| 1. |
- Akhlaghi, Shahin, et al.
(författare)
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Deterioration of acrylonitrile butadiene rubber in rapeseed biodiesel
- 2015
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 111, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- The deterioration of acrylonitrile butadiene rubber (NBR) exposed to rapeseed biodiesel at 90 degrees C was studied. The oxidation of biodiesel and NBR during ageing was monitored by H-1 NMR and infrared spectroscopy, HPLC and titration methods. The oxidation of biodiesel was impeded in the presence of NBR, but promoted in biodiesel-exposed rubber. This was explained as being due to the migration of stabilizer from the rubber to biodiesel, the diffusion of dissolved oxygen from biodiesel into NBR and the absorption of oxidation precursors of biodiesel by the rubber. The resemblance between the anomalous sorption kinetics of biodiesel in NBR and the equilibrium benzene uptake by the aged rubbers revealed that biodiesel caused a network defect in NBR, resulting in a gradual increase in the equilibrium swelling. The cleavage of crosslinks was implausible since the Young's modulus of the rubber at low strains, disregarding an initial decrease, increased with increasing exposure time. The appearance of 'naked' carbon black particles in the scanning electron micrographs of the aged rubbers and a drastic decrease in the strain-at-break of NBR after exposure to biodiesel suggests that internal cavitation was caused by the attack of biodiesel on the acrylonitrile units of NBR.
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| 2. |
- Zamiri Akhlaghi, Farshid, 1975, et al.
(författare)
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Welding simulation of tubular k-joints in steel s690qh
- 2015
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Ingår i: Proceedings of the 15th International Symposium on Tubular Structures, ISTS 2015; Rio de Janeiro; Brazil; 27 May 2015 through 29 May 2015. - : CRC Press. - 9781138028371 ; , s. 481-488
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Konferensbidrag (refereegranskat)abstract
- Residual stress state in planar tubular K-joints, in the chord within the gap region between the two braces, is studied using numerical weld modelling. The motivation comes from past full-scale fatigue tests on tubular trusses made of various steel grades with sizes typical of bridge trusses, which shows that the cracking occurs at the hot spots located in this region. Residual stress field characterization is needed in order to assess its role in fatigue cracking, especially for the case of cracks occurring on the compression brace side. Comparison between residual stress field in a Y-joint and a K-joint is made to assess the significance of restraining effect in the gap region. Phase transformations during welding and cooling down are determined and their impact on the final residual stress state is evaluated. Computed residual stresses are compared to the neutron diffraction measurements. Transient thermal field and cooling times substantially affect phase transformations. Therefore, their accurate reproduction in the analysis is important.
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