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 $$7 \%$$7%. A comparison between a calibration of the experimental results by isotropic and orthotropic elastic models shows that the peak load is 10–$$13\%$$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.

中文翻译：

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新旧橡木的断裂行为

最近的博物馆研究表明，在历史悠久的荷兰橱柜和面板绘画中，装饰橡木面板上出现了裂缝和尺寸变化。需要对这些破坏机制进行彻底分析，以全面了解破坏的原因，并就未来的可持续保护策略和室内气候规范的合理指南向博物馆提出建议。为此，本文介绍了不同年龄橡木断裂行为的组合实验-数值表征。对公元 1300 年和 1668 年的历史样品和新样品进行了三点弯曲试验。将测量的失效响应和断裂路径与有限元模型计算的数值结果进行比较。通过使用稳健的界面损伤模型与基于耗散的路径跟踪技术相结合，可以准确地模拟离散断裂行为。结果表明，公元 1300 年的样品显示出准脆性断裂响应，而公元 1668 年的样品和新样品显示出相当脆的破坏响应。此外，橡木的局部拉伸强度以近似线性的方式随着年龄的增长而降低，因此表明了所谓的老化效应。数值模拟表明，由于试样缺口尖端处的小缺陷，三点弯曲下的最大承载能力可能会最大降低$$7\%$$7%。通过各向同性和正交各向异性弹性模型校准实验结果的比较表明，正交各向异性弹性模型的峰值载荷高出 10–$$13\%$$13%。最后，没有发现断裂韧度与橡木的年龄和断裂面方向的显着相关性。测量的强度和韧性值可用作高级数值模拟的输入，用于对装饰橡木板和板画中的气候引起的损害进行高级数值模拟。