The Development of a Methodology to Understand Climate-induced Damage in Decorated Oak Wood Panels

Climate-induced damage in decorated oak wood panels is considered to be a high risk for pre-eminent museum collections. To advise museums on the development of sustainable future preservation strategies and rational guidelines for indoor climate specifications, the risk of this type of damage – physical and mechanical is analysed in full depth in this research. A comprehensive methodology is required that meets the requests of the conservation community and also helps to bridge the gap between scientists and conservators. Therefore, this research couples an extensive examination of empirical data obtained from naturally aged museum objects, i.e. a collection analysis, with numerical modelling and experimental testing. A multidisciplinary collaboration has been initiated, whereby conservators and scientists are working together to fulfil the common objectives of sustainable and low-risk preservation of valuable museum collections. In this paper, the methodology is outlined and some results are presented

Local mechanical behaviour of structural sandwich elements at an intermediate support

Structural sandwich elements composed of chipboard facings and an EPS core are ideal for application in roof structures. The advantageous properties of chipboard and EPS are used to strive for optimum use of materials, low dead weight, high strength and high thermal insulation capacity. As a consequence, structural sandwich elements are sensitive for local brittle bending tensile failure of inside of the lower facing at an intermediate support. In this research, an analytical, experimental and numerical analysis of the local mechanical behaviour of structural sandwich elements at an intermediate support is performed. An improved and reliable analytical design approach for this local mechanical behaviour is determined and proposed to be used in practice.</p

Local mechanical behaviour of structural sandwich elements at an intermediate support

Structural sandwich elements composed of chipboard facings and an EPS core are ideal for application in roof structures. The advantageous properties of chipboard and EPS are used to strive for optimum use of materials, low dead weight, high strength and high thermal insulation capacity. As a consequence, structural sandwich elements are sensitive for local brittle bending tensile failure of inside of the lower facing at an intermediate support. In this research, an analytical, experimental and numerical analysis of the local mechanical behaviour of structural sandwich elements at an intermediate support is performed. An improved and reliable analytical design approach for this local mechanical behaviour is determined and proposed to be used in practice.</p

Fracture behaviour of historic oak wood under three-point bending : an experimental-numerical study

Historical Dutch oak wood cabinets occasionally show cracks that might originate from hygro-thermal climate fluctuations. This damage mechanism needs to be understood in full detail in order to optimally preserve these museum objects for future generations. For this purpose, in this paper the fracture response of historic oak wood beams is analysed under three-point bending in a combined experimental-numerical study. The numerical results are computed with the finite element method (FEM), whereby the discrete fracture behaviour is simulated using interface elements equipped with an interface damage model. Both the experimental failure response and cracking path are in good agreement with the FEM results. Scanning electron microscopy photos taken at the crack plane illustrate that the fracture toughness includes the effect of cell bridging. The influence on the failure response by material anisotropy and the location of a geometrical imperfection at the beam notch are demonstrated

Failure behaviour of historic oak wood under three-point bending – an experimental-numerical study

Historische Nederlandse eikenhouten kabinetten vertonen scheuren die mogelijk veroorzaakt zijn door hygroscopische en thermische klimaatfluctuaties. Dit schademechanisme moet volledig inzichtelijk gemaakt worden om museumobjecten optimaal te kunnen behouden voor toekomstige generaties. Om deze reden wordt in deze paper het bezwijkgedrag van historische eikenhouten balken onder drie-puntsbuiging onderzocht in een gecombineerde experimenteel-numerieke studie. De numerieke resultaten zijn gegenereerd met de eindige-elementenmethode (EEM), waarin discreet scheurgedrag is gesimuleerd met behulp van interface-elementen die zijn voorzien van een interface-schademodel. Zowel het experimenteel bezwijkgedrag als het scheurpad komen goed overeen met de EEM resultaten. Scanning elektronenmicroscopische foto’s van het scheurvlak laten zien dat de breuktaaiheid wordt beïnvloed door het zogenoemde “cel-overbruggingseffect”. De invloed van anisotroop materiaalgedrag en de locatie van geometrische imperfecties op het bezwijkgedrag is aangetoond.Historische Nederlandse eikenhouten kabinetten vertonen scheuren die mogelijk veroorzaakt zijn door hygroscopische en thermische klimaatfluctuaties. Dit schademechanisme moet volledig inzichtelijk gemaakt worden om museumobjecten optimaal te kunnen behouden voor toekomstige generaties. Om deze reden wordt in deze paper het bezwijkgedrag van historische eikenhouten balken onder drie-puntsbuiging onderzocht in een gecombineerde experimenteel-numerieke studie. De numerieke resultaten zijn gegenereerd met de eindige-elementenmethode (EEM), waarin discreet scheurgedrag is gesimuleerd met behulp van interface-elementen die zijn voorzien van een interface-schademodel. Zowel het experimenteel bezwijkgedrag als het scheurpad komen goed overeen met de EEM resultaten. Scanning elektronenmicroscopische foto’s van het scheurvlak laten zien dat de breuktaaiheid wordt beïnvloed door het zogenoemde “cel-overbruggingseffect”. De invloed van anisotroop materiaalgedrag en de locatie van geometrische imperfecties op het bezwijkgedrag is aangetoond

Fracture behaviour of historic and new oak wood

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

Hygro-mechanical response of oak wood cabinet door panels under relative humidity fluctuations

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 under several relative humidity variations. In specific, the mock-ups were subjected to (i) an instantaneous decrease of 40% relative humidity, (ii) eight successive, instantaneous drops of 5% relative humidity, and (iii) a varying relative humidity profile ranging between 35 and 71%. The shrinkage characteristics of 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. Further, by accounting for the age-dependency of the fracture strength of oak wood, a clear distinction can be made between the damage susceptibility of new door panels and historical door panels present in museum cabinets. The six main conclusions of the experimental study—conveniently summarized at the end of this paper—provide a scientific basis for the understanding of shrinkage cracks and dimensional changes observed on decorated oak wooden panels in historical Dutch cabinets, and thus may assist in advising museums on future sustainable preservation strategies and rational guidelines for indoor climate specifications

Bezwijkgedrag van historisch eikenhout onder drie-puntsbuiging – een experimenteel-numerieke studie

Historische Nederlandse eikenhouten kabinetten vertonen scheuren die mogelijk veroorzaakt zijn door hygroscopische en thermische klimaatfluctuaties. Dit schademechanisme moet volledig inzichtelijk gemaakt worden om museumobjecten optimaal te kunnen behouden voor toekomstige generaties. Om deze reden wordt in deze paper het bezwijkgedrag van historische eikenhouten balken onder drie-puntsbuiging onderzocht in een gecombineerde experimenteel-numerieke studie. De numerieke resultaten zijn gegenereerd met de eindige-elementenmethode (EEM), waarin discreet scheurgedrag is gesimuleerd met behulp van interface-elementen die zijn voorzien van een interface-schademodel. Zowel het experimenteel bezwijkgedrag als het scheurpad komen goed overeen met de EEM resultaten. Scanning elektronenmicroscopische foto’s van het scheurvlak laten zien dat de breuktaaiheid wordt beïnvloed door het zogenoemde “cel-overbruggingseffect”. De invloed van anisotroop materiaalgedrag en de locatie van geometrische imperfecties op het bezwijkgedrag is aangetoond