Abstract
With the increase in structural applications of bio-based composites, the study of long-term creep behavior of these materials turns into a significant issue. Because of their bond type and structure, natural fibers and thermoset resins exhibit nonlinear viscoelastic behavior. Time-temperature superposition (TTS) provides a useful tool to overcome the challenge of the long time required to perform the tests. The TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior, therefore creep tests performed at elevated temperatures may be converted to tests performed at longer times. In this study, flax fiber composites were processed with a novel liquid molding methacrylated epoxidized sucrose soyate (MESS) resin. Frequency scans of flax/MESS composites were obtained at different temperatures and storage modulus and loss modulus were recorded and the application of horizontal and vertical shift factors to these viscoelastic functions were studied. In addition, short-term strain creep at different temperatures was measured and curves were shifted with solely horizontal, and with both horizontal and vertical shift factors. The resulting master curves were compared with a 24-h creep test and two extrapolated creep models. The findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curves for loss modulus and storage modulus, while use of only horizontal shift factors for creep data provides acceptable creep strain master curves. Based on the findings of this study, flax/MESS composites can be considered as thermorheologically complex materials.
Highlights
Frequency scans of flax/methacrylated epoxidized sucrose soyate (MESS) composites were obtained at different temperatures and storage modulus, loss modulus and tan δ were recorded
The resulting master curves were compared with a 24-h creep test and two creep models that were mentioned previously
In order to study the thermal and mechanical behavior of methacrylated epoxidized sucrose soyate (MESS) resin reinforced with flax fiber, frequency scans of flax/MESS composites were obtained at different temperatures and storage modulus, loss modulus were recorded
Summary
Because of environmental impact of natural fibers [1], and having lower density, higher toughness and comparable specific strength and specific stiffness to mineral fibers, such as glass fiber, bio-based composites are considered a preferred alternative to conventional composites [2,3]. When using natural fibers it is important to understand that unlike synthetic or mineral-based fibers, natural fibers exhibit nonlinear elastic behavior. The nonlinearity in elastic behavior is the result of the natural fiber’s structure. The multiple layers (primary and secondary walls) that make up the natural fiber’s structure lead to the viscoelastic behavior. There are several different layers that make up the fiber’s structure, which are the primary wall, secondary wall, and the center lumen [4,5].
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