Scaling effects on the mechanical performance of symmetrical and balanced thermoplastic laminates

Symmetrical and balanced (±45°) composites of polypropylene reinforced with Twaron fiber were studied to understand the scaling effects on their mechanical performance when tested under tension. The prepregs were prepared in an electrostatic machine by the powder method. The laminates, prepared by compression molding, had an architecture based on an 8-ply laminate, which consisted of unidirectional plies arranged in the sequence [+45°, −45°, +45°, −45°]s; this laminate was considered as the baseline, used to scale one (thickness by sublaminate level scaling method), two (in-plane) and three (volume) dimensions. Tensile properties between the different scaled compounds were compared and the influence of specimen dimensions on stress/strain response was studied. For thickness scaled compounds, no significant size effect was observed, but the results showed a clear influence on the mechanical performance for the in-plane and volume scaled compounds; the increasing size scale made them more ductile. The evidence showed that the failure mechanism of thermoplastic laminates was governed by interfacial failure.