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  • 1.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Evaluation of preservative distribution in thermally modified European aspen and birch boards using computed tomography and scanning electron microscopy2013In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 59, no 1, p. 57-66Article in journal (Refereed)
    Abstract [en]

    The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Träskydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.

  • 2.
    Blomberg, Jonas
    Luleå tekniska universitet.
    Elastic strain at semi-isostatic compression of Scots pine (Pinus sylvestris)2005In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 51, no 4, p. 401-404Article in journal (Refereed)
    Abstract [en]

    Quarter-sawn and plain-sawn specimens of Scots pine were semi-isostatically compressed at 5, 15, 50, and 140MPa in a Quintus press. Elastic strain was measured using a telescope device that was pushed together when wood was compressed and remained in this position at release of pressure. Delayed elastic and plastic strains were assessed through repeated callipering during 5 years after densification. At 140MPa, wood reached an almost compact structure (ρ ≈ 1450kg/m3) but as a result of elastic springback the density decreased to just below 1000kg/m3. At 140MPa, the elastic and delayed elastic strains were 14.6% and 1.8%, respectively, in quarter-sawn specimens, and were 13.1% and 0.8%, respectively, in plain-sawn specimens. The higher elastic strains in quarter-sawn specimens can be attributed to elastic springback in the tangentially deformed latewood bands

  • 3.
    Blomberg, Jonas
    et al.
    Luleå tekniska universitet.
    Persson, Bengt
    Department of Mathematics, Natural Science and Technology, Dalarna University.
    Plastic deformation in small clear pieces of Scots pine (Pinus sylvestris) during densification with the CaLignum process2004In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 50, no 4, p. 307-314Article in journal (Refereed)
    Abstract [en]

    Specimens made of clear wood from Scots pine (Pinus sylvestris L.) were compressed semi-isostatically at 25 deg C in a Quintus press. Pressure ranged from 0 to 140 MPa and the maximum decrease in the crosscut area was about 60%. Quarter-sawn and plain-sawn specimens were densified with the inside face (pith side) up or down. A laser-made dot grid on the crosscut area of the uncompressed specimen was used to calculate plastic strains by image analysis of the displacement

  • 4.
    Breinig, Lorenz
    et al.
    Forest Research Institute of Baden-Württemberg, 79100 Freiburg.
    Leonhart, Rainer
    Institute of Psychology, University of Freiburg.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Manuel, Andreas
    University of Freiburg, Institute of Forest Sciences, University of Freiburg.
    Brüchert, Franka
    Forest Research Institute of Baden-Württemberg, 79100 Freiburg.
    Becker, Gero
    Institute of Forest Sciences, University of Freiburg.
    Classification of wood surfaces according to visual appearance by multivariate analysis of wood feature data2015In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 61, no 2, p. 89-112Article in journal (Refereed)
    Abstract [en]

    Its natural aesthetics make wood an attractivematerial for construction and design. However, there is nodetailed understanding of the relationships between humanperception of the appearance and measurable features ofwood surfaces that could be used for controlling sawntimber production. This study investigated whether woodsurfaces can be classified according to their visualappearance on the basis of wood feature measurements.Cluster analysis was used to discover a classification basedon a set of feature pattern variables in a sample of 300softwood floorboards. A finely graded visual appearancesorting provided a reference. Discriminant analysis wasapplied to identify the relevant variables from the tested setand to assess predictability of the classification. The resultsindicated that visual appearance sorting could be approximatedquite well by the variable-based classification afterpregrouping according to board position in the log.Ambivalent results were obtained for group predictionwithin the validation sample. While for boards from somegroups prediction was mostly or entirely correct, boardsfrom other groups were largely misclassified. An effect ofthe available sample was one of the surmised causes,making repetition of the analysis based on a larger sample adesirable focus of further research.

  • 5.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Aesthetic properties in knotty wood surfaces and their connection with people's preferences2001In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 47, no 3, p. 192-198Article in journal (Refereed)
    Abstract [en]

    For wood products that contain visible wood surfaces it is important to be able to describe, measure, and communicate the aesthetic properties desired. The aims of this investigation were to shed light on how people's preferences toward different wood appearances containing knots can be described and to create a better understanding of how to measure those preferences. A total of 215 persons from Sweden with different backgrounds were interviewed as to their preferences for 10 Scots pine wood surfaces containing knots. Their impressions and preferences were documented by a questionnaire with 54 questions and analyzed by a principal component analysis. A thorough description of what people see and value in a wood surface with knots is given in the body of the text. People's preferences are affected by a balance between two main properties: the degree of harmony and activity, and the importance of avoiding a state of disharmony when composing wood surfaces. When investigating people's preferences toward a knotty wood appearance, 13 of 54 questions proved to be important. Three questions detect the final assessment, and four describe the reasons for the final assessment. Finally, six questions describe the blend of wood properties in a more objective way and are to only a minor extent connected with the final assessments.

  • 6.
    Danvind, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Local water vapor diffusion coefficient when drying Norway spruce sapwood2006In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, no 3, p. 195-201Article in journal (Refereed)
    Abstract [en]

    In this article, a one-dimensional and a two-dimensional approach to the evaluation of local diffusion coefficients for Norway spruce sapwood from measured moisture content (MC) values are presented. A studied wood sample was dried from the initial green condition to about 15% mean MC, but here only the diffusive part of the drying process between approximately 25% and 15% mean MC was treated. Measured local MC values were based on nondestructive X-ray computed tomography data. Finite element calculations were performed with two alternative diffusion coefficients to test the appropriateness of the diffusion coefficients that were evaluated from the measured MC values. The evaluated diffusion coefficients show interesting dependence on MC and distance from the evaporation surface. The advantage of using the methods presented is that the diffusion coefficient is calculated on a local level without having to define a function for the diffusion coefficient's dependency on other parameters

  • 7.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Method to compute fiber directions in wood from computed tomography images2004In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 50, no 1, p. 41-46Article in journal (Refereed)
    Abstract [en]

    This paper describes a new method, called the CT-direction method, in which the fiber directions in wood in three-dimensional space are calculated from the pixel information on a series of two-dimensional computed tomography images. Local fiber directions are calculated from the principal directions of inertia of measurement spheres distributed throughout the body of the wood object. The calculated fiber directions are probably due to density streaks in the material, such as fiber bundles, which are directed in the fiber direction, and not the density of individual fibers, which are too small to be detected. The fiber directions vary locally, and density streaks from knots, growth rings, and compression wood influence the results, which adds spread to the results. The fiber directions are presented as spiral grain angles and conical angles and are compared with spiral grain angles measured with the tracheid-effect method. The comparisons show that the CT-direction method is a nondestructive way to measure fiber directions locally and in the interior of the body of a piece of wood.

  • 8.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Twist of wood studs: dependence on spiral grain gradient2005In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 51, no 5, p. 455-461Article in journal (Refereed)
    Abstract [en]

    Distortions due to moisture changes during drying or in service are a major problem for construction timber. Twist, caused mainly by the cylindrical geometry, the orthotropic nature of the wood material, and the tendency of the wood fibers to grow in a spiral around the stem, is often regarded as the most detrimental distortion of sawn timber. There is a need for a basic mechanical understanding of how the twist distortion arises and also a need for a simple formula to predict the amount of twist distortion. In this article such a formula is proposed, and theory and experimental data that indicate the validity of the formula are shown. The first term in the formula is a modification of a traditional expression which is proportional to the mean value of the spiral grain angle in the cross section in question. The second term in the formula is new and is proportional to the gradient of the spiral grain angle, and this term normally counteracts the first term so that a stud with a left-handed spiral grain might achieve a right-handed twist. Linear elastic finite element method (FEM) results and comparisons with experimental data show that the formula works well and that linear FEM calculations exaggerate the twist, which is probably partly due to nonlinear effects. The formula could be used to predict the twist of sawn timber from measured spiral grain angles on the log surface.

  • 9.
    Elustondo, Diego
    et al.
    Department of Wood Science, University of British Columbia, Vancouver.
    Avrimidis, Stavros H.
    Department of Wood Science, University of British Columbia, Vancouver.
    Stochastic numerical model for conventional kiln drying of timbers2003In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 49, no 6, p. 485-491Article in journal (Refereed)
    Abstract [en]

    A numerical model that predicts the stochastic dispersion associated with industrial kiln drying of timber was adapted to conventional drying and evaluated with experimental data. The theoretical aspects of the model are briefly explained, a selection of the calibration parameters was carried out, and a new empirical dispersion factor is proposed to account for all unknown sources of random behavior. The model was calibrated with six experimental runs of western hemlock and amabilis fir (116 mm2 timbers) to an average moisture content (target) of 14%-20%. It was found that with implementation of the dispersion factor, the number of required simulations is considerably reduced, the calibration results are consistent for all the experimental runs, and the target moisture content along with its standard deviation can be well reproduced using the all-run average parameters.

  • 10.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Handling positioning errors when optimizing sawing of Scots pine and Norway spruce logs using CT scanning2016In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 62, no 5, p. 400-406Article in journal (Refereed)
    Abstract [en]

    Since computed tomography (CT) X-ray scanning is becoming a reality in sawmills, different studies have been made to establish how well the sawing position of a log can be optimized using CT data. It is also known that positioning errors have an adverse effect on optimization, since the optimization methods used are rather sensitive to positioning errors. To mitigate the effect of positioning errors, a method is proposed in this article that filters results produced by sawing simulation, using a Gaussian filter of a size according to the positioning error. Using these filtered values for optimization, it is possible to retain two percent extra value of the sawn timber, when rotation and offset errors are present, compared to a regular optimization method. A method more robust to positioning errors is more useful in practice, since positioning errors of various magnitudes are always present in sawmills. The main contribution of this paper is, therefore, an optimization method that reduces the effect of positioning errors.

  • 11.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Optimizing sawing of boards for furniture production using CT scanning technique2015In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 61, no 5, p. 474-480Article in journal (Refereed)
    Abstract [en]

    The inherent variability of wood material together with sub-optimization in production processes means that a lot of potential value is lost. Computed tomography scanning together with simulation models of the production processes could remedy this, and ensure optimization of the entire production process. Therefore, the purpose of this study was to investigate if such methods can be used to optimize the sawing position of logs in a production process including further processing, in this case crosscutting to make a furniture product with strict quality requirements on dead knots. This was done on 47 Scots pine (Pinus sylvestris L.) logs. The results show a potential yield increase of more than 11 % points in the crosscutting operation and more than 4 % points when viewing the process as a whole, compared to sawing the logs horns down and centered

  • 12.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Antti, Lena
    Lundgren, Nils
    Hagman, Olle
    Finite element modeling (FEM) simulation of interactions between wood and microwaves2006In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, no 5, p. 406-410Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to use finite element modeling (FEM) as a tool to analyze microwave scattering in wood and to verify the model by measurements with a microwave scanner. A medical computed tomography scanner was used to measure distribution of density and moisture content in a piece of Scots pine (Pinus sylvestris). Dielectric properties were calculated from measured values for cross sections from the piece and used in the model. Images describing the distribution of the electric field and phase shift were obtained from the FEM simulation. The model was verified by measurements with a scanner based on a microwave sensor. The results show that simulated values correspond well to measured values. Furthermore, discontinuities in the material caused scattering in both the measured and the simulated values. The greater the discontinuity in the material, the greater was the need for computational power in the simulation.

  • 13.
    Johansson, Jan
    et al.
    Luleå tekniska universitet.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fjellner, Bengt-Arne
    Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber2003In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 49, no 4, p. 312-316Article in journal (Refereed)
    Abstract [en]

    This study was carried out to investigate the possibility of calibrating a prediction model for the moisture content and density distribution of Scots pine (Pinus sylvestris) using microwave sensors. The material was initially of green moisture content and was thereafter dried in several steps to zero moisture content. At each step, all the pieces were weighed, scanned with a microwave sensor (Satimo 9,4 GHz), and computed tomography (CT)-scanned with a medical CT scanner (Siemens Somatom AR.T.). The output variables from the microwave sensor were used as predictors, and CT images that correlated with known moisture content were used as response variables. Multivariate models to predict average moisture content and density were calibrated using the partial least squares (PLS) regression. The models for average moisture content and density were applied at the pixel level, and the distribution was visualized. The results show that it is possible to predict both moisture content distribution and density distribution with high accuracy using microwave sensors.

  • 14.
    Johansson, Marie
    et al.
    Chalmers University of Technology.
    Nyström, Jan
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Prediction of longitudinal shrinkage and bow in Norway spruce studs using scanning techniques2003In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 49, no 4, p. 291-297Article in journal (Refereed)
    Abstract [en]

    Straightness is one of the most important properties for making timber an attractive material for modern mechanized building. Several studies have shown that a lack of straightness is one of the main reasons for choosing materials other than timber in the construction industry. This paper presents a way to model moisture-induced bow from longitudinal shrinkage data predicted from an analysis of images of the surface of Norway spruce studs. For this study, eight studs (45 x 95 x 2500 mm and 45 x 120 x 3000 mm) of Norway spruce timber were selected. Bow in these studs was measured at two moisture contents below the fiber saturation point. The studs were then split into three slices 11 mm thick, and the surfaces of these slices were scanned to obtain color information and images of the tracheid effect. The slices were cut into sticks with dimensions of 10 x 10 x 200 mm. The longitudinal shrinkage coefficient of these sticks was measured. A multivariate model was created to model the longitudinal shrinkage coefficient data from the information in the images. The predicted longitudinal shrinkage data was used to model bow. The mean value of the measured longitudinal shrinkage was 0.0121 (SD 0.0123). The root mean square error of prediction (RMSEP) for the multivariate model was 0.0079, which is regarded as good. Thus, it was possible to model moisture-induced bow with good accuracy using the predicted longitudinal shrinkage data.

  • 15.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ikeda, Tsutomu
    Wood Chemistry Laboratory.
    Kishimoto, Takao
    Wood Chemistry Laboratory.
    Magara, Kengo
    Wood Chemistry Laboratory.
    Matsumoto, Yuji
    Wood Chemistry Laboratory.
    Hosoya, Shuji
    Wood Chemistry Laboratory.
    Isolation of lignin-carbohydrate bonds in wood: model experiments and preliminary application to pine wood2004In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 50, no 2, p. 141-150Article in journal (Refereed)
    Abstract [en]

    A novel method for analysis of benzylic ether type lignin-carbohydrate bonds has been developed by using model compounds. Four diastereomers of model compound 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-3-(methyl -d-glucopyranoside-6-O-yl)-1-propanol (GGMGP), were ozonized in acetic acid/water/methanol 16:3:1 for 1h at 0°C. The product from ozonation of each diastereomer was saponified and the corresponding -etherified tetronic acid (TAMGP) was isolated using ion exchange chromatography. Minor amounts of methyl -d-glucopyranoside (MGP) and small amounts of a gluconic acid etherified with tetronic acid (TAGLCA), tetronic acid, gluconic acid, and glyceric acid were detected in the product mixture of ozonated benzylic ether type model compounds. The results suggest that a benzyl ether bond between lignin and carbohydrate is rather stable during the ozone treatment. Acid treatments with sulfuric acid or trifluoroacetic acid of the derived TAMGP led to cleavage of the glucosidic bond but only a small amount of products (tetronic acid and glucose) resulting from cleavage of the -ether bond were formed. The successful chemical treatments were used for studies of benzylic ether bonds in Japanese red pine. The results suggest the presence of benzylic ether bonds to polysaccharides in the wood.

  • 16.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ikeda, Tsutomu
    Forestry and Forest Products Research Institute.
    Kishimoto, Takao
    Forestry and Forest Products Research Institute.
    Magara, Kengo
    Forestry and Forest Products Research Institute.
    Matsumoto, Yuji
    Forestry and Forest Products Research Institute.
    Hosoya, Shuji
    Forestry and Forest Products Research Institute.
    Ozonation of a lignin-carbohydrate complex model compound of the benzyl ether type2000In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 46, no 3, p. 263-265Article in journal (Refereed)
    Abstract [en]

    Evidence for the presence of lignin-carbohydrate bonds of the benzylic ether type in wood and pulps may be obtained by use of ozonation treatment to selectively degrade the lignin. It was found that the benzyl ether bond in 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxy-phenoxy)-3-(methyl--d-glucopyranosid-6-O-yl)-1-propanol was rather stable during ozonation in acetic acid-water-methanol 1631 at 0°C. The corresponding acid, 3,4-dihydroxy-2-(methyl--d-glucopyranosid-6-O-yl)-butanoic acid, was found to be the major reaction product. The use of ozonation followed by acid hydrolysis in connection with studies of lignincarbohydrate linkages is briefly discussed.

  • 17.
    Kishimoto, Takao
    et al.
    Forestry and Forest Products Research Institute.
    Ikeda, Tsutomu
    Wood Chemistry Laboratory, Forestry and Forest Products Research Institute, 305-8687 Ibaraki.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Magara, Kendo
    Wood Chemistry Laboratory, Forestry and Forest Products Research Institute, 305-8687 Ibaraki.
    Hosoya, Shuji
    Wood Chemistry Laboratory, Forestry and Forest Products Research Institute, 305-8687 Ibaraki.
    Reactivity of secondary hydroxyl groups in methyl β-D-xylopyranoside toward a β-O-4-type quinone methide2002In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 48, no 1, p. 32-37Article in journal (Refereed)
    Abstract [en]

    Methyl β-D-xylopyranoside was allowed to react with β-O-4-type quinone methide without a catalyst to elucidate the reactivities of secondary hydroxyl groups at the C2, C3, and C4 positions. Benzyl ether-type lignin-carbohydrate complex (LCC) compounds linked at the C2 and C4 positions were predominant, at a ratio of 2:3. However, the reactivity of the hydroxyl group at the C3 position was quite low. These results strongly suggest that the reactivity of the C2 hydroxyl group in xylan toward quinone methide intermediate is higher than that of the C3 hydroxyl group during biosynthesis of LCCs

  • 18. Lundgren, Nils
    et al.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Flodin, Jens
    Choosing green sawing dimensions for Norway spruce from stochastic simulations2011In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 57, no 2, p. 94-99Article in journal (Refereed)
    Abstract [en]

    The high accuracy of log positioning and the stability of saw blades in breakdown machinery in modern sawmills have reduced the need to add margins for sawing variations. Oversize green sawing dimensions are still needed, but mainly to allow for drying shrinkage. This has put a new focus on better adapting green sawing dimensions to the shrinkage behavior of wood. In this study, a method for optimization of green sawing dimensions using stochastic simulation is presented. Normal distributions were generated for planed dry dimensions, kerf width, and target moisture content. The minimum share of boards exceeding the specified dry dimensions was decided, and deformations in boards from all positions in the cross section in a number of logs were simulated. The simulated shrinkage allowance from stochastic simulations was compared to experimental results from an industry test and to finite element results based on material data for Norway spruce. The results showed that the green width of the sawn boards should increase when the number of boards in the center yield increases. The green thickness of boards should be thinner for center boards and outer boards than for inner boards

  • 19. Lundgren, Nils
    et al.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Johansson, Jan
    Luleå tekniska universitet.
    Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber II:: Evaluation of models generated on a pixel level2006In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, no 1, p. 39-43Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to use images from a microwave sensor on a pixel level for simultaneous prediction of moisture content and density of wood. The microwave sensor functions as a line-scan camera with a pixel size of 8mm. Boards of Scots pine (Pinus sylvestris), 25 and 50mm thick, were scanned at three different moisture contents. Dry density and moisture content for each pixel were calculated from measurements with a computed tomography scanner. It was possible to create models for prediction of density on a pixel level. Models for prediction of moisture content had to be based on average values over homogeneous regions. Accuracy will be improved if it is possible to make a classification of knots, heartwood, sapwood, etc., and calibrate different models for different types of wood. The limitations of the sensor used are high noise in amplitude measurements and the restriction to one period for phase measurements

  • 20. Nordvik, Enar
    et al.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Looking at computer-visualized interior wood: a qualitative assessment using focus groups2009In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 55, no 2, p. 113-120Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to explore and gather human reactions and perceptions on computer visualizations of interior wood. The subjective qualities of such products are important because they infl uence the most critical of consumer decisions: to buy or not. To learn more about a phenomenon than quantitative data can provide, qualitative methods are needed. Here, grounded theory was used with focus groups to form a map of 14 people's experiences of wood. Six computer-generated pictures with visible wood were varied into 18 pictures, such that two-by-two comparison resulted in 3500 words. These were combined into a map that was generated earlier, which had found 2000 words. The main dimensions found were light, color, unity, and authenticity. Light is more than brightness; shadows and lighting seemed more important for the wood feeling, and color and contrast gave life and warmth to the material on the screen. Respondents wanted wood that was more "woody" and "warmer" than wood actually is, that is, a hyper-realistic picture. Perhaps smart modification rather than photorealism should be the goal. Distribution of the earlier found activity and harmony was important for most respondents. In addition, many subjects discussed the composition and/or the context or purpose of the pictures. The impact of wood is not just related to the wood itself; it is also intertwined with its surroundings.

  • 21. Nyström, Jan
    et al.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Real-time spectral classification of compression wood in Picea abies1999In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 45, no 1, p. 30-37Article in journal (Refereed)
    Abstract [en]

    Compression wood is formed by the living tree to compensate for external loads. It creates wood fibers with properties undesirable in sawn products. Automatic detection of compression wood can lead to production advantages. A wood surface was scanned with a spectrometer, and compression wood was detected by analyzing the spectral composition of light reflected from the wood surface within the visible spectrum. Linear prediction models for compression wood in Norway spruce (Picea abies) were produced using multivariate analysis and regression methods. The resulting prediction coefficients were implemented in a scanning system using the MAPP2200 smart image sensor combined with an imaging spectrograph. This scanning system is capable of making a pixelwise classification of a wood surface in real time. Classification of one spruce plank was compared with analysis by scanning electron microscopy, showing that the automatic classification was correct in 11 of 14 cases.

  • 22. Olsson, Tomas
    et al.
    Megnis, Modris
    Luleå tekniska universitet.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Measurement of the uptake of linseed oil in pine by the use of an X-ray microdensitometry technique2001In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 47, no 4, p. 275-281Article in journal (Refereed)
    Abstract [en]

    Pine sapwood (Pinus sylvestris) was impregnated with linseed oil to three levels of uptake. The distribution of the penetrant was found by taking microdensity measurements of an impregnated sample and then using an ethanol extraction procedure to remove the linseed oil. A second set of X-ray measurements at identical locations in the same sample allowed the linseed oil to be indirectly mapped. An uneven distribution of linseed oil in the specimens with the lowest uptake (25% increase in weight) was seen as sharp gradients in the densitometry curves. With increased filling by the linseed oil, these gradients were gradually smoothed. Microstructural changes in specimens with high uptake were revealed using scanning electron microscopy. Through a combination of X-ray microdensitometry investigation and changes observed in the wood''s mechanical properties and morphology, it was concluded that liquid flow during impregnation results in significant damage to the cell structure.

  • 23.
    Olsson, Tomas
    et al.
    Luleå tekniska universitet.
    Megnis, Modris
    Luleå tekniska universitet.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy2001In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 47, no 4, p. 282-288Article in journal (Refereed)
    Abstract [en]

    Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnated with a low-viscous epoxy resin using a vacuum process. The epoxy was cured in situ and the specimens sectioned. Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The investigation concentrated on tracing the transverse movements of a viscous liquid in the wood, and special attention was therefore given to the cross-field area between ray cells and longitudinal tracheids. A damage hypothesis is proposed based on the results obtained in the present investigation in combination with those from earlier studies on linseed oil-impregnated pine: In addition to the morphology of the bordered pits, viscous liquid flow in wood is dependent on damage that occurs during the impregnation procedure. For pine sapwood, liquid flow is enabled through disrupted window pit membranes, which divide the longitudinal tracheids and the ray parenchyma cells. A mechanism accounting for the reduced permeability of pine heartwood is believed to be deposits of higher-molecular-weight substances (extractives) in the ray parenchyma cells and on the cell walls. In spruce the thicker ray cells in combination with the smaller pits, which are connected to the longitudinal tracheids, reduce permeability considerably.

  • 24.
    Sehlstedt-Persson, Margot
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wamming, Thomas
    SP Trätek Technical Research Institute of Sweden, Skellefteå.
    Wood drying process: impact on Scots pine lumber durability2010In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 56, no 1, p. 25-32Article in journal (Refereed)
    Abstract [en]

    There are indications that the drying process may have negative effects on the natural durability of wood. The impact of various drying processes on the durability of Scots pine lumber has been evaluated with mass loss in a decay test with brown rot fungus, Coniophora puteana, as measure of the decay resistance of sapwood and inner and outer heartwood. Drying with or without steam conditioning was performed in six different series: air drying, kiln drying at temperature ranges commonly used in Swedish sawmills at 70°C and 90°C with two different regulation principles, and one high-temperature drying at 110°C. Durability varied considerably both between and within boards. Sapwood showed considerable less durability than heartwood. No difference in durability was found between inner heartwood and outer heartwood. Air-dried heartwood showed the highest durability compared to other drying series. The lowest durability in sapwood and heartwood was found for series dried at the 90°C temperature level with high material temperature early in drying. The interpretation is that the duration of high material temperature at high moisture content (MC) is the critical combination for decay resistance in heartwood. Steam conditioning after drying decreased durability in sapwood.

  • 25.
    Sepulveda, Paul
    Luleå tekniska universitet.
    Measurement of spiral grain with computed tomography2001In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 47, no 4, p. 289-293Article in journal (Refereed)
    Abstract [en]

    Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. In sawmills the spiral grain in logs is judged manually. For research purposes the spiral grain in stems and logs is normally measured by destructive methods. In this study the spiral grain of the stems was measured nondestructively with a computed tomography (CT) scanner. Twelve Norway spruce (Picea abies) stems from two stands in Sweden were scanned with a CT scanner with one cross-sectional scan every 10mm along the stem. Concentric surfaces at various distances from the pith were reconstructed from the stack of CT images. In these concentric-surface images, which show various internal features of the log, the spiral grain angle was measured at different distances from the pith and at different heights in the stem. The destructive measurements of the spiral grain were carried out on disks from the top ends of the logs. On these disks the spiral grain was measured at different distances from the pith with a protractor. Finally, the results from the destructive method were compared with the results from analysis of the CT images. The nondestructive and destructive measurements were compared in pairs with the same radial and approximately the same height position in each pair. The correlations (r) between the two methods were 0.81 and 0.71, respectively, for the two stands. It was concluded that it is possible to measure the spiral grain angle nondestructively with a CT scanner

  • 26.
    Sepulveda, Paul
    et al.
    Luleå tekniska universitet.
    Oja, Johan
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Predicting spiral grain by computed tomography of Norway spruce2002In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 48, no 6, p. 479-483Article in journal (Refereed)
    Abstract [en]

    Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. The aim of this study was to investigate the possibility of predicting spiral grain based on variables that should be measurable with an X-ray LogScanner. The study was based on 49 Norway spruce (Picea abies) logs from three stands in Sweden. The logs were scanned with a computed tomography (CT) scanner every 10 mm along the log. Concentric surfaces at various distances from the pith were then reconstructed from the stack of CT images. The spiral grain angle was measured in these concentric surface images, and a statistical model for predicting spiral grain was calibrated using partial least squares (PLS) regression. The PLS model predicts the spiral grain of a log at a distance 50 mm from the pith based on different variables that should be measurable with an industrial X-ray LogScanner. The result was a PLS model with R2 = 0.52 for the training set and R 2 = 0.37 for the test set. We concluded that it should be possible to predict the spiral grain of a log based on variables measured by an industrial X-ray LogScanner. The most important variables for predicting spiral grain were measures of sapwood content, variation in the ratio between the heartwood and log areas, and the standard deviation for the mean log density in 10 mm thick cross slices along the log. The accuracy when sorting the logs into two groups with spiral grain of greater than or equal 2.0° and of less than or equal 2.0°, respectively, was 84% of the correctly sorted logs.

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