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| 2. |
- Kifetew, G
(författare)
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Application of the deformation field measurement method to wood during drying
- 1996
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Ingår i: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 30:6, s. 455-462
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Tidskriftsartikel (refereegranskat)abstract
- A method for measuring the deformation field on small wood specimens during drying using a regular grid pattern is described. Preliminary results showed a large variation in surface deformation in the range 0% to 6.2%. To explain the transverse deformation field on the radial face, the different deformation ranges were related to the macrostructure of wood. The latewood region was responsible for the higher deformation field range, while the earlywood layer explained the lower strain held range. The method described could provide important information regarding the history of a specimen which has not so far considered in previous studies on the dynamic behaviour of wood.
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| 3. |
- Kifetew, G, et al.
(författare)
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Tangential and radial deformation field measurements on wood during drying
- 1997
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Ingår i: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 31:1, s. 35-44
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Tidskriftsartikel (refereegranskat)abstract
- In a previous study, the deformation field measurement method on wood during drying was described. This paper discusses the deformation field measurement results during drying to 8.2% moisture content on the radial and tangential surfaces. It also attempts to explain the observations by an approximate expression based onearlywood-latewood interaction theory. The deformation on the radial surface varied between -0.7% and 7.5%. The actual measurements on the radial surfaces support previous work. Deformation measurements on the tangential surfaces were between -0.5% and 9.0%. Although the investigations were carried out on gross wood specimens, the results provide an insight into the extent to which local density variation within the early- and latewood layers may influence the magnitude of surface deformation.
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| 5. |
- Kifetew, G, et al.
(författare)
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The effect of drying on wood fracture surfaces from specimens loaded in wet condition
- 1998
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Ingår i: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 32:2, s. 83-94
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Tidskriftsartikel (refereegranskat)abstract
- The study describes the effect of drying on fracture surfaces of Scots pinePinus silvestris L. Microtomed specimens of isolated and combined early-and latewood, in green and oven-dried/resoaked state were loaded to failure in uniaxial tension parallel to the grain. The fracture surfaces were studied using scanning electron microscopy (SEM). Both green early- and latewood samples showed rough fracture surfaces, which in latewood was dominated by intrawall failure. In the resoaked state, transwall failure dominated and fracture surfaces were more flat, indicating a more brittle fracture process. Although variation in the data was large, the strength of the resoaked samples were generally lower than those of paired green samples. The observations support irreversible cell wall damage formed during drying which severely affects the failure mechanism.
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| 6. |
- Kifetew, G
(författare)
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The influence of the geometrical distribution of cell-wall tissues on the transverse anisotropic dimensional changes of softwood
- 1999
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 53:4, s. 347-349
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the geometrical distribution of cell-wall tissues on the transverse anisotropic dimensional changes of softwood has been studied using two isotropic models. A finite element model has been used to calculate the thermal expansion of two aluminium plates without and with holes in the two perpendicular directions. Moisture expansion measurements in the two perpendicular directions were conducted using a polyamide (PA6) plate containing several holes. No differences were found in either the thermal expansion of the aluminium plates or the moisture expansion of the PA6 plate between the two perpendicular directions. Thus, the investigation suggests that the geometrical distribution of cell-wall tissues has no effect on the transverse anisotropic shrinkage of softwood.
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| 7. |
- Thuvander, Fredrik, et al.
(författare)
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Modeling of cell wall drying stresses in wood
- 2002
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 36:3, s. 241-254
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Tidskriftsartikel (refereegranskat)abstract
- All applications of wood involve drying the material from the green state. The cell wall may be viewed as a laminate consisting of different layers. The layers have different orientations and therefore different moisture expansion characteristics. As a result, stresses will develop in the layers due to drying. Micromechanical models for fibre composite materials were used in combination with a laminate analogy in order to calculate these drying stresses in the cell wall layers S1, S2 and S3. Resulting stresses were very high. In reality viscoelastic effects will significantly reduce stresses at high moisture content. However, at lower moisture content irreversible cell wall damage is likely to form as a result of the stresses computed by the model.
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