| 1. |
- Afshar, R, et al.
(författare)
-
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
-
Ingår i: Engineering structures. - : ELSEVIER SCI LTD. - 0141-0296 .- 1873-7323. ; 147, s. 62-76
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Almkvist, Gunnar, et al.
(författare)
-
Prediction of tensile strength in iron-contaminated archaeological wood by FT-IR spectroscopy - a study of degradation in recent oak and Vasa oak
- 2016
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 70:9, s. 855-865
-
Tidskriftsartikel (refereegranskat)abstract
- Oak from the Swedish warship Vasa and recent oak that was aged after impregnation with iron(II) chloride has been analyzed by FT-IR spectroscopy and submitted to tensile strength testing. The aim was to investigate correlations between FT-IR bands in the fingerprint region, chemical degradation, and tensile strength in iron contaminated oak. The concentration of carboxylic functions increased and the acetyl groups in the hemicellulose fraction were decreasing as a function of degradation time. These changes are accompanied by reduced tensile strength and elevated content of oxalic acid (OA) in both Vasa wood and the impregnated recent oak samples. To evaluate the possibility to predict tensile strength from spectral data, chemometric modeling by partial least-squares (PLS) regression was applied. The strategy of repeated double cross validation (rdCV) allowed a realistic prediction of tensile strength. Overall, chemical changes and mechanical performances of iron contaminated wood are strongly correlated and thus FT-IR spectroscopy is suited to predict the strength properties of the degraded wood.
|
|
| 3. |
|
|
| 4. |
- Bjurhager, Ingela
(författare)
-
Effects of Cell Wall Structure on Tensile Properties of Hardwood : Effect of down-regulation of lignin on mechanical performance of transgenic hybrid aspen. Effect of chemical degradation on mechanical performance of archaeological oak from the Vasa ship.
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood is a complex material and the mechanical properties are influencedby a number of structural parameters. The objective of this study has been toinvestigate the relationship between the structure and the mechanical propertiesof hardwood. Two levels were of special interest, viz. the cellular structureand morphology of the wood, and the ultra-structure of the cell wall. In thenext step, it was of interest to examine how the mechanical properties ofhardwood change with spontaneous/induced changes in morphology and/orchemical composition beyond the natural variation found in nature. Together, this constituted the framework and basis for two larger projects,one on European aspen (Populus tremula) and hybrid aspen (Populus tremulax Populus tremuloides), and one on European oak (Quercus robur). Amethodology was developed where the concept of relative density and compositemechanics rules served as two useful tools to assess the properties ofthe cell wall. Tensile testing in the longitudinal direction was combined withchemical examination of the material. This approach made it possible to revealthe mechanical role of the lignin in the cell wall of transgenic aspen trees,and investigate the consequences of holocellulose degradation in archaeologicaloak from the Vasa ship. The study on transgenic aspen showed that a major reduction in lignin inPopulus leads to a small but significant reduction in the longitudinal stiffness.The longitudinal tensile strength was not reduced. The results are explainableby the fact that the load-bearing cellulose in the transgenic aspen retained itscrystallinity, aggregate size, microfibril angle, and absolute content per unitvolume. The results can contribute to the ongoing task of investigating andpinpointing the precise function of lignin in the cell wall of trees. The mechanical property study on Vasa oak showed that the longitudinaltensile strength is severely reduced in several regions of the ship, andthat the reduction correlates with reduced average molecular weight of theholocellulose. This could not have been foreseen without a thorough mechanicaland chemical investigation, since the Vasa wood (with exception fromthe bacterially degraded surface regions) is morphologically intact and witha micro-structure comparable to that of recent oak. The results can be usedin the ongoing task of mapping the condition of the Vasa wood.
|
|
| 5. |
|
|
| 6. |
- Bjurhager, Ingela
(författare)
-
Mechanical behaviour of hardwoods : effects from cellular and cell wall structures
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med den här avhandlingen var att undersöka mekaniska egenskaper hos olika arter av lövträd, och koppla egenskaperna till cell- och cellväggsstrukturen i materialet. Arterna som omfattades av undersökningen var Europeisk asp (Populus tremula), hybridasp (Populus tremula x Populus tremuloides) och ek (Quercus robur). Arterna inom familjen Populus, inklusive den snabbväxande hybridaspen, har på senare tid kommit att användas inom ett stort antal projekt inom genforskningen. Det har i sin tur ökat behovet av noggrannare bestämning av mekaniska egenskaper hos dessa arter. Ek har sedan tusentals år tillbaka varit ett populärt konstruktionsmaterial; något som har resulterat i ett stort antal arkeologiska ekfynd. Konservering av dessa inkluderar ofta dimensionsstabilisering med hjälp av polyetylen-glykol (PEG); en kemikalie som man vet påverkar de mekaniska egenskaperna. I vilken utstäckning detta sker är däremot inte helt klarlagt. Studien på euoropeisk asp och hybridasp inkluderade utveckling av en ny metod för provning av små juvenila prov i grönt tillstånd. Töjningsmätningar gjordes med hjälp av digital speckelfotografering (DSP). Axiell dragstyvhet och draghållfasthet var av speciellt intresse. Sämre mekaniska egenskaper hos hybridaspen korrelerade med medelvärden på densitet, som var lägre för hybriden än för den Europeiska aspen. Ek undersöktes i svällt tillstånd, där svällningen inducerades med hjälp av PEG (molekylvikt 600). Axiell dragstyvhet och draghållfasthet samt radiell tryckstyvhet och ytspänning undersöktes. Töjningsmätningar i axiell riktning gjordes med hjälp av videoextensiometer, medan töjning i radiell riktning gjordes med hjälp av DSP. Övrig karakterisering av materialet inkluderade scanning electron microscopy (SEM), röntgenmikrotomografi och wide angle X-ray scattering (WAXS) för bestämning av mikrofibrillvinkel. Axiell dragstyvhet och draghållfasthet påverkades bara marginellt av PEG-behandlingen. WAXS-mätningarna visade att mikrofibrillvinkeln i materialet var mycket liten. Därigenom blir de mekaniska egenskaperna i axiell riktning till stor del beroende av mikrofibrillerna, vilket samtidigt minimerar den mjukningseffekt som PEG-impregneringen har på cellväggsmatrisen. De mekaniska egenskaperna i radiell kompression påverkades däremot starkt negativt av impregneringen. Detta antogs bero på den försvagande och uppmjukande effekt som PEG:en har på de radiellt orienterade märgstrålarna i veden.
|
|
| 7. |
- Bjurhager, Ingela, et al.
(författare)
-
Mechanical characterization of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula × Populus tremuloides) using full-field strain measurements
- 2008
-
Ingår i: Journal of Wood Science. - : Springer Science and Business Media LLC. - 1435-0211 .- 1611-4663. ; 54:5, s. 349-355
-
Tidskriftsartikel (refereegranskat)abstract
- Functional analysis of genes and proteins involved in wood formation and fiber properties often involves phenotyping saplings of transgenic trees. The objective of the present study was to develop a tensile test method for small green samples from saplings, and to compare mechanical properties of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula × tremuloides). Small microtomed sections were manufactured and successfully tested in tension parallel to fiber orientation. Strain was determined by digital speckle photography. Results showed significantly lower values for juvenile hybrid aspen in both Young's modulus and tensile strength parallel to the grain. Average Young's moduli spanned the ranges of 5.9-6.6 and 4.8-6.0 GPa for European aspen and hybrid aspen, respectively. Tensile strength was in the range of 45-49 MPa for European aspen and 32-45 MPa for hybrid aspen. The average density (oven-dry) was 284 kg/m3 for European aspen and 221 kg/m3 for hybrid aspen. Differences in mechanical properties correlated with differences in density.
|
|
| 8. |
- Bjurhager, Ingela, et al.
(författare)
-
Mechanical performance of yew (Taxus baccata L.) from a longbow perspective
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:7, s. 763-770
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 9. |
|
|
| 10. |
- Bjurhager, Ingela, et al.
(författare)
-
State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
-
Tidskriftsartikel (refereegranskat)abstract
- In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.
|
|
| 11. |
- Bjurhager, Ingela, et al.
(författare)
-
Towards improved understanding of PEG-impregnated waterlogged archaeological wood : A model study on recent oak
- 2010
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:2, s. 243-250
-
Tidskriftsartikel (refereegranskat)abstract
- To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.
|
|
| 12. |
- Bjurhager, Ingela, et al.
(författare)
-
Ultrastructure and Mechanical Properties of Populus Wood with Reduced Lignin Content Caused by Transgenic Down-Regulation of Cinnamate 4-Hydroxylase
- 2010
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:9, s. 2359-2365
-
Tidskriftsartikel (refereegranskat)abstract
- Several key enzymes in lignin biosynthesis of Populus have been down-regulated by transgenie approaches to investigate their role in wood lignification and to explore their potential for lignin modification. Cinnamate 4-hydroxylase is an enzyme in the early phenylpropanoid pathway that has not yet been functionally analyzed in Populus. This study shows that down-regulation of cinnamate 4-hydroxylase reduced Klason lignin content by 30% with no significant change in syringyl to guaiacyl ratio. The lignin reduction resulted in ultrastructural differences of the wood and a 10% decrease in wood density. Mechanical properties investigated by tensile tests and dynamic mechanical analysis showed a decrease in stiffness, which could be explained by the lower density. The study demonstrates that a large modification in lignin content only has minor influences on tensile properties of wood in its axial direction and highlights the usefulness of wood modified beyond its natural variation by transgene technology in exploring the impact of wood biopolymer composition and ultrastructure on its material properties.
|
|
| 13. |
- Fortino, Stefania, et al.
(författare)
-
Scratch resistance of PEG-impregnated green wood : a method for evaluation of swollen wood properties
- 2020
-
Ingår i: Wood Science and Technology. - : Springer Nature. - 0043-7719 .- 1432-5225. ; 54:3, s. 715-735
-
Tidskriftsartikel (refereegranskat)abstract
- This work proposes an experimental approach to study the scratch resistance of green wood under the effect of polyethylene glycol (PEG) impregnation. To this end, small-scale green spruce samples are stabilized against water by using the technique of PEG impregnation to prevent water to seep out of the wood during experimental tests. Scratches are performed in the radial-longitudinal and tangential-longitudinal planes of cubic wood samples by using two different indenter tips under constant and progressive normal loads. Scratch testing has previously been used mainly to characterize the abrasion resistance of coatings. Since PEG simulates the swelling effect of water in wood, this paper shows that the scratch tests on PEG-impregnated green wood can be adopted as a simple technique to understand the scratch resistance in swollen wood and the related mechanisms. The scratch test results, quantified in terms of frictional forces and permanent residual depths, reveal that the scratch resistance of wood samples depends on their PEG concentration and density, as well as on the indenter tip size and material, and on the normal force and direction during scratching. Due to the lack of literature on the scratch tests of wood, the results presented in this paper will serve as a scientific reference for future studies on the scratch resistance of untreated or treated dry wood and other wood-based products.
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Khosravi, Sara, et al.
(författare)
-
Wetting and film formation of wheat gluten dispersions applied to wood substrates as particle board adhesives
- 2015
-
Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 67, s. 476-482
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 19. |
- Lechner, Thomas, 1979, et al.
(författare)
-
Strategy for developing a future support system for the Vasa warship and evaluating its mechanical properties
- 2013
-
Ingår i: Heritage Science. - : Springer Science and Business Media LLC. - 2050-7445. ; 1:35
-
Forskningsöversikt (refereegranskat)abstract
- To maintain the integrity of the Vasa warship after salvage in 1961, conservation treatment with polyethylene glycol was carried out to prevent the collapse of cell walls. This treatment had negative effects on the strength and stiffness of the oak and the hull structure has been found to slowly deform over time. It is of interest to construct a three-dimensional numerical computer model to model and predict the deformation of the warship. This creates difficulties related to the complexity of measuring the detailed material properties that are required as input. In this context, a non-destructive methodology to predict the stiffness of the Vasa oak in terms of moduli of elasticity in the three principal directions of timber at critical positions in the ship would be useful. The twofold aim of the paper is to propose a strategy for a support system and to conduct an on-site assessment of the warship to predict the mechanical properties of the Vasa oak material. This paper also contains an up-to-date review of all essential mechanical data measured on the Vasa oak. The preliminary investigation using an X-ray technique to investigate the density properties produced promising results for future use in the evaluation of the mechanical performance. Based on these results, a procedure to establish the stiffness properties of the Vasa oak in terms of MOE was suggested, using a combination of data from previous measurements, in combination with extended tests on Vasa oak specimens and an X-ray-based density calibration procedure. The general complexity of the Vasa warship can be mainly attributed to large variations in the properties of Vasa oak due to surface degradation, chemical treatment and the disintegration of the cell-wall structure originating from centuries of waterlogged conditions. That causes difficulties when assessing mechanical and physical properties on a structural level. A combination of visual inspection together with X-ray investigation is of great importance to evaluate those properties and to obtain more accurate estimates. The results from evaluating mechanical properties can serve as input in a numerical model and serve as a foundation for decision-making relating to the modification of the support system.
|
|
| 20. |
- Leppänen, Kirsi, et al.
(författare)
-
X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying
- 2011
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:6, s. 865-873
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (mu CT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2-0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between microfibrils decreased during drying. It was detected by mu CT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.
|
|
| 21. |
- Norbakhsh, Shahin, et al.
(författare)
-
Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:6, s. 649-655
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 22. |
- Norbakhsh, Shahin, et al.
(författare)
-
Mimicking of the strength loss in the Vasa : model experiments with iron-impregnated recent oak
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:6, s. 707-714
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 23. |
- Olsson, Anne-Mari, et al.
(författare)
-
Ultra-structural organisation of cell wall polymers in normal and tension wood of aspen revealed by polarisation FTIR microspectroscopy
- 2011
-
Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 233:6, s. 1277-1286
-
Tidskriftsartikel (refereegranskat)abstract
- Polarisation Fourier transform infra-red (FTIR) microspectroscopy was used to characterize the organisation and orientation of wood polymers in normal wood and tension wood from hybrid aspen (Populus tremula x Populus tremuloides). It is shown that both xylan and lignin in normal wood are highly oriented in the fibre wall. Their orientation is parallel with the cellulose microfibrils and hence in the direction of the fibre axis. In tension wood a similar orientation of lignin was found. However, in tension wood absorption peaks normally assigned to xylan exhibited a 90A degrees change in the orientation dependence of the vibrations as compared with normal wood. The molecular origin of these vibrations are not known, but they are abundant enough to mask the orientation dependence of the xylan signal from the S-2 layer in tension wood and could possibly come from other pentose sugars present in, or associated with, the gelatinous layer of tension wood fibres.
|
|
| 24. |
|
|
| 25. |
- Svedström, Kirsi, et al.
(författare)
-
Structure of oak wood from the Swedish warship Vasa revealed by X-ray scattering and microtomography
- 2012
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66:3, s. 355-363
-
Tidskriftsartikel (refereegranskat)abstract
- The degradation of oak wood of the historical warship Vasa was studied, focusing on cellular structure by X-ray microtomography (mu CT) and on the nanostructure of the cell wall by wide- and small-angle X-ray scattering (WAXS, SAXS). Solid samples [polyethylene glycol (PEG)-, impregnated and PEG-extracted] were submitted to X-ray analysis and the results compared to those of recent oak. The cellular structure of the Vasa oak was surprisingly well preserved at the micrometer level, according to the mu CT images. As revealed by WAXS, the fraction of crystalline cellulose was lower in the Vasa samples compared with recent oak, but the average length and width of cellulose crystallites (25 +/- 2 nm and 3.0 +/- 0.1 nm, respectively), and the mean microfibril angles (4-9 degrees), showed no significant differences. Accordingly, the crystalline parts of cellulose microfibrils are well preserved in the Vasa oak. The SAXS results indicated a declined short-range order between the cellulose microfibrils and a higher porosity of the Vasa oak compared with recent oak, which may be explained by modification of the hemicellulose-lignin matrix.
|
|
| 26. |
- van Dijk, Nico P, et al.
(författare)
-
Monitoring archaeological wooden structures : Non-contact measurement systems and interpretation as average strain fields
- 2016
-
Ingår i: Journal of Cultural Heritage. - : Elsevier BV. - 1296-2074 .- 1778-3674. ; 17, s. 102-113
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Vorobyev, Alexey, 1985-, et al.
(författare)
-
Effects of barrelling during axial compressive tests of cubic samples with isotropic, transversely isotropic and orthotropic elastic properties
- 2016
-
Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 137, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 31. |
- Wagner, Leopold, et al.
(författare)
-
The influence of chemical degradation and polyethylene glycol on moisture-dependent cell wall properties of archeological wooden objects : a case study of the Vasa shipwreck
- 2016
-
Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 50:6, s. 1103-1123
-
Tidskriftsartikel (refereegranskat)abstract
- Cell wall measures allow for direct assessment of wood modification without the adverse effect of varying density and microstructure. In this study, cell wall properties of recent and archeological oak wood from the Vasa shipwreck were investigated for cell wall stiffness, hardness and creep with respect to effects of chemical degradation, impregnation with a preservation agent, namely polyethylene glycol, and moisture. For this purpose, nanoindentation tests were performed at varying relative humidity, leading to different moisture contents in the wood samples. Concurrently, microstructural and chemical characterization of the mate- rial was conducted. Impregnated and untreated recent oak wood showed a softening effect of both moisture and preservation agent at the wood cell wall level. On the contrary, increased stiffness was found for non-impregnated Vasa oak, which can be explained by aging-related modifications in cell wall components. These effects were counteracted by the softening effect of polyethylene glycol in the impregnated Vasa material, where a lower overall stiffness was measured. The reverse effect of the preservation agent and moisture, namely increased indentation creep of the cell wall material, was revealed. The loss of acetyl groups in the hemicelluloses explained the decreased hygroscopicity of the Vasa oak. In the impregnated Vasa oak, this effect seemed to be partly counteracted by the presence of low-molecular polyethylene glycol contributing to higher hygroscopicity of the cell wall. Thus, the higher overall sorptive capacity of the impregnated Vasa material, with respect to the non-impregnated material, was detected, which has resulted in a sorptive behavior similar to that of recent oak wood. The proposed approach requires only small amounts of material, making it especially suitable for application to precious historical wooden artifacts.
|
|
| 32. |
- Walther, Andreas, et al.
(författare)
-
Large-Area, Lightweight and Thick Biomimetic Composites with Superior Material Properties via Fast, Economic, and Green Pathways
- 2010
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 10:8, s. 2742-2748
-
Tidskriftsartikel (refereegranskat)abstract
- Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-Wading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation.
|
|
| 33. |
|
|
