Numerical modelling of moisture movement and related stress field in lime wood subjected to changing climate conditions

Numerical modelling was used to follow the evolution of the moisture content gradient and the stress field resulting from the restrained differential dimensional response across a wooden cylinder, simulating sculptures, in response to variations in temperature (T) and relative humidity (RH). Material properties of lime wood (Tilia sp.) were used in the modelling as this wood species was historically widely used. The allowable RH variations, below which mechanical damage will not occur, were derived as functions of the amplitude, time period and starting RH level of the variation. Lime wood can endure step RH variations of up to 15% in the moderate RH region, but the allowable domain narrows when RH levels shift from the middle range. The allowable amplitude of the variations increases when time allowed for the change increases. The stress field does not vanish even for slow, quasi-static changes in RH due to structural internal restraint resulting from the anisotropy in the moisture-related dimensional change.