Preliminary Study of the Effect of Micro-Scale Dimple Size on Friction and Wear under Oil-Lubricated Sliding Contact (original) (raw)
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Micro-dimpled surface by ultrasonic nanocrystal surface modification and its tribological effects
Wear, 2012
It is well known that dimpled surface can improve tribological characteristics. The fundamental aim of the present research is to demonstrate the process of making micro-dimples by ultrasonic nanocrystalline surface modification (UNSM) technology and to evaluate its effects on tribological characteristics. Ball-ondisk test was performed in order to reveal the influence of mechanism and micro-dimples. UNSM-treated surface is compared to ground surface and friction coefficient of the UNSM-treated surface has been reduced by about 25%, which is a significant phenomenon in improving tribological properties of mating surfaces. Wear volume loss of UNSM-treated surface has also been reduced by about 60%. Scanning electron microscopy (SEM) and surface roughness profile measurement were utilized to study the worn surface.
Tribology in Industry
The wear and surface morphology between steel (EN24, 22-24Rc)-steel (EN 31, 58-60Rc) contacts was investigated in presence of friction modifiers based (micro-graphite/nano particles-multi wall carbon nano tubes and zinc oxide) mineral oil. Though a decrease in wear was observed (upto a certain concentration of nano friction modifiers) but a weight-gain in pins after the tests was observed for all tests with ZnO nanoparticles while weight loss was observed in tests with multi wall carbon nano tubes and graphite particles based oil samples. Surface characterization of the worn surfaces showed more surface deteriorations in case of mineral oil (no friction modifiers) and mineral oil with graphite as compared with nano particles/tubes based lubricants. The occurrence of a tribo film due to the deposition of nano particle and the formation of a modified layer on the pin surfaces are likely to be responsible for the reduction of coefficient of friction and better surface roughness. Apart from investigating the wear behaviour between two steel surfaces under micro and nano particles based lubricant and analysing the surfaces of the samples a part of the work was also focussed on the weight gain after tribo tests with ZnO nano particle additions.
Investigating the friction reduction capability of dimpled surface using CNSL as lubricant
This work investigates the friction reduction capability of dimple-textured steel surface created using a vertical milling machine. A suitable geometry for creation of dimples was chosen and cashew nut shell liquid (CNSL) was used as lubricant. A L9 orthogonal array was created using Taguchi design of experiment where load, speed of disc and duration of the test were chosen as the parameters. A pin-on-disc tribometer is used to find the coefficient of friction (COF) between an EN 24 steel pin and the dimple-textured steel disc made of low carbon steel. ASTM G99 standard was used for the test and the lubricant was supplied intermittently. Optimization was carried out using Taguchi method, where the optimized condition of the input parameters influenced a substantial change of 32.38% in COF as compared to the non-textured disc surface. The lubricant retention capacity of the dimple was the primary cause for the decrease in COF.
Wear performance of oil lubricated silicon nitride sliding against various bearing steels
Wear, 2003
The selection of bearing steel surfaces for use with silicon nitride rolling elements within hybrid bearings is critical to the performance and life of such components, which have potential applications in advanced high speed aircraft. The wear and friction performance of these combinations is a major factor currently being considered for the next generation hybrid bearings. This paper reports on hybrid bearing contacts that have lubricated Si 3 N 4 elements, which have been loaded against various bearing steels under pure sliding contact conditions on a fully instrumented pin-on-disc wear test rig. The wear and friction performance of Si 3 N 4 has been compared to a baseline case of bearing steel M50 ball sliding against a M50 disc. Both hybrid and steel on steel contacts were lubricated by an aircraft engine oil Mobil Jet II. Wear mechanisms were determined by post-test analysis of the pin wear scars, disc wear surface and wear debris using optical microscopy, surface profilometry and FEG-SEM (scanning electron microscopy). The wear rates of Si 3 N 4 sliding against different bearing steels are ranked by performance and related to their wear mechanisms, hardness and microstructure. Typical sliding contact wear mechanisms were found for the steel on steel combination while Si 3 N 4 sliding against steel showed that transgranular and sub-micron-cracking mechanisms predominate. Evidence of material transfer (steel onto the silicon nitride) was found. Friction values for the various combinations are also reported and found to be substantially lower (µ = 0.04) than bearing steel on bearing steel combinations (µ = 0.17). The disc and pin wear was monitored on-line by an electrostatic wear sensor, LVDT and laser displacement probe, a friction strain gauge, and an infrared thermometer. Correlations between wear rate and charge generation/level, friction, contact temperature, and disc hardness are presented.
Effect of Low Depth Surface Texturing on Friction Reduction in Lubricated Sliding Contact
Lubricants
Laser surface texturing is an interesting possibility to tailor materials’ surfaces and thus to improve the friction and wear properties if proper texture feature sizes are selected. In this research work, stainless steel surfaces were laser textured by two different laser techniques, i.e., the direct laser interference patterning by using a nanosecond pulsed Nd:YAG laser and additionally by an ultrashort pulsed femtosecond Ti:Sa. The as-textured surfaces were then studied regarding their frictional response in a specially designed linear reciprocating test rig under lubricated conditions with a fully formulated 15W40 oil. Results show that dimples with smaller diameter lead to a significant reduction in the coefficient of friction compared to the dimples with a larger diameter and surfaces with a grid-like surface pattern produced by direct laser interference patterning.
Lubricants, 2016
Surface texturing has been shown to be an effective modification approach for improving tribological performance. This study examined the friction reduction effect generated by square dimples of different sizes and geometries. Dimples were fabricated on the surface of ASP2023 steel plates using femtosecond laser-assisted surface texturing techniques, and reciprocating sliding line contact tests were carried out on a Plint TE77 tribometer using a smooth 52100 bearing steel roller and textured ASP2023 steel plates. The tribological characterization of the friction properties indicated that the textured samples had significantly lowered the friction coefficient in both boundary (15% improvement) and mixed lubrication regimes (13% improvement). Moreover, the high data sampling rate results indicated that the dimples work as lubricant reservoirs in the boundary lubrication regime.
Friction Analyses of Dimple-Structured Surface
Journal of Mechanics Engineering and Automation, 2016
This paper proposes an investigation of the effects of laser engineering surface with dimple operating under lubrication. Dimples with semi-spherical geometry, with 100 μm in diameter and 25 μm in depth, were Laser-machined on the surfaces of high speed steel AISI H13 discs, with three different distribution densities applied over the surface. Pin-on-disc experiments were performed by using counter bodies made with AISI 440C and Tungsten carbide ISO K20 pins. The experiments provided data information on the influence of dimple distribution on the coefficient of friction. Numerical simulations were performed to understand the influence of the pin and disc surface roughness on the contact problem. The results suggest that the design of dimple-structured surfaces rely on nine main parameters: material contact pair and its respective hardness, Young Modulus, the roughness of the surfaces, the dimple design, the dimple distribution, the load applied, the velocity and the type of lubricant. A better performance can be obtained from a compromise solution over these parameters, and the dimple concentration has a dominance over the other parameters. The best results were obtained with a lower concentration of dimples, under higher speed and load. Numerical simulations can also be used as a design tool, supporting decisions regarding shape and distribution of the dimples and material selections for the contact pair.
Applied Surface Science, 2015
In this study, the effect of surface texturing parameters on the tribological performance of amorphous hydrogenated diamond-like carbon (DLC) under oil lubrication has been investigated. Micro dimples were created on a substrate by using a picosecond laser. After surface texturing was performed, amorphous hydrogenated diamond-like carbon (DLC) coating was deposited through magnetron sputtering. Dimple diameter varied from 50 µm to 300 µm, and dimple depth varied from 6 µm to 30 µm. Results show that at respective dimple diameter and depth of 100 and 6 µm, surface texturing improved the tribological performance of the amorphous hydrogenated DLC coating. Whereas, at a higher dimple diameter of 300 µm and dimple depth of 30 µm, the tribological performance of textured amorphous hydrogenated DLC was worse than that of un-textured amorphous hydrogenated DLC. The performance enhancement in the case of dimple diameter and depth of 100 µm and 6 µm can be due to micro textures, which can serve as a lubricant reservoir at the interface during sliding and remove wear particles from the contact. However, this beneficial mechanism could be obtained at an optimum texture diameter and depth.