Layer orientation and size effects on micropillar compression of Al/SiC nanolaminates

Nanolaminates consisting of alternating layers of two dissimilar materials can possess extraordinary mechanical properties compared to their bulk counterparts, making them promising for engineering applications. Extremely high room temperature strengths and damage tolerance have been reported when the individual layer thicknesses are less than 100 nm, and this has been attributed to the large density of interfaces and grain boundaries that act as barriers for pinned dislocations [1–3]. Micropillar compression tests have been extensively employed to study nanolaminate deformation with the force generally applied perpendicular to the individual layers [1,4,5]. However, studies covering the effect of pillar size and layer orientation with respect to the pillar axis in metal-ceramic nanolaminates are still scarce. This work is mainly focused on the study, by micropillar compression, of the deformation and failure mechanisms of metal-ceramic Al/SiC nanolaminates, with layer thickness between 10 and 100 nm, as a function of layer orientation and pillar size,. Finite element modeling (FEM) was used to support the experimental observations, when needed. Deformation mechanisms and stress-strain behavior were determined for layers oriented at 0º, 45 º and 90º, for two different pillar sizes. The results revealed that the main initial deformation mechanism at room temperature was plasticity of the Al layers, constrained by the ceramic SiC layers, but that the final failure is very dependent on layer orientation and other microstructural features apart from layer thickness. While the micropillars loaded parallel (0º) and at 45º to the layers failed by the formation of shear and kink bands, triggered by the pre-existing layer waviness, micropillar loaded in the perpendicular direction fail by cracking of the SiC layers, without any appreciable effect of layer waviness. Two size effects were observed, one intrinsic and related to the individual thickness and the other, extrinsic, related to the pillar size. The origin and competition between these two size effects will be discussed

Towards an assessment of the balance state of the Greenland Ice Sheet

The climate of Europe is strongly influenced by heat transport by ocean currents flowing from equatorial regions towards the Arctic (Clark et al. 2002). During recent years, research has been increasingly focused on factors affecting this circulation, e.g. the freshwater budget of the Arctic which is influenced by glacial meltwater from North and East Greenland outlet glaciers (Linthout et al. 2000, Mayer et al. 2000). Furthermore, the climate is affected by snow cover that, apart from its contribution to the freshwater budget, provides feedback effects in that it reflects most of the solar radiation. Apart from Arctic sea-ice cover, the Greenland Ice Sheet is the largest permanent ice- and snow-covered area in the northern hemisphere, with an area of 1.67 ×106 km2 and by far the largest storage of ice with a volume of 2.93 × 106 km3 (Bamber et al. 2001). Most of the mass loss from the Greenland Ice Sheet (the least known mass-balance parameter) occurs in the marginal region of the ice sheet, which is also the area where the largest changes in albedo occur. The Geological Survey of Denmark and Greenland (GEUS) has for many years carried out research along the Greenland Ice Sheet margin to monitor changes of mass balance and melt conditions

An impact analysis of the Salem urban growth boundary on rural residential development and land value

An attempt is made to identify any significant impact of the Salem urban growth boundary implementation on rural residential development and land value outside of the boundary. Studies done in 1972 examine possible boundary impacts, but definite conclusions were not made because county rural development policy had not been finalized. This research analyzes subdivision trends and land value impacts in relation to boundary and rural development policy implementation. A multiple regression analysis of land value on independent variables is done n an attempt to isolate boundary and rural zoning impacts on the land value of parcels between one and fifteen acres (.405 and 6.07 hectares) outside of the boundary. Results of the multiple regression analysis show that zoning in accordance to rural development policy had more of a significant impact on land value than boundary implementation. Limitations of this research must be considered with the results. The possibility exists that impact associated with the urban growth boundary could have occurred prior to 1973 when the boundary was in its proposal stage

De phlebectasi crurum adumbratio succincta : dissertatio inauguralis / quam consensu et auctoritate gratiosi medicorum ordinis in Universitate Literarum Caesarea Dorpatensi ad gradum doctoris medicinae rite adipiscendum loco consueto publice defendet auctor Carolus de Mayer, Petropolitanus

http://tartu.ester.ee/record=b2602449~S1*es