This effort demonstrates the development of a novel, graphene oxide nanoscale thermite composite with thermally tunable microwave ignitability. A model thermite system containing nanoscale aluminum and nanoscale iron(II) oxide in a stoichiometric ratio (30/70 wt %) was combined with sheets of graphene oxide (GO) or reduced graphene oxide (rGO) using an immiscible two-fluid sonication and tape casting process. The samples were microwave irradiated within a singlemode resonant microwave cavity to determine the microwave ignition delay. Neat thermites were found to ignite after 4.34 s of microwave illumination, whereas 30 wt % rGO thermite composite ignition delay was an order of magnitude shorter (0.43 s). For most samples (4 of 6 trials), it was found that application of a 30 wt % GO coating inhibits microwave ignition of the thermite. Thermal treatment of the GO thermite composite led to switching of thermites from unignitable to ignitable with microwave field application as short as 0.24 s due to GO reduction. Optimum heat treatment time and GO content are explored with SEM, DSC/TGA-MS, Raman, and XPS deconvolution. This effort demonstrates the use of GO and rGO addition to achieve thermally switchable microwave ignitability to electromagnetically shield or enhance nanoscale energetic ignition by microwave energy.
The effects of considering thermal transport in weld modelling of residual stress and distortion are evaluated by performing a thermal transport analysis first to compute the temperature history which is then used as loading in a conventional elastoplastic analysis to compute the residual stress. A gas metal arc welding (GMAW) and a hybrid GMAW/laser welding case are used as examples. For each weld, residual stresses are computed once assuming conductive heat transfer only and once assuming convective (thermal transport) heat transfer. For GMAW welding, both heat conduction and thermal transport analyses produced similar temperature, residual stress and distortion results, indicating that heat conduction modelling with the double ellipsoid model may be sufficient for modelling GMAW. For hybrid welding, the heat conduction and thermal transport analyses produced different temperature histories and distortion results, demonstrating the need for including thermal transport effects in modelling keyhole welding. However, the residual stress results were in close agreement, suggesting that heat conduction analyses may be sufficiently accurate for computing residual stress even in keyhole welding.
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