Finite Element Modelling of the Checking of Wood Exposed to Accelerated Weathering

IRG/WP 10-20459

S G Ribarits, P D Evans

The surface checking that develops when wood is exposed to the weather reduces the visual appeal of treated wood products and can reduce the effectiveness of preservative treatments. There is strong interest in developing solutions to this problem and also a growing realization that such solutions may evolve from a deeper understanding of the mechanisms responsible for surface checking. In this paper we describe a two-dimensional finite element model that couples moisture diffusion, dimensional change and the development of strains in wooden decking boards exposed to accelerated weathering. The model successfully predicts the strains that cause checks to form in decking boards exposed to accelerated weathering. High tension strains develop at the surface of boards, as expected, but we also observe high strains in the rays and in the core of boards. Such strains explain how checks propagate radially and why internal checks can develop in decking boards. These internal checks may create large cracks when they coalesce with surface checks. In summary, the model we have developed has provided useful insights into the mechanisms responsible for the checking of wood. Further development of the model could provide additional insights and allow it to be used as a tool to optimize the weathering cycles of devices designed to accelerate the checking of wood, or to virtually screen chemical or physical treatments designed to reduce the checking of wooden decking boards.


Keywords: checking, model, finite element, moisture diffusion, strain

Conference: 10-05-09/13 Biarritz, France


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