Mechanical performance of stretched knitted fabric glass fibre reinforced poly(ethylene terephthalate) composites produced from commingled yarn

Weft knitted glass libre (GF) fabric reinforced poly(ethylene terephthalatc) (PKT) composite sheets were manufactured by hoi pressing of stacked plain knitted fabric layers. The knits were produced from a commingled yarn containing 70 wt-% (~~50 vol.-%) GF. The reinforcing knits were stretched in the wide direction at various ratios prior to consolidation. The PET matrix of the composite was either amorphous or semicrystallinc. The static mechanical performance of the knitted GF-PBT composite sheets was studied in tension, compression, and flexure. Measurements were carried out on specimens in both wale and course directions of the reinforcing knit in order to assess the structural anisotropy. The inherent anisotropy of the unstretched knit was well reflected in the strength data: the response in the wale direction was superior to that measured in the course direction. The mechanical anisotropy increased with increasing stretching of the knit. The dynamic perforation impact behaviour of the composites was determined by instrumented falling weight impact tests. The static and particularly the dynamic performance of thc composites with amorphous PET was superior to that of the semicrystalline version.