Modelling of stress development during drying and relief during steaming in Pinus radiata lumber

A one-dimensional stress model was proposed for drying of radiata pine lumb er, which has considered wood moisture shrinkage, instantaneous stress-stra in relationships, mechano-sorptive creep, time-induced creep and temperatur e effects. In addition, wood hardening behaviour in the plastic region and differences between stress increase and decrease have been taken into accou nt. The proposed stress model can predict stress development and relief in a drying cycle once the required wood mechanical and rheological properties have been quantified. Drying experiments were performed to dry Pinus radiata sapwood boards of 10 0x40x590 mm in a tunnel dryer. In the experiment, wood temperature, moistur e content gradient and residual stress through board thickness were measure d. The drying cycle included HT drying, cooling and final steam conditionin g. The measured stress patterns were in agreement with the model prediction s. However, more accurate calculations will be made once the detailed exper imental data for radiata pine wood mechanical and rheological properties ar e available.