Microscale elastic strain evolution following damage in Ti-SiC composites

Fiber fractures are crucial in initiating damage zones that ultimately determine the strength and lifetime of fiber-reinforced metal matrix composites. The evolution of damage in a metal matrix composite (MMC) comprised of a row of unidirectional SiC fibers (32 vol pct) surrounded by a Ti matrix was examined, for the first time, using X-ray microdiffraction. Multiple strain maps including both phases were collected in situ under applied tensile stress. The elastic axial strains were then compared to predictions from a modified shear-lag model, which, unlike other shear-lag models, considers the elastic response of both constituents. The strains showed good correlation with the model. The results confirmed, for the first time, both the need and validity of this new model specifically developed for large scale multifracture simulations of MMCs. The results also provided unprecedented insight for the model, revealing the necessity of incorporating such factors as plasticity of the matrix, residual stress in the composite, and selection of the load sharing parameter

Supply limited sediment transport in a high-discharge event of the tropical Burdekin River, North Queensland, Australia

An erratum for this article has been published. Please click on the description link below to view the erratum.Interactions between catchment variables and sediment transport processes in rivers are complex, and sediment transport behaviour during high-flow events is not well documented. This paper presents an investigation into sediment transport processes in a short-duration, high-discharge event in the Burdekin River, a large sand- and gravel-bed river in the monsoon- and cycloneinfluenced, semi-arid tropics of north Queensland. The Burdekin’s discharge is highly variable and strongly seasonal, with a recorded maximum of 40 400 m3 s)1. Sediment was sampled systematically across an 800 m wide, 12 m deep and straight reach using Helley-Smith bedload and US P-61 suspended sediment samplers over 16 days of a 29-day discharge event in February and March 2000 (peak 11 155 m3 s)1). About 3Æ7 · 106 tonnes of suspended sediment and 3 · 105 tonnes of bedload are estimated to have been transported past the sample site during the flow event. The sediment load was predominantly supply limited. Wash load included clay, silt and very fine sand. The concentration of suspended bed material (including very coarse sand) varied with bedload transport rate, discharge and height above the bed. Bedload transport rate and changes in channel shape were greatest several days after peak discharge. Comparison between these data and sparse published data from other events on this river shows that the control on sediment load varies between supply limited and hydraulically limited transport, and that antecedent weather is an important control on suspended sediment concentration. Neither the empirical relationships widely used to estimate suspended sediment concentrations and bedload (e.g. Ackers & White, 1973) nor observations of sediment transport characteristics in ephemeral streams (e.g. Reid & Frostick, 1987) are directly applicable to this river.Kathryn J. Amos, Jan Alexander, Anthony Horn, Geoff D. Pocock and Chris R. Fieldinghttp://www3.interscience.wiley.com/journal/118763463/abstrac