Towards Assessment of Reliable Mechanical Properties for Knitted Fabric-Reinforced Thermoplastic Composites

Abstract

Since the mechanical performance of knitted fabric-reinforced thermoplastic (KFRT) composites is closely matched to composite laminates composed of unidirectional (UD) plies, attempts are made to adopt the characterization methods of the latter also for KFRT. This approach is not straightforward, and even not viable in many cases due to a peculiar load transfer and damage development associated with the knit structure. Although produced in plane, the knitted layers in the composites are never planar anymore, but tend to adopt a higher than two-dimensional (2D) reinforcing sructure. That is the main reason why established testing techniques which work well for advanced composites fail for KFRT. In order to determine reliable mechanical parameters for KFRT, the size of the damage zone (where stress transfer occurs) should also be considered. This paper lists some suitable measuring techniques and related aspects based on the experience gained on multilayer, plain weft knit-reinforced composites with various thermoplastic matrices.