Moisture Dependence of Mechanical Properties of Beech and Birch in Compression Perpendicular to Grain and Rolling Shear

The forests in Europe are changing in response to climate change, resulting in an increased proportion of hardwood species in mixed forests. Mechanical characterization of hardwood species, an understudied area in the past, is now gaining prominence in research. Our experimental investigation of moisture dependence of mechanical strength of South Swedish hardwoods encompassed the species beech and birch and relative humidity levels of 40, 65, and 85 % at 20 °C. Mechanical strength was determined on two different scales, namely on the board level, which includes effects of the cylindrical orthotropy of the annual ring structure of wood, and on the material level, where this influence is minimized due to the small specimen size. For these different scales, different experimental setups were used, with a similar experimental evaluation. The results showed that compressive strength perpendicular to the grain increased with decreasing moisture content at both scales. Material level tests resulted in higher compressive strengths compared to the board level. Conversely, rolling shear strength was consistently higher on the board level than on the material level. ... mehrThe dependence of the rolling shear strength on the moisture content was distinct on the board level, but not on the material level.