Tribologia - Finnish Journal of Tribology

Foreword No 1−2 (2023)

Vuokko Marjamaa — Tue, 18 Jul 2023 00:00:00 +0300

Dear Readers,

We are delighted to publish our first double issue for this year. This time we have five research papers related to different aspects of tribology from improving the tribological properties by tailoring the material composition and improving the rolling contact fatigue via surface hardening to hydrodynamic lubrication on shaped surfaces.

Our journal is published by Finnish Society for Tribology since 1982. Earlier this year, we had our annual meeting hosted by Metlab Oy. After the official meeting we had company introduction followed by tour in their facilities. Metlab is accredited and independent laboratory for material testing and research services.

We hope you enjoy reading our current issue and have pleasant summer time.

All the best,

Vuokko Marjamaa

Editor-in-Chief

Group photo from the annual meeting of Finnish Society for Tribology at Metlab Oy.

Prediction Of The Coefficient Of Friction In The Single Point Incremental Forming Of Truncated Cones From A Grade 2 Titanium Sheet

Marcin Szpunar, Tomasz Trzepieciński — Tue, 18 Jul 2023 00:00:00 +0300

The aim of this paper is to analyze the effect of the process parameters on the coefficient of friction (COF) in the single-point incremental forming process. This investigation may be useful for further FEM analyses where the tool-workpiece contact must be set appropriately to obtain adequate results. The friction was analyzed between a solid tungsten carbide ⌀8 hemispherical ended tool with a radius of 4 mm and a grade 2 pure titanium sheet. As a lubricant, 10W40 engine oil was used. The experiment was of a central composite design and 20 runs in random order were carried out. The influence of input factors, namely spindle speed, tool feed and incremental step depth, was analyzed for the COF response. Two type of equations founded in the literature have been acquired to calculate COF values. An investigation of COF analysis was done for initial tool contact, the first tool full depth contact and stabilized forming region. Additionally, single components of the horizontal force (X-axis and Y-axis) were taken into account. Analysis of variance shows that there is no correlation between the input factors and the COF responses. However, the mean model fitted to the results obtained allows for the prediction of the COF by using the vertical force component and only one horizontal force component. The resulting mean value of the COF between the tool and the workpiece equals 0.4 for Eq. (1) initial contact, stabilized forming: Eq. (1) 0.656 and Eq. (2) 0.469.

Design and Development of Different Applications of PATB (Porous Aerostatic Thrust Bearing): A Review

MR. BIVASH CHAKRABORTY, DR. PRASUN CHAKRABORTI — Tue, 18 Jul 2023 00:00:00 +0300

In several applications demanding precise and ultra-precision movements, porous aerostatic thrust bearings had been employed as a crucial precision engineering component and enabling technology. By acting as a lubricant between the moving part and the stationary part in aerostatic bearings, pressurized air almost completely eliminates friction. Since air acts as the lubricant, oil-based lubricants leave no debris behind. The air prolongs the life of the substances by preventing them from slipping and wearing. The aerostatic type uses graphite as a porous film to disrupt the air uniformly over the surface, or a tiny hole is drilled through the centre of the bearing to let the air circulate and produce a thin layer between the components. With an increased reliance on computational and mathematical methodologies for design and bearing performance optimization, this review paper aims to present the state-of-the-art in aerostatic bearings advancement and research. It also conducts a critical analysis of their future research directions and development trends in the next ten years and beyond. Air bearings are utilized in the production of tools like lathes, CMM, and grinders because they are highly precise in their operation and decrease mistakes and production time. Air bearings are available in a variety of forms and sizes. The assessment of future trends and obstacles in aerostatic bearings investigation, as well as their prospective applications in the precision engineering sectors, concludes the study.

Effect of Shot Peening Process on Rolling Contact Fatigue Performance of EN 31 Alloy Steel

Ranju M R, Kesavan D — Tue, 18 Jul 2023 00:00:00 +0300

This paper aims to study the effect of shot peening on the Rolling Contact Fatigue (RCF) life of EN 31 Steel subjected to a pure rolling condition. Tests were carried out under lubricated contact conditions using a two-disc on-cylinder test rig. The orthogonal stress distributions and depth of deformation zones under static loading conditions were calculated using an elastic model by Finite Element Analysis (FEA) method. Shot peening increased the surface hardness by 20 % and imparted residual stress, which resulted in a 2-fold improvement of life. The depth of origin of the crack from the sub-surface was found to be in good agreement with the depth of maximum shear region obtained from the finite element model.

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

Md Jalal Uddin Rumi, Muzib — Tue, 18 Jul 2023 00:00:00 +0300

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.

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

Hardik Gangadia, Saurin Sheth — Tue, 18 Jul 2023 00:00:00 +0300

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.