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| 2. |
- Wu, Lisha, 1984, et al.
(författare)
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Initial DNA Interactions of the Binuclear Threading Intercalator Λ,Λ-[μ-bidppz(bipy)4Ru2]4+: An NMR Study with [d(CGCGAATTCGCG)]2
- 2013
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 19:17, s. 5401-5410
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Tidskriftsartikel (refereegranskat)abstract
- Binuclear polypyridine ruthenium compounds have been shown to slowly intercalate into DNA, following a fast initial binding on the DNA surface. For these compounds, intercalation requires threading of a bulky substituent, containing one RuII, through the DNA base-pair stack, and the accompanying DNA duplex distortions are much more severe than with intercalation of mononuclear compounds. Structural understanding of the process of intercalation may greatly gain from a characterisation of the initial interactions between binuclear RuII compounds and DNA. We report a structural NMR study on the binuclear RuII intercalator -B (-[-bidppz-(bipy)4Ru2]4+; bidppz=11,11’-bis(di-pyrido[3,2-:2’,3’-c]phenazinyl, bipy = 2,2’-bipyridine) mixed with the palindromic DNA [d(CGCGAATTCGCG)]2. Threading of -B depends on the presence and length of AT stretches in the DNA. Therefore, the latter was selected to promote initial binding, but due to the short stretch of AT base pairs, final intercalation is prevented. Structural calculations provide a model for the interaction: -B is trapped in a well-defined surface-bound state consisting of an eccentric minor-groove binding. Most of the interaction enthalpy originates from electrostatic and van der Waals contacts, whereas intermolecular hydrogen bonds may help to define a unique position of -B. Molecular dynamics simulations show that this minor-groove binding mode is stable on a nanosecond scale. To the best of our knowledge, this is the first structural study by NMR spectroscopy on a binuclear Ru compound bound to DNA. In the calculated structure, one of the positively charged Ru2+ moieties is near the central AATT region; this is favourable in view of potential intercalation as observed by optical methods for DNA with longer AT stretches. Circular dichroism (CD) spectroscopy suggests that a similar binding geometry is formed in mixtures of -B with natural calf thymus DNA. The present minor-groove binding mode is proposed to represent the initial surface interactions of binuclear RuII compounds prior to intercalation into AT-rich DNA.
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| 3. |
- Ahlström, Johan, 1969, et al.
(författare)
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3D characterisation of RCF crack networks
- 2014
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Ingår i: MATEC Web of Conferences. - : EDP Sciences. - 2261-236X. ; 12
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Konferensbidrag (refereegranskat)abstract
- Rolling contact fatigue (RCF) damage is becoming more frequent with increased traffic and loading conditions in the railway industry. Defects which are characterized by a two-lobe darkened surface and a V-shaped surface-breaking crack are often so-called squats. The origination and propagation of squats in railway rails is the topic of many recent studies; the associated crack networks develop with complicated geometry near the surface of rails that is difficult to characterise using most non-destructive methods. The cracks can be examined with repeated metallographic sectioning, but the process is time-consuming and destructive. In order to reduce time, as well as information and material loss, high-resolution and high-energy X-ray imaging of railway rails was done in the current study. Combining the exposures from a range of angles using image analysis, a 3D representation of the complex crack network is achieved. The latter was complemented with metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction.
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| 4. |
- Bennich-Björkman, Li, 1960-, et al.
(författare)
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Dags för Lemne att lämna
- 2015
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Ingår i: Upsala Nya Tidning. ; march 13
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 5. |
- Brommesson, Rebecka, 1985, et al.
(författare)
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Experimental observations and modelling of cyclic and relaxation behaviour of the Ni-based superalloy Haynes 282
- 2016
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 87, s. 180-191
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier Ltd. In this paper, the high temperature cyclic and relaxation behaviour of Ni-based superalloy Haynes 282 is investigated. Low-cycle fatigue (LCF) tests with and without hold time have been performed at two elevated temperatures, 650 and 730 °C. The test results are presented and analysed with respect to the cyclic behaviour and the stress relaxation behaviour. Based on this analysis, a Chaboche type of elasto-viscoplastic material model is formulated and calibrated with respect to the cyclic experimental data. Furthermore, the effect of the scatter, observed in the initial yield stresses of the LCF tests, is considered in the calibration of the material model. Finally, a Golos-Ellyin strain energy density fatigue criterion is used to predict the fatigue life and how the scatter in the LCF tests influences the predicted fatigue lives is studied. Moreover, to account for the reduction in fatigue life due to stress relaxation, a frequency modification of the Golos-Ellyin fatigue criterion is proposed and evaluated.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- Cvetkovski, Krste, 1983, et al.
(författare)
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Subsurface crack networks and RCF surface cracks in pearlitic railway wheels
- 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. 425-431
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Konferensbidrag (refereegranskat)abstract
- Subsurface cracks developed by rolling contact fatigue (RCF) are both a lifetime limiting factor for railway wheels and a safety issue. In the current study a severe subsurface crack network has been studied and compared to RCF cracks on the surface. Microstructural characteristics, determination of local chemical compositions with Auger electron spectroscopy and microhardness within cracks and around crack faces were examined. Both damage types showed similar crack growth characteristics, with small cracks branching from the main cracks. Continuous third body material resembling wear particles were identified in many cracks. The analyses showed that this material does not originate from external contamination or oxide inclusions but is produced by shear deformation and wear within crack faces by mode II and III crack growth. The third body material showed a higher hardness than the surrounding base material indicating a high shear deformation and work hardening. While microstructural appearance at lower magnification appeared different to the bulk material, high magnification revealed that the third body material mainly consisted of deformed flakes of base material, wear and oxide particles. Auger electron spectroscopy confirmed the theory that the third body consists of several layers of deformed metallic flakes covered with thin oxide layers indicated by the variation in oxygen content.
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| 9. |
- Dalaei, Kamellia, 1975, et al.
(författare)
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Stability of Residual Stresses Created by Shot Peening in Monotonic Loading and at the Presence of Load Reversals - Experiments and Modeling
- 2012
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Ingår i: Journal of Engineering Materials and Technology, Transactions of the ASME. - : ASME International. - 1528-8889 .- 0094-4289. ; 134:2, s. 021010-
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Tidskriftsartikel (refereegranskat)abstract
- As a method for mechanical surface treatment, shot peening has been widely used to improve the fatigue strength of materials. However, the influence of residual stresses introduced by shot peening depends on their stability. The stability of residual stresses during fatigue may be studied in two stages: the first cycle and successive cyclic loading. In this study the stability and development of the residual stresses during the first cycle of strain controlled fatigue of normalized steel was investigated. The influence of total strain amplitude and the loading direction was studied. The residual stresses were obtained using the x-ray diffraction technique. It was shown that the stability and relaxation of the residual stresses depend both on the amount and the direction of the loading stresses. Finite element modeling (FEM) was used to rationalize the experimental data. Very good agreement between the experimental and FEM results were observed
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| 10. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(författare)
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Dynamic strain aging in Haynes 282 superalloy
- 2014
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Ingår i: MATEC Web of Conferences. - : EDP Sciences. - 2261-236X. ; 14, s. Art. no. 16002-
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Konferensbidrag (refereegranskat)abstract
- Haynes 282 is a newly introduced Ni-based superalloy, developed to provide a combination of high-temperature mechanical properties, thermal stability and processability. The present contribution investigates the effect of dynamic strain aging (DSA) on the deformation behaviour of Haynes 282 during monotonic and cyclic loading. It is shown that DSA (presumably related to carbon diffusion based on rough estimates of the activation energy) completely dominates the development of the stress during cycling at intermediate temperatures, leading to extensive cyclic hardening and serrated yielding. However, no clear effects on the fatigue life or the resulting dislocation structure could be observed. The tensile properties were not severely affected, in spite of the presence of extensive serrated yielding, although a reduction in ductility was observed in the DSA temperature regime. During monotonic loading at lower strain rates indications of an additional DSA mechanism due to substitutional elements were observed.
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