Introduction: Throughout many parts of the world, forests exist in one form or another. And for the timber from these forests to be used, it must be processed by, for example, sawing into planks and dried. Studies have shown that profits for the forest owners increase from beneficial processing of these raw materials. An efficient use of this raw material is to process it into lightweight panels. Some general incentives for using lightweight constructions are: economical, technical and environmental. Some general weaknesses with sandwich constructions are more sensitive to impact and bumps, risk for delamination, harder to make fastenings, and more sensitive to the concentration of point loads. This work aims to increase the knowledge of properties and design of wood based lightweight panels used for interiors and furniture. The intention with this knowledge is that it can contribute to the development of lightweight panels.

Material and method: A lightweight panel of cross glued sandwich type and a cross-glued multi-layered panel with densified face sheets have been used as an example to investigate and understand which parameters are crucial for a lightweight panel, made of wood. The lightweight panel of sandwich construction has been studied to consider the changes of shape brought about by moisture, as well as which mechanical properties this panel has, with a focus on creep deformation. Two methods for reducing the moisture-generated shape changes so as to increase the shape stability of the panel have also been studied. The methods are crossgluing and thermal treatment of the wood material. In the investigations of the panels, primarily quantitative methods in the form of empirical tests have been used. Some numerical simulations describing the moisture-generated shape changes and stresses that arise in the investigated lightweight panels were also made.

Results and discussion: Cross-gluing of a multi-layered panel and also for the lightweight panel used in this study is a way to reduce the movement in the panel, generated by moisture. The drawbacks with this method are that stresses occur in the panels when the moisture change, and this can lead to a decrease in the shape stability of the panel. Thermal treatment can also be used to decrease the moisture-generated movement in wood, and in this way increase the shape stability of the product. In those cases where the empirical experiments were combined with numerical simulations, there was good agreement between the experimental and the numerical results. With the lightweight panels a weight reduction was achieved from 307 to 540 kg/m3 compared with a solid beech wood panel. The creep deformation of the lightweight panel was better or comparable for 6 of the 8 studied groups, compared to solid beech wood panel. The study also show that is possible to adapt the mechanical properties through its design of this lightweight panel.