Macro- and micro-scale investigation of tensile behavior of thermoplastic weft knitted textile composites

This study investigates in-plane deformation of thermoplastic weft-knitted textile composites under tensile loading in both macro- and micro-scales. Interlock knitted textile preform was produced by co-knitting polyester (polyethylene terephthalate) continuous filament yarns as the fabric reinforcement and polypropylene yarns to be melted as the matrix material. Details of the consolidation process of this composite material will be described. In macro-scale characterization, the tensile properties of composite specimens were determined on the MTS Universal Testing Machine. The distinct tensile properties of the composite materials were compared with its individual components – fabric perform and brittle matrix. In micro-scale, in-situ SEM observation allowed critical points during tensile loading to be identified, including the brittle matrix crack initiation from imperfect composite surfaces, fibre/matrix debonding and serious loop distortion along the loading directions during the large deformation until composite fracture. Material characterization on the mechanical properties would be important for this kind of material to be further molded into three-dimensional structures.