a b s t r a c tTorrefaction process of wood residue was tested at 230 C, 260 C and 290 C temperatures under 0.5 h, 1.0 h and 1.5 h time in an electrical furnace. The studied material was characterised in terms of its proximate and ultimate analysis. HHV before and after torrefaction was calculated. The behaviour of raw and torrefied biomass was moreover investigated by thermogravimetric analysis, (TG, DTG) and the structural shrinkage was studied by SEM, too. It was found that the most efficient carbonising process among the tested samples is the process operated under 260 C and 1.0 h time of heating. The results confirmed the great advantages of torrefied material (charcoal) in contrast to raw biomass. Torrefied biomass has been processed successfully, because torrefied biomass has a higher calorific value and energy density, a lower O/C ratio and moisture content, and is easier to grind and has hydrophobic character. The difference in energy yields has shown lower values at the higher torrefaction temperatures.
This research programme evaluates the as welded properties of Al 7136-T76511 extrusions joined through friction stir welding (FSW). Microstructural characterisation and mechanical testing were performed on the baseline material and on panels friction stir welded at 250 and 350 rev min 21 (all other weld parameters held constant). Transmission electron microscopy revealed the microstructural features in each of the unique weld regions and demonstrated that the precipitate density and morphology in these regions correlates with the temperature profile produced by the FSW process. A thermal model of FSW is developed that utilises an energy based scaling factor to account for tool slip. The slip factor is derived from an empirical relationship between the ratio of the maximum welding temperature to the solidus temperature and energy per unit length of weld. The thermal model successfully predicts the maximum welding temperatures and profiles over a range of energy levels. The mechanical behaviour after welding is correlated to the temperature distribution predicted by the model and to the observed microstructural characteristics. As welded mechanical properties of the alloy trended positively with the energy per unit length of weld, i.e. the highest joint efficiency was achieved at the highest welding temperature.
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