Performance evaluation of kenaf-epoxy core sandwich structure via modeling and simulation

Abstract

In this work, the honeycomb core of sandwich panel was reinforced by kenaf fibres. The kenaf fibre was chosen since it has high stiffness-to-weight ratio and is environmentally friendly, cheap and easily machinable. The aim of this work was to determine the orthotropic material properties of the kenaf-epoxy core and to evaluate the performance of the kenaf-epoxy sandwich panel through the simulation of the simple bending test. The orthotropic material properties and performance in simulation of the kenaf-epoxy sandwich panel were compared with those of the glass-epoxy sandwich panel. Also, the objective of this work was to determine the effect of several parameters on the material properties and performance in simulation of the kenaf-epoxy sandwich panel. Two types of kenaf fibre -- short and long fibre -with varying fibre modulus, Ef, and fibre volume fraction, Vf, were utilised. Three different analysis cases were executed; varying cell wall thickness, varying cell wall length and varying core density.The finite element software ANSYS Mechanical APDL v13 was used to simulate the simple bending test. To model the kenaf core sandwich panel, continuum modeling was adopted since it could account for the extension of the adhesives into the composite honeycomb cells. Compared to the glass-epoxy core, the long kenaf-epoxy core had greater values of orthotropic material properties. On the other hand, the short kenaf-epoxy core had greater values of the in-plane moduli but smaller values of the out-of-plane modulus. The maximum displacement of the long kenaf-core sandwich panel obtained through the simulation was lower compared to that of the glass-core sandwich panel. On the other hand, the maximum displacement of the short kenaf-core sandwich panel was generally higher than the glass-core sandwich panel, except when the kenaf fibre was stiffer and fewer. Also, the short kenaf-core sandwich panel had the least higher stressed region compared to other cores as shown by the Von-Mises stress distribution. From the analysis it was concluded that the kenaf cores had better performance than the glass core when the weight and density of the cores were the same. Also, as the fibre volume fraction, Vf increased, the longitudinal and unidirectional fibre reinforcement of the long kenaf-epoxy core became more effective, while the random discontinuous fibre reinforcement of the short kenaf-epoxy core became less effective. Conversely, as the kenaf fibre modulus, Ef increased, the longitudinal and unidirectional fibre reinforcement of the long kenaf-epoxy core became less effective, while the the random discontinuous fibre reinforcement of the short kenaf-epoxy core became more effective. Additionally, when the core density was not altered, significant change did not occur, regardless of the change in the thickness and size of the core. The core density was the most decisive parameter to determine the properties of the continuum core.