Wood Fracture Pattern during the Water Adsorption Process

Abstract

Summary A research program was conducted to investigate the effect of water transition on wood fracture properties, focusing on fracture behavior and patterns with different crack orientations of Betula platyphylla Suk. and Pinus bungeana in three different moisture adsorption processes. At a constant temperature of 20°C, three levels of relative humidity were considered: 66%, 82% and 100%. The results indicated that moisture content did not influence the crack propagation path, while specimen crack orientation did. With longer moisture adsorption times, the time needed to reach the maximum load from the critical load also grew; this is because below the fiber saturation point, from excessive dryness to a certain moisture content, the cell wall becomes less brittle and the toughness is enhanced. At 20°C constant temperature, the fracture toughness gradually increased from oven-dry state adsorbing moisture to 82% relative humidity, but decreased from 82% to 100% relative humidity. Within a tree species, fracture toughness depended on specimen type. The fracture toughness of LT specimens was by far higher than that of TL and TR specimens. The LT specimen fracture toughness of Betula platyphylla Suk. was comparable to that of Pinus bungeana.