Jämsä, Saila

Löija, Mia

Ojanen, Tuomo

Wetting and drying of wood cause stresses and deformations in the material.These changes may cause cracks in the wood and wood coatings.Crack formation is a serious defect that may reduce the service life of the structure.Cracking of wood has usually been studied as a result of stresses induced by moisture content difference between surface and interior.Minor attention has been paid to the stresses between earlywood and latewood.VTT has developed an application based on NIR spectroscopy to determine the moisture content in wood.FT-NIR mapping made it possible to distinguish earlywood and latewood of wood samples and enabled detecting of the moisture distribution along the surface of materials.The NIR- method confirmed the assumption that under the same relative humidity conditions the latewood had a higher moisture content than early wood.In a series of moisture load tests, the cracking of wood was observed to start close to the border of earlywood and latewood, but typically in the early wood region.This is an indication of internal stresses caused by moisture gradients between earlywood and latewood.The dynamic moisture behavior of timber material layer consisting of earlywood and latewood plies having (assumed) different moisture properties were numerically simulated.The results showed how the local moisture gradients might have very high levels and variations by the border of earlywood and latewood during dynamic moisture load conditions

New aspects for the cracking behavior of wood

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