A comparison of mechanical properties of some foams and honeycombs

The mechanical properties of foams and honeycombs are compared using a normalizing procedure and it is suggested that ideal closed cell foams may be comparable or superior to honeycombs.     

Symmetric Galerkin boundary formulations employing curved elements

Accounts of the symmetric Galerkin approach to boundary element analysis (BEA) have recently been published. This paper attempts to add to the understanding of this method by addressing a series of fundamental issues associated with its potential computational efficiency. A new symmetric Galerkin theoretical formulation for both the (harmonic) heat conduction and the (biharmonic) elasticity problem that employs regularized singular and hypersingular boundary integral equations (BIEs) is presented. The novel use of regularized BIEs in the Galerkin context is shown to allow straightforward incorporation of curved, isoparametric elements. A symmetric reusable intrinsic sample point (RISP) numerical integration algorithm is shown to produce a Galerkin (i.e. double) integration strategy that is competitive with its counterpart (i.e. singular) integration procedure in the collocation BEA approach when the time saved in the symmetric equation solution phase is also taken into account. This new formulation is shown to be capable of employing hypersingular BIEs while obviating the requirement of C¹ continuity, a fact that allows the employment of the popular continuous element technology. The behaviour of the symmetric Galerkin BEA method with regard to both direct and iterative equation solution operations is also addressed. A series of example problems are presented to quantify the performance of this symmetric approach, relative to the more conventional unsymmetric BEA, in terms of both accuracy and efficiency. It is concluded that appropriate implementations of the symmetric Galerkin approach to BEA indeed have the potential to be competitive with, if not superior to, collocation-based BEA, for large-scale problems.     

Parallel merging: algorithm and implementation results

An efficient parallel algorithm for merging two sorted lists is presented. The algorithm is based on a novel partitioning algorithm that splits the two lists among the processors, in a way that ensures load balance during the merge. The partitioning algorithm can itself be efficiently parallelized, allowing the solution to scale with increased numbers of processors. A shared memory multiprocessor is assumed. The time complexity for partitioning and merging is O(N/p + log N), where p is the number of processors and N is the total number of elements in the two lists. Implementation results on a twenty node Sequent Symmetry multiprocessor are also presented.     

Kinetics of fluorescence properties of Eu~(3+) ion in strontium-aluminiumbismuth-borate glasses

Eu3＋ doped strontium-aluminium-bismuth-borate glasses with the chemical composition（50–x）B2O3＋20Bi2O3＋7Al F3＋ 8Sr O＋15Sr F2＋x Eu2O3（where x=0.1 mol.%, 0.5 mol.%, 1.0 mol.% and 1.5 mol.%） were prepared by the conventional melt quenching technique.Structural properties of the prepared glasses were analysed through X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and Raman spectral techniques.Thermal stability of glass was analysed by differential thermal analysis（DTA） curve.Photoluminescence characteristics were studied using excitation, emission spectra and decay curves of Eu3＋ doped strontium-aluminium-bismuth-borate glasses.The Judd-Ofelt（J-O） intensity parameters, Ωλ（λ=2, 4 and 6） were obtained using emission spectra and was used to identify the nature of Eu3＋ ions with their surrounding ligands.Using J-O parameters the transition probabilities（A）, stimulated emission cross-sections σE p, branching ratios（βR） and radiative lifetimes（τmeas and τcal） were evaluated for the 5D0→7F J（J=0, 1, 2, 3 and 4） transition of Eu3＋ ions in the present glasses.The decay profiles were found to be non exponential for all the concentrations and the measured lifetimes（τmeas） were obtained from the decay profiles.The higher values of A, σE p, βR and quantum efficiency（η） for 5D0→7F2 emission transition at 617 nm confirmed the present glass was as active medium for red laser emission applications.     

Effect of cold rolling on mechanical properties and ballistic performance of nitrogen-alloyed austenitic steels

In this paper, the effects of different amount of cold rolling on mechanical properties, microstructure and ballistic resistance of nitrogen containing austenitic stainless steel in two different conditions have been presented. The ballistic performance was measured in terms of energy absorption against deformable projectiles. It is found that increased percentage of cold reduction increases the strength and hardness with loss of ductility and decreases the energy absorption of material. The nature of failures and damages of the targets has been studied and also the microstructural characterization has been carried out.     

An experimental study on the ballistic impact behavior of some metallic armour materials against 7.62 mm deformable projectile

The investigation describes and analyses the ballistic impact behavior of a high strength armour steel and Al-7017 alloy under 7.62 mm deformable projectiles at a velocity of 830 ± 10 m/s at normal angle of attack. The high strength armour steel is subjected to two different heat treatments to see the effect of different mechanical properties on the ballistic behavior. The ballistic result of the Al-7017 alloy is compared with that of the steel. Some observations relating to the adiabatic shear bands formation have also been presented. Experimental results showed that among the investigated materials, the best ballistic performance was attained with the armour steel at 910 °C austenitisation followed by 200 °C tempering condition.     

A new approach to optimise placement of wind turbines using particle swarm optimisation

In the present study, particle swarm optimisation has been used to resolve the placement of wind turbines in a wind park giving maximum power and efficiency with minimum number of turbines. Unlike past approaches where each plot was subdivided into smaller square grids at the centre of which a turbine can be placed, the present study does not require division of the plot. Thus, a turbine now has more flexibility to be placed anywhere outside a radius of 200 m of each other yielding better results. The case of unidirectional uniform wind is considered in this study. Along with the optimal layout, fitness value, total power output, efficiency and number of turbines have also been reported. Comparison with results of earlier study and possible explanation is also provided.