Micromechanical elastic cracktip stresses in a fibrous composite

This paper presents elastic stress distributions near a cracktip in a continuous fiber composite. The material heterogeneity is explicitly accounted for by using the finite element method and a new Mesh Superposition Technique. This new technique superposes a fine mesh with heterogeneous material properties over a coarse mesh with homogeneous ones. The results indicate that the load transferred by fibers near a cracktip may be well described by the homogeneous orthotropic elastic K ₁ field. A technique to postprocess the K ₁ field to accurately obtain the detailed stress distributions within the fiber and matrix is also presented.     

Nonaxisymmetric unsteady motion over a rotating disk in the presence of free convection and magnetic field

The nonaxisymmetric unsteady motion produced by a buoyancy-induced cross-flow of an electrically conducting fluid over an infinite rotating disk in a vertical plane and in the presence of an applied magnetic field normal to the disk has been studied. Both constant wall and constant heat flux conditions have been considered. It has been found that if the angular velocity of the disk and the applied magnetic field squared vary inversely as a linear function of time (i.e. as (1−λt*)⁻¹, the governing Navier-Stokes equation and the energy equation admit a locally self-similar solution. The resulting set of ordinary differential equations has been solved using a shooting method with a generalized Newton's correction procedure for guessed boundary conditions. It is observed that in a certain region near the disk the buoyancy induced cross-flow dominates the primary von Karman flow. The shear stresses induced by the cross-flow are found to be more than these of the primary flow and they increase with magnetic parameter or the parameter λ characterizing the unsteadiness. The velocity profiles in the x- and y-directions for the primary flow at any two values of the unsteady parameter λ cross each other towards the edge of the boundary layer. The heat transfer increases with the Prandtl number but reduces with the magnetic parameter.     

Adaptive and hierarchical modelling of fatigue crack propagation

A methodology is developed to simulate adaptively and hierarchically fatigue crack growth in structural components. Cracks are modelled, by overlaying portions of the finite element mesh free of cracks with a discontinuous finite element field containing unconstrained double nodes along the discontinuity. Crack propagation is simulated by advancing the crack front in the superimposed mesh only keeping the underlying mesh fixed. Adaptivity in time and space domain together with the hierarchical nature of the method ensure both economical and reliable simulation of crack propagation. Numerical results of fatigue crack growth in the attachment lug were found to be, in good agreement with the experimental data.     

A Monte Carlo C-code for calculating transmission efficiency of recoil separators and viewing residue trajectories

We present a semimicroscopic Monte Carlo code for calculating absolute transmission efficiency of recoil separators for heavy ion-induced complete fusion reactions. The code generates realistic distributions for energy, charge state and angle of evaporation residues. Residue trajectories are calculated using first order ion optical transfer matrices. Trajectory plots in the dispersive and the non-dispersive planes are generated. Using this code, we have obtained good agreement between calculated and measured transmission efficiencies for the Heavy Ion Reaction Analyzer at IUAC. The code can be adapted easily to any other electromagnetic recoil separator.

Program summary

Program title: TERSCatalogue identifier: AEBD_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBD_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 6818No. of bytes in distributed program, including test data, etc.: 1 216 097Distribution format: tar.gzProgramming language: CComputer: The code has been developed and tested on a PC with Intel Pentium IV processorOperating system: LinuxRAM: About 8 MbytesClassification: 17.7External routines: pgplot graphics subroutine library [1] should be installed in the system for generating residue trajectory plots.Nature of problem: Recoil separators are employed to select and identify nuclei of interest, produced in a nuclear reaction, rejecting unreacted beam and other undesired reaction products. It is important to know what fraction of the selected nuclei, leaving the target, reaches the detection system. This information is crucial for determining absolute cross section of the studied reaction.Solution method:Interaction of projectiles with target nuclei is treated event by event, semimicroscopically. Position and angle (with respect to beam direction), energy and charge state of the reaction products are calculated by Monte Carlo method. Trajectory of each nuclei inside the separator is then calculated by ion optical transfer matrix method. Ratio of the number of trajectories completing their journey up to the detection system to the total number of trajectories is a direct measure of absolute transmission efficiency of the separator.Restrictions: The present version of the code is applicable to complete fusion reactions only. The code can be applied to other types of reactions (e.g., few nucleon transfer) as well, by suitably modifying energy and angular distribution of reaction products. Also, ion optical specifications and acceptance are unique for each recoil separator. Transmission efficiency calculation has been done for a specific recoil separator, viz. the Heavy Ion Reaction Analyzer [2,3] at IUAC. One has to make necessary changes in the code, while performing calculations for other recoil separators. Further, atomic number of the residual nucleus should not exceed 92, as the method used for calculating stopping power of ions [4] is valid for Z?92.Running time: From few seconds to several minutes depending on the reaction, number of events and separator layout.References:

[1]

http://www.astro.caltech.edu/~tjp/pgplot/.

[2]

A.K. Sinha, N. Madhavan, J.J. Das, P. Sugathan, D.O. Kataria, A.P. Patro, G.K. Mehta, Nucl. Instr. Methods A 339 (1994) 543.

[3]

S. Nath, Nucl. Instr. Methods A 576 (2007) 403.

[4]

J.F. Ziegler, J.P. Biersack, U. Littmark, The Stopping and Range of Ions in Solids, vol. I, Pergamon Press, Oxford, 1984.

     

Laser boronising of Ti–6Al–4V as a result of laser alloying with pre-placed BN

This paper discusses the effect of CO₂ laser alloying of pre-placed BN coating with Ti–6Al–4V alloy. The formation of titanium boride and titanium nitride investigated using energy dispersive X-ray diffraction (EDXRD) result were related to the microhardness and microstructure. The nitrogen and boron diffusion during the laser boronising process identified using secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectrometry (XPS) analysis was compared with the EDXRD results. The surface hardness HV1500–1700 observed at the boronised layer was five to six times higher than that of untreated Ti–6Al–4V alloy. This was compared with needle platelet and dendrite type microstructures. Theoretically estimated surface temperature values were used to interpret the compound formation in the laser alloyed layer.     

Content-based image classification with wavelet relevance vector machines

This paper introduces the use of relevance vector machines (RVMs) for content-based image classification and compares it with the conventional support vector machine (SVM) approach. Different wavelet kernels are included in the formulation of the RVM. We also propose a new wavelet-based feature extraction method that extracts lesser number of features as compared to other wavelet-based feature extraction methods. Experimental results confirm the superiority of RVM over SVM in terms of the trade-off between slightly reduced accuracy but substantially enhanced sparseness of the solution, and also the ease of free parameters tuning.     

Preparation of In2O3 and tin-doped In2O3 films by a novel activated reactive evaporation technique

High quality films of In₂O₃ and tin-doped In₂O₃ were prepared by a novel activated reactive evaporation technique developed for use with resistively heated evaporation sources. Transparent conducting coatings of In₂O₃ have a sheet resistance of 80 Ω/□ with an optical transparency of more than 95% in the 0.4–1.6 μm wavelength range. Thin (0.4 μm) In₂O₃(Sn) films have a sheet resistance of 25 Ω/□ and an optical transparency as high as 99% at some wavelengths with an average transmission between 0.4 and 1.6 μm of 96%. Thicker films have a sheet resistance as low as 2.2 Ω/□. A comparison of the properties of In₂O₃(Sn) films with those of transparent conducting films produced by other techniques is made.     

ESR of vanadyl ions in borate glasses A. YADAV,V. P. SETH

The electron spin resonance (ESR) of VO²⁺ in Li₂O-RO-B₂O₃ (where R = Sr, Zn) glasses hasbeen studied. Spin Hamiltonian parametersg _\tT,g\t],A _\tT andA\t], dipolar hyperfine coupling parameterP and Fermi contact interaction parameter K have been calculated. It is found that with a decrease in the percentage of B₂O₃ there is an improvement in the octahedral symmetry of the V⁴⁺ site. The theoretical optical basicity A_th, of the glasses has also been calculated.     

Laser etching and dry processing

Controlled, anisotropic etching of different materials commonly used in microelectronics is an important processing step in microfabrications. During recent years it has been demonstrated that lasers can be used for initiating and enhancing the etching process in many gas-solid (dry processing) and liquid-solid (wet processing) systems. The laser-induced reaction could be either photochemical or thermochemical. Using laser etching technique a variety of materials such as Al, Ta, Ni/Fe, GaAs, InP, Si, SiO₂ mylar, different polymers and superconducting materials have been processed. In this paper we briefly review these laser etching experiments.     

Electrical and optical properties of In2O3: Sn films prepared by activated reactive evaporation

In₂O₃: Sn films were prepared by an activated reactive evaporation technique developed for this purpose. The films were characterized by transmission electron microscopy, electron diffraction, electrical resistivity and measurements of transmittance as a function of wavelength. The electrical resistivity is found to be strongly dependent on process parameters such as the tin content and the deposition temperature. In contrast, the transmittance is found to be only weakly dependent on various process parameters. Under optimum conditions, films with an electrical resistivity of 7 × 10^?5 Ω cm with an integrated (0.4–1.2 μ) transmittance of over 90% were obtained.