Effect of relative humidity and temperature on the strength properties of finger-jointed furniture components from solid scots pine

Abstract: Mechanical strength in wood has always been compromised due to the complex behaviours of the material when interfered with moisture and heat. These factors has always limited the use of the material. However, the will of using more sustainable materials such as wood has contributed to a wider use of the material and several new ways that lead to improvement. Several of these methods emphasizes the joining of two wood components together endwise, where finger-joints are the most commonly used method. Several studies regarding how well finger-joints can withstand external load has been made over the years. However, many of these studies focuses on geometrical properties or strength varying in different species. This study focuses on how relative humidity and temperature affects mechanical strength in finger-jointed wood products. There were beliefs before the research started that increasing temperature would affect mechanical strength greatly. However, it turned out to only affect the mechanical strength marginally, and that relative humidity was the largest contributor to decreasing tolerance levels. It is important to notify that mechanical strength seemed to be directly affected to moisture content (MC), which is a result of an interactive relationship with both temperature and RH. It was particularly MC-levels above 9.2% that showed a decrease in mechanical strength. This research also focused on estimating the relative MOR per cross-section in varying conditions. This method could be used to better understand to which degree hygroscopic factors affects mechanical strength relative to the glued-surface area between finger-joints. Even though the findings in this study indicates that there seems to be possible to estimate strength in regards to relative MOR per cross-section, the results were not sufficient to be viewed as scientifically proof. The findings could however be used as ground for future studies.