Transverse mechanical behaviour and moisture absorption of waterlogged archaeological wood from the Vasa ship

Damage on the hull of the 17th century Swedish warship Vasa has been observed recently. Damage in the form of indentations in the wood is caused by high compressive loads from the support structure. In the process of developing an improved support structure, radial mechanical properties and the deformation mechanisms of Vasa oak are particularly important. Causes of differences in PEG content and oak degradation are also of interest. The radial modulus and compressive strength of Vasa oak are 50% lower than for recent oak. Furthermore, a significant change in failure mechanism is observed. More brittle separation fracture of the rays of Vasa oak is observed compared to the continuous folds of rays in recent oak. Tangential stiffness and strength are also 30% and 50% lower, respectively. Comparably small differences in moisture absorption between PEG-extracted Vasa oak and recent oak indicate a low extent of degradation of the Vasa oak.