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  • 1.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    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.
    Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 4, p. 257-262Article in journal (Refereed)
    Abstract [en]

    The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.

  • 2.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Finell, Michael
    Swedish University of Agricultural Sciences.
    Arshadi, Mehrdad
    Swedish University of Agricultural Sciences.
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences.
    Effects of microwave drying on biomass fatty acid composition and fuel pellet quality2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 1-2, p. 34-40Article in journal (Refereed)
  • 3.
    Axelsson, Ann
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Effect of planing on warp in Scots Pine (Pinus sylvestris)2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 154-161Article in journal (Refereed)
    Abstract [en]

    If a sawn board or plank that is warped after drying is being planed, the feed rollers and the pressure elements will more or less straighten the wood during planing. However, when the pressure is released, some degree of warp will recur since the wood will spring back. With a large amount of straightening, only the cross-sectional dimensions of the wood should be affected by the planing operation, leaving warp unchanged, while a small amount of straightening should have a larger impact on warp. The objective of this study was to evaluate how warp is affected by planing in an industrial planer with standard configuration. A total of 20 pine planks with the dry target dimension 50 mm×150 mm were selected, of which half were severely warped. The worst twist, crook and bow per two metres and maximum cup were measured both before and after planing.The planer in the experiment had different impacts on the different warp types. For the individual planks, twist was reduced by 25% and crook was reduced by about 20% on average. Although bow decreased for half of the planks, the total average change for individual planks was a slight increase. Cupping practically vanished.

  • 4.
    Axelsson, Ann
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Rectangularity of planed Scots Pine (Pinus sylvestris) planks2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 2, p. 145-151Article in journal (Refereed)
    Abstract [en]

    This study deals with how warp affects the cross-sectional shape of planed planks. A total of 20 planks with dry target cross-sectional dimensions of 50×150 mm were planed to 45×145 mm. The rectangularity of five cross sections of every plank was measured before and after planing. The cutting depths were measured in 10 positions in the cross sections, and the angles between the planks and the cutters were calculated. Also, the warp, that is, twist, bow, crook, and cup, was measured before and after planing. All the studied properties pointed in the same direction. In terms of both rectangularity and angles of cut, the problems were larger in the top and butt ends of the investigated planks than in the intermediate parts, and the main reason for deviations from the desired result after planing was twist.

  • 5.
    Axelsson, Ann
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Potential for increasing volume yield by reducing planing allowance2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 5, p. 301-306Article in journal (Refereed)
    Abstract [en]

    About half the volume of sawlogs ends up as sawn and planed timber. The rest is lost due to drying shrinkage or is turned into by products. As the raw material is a major expense for a sawmill, it is important to reduce waste.

    To investigate how much the volume yield in the production of sawn and planed timber could be increased by reducing the target dimensions in the sawing stage in a sawmill, two groups of sawn timber were planed under similar conditions. One group consisted of sawn Scots pine timber with a large variation in twist. The other group consisted of sawn Norway spruce timber planed under different pressure settings. Using X-ray images, the minimum dimension for avoiding planer misses was calculated for each board, to find the smallest green target dimension. This was compared to actual measured dimensions.

    It was found that most sawn timber had unnecessarily large dimensions, and it was also found that a reduction in the target dimensions could increase the volume yield for sawn and planed timber by more than 3 percentage points. Boards with large twist would however need a higher planing allowance. The effect of the planer pressure setting was negligible.

  • 6.
    Berg, Sven
    et al.
    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.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Crack influence on load-bearing capacity of glued laminated timber using extended finite element modelling2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 335-343Article in journal (Refereed)
    Abstract [en]

    Most of the cracks are caused by changes in temperature and relative humidity which lead to shrinkage and swelling of the wood and thereby induce stresses in the structure. How these cracks influence the strength of the wooden structure, especially the shear strength, is not well understood. However, it is reasonable to expect that cracks have an impact on the shear strength as they preferably run along the beams in the direction of grain and bond lines. The purpose of this study was to investigate the load-bearing capacity of cracked glulam beams and to find a model that could predict the failure load of the beams due to the cracks. Three-point bending tests were used on glulam beams of different sizes with pre-manufactured cracks. An orthotropic elastic model and extended finite element method was used to model the behaviour of the cracked beams and to estimate the load-bearing capacity. The conclusions were validated by numerical simulations of the mechanical behaviour of three-point bending of glulam beams with different crack locations. The crack initiation load was recorded as the failure load and compared to the experimental failure load. The results of the compaction simulations agree well with the experimental results

  • 7.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Turesson, Jonas
    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.
    Huber, Johannes Albert Josef
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Finite element analysis of bending stiffness for cross-laminated timber with varying board width2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 6, p. 392-403Article in journal (Refereed)
    Abstract [en]

    ross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.

  • 8.
    Berglund, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Dahlquist, Simon
    SP Trä.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Detection of saw mismatch in double arbor saw machines using laser triangulation2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 4, p. 219-225Article in journal (Refereed)
    Abstract [en]

    In the sawing process of a sawmill, not only are the target sizes of great importance. The saw mismatch that may occur in double arbor saw machines is also an essential parameter that affects the planing allowance, as well as the quality of the sawn products. In this study, a newly developed measurement equipment for detecting saw mismatch in the green sorting line of a sawmill has been evaluated in an initial experimental test. The obtained data has been compared to manual measurements of saw mismatch with good results. Also, based on a small sample, 75 – 95% of the boards with a maximal saw mismatch exceeding 0.5 mm are detected. The rate of detection depends on the number of cameras used.

  • 9.
    Blomqvist, Lars
    et al.
    Linnéuniversitetet.
    Johansson, Jimmy
    Linnéuniversitetet.
    Sandberg, Dick
    Shape stability of laminated veneer products: an experimental study of the influence on distortion of some material and process parameters2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 3, p. 198-211Article in journal (Refereed)
    Abstract [en]

    A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. In this study, we have examined the influence of different UF-adhesive systems, adhesive distribution, and veneer properties such as species, moisture content, and fibre orientation. Two different species were studied: beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.). Distortion was determined directly after moulding and after storage in a changing relative humidity. The aim of the work was to study how the above-mentioned material and process parameters influence the distortion. The results show that the material and process parameters and the storage in a changing relative humidity had a clear impact on distortion. Fibre orientation, differences in moisture content between veneers, and the moisture gradient in the final product are identified in this study as being the most important parameters influencing the distortion and shape stability of laminated veneer products

  • 10.
    Blomqvist, Lars
    et al.
    Forest and Wood Technology, Linnæus University.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Johansson, Jimmy
    Linnæus University, Forestry and Wood Technology.
    Influence of veneer orientation on shape stability of plane laminated veneer products2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 4, p. 224-232Article in journal (Refereed)
    Abstract [en]

    One of the most important quality aspects of a laminated veneer product is its shape stability under changing relative humidity (RH). This study aimed to establish an understanding of how the orientation of individual veneers in the laminate, i.e., orientation according to fibre orientation and orientation of the loose (the side with ‘lathe checks’) or tight side of the veneer, affects the shape stability. Three-ply laminates from peeled veneers of beech (Fagus sylvatica L.) were studied. The four types of laminate were the following: loose sides of all veneers in the same direction (cross and parallel centre ply) and loose sides of the outer veneers facing inward (cross and parallel centre ply). Four replicates of each type yielded 16 samples. The samples were exposed to RH cycling at 20% and 85% RH at 20°C, and the shapes of the samples were determined. The shape stability was influenced by the veneer orientation. Laminations with the middle veneer perpendicular to the top and bottom veneer (cross-laminated) showed the best shape stability, especially when the loose sides of the veneers were oriented the same direction. In parallel-laminated veneers, the laminates with opposite directions of the loose sides in the two outermost veneers showed the best shape stability. The major explanation of the behaviour of the laminates is that the loose side expanded more than the tight side from the dry to the humid climate, which was shown by optical 3D deformation analysis (ARAMISTM). After RH cycling, the laminates with cross plies showed visible surface checks only when the tight side was facing outwards.

  • 11.
    Breinig, Lorenz
    et al.
    Forest Research Institute of Baden-Württemberg, 79100 Freiburg.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Brüchert, Franka
    Forest Research Institute of Baden-Württemberg, 79100 Freiburg.
    Becker, Gero
    Institute of Forest Sciences, University of Freiburg.
    Optimization potential for perception-oriented appearance classification by simulated sawing of computed tomography-scanned logs of Norway spruce2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 319-334Article in journal (Refereed)
    Abstract [en]

    Wood, as a natural material, has favourable properties in both technical and aesthetic aspects. Due to its inherent variability,production of high-quality sawn timber demands adequate control of log conversion, which is feasible with computedtomography (CT) log scanning. Existing appearance grading rules for sawn timber might not fully reflect people’s visualperception of wood surfaces, and therefore, an alternative, more perception-oriented appearance classification could bebeneficial. An appearance classification of sawn timber based on partial least squares discriminant analysis (PLS-DA) ofknot-pattern variables was developed and tested. Knot-pattern variables derived from images of board faces were used intraining PLS-DA models against an initial classification of the board faces previously established by aid of cluster analysis.Virtual board faces obtained from simulated breakdown of 57 CT-scanned Norway spruce logs were graded according tothe developed classification. Visual assessment of the grading results indicated that the classification was largely consistentwith human perception of board appearance. An initial estimation of the potential to optimize log rotation, based on CTdata, for the established appearance grades was derived from the simulations. Considerable potential to increase the yield ofa desired appearance grade, compared to conventional log positioning, was observed.

  • 12.
    Broman, Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wood material features and technical defects that affect yield in a finger joint production process2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 4, p. 167-175Article in journal (Refereed)
    Abstract [en]

    A cost efficient process is the goal of all production, and each manufacturing step affects the material utilization and cost efficiency. There is high diversity in the inherent features of wood, and manufacturing steps must be able to handle this. The overall objective was to study the potential and problems in manufacturing production processes in terms of material utilization efficiency. The production of finger jointed bed sides was chosen as a study case, where the chain of production units are the sawmill, finger joint plant and furniture plant. This article describes the impact of raw material and wood defects that could affect the total yield. A total of 177 logs of three types were tested: butt, intermediate and fresh knot logs. The test material quality was detected and measured through all steps in the manufacturing chain. The results show differences between log types in down-grade causes, reject volume and final yield. Also, the test material showed high levels of defective components with process-related defects, which suggested the need for technical improvement in the manufacturing process. The intermediate log group showed the overall best result.

  • 13.
    Butylina, Svetlana
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Martikka, Ossi
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Comparison of water absorption and mechanical properties of wood-plastic composites made from polypropylene and polylactic acid2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 3-4, p. 220-228Article in journal (Refereed)
    Abstract [en]

    This study focuses on the water absorption and mechanical properties of composites made from softwood sawdust and plastics, such as virgin and recycled polypropylene and polylactic acid (PLA). The composites were processed by extrusion, and their properties were investigated by a water immersion test, mechanical tests and a cyclic test for moisture resistance. Scanning electron microscopy was used to study the morphology of the fracture surfaces of the composites. The composites made with recycled polypropylene had the lowest water absorption and thickness swelling of the studied composites. The PLA composites made with heat-treated sawdust showed the highest flexural strength. Of the polypropylene based composites, virgin polypropylene resulted in composites with higher flexural strength. The Charpy impact strength of the composites was found to have an inverse trend compared to flexural strength. Cyclic treatment of the studied composites resulted in 20-60% loss of flexural strength, depending on type of composite.

  • 14.
    Caprolu, Giuseppe
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Källsner, Bo
    School of Engineering, Linnæus University, Växjö, Linnéuniversitetet, Linnaeus University, Växjö.
    Analytical models for splitting capacity of bottom rails in partially anchored timber frame shear walls based on fracture mechanics2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 3, p. 165-188Article in journal (Refereed)
    Abstract [en]

    Plastic design methods can be used for determining the load-carrying capacity of partially anchored shear walls. For such walls, the leading stud is not fully anchored against uplift and tying down forces are developed in the sheathing-to-framing joints and the bottom rail will be subjected to crosswise bending, leading to possible splitting failure of the rail. In order to use these plastic design methods, a ductile behaviour of the sheathing-to-framing joints must be ensured. In two earlier experimental programmes, the splitting failure capacity of the bottom rail has been studied. Two brittle failure modes occurred during testing: (1) a crack opening from the bottom surface of the bottom rail and (2) a crack opening from the side surface of the bottom rail. In this article, a fracture mechanics approach for the two failure modes is used to evaluate the experimental results. The comparison shows a good agreement between the experimental and analytical results. The failure mode is largely dependent on the distance between the edge of the washer and the loaded edge of the bottom rail. The fracture mechanics models seem to capture the essential behaviour of the splitting modes and to include the decisive parameters. 

  • 15.
    Couceiro, José
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Department of Ocean Operations and Civil Engineering, Norwegian University of Science and Technology (NTNU), Ålesund, Norway.
    Söderström, Ove
    c Professor Emeritus of Building Materials, Stockholm, Sweden.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Real-time wood moisture-content determination using dual-energy X-ray computed tomography scanning2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 6, p. 437-444Article in journal (Refereed)
    Abstract [en]

    The estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

  • 16.
    Cristescu, Carmen
    et al.
    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.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of pressing parameters on mechanical and physical properties of self-bonded laminated beech boards2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 2, p. 205-214Article in journal (Refereed)
  • 17. Cristovao, Luis
    et al.
    Broman, Olof
    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.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Sitoe, Rui
    Main cutting force models for two species of tropical wood2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 143-149Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to evaluate the main cutting force for two species of tropical Mozambican wood and to develop predictive models. Cutting these hardwoods is difficult. Determination of cutting parameters is required to optimize cutting processes, machines and tools in the cutting operations. This determination would enable the forestry and wood sector to achieve higher financial results. Samples of a lesser-known wood species Pseudolachnostylis maprounaefolia (ntholo) and a well-known wood species Swartzia madagascariensis (ironwood) were machined in a test apparatus. A standard single saw tooth mounted on a piezoelectric load cell was used to evaluate the main cutting force. Data were captured using an A/D converter integrated with National Instruments LabVIEW software. The measured signals were recorded at a sampling frequency of 25 kHz. The experimental set-up used response surface methodology for developing predictive models. The experimental clearly determined the relationship between the main cutting force and edge radius, wood density, rake angle, chip thickness, moisture content (MC) and cutting direction (CD). Among the studied variables, chip thickness and CD had the highest effect on the main cutting force level while wood density, MC and rake angle had the lowest effect.

  • 18. Cristovao, Luis
    et al.
    Lhate, Imacio
    Swedish University of Agricultural Sciences.
    Grönlund, Anders
    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.
    Sitoe, Rui
    Department of Mechanical Engineering, Eduardo Mondlane University, Maputo.
    Tool wear for lesser known tropical wood species2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 3, p. 155-161Article in journal (Refereed)
    Abstract [en]

    This study investigated the relationship between tool wear and some chemical and physical properties for four different Mozambican lesser known tropical species,: Pseudolachnostylis maprounaefolia (ntholo), Sterculia appendiculata (metil), Acacia nigrescens (namuno) and Pericopsis angolensis (muanga). Tool wear is an important aspect for sawmilling and for the woodworking industry. For Mozambique, the utilization of available lesser known wood species will help to increase domestic industry and the economic usage viability of sustainable forest management. A set of experiments was performed on a shaper with a mechanical feed mechanism. Tools of a cemented carbide grade for woodworking were used, and the cutting parameters were fixed. Edge recession and tool wear radius were measured for monitoring tool wear. The wear mechanism was investigated using a scanning electron microscope. The experimental results showed that the chemical properties of the wood species have a great effect on tool wear. Wood silica content was the most important factor affecting tool wear. Wood density and extractives had a low influence on tool wear. The highest tool wear was observed in ntholo, which also had the highest ash and silica contents. A single parameter for evaluation of tool wear was not sufficient to describe the amount of total tool wear

  • 19.
    Dagbro, Ola
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Torniainen, Petteri
    Department of Forest Products, Swedish University of Agricultural Sciences, Uppsala.
    Karlsson, Olov
    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.
    Colour responses from wood, thermally modified in superheated steam and pressurized steam atmospheres2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 3, p. 211-219Article in journal (Refereed)
    Abstract [en]

    In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20-308C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process

  • 20. Dvinskikh, Sergey V.
    et al.
    Furó, István
    Sandberg, Dick
    Söderström, Ove
    Kungliga tekniska högskolan, KTH.
    Moisture content profiles and uptake kinetics in wood cladding materials evaluated by a portable nuclear magnetic resonance spectrometer2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 3, p. 119-127Article in journal (Refereed)
    Abstract [en]

    This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [1H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.

  • 21.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cristovao, Luis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Marklund, Birger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lateral cutting forces for different tooth geometries and cutting directions2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 126-133Article in journal (Refereed)
    Abstract [en]

    Lateral (sideways) cutting forces were measured for 6 different tooth geometries when cutting green spruce and pine heartwood. The teeth were intended for use on circular saw blades for the rip sawing of logs. The 6 tooth geometries were designated straight, pointed, bevelled, rounded, trapezoidal and hollowed out. Cutting speed was 15 m/s, feed per tooth was 0.3 mm and the cutting directions were 90°–90° (rip sawing) and 90°–0° (milling), with two different variants of growth ring angles for each direction. The tools were tested in sharp conditions, in dull conditions and in a dull condition with a corner broken off. All lateral forces were small when cutting with sharp teeth, except for the rounded and bevelled teeth. Lateral forces increased with wear, except for a period of initial wear where the lateral forces were reduced. High wear resulted in greater lateral forces, most probably due to unsymmetrical wear. Growth ring direction did not generally affect lateral forces. The teeth with acute corners, which were the straight and hollowed out tooth, were most sensitive to a broken off corner. The lateral forces in the cases of wood cutting at 90°–90° increased less with wear compared to the 90°–0° cases.

  • 22.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cristovao, Luis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Marklund, Birger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wear of teeth of circular saw blades2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 150-153Article in journal (Refereed)
    Abstract [en]

    Measured wear data is presented for three different carbide grades. The data were collected during rip sawing wood with a double arbour saw. The purpose of the test was to determine the suitability of different grades for sawing frozen timber. A set of circular saw blades of diameter 350 mm was equipped with teeth comprised of three different cemented carbide grades, denoted A, B and C. The double arbour saw was equipped with six saw blades for cutting two centre boards and two side boards. The six saw blades with different teeth were mounted in a mixed manner on the arbours, and after sawing a number of logs the wear of teeth was measured. The thickness of boards was also measured and the standard deviation was calculated. The results showed that grade A had the highest wear and grades B and C the lowest wear. There was no significant edge damage during the tests. Grade C did not suffer problems of chipping from cutting edges and was found to be suitable for sawing frozen timber. The thickness standard deviations were constant at about 0.2 mm, and not a function of the number of logs sawn.

  • 23.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Guo, Xiaolei
    Nanjing Forestry University, Faculty of Material Science & Engneering, Nanjing Forestry University.
    Li, Rongrong
    Nanjing Forestry University, Nanjing Forestry University, Faculty of Material Science & Engneering.
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Curve sawing effects on board dimensions when rip-sawing with a circular saw blade2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 3, p. 135-141Article in journal (Refereed)
    Abstract [en]

    Curve sawing means advantages for yield and quality of sawn boards. However, for circular saw machinery deviations of saw kerfs give losses of valuable board volume. Deviations give thinner boards but also slight cupping of the cross sections. Theoretical calculations show that even with moderate (large) curve radii, these saw kerf deviations are typically 0.2–0.6 mm for normal circular saw machinery and Swedish log material. The test sawing reported here was made in order to give experimental values that can be compared to theoretical values. Fifty normal logs and 50 curved with top diameter 236–248 mm were cut with sawing pattern 3X with center boards 51 × 149 mm. The average curve radius of the curved cants that were cut in the resaw was 132 m (bow height 19 mm) and the theoretical saw kerf deviation for this radius is 0.31 mm. The experimental results show that the thickness reduction at the measuring points for curve sawn boards compared to straight sawn boards was in average 0.19 mm to be compared with the theoretical value of 0.20 mm. Cupping was more difficult to measure but results seem to agree well between theory and experiments.

  • 24.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundgren, Nils
    Flodin, Jens
    Drying shrinkage of sawn timber of Norway spruce (Picea abies): industrial measurements and finite element simulations2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 1-2, p. 41-48Article in journal (Refereed)
    Abstract [en]

    Industrial measurements of green and dry cross-section dimensions were performed for 189 Norway spruce (Picea abies) centre-yield boards with dry dimensions 51 times 149 mm. Two, three or four boards were sawn from each log, depending on log size. Different approaches were used for simulations of cross-section shrinkage during drying. An analytical model, an elastic, an elastic- mechanosorptive and an elastic- plastic finite element simulation model were tested. Thickness and width shrinkage and deformation were simulated. Shrinkage results were compared with each other and with the experimental results. All simulation models gave roughly the same degree of agreement with experimental results except for the centre board from the three-board sawing pattern. For the other boards, the analytical model was not generally better or worse than the results from the finite element models. Shrinkage deformations in finite element models that included mechanosorption or plasticity were nearly the same as for the elastic finite element model except for the centre board of the three-board sawing pattern. The mechanosorptive model was the best model for the shrinkage of the centre board of this sawing pattern except for mid-thickness shrinkage. Comparison between the different finite element simulation models of stresses in the centre board revealed large differences.

  • 25.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Marklund, Birger
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wood-chip formation in circular saw blades studied by high-speed photography2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 3, p. 115-119Article in journal (Refereed)
    Abstract [en]

    Films of wood-chip formation were captured with a high-speed camera during rip sawing of wood with a circular saw blade. The saw blade diameter was 400 mm and the rotational speed was 3250 rpm. The saw blade had four teeth with rake angles of 0°, 10°, 20° and 30° to ascertain the influence of different rake angles. Wooden boards were cut along the side so that the camera could record the cutting sequence without any interference from material between the cutting teeth and the camera. Tests were made for green, dry and frozen green pine boards, for both counter-cutting and climb-cutting cases. In addition, some Mozambican wood species were cut. The films, recorded at 40,000 frames s−1, show the cutting sequence along the trajectory of the tooth in question and the creation of the wood chip. Details such as the compression of the wood chip in the gullet, the movement of the wood chip inwards and outwards in the gullet and finally the exit from the gullet are visible. The chip size and chip movement depend strongly on the rake angle and on whether the wood is green, dry, frozen or unfrozen.

  • 26.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Salin, Jarl-Gunnar
    Grundberg, Stig
    Nyström, Jan
    Grönlund, Anders
    Modelling of adequate pretwist for obtaining straight timber2006In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 1, no 2, p. 76-84Article in journal (Refereed)
    Abstract [en]

    Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic-ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists

  • 27. Elustondo, Diego
    Lumber quality model: The theory2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 3-4, p. 162-172Article in journal (Refereed)
    Abstract [en]

    A new model for predicting moisture content, distortion and shrinkage distribution after lumber drying has been designed, implemented and tested. The model was implemented using Monte Carlo simulation, and it involves three empirical equations that were developed on the basis of experimental data. The model is referred as the Lumber Quality Model, and it is designed to be calibrated by knowing the initial and final moisture content, distortion and shrinkage distribution for a reference drying run. After calibration, the model can be used to predict the same information for other hypothetical drying scenarios. The present study explains the theoretical aspects of the model and the methodology for implementation. The model was validated with experimental data measured in a laboratory kiln. A full-scale industrial validation will be reported in a future paper.

  • 28. Elustondo, Diego
    et al.
    Oliveira, Luiz C De S
    FPInnovations-Wood Products, Vancouver, British Columbia.
    Moisture content target optimization in lumber drying2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 4, p. 190-195Article in journal (Refereed)
    Abstract [en]

    A Lumber Quality Model developed to predict lumber grade after drying was applied and validated in industry. The model was calibrated with a 198-piece lumber package that was dried at a local sawmill in British Columbia, Canada, and 30 sawmill grade reports were recorded from 2008 to 2010. The calibrated model was then used to predict the target moisture content that would result in the maximum lumber value. It was predicted that lumber value should increase by approximately 17 CAD (Canadian dollars) m -3 if the target moisture content were reduced from the historic 17% to an optimum of approximate 13%. The sawmill implemented the recommendations and the predictions were validated with another seven industrial drying runs

  • 29.
    Forsman, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Laitila, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Applicability of as-built 3-D sensing technologies for improved efficiency when supplying joinery products2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed)
    Abstract [en]

    With currently used surveying methods, the on-site assembly of joinery products often consumes half the supplier budget. Due to spatial uncertainties, the manual product-to-room fitting of components is a major consumer of time and labour resources. With reliable as-built construction site geometrical information, this fitting could be moved to the design stage early in the supplier process. In this study, the currently used manual surveying methods were compared with two different 3-D sensing surveying methods, a portable wire-bound coordinate measuring machine (CMM) and a laser-scanning machine. The comparison evaluates the applicability of the on-site surveying methods and their potential for improving the current surveying process, moving the product-to-room fitting to the design stage. Results show that currently used manual surveying methods leave uncertainties regarding the dimensions of a construction site and are insufficient for moving the product-to-room fitting to the design stage. CMM surveying has the potential to supply coordinate registrations on a par with desired accuracy requirements, but it has limitations at the practically possible detailing level. Laser scanning seems to be applicable for the surveying for a joinery products supplier, but the accurate and detailed 3-D reconstruction of the point cloud data is difficult and requires extensive processing. It can be concluded that the concept of digitized measurement of the as-built spatial dimensions of a construction site to enable product-to-room during the design stage has the potential to succeed with currently available digitizing technologies, but that some challenges remain.

  • 30.
    Forsman, Samuel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Laitila, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Three-dimensional, as-built site verification in supplying engineer-to-order joinery products to construction2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 353-367Article in journal (Refereed)
    Abstract [en]

    With currently used surveying methods, the on-site assembly of joinery products often consumes half the supplier budget. Due to spatial uncertainties, the manual product-to-room fitting of components is a major consumer of time and labour resources. With reliable as-built construction-site geometrical information, this fitting could be moved to the design stage early in the supplier process. In this study, the currently used manual surveying methods were compared with two different three-dimensional (3-D) sensing surveying methods, a portable wire-bound coordinate measuring machine (CMM) and a laser-scanning machine. The comparison evaluates the applicability of the on-site surveying methods and their potential for improving the current surveying process, moving the product-to-room fitting to the design stage. Results show that currently used manual surveying methods leave uncertainties regarding the dimensions of a construction site and are insufficient for moving the product-to-room fitting to the design stage. CMM surveying has the potential to supply coordinate registrations on a par with desired accuracy requirements, but it has limitations at the practically possible detailing level. Laser scanning seems to be applicable for the surveying for a joinery products supplier, but the accurate and detailed 3-D reconstruction of the point-cloud data is difficult and requires extensive processing. It can be concluded that the concept of digitized measurement of the as-built spatial dimensions of a construction site to enable product-to-room during the design stage has the potential to succeed with currently available digitizing technologies, but that some challenges remain

  • 31.
    Fredriksson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Log Sawing Position Optimization using Computed Tomography Scanning2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 2, p. 110-119Article in journal (Refereed)
    Abstract [en]

    When disjoining a log, several factors affect the value of the sawn timber. There are log features, such as outer shape, knots, rot, and so on. There are also sawing parameters, such as sawing pattern, log position, and so on. If full information about log features is available, sawing parameters can be adapted in order to maximize product value in sawmills. This is soon possible, since computed tomography (CT) scanners for the sawmill industry are being realized. This study aimed at investigating how CT data can be used to choose rotational position, parallel displacement, and skew of sawlogs, to maximize the value of the sawn products. The study was made by sawing simulation of 269 CT scanned logs of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] H. Karst.). The results showed that value recovery could be improved by 13% in average, compared to a sawing position based on log outer shape, and 21% compared to sawing logs centered and horns down. It can be concluded that a CT scanner, used in a sawline to optimize sawing parameters, has a large potential for increasing value recovery and thus profit.

  • 32.
    Fredriksson, Magnus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Persson, Fredrik
    SP Trä.
    Axelsson, Ann
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ah Shenga, Pedro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Rotational Position of Curved Saw Logs and Warp of the Sawn Timber2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 1, p. 31-39Article in journal (Refereed)
    Abstract [en]

    With the development of scanning technology in sawmills, it is possible to optimise log rotational position when sawing. However, choosing a different rotational position than horns down might be detrimental for the board shape after drying, especially for curved logs. Thus, there is a need to investigate at what level of log curve it is possible to freely rotate logs without causing board warp. This study was carried out through a test sawing that was conducted at a sawmill situated in the middle of Sweden. The tests were made on 177 Norway spruce logs, with varying amount of curve. Half of the logs were sawn in the horns-down position, half were sawn rotated perpendicular to horns down. Log shape and warp of the dried boards were measured. The results indicated a relationship between board spring, log curve and choice of rotational position. Furthermore, board bow was related to log curve but not rotational position. It can be concluded that for straight logs, with a bow height of less than 15 mm, an unconventional rotational position does not cause excess spring in the boards. Bow and twist are not affected by the rotational position at all.

  • 33.
    Fredriksson, Maria
    et al.
    Division of Building Materials, Lund University.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    End grain water absorption and redistribution in slow-grown and fast-grown Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 4, p. 245-252Article in journal (Refereed)
    Abstract [en]

    Wood is susceptible to decay by rot fungi if it is exposed to high-moisture contents during long periods of time and it is therefore important to limit the duration of such periods. Critical points in outdoor wood structures are, for example, end grain surfaces in joints where water can get trapped after a rain. It is therefore of interest to study both absorption and redistribution of moisture in wood. This paper presents moisture content profiles during end grain water absorption and redistribution in Norway spruce (Picea abies (L.) Karst.) measured by computed tomography with the specimens in individual climate boxes. Heartwood and sapwood of two provenances (slow-grown and fast-grown wood) were included. No major differences were seen between the water uptake of the slow-grown and the fast-grown wood since the densities were similar despite of the large difference in growth ring width. However, for the sapwood specimens, the moisture content was higher further into the specimens than for the heartwood specimens in agreement with previous studies. For the slow-grown wood, the redistribution was also generally more rapid for the sapwood specimens than for the heartwood specimens.

  • 34.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cherepanova, Ekaterina
    Luleå University of Technology.
    Determination of wood moisture properties using a CT-scanner in a controlled low-temperature environment2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 2, p. 87-92Article in journal (Refereed)
    Abstract [en]

    The aim of the present work was to examine an advanced image-processing algorithm for moisture content (mc) calculation and also to use this algorithm to analyse moisture loss data for low temperature drying. Since wood starts to shrink below the fibre saturation point during drying, the geometrical shape of the wood piece will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight mc. The results show that the algorithm for the dry weight mc on density data from the CT-scanning during low-temperature drying in the climate chamber is a powerful tool for analysing the moisture loss inside the wood piece. This method can make it possible to get a higher quality on the product

  • 35.
    Hansson, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Faculty of Engineering and Natural Sciences, Norwegian University of Science and Technology (NTNU), Ålesund.
    Couceiro, José
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fjellner, Bengt-Arne
    Luleå University of Technology, Professional Support, IT-Service.
    Estimation of shrinkage coefficients in radial and tangential directions from CT images2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 4, p. 251-256Article in journal (Refereed)
    Abstract [en]

    The aim of the present work was to use the displacement information generated from the spatial alignment in order to compute wood shrinkage in the radial and tangential directions in computed tomography (CT) images, and to compare the results with those obtained with computer-aided design software on the same images. To estimate the shrinkage coefficients from tomography images, wood specimens in the green state, equilibrium moisture content 15% and 8% state and oven dry condition were scanned. Specimens were taken from Norway spruce and Scots pine logs. The root-mean-square-error calculations showed acceptable small differences between the two measuring methods, which means that the algorithm is a useful tool for estimating the shrinkage coefficients in radial and tangential direction from CT images. This provides an image processing tool to monitor the dimensional changes during the drying and heat treatment process. 

  • 36.
    Huber, Johannes Albert Josef
    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.
    Girhammar, Ulf Arne
    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.
    Structural robustness and timber buildings: a review2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 2, p. 107-128Article in journal (Refereed)
    Abstract [en]

    Timber buildings are increasing in their dimensions. Structural robustness is imperative for all buildings and specifically important for tall buildings. Lives can be saved if disproportionate collapse can be avoided after a catastrophic event (e.g. accident, terrorism). The literature about robustness is comprehensive concerning concrete and steel buildings, but is rather limited regarding timber. This paper reviews robustness in general and robustness of timber buildings in particular. Robustness is an intrinsic structural property, enhancing global tolerance to local failures, regardless of the cause. A deterministic approach to assess robustness is to remove certain load-bearing elements from the structure and compare the consequences to given limits. Design methods for robustness may be direct by assessing effects of local failure, or indirect by following guidelines. For robust timber buildings, the connections are the key aspects. Usually, metal connectors may provide the required joint ductility. For robust light timber-frame construction, rim beams may be designed. For timber posts and beams and cross laminated timber, guidance regarding robustness is scarce, but in some aspects they seem to be similar to steel frames and precast concrete. Future research should assess the capacity of connections, and evaluate the adequacy of seismic connectors for robust timber buildings.

  • 37.
    Huuhilo, Tiina
    et al.
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Martikka, Ossi
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Butylina, Svetlana
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Kärki, Timo
    Lappeenranta University of Technology, Department of Mechanical Engineering.
    Mineral fillers for wood-plastic composites2010In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 5, no 1, p. 34-40Article in journal (Refereed)
    Abstract [en]

    Five mineral fillers were tested for wood-plastic composites (WPCs): calcium carbonate, two different types of wollastonite, soapstone and talc. The impact of the fillers on the mechanical properties of the composites was studied. The experiments included bending tests, tensile tests, Brinell hardness and scanning electron microscopy experiments. The amount of wood, mineral and plastic (polypropylene) was kept steady. Only the mineral type was changed during the tests. A control sample without any mineral added was also manufactured. The mineral addition improved the tensile strength of the WPCs. The hardness of the composite was also improved when the minerals were added, and along with the increasing mineral hardness, the hardness of the composite increased. The wollastonite acicular shape was crushed during the manufacturing process, so the phase of the process in which the minerals are added requires careful consideration.

  • 38.
    Johansson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berglund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. SP Sveriges Tekniska Forskningsinstitut, SP Trä.
    Comparing predictability of board strength between computed tomography, discrete x-ray, and 3D scanning of Norway spruce logs2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 2, p. 116-125Article in journal (Refereed)
    Abstract [en]

    Strength graded boards of Norway spruce (Picea abies (L.) Karst.) are important products for many Scandinavian sawmills. If the bending strength of the produced boards can be predicted before sawing the logs, the raw material can be used more efficiently. In previous studies it is shown that the bending strength can be predicted to some extent using discrete X-ray scanning of logs. In this study, we have evaluated if it is possible to predict bending strength of Norway spruce boards with higher accuracy using computed tomography (CT) scanning of logs compared to a combination of discrete X-ray and 3D scanning. The method was to construct multivariate models of bending strength for three different board dimensions. Our results showed that CT scanning of logs produces better models of bending strength compared to a combination of discrete X-ray and 3D scanning. The main reason for this difference was the benefit of knowing the position of where the boards were cut from the logs and therefore detailed knot information could be used in the prediction models. Due to the small number of observations in this study, care should be taken when comparing the resulting prediction models to results from other studies

  • 39.
    Jones, Dennis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    COST FP1303 “performance of bio-based building materials”2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 1Article in journal (Refereed)
  • 40.
    Lindgren, Owe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Seifert, Thomas
    Department of Forest & Wood Science, Stellenbosch University.
    Plessis, Anton du
    Central Analytical Facilities, Stellenbosch University.
    Moisture Content Measurements in Wood Using Dual Energy CT-scanning: A Feasibility Study2016In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 11, no 5, p. 312-317Article in journal (Refereed)
    Abstract [en]

    Currently computed tomography (CT) scanning provides a non-destructive method to determine moisture content in wood in three dimensions. With the current methodology two measurements are needed, one with the scanned piece of wood’s moist state and one after drying. Then the difference of the images can be calculated. The drawback and challenge is that dimensional changes due to shrinkage of wood in the drying process have to be compensated for by image processing. In this study a dual-energy CT scanning method is tested based on the consecutive scanning of wood samples at different energy levels to differentiate water from wood, without the necessity to dry the sample and thus without the need for complex image correction. Not quantified but visible differentiations due to moisture content were obtained on small cubical pine samples of different densities by quick consecutives scans at 60 and 200 kV. The results suggest that given that the pixels in the CT images are representing absorption coefficients it should be possible to directly measure moisture content in wood non-destructively in small volume elements inside solid wood in three dimensions. Further applications of this technique in industrial CT scanning of wood are discussed.

  • 41.
    Markström, Emillia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Kuzman, Manja Kitek
    Biotechnical Faculty, Wood Science and Technology, University of Ljubljana, Ljubljana, Slovenija.
    Bystedt, Anders
    RISE Bioeconomy, RISE Research Institutes of Sweden, Skellefteå, Sweden.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Department of Wood Processing and Biomaterials, Czech Universty of Life Sciences Prague, Suchdol, Czech Republic.
    Use of wood products in multi-storey residential buildings: views of Swedish actors and suggested measures for an increased use2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, p. 404-419Article in journal (Refereed)
    Abstract [en]

    Many studies have shown that wooden buildings in general have a lower climate impact than buildings built of conventional materials such as concrete and steel. In Sweden, however, only about 10% of the multi-dwelling buildings are built with timber frames. The goal of this empirical study is to provide a broad picture of the views of Swedish actors regarding the use of wood products in multi-storey residential buildings and suggest measures for an increased use. A questionnaire concerning the use of wood products in construction was sent out to Swedish developers, main contractors, and architects and 100 answers were received. The study shows that the views of the groups of actors differ in some respects and factors that may either facilitate or be obstacles to an increased use of wood products were identified and discussed.

  • 42.
    Martikka, Ossi
    et al.
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Huuhilo, Tiina
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    Butylina, Svetlana
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Mechanical Engineering, Lappeenranta University of Technology.
    Kärki, Timo
    Department of Mechanical Engineering, Lappeenranta University of Technology.
    The effect of mineral fillers on the thermal properties of wood-plastic composites2012In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 7, no 2, p. 107-114Article in journal (Refereed)
    Abstract [en]

    The thermal properties of wood-plastic composites with five different mineral fillers were studied. The tested mineral fillers were calcite (CaCO 3), two different qualities of wollastonite, soapstone, and talc. The amount of wood, mineral, and plastic (polypropylene) was kept constant. Only the mineral type has been changed during the tests. The thermal behavior of the samples was studied by using a differential scanning calorimeter, a thermogravimetric analyzer and by determining the heat build-up. The analyzed properties were compared with a reference sample made without adding any minerals. The results show that the addition of mineral fillers does not remarkably change the thermal stability of composites. All the studied mineral fillers except soapstone had a small effect on the heat build-up

  • 43.
    Neyses, Benedikt
    et al.
    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.
    A new methodology to select hardwood species for wooden products2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 344-352Article in journal (Refereed)
    Abstract [en]

    In general, only a few wooden species are used or even considered for any given wooden product, even though hundreds of alternative wood species are available. In many cases, the reason for this is tradition rather than availability, technical or aesthetic considerations and it can result in endangered species being used to an unnecessarily high degree. The purpose of this study was to develop a structured, quantifiable, and easy-to-use methodology to identify suitable hardwood species for a specific product. The methodology combines processes based on quality function deployment and multivariate data analysis in a three-step workflow, and takes different criteria into consideration. To verify the methodology, it was applied to an example product: an electric guitar. It was shown that the methodology was easy to use and provided useful and quantifiable results. Expansion of the underlying wood species data-set will be necessary to improve the performance in the future.

  • 44.
    Nilsson, Jonaz
    et al.
    Linnéuniversitetet.
    Johansson, JImmy
    Linnéuniversitetet.
    Kifetew, Girma
    Linnéuniversitetet.
    Sandberg, Dick
    Shape stability of modified engineering wood product subjected to moisture variation2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 3, p. 132-139Article in journal (Refereed)
    Abstract [en]

    A modified softwood product would enable the utilization of softwood in new areas. Densification is an old modification method to improve wood properties such as hardness and resistance to abrasion. A major problem with densified wood is, however, its ability to retain its original dimensions under the influence of moisture. Therefore, this study investigated the influence of surface to bottom layer thickness ratio on the shape stability of a modified and three-layered cross-laminated engineering wood product (EWP) subjected to moisture variations. The study describes a simple solid wood densification technique based on compressing a clear solid piece of softwood with vertical annual rings in the radial direction by restraining the tangential expansion. Three-layered cross-laminated EWP was manufactured with the densified wood as a surface layer. The recovery of the densified wood in the surface layer was then reduced to movements in the same level as the other two layers of unmodified wood. The EWP was subjected to climatic variations in order to investigate its shape stability. The results disclosed that an appreciable degree of shape stability was obtained by an increase in the surface to bottom layer thickness ratio of the EWP

  • 45.
    Olofsson, Linus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    RISE Bioeconomy, Research Institutes of Sweden, Skellefteå, Sweden.
    Fredriksson, Magnus
    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.
    Multivariate product adapted grading of Scots pine sawn timber for an industrial customer, part 1: Method development2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 6, p. 428-436Article in journal (Refereed)
    Abstract [en]

    Rule-based automatic grading (RBAG) of sawn timber is a common type of sorting system used in sawmills, which is intricate to customise for specific customers. This study further develops an automatic grading method to grade sawn timber according to a customer’s resulting product quality. A sawmill’s automatic sorting system used cameras to scan the 308 planks included in the study. Each plank was split at a planing mill into three boards, each planed, milled, and manually graded as desirable or not. The plank grade was correlated by multivariate partial least squares regression to aggregated variables, created from the sorting system’s measurements at the sawmill. Grading models were trained and tested independently using 5-fold cross-validation to evaluate the grading accuracy of the holistic-subjective automatic grading (HSAG), and compared with a resubstitution test. Results showed that using the HSAG method at the sawmill graded on average 74% of planks correctly, while 83% of desirable planks were correctly identified. Results implied that a sawmill sorting station could grade planks according to a customer’s product quality grade with similar accuracy to HSAG conforming with manual grading of standardised sorting classes, even when the customer is processing the planks further.

  • 46.
    Olofsson, Linus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Skog, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Fredriksson, Magnus
    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.
    Multivariate Product Adapted Grading of Scots Pine Sawn Timber for an Industrial Customer, Part 2: Robustness to Disturbances2019In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, no 6, p. 420-427Article in journal (Refereed)
    Abstract [en]

    Holistic-subjective automatic grading (HSAG) of sawn timber by an industrial customer's product outcome is possible through the use of multivariate partial least squares discriminant analysis (PLS-DA), shown by part one of this two-part study. This second part of the study aimed at testing the robustness to disturbances of such an HSAG system when grading Scots Pine sawn timber partially covered in dust. The set of 308 clean planks from part one of this study, and a set of 310 dusty planks, that by being stored inside a sawmill accumulated a layer of dust, were used. Cameras scanned each plank in a sawmill's automatic sorting system that detected selected feature variables. The planks were then split and processed at a planing mill, and the product grade was correlated to the measured feature variables by partial least squares regression. Prediction models were tested using 5-fold cross-validation in four tests and compared to the reference result of part one of this study. The tests showed that the product adapted HSAG could grade dusty planks with similar or lower grading accuracy compared to grading clean planks. In tests grading dusty planks, the disturbing effect of the dust was difficult to capture through training.

  • 47.
    Omarsson, S.
    et al.
    Technical University of Denmark.
    Sandberg, Dick
    Numerical simulation of hot-pressed veneer products: Moulding, spring-back and distortion2007In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 2, no 3-4, p. 130-137Article in journal (Refereed)
    Abstract [en]

    Customers demand a very a high quality of veneered furniture products with regard to surface appearance, shape stability and rigidity. To meet these requirements, it is important to improve the manufacturing process by a better understanding of the thermohydromechanical behaviour of the individual veneers. During the manufacture of strongly curved products, the veneers are exposed to large membrane and bending deformations and to a high pressure in the radial fibre direction. When hot-press forming is used, the veneers are also exposed to a high surface temperature during the pressing time (curing time). These severe conditions can result in plastic deformation perpendicular to the veneer surface as well as mechanosorptive strains in the curved regions, since the heating can significantly affect moisture distribution. How strong an influence these factors have on the distortion of the veneered product is far from being fully clarified. To study this complex multiphysical problem including temperature, moisture, large deformations for orthotropic materials, surface constraints and progressive glue interaction, a three-dimensional finite element simulation was performed. In this study, the simulation of deformations and stresses occurring during the manufacture of a curved veneered product (chair seat) of birch wood is described. The results show that heating, pressure and the fibre orientation in the veneers have a significant influence on the distortion of the chair seat.

  • 48.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Swerea SICOMP, Piteå.
    Berthold, Fredrik
    Rise Bioeconomy/Innventia AB, Stockholm.
    Miettinen, Arttu
    Department of Physics, University of Jyväskylä.
    Mechanical properties of natural fiber composites produced using dynamic sheet former2018In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed)
    Abstract [en]

    Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences in behavior are discussed attributing them to fiber/ fiber interaction in wood fiber composites which does not happen in man-made fiber composites, and by rather weak fiber/matrix interface for man-made fibers leading to macro-crack formation in large porosity regions.

  • 49. Sandberg, Dick
    et al.
    Haller, Peer
    Institute of Steel and Timber Construction, Technische Universität Dresden.
    Navi, Parviz
    Wood and Civil Engineering, Bern University of Applied Science, Biel.
    Thermo-hydro and thermo-hydro-mechanical wood processing: An opportunity for future environmentally friendly wood products2013In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 8, no 1, p. 64-88Article in journal (Refereed)
    Abstract [en]

    This state-of-the-art report presents the basic concepts of some of the thermo-hydro (TH) and thermo-hydro-mechanical (THM) wood processes that are in use today, i.e. heat treatment, compression of wood in the longitudinal or transverse direction and wood welding. The reasons for the growing interest in TH and THM techniques are discussed, and the development of the different concepts, from first ideas to current status, is briefly presented. The physical and chemical changes that occur in wood during TH and THM processing according to the latest research are also presented. Finally, developments that are close to or already have an industrial application are presented, and the challenges for further development of the heat treatment, compression and wood welding processes are discussed. The TH processing of wood is based entirely on water and heat, and a THM process incorporates an additional mechanical force. The purpose of wood transformation by a TH or a THM process is to improve the intrinsic wood properties, to acquire a form and functionality desired by engineers without changing its eco-friendly characteristics or hindering its further use in the total material life cycle. Only a few of the recently developed techniques, e.g. heat treatment, wood welding and various densification applications, have been industrialized to some extent. There are many reasons for this relatively low transfer of the research results to a full up-scaled industrial production. Some of them are related to unsolved problems at the laboratory level on small-sized samples and others are related to the scaling-up processes in industry. Furthermore, the ageing of heated wood leads to deterioration with time, in some cases there is an unpleasant odour, the strength of the wood decreases substantially and the wood becomes more brittle. These are new challenges which need to be resolved by the collaboration of researchers from the different scientific domains of academia, research institutes and industry.

  • 50. Sandberg, Dick
    et al.
    Johansson, Jimmy
    Växjö universitet, Fakulteten för matematik/naturvetenskap/teknik, Institutionen för teknik och design.
    Simulation of the yield of knot-free components from Scots pine (Pinus sylvestris L.): A comparative study of star-sawing and square-sawing2006In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 1, no 3-4, p. 108-115Article in journal (Refereed)
    Abstract [en]

    The production of knot-free wood is important since the market demands wood without knots for reasons of both appearance and material properties. This work describes a simulation of the removal of knots from star-sawn timber and square-sawn. The efficiency of the two methods is compared in terms of the length of the knot-free components obtained and the volume yield.The simulation is based on data for trees and logs taken from The Swedish Stem Bank. These data are then used to simulate the sawmill process in a computer program called the Virtual Sawmill. Data related to the boards obtained are then used in a MATLAB model simulating the cross-cutting of knots.Simulated star sawing of logs with a top diameter exceeding 230 mm gave a mean knot-free component length of 417 ±321 mm, while the mean length of knot-free components for simulated square sawing of the same logs was 298 ±122 mm. The volume yield of knot-free components from the two sawing patterns was 91 % for star sawing and 87 % for square sawing. For timber with cross-section dimensions of 38 x 75 mm2, the mean length and yield of knot-free components from simulated star sawing were 451 ±349 mm and 90 % respectively. In simulated square sawing, the corresponding values were 263 ±197 mm and 82 % respectively. This shows that star sawing has a potential for the production of knot-free timber.

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