Glass/polypropylene hybrid knitted fabrics for toughening of thermoset composites

This paper investigates tensile, flexural, impact and compression after impact (CAI) performance of weft knitted fabric reinforced thermoset composites containing glass/polypropylene (PP) hybrid yarns. Glass and PP yarns were combined at three different PP ratios and converted to supreme hybrid knitted structures using a circular knitting machine. Using PP yarns helped to decrease glass fibre breakages during the knitting process. It was observed that the addition of PP yarns decreased overall density of composites up to 22%. Fabric tensile test indicated that using PP yarns enhanced ductility of the knitted fabrics. Flexural strength of composites was decreased by addition of PP yarns for both wale and course direction at 3 and 4-point bending tests. However, hybrid composites had higher specific flexural strength when they all had same glass fibre volume fraction for 3-point bending strength. Similar results were achieved for tensile properties whilst hybrid composites had higher values after normalising the same fibre volume fractions. Impact and CAI test results exhibited that the addition of PP yarns enhanced impact and damage tolerance of composites as well as reducing impact induced areas.