2,675 research outputs found
Spring forward of woven fabric reinforced composites
Continuous-fibre-reinforced plastic products are usually formed at elevated temperatures. They exhibit distortions when they are cooled to room temperature and released from the mould. For example, the enclosed angle of an L-shaped product decreases, see Fig. 1. This effect is known as spring-forward. It is mainly due to the anisotropic thermal shrinkage of the composite, which is small in the fibre direction and relatively large in the direction normal to the fibres. The costs of forming a product with the demanded dimensions by trial and error are high. To reduce these costs, the objective of the research described in this paper is to develop a model, which predicts the occurring distortions
Modelling the thermo-elastic properties of skewed woven fabric reinforced composites
Woven fabrics prove to be a very convenient fibre reinforcement when prepreg layers have to be draped on to double curvature moulds. The process of draping causes the angle between the warp and weft yarns to vary over the product with this double curvature. As a result, the thermomechanical properties of the fibre reinforced composite material show a corresponding distribution. These thermo-elastic properties must be known in order to predict the shrinkage\ud
and warpage of the product. Normally, composites consist of multiple fabric layers. These layers are oriented and skewed differently, and each contributes to the overall composite properties. Therefore, in order to predict the overall thermo-elastic properties of the composite as a whole, the properties of each individual layer must be known. In this paper, the inplane thermo-elastic\ud
properties of a woven fabric reinforced composite with an arbitrary weave type are analysed as a function of the skew angle, using micromechanics. Three different levels of material structure are modelled, the micro-, the meso- and the macro level. The inplane thermo-elastic properties of four different basic elements are determined at the micro level, using geometrical shape functions and a two-dimensional thermo-elastic model. The inplane properties of one fabric layer are determined at the meso level, using the fabric pattern and the properties of the basic elements. At the macro level the homogeneous properties and warpage of woven fabric composites are considered. Here the composite structure and the properties of the individual layer are used. The method proves to be a convenient way to model the skew deformation of the woven fabric composite and the resulting variation in the thermo-elastic properties. The theoretical predictions are verified by experiments on multiple-layered satin 5H woven fabric composites
Residual stresses in non-symmetrical carbon/epoxy laminates
The curvature of unsymmetrical [0/90] laminates moulded from AS4/8552 uni-directional tape has been measured. A linear thermoelastic approach has been applied to predict the related residual stress state before demoulding, giving an estimate of the stress induced by polymerisation strain. The results from the linear approach are confirmed by a viscoelastic finite element model including the cure conversion and related change in viscosity. It is concluded that the curvature measurement of unsymmetrical laminates is an accurate method for the prediction of the transverse residual stress, making it suitable as a benchmark for complex stress modelling
Making information accessible for the conservation and use of biodiversity. A novel initiative to facilitate access to information and use of agricultural and tree biodiversity
Poster presented at Science Week 2014 - Bioversity International HQ, Rome (Italy), 24-27 Feb 201
Towards Understanding The B[e] Phenomenon: IV. Modeling of IRAS 00470+6429
FS CMa type stars are a recently described group of objects with the B[e]
phenomenon that exhibit strong emission-line spectra and strong IR excesses. In
this paper we report the first attempt for a detailed modeling of IRAS
00470+6429, for which we have the best set of observations. Our modeling is
based on two key assumptions: the star has a main-sequence luminosity for its
spectral type (B2) and the circumstellar envelope is bimodal, composed of a
slowly outflowing disk-like wind and a fast polar wind. Both outflows are
assumed to be purely radial. We adopt a novel approach to describe the dust
formation site in the wind that employs timescale arguments for grain
condensation and a self-consistent solution for the dust destruction surface.
With the above assumptions we were able to reproduce satisfactorily many
observational properties of IRAS 00470+6429, including the H line profiles and
the overall shape of the spectral energy distribution. Our adopted recipe for
dust formation proved successful in reproducing the correct amount of dust
formed in the circumstellar envelope. Possible shortcomings of our model, as
well as suggestions for future improvements, are discussed.Comment: 11 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Mach's Principle and Model for a Broken Symmetric Theory of Gravity
We investigate spontaneous symmetry breaking in a conformally invariant
gravitational model. In particular, we use a conformally invariant scalar
tensor theory as the vacuum sector of a gravitational model to examine the idea
that gravitational coupling may be the result of a spontaneous symmetry
breaking. In this model matter is taken to be coupled with a metric which is
different but conformally related to the metric appearing explicitly in the
vacuum sector. We show that after the spontaneous symmetry breaking the
resulting theory is consistent with Mach's principle in the sense that inertial
masses of particles have variable configurations in a cosmological context.
Moreover, our analysis allows to construct a mechanism in which the resulting
large vacuum energy density relaxes during evolution of the universe.Comment: 9 pages, no figure
Radiation driven winds with rotation: The oblate finite disc correction factor
We have incorporated the oblate distortion of the shape of the star due to
the stellar rotation, which modifies the finite disk correction factor (f_D) in
the m-CAK hydrodynamical model. We implement a simplified version for the f_D
allowing us to solve numerically the non-linear m- CAK momentum equation.We
solve this model for a classical Be star in the polar and equatorial
directions. The star's oblateness modifies the polar wind, which is now much
faster than the spherical one, mainly because the wind receives radiation from
a larger (than the spherical) stellar surface. In the equatorial direction we
obtain slow solutions, which are even slower and denser than the spherical
ones. For the case when the stellar rotational velocity is about the critical
velocity, the most remarkable result of our calculations is that the density
contrast between the equatorial density and the polar one, is about 100. This
result could explain a long-standing problem on Be stars.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
On the Interpretation of the Age Distribution of Star Clusters in the Small Magellanic Cloud
We re-analyze the age distribution (dN/dt) of star clusters in the Small
Magellanic Cloud (SMC) using age determinations based on the Magellanic Cloud
Photometric Survey. For ages younger than 3x10^9 yr the dN/dt distribution can
be approximated by a power-law distribution, dN/dt propto t^-beta, with
-beta=-0.70+/-0.05 or -beta=-0.84+/-0.04, depending on the model used to derive
the ages. Predictions for a cluster population without dissolution limited by a
V-band detection result in a power-law dN/dt distribution with an index of
~-0.7. This is because the limiting cluster mass increases with age, due to
evolutionary fading of clusters, reducing the number of observed clusters at
old ages. When a mass cut well above the limiting cluster mass is applied, the
dN/dt distribution is flat up to 1 Gyr. We conclude that cluster dissolution is
of small importance in shaping the dN/dt distribution and incompleteness causes
dN/dt to decline. The reason that no (mass independent) infant mortality of
star clusters in the first ~10-20 Myr is found is explained by a detection bias
towards clusters without nebular emission, i.e. cluster that have survived the
infant mortality phase. The reason we find no evidence for tidal (mass
dependent) cluster dissolution in the first Gyr is explained by the weak tidal
field of the SMC. Our results are in sharp contrast to the interpretation of
Chandar et al. (2006), who interpret the declining dN/dt distribution as rapid
cluster dissolution. This is due to their erroneous assumption that the sample
is limited by cluster mass, rather than luminosity.Comment: 8 pages, 4 figures, accepted for publication in Ap
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