Calculation of residual principal stresses in CVD boron on carbon filaments

A three-dimensional finite element model of the chemical vapor deposition of boron on a carbon substrate (B/C) is developed. The model includes an expansion of the boron after deposition due to atomic rearrangement and includes creep of the boron and carbon. Curves are presented showing the variation of the principal residual stresses and the filament elongation with the parameters defining deposition strain and creep. The calculated results are compared with experimental axial residual stress and elongation measurements made on B/C filaments. For good agreement between calculated and experimental results, the deposited boron must continue to expand after deposition, and the build up of residual stresses must be limited by significant boron and carbon creep rates

System measures unidirectional forces, excludes extraneous forces

System measures unidirectional force without interference from other directional forces. The measuring apparatus is mounted so that it only moves vertically and is constrained from horizontal and rotational movement. This system can be used to accurately measure small forces in one direction, or as an analytic balance

Image effects and the vibrating sample magnetometer

Image effects and vibrating sample magnetomete

Axial residual stresses in boron fibers

The axial residual stress distribution as a function of radius was determined from the fiber surface to the core including the average residual stress in the core. Such measurements on boron on tungsten (B/W) fibers show that the residual stresses for 102, 142, 203, and 366 micron diameter fibers were similar, being compressive at the surface and changing monotonically to a region of tensile within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile stress of about 860 mn/sq.m and then decreases to a compressive stress near the tungsten boride core. Data were presented for 203 micron diameter B/W fibers that show annealing above 900 C reduces the residual stresses. A comparison between 102 micron diameter B/W and boron on carbon (b/C) shows that the residual stresses were similar in the outer regions of the fibers, but that large differences near and in the core were observed. The effects of these residual stresses on the fracture of boron fibers were discussed

Residual stresses in boron/tungsten and boron/carbon fibers

By measuring the change in fracture stress of 203 micrometer diameter fibers of boron on tungsten (B/W) as a function of fiber diameter as reduced by chemical etching, it is shown that the flaws which limit B/W fiber strength are located at the surface and in the tungsten boride core. After etching to a diameter of 188 micrometers m virtually all fiber fractures were caused by core flaws, the average strength being 4.50 GN/sq m. If both the surface and core flaws are removed, the fracture strength, limited by flaws in the boron itself, is approximately 6.89 GN/sq m. This was measured on B/W fibers which were split longitudinally and had their cores removed by chemical etching. The longitudinal residual stress distribution was determined for 102 micrometer diameter B/W and B/C fibers

Longitudinal residual stresses in boron fibers

A method of measuring the longitudinal residual stress distribution in boron fibers is presented. The residual stresses in commercial CVD boron on tungsten fibers of 102, 142, and 203 microns (4, 5.6, and 8 mil) diameters were determined. Results for the three sizes show a compressive stress at the surface 800 to -1400 MN/sq m 120 to -200 ksi), changing monotonically to a region of tensile stress within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile 600 to 1000 MN/sq m(90 to 150 ksi) and then decreases to compressive near the tungsten boride core. The core itself is under a compressive stress of approximately -1300 MN/sq m (-190 ksi). The effects of surface removal on core residual stress and core-initiated fracture are discussed

An explanation of anomalous non-Hookean deformation of ionic single crystals

Anomalous non-Hookean deformation of ionic single crystal

Product Service System Innovation in the Smart City

Product service systems (PSS) may usefully form part of the mix of innovations necessary to move society toward more sustainable futures. However, despite such potential, PSS implementation is highly uneven and limited. Drawing on an alternate socio-technical perspective of innovation, this paper provides fresh insights, on among other things the role of context in PSS innovation, to address this issue. Case study research is presented focusing on a use orientated PSS in an urban environment: the Copenhagen city bike scheme. The paper shows that PSS innovation is a situated complex process, shaped by actors and knowledge from other locales. It argues that further research is needed to investigate how actors interests shape PSS innovation. It recommends that institutional spaces should be provided in governance landscapes associated with urban environments to enable legitimate PSS concepts to co-evolve in light of locally articulated sustainability principles and priorities

Electrically-assisted bikes: potential impacts on travel behaviour

This paper reports on a review of the European literature about the impacts of having an electrically-assisted bike available to use, together with results from a trial in the UK city of Brighton, where 80 employees were loaned an electrically-assisted bike for a 6–8 week period. In the Brighton trial, three-quarters of those who were loaned an e-bike used them at least once a week. Across the sample as a whole, average usage was in the order of 15–20 miles per week, and was accompanied by an overall reduction in car mileage of 20%. At the end of the trial, 38% participants expected to cycle more in the future, and at least 70%said that they would like to have an e-bike available for use in the future, and would cycle more if this was the case. This is consistent with the results of the European literature which shows that when e-bikes are made available, they get used; that a proportion of e-bike trips typically substitutes for car use; and that many people who take part in trials become interested in future e-bike use, or cycling more generall

Dynamics of myelin content decrease in the rat stroke model

A majority of studies were usually focused on neuronal death after brain ischemia, however, stroke affects all cell types including oligodendrocytes that form myelin sheath in the CNS. Our study is focused on the changes of myelin content in ischemic core and neighbor structures in early terms (1, 3 and 10 days) after stroke. Stroke modeled with middle cerebral artery occlusion (MCAo) in 15 male rats that were divided in three groups by time-points after operation. Brain sections were histologically stained with Luxol Fast Blue (LFB) for myelin quantification. The significant demyelination was found in the ischemic core, corpus callosum, anterior commissure, whereas myelin content was increased in caudoputamen, internal capsule and piriform cortex compared with the contralateral hemisphere. The motor cortex showed a significant increase of myelin content on the 1st day and a significant decrease on the 3rd and 10th days after MCAo. These results suggest stroke influences myelination not only in ischemic core but also in distant structures