Strength-Based Design Optimization Studies on Rigid Polyurethane Foam Core-Glass and Carbon-Glass Fabric Face Sheet/Epoxy Matrix Sandwich Composites

Abstract

This investigation aims at designing and fabricating rigid polyurethane foam core/glass fabric-epoxy and carbon-glass fabric-epoxy sandwich composites with and without design optimization. Optimization of design was done for the sandwich beams using modified beam equations so as to obtain maximum strength in bending. Parameters like deflection, flexural rigidity, bending and shear stress, normal stress, and shear strain were determined for the sandwich composites and due comparison was made with the results evaluated for samples without design optimization. The above-mentioned sandwich composites with different low foam density values were fabricated using the conventional hand lay-up technique. Test samples were machined and the testing was carried out keeping the existing ASTM standard guidelines in mind, using a three-point bend test apparatus. It was observed that, though only the normal stress, bending stress, and shear stress were design optimized, the flexural rigidity also showed a considerable increase when compared with the results of the investigation where no design optimization was done. The observed failure modes of the specimens indicate that the true design optimized values for strength were not obtained despite considerable gains due to optimization. More insight towards achieving a closer optimization can be obtained by conducting the studies using higher densities of rigid foams of various materials and better epoxy resins keeping cost in mind. The existing standard regulations in the testing of sandwich specimens also deserve another look. The highlight of the work is in comparison of the optimized sandwich properties with the shape factors.