| 1. |
- Aiso, Toshiharu, 1983-
(författare)
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Workpiece steels protecting cutting tools from wear : A study of the effects of alloying elements on material transfer and coating damage mechanisms
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The vision of this thesis is to improve the machinability of workpiece steels. Workpiece material frequently transfers to the cutting tools during machining, and the transfer layers then forming on the tools may give both good and bad effects on machining performance and tool life. The objective of this work is to understand the effects of alloying element additions to workpiece steels on material transfer and the roles of the formed transfer layers on friction characteristics and wear of tools.To isolate and study the influence of the individual alloying elements, model steels are specifically designed. These steels include one reference with C as the only alloying element and others alloyed also with single additions or combined additions of 1 mass% Si, Mn, Cr and Al. The experiments are performed using both a sliding test, simulating the material transfer in milling, and a turning test.In a sliding contact, the mode of transfer is strongly dependent on the normal load and sliding speed. Material transfer initiates extremely fast, in less than 0.025 s, and characteristic transfer layers develop during the first few seconds. The different steel compositions result in the formation of different types of oxides in the transfer layers. At the workpiece/tool interface where the conditions involve high temperature, high pressure and low oxygen supply, easily oxidized alloying elements in the steel are preferentially transferred, enriched and form a stable oxide on the tool surface. The degree of enrichment of the alloying elements in the oxides is strongly related to their tendencies to become oxidized.The difference in melting temperature of the oxides, and thus the tendency to soften during sliding, explains the difference in the resulting friction coefficient. The widest differences in friction coefficients are found between the Si and Al additions. A Si containing oxide shows the lowest friction and an Al containing oxide the highest.The damage mechanism of coated tools is chiefly influenced by the form and shear strength of the transferred material. Absence of transfer layer or non-continuous transferred material leads to continuous wear of the coating. Contrastingly, continuous transfer layers protect it from wear. However, transfer layers with very high shear strength result in high friction heat and a large amount of steel transfer. This leads to rapid coating cracking or adhesive wear.
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| 2. |
- Ahrens, J., et al.
(författare)
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Results from the Antarctic muon and nuetrino detector array
- 2003
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Ingår i: Nuclear physics B, Proceedings supplements. - : Elsevier. - 0920-5632 .- 1873-3832. ; 118, s. 371-379
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Tidskriftsartikel (refereegranskat)abstract
- We show new results from both the older and newer incarnations of AMANDA (AMANDA-B10 and AMANDA-II, respectively). These results demonstrate that AMANDA is a functioning, multipurpose detector with significant physics and astrophysics reach. They include a new higher-statistics measurement of the atmospheric muon neutrino flux and preliminary results from searches for a variety of sources of ultrahigh energy neutrinos: generic point sources, gamma-ray bursters and diffuse sources producing muons in the detector, and diffuse sources producing electromagnetic or hadronic showers in or near the detector.
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| 3. |
- Aiso, Toshiharu, 1983-, et al.
(författare)
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Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact
- 2017
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 388-389, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- Material transferred from steel work materials onto the cutting tools largely affects tool life and machining performance. This material transfer is strongly influenced by the steel composition, and different alloying can have very different effects. Crossed cylinders sliding tests can be used to simulate the contact between the chip and the tool in machining. In this work such a test is used to evaluate material transfer and friction characteristics of a TiN coated tool sliding against five model steels. These model steels are especially designed to study the effects from specific combination of alloy elements, i.e. the steels, containing 0.55 mass% C and 1 mass% Si, are alloyed with one or more of 1 mass% Mn, Cr and Al. When using the steels alloyed without Al, Si-rich oxide layers are formed on the coating, resulting in a low friction coefficient. When using the steels alloyed with Al, almost pure Al–O layers are formed, resulting in a higher friction coefficient and rapid coating cracking. Essentially, the most easily oxidized alloy element is most strongly enriched in the oxide and decides the main mechanism of the material transfer and friction behavior.
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| 4. |
- Aiso, Toshiharu, 1983-, et al.
(författare)
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Effect of Si and Al additions to carbon steel on material transfer and coating damage mechanism in turning with CVD coated tools
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 368-369, s. 379-389
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Tidskriftsartikel (refereegranskat)abstract
- Material transfer from the work materials to the tools strongly influences machining performance and tool life. The influence of Si and Al additions to carbon steel on the material transfer and coating wear in turning with CVD coated carbide tools is investigated. Three model steels are specifically designed to separately study the effects of the individual alloying elements: one reference steel with C as the only alloying element (Base steel), and two steels alloyed also with 1 mass% Si or Al. In the region around the depth of cut on the rake face, where the outside edge of the chip passes over the tool surface, the coating is worn mainly by abrasion when cutting the Base steel. When cutting the Si alloyed steel, an almost pure Si–O transfer layer covers the coating surface, which protects it from wear. When cutting the Al alloyed steel, an almost pure Al–O transfer layer forms on the coating. This layer promotes steel transfer and associated adhesive wear of the coating, which rapidly results in coating detachment and eventually causes notch wear. In the crater region, only the Al alloyed steel results in a transfer layer, an AlN layer that reduces the crater wear.
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| 5. |
- Aiso, Toshiharu, 1983-, et al.
(författare)
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Effect of Si and Cr additions to carbon steel on material transfer in a steel/TiN coated tool sliding contact
- 2016
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 97, s. 337-348
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Tidskriftsartikel (refereegranskat)abstract
- A crossed cylinders sliding test, simulating the contact between the chip and the tool in machining, is used to evaluate material transfer and friction characteristics of a TiN coating against specifically designed model steels. These include one base reference, only alloyed with C (Base steel) and two alloyed also with 1 mass% Si or Cr. When sliding against the Base steel, an Fe-O layer is formed on the coating. Against the Si and Cr alloyed steels, Fe-Si-O and Fe-Cr-O layers are formed. In these oxides, Si and Cr are enriched, i.e. preferentially transferred from the steels. Compared to the Base steel, the friction coefficient is significantly lower against the Si alloyed steel and higher against the Cr alloyed steel.
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| 6. |
- Aiso, Toshiharu, 1983-, et al.
(författare)
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Influence of Mn and Al additions to carbon steel on material transfer and coating damage mechanism in a sliding contact between steel and TiN coated HSS tool
- 2016
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 101, s. 414-424
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Tidskriftsartikel (refereegranskat)abstract
- A crossed cylinders sliding test, simulating the contact between the chip and the cutting tool, is used to evaluate material transfer, friction characteristics and coating damage of a TiN coated high speed steel against specifically designed model steels. These steels include one reference with C as the only alloy element (Base steel), and two alloyed also with 1 mass% Mn or Al. When sliding against the Base steel, an Fe–O layer forms on the coating and protects it from wear. Against the Mn alloyed steel, Fe–Mn–O forms, which has no protective effect. Against the Al alloyed steel, an almost pure Al–O layer forms. This leads to the highest friction, rapidly causing substrate softening and coating fracture.
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| 7. |
- Alemani, Mattia
(författare)
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Particle emissions from car brakes : The influence of contact conditions on the pad-to-rotor interface
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to their adverse health effects emissions have been regulated for over three decades. Brake wear particulate matter is the most important non-exhaust source, however current knowledge is mainly limited to observational studies. This thesis aims to investigate relations between the brake system contact conditions and the related emissions on a model scale; validate the results on a component level; and understand to what extent they are significant on a full-scale.Paper A investigates the influence of nominal contact pressure on a model scale. Results show that higher pressure corresponds to higher emissionsPaper B investigates the influence of the nominal contact pressure, for different friction materials, on a model scale. A temperature threshold, responsible for a relevant emission increase, is identified.Paper C investigates particle characteristics and wear mechanisms for different nominal contact pressures, on a model scale. Results show an enhanced tribo-layer at higher pressure levels.Paper D investigates the influence of brake system conditions on emissions, on a model scale. Results show that frictional power is the most important parameter. A transition temperature independent of the contact condition is identified.Paper E investigates similarities occurring on a component scale and a model scale in terms of emissions. Results show a promising correlation, and the possibility of using a pin-on-disc tribometer for R&D activities.Paper F investigates analogies occurring on a component scale and a model scale, in terms of friction performance, fictional surface and chemical composition. Results show similar phenomena occurring for the two test stands.Paper G analyses real brake system working conditions in a urban environment defining, by means of an inertia dyno bench, the related emissions. Results reveal emission factors compliant to EURO6 and EURO2 regulations, in terms of number and mass, respectively.
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| 8. |
- Alfredsson, Sara, et al.
(författare)
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Tribological conditions of curling - the ultimate friction sport?
- 2011
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Ingår i: 18th International Conference on Wear of Materials, Philadelphia, USA, April 3-7, 2011.
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Konferensbidrag (refereegranskat)abstract
- Curling is an Olympic winter sport in which 8 players forming two teams slide stones across a sheet of ice towards a target area. The two teams have eight stones each and take turns to slide the stones over to the target area, some 28 m away from the release line. After being released, the stone is only affected by the sliding friction. However, this friction may be somewhat modified by sweeping the ice just in front of the sliding stone, using special curling brooms. Further, the trajectory of the stone becomes slightly curled. By slowly turning the stone clockwise when it is released, it will turn to the right, and vice versa. The best team in each round of 16 stones score one point for each stone resting closer to the target than the best stone from the opponent team.The game makes up a very interesting tribological system, presenting a number of challenging problems. These problems include understanding exactly:what determines the level of friction, and how it is affected by the sweeping,how the roughness of the stone influences the friction, and how the sliding surface should best be prepared to give a stable and repeatable friction,how the intentionally bumpy "pebbled" ice structure influences the friction,the size and distribution of the contact spots between the rough stone and the pebbled ice,the mechanism causing the curl of the stone - "Why does the stone curl?".This poster is based on an experimental project, and presents this very intriguing tribological system. It offers some ready explanations and challenges the visiting tribologists to contribute their insights.
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