Micro and macro analysis of sisal fibre composites hollow core sandwich panels

In the view of the growing environmental concerns, hollow cores from recyclable natural fibre composites were manufactured to reduce the undesirable impact on the environment. To evaluate the feasibility of using short sisal fibres as reinforcements in the composites, existing micromechanical models have been used to predict properties starting from the intrinsic properties of its constituents. The stress relaxation behaviour of the composites was examined experimentally by performing tensile stress relaxation tests and to understand the process, it was modelled using variations of Maxwell's model. A steady-state finite element analysis in the linear range was performed in ANSYS environment to examine flexural properties of the panels, and the shear strength of the hollow cores was experimentally determined by subjecting them to flexural loads in a four-point bending scheme. The micromechanics models indicated that the fibres had failed to provide effective reinforcements with their existing lengths, acting as fillers rather than reinforcements. The stress relaxation models indicated that the formed part needs to be cooled to room temperature within the die under suitable forming loads to avoid local deformations due to warping. The mid-span deflections of the sandwich panels predicted by the FE model agree well with the experimental results, the analysis predicted facing buckling as a mode of failure when wood veneers facings of modulus 4.5 GPa and thickness 1.7 mm were used. The specific shear strengths of the reinforced core are more than twice than those of the unreinforced polypropylene cores, increasing the scope of such panels as structural members in various engineering facets.