Mechanical behaviour in shear and compression at elevated temperature of polyethylene terephthalate (PET) foam

Polyethylene terephthalate (PET) foams are being increasingly used as core of composite sandwich panels because of their improved thermal insulation and good strength-to-weight ratio. However, there is a major gap in the knowledge about PET foams: the lack of information about their mechanical response at elevated temperature or under fire. This paper presents experimental and analytical investigations regarding the influence of elevated temperature on the shear and compressive properties of PET foam. The glass transition temperature (T-g, similar to 65 degrees C) of PET foam was defined based on results obtained from dynamic mechanical analysis (DMA). Next, mechanical tests were carried out in PET foam specimens at elevated temperature, under steady-state conditions, for temperatures ranging from 20 degrees C to 190 degrees C, to determine the degradation of its shear and compressive properties with temperature. In the analytical study the suitability of four empirical formulations to describe the degradation of those mechanical properties of PET foam with temperature was assessed. The results obtained show that the compressive and shear properties of PET foam suffer drastic reductions with temperature, especially when its T-g is approached and exceeded. Such reductions occur for lower temperature when compared to other conventional polymeric foams, namely polyurethane, and this is mainly due to the lower T-g of the PET foam. All the analytical models were able to estimate with good accuracy the variation of the mechanical properties of PET foam as a function of temperature.