Multiscale analysis of free swelling of Norway spruce

The swelling of the hierarchical cellular structure of wood can be properly predicted when both the cellular and the growth ring scales are taken into account. In this study, a multiscale computational upscaling finite element model is utilized for the estimation of the free swelling behavior of Norway spruce softwood. The microstructural information, e.g. the geometry of the wood cells, the local density and the microfibril angle across the growth rings is the input of the lower scale cellular model. The elastic properties and the swelling coefficients within the growth ring are estimated using a periodic honeycomb unit cell model. Based on this model, the transverse anisotropy in the swelling behavior of softwood at timber or growth ring level is then predicted. Comparison of simulation results with experimental measurements obtained using digital image correlation shows very good agreement.