In load-bearing timber structures, bonded laminated materials are particularly relevant due to the fact that they are good at absorbing and transferring loads. These include glued laminated wood and laminated plywood as well as veneer laminated wood and veneer plywood. In addition, bonded combinations of wood veneers and other materials such as metal or (fiber-composite) plastics are increasingly being developed. These hybrid materials combine the specific advantages of the differing materials and enable the production of very slender, highly functional components.
As wood is a natural material that also possesses anisotropic properties, composite bonding poses different challenges from those of metallic or polymeric materials.
Established testing methods exist for determining the durability of wood-based materials for exterior use: outdoor weathering tests and rapid-aging methods. Both are often costly and difficult to implement, particularly for small and medium-sized companies.
Outdoor weathering tests last several years; as a consequence, they slow down the process for the commercial launch and represent a high economic risk for the manufacturers. In addition, due to the influence of macro- and microclimatic factors, they provide results that are sometimes barely reproducible.
Conventional rapid-aging methods sometimes rely on drastic test parameters such as temperature increases, water storage or boiling in water in order to shorten the test period. This, however, does not adequately reflect real aging, for example swelling and shrinkage due to the natural interplay of temperature and wood moisture. Unrealistic test criteria can lead to wood-containing components being over-dimensioned, i.e. “larger” than necessary.
Our goal is to develop a better rapid-aging procedure that takes into account the climatic, mechanical and other influences on wood and bonding in a more realistic way. These include:
- Temperature
- Humidity
- Static loads (weight)
- Dynamic loads (e.g. due to wind, vibrations)
- Aggressive media (e.g. wood preservative, road salt)
- Wood species (e.g. beech, spruce)
- Chemical alterations to the adhesive as a result of the differing wood constituents (e.g. wood sugar)
Our procedure is designed to shorten the realistic aging from several years to a few weeks. UV-related and microbiological influences will not form the initial focus of the project, but a subsequent extension of the rapid-aging procedure will be prepared through the analysis of the environmental data.
Fraunhofer Institute for Wood Research 
