Numerical modelling of moisture related mechanical stress in wooden cylindrical objects using COMSOL: a comparative benchmark

For preservation of artefacts in a museum the indoor climate is often restricted to a very narrow interval for temperature, but most of all for relative humidity (1,7). In old buildings the museum conditions of artefacts, e.g. near cold walls, mostly are not in line with museum recommendations. To have an impression of indoor museum climates in old buildings, a large number of case studies were carried out in several Dutch museums. For at least one year, temperature and relative humidity were recorded in different rooms and at different external wall surfaces of the museums. The results of this measurement campaign reveal that there were a large number of indoor climate conditions that did not satisfy the originally formulated restricted climate (1). To have an impression of the impact of the measured indoor climates on the conservation properties of objects, a numerical simulation model was needed. The model should be able to determine the temperature and moisture content gradients in organic objects and the related mechanical stress due to changing environmental indoor climate conditions. For this purpose a three dimensional numerical simulation model was constructed in COMSOL. The partial differential equations for heat and moisture transport in objects were implemented in COMSOL and coupled to the mechanical stress module of COMSOL. The results were temperature and moisture profiles in three dimensional objects due to dynamically changing (measured) environmental conditions. The resultant mechanical stresses were calculated and compared to maximum allowable threshold stresses to stay in the safe elastic strain regime.