| 1. |
- Ahlfors, Ulf, et al.
(författare)
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Overload control strategies in a multiprocessor system with distributed data
- 1995
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Ingår i: Proceedings of the 5th IEE Conference on Telecommunications, Brighton, UK, March 1995. - 0852966342 ; , s. 145-149
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Konferensbidrag (refereegranskat)abstract
- This paper addresses overload control issues for distributed control systems, i.e. multiprocessor systems, in telephone exchanges, signalling transfer points, service control points, home location registers, etc. Three different strategies for rejecting calls, due to severe overload conditions, are examined. The strategies differ in that they allow call rejection during different time epochs of the entire life time of the call. The optimal solution, i.e. the largest throughput, can only be obtained by a centrally placed overload control mechanism which collects data from all processors in the system
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| 2. |
- Johansson, Daniel, et al.
(författare)
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Shock front curvature measurements of emulsion explosives
- 2019
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Ingår i: Tenth EFEE World Conferenceon Explosives and Blasting. - : European Federation of Explosives Engineers. - 9780955029066 ; , s. 409-416
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Konferensbidrag (refereegranskat)abstract
- This paper will discuss a suggested methodology and data collection carried out within the EU-project SLIM (Sustainable Low Impact solution for exploitation of small Mineral deposits based on advanced rock blasting and environmental technologies). The field work took place during 2017 at a test site near Stockholm, Sweden. This paper suggests a method to measure the detonation front curvature and the velocity of detonation of explosives. The purpose for this is to increase the understanding of the detonation properties of emulsion explosives as used in many blasting operations around the world. In this study, the key parameters of the performance of the emulsion explosive are its non-ideal detonation front curvature and its velocity of detonation (VOD). The charge diameters have been varied Ø25 mm up to Ø65 mm i.e. from nearly critical diameters for a steady detonation up to diameters used in mining/quarrying and tunnelling. The suggested methodology also introduces a heavy and thick-walled mortar as a confiner for the explosive. This to simulate similar conditions as in blasting in rock. Additional to the proposed methodology and set-up, a scheme to analyse and evaluate the measurements is also proposed.
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| 3. |
- Nyberg, Harald, et al.
(författare)
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Extreme friction reductions during inital running-in of W-S-C-Ti low-friction coatings
- 2013
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Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 302:1-2 SI, s. 987-997
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Tidskriftsartikel (refereegranskat)abstract
- The disulphides of tungsten and molybdenum are known for their low friction properties when used as solid lubricants. Due to their low hardness, their load bearing capacity when used as thin films is poor. When carbon is added to a WS2 coating, both of these shortcomings are improved, and a structure consisting of nanocrystals of WS2, and possibly tungsten carbide, in a matrix of amorphous carbon is formed. In this study, an attempt is made for further increasing the hardness of such coatings, by addition of Ti, a strong carbide former. A number of W–S–C(–Ti) coatings were deposited using magnetron co-sputtering, and characterised with regard to chemical composition, structure and tribological properties. It was seen that addition of Ti significantly increased the hardness of the coatings, while maintaining their excellent low friction properties in dry atmosphere. However, the coatings with Ti showed extremely high initial friction, a feature not seen for the coatings without Ti. The mechanisms behind this running-in behaviour were investigated by studying surfaces at early stages of wear. It was observed that tribofilms formed during sliding for the coatings containing Ti consisted mainly of TiO2, with platelets of WS2 appearing in the contact only after prolonged sliding. For the pure W–S–C coatings, WS2 was observed in the sliding interface almost instantly at the onset of sliding.
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| 4. |
- Nyberg, Harald, et al.
(författare)
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Tribochemical formation of sulphide tribofilms from a Ti-C-S coating sliding against different counter surfaces
- 2014
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Ingår i: Tribology letters. - : Springer Science+Business Media B.V.. - 1023-8883 .- 1573-2711. ; 56:3, s. 563-572
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Tidskriftsartikel (refereegranskat)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 A mu = 0.06). Furthermore, increasing normal load on the W balls was found to lead to a strong decrease in A mu 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.
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| 5. |
- Petropoulos, Nikolaos, et al.
(författare)
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A Method to Measure Detonation Front Curvature of Emulsion Explosives
- 2020
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Konferensbidrag (refereegranskat)abstract
- The optimization of the explosive performance is of great importance since blasting is extensively usedin civil projects and mining industry. An improved understanding of how the energy from thedetonation of an explosive is transmitted to the surrounding rock mass is critical information for theproper selection of an explosive. Therefore, an extensive study was done on the influence of theblasthole diameter on the Velocity of Detonation (VoD) and the detonation front curvature. In thisstudy, pure emulsion was tested in confined conditions to better simulate the behavior of the detonationof the explosive in rock mass conditions. A methodology is proposed for carrying out the evaluationof the explosive performance. The blasthole diameter of the samples varied from Ø 25 mm (0.98 in)up to Ø 65 mm (2.55 in). The confiner was a magnetic mortar cylindrical sample with mechanicalproperties similar to a rock mass. A streak camera and VoD probes were used to measure detonationfront curvature and VoD. The data was analyzed and correlated with the physical parameters of theexplosive. Additional to this, the data was further used to calibrate numerical models in LS-Dyna.
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| 6. |
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| 8. |
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| 9. |
- Sundberg, Jill, 1986-, et al.
(författare)
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Influence of composition, structure and testing atmosphere on the tribological performance of W-S-N coatings
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 258, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- W-S-N coatings deposited by reactive magnetron sputtering offer the possibility of ultra-low friction in unlubricated sliding. In this work, W-S-N coatings of different composition and structure have been deposited, characterised and evaluated with respect to the tribological performance and tribofilm formation. The composition was varied by changing the flow of N-2 into the deposition chamber, leading to N contents ranging from 0 to 47 at.%. W-S-N coatings deposited without substrate heating are amorphous, while substrate heating results in coatings containing nanocystalline tungsten sulphide (WSx) for low N contents, and nanocrystalline tungsten nitride (WyN) at a high N content. The coatings were tribologically tested against steel balls in four different atmospheres dry N-2, dry air, humid N-2 and humid air to study the effects of atmospheric O-2 and H2O both separately and simultaneously. In dry N-2, all coatings exhibited an excellent performance with very low friction (mu approximate to 0.02) and wear. Notably, this included the N-richest and hardest coating, containing nanocrystalline WyN and only 13 at.% of S. The friction and wear increased on changing the atmosphere, in the order of dry air-humid N-2-humid air. In these three non-inert atmospheres, the friction and wear also increased with increasing N content of the coating. It is thus concluded that the presence of O-2, the presence of H2O, and a high N content (i.e., low Wand S contents) are three factors increasing the risk of high friction and wear, especially when occurring together. Raman spectroscopy mapping of the contact surfaces on the coatings and the balls showed that low friction and wear is connected to the presence of WS2 tribofilms in the contact, and that the three previously mentioned factors affect the formation and function of this tribofilm.
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| 10. |
- Sundberg, Jill, et al.
(författare)
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Influence of Ti addition on the structure and properties of low-friction W–S–C coatings
- 2013
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 232, s. 340-348
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal dichalcogenides, such as WS2 and MoS2, are known for their layered structure and lubricating properties. When deposited as thin coatings, however, their use as solid lubricants is limited by their low hardness and load-bearing capacity. The addition of another element, such as carbon, can improve the mechanical properties, although the hardness of for example W-S-C coatings is still rather low. In this work, Ti has been added to W-S-C coatings in order to further increase the hardness by carbide formation. W-S-C and W-S-C-Ti coatings were deposited by non-reactive magnetron sputtering, and characterized with regard to composition, structure and mechanical and tribological properties. It was found that the addition of Ti leads to the formation of a new carbide phase, and a significant increase in hardness for coatings with moderate carbon contents. The friction properties of W-S-C-Ti coatings were found to be comparable to that of W-S-C coatings, with friction coefficients down to mu approximate to 0.02 and similar wear rates against steel in a dry atmosphere. Formation of WS2 in the wear track of W-S-C-Ti was confirmed by transmission electron microscopy. It has thus been shown that the addition of Ti to W-S-C coatings can increase the hardness, while still maintaining WS2 lubrication.
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