Viscoelasticity of transparent wood-polymer biocomposites : Measuring the time-dependence of a delignified birch and poly(methyl methacrylate) composite’s mechanical properties, using digital image correlation

Sammanfattning: The viscoelastic behavior of a delignified birch and poly(methyl methacrylate) (PMMA) composite was investigated, in an effort to learn more about the mechanical properties of transparent wood-polymer biocomposites. Tensile creep tests with constant load were performed for native wood, non-delignified, and delignified wood-polymer composites. Both longitudinal (fibre direction) and transverse (perpendicular to fibre direction) loading directions were tested. Full-field strain analysis was performed using a digital image correlation (DIC) technique. The time-dependence of transverse strain, longitudinal strain, elastic modulus, and Poisson ratio was reported. The creep strain in the transverse fibre direction increased more than two times the longitudinal creep strain. The polymer phase in the wood-polymer biocomposites reduces the relative creep strain compared to native wood. A Kelvin model was used to determine the creep properties of the nominal strain data. Model parameters were obtained for the materials and the model shows a good fit for most materials. However, the Kelvin model parameters were not validated against other tests and are only used here for material comparison.