A radial distribution of moistures and tangential strains within a larch log cross section during radio-frequency/vacuum drying

Abstract

This study was performed to investigate a radial distribution of moistures and tangential strains within a 30 mm thick log cross section of larch by a circumferential slicing-method during radio-frequency/vacuum (RF/V) drying. Before the RF/V drying, the moisture contents (MC) at the heartwood zone remained nearly constant in the range of about 42 percent MC to 53 percent MC, while from around 0.80 diameters away from the pith toward bark they abruptly raised to maximum 149.4 percent MC and then decreased slightly. From 79 hours of the drying times to end of the drying the moisture distribution along the radial direction remained almost uniform. When the log cross section fell below fiber saturation point at 79 hours of drying, most of the slices represented the maximum tensile strains, and from that time the tangential strains in tension steadily increased toward the bark side, and reached the maximum value at the border zone between heartwood and sapwood. Most of log cross sections of larch could be dried without formation of checks and V-shaped cracks during the RF/V drying process.