Thermal imaging has been demonstrated as a subjective indicator of internal anomalies in trees including decay (Catena and Catena, 2007). To determine whether the procedure could be used to evaluate radial wood thickness, thermal images of the stems of twelve mature trees were used to investigate the relationship between surface temperature and visually apparent radial wood thickness. The trees were harvested from Cragmoor Road, Nottinghamshire in winter 2005. Surface anomalies such as bark structure and surface damage caused 'noise' that accounted for around 30% of the variance. When a clearly-defined cavity was present, this accounted for a further 50%, showing a robust relationship between changes in surface temperature and the radial wood thickness. When the internal anomaly was less clear, then the anomaly was better defined by the mean relative temperature. Changes to the thermal properties of wood other than from decay must be considered.
Computer modelling techniques are used to predict the distribution of residual stresses in a machined uranium surface. The predictions are used to address the ageing of uranium exposed to inert gas based environments in terms of microcrack initiation and subsequent propagation. Metallographic observations of microcracking are used as the basis for the initial assessment of ageing behaviour.It is proposed that the near-surface residual stress field produced by machining influences the occurrence of microcracking. It is also suggested that corrosion-induced surface features act as initiation sites for microcracks, which begin to propagate by an environmentally assisted mechanism when the surface features reach a critical depth within the residual stress field of between 5 and 10 mm. However, the majority of the microcracks appear to arrest at about 150 mm. This behaviour is discussed in terms of the predicted threshold stress intensity for crack nucleation, uranium metallurgy, and the possible effects of crack coalescence on growth.
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