34: Stress and strain in drying wood - a literature survey

Summary

When a plank dries in a warm air climate, a moisture gradient from the surface to the inner core of the wood will occur. As a result tension stress will develop in the outer layer of the plank when it dries under to the fibre saturation point.

The wood when loaded is capable of going through creep deformations. In the first phase of the drying process when there is tension stress in the outer layer of the plank, the mechano-sorptive creep is the most important. However, also the visco-elastic creep has some influence.

Strength and elasticity properties of wood change characteristics during changes in temperature, moisture content, density and species. This fact must be accounted for when considering stress development and checking probability during a wood drying process.

In the work of modelling strain and stress in wood during drying, there are many factors which must be considered. However, it is necessary to simplify and concentrate the attention on the most important phenomena. There are also phenomena which are not fully understood today, and therefore it is difficult in some cases to explain why a model does not satisfactorily fit the experimental results.