| 1. |
- Fridell, Erik, 1963, et al.
(författare)
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On-board measurements of particulate matter emissions from a passenger train
- 2011
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - 0954-4097 .- 2041-3017. ; 225:1, s. 99-106
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Tidskriftsartikel (refereegranskat)abstract
- A number of measurements of particle emission from railways are presented. The measurements featured a particle instrument mounted in a compartment under a Regina train. The particles were probed in a volume between the coaches. The measurements were done in two campaigns and provide information on how the particle emissions vary with driving patterns. The measurements showed elevated particle concentrations when the train was running. Further, sharp peaks in the particle concentration were observed. It was noted that these peaks coincided with retardation of the train. However, there are also retardations where no peaks were observed. This can be explained from the two parallel breaking systems, one with regenerative breaking and one with mechanical breaks that are present on the Regina train. It is suggest that the observed peaks coincide with the use of the mechanical breaks. It was not possible to fully establish that increased particle concentration coincides with curvature of the rail, even though this was indicated in parts of the data. The size-resolved data showed maxima for the smallest fraction (350 nm) for the number distribution.
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| 2. |
- Bjarnason, Thordur, et al.
(författare)
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One-Year Follow-up After Open Abdomen Therapy With Vacuum-Assisted Wound Closure and Mesh-Mediated Fascial Traction
- 2013
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Ingår i: World Journal of Surgery. - : Springer Science and Business Media LLC. - 0364-2313 .- 1432-2323. ; 37:9, s. 2031-2038
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Tidskriftsartikel (refereegranskat)abstract
- Open abdomen (OA) therapy frequently results in a giant planned ventral hernia. Vacuum-assisted wound closure and mesh-mediated fascial traction (VAWCM) enables delayed primary fascial closure in most patients, even after prolonged OA treatment. Our aim was to study the incidence of hernia and abdominal wall discomfort 1 year after abdominal closure. A prospective multicenter cohort study of 111 patients undergoing OA/VAWCM was performed during 2006-2009. Surviving patients underwent clinical examination, computed tomography (CT), and chart review at 1 year. Incisional and parastomal hernias and abdominal wall symptoms were noted. The median age for the 70 surviving patients was 68 years, 77 % of whom were male. Indications for OA were visceral pathology (n = 40), vascular pathology (n = 22), or trauma (n = 8). Median length of OA therapy was 14 days. Among 64 survivors who had delayed primary fascial closure, 23 (36 %) had a clinically detectable hernia and another 19 (30 %) had hernias that were detected on CT (n = 18) or at laparotomy (n = 1). Symptomatic hernias were found in 14 (22 %), 7 of them underwent repair. The median hernia widths in symptomatic and asymptomatic patients were 7.3 and 4.8 cm, respectively (p = 0.031) with median areas of 81.0 and 42.9 cm(2), respectively (p = 0.025). Of 31 patients with a stoma, 18 (58 %) had a parastomal hernia. Parastomal hernia (odds ratio 8.9; 95 % confidence interval 1.2-68.8) was the only independent factor associated with an incisional hernia. Incisional hernia incidence 1 year after OA therapy with VAWCM was high. Most hernias were small and asymptomatic, unlike the giant planned ventral hernias of the past.
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| 3. |
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| 4. |
- Caprioli, Sara, 1978, et al.
(författare)
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Influence of short thermal cracks on the material behaviour of a railway wheel subjected to repeated rolling
- 2014
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Ingår i: Advanced Materials Research. - 1662-8985 .- 1022-6680. - 9783038350088 ; 891-892, s. 1139-1145
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Konferensbidrag (refereegranskat)abstract
- An analysis of whether and how the occurrence of shallow (radial) thermal cracks promotes additional plastic deformation of a mechanically loaded wheel tread is carried out. The study employs numerical simulations of a 2D slice of an elastoplastic railway wheel tread containing thermal (radial) cracks. The cracked wheel material is subjected to repeated passes of a frictional rolling contact load. The effect of the existing thermal cracks on bulk deformation and subsequent rolling contact promoted growth is quantified. Results indicate that thermal cracks of a depth of 0.1 mm have a negligible effect, whereas 1.0 mm cracks significantly decrease the bulk resistance of the wheel material. Further, it is shown how the magnitude of stress, strain and deformation depends on the direction of applied traction.
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| 5. |
- Caprioli, Sara, 1978, et al.
(författare)
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Numerical evaluation of the material response of a railway wheel under thermomechanical braking conditions
- 2012
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Ingår i: Proceedings of the 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2012). ; , s. 460-467
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Konferensbidrag (refereegranskat)abstract
- The material response of a railway wheel subjected to thermomechanical rolling contact is evaluated. Thermal and mechanical loads are combined in a three-dimensional sequentially coupled analysis where nodal temper- atures from a transient thermal analysis are applied as predefined fields in a structural analysis featuring an elastic-plastic material model. The mechanical contact load is prescribed as a moving Hertzian contact stress distribution with a surface shear stress distribution corresponding to full or partial slip conditions. Modelling aspects studied in detail are feasible model resolution at the contact patch, the influence of sequences of thermal and mechanical loads, and the influence of wheel–rail interfacial shear distributions. The study identifies fea- sible mesh sizes and load application strategies to obtain a good accuracy at reasonable computational efforts. Further, differences in predicted material response under full slip and partial slip conditions are assessed. It is found that for a given total tangential force, partial slip conditions result in larger plastic strain magnitudes in a thin layer near the contact surface.
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| 6. |
- Caprioli, Sara, 1978, et al.
(författare)
-
Numerical evaluation of the material response of a railway wheel under thermomechanical braking conditions
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 314:1-2, s. 181-188
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Tidskriftsartikel (refereegranskat)abstract
- The material response of a railway wheel subjected to thermomechanical rolling contact is evaluated. Thermal and mechanical loads are combined in a three-dimensional sequentially coupled analysis where nodal temperatures from a transient thermal analysis are applied as predefined fields in a structural analysis featuring an elastic-plastic material model. The mechanical contact load is prescribed as a moving Hertzian contact stress distribution with a surface shear stress distribution corresponding to full or partial slip conditions. Modelling aspects studied in detail are feasible model resolution at the contact patch, the influence of sequences of thermal and mechanical loads, and the influence of wheel--rail interfacial shear distributions. The study identifies feasible mesh sizes and load application strategies to obtain a good accuracy at reasonable computational efforts. Further, differences in predicted material response under full slip and partial slip conditions are assessed. It is found that for a given total tangential force, partial slip conditions result in larger plastic strain magnitudes in a thin layer near the contact surface
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| 7. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal Cracking of a Railway Wheel Tread due to Tread Braking – Critical Crack Sizes
- 2011
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Ingår i: Proceedings 2011 International Heavy Haul Association Conference. ; , s. 8-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A numerical study of tread cracking due to thermal loading induced by tread braking is carried out. The analysis features a computationally efficient approach combining 2D FE-simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects a severe drag braking due to malfunctioning brakes may cause very deep cracking. Further the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Preliminary 3D FE-simulations that have been performed indicate the presented results to be conservative.
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| 8. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal cracking of a railway wheel tread due to tread braking -- critical crack sizes and influence of repeated thermal cycles
- 2013
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 227:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study of tread cracking due to thermal loading induced by tread braking is carried out. The analysis features a computationally efficient approach combining two-dimensional finite-element simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects, a severe drag braking due to malfunctioning brakes may cause very deep cracking. Furthermore, the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Additional three-dimensional finite-element simulations are used to validate the model, and they indicate two-dimensional results to be on the conservative side.
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| 9. |
- Caprioli, Sara, 1978, et al.
(författare)
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Thermal cracking of a railway wheel tread due to tread braking – critical crack sizes and influence of repeated thermal cycles
- 2011
-
Ingår i: International Heavy Haul Association Special Technical Session (IHHA STS 2011). ; , s. 8-
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Konferensbidrag (refereegranskat)abstract
- A numerical study of tread cracking due to thermal loading induced by block braking is carried out. The analysis features a computationally efficient approach combining 2D FE-simulations with an analytical evaluation of resulting stress intensity factors. The analysis identifies critical sizes for when existing surface cracks are prone to propagate under thermal loading and resulting crack lengths after propagation. The results imply that fully functional brake systems are not likely to induce thermal crack propagation under normal stop braking, but that with pre-existing defects a severe drag braking due to malfunctioning brakes may cause very deep cracking. Further the analysis concludes the cracking to be a static phenomenon related to the most severe brake cycle, i.e. later brake cycles of similar or lower severity will not cause any significant propagation of existing cracks. Finally it should be noted that preliminary FE-simulations that have been performed indicate the presented results to be conservative.
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| 10. |
- Caprioli, Sara, 1978, et al.
(författare)
-
THERMO-MECHANICAL CRACKING OF RAILWAY WHEEL
- 2011
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Ingår i: Proceedings for Svenska mekanikdagar 2011. ; , s. 1-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Thermo-mechanical wheel tread damages are common in railway wheels. While the damagemagnitude is limited this is a rather benign phenomenon. However under harsher operationalconditions (winter conditions, poorly tuned damping/suspension, poorly matched wheel–railcontact profiles etc) the extent of the problem may increase dramatically and lead to epidemicsof wheel damages. Since this calls for wheel re-profiling, the result may be extensiveoperational disturbances.The presentation deals with thermo-mechanical damage. In practice one of the failuremodes, thermal cracking or rolling contact fatigue, usually dominates. However, it is mostlikely that the combined thermal and rolling contact loading will have an influence in increasingthe resulting damage as compared to both phenomena acting separately.In the literature there are a multitude of studies on both thermal and rolling contactloading. analyses of the combined load case are however scarce. One major reason for this isthat a combined loading makes a simplification to 2D very cumbersome (not to say futile).Here, a numerical study of the impact of simultaneous thermal and mechanical loading on arailway wheel tread as imposed by braking and rolling contact is presented. 3D finite element(FE) simulations of the thermo-mechanical problem featuring a material model which accountsfor thermal expansion and plastic deformations are carried out. Both pure rolling and tractiverolling are considered. The results indicate a significant influence of the thermal loading onthe resulting stress/strain response also in cases of relatively moderate temperature increases.In particular, a combination of thermal loading and high traction rolling is found to be verydetrimental.The resulting damage of the wheel tread is manifested by the formation of small surfacecracks. In cases of high thermal loading, these cracks will evolve to deep radial cracks thatcan, in a worst-case scenario, cause catastrophic wheel failures. Since this is a potential safetyproblem it is important to understand the driving mechanisms behind these cracks.To this end, a numerical study of thermal cracking of a wheel subjected to high thermalloading was carried out. The analysis features a computationally efficient approach where2D FE stress analysis owing to thermal loading during braking and subsequent cooling iscombined with an analytical evaluation of resulting stress intensity factors of a radially orientedsurface crack in the wheel tread. The analysis identifies critical sizes for when existingsurface cracks are prone to propagate under thermal loading and resulting crack lengths afterpropagation. The results imply that fully functional brake systems are not likely to inducethermal crack propagation under normal stop braking, but that with pre-existing defects asevere drag braking due to malfunctioning brakes may cause very deep cracking. Further theanalysis concludes the thermal cracking to be a (more or less) static phenomenon related tothe most severe brake cycle. In other words: later brake cycles of similar or lower severitywill not cause any significant propagation of existing cracks. To further validate the analysisof the semi-analytical analysis, preliminary 3D FE-simulations have been performed.
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