Effect of the loading duration on the linear viscoelastic parameters of tropical wood: case of Tectona grandis L.f (Teak) and Diospyros mespiliformis (Ebony) of Benin Republic

Judicious and regulated use of wood as a building material is better than that of many other conventional materials in terms of environmental issues of this century. The study of the behavior of wood requires a better understanding of the characteristics in different possible cases of loading including loads applied instantly, loads applied for a short time and loads applied for a long time. The purpose of this study is to evaluate the influence of the loading duration on the linear viscoelastic parameters of tropical wood in creep test. Creep tests conducted on two species of tropical wood, Tectona grandis L.f and Diospyros mespiliformis, were carried out for a total loading duration of 15 hours by subjecting samples to bending test through with equal strain in all sections. After measuring the instantaneous deflection, the other measurements were carried out at regular time each 30 minutes. Each recorded deflection was converted into longitudinal deformation and the data were analyzed by considering fourteen loading durations. Using the least squares method, the dynamic modulus of elasticity and the modulus of dynamic viscosity were determined for each loading time. The results showed that the loading time has no influence on the modulus of dynamic viscosity. On the other hand, the dynamic modulus of elasticity decreases and tends towards zero. Good agreement between creep test data and dynamic modulus of elasticity was found using mathematical function in power. Suitably, the "power" function established between the elastic dynamic modulus and the loading duration can be used to extrapolate deformations values.