![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
Abstract
The present study examines the three-dimensional hygric and mechanical behavior of oak wood. The moisture equilibrium state, characterized by the sorption isotherms, was obtained from measurements taken during adsorption and desorption cycles. Sorption behavior was analyzed with the Dent theory and compared considering the sorption direction (adsorption/desorption cycle). Sorption parameters were provided for possible numerical applications in hygric material models. The corresponding swelling and shrinkage behavior was examined and characterized by the moisture expansion parameters for all anatomical directions. Orthotropic mechanical material behavior was characterized by determining the elastic engineering (Young's moduli, shear moduli, and Poisson's ratios) and the bending, compressive and compressive shear strength material parameters. Influence of moisture content (MC) on the mechanical material properties was studied using Young's moduli, Poisson's ratios, and the investigated strength parameters. A significant difference between the sorption behavior in adsorption and desorption, known as the hysteresis effect, could be proved. Furthermore, swelling and shrinkage behavior did not show any dependency on the adsorption/desorption cycle. The results confirm the significant influence of MC on the Young's moduli and the strength properties, however, did not validate an influence on the Poisson's ratios.
Summary
A direct comparison of the equilibrium MCs determined during adsorption and desorption experiments confirmed the well-known hysteresis effect for wood. The application of the Dent theory (Dent Citation1977) allowed the characterization and verification of the sorption behavior with comparable literature references. Corresponding sorption parameters provided in this study can potentially be applied to other sorption models. The swelling and shrinkage behavior did not show any dependency on the adsorption/desorption cycle. Moisture expansion parameters determined in adsorption and desorption did not vary significantly and were found to be comparable with reference values.
The results of this study show a distinctive moisture dependency of the mechanical material parameters of oak. Young's moduli, compressive strength, and shear strength decreased with increasing MC in all orthotropic directions. A linear relationship with MC is also expected for the shear moduli; however, additional experiments are needed to determine the exact moisture-dependent relationship. The results did not confirm any influence of MC on the Poisson's ratios. A nearly linear bending strength relationship with density demonstrated in this study emphasizes the need for density considerations. This becomes even more important when considering the reported high variation in density and the combined effect of MC and density as demonstrated by the bending strength response surface.