| 1. |
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| 2. |
- Fomalont, E. B., et al.
(författare)
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THE 2014 ALMA LONG BASELINE CAMPAIGN: AN OVERVIEW
- 2015
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 808:1
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Tidskriftsartikel (refereegranskat)abstract
- A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to similar to 15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at similar to 350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.
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| 3. |
- LARIJANI, NASIM, 1983, et al.
(författare)
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The effect of anisotropy on crack propagation in pearlitic rail steel
- 2012
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Ingår i: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012; Chengdu; China; 27 August 2012 through 30 August 2012. ; , s. 432-441
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Konferensbidrag (refereegranskat)abstract
- One of the main sources of damage caused by Rolling Contact Fatigue (RCF) in railway components are the large plastic deformations that accumulate in the surface layer under rolling contact loading. Large irreversible deformations in components made of pearlitic steel induce anisotropy in mechanical properties of the material in the surface layer. In the present work the influence of the anisotropic layer on propagation of cracks in rail head is investigated. Based on the concept of material forces, a computational framework for simulation of propagation of planar cracks is formulated where the propagation rate is linked to a crack-driving force. An anisotropic fracture surface model is employed to capture the effect of changes in the resistance against crack propagation in different directions and depths in the surface layer. Results of simulations for cases with different characteristics in the surface layer show that the anisotropic layer has a substantial influence on the crack path.
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| 4. |
- LARIJANI, NASIM, 1983, et al.
(författare)
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The effect of anisotropy on crack propagation in pearlitic rail steel
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 57-68
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Tidskriftsartikel (refereegranskat)abstract
- One of the main sources of damage %caused by Rolling Contact Fatigue (RCF)in railway components is the large plastic deformations that accumulate in the surface layer under rolling contact loading. Large irreversible deformations in components made of pearlitic steel induce anisotropy in mechanical properties of the material in the surface layer. In the present work the influence of the anisotropic layer on propagation of cracks in rail head is investigated. Based on the concept of material forces, a computational framework for simulation of propagation of planar cracks is formulated where the propagation rate is linked to a crack-driving force. An anisotropic fracture surface model is employed to capture the effect of changes in the resistance against crack propagation in different directions and depths in the surface layer. Results of simulations for cases with different characteristics in the surface layer show that the anisotropic layer has a substantial influence on the crack path.
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| 5. |
- Lindfeldt, Erik, 1982, et al.
(författare)
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Using DIC to Identify Microscale Strain Fields from in-situ SEM Images of a Pearlitic Steel
- 2014
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Ingår i: Experimental Mechanics. - : Springer Science and Business Media LLC. - 1741-2765 .- 0014-4851. ; 54:9, s. 1503-1513
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Tidskriftsartikel (refereegranskat)abstract
- Digital Image Correlation (DIC) is used to analyze in-situ obtained SEM images of a pearlitic steel. Rather than using a synthetic speckle the microstructure of the material (cementite lamellae embedded in a ferrite matrix) is used as a natural speckle. The impact of the DIC method parameters on the identified motion (displacements and strains) is studied and it is shown that the method is robust, in the sense of being insensitive to the subset size, when it comes to determining the local subset displacements. However, a sufficiently large subset size is required in order for the local subset strains to converge.
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| 6. |
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| 7. |
- Schilke, Martin, 1980
(författare)
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Comparability of Railway Rail Steels Low Cycle Fatigue Behaviour
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several different kinds of steel are used for railway rails. From simple pearlitic steels for rarely used tracks over premium pearlitic steels for high performance lines to special bainitic, martensitic and austenitic steels for switches and crossings. Most of these steels have been trial and error developed over time in track. The main reasons for replacement of rails are fatigue and wear. For material selection purposes fatigue properties must be taken into account. Simple fatigue testing methods that allow comparison of different steels are scarce in literature.In this thesis results from low cycle fatigue test of four different steels are compiled and a comparison based on strain energy density is presented. The steels are all used for railway rail application. One is near fully pearlitic steel which is mainly employed in common track. The other three are used for different parts in switches and crossings. It is one carbide free bainitic steel, one high manganese austenitic steel and a martensitic steel. Results show the martensitic and bainitic steel as the superior steels at low strain ranges (
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| 8. |
- Schilke, Martin, 1980
(författare)
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Degradation of railway rails from a materials point of view
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- From time to time railway rails need to be replaced. In that case and when new track is built, a decision has to be made about which rail grade that is going to be installed. The intention of this work was to compare different rail steels concerning their suitability from a mechanical durability perspective. The most common steel types used for rails are presented as well as the most common damages that occur as part of the degradation process. The rail-wheel contact is the primary source for damages. Two types of damages were studied in detail, white etching layers (WEL) and rolling contact fatigue (RCF) cracks.The WEL that was investigated originates from a metro rail with heavy traffic. It can be shown, that the WEL is more brittle than the pearlitic base material of the rail. Also, evidence can be provided for a type of crack that is exclusive to WEL in rails. This crack type is perpendicular to the surface of the rail and can initiate or be connected to other cracks in the base material. Retained austenite measurements in the WEL prove that the microstructure was produced under the influence of high temperatures and suggests that there is martensite present.Rolling contact fatigue cracks from field samples and from test rig samples were investigated. Three-dimensional images were produced. Interaction between the plastically deformed microstructure and cracks could be shown as well as shielding of cracks by other cracks or their own branches.When determining which rail grade is best suited, a holistic view must be adopted, including all relevant influencing factors, such as traffic, track geometry, maintenance regime and climate. The problem of rail degradation cannot be solved by material choice alone.
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| 9. |
- Schilke, Martin, 1980, et al.
(författare)
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Interaction between cracks and microstructure in three dimensions for rolling contact fatigue in railway rails
- 2014
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Ingår i: Fatigue and Fracture of Engineering Materials and Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 37:3, s. 280-289
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Tidskriftsartikel (refereegranskat)abstract
- The rail–wheel contact generates plastic deformation and cracks in the top layer of a rail. Rolling contact fatigue (RCF) cracks in rail samples from track and from a full scale test rig were examined. Due to the shear forces arising in the wheel rail contact, the microstructure close to the surface becomes aligned in the shear direction. Thereby, the pearlite becomes anisotropic, and resistance to cracks is lower in certain directions. RCF cracks follow the weakest direction of the microstructure, which in pearlitic railway rails is the aligned pearlite structure or singular weaknesses such as pro-eutectoid ferritesor slags. The deformation of the microstructure is different depending on loading situation and original microstructure (rail grade). Once the plastic deformation is present, the cracks follow the path of the weakest crack resistance. Cracks close to each other can interact or shield each other; it is unclear, however, to what extent. In this paper, a new method is described that allows the presentation of RCF cracks in three dimensions.
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| 10. |
- Schilke, Martin, 1980, et al.
(författare)
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Low cycle fatigue and deformation behaviour of austenitic manganese steel in rolled and as-cast conditions
- 2010
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Ingår i: Procedia Engineering: 10th International Fatigue Congress, FATIGUE 2010; Prague; Czech Republic; 6 June 2010 through 11 June 2010. - : Elsevier BV. - 1877-7058. ; 2:1, s. 623-628
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Konferensbidrag (refereegranskat)abstract
- This paper presents a characterisation of two austenitic manganese (~12-13 wt%) rail steels, one in rolled (Mn13(R)) and the other in as-cast (Mn13(C)) condition. Cyclic and monotonic behaviour as well as hardness and microstructure have been investigated. The results do not show any major difference between the materials, but comparison with literature reveals large differences compared to pearlitic and bainitic rail steels. The manganese steels are softer initially and harden during cyclic and monotonic loading.
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| 11. |
- Schilke, Martin, 1980, et al.
(författare)
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White etching layers on the Stockholm local traffic network
- 2012
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Ingår i: Proceedings 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems. ; , s. 589-596
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Konferensbidrag (refereegranskat)abstract
- Top layers of railway rails are subjected to microstructural changes sometimes resulting in white etching layers. These thin layers are more brittle than the base material and show increased cracking and spalling. For the present study pearlitic rail samples from curves without corrugation from the Stockholm local traffic network (SL) have been investigated concerning their influence on the crack initiation and crack propagation into the base material. Samples with white etching layers were subjected to tensile loads. The white etching layers and crack surfaces were examined with light and scanning electron microscope. White etching layers with a thickness of 200µm were found. It can be concluded that they consist mostly of martensite with a hardness two to three times higher than the base material. Cracks growing through the white etching layer initiating cracks in the pearlite have been found. Also, the crack sensitivity is higher for the white etching layer as compared to the base material and it creates initiation points for cracks in the pearlitic part of the rail.
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| 12. |
- Torstensson, Peter, 1981, et al.
(författare)
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Rail corrugation growth on small radius curves—Measurements and validation of a numerical prediction model
- 2013
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 303:1-2, s. 381-396
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Tidskriftsartikel (refereegranskat)abstract
- The development of low rail corrugation (rutting corrugation) on a 120 m radius curve on the Stockholm metro is studied by field measurements, laboratory measurements and numerical simulations. The corrugation develops exclusively on the low rail with wavelengths of about 5 cm and 8 cm. It is concluded by field measurements that the application of friction modification effectively mitigates the corrugation growth on the curve. For the low rail, high levels of lateral acceleration and plastic material flow in the surface layer orientated towards the field side indicate large magnitude lateral creep forces generated by the curving vehicles. A time-domain model for prediction of roughness growth on small radius curves is applied to obtain an improved understanding of the wheel rail interaction leading to rutting corrugation. The model is validated by comparison of predicted long-term rail roughness growth against measured data, and it is concluded that the corrugation is generated by the low rail contact of the leading wheelset of passing bogies. The corrugation wavelengths observed on the curve are related to excitation of the first symmetric and first antisymmetric bending eigenmodes of the leading wheelsets. Important parameters for the identified wavelength-fixing mechanisms are investigated.
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