Creep behaviour of Japanese cypress timber under various hygrothermal conditions

Abstract

This study presents the creep behaviour of inner- and surface-layers of Japanese cypress boxed-heart timber under constant and cyclic moisture sorption using cantilever creep test at a temperature of 20, 65, and 80°C. The objective was to measure the viscoelastic and mechanosorptive creep parameters of the timber at each temperature. A load representing 20% of the ultimate rupture load under equilibrium moisture content (EMC) of around 12% at each temperature was applied at the free-end of the cantilever specimen. The specimen was exposed to constant moisture conditions and then subjected to cyclic moisture sorption, consist of adsorption and desorption. The surface strains of the specimen were then recorded, and models were used to measure the creep parameters. The results show that the creep behaviour of the specimen depends on the temperature, and its creep compliances tend to increase as the temperature increased. The results confirmed that the viscoelastic and mechanosorptive creep dependence on time and cumulative moisture content change (CMCC), respectively. Fitting the experimental data with the models used in this study shows good agreement, and the creep parameters at each temperature were successfully measured. These findings indicate the potential to model stress occurrence in the timber during the drying.