W. Karunasena

Wave Propagation in a Multilayered Laminated Cross-Ply Composite Plate

Dispersion of guided waves in a cross-ply laminated plate has been studied here using a stiffness method and an exact method. It is shown that the number of laminae strongly influences the dispersion behavior. Further, it is found that when the number of laminae is sufficiently large, then the dispersion behavior can be predicted by treating the plate as homogeneous with six stiffness constants obtained by using an effective modulus method.

Characterisation of recycled mixed plastic solid wastes: Coupon and full-scale investigation.

In Australia, the plastic solid waste (PSW) comprises 16% by weight of municipal solid waste but only about one-fourth are recycled. One of the best options to increase the recycling rate of mixed PSW is to convert them into products suitable for construction. However, a comprehensive understanding on the mechanical behaviour of mixed PSW under different loading conditions is important for their widespread use as a construction material. This study focuses on investigating the mechanical behaviour of recycled mixed PSW containing HDPE, LDPE and PP using coupon and full-scale specimens. From coupon test, the strength values were found to be 14.8, 19.8, 20, 5.6MPa in tension, compression, flexure and shear respectively, while the modulus of elasticity are 0.91, 1.03, 0.72GPa in tension, compression and flexure respectively. The coefficient of variance of the measured properties for coupon and fullscale specimens was less than 10% indicating that consistent material properties can be obtained for mixed PSW. More importantly, the strength properties of mixed PSW are comparable to softwood structural timber. The flexural behaviour of full-scale specimens was also predicted using fibre model analysis and finite element modelling. Comparison showed that using coupon specimens properties, the flexural behaviour of the full-scale specimens can be predicted reliably which can eliminate the costly and time consuming arrangements for full-scale experimental tests.

Reflection of plate waves at the fixed edge of a composite plate

An approximate method based on the wave‐function expansion procedure has been used to solve the problem of reflection of time harmonic plane strain waves normally incident upon the fixed edge of a semi‐infinite, uniaxially fiber‐reinforced, composite plate of linearly elastic materials. Both symmetric and antisymmetric incident waves have been considered. The dispersion relation of the infinite plate has been solved through an approximate technique to obtain wave functions. The amplitudes of reflected waves have been determined by satisfying the fixed edge condition through the application of a variational principle. It is shown that the results agree well with known solutions for homogeneous isotropic plates. Numerical results are presented for a graphite/epoxy composite plate. The accuracy of the results is demonstrated through satisfaction of the principle of energy conservation and the reciprocity relations. The influence of fiber‐direction elastic stiffness on reflection coefficients has also been st...

Vibration of unsymmetrically laminated thick quadrilateral plates

The problem of free vibration of arbitrary quadrilateral unsymmetrically laminated plates subject to arbitrary boundary conditions is considered. The Ritz procedures supplemented by the simple polynomial shape functions are employed to derive the governing eigenvalue equation. The displacements are approximated by a set of polynomials which consist of a basic boundary function that impose the various boundary constraints. A first-order shear deformable plate theory is employed to account for the effects of the transverse shear deformation. The numerical accuracy of the solution is verified by studying the convergence characteristics of the vibration frequencies and also by comparison with existing results. The new results of this study include the sensitivity of the vibration responses to variations in the lamination, boundary constraints and thickness effects, and also their interactions. These numerical values are presented for a typical graphite/epoxy material, in tabular and graphical forms.

Exact solutions for axisymmetric bending of continuous annular plates

This paper is concerned with obtaining exact solutions for the axisymmetric bending problem of elastic annular plates with internal concentric supports. The standard stiffness method of analysis is employed to solve the problems. The solutions can be obtained either numerically or in closed-form. Both thin and thick plates can be handled. For the thick plate analysis, the Mindlin plate theory has been adopted to cater for the effect of transverse shear deformation. Relationships between Kirchhoff and Mindlin plate solutions have been used to derive the stiffness matrix of thick plates. Present solutions are compared with published results for some representative annular plate bending problems to demonstrate their validity. Exact solutions for displacement, shear force and bending moment for an annular plate with an internal concentric support are presented. Numerical results showing the influence of transverse shear deformation on edge displacement under a concentric ring load applied at the free inner edge of a free/continuous support/fixed plate are also presented.

Vulnerability of floodways under extreme flood events

Floodways are commonly used in rural road networks due to the economic and environmental benefits offered as a low-cost and practical road crossing in flood-prone areas. They are designed with provision for submergence so that water flows over with minimum impediment to flow, at a probability given design flood. The floodway design process is traditionally governed by hydraulic aspects rather than structural aspects. Hydrological condition, availability of material, and familiarity of construction techniques are significant when selecting the floodway type. Nevertheless, extreme conditions can cause significant damage to floodways, as was evident from the 2011 and 2013 Queensland flood events, during which 58% of floodways in the Lockyer Valley Regional Council (LVRC) area in Queensland, Australia, which is the case study area of this paper, were damaged, causing huge economic lost at council and national level. This created a new track in research and development activities to assess vulnerability and to find methods for improving the resilience of floodways during extreme flood events. In line with this, the present study evaluates local design guidelines and damaged floodways to assess failure modes and severity of damage using a damage index (DI) method.

Guided waves in a jointed composite plate

Reflection of guided waves by a thin region of bonding material at the interface between two composite plates has been investigated in this paper. The study is motivated by the need to develop a quantitative ultrasonic technique to characterize properties of joints between two plates, which may be laminated and anisotropic. Although there have been some recent studies that have examined the reflection and transmission of surface waves at the interface between two plates, they consider the two plates to be semi‐infinite in thickness. Thus the mode conversion of waves into higher guided modes of the plates are not taken into account. In this paper, a model study of the interaction of the A0 and S0 guided wave modes with the joint material is presented. It is shown that as the frequency increases the coefficient of reflection shows resonant peaks at the cutoff frequencies of higher guided modes. These peaks become increasingly pronounced as the thickness of the joint increases. Another interesting feature is...

Behaviour of hollow pultruded GFRP square beams with different shear span-to-depth ratios

It is important to determine accurately the elastic properties of fibre-reinforced polymer composites material, considering that their member design is often governed by deflection rather than strength. In this study, the elastic properties of the pultruded glass fibre-reinforced polymer square sections were evaluated firstly using full-scale with different shear span to depth (a/d) ratios and tested under static four-point bending. Back calculation and simultaneous methods were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the coupon tests. Secondly, the full-scale beams were tested up to failure to determine their capacity and failure mechanisms. Finally, prediction equations describing the behaviour of the pultruded glass fibre-reinforced polymer square beams were proposed and compared with the experimental results. The results indicate that the back calculation method gives more reliable values of elastic properties of glass fibre-reinforced polymer profiles. In addition, the behaviour of the beams is strongly affected by the a/d ratios. The shear was found to have a significant contribution on the behaviour of beams with lower a/d ratios while the flexural stress played a major part for higher a/d ratios. The proposed equation, which accounts for the combined effect of the shear and flexural stresses, reasonably predicted the failure load of pultruded glass fibre-reinforced polymer square beams.

Mechanical properties characterization of the skin and core of a novel composite sandwich structure

This study has investigated the mechanical properties of the constituent materials of a novel structural composite sandwich panel developed for structural applications. Properly designed and carefully conducted experiments using coupon specimens following ISO and ASTM test standards were performed to characterize the flexural, tensile, compressive and shear properties of the fiber composite skins and the modified phenolic core of the composite sandwich structure. As a general behavior, the glass fiber composite skins behaved linearly elastic up to failure in both tension and compression with the tensile strength much higher than the compressive strength. The modified phenolic core behaved linearly elastic in tension but exhibited non-linear behavior in compression. The modified phenolic core material exhibited higher strength and modulus in shear and compression compared to the traditional core material systems. The improved mechanical properties of the core structure combined with the high-strength and lightweight glass fiber composite skins suggest a high potential of the novel composite sandwich panel for structural applications. Furthermore, the results of this study provide an understanding of the fundamental behavior of the constituent materials of a novel sandwich structure providing a base knowledge from which further research could continue.

Ductility enhancement of geopolymer concrete columns using fibre-reinforced polymer confinement

Geopolymer concrete is an environmentally friendly, green construction material. However, its use is constrained by its increased brittleness and lack of understanding of its behaviour under multi-axial loadings. Similar to ordinary portland cement concrete (OPC), the ductility of geopolymer concrete columns can be increased by lateral confinement and using fibre-reinforced polymers is one option in doing that. This research paper aims at investigating the effect of different confinements on the ductility of geopolymer concrete. Three different mixes with varying binder (fly ash and slag) and different curing conditions together with different levels of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) confinement were investigated in this research paper. FRP confined normal strength geopolymer concrete shows similar stress–strain behaviour when compared to that of high-strength OPC concrete When compared with the same level of confinement, CFRP confined geopolymer concrete marginally outperforms GFRP confined geopolymer concrete in 28-day compressive strength. However, ductility levels with GFRP confinement are better than those with CFRP confinement.