Mechano-sorptive bending creep of timber - influence of material parameters

In this paper mechano-sorptive creep test results from twelve Norway spruce trees are presented. The wood material was well defined with respect to gr owth conditions, position in the tree and material parameters, such as annu al ring width, slope of grain, knots, compression wood, density and modulus of elasticity. The influence of these parameters on the creep behaviour wa s studied. The creep tests were conducted in a climate room with varying re lative humidity of 30%-90% and the duration of the creep tests was at least 100 days. For seven of the twelve studied trees there was a radial variati on in relative creep between the pith and the bark. The specimens cut near the pith showed larger relative creep than the specimens cut near the bark. When all the 59 specimens included in this study were examined together, t he modulus of elasticity seemed to be the best parameter, measured in this study, to predict the magnitude of relative creep. The correlations between relative creep and material parameters varied between the specimens from t he different trees. Also the appearance of the creep curves varied between different specimens. Some specimens showed large variations in relative cre ep within the moisture cycles, some specimens did not at all seem to be sen sible to moisture changes. The reason for these differences were not explai ned successfully in this study.