283 results on '"Staffan Jacobson"'
Search Results
2. Long-term effects on soil-water chemistry of wood ash and nitrogen application in a conifer forest
- Author
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Lars Högbom, Eva Ring, Gunnar Jansson, and Staffan Jacobson
- Subjects
Global and Planetary Change ,Residue (complex analysis) ,010504 meteorology & atmospheric sciences ,Ecology ,Logging ,chemistry.chemical_element ,Forestry ,Wood ash ,010501 environmental sciences ,01 natural sciences ,Nitrogen ,Nutrient ,chemistry ,Boreal ,Agronomy ,Soil water ,Soil solution ,0105 earth and related environmental sciences - Abstract
Wood-ash application to forestland has been proposed as a means to compensate for increased nutrient removal when harvesting logging residue in addition to stems. A study-plot experiment was established on a mineral soil site in Sweden to investigate how this measure affects soil-water chemistry. In 1995, 10 treatments were applied. Here, we present results from 9 to 17 years after application for eight of the treatments: control; 3 × 103, 6 × 103, and 9 × 103 kg·ha−1 of self-hardened and crushed wood ash (WA); 150 kg N·ha−1 supplied as ammonium nitrate; 3 × 103 kg WA and 150 kg N·ha−1 applied simultaneously; 3 × 103 kg WA with 150 kg N·ha−1 applied 1 month before the ash; and 3 × 103 kg·ha−1 of pelleted ash. Soil-water samples were collected from a depth of 50 cm. Treatment effects (p < 0.05) were detected in the electrical conductivity, pH, and concentrations of K+, Mg2+, Ca2+, Al, SO42−-S, and B. Elevation of K+ and SO42−-S concentrations tended to cease toward the end of the study period. Effects were generally more pronounced with increasing ash dosage. No difference was detected between the 150 kg N·ha−1 treatment and the control. Despite the high solubility of the ash, its effects on soil-water chemistry could still be detected 9–17 years after application.
- Published
- 2021
3. Long-term responses of understory vegetation in boreal Scots pine stands after nitrogen fertilization
- Author
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Eva Ring, Staffan Jacobson, and Lars Högbom
- Subjects
biology ,fungi ,technology, industry, and agriculture ,Scots pine ,food and beverages ,Species diversity ,Forestry ,Understory ,Vegetation ,biology.organism_classification ,Term (time) ,Agronomy ,Boreal ,Environmental science ,Ecosystem ,sense organs ,skin and connective tissue diseases ,Lichen - Abstract
Nitrogen fertilization can increase above- and belowground forest growth and carbon storage in low nitrogen (N) environments. However, it may also induce changes in other parts of the ecosystem, su...
- Published
- 2020
4. Natural regeneration of lodgepole pine in boreal Sweden
- Author
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Mats Hannerz and Staffan Jacobson
- Subjects
Current range ,Pinus contorta ,Altitude ,Ecology ,Boreal ,Range (biology) ,Forestry ,Natural regeneration ,Biology ,biology.organism_classification ,Ecology, Evolution, Behavior and Systematics ,Latitude - Abstract
The large-scale introduction of lodgepole pine (Pinus contorta ssp. latifolia, LP) into Swedish forests was initiated around 1970, and currently 520,000 hectares of the forest land are dominated by the species. Even though the tree has mostly serotine cones, adapted to open after forest fires, it has proved able to self-regenerate in Sweden. This study is the first to present, scientifically, the extent of self-regeneration covering the whole current range of LP-forests in Sweden. LP-saplings were recorded for three years, 2015–2017, in 8194 subplots distributed over 214 randomly selected LP-stands from latitude 59.6–66.9°N and altitude 88–710 m asl. Of all subplots, 3% contained LP-saplings, and regeneration was found in 53% of all stands. The probability of finding LP-saplings was significantly dependent on the plots’ distance from the edge of the LP-stand, and 78% of all saplings were found within and up to 15 m beyond the stand edge. Most, 63%, of the plots with LP were found on disturbed ground such as wheel tracks, roadsides and where there had been site preparation. The results show that LP can naturally spread under a range of conditions in the studied region. The regeneration is, however, concentrated in particular stands and should be possible to control with monitoring programmes and measures to eradicate self-dispersed trees in unwanted areas.
- Published
- 2020
5. Tribological evaluation of a boric acid fuel additive in various engine fuels
- Author
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Elin Larsson, Jannica Heinrichs, and Staffan Jacobson
- Subjects
Friction ,Wear ,Mechanics of Materials ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Materials Chemistry ,Fuel additive ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,Surfaces and Interfaces ,Condensed Matter Physics ,Boric acid ,Fuel ,Surfaces, Coatings and Films - Abstract
A boric acid fuel additive has shown promising results in field-tested internal combustion engines by resulting in substantial fuel consumption reductions. The present study evaluated the lubricating, tribofilm forming, and wear protective abilities of the fuel additive when mixed into four fuels; ethanol (E85), gasoline, diesel and marine gas oil (MGO). A reciprocating ball-on-disc setup was used for the test, to mimic the conditions of components that run lubricated by the fuel, such as fuel pumps and fuel injection systems. The chemistry of the varying fuels as well as the concentration of fuel additive was found to strongly affect the tribofilm formation on the sliding surfaces. The fuel additive showed no friction or wear reducing effect in any of the fuels, except for in E85.
- Published
- 2022
6. Unraveling the lubrication mechanisms of lithium complex (LiX)- and polypropylene (PP)- thickened greases in fretting – Part I : Fretting experiments and surface analysis
- Author
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Åsa Kassman Rudolphi, René Westbroek, Staffan Jacobson, Johan Leckner, and Elin Larsson
- Subjects
Polypropylene ,Materials science ,Base oil ,chemistry.chemical_element ,Fretting ,Surfaces and Interfaces ,Lithium complex (LiX) grease ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Viscosity ,chemistry ,Mechanics of Materials ,Grease ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Materials Chemistry ,Lubrication ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,Grease lubrication ,Lithium ,Polypropylene (PP) grease ,Composite material ,Contact area - Abstract
Greases with two different thickeners, namely lithium complex (LiX) and polypropylene (PP), and three different base oil viscosities were investigated in fretting with varying displacement amplitude and applied normal load. The material combinations silver-coated copper/silver-coated copper (Ag/Cu vs Ag/Cu) and steel/steel were investigated. Fretting maps of four of the six evaluated greases were constructed as a tool to better understand and compare the lubrication mechanisms of the varying grease types. Parameters such as applied normal load, displacement amplitude, material combination, contact area growth, thickener type, base oil viscosity, chemical effects, etc. all influence the grease lubricating properties and the prevailing fretting regime. This study shows the importance of understanding the application and its contact conditions, as well as how different grease types are affected by varying test parameters. Very different lubrication effects are found for the same grease type, depending on test conditions. Surface analysis of the formed wear marks is presented.
- Published
- 2022
7. Unraveling the lubrication mechanisms of lithium complex (LiX)- and polypropylene (PP)- thickened greases in fretting – Part II: Lubrication model
- Author
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Elin Larsson, René Westbroek, Johan Leckner, Staffan Jacobson, and Åsa Kassman Rudolphi
- Subjects
Mechanics of Materials ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,Materials Chemistry ,Lubrication model ,Lithium complex (LiX) grease ,Polypropylene (PP) grease ,Surfaces and Interfaces ,Fretting ,Grease lubrication ,Condensed Matter Physics ,Surfaces, Coatings and Films - Abstract
In a previous investigation, greases with two different thickeners, namely lithium complex (LiX) and polypropylene (PP), and three different base oil viscosities were investigated in fretting with varying displacement amplitude, applied normal load and material combination. The tribological behavior of grease in fretting is extremely complex. Very different lubrication effects were found for the same grease type, depending on test conditions. The grease properties (thickener type and base oil viscosity) together with the applied normal load, displacement amplitude and the material combination all influence the prevailing fretting regime. The aim of the present paper is to unravel the lubrication mechanisms of LiX and PP greases in fretting. Cross sections of selected wear marks from the fretting tests are presented and they are, together with the results from the fretting maps presented in the previous investigation, used as tools to better understand the mechanisms. The exact lubrication mechanisms of the two thickener types are not yet fully understood and confirmed but a lubrication model is suggested, based on the present knowledge and hypotheses.
- Published
- 2022
8. Wear mechanisms of WC-Co cemented carbide tools and PVD coated tools used for shearing Cu-alloy wire in zipper production
- Author
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Jannica Heinrichs, Hiroko Mikado, Shingo Kawamura, Staffan Jacobson, A. Kawakami, and Urban Wiklund
- Subjects
Materials science ,Zipper ,Alloy ,Metallurgy ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Copper alloy ,Materials Chemistry ,engineering ,Cemented carbide ,0210 nano-technology ,Shearing (manufacturing) - Abstract
To form the individual elements, that together form a zipper, a pre-formed Cu-alloy wire is sheared using cemented carbide tools. The wear caused by the relatively soft copper alloy on the much har ...
- Published
- 2019
9. Tribofilm formation of a boric acid fuel additive – Material characterization; challenges and insights
- Author
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Elin Larsson, Olivier Donzel-Gargand, Jannica Heinrichs, and Staffan Jacobson
- Subjects
Mechanics of Materials ,Mechanical Engineering ,Surfaces and Interfaces ,Surfaces, Coatings and Films - Published
- 2022
10. Boric acid as fuel additive – Friction experiments and reflections around its effect on fuel saving
- Author
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Petra Olander, Staffan Jacobson, and Elin Larsson
- Subjects
Materials science ,Mechanical Engineering ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Boric acid ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Chemical engineering ,Mechanics of Materials ,0210 nano-technology - Abstract
Boric acid as fuel additive : Friction experiments and reflections around its effect on fuel saving
- Published
- 2018
11. On the deformation mechanisms of cemented carbide in rock drilling – Fundamental studies involving sliding contact against a rock crystal tip
- Author
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Mikael Olsson, Staffan Jacobson, Jannica Heinrichs, and Karin Yvell
- Subjects
Materials science ,020502 materials ,Drilling ,chemistry.chemical_element ,02 engineering and technology ,Matrix (geology) ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0205 materials engineering ,0203 mechanical engineering ,Deformation mechanism ,chemistry ,Tungsten carbide ,visual_art ,Phase (matter) ,visual_art.visual_art_medium ,Cemented carbide ,Ceramic ,Composite material ,Cobalt - Abstract
Cemented carbide is a composite material, most commonly consisting of tungsten carbide grains in a metallic matrix of cobalt. The combination of a hard ceramic phase in a ductile metallic matrix co ...
- Published
- 2018
12. Influence of binder metal on wear initiation of cemented carbides in sliding contact with granite
- Author
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Jannica Heinrichs, Staffan Jacobson, Susanne Norgren, Karin Yvell, and Mikael Olsson
- Subjects
Materials science ,Rock drilling ,Carbide ,Metal ,Wear ,Materialteknik ,Materials Chemistry ,Manufacturing, Surface and Joining Technology ,Sliding ,Bearbetnings-, yt- och fogningsteknik ,Drill ,Metallurgy ,Drilling ,Surfaces and Interfaces ,Materials Engineering ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Mechanics of Materials ,Sliding contact ,visual_art ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,visual_art.visual_art_medium ,Cemented carbide ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,Cemented carbides ,Alternative binder - Abstract
Drill bits equipped with WC-Co cemented carbide buttons offer great performance in many rock drilling applications. Generally, the wear of these buttons against the rock is gradual and moderate, or even slow depending on the rock conditions. However, the Co binder has recently been found to cause health issues and an alternative binder, which does not compromise the performance of the cemented carbide, is needed. In the present work, the performance of WC-Fe and WC-Ni is investigated and compared to the common WC-Co in a sliding test against granite. The results show immediate scrape-off of granite against protruding WC grain edges. Some WC grains crack and fragments are subsequently removed, adding up to loss of entire WC grains. A nanoscale pattern gradually evolves on other WC grains, implying also nanoscale wear. Both WC-Fe and WC-Ni show significantly faster wear initiation and early propagation compared to WC-Co, although the wear characteristics are similar.
- Published
- 2021
13. On the critical roles of initial plastic deformation and material transfer on the sliding friction between metals
- Author
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Staffan Jacobson, Magnus Heldin, and Jannica Heinrichs
- Subjects
Work (thermodynamics) ,Materials science ,Friction ,Galling ,Surfaces and Interfaces ,engineering.material ,Condensed Matter Physics ,Flattening ,Surfaces, Coatings and Films ,Dry contact ,Transfer ,Mechanics of Materials ,visual_art ,Tool steel ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Materials Chemistry ,engineering ,Aluminium alloy ,visual_art.visual_art_medium ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,Surface modification ,Deformation (engineering) ,Composite material ,Contact area ,Sliding - Abstract
It is well known that the friction level rapidly shifts during the initial sliding between two unlubricated metals. Often this change is so rapid that the initial friction level is not even noticed, owing to initial surface contamination or roughening of the contacting surfaces, either due to plastic deformation and wear, or transfer. The present work uses a unique experimental set-up – the Uppsala Load Scanner – to generate detailed information on friction and surface modification in initial sliding contact between pairs of crossed metal cylinders. A wide range of loads, each exclusively coupled to a well-defined contact area on both contacting bodies, is evaluated in a single test. By performing repeated scans, intertwined with high resolution FEG-SEM studies of the contact surfaces, investigations of the couplings between local load, friction, surface modification, topography, transfer, etc. is facilitated and the progress of deformation and friction can be followed. The SEM studies also include local FIB cross sectioning of selected samples to learn more about the sub-surface modifications. The materials selected include a PM tool steel, a case-hardened component steel and an aluminium alloy. All tests were conducted in dry contact. The roles of the large initial surface roughening or flattening, the following material transfer and other gradual surface modifications in determining the friction level, are discussed.
- Published
- 2021
14. Root associated fungi respond more strongly than rhizosphere soil fungi to N fertilization in a boreal forest
- Author
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Shahid Mahmood, Roger D. Finlay, Karina E. Clemmensen, Srisailam Marupakula, Lars Högbom, and Staffan Jacobson
- Subjects
Environmental Engineering ,010504 meteorology & atmospheric sciences ,chemistry.chemical_element ,010501 environmental sciences ,Biology ,01 natural sciences ,Plant Roots ,Soil ,Human fertilization ,Mycorrhizae ,Taiga ,Environmental Chemistry ,Waste Management and Disposal ,Soil Microbiology ,0105 earth and related environmental sciences ,Ecological niche ,Rhizosphere ,Community structure ,Fungi ,Pollution ,Nitrogen ,Agronomy ,chemistry ,Fertilization ,Soil horizon ,Species richness - Abstract
Nitrogen (N) fertilization is a routine practice in boreal forests but its effects on fungal functional guilds in Pinus sylvestris forests are still incompletely understood. Sampling is often restricted to the upper organic horizons and based on DNA extracted from mixtures of soil and roots without explicitly analysing different spatial niches. Fungal community structure in soil and roots of an 85-y-old Pinus sylvestris forest was investigated using high throughput sequencing. Fertilized plots had been treated with a single dose of N fertilizer, 15 months prior to sampling. Species richness of fungi colonizing roots was reduced in all horizons by N fertilization. In contrast, species richness of soil fungi in the organic horizon was increased by N fertilization, but unaffected in the mineral horizons. Community composition of fungi colonizing roots differed from that of soil fungi, and both communities were significantly influenced by soil horizon and N. The ectomycorrhizal community composition in both roots and soil was significantly affected by N fertilization but no significant effect was found on saprotrophic fungi. The results highlight the importance of analysing the rhizosphere soil and root compartments separately since the fungal communities in these two niches appear to respond differently to environmental perturbations involving the addition of nitrogen.
- Published
- 2020
15. Tailoring residual stresses in CrNx films on alumina and silicon deposited by high-power impulse magnetron sputtering
- Author
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Tomas Kubart, Robin Elo, and Staffan Jacobson
- Subjects
Materials science ,Silicon ,Chromium nitride ,Residual stress ,chemistry.chemical_element ,02 engineering and technology ,01 natural sciences ,010305 fluids & plasmas ,chemistry.chemical_compound ,Sputtering ,Materialteknik ,0103 physical sciences ,Ultimate tensile strength ,Materials Chemistry ,Annan elektroteknik och elektronik ,Composite material ,Scratch resistance ,computer.programming_language ,Other Electrical Engineering, Electronic Engineering, Information Engineering ,HiPIMS ,Surfaces and Interfaces ,General Chemistry ,Materials Engineering ,Sputter deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry ,Scratch ,High-power impulse magnetron sputtering ,0210 nano-technology ,computer ,Magnetron sputtering - Abstract
Chromium nitride films, deposited using reactive magnetron sputtering, were optimised for wear resistance. The performance was measured by scratch resistance and optimised by tailoring the residual stresses. The depositions were carried out with either direct current magnetron sputtering (DCMS) or high-power impulse magnetron sputtering (HiPIMS), and with varying substrate bias and nitrogen gas flow. With DCMS, all films remained under tensile stresses and exhibited poor performance in scratch testing. Although the tensile stresses could be reduced by increasing the nitrogen flow, compressive stresses could only be induced when employing HiPIMS. Substrate bias had a strong effect in HiPIMS in contrast to the DCMS. The effect of the substrate bias in HiPIMS can be explained by the high ionisation of the flux of film forming species. In all cases, increased nitrogen flow favoured formation of CrN over Cr2N. All films showed signs of limited adhesion, which was improved using a titanium interlayer. Cracking across the scratch could be completely avoided for films with lower tensile or compressive stresses, the latter also exhibiting the highest critical load. The results show that it is possible to increase the scratch resistance by tailoring the residual stresses, for which HiPIMS proved a very useful tool.
- Published
- 2020
16. Long-term effects on soil-water nitrogen and pH of clearcutting and simulated disc trenching of previously nitrogen-fertilised pine plots
- Author
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Hans-Örjan Nohrstedt, Staffan Jacobson, Lars Högbom, Gunnar Jansson, and Eva Ring
- Subjects
040101 forestry ,Clearcutting ,Global and Planetary Change ,Ecology ,chemistry.chemical_element ,Forestry ,04 agricultural and veterinary sciences ,010501 environmental sciences ,01 natural sciences ,Nitrogen ,chemistry ,Boreal ,Soil pH ,Environmental chemistry ,Soil water ,0401 agriculture, forestry, and fisheries ,Environmental science ,Soil solution ,Leaching (agriculture) ,0105 earth and related environmental sciences - Abstract
Forest fertilisation with nitrogen (N) typically increases N leaching for 1–2 years. Some studies have reported effects also after clearcutting. This study presents an analysis of soil-water chemistry data from the 3rd to the 15th year after clearcutting of fertilised experimental plots on a low-fertility site in Sweden. Before clearcutting in 1987, study plots had been fertilised with NH4NO3 in 1967, 1974, and 1981, resulting in total applications ranging from 0 to 1800 kg N·ha−1. In 1989, disc trenching was simulated by manual digging on small subplots within the fertilised main plots. Soil-water samples were collected at a depth of 50 cm. Previous N fertilisation and site preparation, respectively, affected (p < 0.05) the total N and NO3–-N concentrations and pH of soil water, but no statistical interaction between fertilisation and site preparation was found. The NO3–-N concentration was elevated for total N applications above 720 kg·ha−1 (mean NO3–-N concentration of 0.93 mg·L−1 for 1080 kg N·ha−1, 1.6 mg·L−1 for 1440 kg N·ha−1, and 2.4 mg·L−1 for 1800 kg N·ha−1 compared with 0.20 mg·L−1 for the control) and lower after simulated disc trenching (0.63 mg·L−1) than in nontrenched soil (1.3 mg·L−1). The elevations in the soil-water NO3–-N concentration for the fertiliser treatments seemed to be related to changes in the soil N store created by previous fertilisation.
- Published
- 2018
17. Initial surface failure and wear of cemented carbides in sliding contact with different rock types
- Author
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Mikael Olsson, Jannica Heinrichs, Staffan Jacobson, and Bjarne Almqvist
- Subjects
Materials science ,020502 materials ,technology, industry, and agriculture ,02 engineering and technology ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Carbide ,020303 mechanical engineering & transports ,0205 materials engineering ,0203 mechanical engineering ,Mechanics of Materials ,Sliding contact ,Materials Chemistry ,Cemented carbide ,Cylinder ,Rock types ,Composite material ,Deformation (engineering) - Abstract
The initial wear, deformation and degradation of cemented carbide in contact with different rock types are studied using a crossed cylinder sliding test. The sliding distance is limited to centimet ...
- Published
- 2018
18. Clonal variation in root suckering ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.)
- Author
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Staffan Jacobson and Lars Rytter
- Subjects
Biomass (ecology) ,010504 meteorology & atmospheric sciences ,Thinning ,020209 energy ,Forestry ,02 engineering and technology ,Natural regeneration ,Biology ,01 natural sciences ,Horticulture ,Basal shoot ,Productivity (ecology) ,parasitic diseases ,0202 electrical engineering, electronic engineering, information engineering ,Sucker ,0105 earth and related environmental sciences ,Sprouting - Abstract
Current information on the root sucker ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is in most cases based on clone mixtures. In this study, we could separate the performance among clones by using two experimental sites with monoclonal plots of the crossing. The natural regeneration was followed for 2 years after harvest of the formerly planted stands, clear-cut at 22 and 25 years of age, respectively. We found that clonal differences were present in the number of root suckers produced per area unit and their biomass production. However, all included clones produced sufficiently many root suckers for a successful regeneration. To receive a more complete evaluation of the root sucker dynamics for future selection on the clonal level, further studies are needed where vitality, self-thinning and effects of thinning measures are coupled to the goal of the aspen forestry.
- Published
- 2018
19. Grease-lubricated tribological contacts – Influence of graphite, graphene oxide and reduced graphene oxide as lubricating additives in lithium complex (LiX)- and polypropylene (PP)-thickened greases
- Author
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Staffan Jacobson, Johan Leckner, Åsa Kassman Rudolphi, René Westbroek, and Elin Larsson
- Subjects
Materials science ,Friction ,Base oil ,Oxide ,Fretting ,law.invention ,chemistry.chemical_compound ,law ,Grease ,Materials Chemistry ,Additive ,Graphite ,Composite material ,Graphene oxide ,Graphene ,Electrical contacts ,Surfaces and Interfaces ,Tribology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry ,Mechanics of Materials ,4-ball tests ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) - Abstract
Two types of thickener systems, lithium complex (LiX) and polypropylene (PP), were chosen to evaluate graphite, graphene oxide (GO) and reduced graphene oxide (rGO) as grease additives at a concentration of 0.1 wt%. To enhance the additive dispersibility, a mixture of polyalphaolefin oil (PAO) and oil soluble synthetic polyalkylene glycol (OSP-68) was used as base oil. The greases were evaluated in i) silver-coated copper contacts simulating high-load electrical contact applications subjected to fretting and ii) a steel/steel 4-ball wear test equipment. The additives showed no positive effect on friction and wear, neither in fretting nor in 4-ball tests. However, there is a statistically significant difference in wear scar diameter on the 4-ball steel contacts between the two thickener types, LiX and PP. Thus, the PP-grease lubricated steel contacts showed more wear and more tribofilms of iron oxide and grease constituents, indicating more metal-to-metal contact. Hence, the thickener type has a larger impact on the lubricating performance of the grease than do the graphite, GO and rGO additions. The results demonstrate that the addition of graphene-based materials to improve greases is not straightforward. Rather, the grease/graphene-based additive system is complex and many parameters influence the friction and wear results. Hence, more work is needed to obtain a better understanding and possibly better lubricating effects from the graphene-based additives.
- Published
- 2021
20. Surface texturing to promote formation of protective tribofilms on combustion engine valves
- Author
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Staffan Jacobson, Robin Elo, and Jannica Heinrichs
- Subjects
Surface (mathematics) ,Materials science ,Scanning electron microscope ,Mechanical Engineering ,02 engineering and technology ,Surfaces and Interfaces ,Surface finish ,Tribology ,021001 nanoscience & nanotechnology ,Combustion ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Composite material ,0210 nano-technology - Abstract
In a combustion engine, the valve system controls the flow of gases in to and out of the combustion chamber. The contacting surfaces experience a harsh tribological situation with high temperatures, high speed impacts, corrosive environment and high closing forces causing micro sliding in the interface. The components have to endure in the range of hundreds of millions to a billion operational cycles, resulting in extreme demands on low wear rate. Such low wear rates can be accomplished by the protective action from tribofilms forming from oil residues, avoiding a pure metal-to-metal contact. Such tribofilms are found on well-functioning engine valves from a variety of engines, but some stationary gas engines experience problems with wear occurring seemingly randomly at normal running conditions. For some reason, the tribofilm has not protected the surfaces sufficiently, causing wear. One way to combat the random behaviour could be to promote robust function of the protective tribofilms by texturing the valve sealing surfaces to improve the capture and storage of oil residues. By stabilising the supply in this way, the damage from periods with low access to tribofilm forming material could be reduced. The present work demonstrates that turning of the valve seat inserts, creating valleys perpendicular to the sliding motion, can be developed into a useful solution. The amount and localisation of tribofilms became more predictable and stable than without the texture, leading to reduced component wear. The valleys should not be too wide, since this increased the amount of exposed metal if the tribofilm flaked off. When having the same width, the deeper valleys showed less flaking off of the tribofilm.
- Published
- 2017
21. Correction: Long-term effects on soil-water nitrogen and pH of clearcutting and simulated disc trenching of previously nitrogen-fertilised pine plots
- Author
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Eva Ring, Lars Högbom, Staffan Jacobson, Gunnar Jansson, and Hans-Örjan Nohrstedt
- Subjects
Global and Planetary Change ,Ecology ,Forestry - Published
- 2021
22. Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact
- Author
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Staffan Jacobson, Toshiharu Aiso, Manabu Kubota, and Urban Wiklund
- Subjects
Work (thermodynamics) ,Materials science ,Carbon steel ,Alloy ,Metallurgy ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Cracking ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Coating ,Machining ,chemistry ,Mechanics of Materials ,Materials Chemistry ,engineering ,0210 nano-technology ,Tin - 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.
- Published
- 2017
23. Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling
- Author
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Karin Yvell, Jannica Heinrichs, Mikael Olsson, M. Bengtsson, and Staffan Jacobson
- Subjects
Materials science ,Drill ,020502 materials ,Metallurgy ,Drilling ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,Condensed Matter Physics ,Microstructure ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0205 materials engineering ,0203 mechanical engineering ,Iron ore ,Mechanics of Materials ,Materials Chemistry ,engineering ,Cemented carbide ,Degradation (geology) - Abstract
The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock mat ...
- Published
- 2017
24. Recovery of crown transparency and stem growth of Pinus sylvestris after infestation by Gremmeniella abietina
- Author
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Staffan Jacobson, Ulf Sikström, and Folke Pettersson
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,biology ,Crown (botany) ,Scots pine ,Outbreak ,Forestry ,Management, Monitoring, Policy and Law ,biology.organism_classification ,medicine.disease_cause ,01 natural sciences ,Horticulture ,Boreal ,Botany ,Infestation ,medicine ,Silviculture ,010606 plant biology & botany ,0105 earth and related environmental sciences ,Nature and Landscape Conservation ,Scleroderris canker ,Woody plant - Abstract
In Sweden, in the year 2000, an outbreak of the fungus Gremmeniella abietina (Lagerb.) Morelet resulted in varying severities of defoliation of mainly 30–50 year old Scots pine (Pinus sylvestris L.) stands. The main aims of this study were to investigate the recovery of the trees at permanent sample plots up to 13 years after the infestation, in terms of crown transparency (CT) and stem growth, as well as to draft recommendations for silvicultural practices in boreal Scots pine forests attacked by G. abietina. In the five infested stands monitored, the total mortality averaged 506 trees ha−1 (44%) and 8.9 m2 ha−1 (37%). Most of the mortality occurred within two years of the attack. Over the final 8-year period, the mortality was at a similar level to the reference stands. Infested Scots pine trees, still living 13 years after the infestation, had recovered at this final assessment in terms of CT and showed similar CT levels as the trees in reference stands lacking obvious infestation. The stem growth of individual trees with a low initial CT ( 40%, and the reduction lasted 2–8 years, depending on the initial CT, after which the growth increased compared to reference trees. The most damaged small trees (CT > 80%, diameter
- Published
- 2017
25. Boric acid as a lubricating fuel additive – Simplified lab experiments to understand fuel consumption reduction in field test
- Author
-
Staffan Jacobson, Elin Larsson, and Petra Olander
- Subjects
Materials science ,Metallurgy ,02 engineering and technology ,Surfaces and Interfaces ,Field tests ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Pulp and paper industry ,Surfaces, Coatings and Films ,Boric acid ,Reduction (complexity) ,Diesel fuel ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Mechanics of Materials ,Materials Chemistry ,Fuel efficiency ,0210 nano-technology - Abstract
In field tests, a boric acid based fuel additive has led to reduced fuel consumption. The reduction was substantial, an average of 6 and 10% in passenger cars and diesel generators respectively. Ai ...
- Published
- 2017
26. Life time of cemented carbide inserts with Ni-Fe binder in steel turning
- Author
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Susanne Norgren, Staffan Jacobson, and Lisa Toller
- Subjects
Materials science ,020502 materials ,Metallurgy ,Life time ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Carbide ,0205 materials engineering ,chemistry ,Mechanics of Materials ,Materials Chemistry ,Cemented carbide ,0210 nano-technology ,Cobalt - Abstract
Health concerns associated with cobalt powder are a strong motivator for conducting research on alternative binders for cemented carbides. It has previously been shown possible to make cemented car ...
- Published
- 2017
27. Initial deformation and wear of cemented carbides in rock drilling as examined by a sliding wear test
- Author
-
Jannica Heinrichs, Mikael Olsson, and Staffan Jacobson
- Subjects
Toughness ,Materials science ,020502 materials ,Metallurgy ,Drilling ,02 engineering and technology ,Deformation (meteorology) ,Crusher ,Carbide ,Wear resistance ,020303 mechanical engineering & transports ,0205 materials engineering ,0203 mechanical engineering ,Sliding wear - Abstract
Due to a combination of high hardness and toughness, resulting in excellent wear resistance, cemented carbides are commonly used as the rock crushing component in rock drilling. The present paper p ...
- Published
- 2017
28. Wear protective capacity of tribofilms formed on combustion engine valves with different surface textures
- Author
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Jannica Heinrichs, Staffan Jacobson, and Robin Elo
- Subjects
Protective capacity ,Materials science ,Metallurgy ,Flow (psychology) ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Combustion ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,Materials Chemistry ,Combustion chamber ,0210 nano-technology - Abstract
The valve system controls the flow of gases into and out of the cylinders of combustion engines. As the combustion chamber is repeatedly filled with air and emptied from combustion residues, the co ...
- Published
- 2017
29. Effects of whole-tree harvest on soil-water chemistry at five conifer sites in Sweden
- Author
-
Eva Ring, Lars Högbom, Gunnar Jansson, and Staffan Jacobson
- Subjects
Clearcutting ,Global and Planetary Change ,010504 meteorology & atmospheric sciences ,Ecology ,Soil nutrients ,Logging ,Forestry ,010501 environmental sciences ,01 natural sciences ,Agronomy ,Bioenergy ,Biofuel ,Soil water ,Water quality ,Leaching (agriculture) ,0105 earth and related environmental sciences - Abstract
Logging residues, such as tops and branches, can provide a useful biofuel for large-scale energy production. However, increasing the harvest intensity may affect the soil nutrient stores and water quality. Here, effects on soil-water chemistry after stem-only and whole-tree harvesting were investigated using data from five experimental sites in Sweden, representing medium- to high-fertility sites. They were located in recharge areas on mineral soil and harvested between the years 1995 and 2001. Soil-water samples had previously been collected from below the main part of the root zone in study plots subjected to stem-only or whole-tree harvest. Soil-water chemistry data from the five sites were jointly analyzed by ANOVA using seasonal mean concentrations from the first six seasons after clear-cutting. The concentrations of NO3–-N, K+, and Mg2+were significantly different (p < 0.05) between the two harvest regimes, indicating lower levels after whole-tree harvest than after stem-only harvest. No significant differences were detected for electrical conductivity, pH, or the concentrations of NH4+-N, Al, Ca2+, SO42–-S, and Cl–. Measurements at one site suggested that the logging residues left on the ground increased the influx of Cl–to the soil. Simple budget calculations indicated that the nutrient export by logging-residue harvest was greater than the export by leaching during the regeneration phase.
- Published
- 2017
30. Effect of Si and Al additions to carbon steel on material transfer and coating damage mechanism in turning with CVD coated tools
- Author
-
Staffan Jacobson, Toshiharu Aiso, Urban Wiklund, and Manabu Kubota
- Subjects
Materials science ,Carbon steel ,Metallurgy ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Coating ,Machining ,Mechanics of Materials ,Materials Chemistry ,engineering ,0210 nano-technology ,Material transfer - 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 coa ...
- Published
- 2016
31. Wear of uncoated and PVD coated cemented carbide tools for processing of copper based materials part II: Exploring the sliding contact with pure copper
- Author
-
Urban Wiklund, Jannica Heinrichs, Staffan Jacobson, and Hiroko Mikado
- Subjects
Materials science ,Scanning electron microscope ,Alloy ,Test rig ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,Cemented carbide ,0203 mechanical engineering ,Materials Chemistry ,Surface roughness ,Sliding ,Tool wear ,Cu ,Metallurgy ,Shearing ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Copper ,Surfaces, Coatings and Films ,Shear (sheet metal) ,020303 mechanical engineering & transports ,chemistry ,Mechanics of Materials ,Sliding contact ,PVD coating ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,engineering ,0210 nano-technology - Abstract
Cemented carbide tools are successfully used to shear Cu alloy wire into zipper elements in the zipper industry. However, wear of the tools is the limiting factor for the production rate and the industry would benefit from more wear resistant tools. Previous investigations have indicated that the wear is tribochemical, and to investigate the role of Zn in commonly used Cu alloy testing is repeated against pure Cu in this work. The tool material used is a cemented carbide, in uncoated, CrC coated and CrN coated versions. The tests are performed in a simplified sliding test rig, combined with intermittent scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis. The tools are gradually worn and Cu is adhered and transferred to all tool surfaces. This process results in a pattern consisting of ridges and valleys on uncoated cemented carbide and CrC. Both are worn significantly faster than CrN, where much of the original surface roughness still remains after the full test. These worn surfaces are similar to the corresponding surfaces worn against the previously tested Cu–Zn alloy. However, the wear rate is dramatically higher in the pure Cu tests.
- Published
- 2021
32. Effects of intensive biomass harvesting on forest soils in the Nordic countries and the UK: A meta-analysis
- Author
-
Teresa G. Bárcena, Lars Vesterdal, Dagnija Lazdina, Helena Marta Stefánsdóttir, Inge Stupak, O. Janne Kjønaas, Kęstutis Armolaitis, Lars Pødenphant Kiær, Nicholas Clarke, Leena Finér, Staffan Jacobson, and Bjarni D. Sigurdsson
- Subjects
0106 biological sciences ,Forest floor ,Topsoil ,Nitrogen ,Soil organic carbon ,Soil organic matter ,Forestry ,Soil classification ,Nutrients ,Soil carbon ,Metaanalysis ,Management, Monitoring, Policy and Law ,Whole-tree harvesting ,010603 evolutionary biology ,01 natural sciences ,Stem-only harvesting ,Animal science ,Soil pH ,Cation-exchange capacity ,Environmental science ,Subsoil ,010606 plant biology & botany ,Nature and Landscape Conservation - Abstract
The use of biomass from forest harvesting residues or stumps for bioenergy has been increasing in the northern European region in the last decade. The present analysis is a regional review from Nordic and UK coniferous forests, focusing on the effects of whole-tree harvesting (WTH) or whole-tree thinning (WTT) and of WTH followed by stump removal (WTH + S) on the forest floor and mineral soil, and includes a wider array of chemistry data than other existing meta-analyses. All intensified treaments led to significant decreases of soil organic carbon (SOC) stock and total N stock in the forest floor (FF), but relative responses compared with stem-only harvesting were less consistent in the topsoil (TS) and no effects were detected in the subsoil (SS). Exchangeable P was reduced in the FF and TS both after WTT and WTH, but significant changes in exchangeable Ca, K, Mg and Zn depended on soil layer and treatment. WTH significantly lowered pH and base saturation (BS) in the FF, but without apparent changes in cation exchange capacity (CEC). The only significant WTH-effects in the SS were reductions in CEC and BS. Spruce- and pine-dominated stands had comparable negative relative responses in the FF for most elements measured except Mg and for pH. Relative responses to intensified harvesting scaled positively with growing season temperature and precipitation for most variables, most strongly in FF, less in the TS, but almost never in the SS, but were negative for P and Al. The greater reduction in FF and TS for soil organic carbon after intensive harvesting decreased with time and meta-regression models predicted an average duration of 20–30 years, while many other chemical parameters generally showed linear effects for 30–45 years after intensified harvesting. Exchangeable acidity (EA), BS and pH all showed the reversed effect with time, i.e. an initial increase and then gradual decrease over 24–45 years. The subsoil never showed a significant temporal effect. Our results generally support greater reductions in nutrient concentrations, SOC and total N in forest soil after WTH compared with SOH in northern temperate and boreal forest ecosystems.
- Published
- 2021
33. Wear of uncoated and PVD coated cemented carbide tools for processing of copper based materials part I: Lab test verification in dry and lubricated sliding
- Author
-
Jannica Heinrichs, Urban Wiklund, Staffan Jacobson, and H. Mikado
- Subjects
Materials science ,Zipper ,Scanning electron microscope ,Alloy ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,Cylinder (engine) ,law.invention ,0203 mechanical engineering ,law ,Materials Chemistry ,Tool wear ,Composite material ,Shearing (manufacturing) ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Copper ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,chemistry ,Mechanics of Materials ,Cemented carbide ,engineering ,0210 nano-technology - Abstract
In the manufacturing of metal zippers, including several complicated forming and shearing process steps, the tool wear is a limiting factor, since it deteriorates the quality of the zipper elements. Hence, an increased understanding of the tool wear mechanisms occurring in the zipper production is important to prolong the tool life. To gain deeper insights into the tool wear mechanisms active in the process of shearing Cu alloy wire into separate zipper elements, the present study utilizes a simplified sliding test rig. The rig comprises a small tool material cylinder sliding against a large rotating work material cylinder, in a crossed cylinders configuration. One uncoated and two PVD-coated cemented carbide cylinders were tested under contact conditions similar to those of the actual shearing. The tool material cylinder was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) at selected intervals during the test. The surface appearance was investigated and compared with observations on tools used in actual zipper production. The degradation was found to include gradual wear against the Cu alloy, transfer of the Cu alloy and characteristic modifications of the topography, indicative of wear mechanisms operating at a very small scale, confirming that the wear of the shearing tools can be mimicked by the test.
- Published
- 2020
34. Diverse mechanisms of friction induced self-organisation into a low-friction material – An overview of WS2 tribofilm formation
- Author
-
Fredrik Gustavsson and Staffan Jacobson
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Tungsten disulfide ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Low friction ,engineering.material ,Tungsten ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Coating ,chemistry ,Self organisation ,Mechanics of Materials ,Molybdenum ,engineering ,Shear strength ,Composite material ,0210 nano-technology ,Hard substrate - Abstract
A clever way to accomplish low friction in sliding contacts is to use materials that combine high hardness with low shear strength. Such seemingly paradoxical combination of high resistance and low resistance to plastic deformation can only be realized by combining a hard substrate material with a thin easy-shear coating. Some prominent such coating candidates are sulfides and selenides of mainly molybdenum and tungsten. This paper focuses on tungsten disulfide, WS 2 , and explores the many routes to formation and regeneration of such low-friction tribofilms. The initial surfaces involve various types of coatings, materials and fluids, including W and S in different states, but none of which include crystalline WS 2 . All formation routes result in remarkably similar, pure crystalline WS 2 tribofilms.
- Published
- 2016
35. 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
- Author
-
Manabu Kubota, Staffan Jacobson, Urban Wiklund, and Toshiharu Aiso
- Subjects
Materials science ,Carbon steel ,Cutting tool ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Mechanism (engineering) ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Coating ,Mechanics of Materials ,Sliding contact ,engineering ,0210 nano-technology ,Tin ,Material transfer - 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 hi ...
- Published
- 2016
36. Investigation of material transfer in sliding friction-topography or surface chemistry?
- Author
-
Staffan Jacobson, Jannica Heinrichs, Viktoria Westlund, and Mikael Olsson
- Subjects
Surface (mathematics) ,Topography ,Materials science ,02 engineering and technology ,engineering.material ,Coating ,0203 mechanical engineering ,Materialteknik ,Composite material ,Sliding ,Chemical composition ,Mechanical Engineering ,Metallurgy ,Materials Engineering ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Transfer ,020303 mechanical engineering & transports ,Sliding contact ,Mechanics of Materials ,engineering ,0210 nano-technology ,Material transfer - Abstract
To differentiate between the roles of surface topography and chemical composition on influencing friction and transfer in sliding contact, a series of tests were performed in situ in an SEM. The initial sliding during metal forming was investigated, using an aluminum tip representing the work material, put into sliding contact with a polished flat tool material. Both DLC-coated and uncoated tool steel was used. By varying the final polishing step of the tool material, different surface topographies were obtained.The study demonstrates the strong influence from nano topography of an unpolished DLC coated surface on both coefficient of friction and material transfer. The influence of tool surface chemistry is also discussed.
- Published
- 2016
- Full Text
- View/download PDF
37. The distribution of logging residues and its impact on seedling establishment and early plant growth in two Norway spruce stands
- Author
-
Eva Ring, Staffan Jacobson, Lars Högbom, and Hans-Örjan Nohrstedt
- Subjects
040101 forestry ,Clearcutting ,Plant growth ,Logging ,Sowing ,Forestry ,Picea abies ,04 agricultural and veterinary sciences ,Biology ,biology.organism_classification ,Agronomy ,Seedling ,Botany ,040103 agronomy & agriculture ,Total removal ,0401 agriculture, forestry, and fisheries ,Decreased growth - Abstract
In Fennoscandia, logging residues (LR) are increasingly being harvested to provide fuel for renewable energy. However, the removal of LR is thought to lead to decreased growth in the next generation of trees. The effect on tree growth has generally been obtained by comparing the total removal of residues with retained residues spread evenly on the ground. With current clear-cutting practices, residues can be left with different spatial distributions, confounding the effects of residue removal. Field experiments were, therefore, established at two Norway spruce sites, comprising six treatments with varying distributions and volumes of residues. Before planting seedlings, the sites were disc-trenched. At one of the sites, seedling survival was significantly lower when all residues were removed immediately. At both sites, after 10 years there were statistically significant growth losses after removal of residues. There were no differences in plant growth if the residues were concentrated in small hea...
- Published
- 2016
38. Effect of Si and Cr additions to carbon steel on material transfer in a steel/TiN coated tool sliding contact
- Author
-
Staffan Jacobson, Manabu Kubota, Toshiharu Aiso, and Urban Wiklund
- Subjects
chemistry.chemical_classification ,0209 industrial biotechnology ,Materials science ,Base (chemistry) ,Carbon steel ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,engineering.material ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,Coating ,Machining ,chemistry ,Mechanics of Materials ,Sliding contact ,engineering ,Tin ,Layer (electronics) ,Material transfer - 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.
- Published
- 2016
39. Insights into sliding wear and friction behavior of copper in ethanol containing alkylphosphonic acid molecules
- Author
-
Mikael Olsson, Jean-Marie Melot, Fabrice Lallemand, Staffan Jacobson, X. Roizard, A. Et Taouil, and Jannica Heinrichs
- Subjects
Work (thermodynamics) ,Materials science ,Ethanol ,Mechanical Engineering ,Metallurgy ,Friction modifier ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Low friction ,021001 nanoscience & nanotechnology ,Copper ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Mechanics of Materials ,Molecule ,0210 nano-technology ,Sliding wear - Abstract
In this work, the friction and wear behavior of bare copper was investigated for the first time under lubricated sliding conditions in diluted ethanol solutions of butylhosphonic (C4P), octylphosph ...
- Published
- 2016
40. Deep cryogenic treatment of tool steels
- Author
-
V. Leskovsek, I. Paulin, Staffan Jacobson, Bojan Podgornik, and B. Zajec
- Subjects
Materials science ,Vanadium ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,Industrial and Manufacturing Engineering ,Fracture toughness ,0203 mechanical engineering ,Composite material ,fungi ,Metallurgy ,Abrasive ,technology, industry, and agriculture ,Metals and Alloys ,Tribology ,021001 nanoscience & nanotechnology ,Computer Science Applications ,Wear resistance ,020303 mechanical engineering & transports ,chemistry ,Modeling and Simulation ,Tool steel ,Ceramics and Composites ,engineering ,Cryogenic treatment ,0210 nano-technology ,Carbon - Abstract
The aim of our research work was to investigate the effect of deep cryogenic treatment on fracture toughness, wear resistance and load-carrying capacity of cold work tool steel and to determine the effectiveness of deep cryogenic treatment depending on the tool steel type and chemical composition. The type and chemical composition of the tool steel considerably affect the way how deep cryogenic treatment changes mechanical, tribological and load-carrying capacity of the tool steel. For lower carbon and higher W and Co containing cold work tool steel properties can be improved for up to 70%, but are very limited in the case of high-speed steel. At high carbon and vanadium contents properties of cold work tool steels can even be deteriorated after deep cryogenic treatment. In terms of abrasive wear resistance and load-carrying capacity increasing the hardness is the most decisive factor.
- Published
- 2016
41. Surface degradation of cemented carbides in scratching contact with granite and diamond–The roles of microstructure and composition
- Author
-
Jannica Heinrichs, Mikael Olsson, and Staffan Jacobson
- Subjects
Toughness ,Materials science ,Metallurgy ,Diamond ,Surfaces and Interfaces ,Scratching ,engineering.material ,Condensed Matter Physics ,Microstructure ,Surfaces, Coatings and Films ,Carbide ,Metal ,Mechanics of Materials ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,engineering ,Degradation (geology) ,Deformation (engineering) - Abstract
Cemented carbides are composite materials comprising metal carbide grains in a more ductile metallic binder. This microstructure results in a combination of high hardness and toughness, making them ...
- Published
- 2015
42. Influence of cemented carbide binder type on wear initiation in rock drilling – Investigated in sliding wear against magnetite rock
- Author
-
Karin Yvell, Staffan Jacobson, Jannica Heinrichs, Susanne Norgren, and Mikael Olsson
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Metallurgy ,Cemented carbide ,Drilling ,Crusher ,Magnetite ,Carbide ,Sliding wear - Abstract
Cemented carbides, containing hard WC grains in a ductile Co binder, are commonly used as the rock crushing part of rock drills. They generally work well and show moderate and gradual wear in rock ...
- Published
- 2019
43. On the Role of Material Transfer in Friction Between Metals: Initial Phenomena and Effects of Roughness and Boundary Lubrication in Sliding Between Aluminium and Tool Steels
- Author
-
Viktoria Westlund, Staffan Jacobson, and Jannica Heinrichs
- Subjects
Materials science ,Friction ,Material transfer ,chemistry.chemical_element ,02 engineering and technology ,Surface finish ,engineering.material ,0203 mechanical engineering ,Aluminium ,Lubrication ,Surface roughness ,Lubricant ,Composite material ,Mechanical Engineering ,Friction fundamentals ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Thermal conduction ,Roughness ,Surfaces, Coatings and Films ,020303 mechanical engineering & transports ,chemistry ,Mechanics of Materials ,Tribology (Interacting Surfaces including Friction, Lubrication and Wear) ,Tool steel ,Tribologi (ytteknik omfattande friktion, nötning och smörjning) ,engineering ,0210 nano-technology ,Boundary lubrication - Abstract
In the absence of a lubricant, the friction we measure in sliding contact between metals is typically high and quite erratic, with rapid fluctuations. If we filter out these rapid fluctuations, we can typically also notice slower trends, which can lead to quite dramatic friction changes. Unless careful studies are performed, the cause to this behaviour cannot be understood. How come a material couple cannot be characterised with a specific coefficient of friction? The present paper sets out to add understanding to this area, by conduction and analysing an experimental series involving sliding between a needle-like aluminium tip against tool steel flats. The load is high enough to cause substantial plastic deformation of the aluminium needle; its tip becomes formed by the contact against the tool steel. These small-scale, low sliding distance tests facilitate detailed studies of the initial stages of various friction trends, and the effects of initial surface roughness and shifts of this roughness caused by material transfer between the sliding surfaces. Specifically, the effects on the transfer and friction behaviour from presence or absence of a boundary lubricant film and atmospheric oxygen were studied. It was found that very smooth sliding surfaces can offer low-friction conditions for these metal types. However, the smooth sliding interface is very fragile. In all unlubricated cases tested, it very rapidly (in less than a few mm sliding) became ruined due to transfer, and the friction level correspondingly increased. The boundary lubricant could only offer low friction in cases where the flat steel surface was very smooth. The lubricant also facilitated smoothening of transferred aluminium. As long has been well known, boundary lubrication films typically do not totally hinder direct metallic contact in solid to solid contact. The present results strengthen this view and further suggests that in these direct contacts one of the major friction reducing effects of the lubricant is to efficiently limit transfer, which otherwise acts to make the sliding surface rough.
- Published
- 2018
44. Friction behavior of ferritic stainless steel in a strongly diluted alcohol solution of alkylphosphonic acid
- Author
-
Jean‐Marie Melot, A. Buteri, Fabrice Lallemand, Luc Carpentier, Staffan Jacobson, Jannica Heinrichs, X. Roizard, M. Borgeot, Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), Tribomaterials Group, The Angström Laboratory (Uppsala University), Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Université de Franche-Comté (UFC), and Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)
- Subjects
Materials science ,Mechanical Engineering ,Industrial scale ,Metallurgy ,Alcohol ,02 engineering and technology ,Surfaces and Interfaces ,[PHYS.MECA]Physics [physics]/Mechanics [physics] ,Low friction ,021001 nanoscience & nanotechnology ,Environmentally friendly ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,020303 mechanical engineering & transports ,0203 mechanical engineering ,chemistry ,Mechanics of Materials ,Lubrication ,[CHIM]Chemical Sciences ,0210 nano-technology - Abstract
International audience; The present study investigates the potential for using this more environmentally friendly lubrication at an industrial scale forming of stainless steel. Against this background we analyze the characteristics of the tribofilm formed on a stainless steel surface during sliding experiments performed in solutions containing alkylphosphonic acids, under various contact conditions.Specific tribological tests were designed to analyze the dynamics of the lubricating mechanism. It was found that both the grafting of molecules and the transformation of these into an efficient tribofilm are quick processes, irrespective of substrate roughness or contact pressure, systematically leading to low friction coefficient.
- Published
- 2018
45. Initial degradation of cemented carbides for rock drilling — Model studies of the tribological contact against rock
- Author
-
Mikael Olsson, Jannica Heinrichs, Staffan Jacobson, and Karin Yvell
- Subjects
Fracture toughness ,Materials science ,Composite number ,Metallurgy ,Cemented carbide ,Slip (materials science) ,Tribology ,Microstructure ,Carbide ,Electron backscatter diffraction - Abstract
Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling.
- Published
- 2015
46. Impact of fracture toughness on surface properties of PVD coated cold work tool steel
- Author
-
Bojan Podgornik, Miha Čekada, Staffan Jacobson, B. Zajec, and Marko Sedlaček
- Subjects
Materials science ,chemistry.chemical_element ,Surfaces and Interfaces ,General Chemistry ,Nitride ,engineering.material ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Substrate (building) ,Brittleness ,Fracture toughness ,Coating ,chemistry ,Tool steel ,Materials Chemistry ,engineering ,Cryogenic treatment ,Composite material ,Tin - Abstract
Limited load-carrying capacity and impact loading resistance greatly restrict the use of hard coatings in forming applications, making substrate hardness and resistance crack initiation and propagation very important. Therefore, the aim of this research work was to investigate the effect of substrate fracture toughness and hardness on the load carrying capacity and impact wear resistance of coated tool steel, coated by monolayer (TiAlN), multilayer (AlTiN/TiN) and nano-composite ((Ti,Si)N) PVD coatings. By using different combinations and parameters of vacuum heat treatment and deep cryogenic treatment effect of the substrate fracture toughness and hardness on the load-carrying properties was determined under progressively loading dry sliding conditions, while ball-on-plate impact fatigue test was employed to investigate impact wear resistance. Results clearly show, that substrate hardness is the most important property influencing load-carrying capacity and impact wear resistance of the coated surface. However, with increased hardness and brittleness of the coating increase in fracture toughness although on the expense of the reduced hardness becomes beneficial.
- Published
- 2015
47. Formation and breakdown of oil residue tribofilms protecting the valves of diesel engines
- Author
-
Robin Elo and Staffan Jacobson
- Subjects
Residue (chemistry) ,Diesel fuel ,Materials science ,Mechanics of Materials ,Metallurgy ,Materials Chemistry ,Test rig ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films - Abstract
The contacting surfaces of modern valve systems experience a complex contact situation with repeated micro sliding at high temperatures and pressures. The wear rate of the surfaces has to be extrem ...
- Published
- 2015
48. Tribochemical Formation of Sulphide Tribofilms from a Ti–C–S Coating Sliding Against Different Counter Surfaces
- Author
-
Tomas Nyberg, Harald Nyberg, Staffan Jacobson, Ulf Jansson, Erik Särhammar, and Jill Sundberg
- Subjects
Solid-state chemistry ,Titanium carbide ,Materials science ,Nanocomposite ,Mechanical Engineering ,Metallurgy ,Surfaces and Interfaces ,Low friction ,Tribology ,engineering.material ,Surfaces, Coatings and Films ,Normal load ,chemistry.chemical_compound ,chemistry ,Coating ,Mechanics of Materials ,engineering ,Composite material - Abstract
Tribochemically active Ti–C–S coatings are nanocomposite coatings containing a S-doped titanium carbide, from which S can be released in a tribological contact. This work studies tribochemical reactions between a Ti–C–S coating and various counter surface materials, and their effect on the tribological performance. Tribological tests were performed in a ball-on-disc set-up, using balls of five different materials as sliding partners for the coating: 100Cr6 steel, pure W, WC, 316-L steel and Al2O3. For W balls, a WS2 tribofilm was formed, leading to low friction (down to µ = 0.06). Furthermore, increasing normal load on the W balls was found to lead to a strong decrease in µ and earlier formation of the low-friction WS2 tribofilm. Similar WS2 and MoS2 tribofilms were, however, not formed from WC- and Mo-containing 316-L balls. The performance when using WC and Al2O3 balls was significantly worse than for the two steel balls. It is suggested that this is due to sulphide formation from Fe, analogous to formation of anti-seizure tribofilms from S-containing extreme pressure additives and steel surfaces. The tribochemical activity of Ti–C–S coatings, with the possibility of S release, is thus beneficial not only for pure W counter surfaces, but also for Fe-based sliding partners.
- Published
- 2014
49. A High-Resolution TEM/EELS Study of the Effect of Doping Elements on the Sliding Mechanisms of Sputtered WS2Coatings
- Author
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Fredrik Gustavsson, Matthieu Bugnet, Albano Cavaleiro, Tomas Polcar, and Staffan Jacobson
- Subjects
Materials science ,Mechanical Engineering ,Electron energy loss spectroscopy ,Tungsten disulfide ,Doping ,chemistry.chemical_element ,Nanotechnology ,Surfaces and Interfaces ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Transmission electron microscopy ,Composite material ,High-resolution transmission electron microscopy ,Carbon ,Layer (electronics) ,Molybdenum disulfide - Abstract
It has been shown many times that cosputtering low-friction coatings of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) with other elements can improve the structural, mechanical, and tribological properties. To achieve the lowest friction, MoS2 or WS2 should be doped with element(s) improving the hardness and density of the coatings. On the other hand, such elements, or their compounds, should not be present in the outermost molecular layers at the sliding interface. This article suggests that there are important differences between how MoS2 and WS2 coatings respond to or react with doping elements, despite the almost identical structure and behavior of the undoped materials. Two systems have been investigated by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) electron energy loss spectroscopy (EELS), W-S-C-Cr and W-S-C-Ti, and showed significant amounts of oxides, which typically formed a layer just underneath the crystalline WS2 top layer. Further, carbon was a...
- Published
- 2014
50. Is tree growth in boreal coniferous stands on mineral soils affected by the addition of wood ash?
- Author
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Folke Pettersson, Sten Nordlund, Hagos Lundström, Staffan Jacobson, and Ulf Sikström
- Subjects
biology ,Soil acidification ,Taiga ,technology, industry, and agriculture ,Scots pine ,Forestry ,Soil classification ,Picea abies ,Wood ash ,biology.organism_classification ,complex mixtures ,Agronomy ,Botany ,Soil water ,Environmental science ,Woody plant - Abstract
Increasing use of forest fuels for energy production is generating greater quantities of wood ash. In Sweden, it is recommended that this ash should be returned to the forest to counter soil acidification and avoid potential future nutrient deficiencies, but the effects on tree growth require clarification. Thus, 10 field experiments were established in Sweden in 1990–2006 to study the effects of adding wood ash of various origins, doses and combinations of both ash and nitrogen on stem growth in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) stands on mineral soil. Observations after 5–15 years show that growth responses were strongest when N was added, either alone or with wood ash. Growth responses to additions of wood ash without N were small and variable and statistically insignificant at all study sites. However, there were indications that adding wood ash may increase stem-wood growth at fertile sites and decrease it at less fertile sites. Hence, at fertile sites, it may...
- Published
- 2014
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