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  • 51.
    Sandberg, Dick
    et al.
    Växjö university.
    Söderström, Ove
    Royal Institute of Technology.
    Crack formation due to weathering of radial and tangential sections of pine and spruce.2006In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 1, no 1, p. 12-20Article in journal (Refereed)
    Abstract [en]

    The development of cracks and changes in appearance have been investigated on radial and tangential sections of pine(Pinus sylvestris L.) and spruce (Picea abies Karst.) after exposure outdoors for 61 months. The degradation of the sectionshas also been studied at the micro-level. The annual ring orientation was the most important factor affecting crackdevelopment on weathering. After 61 months of outdoor exposure, the tangential sections of spruce had 1.7/2.2 timesgreater mean total crack length per area unit than the corresponding radial sections. In pine, the total crack length per areaunit on the tangential sections was 2.2/2.6 times greater than that on the radial sections. Tangential and radial sectionsshow the same colour change as a result of weathering. Tangential sections have more and deeper cracks than radial surfaces.The cracks on the tangential sections occur frequently in both earlywood and latewood. On radial sections, cracks occurprimarily at the annual ring borders, but to a certain extent also in the earlywood. Decomposition of the cell wall takes placein both radial and tangential cell walls, and cracks tend to follow the fibril orientation in the S2-layer of the cell wall. Theradial cell wall of the earlywood has a large number of pits which are degraded at an early stage.

  • 52.
    Sandberg, Karin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Degradation of Norway spruce (Picea abies) heartwood and sapwood during 5.5 years' above-ground exposure2008In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 3, no 3-4, p. 83-93Article in journal (Refereed)
    Abstract [en]

    Differences in durability between heartwood and sapwood of Norway spruce [Picea abies (L.) Karst.] were investigated to determine wood qualities most favourable for use in outdoor constructions above ground. Trees grown on sites with either good or poor access to water were used. Seventy-eight specimens measuring 2050300 mm3 separated into heartwood and sapwood, half untreated, half painted, were exposed horizontally outdoors above ground for 5.5 years with the pith side up and the bark side down. Crack length and crack number were measured. Fungus growth and surface changes were visually estimated. Fungus type was determined by microscopic analysis. The main finding was that spruce heartwood had fewer and shorter cracks and less surface-discolouring fungus growth than sapwood. This was valid for both painted and untreated wood. After 2 years' exposure, the cracks in sapwood (upper surface) were more than three times longer and about five times more numerous than in heartwood for both painted and untreated boards. Microscopic study showed that surface discoloration was due mainly to Aureobasidium pullulans, together with a few other discolouring fungi. After 5.5 years, initial decay was established on the surface and in the end grain of four untreated test objects.

  • 53.
    Sandberg, Karin
    et al.
    SP Technical Research Institute of Sweden.
    Mostolygin, Kirill
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Effect of lamellas annual-ring orientation on cracking of glulam beams investigated with computer tomography and image processing2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 3, p. 166-174Article in journal (Refereed)
    Abstract [en]

    Cracks in glulam beams can reduce their strength, depending on the crack's depth, length, and location and can also be a passage for the accumulation of water and dirt. To avoid cracks, the relationship between cracks (area of cracks, mm2) and annual-ring orientation in glulam beams of spruce (Picea abies), and pine (Pinus sylvestris) with different dimensions and surface treatments was investigated using RGB images of the surface and tomography images of the cross-sections. Image processing was used to measure characteristics visible in the photos such as crack area and lamella position in the beam. Combination of lamellas in lay up was measured from computer tomography images. Four types of combinations were defined; type 1 (pith side facing outward), types 2 and 3 (pith to the same side), and type 4 (pith sides meet pith side). It was found that the area close to the glue line in the lamellas in combination type 4 is the most subject to cracking, whereas combinations of type 1 show the highest resistance to cracking. This means that type 4 should not be used in glulam beams, because the lamellas shrink apart from each other causing stresses and resulting cracks.

  • 54.
    Schajer, Gary
    et al.
    Department of Mechanical Engineering, University of British Columbia, Vancouver.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Practical measurement of circular saw vibration mode shapes2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 162-166Article in journal (Refereed)
    Abstract [en]

    Natural frequency measurement provides a convenient quantitative method for monitoring the tensioning state of a circular saw. However, it can often be difficult to interpret the measurements because the corresponding vibration mode shapes are not explicitly known, especially when adjacent natural frequencies are close together. A mode shape identification method is presented. It involves using two vibration sensors, one fixed and one orbiting the sawblade circumference. The performance of a simple prototype measurement device using this technique is described. The device could successfully identify the nodal diameter and nodal circle numbers of the major sawblade vibration modes.

  • 55. Skog, Johan
    et al.
    Vikberg, Tommy
    Oja, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sapwood moisture-content measurements in Pinus sylvestris sawlogs combining X-ray and three-dimensional scanning2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 2, p. 91-96Article in journal (Refereed)
    Abstract [en]

    Because today's sawmill processes are not fully adapted to the variability of the raw material, it is crucial to sort sawlogs according to material properties in order to process the wood efficiently and to obtain high-quality end-products. One material property that could be used for sorting is the moisture content (MC) of the sapwood, an important parameter for both the processing and the end-products. Most sawmills use three-dimensional (3D) scanners to sort logs and some have also invested in X-ray scanners. Previous studies have shown that, by combining raw data from 3D and X-ray log scanners, green sapwood density and dry heartwood density in Scots pine sawlogs can be estimated. In this study, the method was used to estimate sapwood MC in green logs. It was found that the MC estimate could be used to separate the logs into groups with high and low MC, correctly classifying all logs with MC below 100% as low MC logs. Out of all logs, 70% were correctly classified. The MC estimate could also be compared to the dry density-dependent maximum MC and used to identify logs that have actually started to dry.

  • 56.
    Torkaman, Javad
    et al.
    Department of Forestry, Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran.
    Mojgan, Vaziri
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Mohammadi Limaeia, Soleiman
    Department of Forestry, Faculty of Natural Resources, University of Guilan, Sowmeh Sara, Iran.
    Relationship between branch-scar parameters and knot features of oriental beech (Fagus orientalis Libsky)2018In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 13, no 2, p. 117-120Article in journal (Refereed)
    Abstract [en]

    The classification of roundwood is inextricably linked to the measurement of a particular single wood defect. The appearance, location, and number of defects are important in the quality evaluation of logs and sawn timber, and the most important defects are knots. The purpose of this study was to investigate the relationship between the appearance of branch scars and features of the related knot inside oriental beech logs, and to model the relationship between well-defined branch-scar and knot parameters. One hundred and fifty knots in 15 stems of oriental beech trees were studied. Image analysis software was used to measure the branch-scar and knot features. The results showed a significant positive correlation between the branch-scar parameter “moustache length” and the knot length. The ratio of branch-seal length to width was found to be a good estimator of the stem diameter at the time of knot occlusion and the amount of clear wood between the knot occlusion and the bark. The relationship obtained for the oriental beech stem radius at time of knot occlusion confirms relationship reported for European beech (Fagus sylvatica L.).

  • 57.
    Ugovšek, Aleš
    et al.
    M SORA d.d., Žiri, Slovenia.
    Šubic, Barbara
    M SORA d.d., Žiri, Slovenia.
    Starman, Jernej
    M SORA d.d., Žiri, Slovenia.
    Rep, Gregor
    Silvaprodukt d.o.o., Ljubljana, Slovenia.
    Humar, Miha
    Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
    Lesar, Boštjan
    Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
    Thaler, Nejc
    Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
    Brischke, Christian
    Department of Wood Biology and Wood Products, Faculty of Forest Sciences and Forest Ecology, University of Goettingen, Goettingen, Germany.
    Meyer-Veltrup, Linda
    Institute of Vocational Sciences in the Building Trade, Faculty of Architecture and Landscape Sciences, Leibniz University Hannover, Hannover, Germany.
    Jones, Dennis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. DJ Timber Consultancy Limited, Neath, UK.
    Häggström, Urban
    Research Institute of Sweden, Built Environment/Building Technology, Skellefteå, Sweden.
    Lozano, Jose Ignacio
    Tecnologías Avanzadas Inspiralia S.L., Madrid, Spain.
    Short-term performance of wooden windows and facade elements made of thermally modified and non-modified Norway spruce in different natural environments2018In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 1, p. 42-47Article in journal (Refereed)
    Abstract [en]

    Thermally modified wood is becoming an increasingly popular material for different applications in buildings. Laboratory tests indicated a positive effect of thermal modification on durability, dimensional stability and thermal conductivity of wood. Therefore, windows and facade elements made of thermally modified Norway spruce and non-modified Norway spruce were tested in the field and installed in different test objects which were exposed at five locations in Europe (Slovenia, Germany, Sweden, and Spain). Results from monitoring showed that elements and windows made of thermally modified spruce (TMS) had considerably lower wood moisture content compared to the ones made of non-modified spruce and that wax further positively influenced moisture performance. Colour changes of TMS were more intensive compared to non-modified spruce but were successfully retarded by adding pigments to the wax. Mould and stain growth was largely dependent on the location, amount of precipitation and relative humidity.

  • 58.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Gheinani, Iman Tavakoli
    Department of Mechanical Engineering, ENSTIB-LERMAB, University of Lorraine.
    Three-dimensional finite element modelling of heat transfer for linear friction welding of Scots pine2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 2, p. 102-109Article in journal (Refereed)
    Abstract [en]

    Finite element numerical analyses were performed to determine three-dimensional heat flux generated by friction to wood pieces during linear friction welding. The objective was to develop a computational model to explain the thermal behaviour of welded wood material rather than experimental methods, which are usually expensive and time consuming. This model serves as a prediction tool for welding parameters, leading to optimal thermo-mechanical performance of welded joints. The energy produced by the friction welding of small wood specimens of Scots pine (Pinus sylvestris L.) was determined by thermocouples and used as input data in the model. The model is based on anisotropic elasticity and the thermal properties were modelled as isotropic. This numerical simulation gave information on the distribution of the temperature in the welding interface during the entire welding process. A good agreement between the simulation and experimental results showed the appropriateness of the model for planning welded wood manufacture and prediction of thermal behaviour of wood during other mechanically induced vibration processes. The specimens presented in this model required a heat flux of 11 kW/m2 to achieve a satisfactory welding joint

  • 59.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Plessis, Anton du
    University of Stellenbosch.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Nano X-ray tomography analysis of the cell-wall density of welded beech joints.2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 368-372Article in journal (Refereed)
    Abstract [en]

    This paper reports the results of a novel approach using nano X-ray computed tomography (CT) for the non-invasive determination of the weld-line density profile of welded wood joints. As a case study, wood samples with a dimension of 2 mm × 2 mm × 20 mm were cut from a board of welded beech (Fagus sylvatica L.). The spatial resolution of the X-ray scan was 500 nm. Densitometry results showed that welding was accompanied by a considerable increase in the bulk density and a decrease in the cell-wall density at the weld-line. The cell-wall density in the weld-line was almost 33% less than that of the unaffected wood. As an additional application of nano computed tomography, the 3D imaging also revealed details of the internal structure of the welded sample. This study showed that nano-CT is a powerful tool for the descriptive and quantitative study of welded wood

  • 60.
    Vikberg, Tommy
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Basic density determination for Swedish softwoods and its influence on average moisture content of wood packages estimated by measuring their mass2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 4, p. 248-253Article in journal (Refereed)
    Abstract [en]

    In this work, a set-up with a device measuring the mass of wood packages is examined as an aid to estimate the average moisture content (MC) of wood packages. As the basic density needs to be presumed in the set-up, an estimator of the basic density as a function of log diameter is determined for Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris). In total, 1920 specimens were collected at two different sawmills and analysed for this purpose. Specimens collected at the butt-end of pine had the greatest variation in basic density and it is recommended that they should be omitted when sawmills create their own functions for basic density estimation. Furthermore, the variation in basic density was shown to have the greatest impact on the estimated MC. A maximum error estimator of the MC became 14% at a MC of 70% and 9% at a MC of 10%. It was therefore concluded that the described method should not be used to estimate the MC of packages after drying but can serve as a valuable indicator of average green MC of a drying batch.

  • 61.
    Vikberg, Tommy
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. SP Technical Research Institute of Sweden, SP Wood Technology, Skellefteå.
    Hägg, Linus
    SP Technical Research Institute of Sweden, Wood Technology.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of fan speed on airflow distribution in a batch kiln2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 2, p. 197-204Article in journal (Refereed)
    Abstract [en]

    This study reports experimental data of airflow distribution as a function of fan speed in an industrial batch kiln.Measurements were conducted with 20 hot-film anemometers distributed throughout the load at two occasions. The mainresult was that airflow distribution did not change significantly as the fan speed was reduced, and no positions where the airmovement stopped were found. It was also found that relatively more air ran in the bolster spaces in comparison to theadjacent packages as the air ran through the load.

  • 62.
    Öhman, Micael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Grubii, Victor
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    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.
    Moistening of the wood surface before planing for improved surface quality2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 3, p. 156-163Article in journal (Refereed)
    Abstract [en]

    The roughness of a machined wooden surface is affected by a number of factors such as cutting tool geometry, machine settings and wood structure. The influence of wood structure on wood surface quality is difficult to control since the surface roughness is dependent on the local combination of density, grain direction and moisture content (MC). The greater the variation in wood features, the more difficult it is to find a combination of tools and machine settings that will give a high surface quality. The purpose was to study the impact of a surface wetting treatment before planing in order to reduce torn grain in the wood surface near knots in sawn timber of low MC. The study was based on a total of 120 specimens of Scots pine (Pinus sylvestris L.). To maximize the variation in grain orientation and density, the specimens contained both clear wood and knots. The results showed that when the surface was moistened before planing, chipped and torn grain in areas of deviating grain close to knots decreased. The response to wetting was rapid, wetting less than 30 s before planing gave as good an improvement as treatment time of 30 min or more.

12 51 - 62 of 62
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