Mechanical characterization of innovative 3D multi-cell thermoset composites produced with weft-knitted spacer fabrics

Innovative three-dimensional integrated weft-knitted spacer (3D-IWKS) fabrics due to their unique features and flexibility in design, have recently gained significant popularity. These newly-designed fabrics could meet the requirements of numerous technical applications such as composite manufacturing. This work aims to investigate bending and compression resistance of 3D-IWKS composites with different cross-section geometries. Using 400(Tex) E-glass yarns, two types of 3D-IWKS fabric samples as U-shaped single-decker structure (USSD) and V-shaped single-decker structure (VSSD) were knitted on a modern flat knitting machine. The fabric preforms were then molded via vacuum infusion process (VIP) using epoxy resin in order to produce composite panels in the form of multi-cell thin-walled configurations. As far as bending strength and stiffness was concerned, VSSD composites were found to be superior to USSD type. The influence of connecting layers' orientation against the applied loads was also evaluated via flatwise compression test. The results pointed to higher strength of USSD samples with vertical inter-connecting layers in comparison to VSSD samples with angularly inter-connecting layers. By comparing the edge-wisely compressed specimens, it was found that both types of samples are similar in load-bearing capacity. The findings totally confirm the high mechanical applicability of these new structures.