Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Static and time-dependent mechanical behaviour of preserved archaeological wood: Case studies of the seventeenth century warship Vasa
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics. (0000-0001-5855-2260)
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. , p. 52
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1474
Keyword [en]
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: urn:nbn:se:uu:diva-314266ISBN: 978-91-554-9810-8 (print)OAI: oai:DiVA.org:uu-314266DiVA, id: diva2:1070301
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
List of papers
1. Characterisation of cubic oak specimens from the Vasa ship and recent wood by means of quasi-static loading and resonance ultrasound spectroscopy (RUS)
Open this publication in new window or tab >>Characterisation of cubic oak specimens from the Vasa ship and recent wood by means of quasi-static loading and resonance ultrasound spectroscopy (RUS)
Show others...
2016 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 5, p. 457-465Article 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.

Keyword
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:nbn:se:uu:diva-264455 (URN)10.1515/hf-2015-0073 (DOI)000375131700009 ()
External cooperation:
Available from: 2015-10-12 Created: 2015-10-12 Last updated: 2017-12-01Bibliographically approved
2. Effects of barrelling during axial compressive tests of cubic samples with isotropic, transversely isotropic and orthotropic elastic properties
Open this publication in new window or tab >>Effects of barrelling during axial compressive tests of cubic samples with isotropic, transversely isotropic and orthotropic elastic properties
2016 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 137, p. 1-8Article in journal (Refereed) Published
Abstract [en]

For scarce materials, such as archaeological wood, cubic samples are often used instead of standardised prisms for mechanical tests, since the elasticity can be determined in all three directions within a single sample, but with such samples barrelling makes it difficult to identify the elastic properties. The purpose of the present study is firstly to numerically investigate the effects of barrelling in cubic samples during compressive testing; secondly to numerically investigate and compare barrelling on isotropic and transversely isotropic material parameters; thirdly to compare four strain measurement techniques using digital image correlation, strain gauges and direct readings from the testing machine and finally to estimate the error due to barrelling by implementing the experimentally obtained orthotropic material parameters to the numerical model. The presented relative errors provide information when the perturbation caused by barrelling is negligible or significant for various materials and strain measurements. As an example, the results of compressive tests on waterlogged archaeological oak impregnated with polyethylene glycol are discussed.

Keyword
Cubic samples, Compressive testing, Barrelling formation, Wood
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-306193 (URN)10.1016/j.compscitech.2016.10.015 (DOI)000389292600001 ()
Projects
Vasa support structure
Funder
Swedish Research Council FormasVINNOVASwedish Research Council
Available from: 2016-10-26 Created: 2016-10-26 Last updated: 2017-11-29Bibliographically approved
3. Relations of density, polyethylene glycol treatment and moisture content with stiffness properties of Vasa oak samples
Open this publication in new window or tab >>Relations of density, polyethylene glycol treatment and moisture content with stiffness properties of Vasa oak samples
2017 (English)In: Holtzforschung, Vol. 71, no 4, p. 327-335Article in journal (Refereed) Published
Abstract [en]

Treatment with polyethylene glycol (PEG) is the preferred method for conservation of waterlogged archaeological wooden objects. However, PEG impregnation leads to softening and increased hygroscopicity of the material. The present study compiles experimental results concerning the full elastic properties of PEG impregnated archaeological wood from the Vasa ship in relation to its basic density, PEG content (PEGC) and moisture content (MC). The results show a correlation between a more porous microstructure and high PEGC, and consequently, higher MC. The PEG and moisture contribute to the mass of the wooden object as well as to softening of the material, which are undesired properties in a larger load-carrying wooden structure. A compromise between the improved dimensional stability and degradation of mechanical properties should therefore be considered in the conservation of wooden object treated with PEG.

Keyword
archaeological wood, PEG impregnation, moisture content (MC), computed tomography, elastic constants, Vasa ship, basic density, Quercus robur
National Category
Other Natural Sciences Engineering and Technology
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-314263 (URN)10.1515/hf-2016-0202 (DOI)000398974900007 ()
Projects
Stötta Vasa
Funder
Swedish Research CouncilSwedish Research Council FormasVINNOVA
Available from: 2017-02-01 Created: 2017-02-01 Last updated: 2017-05-19Bibliographically approved
4. Orthotropic creep in polyethylene glycol impregnated archaeological oak from the Vasa ship: Results of creep experiments in a museum-like climate
Open this publication in new window or tab >>Orthotropic creep in polyethylene glycol impregnated archaeological oak from the Vasa ship: Results of creep experiments in a museum-like climate
(English)Article in journal (Refereed) Submitted
Keyword
Time dependent, Creep, Vasa ship, Cubic samples, Wood, Climate, Polyethylene glycol
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:uu:diva-314264 (URN)
Available from: 2017-02-01 Created: 2017-02-01 Last updated: 2017-02-01
5. Evaluation of displacements by means of 3D laser scanning in a mechanically loaded replica of a hull section of the Vasa ship
Open this publication in new window or tab >>Evaluation of displacements by means of 3D laser scanning in a mechanically loaded replica of a hull section of the Vasa ship
Show others...
(English)Article in journal (Refereed) Submitted
Abstract [en]

For development of full-scale finite-element models of large objects in culturalheritage it can be useful to mechanically test replicas of key parts toidentify structural properties which would otherwise not be available. Thispaper presents full scale tests on a replica of a section of the hull of the17th century warship Vasa in three load configurations. We focus on determiningdisplacement of the loaded replica from 3D laser measurements.Two measures were found useful, namely (i) 3D displacements at well-definedintersections of the wooden replica, and (ii) normal displacements of largersurfaces. Wood surfaces were preferred to steel parts of the rig since the lattershowed more scatter in displacement values in their point clouds caused bytheir reflective properties. The measurements were verified with draw-wire 

sensors. Some of these sensors were attached to the steel rig supporting thereplica and, therefore, measured relative displacements. The scanning datawas also useful to quantify the absolute movement of the steel rig supportingthe replica, which improved the precision of the measurements of replicadeformation. Finally, it is discussed how the replica test results can be usedin a model of the complete museum ship.

Keyword
3D laser scanning, Structural analysis, Vasa, Wood, Shear
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:uu:diva-314265 (URN)
Available from: 2017-02-01 Created: 2017-02-01 Last updated: 2017-02-01

Open Access in DiVA

fulltext(1627 kB)231 downloads
File information
File name FULLTEXT01.pdfFile size 1627 kBChecksum SHA-512
eb1b0af7d0675d28b1fba4cdfa0ce31fdc1600dd9636ca7b92246071eec466b1b9b5d39e143e6da9c90637aa0ce172f96f8d2485f4d4e07e6d7608614b13f1dc
Type fulltextMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Vorobyev, Alexey
By organisation
Applied Mechanics
Other Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 231 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2012 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf