Abstract
Recent museum studies have indicated the appearance of cracks and dimensional changes on decorated oak panels in historical Dutch cabinets and panel paintings. A thorough analysis of these damage mechanisms is needed to obtain a comprehensive understanding of the causes of damage and to advise museums on future sustainable preservation strategies and rational guidelines for indoor climate specifications. For this purpose, a combined experimental-numerical characterization of the fracture behaviour of oak wood of various ages is presented in this communication. Three-point bending tests were performed on historical samples dated 1300 and 1668 A.D. and on new samples. The measured failure responses and fracture paths are compared against numerical results computed with a finite element model. The discrete fracture behaviour is accurately simulated by using a robust interface damage model in combination with a dissipation-based path-following technique. The results indicate that the samples dated 1300 A.D. show a quasi-brittle fracture response, while the samples dated 1668 A.D. and the new samples show a rather brittle failure response. Further, the local tensile strength of the oak wood decreases with age in an approximately linear fashion, thus indicating a so-called ageing effect. Numerical simulations show that, due to small imperfections at the notch tip of the specimen, the maximal load carrying capacity under three-point bending may decrease by maximally 7 %. A comparison between a calibration of the experimental results by isotropic and orthotropic elastic models shows that the peak load is 10–13% higher for the orthotropic elastic model. Finally, no significant dependence of the fracture toughness on the age of the oak wood and on the orientation of the fracture plane has been found. The strength and toughness values measured can be used as input for advanced numerical simulations on climate-induced damage in decorated oak wooden panels and panel paintings.
Highlights
Decorated oak wooden panels in historical Dutch cabinets and panel paintings occasionally show damage that might originate from thermal and/or hygral climate fluctuations
The fracture behaviour of oak wood under three-point bending has been studied by experiments and numerical simulations for historical samples dated 1300 A.D., 1668 A.D. and new samples
(ii) The fracture response of the historical samples dated 1668 A.D. and the new samples investigated in the present communication show a relatively brittle response, leading to dynamic load drops in the quasi-static failure experiments
Summary
Decorated oak wooden panels in historical Dutch cabinets and panel paintings occasionally show damage that might originate from thermal and/or hygral climate fluctuations. It is further emphasized that the value of the elastic dummy stiffness K used in the interface damage model was set relatively high, as a result of which the overall elastic response of the three-point bending specimen is not affected by this parameter and is fully determined by the elastic properties of the continuum elements.
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