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Characterisation of cubic oak specimens from the Vasa ship and recent wood by means of quasi-static loading and resonance ultrasound spectroscopy (RUS)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Univ Montpellier, LMGC, CNRS UMR 5508, F-34095 Montpellier, France.
Univ Montpellier, IES, CNRS UMR 5214, F-34095 Montpellier, France.
ESEO Grp GSII, F-49107 Angers, France.; LUNAM Univ, LAUM, CNRS UMR 6613, F-72085 Le Mans, France.
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2016 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 5, 457-465 p.Article in journal (Refereed) Published
Abstract [en]

The cylindrical orthotropy, inherent time-dependency response, and variation between and within samples make the stiffness characterisation of wood more challenging than most other structural materials. The purpose of the present study is to compare static loading with resonant ultrasound spectroscopy (RUS) and to investigate how to combine the advantages of each of these two methods to improve the estimation of the full set of elastic parameters of a unique sample. The behavior of wood as an orthotropic mechanical material was quantified by elastic engineering parameters, i.e. Poisson’s ratios and Young’s and shear moduli. Recent and waterlogged archaeological oak impregnated with polyethylene glycol (PEG) from the Vasa warship built in 1628 was in focus. The experimental results were compared, and the difference between RUS and static loading was studied. This study contributes additional information on the influence of PEG and degradation on the elastic engineering parameters of wood. Finally, the shear moduli and Poisson’s ratios were experimentally determined for Vasa archaeological oak for the first time.

Place, publisher, year, edition, pages
2016. Vol. 70, no 5, 457-465 p.
Keyword [en]
archaeological wood; compression test; cubic samples; elastic constants; oak wood; quasi-static loading; resonant ultrasound spectroscopy (RUS); Vasa ship
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:uu:diva-264455DOI: 10.1515/hf-2015-0073ISI: 000375131700009OAI: oai:DiVA.org:uu-264455DiVA: diva2:860545
Available from: 2015-10-12 Created: 2015-10-12 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Static and time-dependent mechanical behaviour of preserved archaeological wood: Case studies of the seventeenth century warship Vasa
Open this publication in new window or tab >>Static and time-dependent mechanical behaviour of preserved archaeological wood: Case studies of the seventeenth century warship Vasa
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wooden objects have been widely used in the history of humanity and play an important role in our cultural heritage. The preservation of such objects is of great importance and can be a challenging task. This thesis investigates the static and time-dependent mechanical behaviour of archaeological oak wood from the Vasa warship. Characterisation of mechanical properties is necessary for the formulation of a numerical model to design an improved support structure. The ship was impregnated with polyethylene glycol (PEG) for dimensional stabilisation. All elastic engineering constants of the Vasa oak have been identified and compared with those of recent oak by means of the static and dynamic testing. The experiments were done on samples with cubic geometry, which allowed obtaining all elastic constants from a single sample. The usage of cubic samples with orthotropic mechanical properties during compressive experiments was validated with finite-element simulations. The Young's moduli of the Vasa oak in all orthotropic directions were smaller than those for the recent oak. The shear moduli of Vasa oak was determined and verified with the resonant ultrasound spectroscopy. The time-dependent mechanical behaviour of the Vasa oak has been studied. Creep studies were performed in uniaxial compression on the cubic samples in all orthotropic directions. The samples loaded in the longitudinal direction were subjected to different stress levels. A stress level below 15% of the yield stress in the longitudinal direction did not result in non-linear creep with increasing creep rates within the time frame of the tests. The results of the studies in radial and tangential directions showed that creep was dominated by the effect of annual fluctuations in relative humidity and temperature. The weight changes based on annual fluctuations of relative humidity were measured for Vasa oak and recent oak. The Vasa oak showed higher variations due to an increased hygroscopicity which is the result of the impregnation with PEG. In conceiving a full-scale finite-element model of Vasa ship, not only the stress-strain relations of the material but also those of the structural joints are needed. Since the in-situ measurement of joints is not an option, a replica of a section of the ship hull was built and tested mechanically. The load-induced displacements were measured using 3D laser scanning which proved to have advantages to conventional point displacement measurements. The mechanical characteristics of the Vasa oak and joint information presented in this work can be used as input for a finite-element model of the Vasa ship for simulation of static and time-dependent behaviour on a larger scale.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1474
Keyword
archaeological wood, compression test, cubic samples, elastic constants, oak wood, barrelling formation, quasi-static loading, resonant ultrasound spectroscopy (RUS), Vasa ship, creep, 3D laser scanning, Time-dependent behaviour
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:uu:diva-314266 (URN)978-91-554-9810-8 (ISBN)
Public defence
2017-03-31, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Projects
Stötta Vasa
Available from: 2017-03-01 Created: 2017-02-01 Last updated: 2017-03-06

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Vorobyev, Alexeyvan Dijk, NicoGamstedt, Kristofer

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