166 research outputs found
Forming simulation of a thermoplastic commingled woven textile on a double dome
This paper presents thermoforming experiments and FE simulations of a commingled glass-PP woven composite on a double dome geometry, with the aim of assessing the correspondence of predicted and experimental shear angles. Large local deformations - especially in-plane shear, i.e. relative rotation between the two yarn families – occur when draping a textile on a three dimensional part and eventually unwanted phenomena like wrinkling or tearing may occur. The macroscopic drape behaviour of a weave is generally subdivided into: 1) The high tensile resistance along the yarn directions, expressed as non-linear stress-strain curves, and 2) The shear resistance, expressed as non-linear shear force versus shear angle curves. The constitutive model is constituted of a dedicated non-orthogonal hypo-elastic shear resistance model, previously described in [1, 2], combined with truss elements that represent the high tensile resistance along the yarn directions. This model is implemented in a user subroutine of the ABAQUS explicit FE solver. The material parameters have been identified via textile biaxial tensile tests at room temperature and bias extension tests at 200°. Thermoforming experiments are performed on a rectangular blank with the warp direction along the second symmetry plane of the tool, with a preheating temperature of 200°C, a constant mold temperature of about 70°C, and a blankholder ring. It was concluded that the shear angles were fairly well predicted for this particular case study, which could be expected in view of the fact that no wrinkles had formed during the thermoforming experiment
In-situ local strain measurement in textile composites with embedded optical fibre sensors
To understand the local strains inside a textile composite, numerical simulations are typically done on the scale of one repetitive unit cell of the weaving pattern. Periodic boundary conditions are applied to the edges of the unit cell and different load cases can then be applied to the unit cell of the textile composite. Most often, the periodic boundary conditions are applied on all faces of the unit cell, which implies the assumption that the material is repeating itself over an infinite distance in all three orthogonal directions. This assumption is more or less valid for the textile composite material in the midplane of thick laminates, where it is constrained by neighbouring material in all three directions. It is very difficult to validate such simulations, because local strain measurements inside a textile composite have rarely been done, and the interpretation is not straightforward. This paper shows the successful use of embedded optical fibre sensors to measure the local strains inside a satin weave carbon/PPS composite (typically used in aerospace applications). The length of the Bragg grating inside the optical fibre sensor has been chosen such that it is longer than the length of one unit cell of the satin weave architecture (7.4 mm). The read-outs of the optical fibre sensor give the minimum and maximum local strains that occur along the length of the Bragg grating
Electron transport and optical properties of shallow GaAs/InGaAs/GaAs quantum wells with a thin central AlAs barrier
Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three
monolayer thick AlAs central barrier have been investigated for different well
widths and Si doping levels. The transport parameters are determined by
resistivity measurements in the temperature range 4-300 K and magnetotransport
in magnetic fields up to 12 T. The (subband) carrier concentrations and
mobilities are extracted from the Hall data and Shubnikov-de Haas oscillations.
We find that the transport parameters are strongly affected by the insertion of
the AlAs central barrier. Photoluminescence spectra, measured at 77 K, show an
increase of the transition energies upon insertion of the barrier. The
transport and optical data are analyzed with help of self-consistent
calculations of the subband structure and envelope wave functions. Insertion of
the AlAs central barrier changes the spatial distribution of the electron wave
functions and leads to the formation of hybrid states, i.e. states which extend
over the InGaAs and the delta-doped layer quantum wells.Comment: 14 pages, pdf fil
Local strain in a 5-harness satin weave composite under static tension: Part II – Meso-FE analysis
Rarita--Schwinger field and multi-component wave equation
We suggest simple method to solve wave equation for Rarita--Schwinger field
without additional constraints. This method based on use of off-shell
projection operators allows to diagonalize spin-1/2 sector of the field.Comment: 6 page
Micro-CT-based analysis of fibre-reinforced composites:Applications
The paper presents an overview of cases in which the analysis of the internal structure and mechanical properties of fibre reinforced composites is performed based on the micro-computed X-ray tomography (micro-CT) reconstruction of the composite reinforcement geometry. In all the cases, the analysis relies on structure tensor-based algorithms for quantification of the micro-CT image, implemented in VoxTex software
Local strain in a 5-harness satin weave composite under static tension: Part I – Experimental analysis
Spin half fermions with mass dimension one: theory, phenomenology, and dark matter
We provide the first details on the unexpected theoretical discovery of a
spin-one-half matter field with mass dimension one. It is based upon a complete
set of dual-helicity eigenspinors of the charge conjugation operator. Due to
its unusual properties with respect to charge conjugation and parity, it
belongs to a non-standard Wigner class. Consequently, the theory exhibits
non-locality with (CPT)^2 = - I. We briefly discuss its relevance to the
cosmological `horizon problem'. Because the introduced fermionic field is
endowed with mass dimension one, it can carry a quartic self-interaction. Its
dominant interaction with known forms of matter is via Higgs, and with gravity.
This aspect leads us to contemplate the new fermion as a prime dark matter
candidate. Taking this suggestion seriously we study a supernova-like explosion
of a galactic-mass dark matter cloud to set limits on the mass of the new
particle and present a calculation on relic abundance to constrain the relevant
cross-section. The analysis favours light mass (roughly 20 MeV) and relevant
cross-section of about 2 pb. Similarities and differences with the WIMP and
mirror matter proposals for dark matter are enumerated. In a critique of the
theory we bare a hint on non-commutative aspects of spacetime, and
energy-momentum space.Comment: 78 pages [Changes: referee-suggested improvements, additional
important references, and better readability
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