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Browsing by Issue Date, starting with "2021-08-05"

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  • Shoulder related temperature thresholds in FSSW of aluminium alloys
    Publication . Andrade, David G.; S, SREE; Leitao, Carlos; Rodrigues, Dulce
    Friction Stir Spot Welding (FSSW) is assumed as an environment-friendly technique, suitable for the spot welding of several materials. Nevertheless, it is consensual that the temperature control during the process is not feasible, since the exact heat generation mechanisms are still unknown. In current work, the heat generation in FSSW of aluminium alloys, was assessed by producing bead-on-plate spot welds using pinless tools. Coated and uncoated tools, with varied diameters and rotational speeds, were tested. Heat treatable (AA2017, AA6082 and AA7075) and non-heat treatable (AA5083) aluminium alloys were welded to assess any possible influence of the base material properties on heat generation. A parametric analysis enabled to establish a relationship between the process parameters and the heat generation. It was found that for rotational speeds higher than 600 rpm, the main process parameter governing the heat generation is the tool diameter. For each tool diameter, a threshold in the welding temperature was identified, which is independent of the rotational speed and of the aluminium alloy being welded. It is demonstrated that, for aluminium alloys, the temperature in FSSW may be controlled using a suitable combination of rotational speed and tool dimensions. The temperature evolution with process parameters was modelled and the model predictions were found to fit satisfactorily the experimental results.
    2021-08-05Journal article Open access Show more
  • Supercritical carbon dioxide extraction, antioxidant activity, and fatty acid composition of bran oil from rice varieties cultivated in Portugal
    Publication . Pinto, Tânia I.; Coelho, Jose; Pires, Bruna I.; Neng, N.R.; Nogueira, José M.; Bordado, João; Sardinha, José P.
    Bran of different rice cultivars produced in Portugal were used to study supercritical carbon dioxide extraction conditions of rice bran oil (RBO) and evaluate and compare antioxidant activity and fatty acid composition of the different rice bran varieties. The effect of plant loading (10-20 g), CO2 flow rate (0.5-1.5 L/min), pressure (20-60 MPa), and temperature (40-80 degrees C) was studied. The amount of oil extracted ranged from 11.72%, for Ariete cultivar, to 15.60%, for Sirio cultivar. The main fatty acids components obtained were palmitic (13.37%-16.32%), oleic (44.60%-52.56%), and linoleic (29.90%-38.51%). Excellent parameters of the susceptibility to oxidation of the oils were obtained and compare. RBO of Ariete and Gladio varieties presented superior DPPH and ABTS radical scavenging activities, whereas, Minima, Ellebi, and Sirio varieties had the lowest scavenging activities. Moreover, the oil obtained towards the final stages of extraction presented increased antioxidant activity.
    2021-08-05Journal article Open access Show more