Perpendicular-to-grain creep of Finnish softwoods in high temperature drying conditions:Experiments and modelling in temperature range 95 - 125 °C

This publication reports the results obtained in a project to clarify the perpendicular-to-grain mechanical properties of spruce (Picea abies) and pine (Pinus sylvestris) in high temperature drying conditions. The work consisted of a literature review, an extensive experimental programme and development of a new constitutive model for the description of the creep behaviour in the high temperature conditions. All these tasks are documented in this publication. The experimental work consisted of tension creep experiments at constant saturated (green) condition at constant temperatures 95, 110 and 125°C and in drying conditions of maximum reached temperature 95, 110 or 125°C. From these experiments a large amount of data was obtained about shrinkage, hygrothermal deformation, modulus of elasticity, viscoelastic creep and mechano-sorptive creep. A limited strength test series was also carried out on spruce at 95 and 125°C. For the use of the obtained knowledge in computational simulation of drying stresses a constitutive model of the creep behaviour was developed for the high temperature conditions. The new model is based on linear shrinkage and on using the time temperature moisture-content superposition principle for modelling elastic and viscoelastic strain. For mechano-sorptive creep a new type of model is introduced, where the developing strain is partly recoverable and partly not