EFFECT OF LOADING TIME ON THE LINEAR VISCOELASTIC PARAMETERS OF BORASSUS AETHIOPUM MART

In the construction sector, wood proves to be an ecologically advantageous material. Its production requires less energy compared to other materials, making it highly beneficial for the environment. It is a natural material whose level of stress and loading duration can significantly influence its physical and mechanical characteristics. For a proper understanding of the instantaneous and delayed behavior of wood, it is essential to subject it to tests under various types of loading, especially in the short and long term. This study focuses on the delayed behavior of Borassus wood, conducting creep tests on suitable samples to analyze the effects of loading duration on its viscoelastic parameters. The creep test was carried out by uniformly subjecting the samples to two-point bending, with a load corresponding to 20% of the breaking load, for a period of 15 hours. The instantaneous deflection was recorded a few seconds after loading, then other deflections were recorded every 30 minutes until the end of the test. Based on the geometry of a deformed beam, the general expression of the longitudinal strain was established, allowing all strains to be calculated as a function of the recorded deflections. The linear viscoelastic parameters of Borassus were determined using the nonlinear least squares method for each observed loading time. Analysis of the results shows that the loading duration does not influence the dynamic viscosity modulus, whereas the elasticity modulus varies decreasingly from the shortest to the longest loading duration. The use of a power function made it possible to establish a relationship between the dynamic elasticity modulus and loading time, which could be used as a means of extrapolation for deformations.