2,311 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
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
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
Finite-size scaling at infinite-order phase transitions
For systems with infinite-order phase transitions, in which an order
parameter smoothly becomes nonzero, a new observable for finite-size scaling
analysis is suggested. By construction this new observable has the favourable
property of diverging at the critical point. Focussing on the example of the
F-model we compare the analysis of this observable with that of another
observable, which is also derived from the order parameter but does not
diverge, as well as that of the associated susceptibility. We discuss the
difficulties that arise in the finite-size scaling analysis of such systems. In
particular we show that one may reach incorrect conclusions from large-system
size extrapolations of observables that are not known to diverge at the
critical point. Our work suggests that one should base finite-size scaling
analyses for infinite-order phase transitions only on observables that are
guaranteed to diverge.Comment: 7 pages, 5 figures, 1 table; v2: publication details adde
Stagnation and Infall of Dense Clumps in the Stellar Wind of tau Scorpii
Observations of the B0.2V star tau Scorpii have revealed unusual stellar wind
characteristics: red-shifted absorption in the far-ultraviolet O VI resonance
doublet up to +250 km/s, and extremely hard X-ray emission implying gas at
temperatures in excess of 10^7 K. We describe a phenomenological model to
explain these properties. We assume the wind of tau Sco consists of two
components: ambient gas in which denser clumps are embedded. The clumps are
optically thick in the UV resonance lines primarily responsible for
accelerating the ambient wind. The reduced acceleration causes the clumps to
slow and even infall, all the while being confined by the ram pressure of the
outflowing ambient wind. We calculate detailed trajectories of the clumps in
the ambient stellar wind, accounting for a line radiation driving force and the
momentum deposited by the ambient wind in the form of drag. We show these
clumps will fall back towards the star with velocities of several hundred
km/sec for a broad range of initial conditions. The infalling clumps produce
X-ray emitting plasmas with temperatures in excess of (1-6)x10^7 K in bow
shocks at their leading edge. The infalling material explains the peculiar
red-shifted absorption wings seen in the O VI doublet. The required mass loss
in clumps is 3% - 30% ofthe total mass loss rate. The model developed here can
be generally applied to line-driven outflows with clumps or density
irregularities. (Abstract Abridged)Comment: To appear in the ApJ (1 May 2000). 24 pages, including 6 embedded
figure
Acoustic spectral analysis and testing techniques
Subjects covered in four reports are described including: (1) mathematical techniques for combining decibel levels of octaves or constant bandwidth: (2) techniques for determining equation for power spectral density function; (3) computer program to analyze acoustical test data; and (4) computer simulation of horn responses utilizing hyperbolic horn theory
Numerical study of the F model with domain-wall boundaries
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
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