Impact Damage Resistance of Knitted Glass Fiber Fabric Reinforced Polypropylene Composites

Knitted glass fiber reinforced polypropylene laminates were fabricated using a combination of co-knitted fabrics and compression molding. The knitted fabrics with different stitch densities were produced using a weft knitting machine. Laminates of 4 and 16 plies were fabricated. Initially, static indentation tests were conducted to determine the approximate energies associated with puncturing of the laminates. Drop tower impact tests were conducted using the same constraint and tup used in the static tests. The trends in peak load and puncture energy observed during static compression testing were similar to those observed in dynamic tests. Parameters that define the impact damage resistance of knitted fabric composites were identified. Both peak load and puncture energy were sensitive to the stitch density, number of plies and imposed strain rate. Efforts were made to compare the impact damage resistance of knitted fabric composites with other conventional reinforcing architectures, including continuous strand mat (CSM), plain weave and orthogonal non-woven fabric. A sensitivity index was proposed to compare the impact damage resistance of these different material systems.