Finite element modelling of inter-ply delamination and intra-yarn cracking in textile laminates

The aim of the current study is to demonstrate the effect of inter-ply delamination on stiffness degradation of multi-ply woven composites. Such a demonstration becomes possible due to new technique of modelling textile laminates. It is based on set of boundary value problems for unit cell of a single ply, where boundary conditions imitate interaction with the other plies. Once these problems are solved, local stress distribution and stiffness of the laminate are determined analytically as function of number of the plies and local stress/strain fields obtained in these problems. Hence, it opens the road for an efficient modelling of delamination, which is described as gradual reduction of plies in the laminate

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

Fermion resonance in quantum field theory

We derive accurately the fermion resonance propagator by means of Dyson summation of the self-energy contribution. It turns out that the relativistic fermion resonance differs essentially from its boson analog.Comment: 8 pages, 2 figures, revtex4 class; references added, style correction

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

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

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

Measurement and analysis of needle penetration forces in industrial high-speed sewing machine

The industrial manufacturing of sewn products has always been one of the critical processes of the textile chain concerning quality assurance. Assuring the appropriate set-up and operation of all the machines, and thus the final seam quality, is a very complex task. Traditionally, this task is accomplished through empirical methods, with the machine setting and quality control relying on the skills of operators and technicians. This work presents an approach to a more knowledge-based and integrated process planning and control. A system was developed to measure and analyze the most important mechanical effects occurring during high-speed sewing. The paper will focus mainly on the measurement and evaluation of needle penetration and withdrawal force. After an overview of the system, the most important experimental results obtained in a series of experiments will be described

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

Top quark as a resonance

We suggest the description of the dressed fermion propagator with parity non-conservation in the form with separated positive and negative energy poles. We found general form of the $\gamma$-matrix off-shell projectors and corresponding resonance factors. The parity violation leads to deviation of resonance factors from the naive Breit--Wigner form and to appearance of non-trivial spin corrections. However, for top quark with SM vertex the resonance factor returns to the standard one due to $\Gamma/m\ll1$.Comment: 8 pages, revtex4, added one section, typos corrected, sync with journal versio