An energy-based analytical push-out model applied to characterise the interfacial properties of knitted glass fibre reinforced PET

In this study, the interfacial properties of weft-knitted glass fibre (GF)-polyethylene terephthalate (PET) composites were examined. On thin polished cut-outs of knitted GF/PET composite parts, push-out experiments were carried out at different temperatures using a push-out device set up in a SEM. Load-displacement curves were digitally recorded. FEM results suggested that crack initiation was located at or near the top of the free specimen surface. To interpret the load-displacement curves from the push-out experiments a new energy-based model was proposed. The model follows the principle of minimal energy and includes the effects of friction, Poisson expansion of the fibre, and energy release of the debonded part of the fibre. Crack progression was calculated applying the concept of interfacial surface fracture energy. With the proposed analytical model, the interfacial properties of GF/PET were extracted. The model is compared with existing approaches.