FEPACS: A computational tool for linear structural analysis

FEPACS (Finite Element Package for linear static, dynamic and instability Analysis of Composite Structures under hygro-thermo-mechanical loads) incorporates a complete library of consistent and correct 1-, 2- and 3-dimensional linear and quadratic general purpose finite elements. In this paper, we shall discuss the finite element technology that has gone into the package as well as its present modelling and solution capabilities. We shall also discuss briefly recent developments toward enhancing the package: Robust composite elements based on aC ⁰-continuous higher order transverse deformation plate/beam theory, and nonlinear element technology and solution strategies. Finally, we shall also briefly touch upon several satellite application modules that are in different stages of planning/development to aid FEPACS: damage assessment/prediction,expert-like advisors for solid modelling and finite element modelling/analysis, pre-/post-processing for FEPACS applications, structural optimisation and related finite element algorithms, and finally, a frontal solution module for FEPACS to enhance its feasibility for vectorisation/parallelisation.     

Reduced integration and the shear-flexible beam element

A clearer insight into the ‘shear locking’ phenomenon, which appears in the development of C₀ continuous element using shear-flexible or penalty type formulations, is obtained by a careful study of the Timoshenko beam element. When a penalty type argument is used to degenerate thick elements to thin elements, the various approximations of the shear related energy terms act as different types of constraints and, depending on the formulation, two types of constraints which are classified as true or spurious may emerge. The spurious constraints, where they exist, are responsible for the ‘shear locking’ phenomenon, and its manifestation and elimination is demonstrated in a very simple example. The source of difficulty is shown to be the mathematical operations involved in the various shape function definitions and subsequent integration of functionals. It is seen that formulations that ensure only true constraints in the extreme penalty limit cases display far superior performance in the thick element situation as well, and thus guidelines for the development of efficient elements are drawn. A similar type of behaviour is observed in a shallow curved beam element and here ‘inplane locking’ can be eliminated by selective integration to obtain an improved curved beam element. However, ‘inplane locking’ does not cause a spurious constraint as the error quickly vanishes with the reduction of element size for a reasonable radius of curvature conforming with shallow shell theory.     

Effect of Carbon Nanotube Dispersion on Mechanical Properties of Aluminum-Silicon Alloy Matrix Composites

This study has been carried out to reinforce the commonly believed fact that the dispersion of carbon nanotubes in a composite has a profound effect on the properties of the composite. In this study, ball milling was carried out using two different parameters to obtain distinctly different degrees of dispersion of carbon nanotubes (4 wt.%) in Al-9 wt.% Si powders. Composite disks, 80 mm in diameter, having good and bad dispersions of carbon nanotubes were obtained by hot pressing. Optical micrographs and Raman spectroscopy images showed the presence of larger carbon nanotube clusters in the bad dispersion sample. Transmission electron microscopy images confirmed the presence of large clusters in the bad dispersion sample, while the good dispersion sample showed individual carbon nanotubes in the Al matrix. Nanoindentation results indicated a 41% increase in the hardness and a 27% increase in the elastic-to-plastic work ratio, while compression tests indicated a 185% increase in compression yield strength and a 109% increase in fracture strength with improvement in carbon nanotube’s dispersion.     

Free Convective Flow in an Open‐Ended Vertical Porous Wavy Channel with a Perfectly Conductive Thin Baffle

The problem of steady two‐dimensional free convective flow of a Walters fluid (model B ′) in a porous medium between a long vertical wavy wall and parallel flat wall in the presence of a heat source is discussed. The channel is divided into two passages by means of a thin, perfectly conductive plane baffle and each stream will have its own pressure gradient and hence the velocity will be individual in each stream. The governing equations of the fluid and the heat transfer have been solved subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and disturbance or perturbed part. Exact solutions are obtained for the mean part and the perturbed part is solved using long wave approximation. Results are presented graphically for the distribution of velocity and temperature fields for varying physical parameters such as Grashof number, wall temperature ratio, porous parameter, heat source/sink parameter, product of non‐dimensional wave number, and space‐coordinate and viscoelastic parameter at different positions of the baffle. The relevant flow and heat transfer characteristics, namely, skin friction and the rate of heat transfer at both walls, has been discussed in detail. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21118     

Substrate temperature dependent physical properties of sprayed Zn0.76Mg0.24O films

The composition, microstructural and opto-electronic properties of Zn_1?x Mg _x O thin films grown by spray pyrolysis have been studied. The films were prepared on glass substrates at different substrate temperatures in the range, 200–350 °C for a fixed magnesium composition of x = 0.24. The films showed the predominant (002) reflection corresponding to the hexagonal wurtzite structure of ZnO. The preferred orientation doesn’t change with the deposition temperature. The films prepared at 300 °C showed good crystallinity with an average surface roughness of 6.2 nm. The optical studies revealed that the optical transmittance increased slightly with the increase of substrate temperature of the films. The variation of energy band gap, photoluminescence and electrical resistivity of the grown layers was also studied.     

Reaction of foetal tissues to intra-uterine subcutaneous injection of barium sulphate

Subpannicular injection of sterile barium sulphate in newborn rabbits produces an acute inflammatory response which is clearly seen at 24 hr and is well established at 48 hr. The processes of repair has begun by the 4th day with the appearance of proliferating capillaries and fibroblasts. In rabbit foetuses both vascular and cellular components of the acute inflammatory response are more prominent and appear earlier than in newborn rabbits, being well developed within 24 hr. The process of repair also begins earlier, proliferation of capillaries and fibroblasts being already prominent by 48 hr. By the 4th day the lesion is compact, less cellular and relatively avascular.