Exact analysis of simply supported rhombic plates under uniform pressure

The simply supported rhombic plate under transverse load has received extensive attention from elasticians, applied mathematicians and engineers. All known solutions are based on approximate procedures. Now, an exact solution in a fast converging explicit series form is derived for this problem, by applying Stevenson's tentative approach with complex variables. Numerical values for the central deflexion and moments are obtained for various corner angles. The present solution provides a basis for assessing the accuracy of approximate methods for analysing problems of skew plates or domains.

Natural frequencies of polar orthotropic annular plates

The classical Rayleigh-Ritz method with simple polynomials as admissible functions has been used for obtaining natural frequencies of transversely vibrating polar orthotropic annular plates. The method in conjunction with transformations introduced in the analysis has been found to be quite effective, particularly for large hole sizes. Estimates of natural frequencies corresponding to modes with one as well as two nodal diameters are obtained for the nine combinations of clamped, simply supported and free edge conditions and for various values of rigidity ratio and hole sizes. Based on the variation of eigenvalue parameter with rigidity ratio, the frequencies of these modes as well as those of axisymmetric modes have been expressed by means of simple formulae in terms of rigidity ratio and the frequencies of corresponding modes in the isotropic case. These formulae have been used in determining the fundamental frequencies of orthotropic plates.

Natural frequencies of circumferentially truncated sector plates with simply supported straight edges

The classical Rayleigh-Ritz method in conjunction with suitable co-ordinate transformations is found to be effective for accurate estimation of natural frequencies of circumferentially truncated circular sector plates with simply supported straight edges. Numerical results are obtained for all the nine combinations of clamped, simply supported and free boundary conditions at the circular edges and presented in the form of graphs. The analysis confirms an earlier observation that the plate behaves like a long rectangular strip as the width of the plate in the radial direction becomes small.

Studies on CNTs/DNA composite

The electrical and optical properties of MWCNTs/DNA composite were studied. Electrical conductivity studies reveal that, the increase in CNTs concentration in DNA increases the conductivity. Fourier transformed Infrared (FTIR) spectrum shows that the CNTs are bonded to DNA covalently at the ends and defects sites and the wrapping of DNA on the CNTs is due to van der Waals force.

Combustion and Thermal Decomposition of Ammonium Perchlorate-Aluminium Composite Pellets: Mechanism for Aluminium Participation

Thermal behaviour of ammonium perchlorate-aluminium composites is studied using differential thermal analysis, thermogravimetry and differential scanning calorimetry. Electrical resistivity studies throw light on the mechanism of ammonium perchlorate decomposition at different aluminium contents. The differences observed in burning behaviour by earlier authors is explained in terms of porosity and thermal conductivity of the composite.

Thin-walled timber and FRP-timber veneer composite CEE-sections

This paper compares the structural performance between thin-walled timber and FRP-timber composite Cee-sections. While, thin-walled composite timber structures have been proven to be efficient and ultra-light structural elements, their manufacturing is difficult and labour intensive. Significant effort and time is required to prevent the cracking of the transverse timber veneers, bent in the grain direction, when forming the cross-sectional shape. FRP-timber structures overcome this disadvantage by replacing the transverse veneers with flexible, unidirectional FRP material and only keeping the timber veneers which are bent in their natural rolling direction. The Cee-sections investigated in this study were 210 mm deep × 90 mm wide × 500 mm high and manufactured from five plies. For both section types, the three internal plies were thin (1 mm thick) softwood Hoop pine (Araucaria cunninghamii) veneers, orientated along the section longitudinal axis. The two outer layers, providing bending stiffness to the walls, were Hoop pine veneers (1 mm thick) for the timber sections and glass fibre reinforced plastic (0.73 mm thick) for the FRP-timber sections orientated perpendicular to the inner layers. The manufacturing process is briefly introduced in this paper. The profiles were fitted with strain gauges and tested in compression. Linear Variable Displacement Transducers also recorded the buckling along one flange. The test results are presented and discussed in this paper in regards to their structural behaviour and performance. Results showed that the use of FRP in the sections increases both the elastic local buckling load and section capacity, the latter being increased by about 24 percent. The results indicate that thin-walled FRP-timber can ultimately be used as a sustainable alternative to cold-formed steel profiles.

Estimation of higher natural frequencies of polar orthotropic annular plates

A method based on an assumption that the radial bending moment is zero at a nodal circle is shown to yield accurate estimates of natural frequencies corresponding to higher modes of transversely vibrating polar orthotropic annular plates for various combinations of clamped, simply supported and free edge conditions. This method is found to be convenient for the determination of locations of nodal circles as well. Numerical investigations revealed that for small holes, nodal circles tend to move towards the outer edge with increasing number of nodal diameters. For large holes, it has been shown that the plate behaves like a long rectangular strip.

Vibration of generally orthotropic skew plates

Vibration problem of generally orthotropic plates with particular attention to plates of skew geometry is studied. The formulation is based on orthotropic plate theory with arbitrary orientation of the principal axes of orthotropy. The boundary conditions considered are combinations of simply supported, clamped, and free-edge conditions. Approximate solution for frequencies and modes is obtained by the Ritz method using products of appropriate beam characteristic functions as admissible functions. The variation of frequencies and modes with orientation of the axes of orthotropy is examined for different skew angles and boundary conditions. Features such as "crossings" and "quasi-degeneracies" of the frequency curves are found to occur with variation of the orientation of the axes of orthotropy for a given geometry of the skew plate. It is also found that for each combination of skew angle and side ratio, a particular orientation of the axes gives the highest value for the fundamental frequency of the plate.

Vibration of skew plates

The vibration problems of skew plates with different edge conditions involving simple support and clamping have been considered by using the variational method of Ritz, a double series of beam characteristic functions being employed appropriate to the combination of the edge conditions. Natural frequencies and modes of vibration have been obtained for different combinations of side ratio and skew angle. These detailed studies reveal several interesting features concerning the frequency curves and nodal patterns. The results presented should, in addition, be of considerable value and practical significance in design applications.

Natural frequencies of circumferentially truncated sector plates with simply supported straight edges

The classical Rayleigh-Ritz method in conjunction with suitable co-ordinate transformations is found to be effective for accurate estimation of natural frequencies of circumferentially truncated circular sector plates with simply supported straight edges. Numerical results are obtained for all the nine combinations of clamped, simply supported and free boundary conditions at the circular edges and presented in the form of graphs. The analysis confirms an earlier observation that the plate behaves like a long rectangular strip as the width of the plate in the radial direction becomes small.

Thermal Decomposition Studies on Ammonium Perchlorate—Polybutadiene Composite Propellant

The thermal decomposition of ammonium perchlorate based solid composite propellant using carboxyl terminated polybutadiene as binder has been studied employing thermogravimetry and differential thermal analysis techniques. The thermal decomposition characteristics of the propellant have been found to be quite similar to those of pure ammonium perchlorate with activation energy, 32 Kcal/mole and 60 Kcal/mole respectively in the low and high temperature regions. The effect of the sample size and shape on the thermal decomposition has also been evaluated.