Browsing by Author "Prask, HJ"

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    Neutron residual stress measurements in rails
    (Taylor & Francis, 2013-07-09) Luzin, V; Prask, HJ; Gnaëpel-Herold, T; Gordon, J; Wexler, D; Rathod, C; Pal, S; Daniel, W; Atrens, A
    Rails were among the first objects of study by neutron diffraction strain measurement and the first experiments were done as early as the late 1980s [1, 2]. This interest is easy to explain: the problem of rail fracturing is critical from the public safety point of view and the penetrating ability of neutrons suggested the possibility of breakthrough experiments and fast progress in this field. It was well-established that residual stresses, both near-surface and interior, played a signifi cant role in the development of defects which led to rail failure. This suggested three distinct approaches of neutron diffraction strain measurement that could contribute to various problems of the rail industry. The first method was to map the complete triaxial stress distribution non-destructively in the interior of an intact rail, ideally before and after significant service. Another approach was to use slices, for example to characterize how different processing methods produce favourable or detrimental stress distributions in rails. A third technique was to make non-destructive measurements, but in critical and not very deep portions of rails, for example, to examine defects and their relation to rail failure in the top running surface of rails, e.g. "white layer" formation. © 2013, Taylor & Francis.
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    Use of neutron diffraction for stress measurements in thin and thick thermal sprayed coatings
    (Maney Publishing, 2010-03-01) Luzin, V; Prask, HJ; Gnaëpel-Herold, T; Sampath, S
    Thermal spraying is a widely used and cost effective technique for the surface protection of engineering components. The spectrum of applications is vast: corrosion protection, wear resistance and abrasion resistance, thermal barriers, electrical (dielectric) coatings, etc. Process induced residual stress has long been recognised as an important factor influencing the integrity and overall performance of coatings. Residual stress generation during thermal spraying is a complex phenomenon. Significant efforts have been made to improve understanding of the evolution of residual stresses during deposition and to develop practical models for numerical prediction of stress distributions in coatings. Owing to the high penetrating power of neutrons and spatial resolution in the millimetre and submillimetre range, neutron diffraction is, perhaps, the most versatile method for stress determination, and has been used extensively for experimental validation of theoretical predictions. Examples of neutron diffraction residual stress results are presented to illustrate the capabilities of the technique: a thin (∼0·3 mm) Mo/Mo2C composite HVOF coating, several examples of millimetre thick ceramic and metallic coatings, and thick coatings (∼10 mm) of iron made by spray forming. © 2010, Maney Publishing