Abstract
Weft knitted glass fiber (GF) fabric reinforced polypropylene (PP) composite sheets were fabricated by hot pressing of stacked rib 1: 1 knitted fabric preform layers. The knitted preforms were made from GF/PP commingled yarn containing 50 vol% (≈73 wt%)GF. Before hot pressing, the preforms were stretched in the wale direction at various ratios. The tensile properties of the pre-stretched GF-PP composites were studied. It was found that there is a critical value of pre-stretch ratio as far as tensile stiffness and tensile strength are concerned. On increasing the pre-stretch ratio within the range of this critical value, both tensile stiffness and tensile strength increase. If the pre-stretch ratio goes beyond this critical value and continues to increase, both tensile stiffness and tensile strength display a tendency of slight decrease because of the break of more glass fibers. The failure strain of the composites decreases with the increase of the pre-stretch ratio because of the decrease of the stretchability of the knitted reinforcements.