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Bjurhager, Ingela
Publications (10 of 14) Show all publications
Afshar, R., van Dijk, N., Bjurhager, I. & Gamstedt, E. K. (2017). Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints. Engineering structures, 147, 62-76
Open this publication in new window or tab >>Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints
2017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, p. 62-76Article in journal (Refereed) Published
Abstract [en]

Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-330536 (URN)10.1016/j.engstruct.2017.05.051 (DOI)000408073500005 ()
Funder
Swedish Research CouncilVINNOVASwedish Research Council Formas
Available from: 2017-10-04 Created: 2017-10-04 Last updated: 2017-10-04
Vorobyev, A., Bjurhager, I., van Dijk, N. P. & Gamstedt, K. (2016). Effects of barrelling during axial compressive tests of cubic samples with isotropic, transversely isotropic and orthotropic elastic properties. Composites Science And Technology, 137, 1-8
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.

Keywords
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
van Dijk, N. P., Gamstedt, E. K. & Bjurhager, I. (2016). Monitoring archaeological wooden structures: Non-contact measurement systems and interpretation as average strain fields. Journal of Cultural Heritage, 17, 102-113
Open this publication in new window or tab >>Monitoring archaeological wooden structures: Non-contact measurement systems and interpretation as average strain fields
2016 (English)In: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674, Vol. 17, p. 102-113Article in journal, Editorial material (Refereed) Published
Abstract [en]

Abstract Large wooden structures of cultural value, such as the Vasa ship, suffer from increasing deformation over time, caused by creep in the wood members, time-dependent deformation of joints and damage accumulation. In this paper, we discuss the suitability of the different available measurement techniques to monitor the increasing deformation and the structural health of wooden structures. In particular, a monitoring system needs to be able to measure the exact same point at different times to measure displacements. For large wooden objects with limited surface texture, the best accuracy for displacement measurements is currently achieved by monitoring well-defined targets with laser-assisted total stations. Furthermore, we emphasize the relation between displacements and deformation and advocate translating the raw displacement data into more meaningful average strain fields. A straightforward method to compute the in-plane average strain field is presented, and illustrated for the Vasa ship. The strain fields can indicate areas with localized strain, caused e.g. by weak zones in the structure with increased creep, damage or cracking. Such zones can then be more closely inspected and considered for improved support.

Keywords
Archaeological wooden structures, Geodetic measurements, Structural monitoring, Strain
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-264241 (URN)10.1016/j.culher.2015.03.011 (DOI)000372484300012 ()
External cooperation:
Funder
Swedish Research Council FormasVINNOVASwedish Research Council
Available from: 2015-10-07 Created: 2015-10-07 Last updated: 2017-12-01Bibliographically approved
Khosravi, S., Nordqvist, P., Khabbaz, F., Öhman, C., Bjurhager, I. & Johansson, M. (2015). Wetting and film formation of wheat gluten dispersions applied to wood substrates as particle board adhesives. European Polymer Journal, 67, 476-482
Open this publication in new window or tab >>Wetting and film formation of wheat gluten dispersions applied to wood substrates as particle board adhesives
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2015 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 67, p. 476-482Article in journal (Refereed) Published
Abstract [en]

The wetting, penetration, and film formation of wheat gluten dispersions on porous wood substrates have been studied using different microscopy techniques. The effect variation of wheat gluten concentration, processing temperatures, dispersion composition, and the application scheme has been studied. The results have been correlated to previously obtained results on the function of wheat gluten dispersions as adhesive binders for particle boards. The results show that the dispersions readily penetrate the porous wood substrate and that the key parameters for a successful gluing are the dispersion viscosity, concentration, and the application scheme. 

National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-238811 (URN)10.1016/j.eurpolymj.2014.11.034 (DOI)000357750900045 ()
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved
Norbakhsh, S., Bjurhager, I. & Almkvist, G. (2014). Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood. Holzforschung, 68(6), 649-655
Open this publication in new window or tab >>Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood
2014 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 6, p. 649-655Article in journal (Refereed) Published
Abstract [en]

In the wood of the Swedish 17th century warship Vasa, iron (Fe)-catalyzed chemical degradation has taken place after the salvation in 1961, which is manifested in increased acidity accompanied by cellulose degradation and reduced strength in the oak hull. Model studies on fresh oak impregnated with Fe(II) also led to tensile strength (TS) reduction in the same order of magnitude as observed in the wood of the Vasa. In the present study, further experiments have been performed concerning the Fe-catalyzed wood degradation. Namely, the degree of wood degradation was monitored quantitatively by measurement of the O-2 consumption of Fe(II)-impregnated oak, kept in closed vials with different relative humidities (RH), as a function of time. The initial O-2 consumption was high and declined with time. After 200 days, the accumulated O-2 consumption was 0.3-0.4 mmol g(-1) wood. Degradation products with low molecular weight were analyzed. The release of CO2 and oxalic acid (OA) was positively correlated with RH (0.235 and 0.044 mmol g(-1), respectively, at RH98% after 200 days). Samples kept for 1500 days at RH54% had accumulated 0.044 mmol OA g(-1) wood, which is equal to the average OA content in the interior of Vasa oak (corresponding to 4 mg g(-1)). Oak samples, from which extractives had been removed prior to Fe(II) impregnation, did not change their O-2 consumption or TS reduction compared to the nonextracted samples, indicating that extractives are not essential for cellulose degradation in this context.

Keywords
degradation, iron compounds, oxalic acid, oxygen consumption, polyethylene glycol, Vasa, waterlogged wood
National Category
Agricultural Science, Forestry and Fisheries Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-235201 (URN)10.1515/hf-2013-0197 (DOI)000342090900005 ()
Available from: 2014-10-31 Created: 2014-10-29 Last updated: 2017-12-05Bibliographically approved
Gamstedt, K., Vorobyev, A., van Dijk, N., Bjurhager, I. & Hassel, I. (2014). Multiscale approach from micromechanics up towards creeping wood structures. In: MS046A in Proceedings of the 11th Word Congress on Computational Mechanics (WCCM XI) and the 5th Europen Conference on Computational mechanics (ECCM V): . Paper presented at The 11th Word Congress on Computational Mechanics (WCCM XI) and the 5th Europen Conference on Computational mechanics (ECCM V), Barcelona, Spain, 2014.
Open this publication in new window or tab >>Multiscale approach from micromechanics up towards creeping wood structures
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2014 (English)In: MS046A in Proceedings of the 11th Word Congress on Computational Mechanics (WCCM XI) and the 5th Europen Conference on Computational mechanics (ECCM V), 2014Conference paper, Poster (with or without abstract) (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-284699 (URN)
Conference
The 11th Word Congress on Computational Mechanics (WCCM XI) and the 5th Europen Conference on Computational mechanics (ECCM V), Barcelona, Spain, 2014
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2018-05-23
Bjurhager, I., Vorobyev, A., van Dijk, N., Gamstedt, E. K., Ahlgren, A. & Olofsson, M. (Eds.). (2013). Investigation of time-dependent deformation of wood from the warship Vasa. Paper presented at 12th ICOM-CC Wet Organic Archaeological Materials Conference. Istanbul, Turkey: Istanbul University
Open this publication in new window or tab >>Investigation of time-dependent deformation of wood from the warship Vasa
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2013 (English)Conference proceedings (editor) (Refereed)
Place, publisher, year, edition, pages
Istanbul, Turkey: Istanbul University, 2013
National Category
Applied Mechanics
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-211367 (URN)
Conference
12th ICOM-CC Wet Organic Archaeological Materials Conference
Available from: 2013-11-22 Created: 2013-11-22 Last updated: 2018-05-23
Bjurhager, I., Gamstedt, K., Keunecke, D., Niemz, P. & Berglund, L. A. (2013). Mechanical performance of yew (Taxus baccata L.) from a longbow perspective. Holzforschung, 67(7), 763-770
Open this publication in new window or tab >>Mechanical performance of yew (Taxus baccata L.) from a longbow perspective
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2013 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 7, p. 763-770Article in journal (Refereed) Published
Abstract [en]

Yew (Taxus baccata L.) longbow was the preferred weapon in the Middle Ages until the emergence of guns. In this study, the tensile, compression, and bending properties of yew were investigated. The advantage of yew over the other species in the study was also confirmed by a simple beam model. The superior toughness of yew has the effect that a yew longbow has a higher range compared with bows made from other species. Unexpectedly, the mechanical performance of a bow made from yew is influenced by the juvenile-to-mature wood ratio rather than by the heartwood-to-sapwood ratio. A yew bow is predicted to have maximized performance at a juvenile wood content of 30-50%, and located at the concave side (the compressive side facing the bowyer). Here, the stiffness and yield stress in compression should be as high as possible.

Keywords
archery, axial strength, bending tests, longbow, yew (Taxus baccata L.)
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-219999 (URN)10.1515/hf-2012-0151 (DOI)000330365900006 ()
Available from: 2014-03-09 Created: 2014-03-09 Last updated: 2017-12-05Bibliographically approved
Norbakhsh, S., Bjurhager, I. & Almkvist, G. (2013). Mimicking of the strength loss in the Vasa: model experiments with iron-impregnated recent oak. Holzforschung, 67(6), 707-714
Open this publication in new window or tab >>Mimicking of the strength loss in the Vasa: model experiments with iron-impregnated recent oak
2013 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 6, p. 707-714Article in journal (Refereed) Published
Abstract [en]

Previous studies of the oak wood of the 17th century warship the Vasa have shown significant changes in the chemical and mechanical properties compared with recent oak. The most important factors contributing to these changes are the incorporation of iron compounds during waterlogging and the uptake of polyethylene glycol (PEG) in the course of the 17 years of preservation treatment. To investigate the effect of iron-dependent oxidative degradation reactions, recent oak wood samples were impregnated with aqueous iron(II) chloride solution (0.1 M) and thereafter exposed to air or pure oxygen at controlled relative humidity in long-term experiments followed by tensile strength (TS) measurements. The iron-impregnated samples exposed to oxygen displayed significant effects already after 1 week and the reduction in TS was similar to 50% after 1 year. The samples treated with additional PEG displayed less TS reduction, whereas the addition of cysteine had no effect. The size exclusion chromatography of treated samples showed that the average molecular weight of holocellulose had decreased. The results confirm that iron compounds have a detrimental effect in wood and indicate that PEG might act as an antioxidant for the degradation processes. Concerning the Vasa, it may be concluded that most degradation related to iron compounds and oxidative processes have taken place during the first period of conservation when the wood was exposed to oxygen in a still very humid state. Thus, the current rate of oxidative degradation under the present relatively dry museum conditions should be relatively low.

Keywords
antioxidant, cysteine, degradation, extractives, iron compounds, oak wood, polyethylene glycol (PEG), preservation, tensile strength, Vasa ship, waterlogged wood
National Category
Engineering and Technology
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-209500 (URN)10.1515/hf-2012-0150 (DOI)000324719100012 ()
Available from: 2013-10-21 Created: 2013-10-21 Last updated: 2017-12-06Bibliographically approved
Vorobyev, A., Berghult, A., Bjurhager, I. & Gamstedt, K. (Eds.). (2012). An analysis of elastic properties of oak from the Vasawarship and European oak. Edinburgh, Scotland: Proceedings of the Annual Workshop of COST Action FP0802: Micro-characterisation of wood materials and properties
Open this publication in new window or tab >>An analysis of elastic properties of oak from the Vasawarship and European oak
2012 (English)Conference proceedings (editor) (Refereed)
Place, publisher, year, edition, pages
Edinburgh, Scotland: Proceedings of the Annual Workshop of COST Action FP0802: Micro-characterisation of wood materials and properties, 2012
National Category
Applied Mechanics
Research subject
Engineering science with specialization in Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-192267 (URN)
Available from: 2013-01-17 Created: 2013-01-17 Last updated: 2013-03-04
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