| 1. |
- Cvetkovski, Krste, 1983, et al.
(författare)
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Analysis of wear debris in rolling contact fatigue cracks of pearlitic railway wheels
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 51-56
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Tidskriftsartikel (refereegranskat)abstract
- In the current study a severe subsurface crack network in a railway wheel has been studied and compared to typical rolling contact fatigue cracks found in the wheel tread surface. Microstructural characteristics, chemical composition and microhardness within the cracks and around crack faces were examined. While the two damage types are principally different, both showed similar crack characteristics, with short cracks branching along the main crack paths and a discontinuous sheared layer of wear debris and metallic flakes within them. Analyses of the wear debris showed that it does not originate from external contamination or being the result of corrosion primarily. Instead it has most likely been produced by shear deformation and wear mechanisms within crack faces caused by mixed-mode crack growth. Although microstructural appearance at lower magnification seemed to differ from the bulk material, at high magnification a lamellar structure was observed consisting of layers of deformed metallic flakes and particles of the base metal. Auger electron spectroscopy was used to analyze these sheared layers; higher concentration of oxygen was measured in between flakes, indicating the presence of oxides and flakes being of similar chemical composition as the base material. A possible explanation is that these layers are created due to high shear forces and friction between crack faces in the service of the wheel. With continued rolling the material being sheared by the cyclic relative motion of the crack faces disintegrates into smaller wear debris particles with concurrent oxidation.
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| 2. |
- Cvetkovski, Krste, 1983, et al.
(författare)
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Rapid thermomechanical tempering of iron–carbon martensite
- 2014
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Ingår i: Materials Science and Technology. - 1743-2847 .- 0267-0836. ; 30:14, s. 1832-1834
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Tidskriftsartikel (refereegranskat)abstract
- Tempering of martensite under simultaneous compressive stress has been studied within thetemperature range of 20–400 deg C. Resistive heating was utilised to obtain rapid heating and coolingcycles of a few seconds. Material was obtained from a medium carbon pearlitic railway wheelsteel, quench hardened to obtain martensitic structure. Above approx 150 deg C dilatation effectswere observed below the global yielding point of the material. Microstraining around dislocationsin the body centred tetragonal crystallographic structure or viscous flow at higher temperatureswas a probable explanation to this material behaviour. Hence, external stress may have animportant influence on the tempering progression of martensitic steel. The trials also showed thattempering of martensite progresses fast, is near instantaneous and is independent of thepresence of external stress or not.
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| 3. |
- 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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