Tensile static, fatigue and relaxation behaviour of closed cell electret PVDF foams

We present the experimental results related to the mechanical behaviour under tensile static, fatigue and compressive relaxation loading of closed cell PVDF electret foams under different loading ratio conditions. The specimens are statically loaded until 60% of their ultimate displacement, and subsequently subjected to cyclic loading under displacement control. The static tests show a stress–strain behaviour and failure mode similar to the one of other polymeric closed cell materials, such as polymetacrylimide-based foams. The fatigue tests show an evolution of the stiffness degradation over the levels of cycles characterised by three distinct phases. The behaviour of the energy dissipated versus the loading ratios and numbers of cycles applied is discussed in this paper, as well as the comparison between the compressive fatigue behavior recorded on similar classes of foams. The compressive relaxation behaviour shows a two-phase dependence over the loading time, with increasing modulus for higher loading ratios, and absence of an asymptotic modulus for long time exposure.