3D Analyses of crack propagation in torsion

The initiation and propagation of fatigue cracks during cyclic torsion loading was studied in a castAl alloy (A357) with a relatively large (~500 ?m) grain size. 2D observations, revealed that multi site crackinitiation occur on the {111} slip planes exhibiting the highest slip activity (iso-strain Taylor analysis),preferentially on planes nearly perpendicular to the sample axis. Within the first grain, the cracks have apronounced crystallographic propagation mode (mode II crack growth) and strongly interact with the grainboundaries. In situ 3D monitoring of torsion fatigue tests using synchrotron X-ray tomography reveal thatpropagation towards the interior of the samples occurs first along the sample periphery in mode II leading torelatively shallow cracks which penetrate towards the sample center only after a large number of cycles isreached .The values of mode I, II and III stress intensity factors have been calculated from finite elementsimulation at the tip of the shallow mode II crack. Those values are used to analyse the bulk propagation of theobserved cracks

Effect of water availability pattern on yield of pearl millet in semi-arid tropical environments

Throughout much of the semi-arid tropics, fluctuations in grain yield can largely be attributed to differences in timing and intensity of drought stress. Since seasonal rainfall in these environments is often poorly related to grain yield, the aim of this paper was to establish a relationship between water availability and grain yield for pearl millet (Pennisetum glaucum (L.) R. Br.), grown across 24 semi-arid tropical environments in India. We used a simple soil water budget to calculate a water satisfaction index (WSI) throughout the season. The cumulative WSI at maturity explained 76% of the variance in grain yield. This was three times as much as explained by actual rainfall, because WSI accounted for differences in water losses and pan evaporation. A classification of environments into four groups of water availability patterns explained 75% of the environmental sum of squares for grain yield. For a subset of 13 environments, environmental differences in grain number could also be explained by water availability patterns, whereas differences in grain mass were related to both water availability and temperature. Our results indicate that cumulative WSI, which is an integrated measure of plant-available water, can provide an adequate estimation of the environmental potential for yield in environments where grain yield is mainly limited by variable availability of water