Bio-based Composites as Thermorheologically Complex Materials

Abstract

Because of their structure, natural fibers exhibit nonlinear viscoelastic behavior. Thermoset resins also behave in a similar way. With the increase in structural applications of bio-based composites, the long-term creep behavior of these materials becomes a significant issue. Time-Temperature superposition (TTS) provides a useful tool to overcome the challenge of needing a long time to perform creep tests. TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior. In this study, frequency scans of flax/VE composites were obtained at different temperatures and storage modulus, loss modulus and tan δ were recorded. Application of horizontal and vertical shift factors to all three viscoelastic functions were studied. In addition, short-term strain creeps at different temperatures were measured and curves were shifted both with only horizontal, and with both horizontal and vertical shift factors. Resulting master curves were compared with a 24-h creep test and two creep models. Findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curve for viscoelastic functions, while use of only horizontal shift factors for creep data provides an acceptable creep strain master curve. Consequently flax/VE composites can be considered as thermorheologically complex materials.