Effect of Drying Temperature and Relative Humidity on Contraction Stress in Wood

As wood shrinks during the drying process, various stresses may develop and cause surface and internal checking. The aim of this study was to systematically investigate the effect of the drying temperature, relative humidity, and specimen thickness on the contraction stress in elm wood (Ulmus pumila L.) specimens during drying. The contraction stress was used as an indirect indicator of drying stresses. A measurement system was developed in-house and used to simultaneously and continuously obtain the required measurements during drying, which were then used to determine the moisture content, amount of shrinkage, and contraction stress of the wood specimens. In the process of drying, the contraction stress was initially negative with a decrease in the moisture content and an increase in the shrinkage. Then the contraction stress increased gradually and eventually stabilized upon reaching the maximum. The results also showed that as the temperature increased, the moisture content decreased, the shrinkage decreased, the maximum contraction stress decreased, and the contraction stress reached a maximum in a shorter amount of time.