Residual stresses are an inescapable consequence of manufacturing and fabrication processes, with magnitudes that are often a high proportion of the yield or proof strength. Despite this, their incorporation into life prediction is primarily handled through sweeping assumptions or conservative application of statistics. This can lead to highly conservative fatigue design methodologies or unforeseen failures under dynamic loading. The push from the desire for higher levels of materials performance, coupled with the pull of more sophisticated techniques for residual stress measurement, favours a reassessment of the accuracy of assumptions made about residual stresses and the modification during fatigue cycling. A viewpoint is also emerging that the fatigue performance of welded joints might be optimised through careful process control, coupled with understanding of the relative positions of, and interaction between, residual stress peaks, weld defects, hardness and microstructure. This paper will present information regarding the residual stress profiles in aluminium and steel welds obtained via synchrotron and neutron diffraction at the ESRF/ILL in Grenoble. Specimens were then subjected to specific cases of fatigue loading and the residual stress field was again measured. Difficulties associated with determining the strain-free lattice spacing will be mentioned, and the import of these data for life prediction modelling will be considered.
We report the conversion of a conventional high energy ion gun into a low energy ion gun. The conversion procedure described here maintains the ion current capability of the high energy gun along with its good spatial and ion energy distribution characteristics. Several low energy ion guns have been described previously in the literature [J. T. Yates, Jr., Experimental Innovations in Surface Science (Springer-Verlag-AIP, New York, 1998), pp. 307–329] but all require the construction of new ion optics, whereas this approach utilizes existing ion optics and electronic control capabilities of a commercial ion gun. This ion gun may be employed for studies where it is desired to use ions as reactive species without significant sputter damage of the target.
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