed. A commercial 400 HB grade wear-resistant steel was included in the wear testing as a reference. The experimental steel showed very high mechanical properties reaching tensile strength up to 2600 MPa with hardness of 750 HV10. Wear testing resulted in only minimal differences between the three variants indicating that the improved impact toughness by tempering did not significantly affect the wear resistance. The reference steel had nearly two times greater mass loss compared to the higher hardness press-hardening steels. Microhardness measurements on the worn surface showed drastic increase in hardness for the deformed structure for all samples. It was concluded that even the high-hardness martensitic steels exhibit notable wear surface work-hardening. Therefore, hardness was determined to be the most significant factor affecting the wear performance of studied steels.

Towards real time automated early gear failure detection

Govindraj Sannellappanavar — 2022-12-31

The ability to stop a gear fatigue test before catastrophic failure has many advantages. However, today, a widely accepted approach is not available. This case study applies a vibration-based condition monitoring methodology to detect early gear failures. The gear studied takes part in an all-wheel-drive drivetrain system. Vibration signals from four run-to-failure fatigue tests at two constant torque-speed combinations were used as input to time-synchronous averaging and autoregression model generation. The applied methodology shows promising results for early failure detection, and the process is feasible for implementation in an automated environment. Real time analysis is also possible since the autoregression model generates a healthy state TSA signal during the early testing stages. However, the time to failure detection varies with operating conditions, with low sensitivity at high-speed and low-torque conditions.