Ingela Bjurhager - Assistant Professor in Applied Mechanics
Phone: +46(0)18-4717259 begin_of_the_skype_highlighting GRATIS +46(0)18-4717259 end_of_the_skype_highlighting, Cell phone: +46(0)70-2938883 begin_of_the_skype_highlighting GRATIS +46(0)70-2938883
Investigating the time-dependent deformation behavior of Vasa oak
The strength in the Vasa has been reduced with up to 80%, while the stiffness is up to 50% lower compared to recent oak. This is due to chemical degradation and impregnation with polyethylene glycol (PEG), respectively. From positioning measurements we have also seen that the ship is also subjected to deformation over time, i.e. creep. Taken together, the reduction in mechanical properties and the creep deformation constitute a serious threat to the mechanical stability.
In this project we are investigating the time-depentent behavior of Vasa oak. The aim is to be able to predict how much additional support the ship needs in order to reduce the onging creep deformation to a minimum.This information can serve as valuable input information for a future computer model of the ship, where different support scenarios are evaluated.
Investigating the relationship between reduction in mechanical strength and rate of degradation in Vasa oak
(performed at KTH in collaboration with Uppsala University, SLU and Innventia)
Chemical investigations of the Vasa were initiated in the beginning of the 21st century. Since then, extensive holocellulose degradation have been reported at numerous locations in the hull. In this project we studied the longitudinal tensile strength of Vasa oak. It was found that the mean tensile strength is reduced by approximately 40-60%, and the most affected areas show a reduction of up to 80%. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, which indicates that the chemical degradation has had a large negative impact on the mechanical integrity of the ship. Surprisingly, while the strength in the surface material (blue and green areas in Fig. 1) is fairly good, the strength in the interior is severly reduced (yellow and red areas).
Figure 1. A cross section of a piece of Vasa oak. (Bjurhager et al.: (2012) Degradation state in archaeological oak from the 17th century Vasa ship – substantial strength loss correlates with reduction in (holo)cellulose molecular weight. Biomacromolecules 13(8):2521-2527)
I. Bjurhager, I., Halonen, H., Lindfors, E-L., Iversen, T., Almkvist, G., Gamstedt, E. K., Berglund, L. (2012) Degradation state in archaeological oak from the 17th century Vasa ship – substantial strength loss correlates with reduction in (holo)cellulose molecular weight. Biomacromolecules 13(8):2521-2527
Svedström, K., Bjurhager, I., Kallonen, A., Peura, M., Serimaa, R. (2012) Structure of oak wood from the Swedish warship Vasa revealed by X-ray scattering and microtomography. Holzforschung 66: 355-363
Leppänen, K., Bjurhager, I., Peura, M., Kallonen, A., Suuronen, J-P., Penttilä, P., Love, J., Fagerstedt, K., Serimaa, R. (2011) X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying. Holzforschung 65:865-873
Olsson, A-M., Bjurhager, I., Gerber, L., Sundberg, B., Salmén, L. (2011) Ultra-structural organisation of cell wall polymers in normal and tension wood of aspen revealed by polarisation FT-IR microspectroscopy. Planta 233(6):1277-1286
Bjurhager, I., Ljungdahl, J., Wallström, L., Gamstedt, E. K., Berglund, L. A. (2010) Towards improved understanding of PEG-impregnated waterlogged archaeological wood: A model study on recent oak.Holzforschung 64(2):243-250
Walther, A., Bjurhager, I., Malho, J-M., Pere, J., Ruokolainen, J., Berglund, L. A., Ikkala, O. (2010) Large-area, lightweight and thick biomimetic composites with superior material properties via fast, economic, and green pathways. Nano Letters 10(8):2742-2748
Walther, A., Bjurhager, I., Malho, J-M., Ruokolainen, J., Berglund, L. A., Ikkala, O. (2010)Supramolecular control of stiffness and strength in lightweight high-performance nacre-mimetic paper with fire-shielding properties. Angewandte Chemie - International Edition 49(36):6448-6453
Bjurhager, I., Ljungdahl, J., Wallström, L., Gamstedt, E. K., Berglund, L. A. (2010) Towards improved understanding of PEG-impregnated waterlogged archaeological wood: A model study on recent oak. Holzforschung 64(2):243-250
Bjurhager, I., Olsson, A-M., Zhang, B., Gerber, L., Kumar, M., Berglund, L. A., Burgert, I., Sundberg, B., Salmén, L. (2010) Ultrastructure and mechanical properties of Populus wood with reduced lignin content caused by transgenic down-regulation of cinnamate 4-hydroxylase. Biomacromolecules 11(9):2359-2365
Bjurhager, I., Berglund, L. A., Bardage, S. L., Sundberg, B. (2008) Mechanical characterization of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula x Populus tremuloides) using full-field strain measurements. Journal of Wood Science 54(5):349-355