Sandwich panels are a type of structural panel, typically comprising two thin layers of high strength and stiffness known as face sheets which separate a thicker lightweight core of lower strength, stiffness and density. When combined, these layers offer excellent flexural strength to weight ratio without compromising on stiffness. Sandwich panels are utilised in a wide range of industries and applications from aerospace to construction. Due to mismatch of properties between face sheets and core, stress concentrations can occur at the interfaces, often causing delamination. One solution is inclusion of a functionally graded core; a core with properties which vary gradually from the face sheets to the centre, eliminating any abrupt changes in properties. Current research presents newly developed three dimensional analytical and numerical solutions used to gain further understanding of the introduction of a functionally graded core. A three dimensional elasticity solution for an isotropic sandwich panel with stiffness of the core graded in the thickness direction was developed, allowing for comparison of panels with functionally graded and homogenous cores to be completed. It was discovered that inclusion of the graded core removes the discontinuity in stresses at the interfaces and decreases both in- and out-of plane displacements throughout the panel. Since many real functionally graded materials do not exhibit isotropic characteristics, a three dimensional elasticity solution was thereafter developed for a sandwich panel with transversely isotropic core. The effects of individual engineering constants on panel performance were then studied and it was noted that the effects of shear deformation are obvious in thinner panels and those with low transverse shear modulus. A finite element model in ABAQUS was also developed, allowing geometry, loading and boundary conditions to be easily varied. To capture the continuously varying properties of the graded core, user defined graded finite elements were implemented.

The load-deflection behavior of a US Army Corps of Engineers available sandwich plates in three-point bending with glass phenolic facings and balsa wood core is being investigated under room and elevated temperatures. Test data on bending rigidity, critical interfacial failure (skin-to-core interface) and shear stress are collected and analyzed. The load-deflection curves plots up to the point of failure initiation are being studied. The effects of the span and the radius of the loading nose on the bending modulus and strength are examined systematically. Theoretical calculations from a modified beam theory of sandwich structure are applied and the effect of the shearing rigidity of the core is studied, and the propensity with respect to the span is also investigated. A finite element model is developed to study the flexural and stress analysis. Based on the results, this thesis proposes a desirable analytical approach that correlates theory with experiment as defined below.

This thesis deals with a systematic procedure for the derivation of exact expression for the frequency equation of composite beams undergoing forced vibration with damping. The governing differential equations of motion of the composite beam are derived analytically for bending and shear deformation. The basic equations of Timoshenko beam theory and assumption of maximum rate of dissipation are employed. The principle involved is that of vibration energy dissipation due to damping as a result of deformation of materials in sandwich beam. The boundary conditions for displacements and forces for the cantilever beam are imposed and the frequency equation is obtained. The expressions for the amplitude of displacements are also derived in explicit analytical form. Numerical results of the displacement amplitude in cantilever sandwich beam varying with damping coefficient are evaluated.

This thesis deals with a systematic procedure for the derivation of exact expression for the frequency equation of composite beams undergoing forced vibration with damping. The governing differential equations of motion of the composite beam are derived analytically for bending and shear deformation. The basic equations of Timoshenko beam theory and assumption of maximum rate of dissipation are employed. The principle involved is that of vibration energy dissipation due to damping as a result of deformation of materials in sandwich beam. The boundary conditions for displacements and forces for the cantilever beam are imposed and the frequency equation is obtained. The expressions for the amplitude of displacements are also derived in explicit analytical form. Numerical results of the displacement amplitude in cantilever sandwich beam varying with damping coefficient are evaluated.

Th. doct.--Paris 7, 2002. / Bibliogr. p. 147-152. Résumé en français et en anglais. L'ouvrage porte par erreur : ISSN 0078-3780.

Thesis (M.S. in civil engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 26, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references.

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This thesis explores two hybrid systems employing a core material reinforced by an external skin, namely, cladding walls composed of polyurethane foam core sandwiched between fibre-reinforced polymer (FRP) skins, and beams composed of concrete-filled FRP or steel tubes. The walls were studied in two phases. In phase I, the polyurethane foam core was injected between two carbon-FRP (CFRP) skins. Ten panels were tested to investigate their structural performance and failure modes. Test parameters included quality control in terms of reproducibility of test results, moment-shear ratio, and the orientation of an architectural masonry-like coating. The study showed that design is governed by stiffness and not strength and that the CFRP was underutilized. Also, quality control was shown to be poor for this method of fabrication. As such, in phase II, ten panels were fabricated by laminating glass-FRP (GFRP) skins to prefabricated polyurethane foam blocks. Similar flexural testing was carried out to investigate two different densities of foam, and moment-shear ratio. The study showed evidence of high quality control and that the density of the foam core significantly affected flexural capacity and stiffness. Rectangular concrete-filled tubes (CFTs), with either steel or pultruded GFRP tubes were fabricated and tested as beams in three-point bending, at different shear span-to-depth (a/d) ratios of 1 to 5 to examine crack patterns, strength and failure modes. It was shown that the critical (a/d) ratio, at which moment capacity drops, is between 4 and 5 for CFTs with GFRP tubes and between 1 and 2 for CFTs with steel tubes. It was also shown that ductility is drastically reduced at (a/d) ratios below 3 for steel tubes. Crack pattern and size were highly dependent on the magnitude of slip between the concrete and tube. A major full depth flexural crack developed in all CFTs with GFRP tubes. However, when internal steel rebar was added, major diagonal cracks were formed in addition to fine flexural cracks. In CFTs with steel tubes, fine flexural cracks developed, except at a/d = 1, where fine diagonal cracks were predominant. A strut-and-tie model was developed and provided reasonable agreement with test results. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-12-23 12:25:09.685

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