Bio-based Composites as Thermorheologically Complex Materials

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 delta 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.