| 1. |
- Bergseth, Ellen, 1979-, et al.
(författare)
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Study of Surface Roughness on Friction in Rolling/Sliding Contacts : Ball-on-Disc Versus Twin-Disc
- 2020
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Ingår i: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 68:2
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Tidskriftsartikel (refereegranskat)abstract
- Although the efficiency of a gear pair is currently high, a better understanding of surface/lubricant contribution on efficiency is critical. Electrified drivelines will, for example, impose higher speed and alternate loading, and it is expected that these new conditions will, to a greater extent, rely on the surface/lubricant characteristics. Phenomena taking place in the gear contact is often measured using ball-on-disc and twin-disc tribometers. In this study, these two test set-ups were compared in order to assess differences in the behaviour of surface/lubricant interactions. Results showed that ball-on-disc and twin-disc set-ups reflect the same friction trends. However, the friction results differed by a factor of roughly two, even though the tribometers were set-up to run at the same contact pressure. The wear mechanisms also differed: micropits occurred on discs used in the twin-disc set-up, whereas normal or no wear was found on the ball-on-disc specimens. The contact conditions for the two test set-ups were also analysed using a numerical model. The comparison of these two machines may aid gear designers in selecting the proper experimental set-up for their purpose.
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| 2. |
- Bergstedt, Edwin, et al.
(författare)
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Gear micropitting initiation of ground and superfinished gears : Wrought versus pressed and sintered steel
- 2021
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the resistance of micropitting on two materials, using an FZG back-to-back test rig with CPT gears. The materials are wrought steel (16MnCr5) and a commercial powder metallurgical material (AstaloyTM Mo). Two finishing methods were studied: grinding and superfinishing. Experimental results show that the superfinishing prevented micropitting, but led to premature failure due to cracks in the root caused by tip-to-root interference. Micropitting was initiated at a higher load stage for the powder metallurgical steel compared to the ground wrought steel. The failure mechanisms were similar between materials with the same surface finish. The powder metallurgical steel showed subsurface initiated fatigue compared to the wrought ground steel having surface-initiated fatigue. Testing new finishing methods and materials, one has to be aware of the influence of the gear micro geometry.
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| 3. |
- Hjelm, Rikard, et al.
(författare)
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A multi-perspective method for gear efficiency and contact analysis
- 2023
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Ingår i: Results in Engineering (RINENG). - : Elsevier BV. - 2590-1230. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Modern gearing applications, in particular electrification, impose new challenges in many different fields of engineering and research. In specific, new demands are imposed on gears, including higher rotational speed, lower noise acceptance, and increased efficiency, as well as increased resistance against pitting and scuffing. To meet these demands, a better understanding of gear contacts is needed. The Eurostars project Effigears proposes a novel multi-perspective methodology for assessment of gear efficiency and contact analysis. The methodology consists of using a novel surface treatment method, Triboconditioning (R), implemented in a streamfinishing process, surface measurements using a scattered light method, experimental testing using the standardized FZG test rig, and contact simulations using a novel thermal elasto-hydrodynamic lubrication tool. It is found, in preliminary tests, that enhanced gear performance may be enhanced due to Triboconditioning (R) surface treat-ment. Findings also include better understanding of how surface characteristics and lubricants affect scuffing and pitting, and the effect of load distribution on gearset behavior.
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| 4. |
- Kumar, Mayank, 1991-
(författare)
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Friction in threaded fasteners : Influence of materials and tooling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Threaded fasteners represent the most common type of machine element, with a unique function that facilitates ease of assembly and disassembly. This ease of disassembly allows machine parts to be reused, refurbished, and recycled. Easy as these components are to assemble, several factors must be considered to achieve the desired clamp force and to utilize the fastener to its full load capacity. The research presented in the thesis compares different tightening strategies and assembly tools to show that the clamp force and it´s scatter are influenced by the variation in the coefficient of friction (CoF) to a much larger extent than by the accuracy of an assembly tool. The research therefore focus on understanding the frictional response in a threaded fastener joint during tightening.A range of design and assembly factors are considered to identify how to increase reliability of the threaded fastener joints. These factors include tightening speed, coating, surface topography, fastener storage conditions, cutting fluid residue and joint material. A torque-controlled, two-step tightening method was mainly used in the studies as it is widely practiced across the production floor of the motor vehicle and general industries to tighten threaded fastener joints. A state-of-the-art friction test rig (FTR) was built to quantify variations in the CoF in the thread and under-head contacts during tightening. Coatings and contact surfaces are also characterized using SEM, FIB, indenters, and optical microscopes to gain an insight to find the likely reasons behind CoF variation. Fasteners with different Zn-based coatings were tightened on plates with surface topographies similar to those found in the motor vehicle industry. The samples were not cleaned before the testing but used "as-received" from the supplier. The degree of damage to the joint surface and fastener thread from the tightening depends on the hardness of the coating. The hardest coating (Zn-Ni) remained relatively unchanged but gave twice as high CoF in the under-head contact compared to the softest coating (Zn-flake). The under-head friction often dominates the tightening process and may be significantly affected by the joint surface topography and the level of cleanliness. In the automotive industry, many parts to be assembled are not thoroughly cleaned, increasing the risk of cutting fluid residue on the joint surface. Different types of cutting fluids were compared in a study with fasteners tightened against “as-received" and cleaned plates. It was shown that CoF might drastically decrease depending on the coating and cutting fluid types. An ester-based fluid performed best, providing the lowest CoF in the under-head contact due to its higher viscosity and polarity. A water-based fluid showed a significantly larger scatter. Water can also influence friction due differences in humidity and temperature. Sometimes fasteners are stored outside a factory which could lead to water diffusion in the coating in hot-humid climate or condensation of water on the fastener surface when it is brought from the outside storage at sub-zero temperatures into the production hall. Water on the coating and inside of it could lead to low CoF, with overtightening and fastener failure as a result. Four Zn-based coatings were compared and showed different response depending on the coating structure and topcoat. Another way to reduce CoF is to use variable speed tightening. It will also increase productivity, as it is faster. It will also improve operator ergonomics, as it gives much lower reaction torque. Much higher CoF was found for EPZ coating when tightened at a constant and very low speed, 5 rpm, due to cohesion that resulted in material transfer, compared to CoF during high, variable speed tightening. At the same time, speed had negligible influence on the CoF when using soft Zn-flake coating as the coating easily sheared off, acting as a solid lubricant.A soft coating is also practical when used in contact with parts made using additive manufacturing (AM). The AM parts are often rough, but a soft coating can mitigate an increase in the under-head CoF. An interesting finding was that the cheapest solution of using an uncoated fastener works very well. An anti-corrosion oil on the plain fastener helped in achieving low CoF. When the AM plate was machined, the CoF and surface damage significantly increased due to the lay of the surface topography created by machining. The findings presented in the thesis increase understanding of how various design and assembly factors govern friction in the thread and under-head contacts. The under-head contact dominates friction response. A proper selection and adjustment of these factors will help design engineers to optimize joint designs and achieve high fastener strength utilization.
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| 5. |
- Olofsson, Ulf, 1962-, et al.
(författare)
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Nanoparticle emissions from the transport sector: health and policy impacts - the nPETS concept
- 2023
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Ingår i: 2022 Conference Proceedings Transport Research Arena, TRA Lisbon 2022. - : Elsevier BV. ; 72, s. 248-255
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Konferensbidrag (refereegranskat)abstract
- Road, rail, air, and sea transport generate a major fraction of outdoor ultrafine particles. However, there is no common methodology for comparable sub 100 nm particle emissions measurement. This paper presents the nPETS (grant agreement No 954377) concept to understand and mitigate the effects of emerging non-regulated nanoparticle emissions. This paper presents the concept and selected results. For example, nucleation and condensation mechanisms occur more frequently in the urban background site, leading to new particle formation, while mostly fresh emissions are measured in the traffic site.
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| 6. |
- Sannellappanavar, G., et al.
(författare)
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Towards real time automated early gear failure detection
- 2022
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Ingår i: Tribologia. - : The Finnish Society for Tribology. - 0780-2285 .- 1797-2531. ; 39:3-4, s. 42-44
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Tidskriftsartikel (refereegranskat)abstract
- The ability to stop a gear fatigue test before catastrophic failure has many advantages. However, today, a wide-ly accepted approach is not available. This case study applies a vibration-based condition monitoring methodologyto detect early gear failures. The gear studied takes part in an all-wheel-drive drivetrain system. Vibration signalsfrom 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 resultsfor early failure detection, and the process is feasible for implementation in an automated environment. Real timeanalysis is also possible since the autoregression model generates a healthy state TSA signal during the early tes-ting stages. However, the time to failure detection varies with operating conditions, with low sensitivity at high-speed and low-torque conditions.
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