On shape stability of panel paintings exposed to humidity variations - A numerical study between science & art part 1: Modeling isothermal moisture movement

A substantial part of museum’s collection is painted on wood, so called panel paintings. In an attempt to protect this part of our cultural heritage against degradation, museums apply strict humidity requirements mainly based upon practical experience and perception: Relative Humidity RH = 55% ±5.0%. Today scientist and conservators ask themselves: “Are these strict requirements really needed and what are the consequences of changing these strict requirements?”. Finite Element Analysis could provide an answer and possibly lead to a more permanent solution.
Due to its hygroscopic behaviour, wood is sensitive to variations in humidity. As a consequence of changing environmental conditions and the hygro-expansional behaviour of wood it tends to deform. When these deformations exceed the elastic limit, it could lead to permanent deformations. Simulation of this behaviour is quite complex, due to wood being a heterogeneous, hygroscopic, cellular and anisotropic material. Without numerical simulation, it is almost impossible to predict the deformation when exposed to moisture variations. This paper discusses the development of a constitutive model for simulations and an example of the analyses for a limewood cylinder. This exercise was carried out previous to the so-called Climate4Wood project, one of the NWO projects within the Science4 Arts projects.