3D modelling of sandwich panels with functionally graded core

• Main Author: Woodward, Ben
• Published: University of Aberdeen 2014
• Subjects: 620; Sandwich construction
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606471

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.