In the present paper, an attempt has been made to link friction stir welding (FSW) process control and response variables. Substantial similarities among the relationships between torque, nugget grain size, x axis force and tool rotation rate have been elucidated for three different aluminium alloys. Comparison of the experimental work to results from process simulation indicates that in each case a temperature limit is reached above some critical value of tool rotation rate. A simple method of estimating the strain and strain rate in friction stir welds is presented. The flow stress during FSW is calculated from measured torque values and analysed with respect to aluminium alloy flow stresses measured in standard, high temperature torsion and tensile tests. Results indicate that perhaps either sticking friction conditions are not always applicable during FSW (on all or part of the tool) or that, above a critical tool rotation rate, intermittently lubricated contact is present due to local melting in the weld process zone.

Angle-resolved, photofragment translational energy distributions, Pϑ(ET)s, arising from 308 nm laser irradiation of CH3Br adsorbed on Pt(111) are presented. Methyl photofragments were observed with translational energies extending to 2 eV and with Pϑ(ET)s which varied sharply with angle of exit from the surface. The fragmentation dynamics were consistent with a mechanism of dissociative electron attachment of subvacuum level, photoexcited substrate electrons to adsorbed CH3Br. The CH3 Pϑ(ET)s and the angular variation of the CH3 yield gave evidence that submonolayers of CH3Br form islands on Pt(111).

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The photoinduced dissociative electron attachment of CH3Br on Pt(111) has been examined by measuring CH3 photofragment translational energy distributions from CH3Br adsorbed on Xe multilayers deposited upon CH3Br covered Pt(111). Subvacuum level, photoexcited substrate electrons produced by 308 nm laser irradiation were found to propagate through the Xe layer where attachment to CH3Br led to fragmentation. A simple model for surface dissociative electron attachment, DEA, was found to quantitatively predict the observed fragmentation dynamics for the CH3Br/Xe/CH3Br/Pt(111) system. The role of the local work function in surface DEA processes was explored by examining the dependence of the photofragment yield upon the thickness of the intermediate Xe layer and the fractional coverage of the Pt(111) bound first layer of CH3Br. Three dimensional variation of the local work function above the substrate was required to account for the observed DEA dynamics.

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