Experimental-numerical investigation of climate-induced damage in historical cabinet door panels

Indoor climate fluctuations are regarded as
one of the major risks for the emergence of
damage in historical works of art. For a safe
preservation of their art objects museums
try to minimize this risk, which is typically done by imposing strict limitations on
the indoor temperature and humidity conditions. The high energy demand resulting
from this approach, however, undermines
the aim of preeminent museums to execute
a sustainable preservation strategy of their
collections. A rational improvement of this
aspect asks for detailed information on the
history of museum objects, complemented
by a thorough comprehension of the failure and deformation behaviour of museum
objects under indoor climate fluctuations.
Accordingly, in this paper the hygro-mechanical response of mock-ups of historical Dutch cabinet door panels made of oak
wood is examined experimentally and numerically under several relative humidity
variations. Furthermore, the shrinkage characteristics of the mock-ups are translated to
their damage susceptibility using an analytical hygro-mechanical bi-layer model. This
model shows that restrained hygral shrinkage may originate from: i) a difference in
moisture content across the thickness direction of the panel, or ii) a directional difference in the coefficient of hygroscopic
expansions of structural components forming a coherent connection. The first type
of shrinkage occurs in the outer regions of
the panel thickness, while the second type
of shrinkage takes place at the cleated ends.
The numerical and experimental results are
in good agreement, and indicate that at the
connection between the cleated end and the
vertical boards the restrained hygric shrinkage is maximal, which stimulates local
crack development. Numerical simulations
have shown that the susceptibility of the
cabinet door panel to fracture only becomes
activated after the oak wood has reached a
certain age, as the effect of aging induces
a decrease of the oak wood tensile strength
perpendicular to the grain direction with
time. Further, when the initial moisture content of the door panel lies on the desorption
boundary curve, the amount of fracture generated is larger compared to when it lies on
the adsorption boundary curve. Also, fracture only nucleates after a specific drop in
relative humidity, whereby the crack growth
under a continuous decrease in relative humidity initially develops relatively fast, but
at a certain stage decreases substantially
and becomes (almost) zero when reaching
a fully developed failure crack. The present
paper contains a summary of the scientific research published recently in [22, 23],
whereby a specific effort has been made to
make the content accessible for a more practically oriented, conservation community