| 1. |
- Adamopoulos, Stergios, et al.
(författare)
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Dimensional changes of extracted and non-extracted small wood specimens of black locust (Robinia pseudoacacia L.)
- 2003
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 61:4, s. 264-268
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Tidskriftsartikel (refereegranskat)abstract
- From straight grained heartwood of black locust (Robinia pseudoacacia L.), specimens, 3 cm×3 cm in cross section and 0.5 mm (or 10 mm) in axial direction, were cut and used for the determination of dimensional changes and the rate of tangential swelling. Mean radial, tangential and axial shrinkage was 5.30%, 6.67% and 0.16%, respectively, while the coefficient of anisotropy was 1.26. Half of the specimens for the determination of the rate of tangential swelling were extracted for 48 h with distilled hot water. The tangential dimensional change and the time taken to attain half maximum swelling in air-dry and oven-dry specimens were assessed according to a common technique. Extractive removal resulted in an increase of the total magnitude of tangential swelling in both air-dry and oven-dry specimens. However, no significant differences in time taken to attain half maximum swelling between air-dry and oven-dry specimens were observed after extraction. The rate of tangential swelling was lower in air-dry specimens than in oven-dry specimens after 30 min of immersion in water when were non-extracted and after 5 min of immersion in water when were extracted. Extracted air-dry specimens had a greater rate of tangential swelling than non-extracted air-dry specimens and the same occurred for oven-dry specimens. Extraction resulted in a higher diffusion coefficient for air-dry specimens. The diffusion coefficient calculated for non-extracted air-dry specimens (0.901×10−4 cm2/min) showed that black locust is a difficult species to impregnate.
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| 2. |
- Adamopoulos, Stergios
(författare)
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Flexural properties of black locust (Robinia pseudoacacia L.) small clear wood specimens in relation to the direction of load application
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 60:5, s. 325-327
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Tidskriftsartikel (refereegranskat)abstract
- Values of pure moduli of elasticity (PMOE), experimental modulus of elasticity (MOE) in static bending and moduli of rigidity (GLR, GLT) were calculated in juvenile and mature black locust defect-free small wood specimens after loading in static bending alternately on true radial and tangential surfaces. For both juvenile and mature specimens, no significant differences (t-test, 95% probability level) were found between the radial and tangential moduli of elasticity and rigidity. Values of PMOE were found to be 27–32% higher than the corresponding values of MOE at the 15:1 span-to-depth ratio.
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| 3. |
- Adamopoulos, Stergios
(författare)
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Influence of hot-water extractives on radial and tangential shrinkage of black locust wood (Robinia pseudoacacia L.)
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 60:5, s. 377-378
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionRemoval of extractives increases the shrinkage and swelling of wood (Nearn 1955, Salamon and Kozak 1968, Cooper 1974, Taylor 1974). The effect of progressive extraction on the above properties has not been investigated much. In oak (Quercus conferta L.), a forest species rich in extractives, the shrinkage progressively increased with progressive extraction (Voulgaridis et al. 1980). In black locust (Robinia pseudoacacia L.), much of the main-stem volume is comprised of heartwood, characterized by the presence of dark yellow-brown extractives. While the extractives of black locust give the heartwood its distinctive color and decay resistance, they comprise only 6.2 to 8.3% of the dry weight of the main stem (Stringer 1992). Hot-water extractives range from 5.2 to 8.6% (Hart 1968, So et al. 1980). The present study was primarily undertaken to determine whether the progressive removal of hot-water extractives affects the radial and tangential shrinkage of black locust heartwood.
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| 4. |
- Danvind, Jonas
(författare)
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PLS prediction as a tool for modeling wood properties
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 60:2, s. 130-140
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Tidskriftsartikel (refereegranskat)abstract
- During an earlier study, material responses of shrinkage and deformation during air-drying were measured on small wood specimens cut from the cross section of a Pinus radiata log. In this paper the analysis of the collected data and the modeling of studied responses were done using multivariate methods. A first model with all variables and all 104 observations was created. In this model there were observations that deviated from the rest and some of them were therefore excluded from further modeling. Also, weak variables and undesired variables were excluded from further modeling. After these exclusions, 77 observations of wood responses below fiber saturation point remained. The results showed good modeling of radial, tangential and volumetric shrinkage between 0-22% MC, with explained variance (R2) and predicted variance (Q2) at approximately 0.9, and moderate modeling of longitudinal shrinkage, R2 = 0.67 and Q2 = 0.65. It was also shown that longitudinal shrinkage has weak correlation to density-related variables in the studied wood. No model with good predictability of deformation was found. This study showed that PLS prediction modeling of shrinkage and deformation in studied wood samples was found to be an effective and easy-to-use tool for untangling relationships between variables and generating information from data.
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| 5. |
- Eklund, Urban
(författare)
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Influencing factors on sawing accuracy in a bandsawmill
- 2000
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 58:1-2, s. 102-106
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the cutting height, the feed speed, the strain in the band and the cutting time for the band on the sawing accuracy has been investigated by fractional factorial analysis in a normal production situation at a sawmill in Sweden. Factorial analysis has proven to be a useful method when checking the situation at a sawmill as there are many factors that influence the sawing results. The findings in this investigation are: (a) the feed speed must be adapted to the actual cutting height to a higher degree than done today; (b) the working time for the band has some influence on the result but not to the great extent as expected; (c) the feeding equipment has probably a big influence on the sawing accuracy
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| 6. |
- Eriksson, John, et al.
(författare)
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Experimental study of shape stability in glued boards
- 2004
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Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 62:3, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of shape stability in wooden glued boards was performed to verify certain results of particular interest obtained earlier in numerical simulations. Possibilities for achieving products of good shape stability by gluing boards together in an optimal way are discussed. Since twist is often the most serious form of distortion defects for the user, it was the main type of board deformation considered. Three types of glued products were tested. The experiments show clearly that glued boards can be produced that remain stable in shape when exposed to extreme variations in moisture. The results agree well with the numerical simulations performed earlier. It was found that initial twist could be reduced by proper application of pressure during gluing and that through gluing the occurrence of cracking defects on visible surfaces could be substantially reduced.
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| 7. |
- Hameed, Mahmood, 1967-, et al.
(författare)
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Eindringtiefe verschiedener Bindemittel in Splintholz- und Kernholzspänen der Kiefer (Pinus sylvestris L.) : [On the penetrability of various glues from sap- and heartwood of Pine (Pinus sylvesteis L.)]
- 2001
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 58:6, s. 432-436
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of the penetrability of various glues [urea-formaldehyde resin (UP-resin), phenol-formaldehyde resin (PP-resin), melamine-urea-phenol-formaldehyde made of pine sapwood and heartwood revealed: the various glues penetrate chips from pine sapwood regardless of tree age, height of the sample studied and surface structure deeper than in those made of heartwood. The various glues more deeply penetrate chips from sapwood and heartwood of the 48-year-old pine than chips from sapwood and heartwood of the 124-year-old pine. The penetrability of various glues in chips from sapwood and heartwood of the 124-year-old pine increases with increasing height of the sample studied. Moreover, glues penetrate sanded surfaces of chips from sapwood and heartwood of the 48- und the 124-year-old pine to a lesser extent than unsanded chip surfaces.
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| 8. |
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| 9. |
- Hansson, Martin, et al.
(författare)
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Capacity of timber roof trusses considering statistical system effects
- 2003
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768. ; 61:3, s. 161-166
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Tidskriftsartikel (refereegranskat)abstract
- For structural timber systems such as trusses, system effects related to strength variation within timber members has a significant effect on reliability. The system effect originates from the reduced probability that weak sections of timber coincide with the most stressed sections in the truss. In this paper, the strength variation within and between timber members is described with a statistical model earlier calibrated against data for Norway Spruce of Scandinavian origin. A method is presented to account for buckling effects when expressing the interaction between axial loading and bending in all sections of the truss members. The interaction is expressed in terms of a combined stress index, CSI, defined so that the failure criterion is CSI=1. For a given truss with given load, the cumulative distribution of CSI can be determined by Monte Carlo simulations based on the statistical model. By comparing the results with corresponding results obtained from deterministic engineering design, the statistical system effect is quantified. It is found that within member variability gives an extra capacity of 12% for Norway Spruce and 24% for Radiata Pine. Design rules proposed for Eurocode accounting for system effects in trusses give results slightly on the safe side compared to the results from the present study.
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| 10. |
- Johnsson, Helena, et al.
(författare)
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Plug shear failure in nailed timber connections : load distribution and failure initiation
- 2004
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 62:6, s. 455-464
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Tidskriftsartikel (refereegranskat)abstract
- Brittle failures in mechanical timber joints should be avoided, because this often results in low capacity and brittle failure of the structure. Nailed joints experience three ultimate failure modes: embedding, splitting or plug stear failure. To avoid plug shear failure, short and wide joints are preferred, limiting the number of fasteners in line with the load and grain direction. Plug shear failure was examined in short-term experiments on nailed steel-to-timber joints in glulam loaded in tension parallel to the grain with five different joint geometries. The aim of the study was to examine if the fastener group layout can be adjusted to avoid plug shear failure and to gain an insight into the causes of failure initiation. Using spring models, it is shown that the load distribution creates pronounced stresses at the last nail in the joint, which probably initiates the plug shear failure. Test results are compared with prediction models found in the literature. It was found that fasteners placed in groups can be a successful way of reducing the risk of plug shear failure. The failure is probably initiated at the nail farthest from the free end, where tensile stresses perpendicular to grain occur.
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| 11. |
- Jönsson, Johan, et al.
(författare)
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The effect of moisture gradients on tensile strength perpendicular to grain in glulam
- 2003
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768. ; 61:5, s. 342-348
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results are presented concerning tension perpendicular to grain in glulam sections where internal stresses induced by climate changes are present. The results reveal that moisture induced internal stresses may affect the tension capacity both in a positive and a negative way compared to reference specimens, free from moisture gradients. The tension capacity is reduced during moistening from RH 40% up to RH 80% whereas it is increased during drying from RH 80% to 40%. The tension capacity during wetting is only 50% of that observed for drying specimens. This behaviour can be explained by the combination between initial moisture induced stresses and stresses from external loading. The same tendency was observed for specimens exposed to cyclic climate changes, where it was also found that time and numbers of cycles do not affect the tension capacity in any specific direction.
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| 12. |
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| 13. |
- Oja, Johan
(författare)
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Evaluation of knot parameters measured automatically in CT-images of Norway spruce (Picea abies (L.) Karst.)
- 2000
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 58:5, s. 375-379
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Tidskriftsartikel (refereegranskat)abstract
- Knot parameters measured automatically in CT-images of Norway spruce have been evaluated on logs from four plots in the Norway spruce stem bank. The evaluation was made through comparisons between measurements on real centre boards and measurements on reconstructed boards. The reconstructions were based on the automatically measured parameter descriptions of knots and log shape and on simulated sawing. The diameter of knots was measured with a mean error of -2 mm and a standard deviation of 3 mm. It was shown that the reconstructed centre boards were well in accordance with the real centre boards in terms of position, number, size and type of knots. The exception is knot type for small knots in large butt logs.
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| 14. |
- Palmqvist, J
(författare)
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Parallel and normal cutting forces in peripheral milling of wood
- 2003
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 61:6, s. 409-415
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the parallel and normal cutting forces on the tip of the tool are examined when altering a number of parameters in peripheral milling. The parameters studied are rake angle, chip thickness and upward/downward milling. The evaluation of the forces has been performed during cutting of the chip and the variation in the forces has been recorded. In this way, important information can be obtained in order to arrive at cutting data and tool geometries that will reduce surface defects such as torn and raised grain. In the past, very few investigations have been carried out on peripheral milling, probably because of the difficulties of measurement. Nowadays, however, new measuring techniques and equipment make it possible to measure cutting forces even in standard milling machines. In this work, a sensor was placed under the workpiece to measure the forces in three directions at frequencies up to 7000 Hz. To obtain detailed data, a plastic material was used so that the cutting (revolution) speed could be kept at a minimum, thereby maximizing the number of readouts per incision. The results show how the normal force (the force component perpendicular to the workpiece) varies during the cut and how it is dependent on the examined parameters. This force changes from negative to positive during the cut. When altering the machining parameters, the normal force changes in both direction and magnitude. The other force component, the parallel force, also shows a dependence on the parameters. The objective of this research is to find parameters that minimize the normal forces in order to avoid damage to the wood.
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| 15. |
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| 16. |
- Sehlstedt-Persson, Margot
(författare)
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The effect of drying temperature on subsequent moisture and dimensional changes for Scots pine and Norway spruce
- 2000
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 58:5, s. 353-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of three different drying procedures on moisture and dimensional changes for Scot pine and Norway spruce during subsequent climate changes was studied. It was found that no difference exists between pine and spruce in maximal radial or tangential shrinkage for the reference material. High temperature (HT) dried spruce showed higher maximal shrinkage at 0% moisture content compared with HT dried pine.
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| 17. |
- Sterley, Magdalena, 1959-, et al.
(författare)
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Edge and face gluing of green timber using a one-component polyurethane adhesive
- 2004
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Ingår i: European Journal of Wood and Wood Products. - : Springer Berlin/Heidelberg. - 0018-3768 .- 1436-736X. ; 62:6, s. 479-482
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Tidskriftsartikel (refereegranskat)abstract
- The edge and face gluing of green timber using a one-component polyurethane adhesive was investigated. Knot free and straight grained lamellae of dimensions were prepared for this purpose. The relationship between final shear strength and wood failure percentage after kiln drying of the edge green glued specimens was shown. A slight increase of the shear strength was obtained for specimens tested 24 hour pressing compared with directly pressing.
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| 18. |
- Sundqvist, Bror
(författare)
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Color response of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula pubescens) subjected to heat treatment in capillary phase
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 60:2, s. 106-114
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Tidskriftsartikel (refereegranskat)abstract
- Clearwood of Scots pine, Norway spruce, and birch was subjected to heat treatment while capillary water was kept in the wood. The treatments were performed on initially green wood from 65 °C to 95 °C from 0 to 6 days, followed by drying at 35 °C for 2 days. Color measurements, CIEL*C*h color space, were made on dry planed samples using a photoelectric colorimeter. Treatment time was more important than temperature for birch sapwood regarding the color responses, while time and temperature were of similar importance for pine and spruce. Birch sapwood became much redder and darker compared with pine and spruce. The darkening accelerated generally when treatment temperature exceeded approximately 80 °C. Pine and spruce showed generally similar color responses, untreated and treated, except for pine heartwood untreated, which showed a more saturated color. Pine treated at 65 °C and 80 °C showed red-yellow shift and yellow-red shift for sap- and heartwood respectively, as time elapsed. The color homogeneity was less for birch sapwood than for pine and spruce, and the homogeneity was generally indicated to decrease with increasing treatment temperature.
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| 19. |
- Sundqvist, Bror, et al.
(författare)
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The influence of wood polymers and extractives on wood colour induced by hydrothermal treatment
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 60:5, s. 375-376
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Tidskriftsartikel (refereegranskat)abstract
- A method to evaluate the influence of wood polymers and extractives on the color of wood subjected to hydrothermal treatment was proposed. As such, the technique used was extraction and color measurements. It was found that both degradation products from wood polymers and extractive compounds were indicated to be participating in the color formation of wood subjected to hydrothermal treatment.
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| 20. |
- Svensson, Staffan, et al.
(författare)
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Aspects on reliability calibration of safety factors for timber structures
- 2003
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768. ; 61:5, s. 336-341
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Tidskriftsartikel (refereegranskat)abstract
- Analyses and a discussion of the consequences for lightweight structures, typical wood frame or truss structures, when a change of the statistical description of random parameters in a reliability based code format is made without considering how the code once was derived is presented. The special case when the statistical description of variable load is altered, is described with and without considering the origin of the current safety indices.
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| 21. |
- Svensson, Staffan, et al.
(författare)
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Simulation of drying stresses in wood. Part II: Convective air drying of sawn timber
- 2002
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Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768. ; 60:1, s. 72-80
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Tidskriftsartikel (refereegranskat)abstract
- This article describes a study where laboratory and theoretical work on the fundamental hygro-mechanical behaviour of wood is applied on convective drying of sawn timber. A material model describing the behaviour of wood during drying is used to simulate drying stresses in timber. Cross-sections containing heartwood, sapwood and a combination of both are studied. Simulations are compared with measurements from whole batches of sawn timber subjected to drying. The stress simulations show good agreement with the measurements. It is further shown how an alteration of a drying schedule changes the results in terms of internal stresses. Simulations of drying may be used to improve the quality of sawn timber and/or for optimising drying schedules. It is believed that simulations of drying instead of using trial and error tests on batches of sawn timber will prove to give economical and environmental benefits.
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