A method for risk of fracture analysis in massive wooden cultural heritage objects due to dynamic environmental variations

Most of the environmental specifications to preserve valuable collections assume hygrothermal equilibrium of the object with the surrounding environment. Though the assumption is valid for most of museum interiors, it does not reflect climate conditions in historic houses and churches whose specificity lies in dynamic temperature and relative humidity (RH) variations, particularly intense in cases of operating heating systems. The present paper analyses the risk of fracture in massive wooden cultural heritage objects, particularly endangered by gradients of moisture forming in their volume due to dynamic environmental variations. The study aimed at elucidating general trends as both crack formation and propagation depend on material parameters of a specific wooden element, which can vary even within the same wood species. A two-dimensional elastic model of a massive object made of pine wood was subjected to two types of RH variations: step and sinusoidal. The critical amplitude and duration of variations inducing crack propagation were determined for both variation types. The modelling showed that the risk of fracture was significantly higher for a sinusoidal variation than for a sudden RH drop. Therefore, sinusoidal variations should be considered the worst-case condition when analysing risk of fracture in wooden objects.