Bearing damage characteristics of fibre-reinforced countersunk composite bolted joints subjected to quasi-static shear loading

This paper studies the progression of damage in carbon fibre-reinforced polymer (CFRP) countersunk composite bolted joints (CBJs) with neat-fit clearance, subjected to quasi-static loading. Damage mechanisms, comprising of fibre buckling and breakage, matrix damage, shear damage and inter-laminar delamination within the CFRP composite parts of the joints have been studied. Load-displacement curves, X-ray and optical microscopic images in single- and three-bolt CBJs were used to investigate damage and deformation characteristics. The observations were then employed to further investigate the type of failure and the extent of damage. The evolution of damage within the composite parts was correlated to the failure characteristics of the joints: It was found that the type and extension of damage is strongly correlated with the ultimate failure load point of the joint in single-bolt CBJs. A combined inter/intra-laminar damage consisting of fibre cluster breakage, extensive fibre buckling, debonding and delamination was observed at the ultimate failure load. This study was then extended to three-bolt CBJ where damage surrounding each bolt and its corresponding failure load was strongly correlated: The final study showed that the ultimate failure point in single-bolt CBJ and the first-bolt-failure point in three-bolt CBJ correspond to the composite plies undergoing intra-laminar damage with the size reaching to the edge of the countersunk head. This damage developed extensively through the thickness of the composite parts underneath the countersink, and in the direction opposite to the loading direction. Outside the countersunk head, debonding and delamination were found to be the dominant damage driving mechanisms. Finally, a new design rule has been proposed to predict the response of multi-bolt joints (damage area and failure load) by using the response in single-bolt CBJ as an initial baseline

Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering

We investigate the properties of the optical model wave function for light heavy-ion systems where absorption is incomplete, such as $\alpha + ^{40}$Ca and $\alpha + ^{16}$O around 30 MeV incident energy. Strong focusing effects are predicted to occur well inside the nucleus, where the probability density can reach values much higher than that of the incident wave. This focusing is shown to be correlated with the presence at back angles of a strong enhancement in the elastic cross section, the so-called ALAS (anomalous large angle scattering) phenomenon; this is substantiated by calculations of the quantum probability flux and of classical trajectories. To clarify this mechanism, we decompose the scattering wave function and the associated probability flux into their barrier and internal wave contributions within a fully quantal calculation. Finally, a calculation of the divergence of the quantum flux shows that when absorption is incomplete, the focal region gives a sizeable contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The figures are only available via anonynous FTP on ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat

Electron-attachment rates for carbon-rich molecules in protoplanetary atmospheres: the role of chemical differences

The formation of anionic species in the interstellar medium from interaction of linear molecules containing carbon, nitrogen and hydrogen as atomic components (polyynes) with free electrons in the environment is modelled via a quantum treatment of the collision dynamics. The ensuing integral cross sections are employed to obtain the corresponding attachment rates over a broad range of temperatures for the electrons. The calculations unequivocally show that a parametrization form often employed for such rates yields a broad range of values that turn out to be specific for each molecular species considered, thus excluding using a unique set for the whole class of polyynes.Comment: accepted to be published on MNRA

Computational fluid dynamic analysis of bioprinted self-supporting perfused tissue models

Natural tissues are incorporated with vasculature, which is further integrated with a cardiovascular system responsible for driving perfusion of nutrient‐rich oxygenated blood through the vasculature to support cell metabolism within most cell‐dense tissues. Since scaffold‐free biofabricated tissues being developed into clinical implants, research models, and pharmaceutical testing platforms should similarly exhibit perfused tissue‐like structures, we generated a generalizable biofabrication method resulting in self‐supporting perfused (SSuPer) tissue constructs incorporated with perfusible microchannels and integrated with the modular FABRICA perfusion bioreactor. As proof of concept, we perfused an MLO‐A5 osteoblast‐based SSuPer tissue in the FABRICA. Although our resulting SSuPer tissue replicated vascularization and perfusion observed in situ, supported its own weight, and stained positively for mineral using Von Kossa staining, our in vitro results indicated that computational fluid dynamics (CFD) should be used to drive future construct design and flow application before further tissue biofabrication and perfusion. We built a CFD model of the SSuPer tissue integrated in the FABRICA and analyzed flow characteristics (net force, pressure distribution, shear stress, and oxygen distribution) through five SSuPer tissue microchannel patterns in two flow directions and at increasing flow rates. Important flow parameters include flow direction, fully developed flow, and tissue microchannel diameters matched and aligned with bioreactor flow channels. We observed that the SSuPer tissue platform is capable of providing direct perfusion to tissue constructs and proper culture conditions (oxygenation, with controllable shear and flow rates), indicating that our approach can be used to biofabricate tissue representing primary tissues and that we can model the system in silico

Trend in ice moistening the stratosphere – constraints from isotope data of water and methane

Water plays a major role in the chemistry and radiative budget of the stratosphere. Air enters the stratosphere predominantly in the tropics, where the very low temperatures around the tropopause constrain water vapour mixing ratios to a few parts per million. Observations of stratospheric water vapour show a large positive long-term trend, which can not be explained by change in tropopause temperatures. Trends in the partitioning between vapour and ice of water entering the stratosphere have been suggested to resolve this conundrum. We present measurements of stratospheric H_(2)O, HDO, CH_4 and CH_(3)D in the period 1991–2007 to evaluate this hypothesis. Because of fractionation processes during phase changes, the hydrogen isotopic composition of H_(2)O is a sensitive indicator of changes in the partitioning of vapour and ice. We find that the seasonal variations of H_(2)O are mirrored in the variation of the ratio of HDO to H_(2)O with a slope of the correlation consistent with water entering the stratosphere mainly as vapour. The variability in the fractionation over the entire observation period is well explained by variations in H_(2)O. The isotopic data allow concluding that the trend in ice arising from particulate water is no more than (0.01±0.13) ppmv/decade in the observation period. Our observations suggest that between 1991 and 2007 the contribution from changes in particulate water transported through the tropopause plays only a minor role in altering in the amount of water entering the stratosphere

Determinations of SIII, OIV and NeV abundances in planetary nebulae from IR lines

Airborne observations of the infrared forbidden lines (SIII) 18.71 microns, (NeV) 24.28 microns and (OIV) 25.87 microns were made for twelve planetary nebulae. One or more of the lines was detected in seven of these nebulae and ionic abundances were calculated. These results are insensitive to nebula temperatures, in contrast to the case for optical or UV lines. However, density estimates from optical and UV forbidden lines were required to obtain abundances. The NeV infrared line flux from NGC 7662 was combined with the 3426A flux to obtain a NeV electron temperature of 11,200 (+2000, - 1100) K, which overlaps OIII temperature measurements. Since the ionization potential of NeIV is much greater than that of OII, T sub e (NeV) would be expected to be much greater than T sub e (OIII). In fact, numerical models predict T sub e (NeV) (16-20) x 1000 K. This discrepancy may indicate inaccuracies in currently available atomic parameters for NeV

A Study of Wakes Behind a Circular Cylinder at M = 5.7

The flow field behind a circular cylinder was investigated experimentally at a nominal Mach number of 5.7, over a range of Reynolds numbers from 4500 to 66,500, based on the cylinder diameter. Pitot pressure, static pressure, and total temperature were measured at various distances behind cylinders of three different diameters in order to determine the flow properties in the wake. To correlate data at different Reynolds numbers and to discriminate turbulent wakes from laminar wakes, a linearized theory for the laminar far wake was developed, which included the effects of axial pressure gradient. The transition from laminar flow to turbulent flow was also determined by computing diffusion coefficients from the velocity profiles. The transition thus determined was correlated with the results obtained from mass-diffusion measurements and hot-wire fluctuation measurements

I-mode studies at ASDEX Upgrade: L-I and I-H transitions, pedestal and confinement properties

The I-mode is a plasma regime obtained when the usual L-H power threshold is high, e.g. with unfavourable ion B ∇ direction. It is characterised by the development of a temperature pedestal while the density remains roughly as in the L-mode. This leads to a confinement improvement above the L-mode level which can sometimes reach H-mode values. This regime, already obtained in the ASDEX Upgrade tokamak about two decades ago, has been studied again since 2009 taking advantage of the development of new diagnostics and heating possibilities. The I-mode in ASDEX Upgrade has been achieved with different heating methods such as NBI, ECRH and ICRF. The I-mode properties, power threshold, pedestal characteristics and confinement, are independent of the heating method. The power required at the L-I transition exhibits an offset linear density dependence but, in contrast to the L-H threshold, depends weakly on the magnetic field. The L-I transition seems to be mainly determined by the edge pressure gradient and the comparison between ECRH and NBI induced L-I transitions suggests that the ion channel plays a key role. The I-mode often evolves gradually over a few confinement times until the transition to H-mode which offers a very interesting situation to study the transport reduction and its link with the pedestal formation. Exploratory discharges in which n = 2 magnetic perturbations have been applied indicate that these can lead to an increase of the I-mode power threshold by flattening the edge pressure at fixed heating input power: more heating power is necessary to restore the required edge pressure gradient. Finally, the confinement properties of the I-mode are discussed in detail.European Commission (EUROfusion 633053