Investigation into design and manufacture of reinforced lightweight composite sandwich plates based on polymer pyramidal kagome core

Abstract

Lattice-based sandwich structures are being widely investigated to meet increasing demands for lightweight components. In the recent research works, lattice-based open cell structures have exhibited higher specific strength compared to closed cell structures, such as a honeycomb structure. Generally, a kagome structure is more effective than other lattice structures for compression and bending. In this study, a Pyramidal Kagome (PK) structure was developed based on the conventional kagome structure. The PK structure was fabricated with three steps: manufacturing of a flat mesh by the injection molding process, forming of the pyramidal shape, and adhesion of two pyramidal structures. The material used for the PK structure was polypropylene (PP). The fabrication time was significantly reduced by employing the injection molding process compared with the conventional wire woven method. Furthermore, mechanical characteristics of the PK structure were examined by three-point bending and drop-weight impact tests. The test results were compared with PP core based commercial honeycomb structures. Moreover, the cross-sections of the strut of PK structure were developed to strengthen the sandwich structure. The tubular shape, semi-circular shape, and conventional flat rectangular shape in cross-section were investigated as the cross-section of the strut of the PK structure. From the modeling design, the cross-sectional areas were all the same as 0.6 mm2, while the geometrical moment of inertia of the semi-circular cross-section (SCC) was 4.4 times as high as that of the flat rectangular cross-section (FRC). The mechanical properties were investigated by the three-point bending and compression tests, and the results were compared with the flat rectangular cross-section (FRC)-based PK sandwich structure.

After the cross-section of the strut of the PK structure was developed, a design widow was investigated from the analysis. The failure modes of the composite PK sandwich structure were different with other metal-based truss sandwich structure because of its high elastic deformation characteristics of polymer. The failure modes of composite PK sandwich structure were thus investigated in this study. The bending deformation modes of the composite sandwich structure were investigated according to the ratio of bending stiffness of the face sheet to the shear stiffness of inner cores, and relative gap distance between PK structures. The failure modes according to the parametric value were defined. The defined failure modes of PK sandwich structure were categorized as the deformation window. Conventionally, sandwich structures have been fabricated as plane panels, which was a limitation when they were applied to the curved components. In this study, a bendable structure that can be applied to the curved surface was developed based on the PK structure. A bending zone for the adaption to the curved surface was designed between the neighboring PK structures. The effect of the bending zone was also considered. The dimension of the bending zone area was designed considering the parametric value from the deformation window. The SCC-PK sandwich structure was applied to the bending zone and the bendable SCC-PK structure was fabricated using the injection molding process. The final bendable SCC-PK sandwich structure was tested by the three-point bending test. The results were compared with the conventional FRC-PK sandwich structure and the conventional PET foam sandwich structure.