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  • 201.
    Cristovao, Luis
    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.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Industrial sawing of Pinus Sylvestris L.: power consumption2013In: Proceedings of the 21th International Wood Machining Seminar: August 4th – 7th, 2013, Tsukuba International Congress Center, Japan, 2013, p. 189-198Conference paper (Other academic)
    Abstract [en]

    Wood industry continues to strive to reduce production cost and increase productivity to maintain competiveness. Hence, knowledge of the effect of wood cutting parameters on power consumption would enable increase energy efficiency, thus, reduce operating costs and enhance profitability. Also measurement of power consumption gives knowledge of other specifics such as: tool edge wear, occurrence of catastrophic failures and other parameters which affect the quality of the sawn boards and the momentary efficiency of the break-down process. In this study, power consumption during sawing of Pinus sylvestris L. using double arbour circular saw was investigated. Both climb-sawing and counter-sawing were considered. The experiments were carried out, under normal production, in two Swedish sawmills. The relationship between cutting parameters and calculated power consumption is discussed. The experimental power consumption increased 11-35% during an 8 hour shift mainly due to increase of the tooth radius. Further, this study also showed the climb-sawing had higher power consumption than counter-sawing.

  • 202.
    Cristovao, Luis
    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.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Industrial Sawing of Pinus Sylvestris L.: Power consumption2013In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 8, no 4, p. 6044-6053Article in journal (Refereed)
    Abstract [en]

    The wood industry continues to strive to reduce production costs and increase productivity to remain competitive. Knowledge of the effect of wood cutting parameters on power consumption could increase energy efficiency, reducing operating costs and increasing profitability. Measuring power consumption also provides information about other variables, such as tool edge wear, occurrence of catastrophic failures, and other parameters that affect the quality of the sawn boards and the momentary efficiency of the breakdown process. In this work, power consumption during sawing of Pinus sylvestris L. using a double arbor circular saw was investigated. Both climb-sawing and counter-sawing were considered. The experiments were carried out under normal production circumstances in two Swedish sawmills. The relationship between cutting parameters and theoretical power consumption was investigated. The experimental power consumption increased by 11 to 35% during an 8-h shift, mainly due to an increase in the tooth radius. Additionally, this study showed that climb-sawing consumed more power than counter-sawing.

  • 203.
    Cristovao, Luis
    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.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Natural frequencies of roll-tensioned circular sawblades: Effects of roller loads, number of grooves and groove positions2012In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 2, p. 2209-2219Article in journal (Refereed)
  • 204. Cristovao, Luis
    et al.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sitoe, Rui
    Ekevad, Mats
    Marklund, Birger
    Brittleness of cutting tools when cutting different wood species2009In: Proceedings of the 19th International Wood Machining Seminar / [ed] Handong Zhou; Nanfeng Zhu; Tao Ding, Nanjing: Nanjing Forestry University , 2009Conference paper (Refereed)
  • 205. 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

  • 206.
    Crocetti, Roberto
    et al.
    Division of Structural Engineering, Lund University.
    Gustafsson, Per Johan
    Department of Building Sciences, Lund Institute of Technology.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Costa, L.
    Structural Engineer, Aurecon Group.
    Asimakidis, A.
    Stuctural Engineer, Sydark Konstruera, Malmö.
    Nailed Steel Plate Connections: Strength and Ductile Failure Modes2016In: Structures, ISSN 2352-0124, Vol. 8, no 1, p. 44-52Article in journal (Refereed)
    Abstract [en]

    This paper deals with theoretical and experimental investigations of nailed steel plate connections. For the experimental part, a total of 99 laboratory tests have been carried out in order to study failure mechanism and shear capacity of nailed steel plate connections. The testing programme comprised two nail lengths, two steel plate thicknesses and five nailing patterns. All tests related to loading of the plate in the direction of the grain of the wood. The nail patterns were designed to give ductile joint failure by yielding of the nails and/or bearing failure of the wood. The failure load was recorded and the mode and course of failure noted. For some of the specimens, deformation of the nails during loading was studied by means of an X-ray equipment.Deviations between the test results and contemporary consensus as manifested in the SS-EN 1995-1-1:2004 and the Johansen theory for ductile failure were found in several respects: development of the plastic hinges in the nails, influence of nail length, steel plate thickness and nail-to-nail and edge distances.The paper also presents an empirical equation based on multiple regression analysis of the test results was proposed as an attempt to predict the load-carrying capacity of nailed connections in shear.

  • 207.
    Daerga, Per-Anders
    et al.
    f.d. Umeå universitet.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Programmering av Matlab-rutiner för utvärdering av experiment med knutpunktsförband i MFB-systemet: Beröringsfri mätning av krafter och deformationer med Qualisys Motion Capture – Beskrivning av mätsystem och efterbehandling av mätdata2017Report (Other (popular science, discussion, etc.))
  • 208.
    Dagbro, Ola
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Spår i paneler: Delprojekt i det större projektet ”Sprickor i konstruktioner, utomhusexponering, optimering och simulering”2009Report (Other (popular science, discussion, etc.))
  • 209.
    Dagbro, Ola
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Studies on Industrial-Scale Thermal Modification of Wood2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wood as a raw material is useful for many purposes even though some properties are less than optimal, for example, dimensional stability and durability. These characteristics can however be improved by different treatment methods. Environmental awareness has led to an increased demand for environmentally friendly processes like thermal modification that does not add any chemicals to the wood in contrast to, for example, CCA-impregnated wood.This thesis mainly focuses on thermally modified wood from species such as pine, spruce and birch. The thesis present studies of physical attributes such as color, and chemical analysis of water-soluble compounds and degradation products. Treatment intensity is compared between two different industrial processes referred as Thermowood and WTT, which use respectively superheated steam and pressurized steam as heating media.Thermal modification processes darken the color of wood throughout its cross-section. The formation of darker color is related to a degradation processes that takes place during thermal modification. During thermal modification wood is exposed to temperatures between 160 - 220°C, and the temperature causes physical and chemical transformations that change some of the wood properties. Dimensional stability and durability are typically improved, but mechanical strength properties are usually negatively affected by the treatment.The studied wood species were Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and Birch (Betula pendula L.). Treatments using pressurized steam were carried out under temperatures of 160°C, 170°C and 180°C, and treatments using superheated steam at normal air pressure were carried out at temperatures of 190°C and 212°C. Results showed that similar L* (lightness) can be reached at lower temperatures using pressurized steam compared to superheated steam. The residual moisture content after completed thermal modification was approximately 10% higher in wood treated with the pressurized steam process. It was found that despite an approximately 25°C lower treatment temperature, birch modified in pressurized steam was more acidic compared to birch modified in superheated steam. This will likely have further consequences, requiring more research concerning surface treatment and fixation.The thesis also includes the development of an industrial-quality control procedure based on nondestructive color measurements verified in industrial environment. Treatment intensity in industry is today certified by inspection of documented process schedule and measuring the temperature and time of the process. Quality control in this context refers to the measurement of wood color as an indirect measure of treatment intensity. The color in our study was measured using L*C*H color space. The study shows that it is possible for quality control purposes to measure the color of thermally modified wood from the surfaces of planed boards instead of sawdust or board cross sections that have been used in other studies.The thesis has a final section about academia-industry collaboration that describes how trust building was established through a fruitful relationship involving academia and regional wood products industry in northern Sweden. The study presents an example of a successful research and development alliance between university and a group of small- and medium-sized enterprises (SMEs). This alliance has been a great example on international collaboration involving researchers originating from Finland, China, Bangladesh, Spain, Russia and Sweden. Through an in-depth multi-year study of how the research cooperation developed, the paper describes how the involved companies successfully entered into a new segment of the market.

  • 210.
    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

  • 211.
    Dagbro, Ola
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Torniainen, Petteri
    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.
    Thermal modification of birch using saturated and superheated steam2011In: Proceedings of the 7th meeting of the Nordic-Baltic Network in Wood Material Science and Engineering (WSE): October 27-28, 2011, Oslo, Norway / [ed] Erik Larnøy; Gry Alfredsen, Ås: Norsk institutt for skog og landskap , 2011, p. 43-48Conference paper (Refereed)
    Abstract [en]

    During the thermal modification, wood is normally exposed to temperatures between 160 - 220°C. As a result physical and chemical changes are taking place and some of the wood properties are changed. Dimensional stability and weather resistance are improved. On the other hand the mechanical strength properties are usually negatively affected by the treatment. The visual appearance is also changed. There were two different types of thermal modification processes used in this study. One of them was using saturated steam and the other one superheated steam. Treatment temperature was 160°C in saturated steam process and 185°C in superheated steam. The wood specie used in this study was Silver birch (Betula pendula). In the chemistry part the acid content was investigated. Despite the 25°C lower treatment temperature, birch modified in saturated steam was more acidic compared to birch modified in superheated steam. Some differences in equilibrium moisture content (EMC) and dimensional stability were found mainly in the environment T=20°C and RH=85%. The colour of birch treated in saturated steam at 160°C was darker than the colour of birch treated in superheated steam at temperature 185°C.

  • 212.
    Danvind, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Analysis of drying wood based on nondestructive measurements and numerical tools2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Improved understanding of moisture and mechanical behaviour is a general objective for wood drying research. The main objective of this doctoral thesis was to develop nondestructive experimental methods suitable for collecting valuable response data related to the moisture behaviour and mechanical behaviour of drying wood and to refine this information into modelling parameters. A method for simultaneous noncontact measurement of two-dimensional surface deformations and interior densities was developed. This was done using Digital Speckle Photography (DSP) and X-ray Computed Tomography (CT). Displacements and densities were used for calculation of strain and of moisture content. Experimental tests of the measurement method were done on cross sections of Scots pine. The following accuracy was stated for different properties: A typical calculated displacement error of approximately 10 micrometre was found. Strains derived from the displacements had a maximal error of 1.11 mstrain. Moisture content measuring accuracy was estimated to +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size 2 x 2 x 1.5 mm3. A similar noncontact technique based only on X-ray CT scanning was developed. Displacements were then estimated from boundary movements of an object in CT images. The estimated standard deviation of the measured moisture content error for this method was 0.04% moisture content. The mean error was unknown. Two different approaches to determining moisture diffusion coefficients from the studied data were presented. The first was based on minimizing the difference between measured and computed values through an optimization scheme. This approach required an initial assumption of the functional form of the diffusion coefficient. The second approach calculated diffusion and mass transfer coefficients through direct finite difference calculations on measured moisture content data. Results on Norway spruce showed interesting local variations of the diffusion coefficient, especially near the evaporation surface. Comparisons between measured and FEM simulated data showed good results. An example showed that a multivariate method of analysis could be an effective and easy-to-use tool for untangling relationships between variables and for generating information from data. Finally, it could be stated that the methods presented will be of use to improve the understanding of the behaviour of drying wood, with the focus on moisture and mechanical properties.

  • 213.
    Danvind, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Methods for collecting and analysing simultaneous strain and moisture data during wood drying2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Improved understanding of moisture and mechanical behaviour is an international objective for wood drying research. The main objective of this licentiate thesis work was to develop an experimental method suitable for collecting valuable response data related to the moisture and mechanical behaviour of drying wood. Another objective was to provide an example on how multivariate methods can be used to analyse response data. A method for simultaneous non contact measuring of two dimensional surface deformations and interior densities have been developed. This was done using Digital Speckle Photography, DSP, and X-ray Computerised Tomography (CT). Displacements and densities were used for calculation of strains and moisture contents using a custom software developed in Matlab. Experimental tests of the measuring method were made on cross sections of Scots pine. The following accuracy was stated for different properties: - Displacements measured with DSP could be measured with a random error down to 0.01 pixels. A more typical calculated displacement error of approximately 10 micrometres, was found in paper I. - Strains derived from the displacements had a maximal error of 1.11 mstrain in an experimental test in paper II. - Accuracy in density measurements was expected to be less than +-6 kg/m3 for wet wood with moisture contents ranging from 6-100% and less than +-2 kg/m3 in dry wood, at a significance level of 0.05. This was estimated for a 2x2x1.5 mm3 measuring volume. - Moisture content measuring accuracy was estimated by simulations in paper II, which resulted in a measuring accuracy of +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size of 2x2x1.5 mm3. A multivariate analysing method has been used to present an example on multivariate modelling of shrinkage behaviour in Radiata pine. The method was found to be an easy-to-use tool and useful for valid prediction of radial, tangential, longitudinal and volume shrinkage in the moisture range between 0% and 22% moisture content of the studied wood. The method also proved to be effective for untangling relationships between variables and generating information out of data. Finally, it can be stated that the developed measuring technique and the tested multivariate analysing method will be of use to improve the understanding of the behaviour of drying wood, focusing on moisture and mechanical properties.

  • 214.
    Danvind, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    PLS prediction as a tool for modeling wood properties2002In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 60, no 2, p. 130-140Article in journal (Refereed)
    Abstract [en]

    During an earlier study, material responses of shrinkage and deformation during air-drying were measured on small wood specimens cut from the cross section of a Pinus radiata log. In this paper the analysis of the collected data and the modeling of studied responses were done using multivariate methods. A first model with all variables and all 104 observations was created. In this model there were observations that deviated from the rest and some of them were therefore excluded from further modeling. Also, weak variables and undesired variables were excluded from further modeling. After these exclusions, 77 observations of wood responses below fiber saturation point remained. The results showed good modeling of radial, tangential and volumetric shrinkage between 0-22% MC, with explained variance (R2) and predicted variance (Q2) at approximately 0.9, and moderate modeling of longitudinal shrinkage, R2 = 0.67 and Q2 = 0.65. It was also shown that longitudinal shrinkage has weak correlation to density-related variables in the studied wood. No model with good predictability of deformation was found. This study showed that PLS prediction modeling of shrinkage and deformation in studied wood samples was found to be an effective and easy-to-use tool for untangling relationships between variables and generating information from data.

  • 215.
    Danvind, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Local water vapor diffusion coefficient when drying Norway spruce sapwood2006In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 52, no 3, p. 195-201Article in journal (Refereed)
    Abstract [en]

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

  • 216.
    Danvind, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Eriksson, John
    Johansson, Håkan
    Calibration of a constitutive model for diffuse moisture transport in wood using data from X-ray CT-scanning and digital speckle photography2004Conference paper (Refereed)
  • 217. Danvind, Jonas
    et al.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Using X-ray CT scanning for moisture and displacement measurements in knots and their surroundings2004Conference paper (Refereed)
  • 218.
    Danvind, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Synnergren, Per
    Method for measuring the shrinkage behaviour of drying woods using digital speckle photography and x-ray computerised tomography2001In: Moisture control in environment-friendly housing and wood drying technology in new century: July 9-13, 2001 Tsukuba, Japan / [ed] K. Hayashi, Ibaraki: Forestry and Forest Products Research Institute , 2001, p. 276-281Conference paper (Refereed)
  • 219.
    Duchesne, Isabelle
    et al.
    Natural Resources Canada, Canadian Wood Fibre Centre, Québec, QC, Canada.
    Vincent, Manon
    Ministère des Forêts, de la Faune et des Parcs du Québec, Québec, QC, Canada.
    Wang, Xiaodong (Alice)
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ung, Chhun-Huor
    Natural Resources Canada, Canadian Wood Fibre Centre, Québec, QC, Canada.
    Swift, D. Edwin
    Natural Resources Canada, Canadian Wood Fibre Centre, Fredericton, NB, Canada.
    Wood Mechanical Properties and Discoloured Heartwood Proportion in Sugar Maple and Yellow Birch Grown in New Brunswick2016In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 1, p. 2007-2019Article in journal (Refereed)
    Abstract [en]

    Rising interest in using wood in non-residential multi-story building structures opens up new opportunities for utilising low-grade hardwoods. The primary objective of this study was to evaluate the geographic variation in modulus of elasticity (MOE) and modulus of rupture (MOR) of sugar maple and yellow birch wood in relation to stand and tree characteristics for two regions in New Brunswick, Canada. Mixed effects statistical models were developed to test the effects of stand, tree, and wood sample variables. A second objective was to examine geographic variation in heartwood discolouration in relation to stand and tree characteristics. Between-tree differences (trees nested within sites) accounted for 44% and 35% of the total variation in yellow birch (MOE and MOR, respectively) and for 69% and 60% of total variation in sugar maple. The fixed effects explained only a very small part for the variation in MOE and MOR in the sugar maple data (10% for MOE and 5% for MOR). For sugar maple, mechanical properties (MOE and MOR) at 50% of the radius were considerably lower than those close to the bark, but this radial variation was not noteworthy for yellow birch. Discoloured heartwood proportion had no significant effect on wood mechanical properties.

  • 220.
    Ekatarina, Siderova
    et al.
    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.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Composition of monosaccharides in aqueous extracts of thermally modified wood.2018In: ECWM9 - The 9th European Conference on Wood Modification / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz, Brigitte Junge and Jos Gootjes, Wageningen: SHR Wageningen, The Netherlands , 2018, p. 575-580Conference paper (Refereed)
  • 221.
    Ekevad, Mats
    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 Blade2015Conference paper (Refereed)
    Abstract [en]

    Curve sawing is a standard method to handle break-down of crooked logs at sawmills and means advantages for yield and quality of sawn boards. However, for circular saw machinery and especially for double arbor saw machinery, deviations of saw kerfs give losses of valuable board volume. Saw kerf deviations give thinner boards compared to straight sawn boards but also slight cupping of the cross sections. Theoretical calculations show that even with the moderate (large) curve radii that is used today in sawmills with circular saw machinery, these saw kerf deviations are typically 0.2-0.6 mm for normal 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. 50 normal logs and 50 curved with top diameter 236-248 mm were cut with sawing pattern 3X with center boards 51x149 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. Keywords: Curve sawing, ripsawing, saw kerf deviation, log break down

  • 222.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Method to compute fiber directions in wood from computed tomography images2004In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 50, no 1, p. 41-46Article in journal (Refereed)
    Abstract [en]

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

  • 223.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Modelling of dynamic and quasistatic events with special focus on wood-drying distortions2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals mainly with computer simulations of wood-drying distortions, especially twist. The reason for this is that such distortions often appear in dried timber, and the results are quality downgrades and thus value losses in the wood value chain. A computer simulation is a way to theoretically simulate what happens in reality when moisture content in timber changes. If the computer simulation model is appropriate and capable of realistic simulations of real events, then it is possible to study what happens with the timber distortions if some parameters in the simulation model are changed. In that way, a good simulation model is a good tool to use when trying to reduce wood-drying distortions by altering some parameters in the process of producing timber. Computer simulations have the comparative advantage over real-world experiments of being cheaper and faster to perform, but the disadvantage that the outcome may be doubtful if the simulation model is bad. Wood is an anisotropic material that is often modelled as an orthotropic material, i.e., a material that has three orthogonal directions at each point with different material properties. A method to measure the orthotropic directions in wood nondestructively was the subject of paper 1. The method was to calculate the directions from the information in a series of two-dimensional computed tomography (CT) images. Fictitious, small calculation spheres were distributed in the wood material, and the principal directions of inertia of these spheres were calculated using the density information in the CT images. The principal directions were assumed to be the radial, the tangential and the fibre direction at the point in question. Tests of the method on three wood samples showed that the method works, but that there was considerable spread in the results from individual spheres. The spread was reduced by calculating mean values for a number of spheres in the vicinity of each other. Twist of timber depends on various influencing variables. Traditionally, a formula from the late 50s by Stevens and Johnston, valid for single growth ring cylinders, has often been used to explain which variables influence twist. One interesting influencing variable in this formula is the spiral grain angle; the others are the moisture content change, the coefficient of moisture expansion and the radius of the growth ring cylinder in question. However, real boards are not single growth ring cylinders, and paper 2 deals with the dependence of twist of realistic boards on various influencing variables. Derivations were made on a theoretical and analytical level of the twist of timber, and the result was a formula whose first term corresponds to Stevens and Johnston's original formula; but the formula has also a second term. This second term is proportional to the gradient of the spiral grain angle and is especially important for timber sawn far from pith. The validity of the second term was shown by comparisons with finite element method (FEM) results and also with experimental results. The first step in simulating wood-drying distortions is to simulate the wood-drying process. The output of this moisture transport simulation is the moisture content of the wood piece as a function of time. We then use this output as input to a second step in which we simulate the shrinkage and deformation of the wood piece. A diffusion model was used here to simulate moisture transport, and this simulation requires diffusion and mass transfer coefficients. Such values from drying Norway spruce (Picea abies) sapwood were measured and reported in paper 3. Measurements of the moisture content during drying of a sample were made with CT, and the diffusion coefficient was evaluated with two methods. The first method used a one-dimensional and the second a two-dimensional diffusion model. No assumptions of the dependence of the diffusion coefficient on any functions or variables were made beforehand. Both methods showed about the same result and dependence on moisture content, but also on depth (distance from surface) of the diffusion coefficient. The depth dependence was only apparent near the surface. Comparisons of the evaluated values of the diffusion coefficient in general terms with other results were made and showed agreement. Industrial process changes aimed at reducing twist distortions are interesting to study. In paper 4, simulations of drying distortions were conducted, and pretwist during drying as a remedy to overcome twist of boards was tried. Paper 4 also contained results from laboratory experiments on the influence of the spiral grain angle and the degree of restraint and pretwist during drying on twist of boards. Results from an industrial test of the influence of the spiral grain angle and the degree of restraint on twist of boards were also described. The laboratory experiments and the industrial test were simulated with an FEM simulation model in two stages. First, the FEM model was calibrated by adjusting the yield stresses of the wood material in order for the results from the laboratory experiments to agree with the simulation model results. Then in a second stage, the simulation model was used to simulate the industrial test. The results showed that the FEM simulation model was capable of producing realistic results, but that there were some discrepancies between the industrial test results and the simulation results. The discrepancies were assumed to be due to biased measurements, insufficient knowledge of the distribution of the spiral grain angle or other causes.

  • 224.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Modelling the effects of local variations in the wood material on the quality of the sawn timber2005In: Proceedings of IUFRO Working Party 5.01.04 Fifth Workshop, "Connection between Forest Resources and Wood Quality: Modelling Approaches and Simulation Software", Waiheke Island Resort, New Zealand, 20-27 Nov, 2005Conference paper (Refereed)
  • 225.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Modelling thermoelasticity and hygroelasticity for orthotropic materials2009In: COST Action FP0802 Experimental and computational methods in wood micromechanics, 2009, p. 1-2Conference paper (Other academic)
  • 226.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Three-dimensional orthotropic elastic-plastic-mechano-sorptive material model for simulation of wood behaviour2010In: ECCM 2010: IV European Conference on Computational Mechanics, Palais des Congrès, Paris, France, May 16-21, 2010, 2010Conference paper (Refereed)
  • 227.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Twist of wood studs: dependence on spiral grain gradient2005In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 51, no 5, p. 455-461Article in journal (Refereed)
    Abstract [en]

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

  • 228.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Axelsson, Ann
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Variation of modulus of elasticity in the tangential direction with moisture content and temperature for Norway Spruce (Picea abies)2012In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 7, no 4, p. 4730-4743Article in journal (Refereed)
    Abstract [en]

    Modulus of elasticity (MOE) in the tangential direction for Norway spruce, Picea abies (L.) H.Karst was measured. Test samples were tested in three-point bending, and moisture content (MC) and temperature were varied between the green condition and 7% MC and between 20°C and 80°C, respectively. An adjustment of measured MOE to the ideally tangential direction was made by using correction factors calculated from finite element simulations. The results show MOE and the gradients with respect to MC and temperature and how they vary with MC and temperature. The gradients are factors in gradient terms in the incremental stress-strain relation for linear elastic behaviour during load cycles where there are mechanical loads and at the same time varying MC and temperature. The gradient terms add to the temperature and MC expansion coefficients and may be of significant size for cases with high stress, high temperature and high MC.

  • 229.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Axelsson, Ann
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Cristovao, Luis
    Model for forces on a cutting tooth of a circular saw blade for wood rip sawing2011Conference paper (Refereed)
    Abstract [en]

    Forces from cutting appear on the front edge and side edges of a straight cutting tooth of a circular saw blade intended for rip sawing of wooden logs. The forces on these three edges add up to a net force on the tooth with three components in the main, normal and lateral directions. Especially the net lateral force is interesting for the stability of a circular saw blade during rip sawing due to the low stiffness of the saw blade in the lateral direction. In this paper, a model for calculating the net force on a cutting tooth is proposed and discussed. The forces on the front cutting edge and the two side cutting edges may for each edge be calculated from literature and experimental data of main and normal forces as a function of cutting parameters such as rake angle, clearance angle, bevel angle, cutting depth and wood cutting direction. The net force is the vectorial sum of the forces on the front and side cutting edges. Thin saw blades cut relatively more with the side edges than thick saw blades for the same cutting depth.A net lateral force appears on the tooth if there are unequal normal forces on the side edges. The reasons for unequal normal forces may be unequal side cutting depths due to a lateral deflection of the saw blade or inhomogenities in the wood material. The net cutting forces from the cutting force model may be applied on the teeth of a mechanical model of the circular saw blade in order to calculate lateral displacements and thus stability of the circular saw blade. Lateral displacement of the saw blade generates unequal side edge cutting forces and thus there is coupling between lateral force and lateral deflection.

  • 230.
    Ekevad, Mats
    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.
    Finite Element Models for Stress-Laminated Solid Wood Decks2015Conference paper (Refereed)
    Abstract [en]

    Stress laminated timber bridge decks consist of planks or glulam timber members that are put together side by side to form plates or solid volumes of wood to be used as bridge decks. The decks may also be used for other purposes than bridge decks. Load-carrying capacities of these decks are very high and friction alone carries load between individual members. Friction is achieved by using prestressed steel rods through the decks that give normal compressive forces between members, see Fig.1. Fig.1. Left: bridge deck in laboratory test situation. Right: FE modelThe load vs. displacement curve for a transversally loaded deck is normally nonlinear even for low load values but especially for high loads due to partial slip between members. FE simulations and laboratory tests for behaviour have been made earlier, see [1], [2], [3]. Two different approaches for FE-simulations have been used, one with an elastic-plastic material model without discrete member modeling and another with discrete member modeling and contact surfaces between members.In the presentation a summary of earlier results are shown and also some recent results due to additional features in the FE models. The additions are possibilities too simulate gaps between members for the elastic-plastic model and results from butt-end modeling with the contact model. Fig. 2 shows an example of a non-linear load vs. displacement curve for a model with butt-end joints in the deck.Fig.2. load vs. displacement curve for a model with butt-end joints in the deck.References[1] Ekevad M.; Jacobsson P.; Forsberg G. (2011). Slip between glulam beams in stress-laminated timber bridges: finite element model and full-scale destructive test. Journal of Bridge Engineering 16:188-196.[2] Ekholm K.; Ekevad M.; Kliger R. (2014). Modelling slip in stress-laminated timber bridges: comparison of two FEM approaches and test values. Journal of Bridge Engineering 19(9) 04014029.[3] Ekevad M.; Jacobsson P.; Kliger R. (2013). Stress-Laminated Timber Bridge Decks: Non-linear Effects in Ultimate and Serviceability Limit States. International Conference on Timber Bridges 2013 (ICTB2013). Arranged by USDA Forest Products Laboratory. Las Vegas, USA, September 30-October 2, 2013.

  • 231.
    Ekevad, Mats
    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.
    Finite Element Simulation of Nailed Glulam Timber Joints2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 318-323Article in journal (Refereed)
    Abstract [en]

    hispaper presents a finite element modeling method for a certain type of nailed jointbetween glulam beams. The joint in question is a traditional arrangement of a horizontal beam anda vertical pillar but herethere is also a nailed steel plate inserted on the two sides in order to strengthen the joint.Experimental results and a comparisonsof simulated and experimental results aremade. The model includes the elastic and plastic orthotropic behaviour of wood and the elastic and plastic behaviour of nails.The nail joint between the steel plate and the wood is modelled as an elastic-plastic surface to surface connection with elastic-plastic properties. Also the reinforcing effect of nails in the nail-affectedvolume of wood is taken into consideration by raising rolling shear yield limitin the affected wood volume.The comparisons showthat the model works well and give results that are comparable to experimental results.

  • 232.
    Ekevad, Mats
    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.
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Guo, Xiaolei
    Nanjing Forestry University.
    Potential Yield Increase with Reduced Saw Kerf Deviations when Curve Sawing2017Conference paper (Refereed)
    Abstract [en]

    Curve sawing with circular saw blades introduces saw kerf deviations due to the combination of the flat sawblade and the curvature of the saw kerf in log or cant direction. Deviations for a double arbor resaw used for curve sawing, are that the saw kerf becomes wider at top and bottom and that the desired rectangular cross sections of the boards become distorted. The yield loss due to the saw kerf deviation in practice for a sawmill was of interest in this study. Earlier and very approximate guesses and simple estimates have been indicating that the loss of income for a sawmill in Sweden producing 200’ m3 of sawn timber may be about 2 MSEK/year (0.22 Meuro/year). In this study calculations were based on true log data and assumed sawing conditions for a sawmill. A true mixed input log assortment (78458 spruce and pine logs taken into the log yard of a sawmill in northern part of Sweden) was used as basis. Individual curvature of these logs was taken into consideration but the calculation was still approximate because not all facts about sawing patterns, log classes etc. for an actual sawmill were known. Instead one single sawing class was used for the calculation of saw kerf deviation.

     

    Results show that the direct yield loss given the assumed input data was 0.61 %-units. This corresponds roughly to the income loss 0.2 Meuro/year mentioned above. Besides from the yield increase there are other advantages gained if the saw kerf deviation can be reduced.

  • 233.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cristovao, Luis
    Grönlund, Anders
    Different methods for monitoring of flatness and tensioning in circular saw blades2009In: Proceedings of the 19th International Wood Machining Seminar / [ed] andong Zhou; Nanfeng Zhu; Tao Ding, Nanjing: Nanjing Forestry University , 2009, p. 78-86Conference paper (Refereed)
    Abstract [en]

    The performance of a circular-saw blade during sawing depends greatly on the mechanical and geometrical properties of the individual saw blade in question. In order to characterize an individual saw blade when manufacturing saw blades or when doing maintenance of the saw blades, flatness and tensioning are important aspects. Flatness and tensioning influence the lateral stability of the saw blade during sawing and thus affect the sawing result, e.g., the accuracy of the dimensions of the sawn timber. Tests and comparisons of different methods for characterizing individual saw blades were done. New and used saw blades with different amounts of tensioning and flatness were used. The tested saw blades had several radial slots and were intended for use in double-arbour saws with collars and no guides. The compared methods were static and dynamic flatness measurements, natural-frequency measurements and theoretical finite-element calculations with different excitation methods and boundary conditions.The results show some of the qualities of the different methods. The benefits and disadvantages are provided, as well. Especially tensioning can be accurately measured and predicted from natural frequency measurements and finite-element calculations

  • 234.
    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.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Geometry of Kerf when Curve Sawing with a Circular Rip-Saw2013In: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, p. 206-213Conference paper (Refereed)
    Abstract [en]

    Rip-sawing following the curvature of a crooked log means advantages for yield. However, the possibility to saw in a narrow curve with a circular saw blade is limited because of the inherent flat geometry of circular sawblades. For a double arbour circular saw the situation is even more problematic because the two blades have a certain overlap and thus the two arbours are not positioned in the same horizontal position. In this study a theoretical geometrical study of the creation of a kerf with a single circular sawblade and with a double arbour circular saw with two sawblades is viewed upon. Input parameters in the study for the double arbour saw are blade diameter, overlap, margin between blades, cant height, curve centre horizontal position and curve radius. Output is the geometry of the kerf that is cut by the teeth. Theoretical results for stiff saw blades show that the kerfs become in general curved and inclined (tilted) in the vertical direction and also that the width of the kerfs for double arbour saws become wider at the top and bottom of the cant than in the middle. Sawing takes place not only in the front part of the blades but also on the back of the blades (back sawing). Parts of the cutting edges of the teeth are cutting when back sawing and not the whole of the width of the teeth. A result is that boards that are cut out of the cant get varying thickness along their width because of the varying kerf width. A comparison with experimental thickness data from four test sawings at a sawmill indicates that the theoretical results are valid and that curve sawn boards become thinner than straight sawn boards.

  • 235.
    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.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Geometry of kerf when curve sawing with a circular rip-saw2014In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 72, no 6, p. 809-814Article in journal (Refereed)
    Abstract [en]

    Rip-sawing following the curvature of a crooked log means advantages for yield. However, the possibility to saw in a narrow curve with a circular saw blade is limited because of the inherently flat geometry of circular saw blades. For a double arbour circular saw the situation is even more problematic because the two blades have a certain overlap and thus, the two arbours are not positioned in the same horizontal position. In this study, a theoretical geometrical study of the creation of a kerf with a single circular saw blade and with a double arbour circular saw with two saw blades was examined. Results for stiff saw blades show that the kerfs become in general curved and inclined (tilted) in the vertical direction and also that the width of the kerfs for double arbour saws becomes wider at the top and bottom of the cant than in the middle. Additionally, the sawn boards obtain varying thickness along their width because of the varying kerf width. A comparison with experimental thickness data from four test sawings at a sawmill indicates that the theoretical results are valid and that curve sawn boards become thinner than straight sawn boards.

  • 236.
    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.

  • 237.
    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.

  • 238.
    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.

  • 239.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Huber, Johannes A.J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacobsson, Peter
    Martinsons Träbroar AB.
    Mechanics of stress-laminated timber bridges with butt end joints2017Conference paper (Refereed)
    Abstract [en]

    A number of variants of single span and three-span stress-laminated timber bridge decks have been studied via finite element simulations and experiments. Glulam beams in the decks were in general shorter than the total length of span which means that there were butt end joints in the decks. The butt end of each beam in a joint was not connected to the other beam which means that each butt end joint reduced the strength and stiffness of the whole of the deck. Results for deflection and stresses were examined for the studied variants in the form of reduction factors for strength and stiffness relative to a deck without butt end joints.

    Factors are shown in diagrams as function of ratio butt end distance/beam width and also butt end distance/span width. Comparison of achieved results with existing Eurocode rules shows that Eurocode rules are not totally appropriate.

  • 240.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacobsson, Peter
    Martinssons Träbroar AB.
    Prestressed timber bridges: simulations and experiments of slip2010In: Proceedings of the International Conference Timber Bridges, ICTB2010: Lillehammer, Norway September 12 -15, 2010 / [ed] Kjell A. Malo; Otto Kleppe; Tormod Dyken, Trondheim: Tapir Akademisk Forlag, 2010Conference paper (Refereed)
    Abstract [sv]

    Martinsons Träbroar produces currently around 40-50 timber bridges each year where more than half of them are transversally prestressed (stress laminated) decks. A semi-empirical beam theory model is and has been used to determine the height of the decks and the prestress levels. An alternative modelling technique using finite element methods is described in this paper. The purpose for investigating this alternative method is to increase the understanding of behaviour and load bearing capacity of prestressed timber decks. Also to increase the accuracy and efficiency of the design process.The alternative simulation model is an elastic-plastic three-dimensional finite element model. It handles all stress components and is well suited for stress design of timber bridges. The plastic material behaviour of the model makes it possible to model slip between glulam beams in a bridge deck of a prestressed timber bridge. Examples of simulation and experimental results for bridge decks are shown. The results are especially interesting when judging the behaviour of bridge decks for low levels of prestress. An important question is how these results can be interpreted when it comes to design of timber bridges and also the long-time behaviour of real timber bridges.

  • 241.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacobsson, Peter
    Martinssons Träbroar AB.
    Forsberg, Göran
    SP Trätek.
    Slip between glulam beams in stress-laminated timber bridges: finite element model and full-scale destructive test2011In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 16, no 2, p. 188-196Article in journal (Refereed)
    Abstract [en]

    Stress laminated timber bridge decks consist of several sawn timber beams or glulam beams held together with prestressed steel bars. Frictional shear stresses between the beams transfer loads between individual beams. The vertical (transverse) shear stress component has been discussed extensively before; this paper further considers the horizontal shear stress. A full-scale test and corresponding finite element simulations for a specific load case confirmed the occurrence of horizontal slip between beams. The finite element model handled both vertical and horizontal frictional slip using an elastic-plastic material model. The results showed that the finite element model gives reliable results and that slip in general leads to permanent deformations that may increase with load cycling. Horizontal slip between beams over a large area of the bridge deck begin at a low load, resulting in a redistribution of load between beams, but do not lead to immediate failure. Vertical slip between beams start at a high load close to the load application point and lead to failure.

  • 242.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jacobsson, Peter
    Martinssons Träbroar AB.
    Kliger, Robert
    Chalmers University of Technology.
    Stress-laminated timber bridge decks: non-linear effects in ultimate and serviceability limit states2013Conference paper (Refereed)
    Abstract [en]

    Stress-laminated timber bridge decks made of glulam beams are advantageous when it comes to their strength, production and construction costs. The thickness of a deck with a specified span and width is typically determined by considering requirements relating to strength and stiffness stipulated in a design code and specifically in Europe the Eurocode 5. Linear stress calculations do not have inherent potential to simulate slip or gaps between beams, but experience from finite element (FE) simulations and full-scale tests shows that these nonlinear effects from slip and gaps between glulam beams exist. In this paper, comparisons between linear and non-linear FE results for two bridge decks with different spans, widths and thicknesses are made. Separate comparisons are made in the ultimate limit state (ULS) and the serviceability limit state (SLS). It is shown that non-linear effects may be important and should be considered, especially in the case of thin decks.Keywords: prestressed, stress laminated, timber bridge deck, finite element, FEM

  • 243.
    Ekevad, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundgren, Nils
    Flodin, Jens
    Choosing green sawing dimensions for best value yield of Norway spruce: industrial measurements and physical modelling2010In: Proceedings, 11th International IUFRO Wood Drying Conference: [... in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying"] / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010, p. 168-174Conference paper (Refereed)
  • 244.
    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.

  • 245.
    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.
    Cristovao, Luis
    Wear of teeth of circular saw blades2011Conference paper (Refereed)
    Abstract [en]

    Measured wear data is presented for 3 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 3 different cemented carbide grades, denoted A, B and C. These 3 grades were chosen out of 6 grades in an earlier preliminary laboratory test. Grade A was a relatively soft and tough standard grade (K1C=17, HV30=1150) normally used in sawmills in winter conditions for frozen wood, grade B was harder and more brittle (K1C=11, HV30=1600) and grade C was even harder and more brittle (K1C=9.5, HV30=1950). The double arbour saw (with vertical arbours) was equipped with 6 saw blades (3 on each arbour) for cutting 2 centre boards and 2 side boards. The 6 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. After some time the blades were removed, inspected, ground and used again for sawing. The thickness of boards was also measured and the standard deviation was calculated.The results show cutting edge radii as a function of the number of logs sawn and also the standard deviation of the thickness of the sawn boards. 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.

  • 246.
    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.

  • 247.
    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

  • 248.
    Ekholm, Kristoffer
    et al.
    Chalmers University of Technology.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Kliger, Robert
    Chalmers University of Technology.
    Modeling slip in stress-laminated timber bridges: comparison of two finite-element-method approaches and test values2014In: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 19, no 9, article id 4014029Article in journal (Refereed)
    Abstract [en]

    Finite-element (FE) simulations of the deformation behavior of a 5.4-m-long, 8-m-wide, and 0.27-m-thick stress-laminated timber bridge deck were conducted. The simulation results were compared with full-scale test results when using a load resembling an axle load placed near the edge and when cycling the load between a high and low value. Two separate approaches to nonlinear FE modeling were used. The first FE model simulates a frictional slip between the glulam beams with an elastic-plastic material model. The second FE model simulates a frictional slip by modeling each discrete contact surface between each beam in the deck. The results show good agreement between simulation and test results and reveal that the simulation model that models contact surfaces produces slightly better results at the expense of a greater modeling effort and increased computational time. Hysteresis in the load versus deformation curves is clearly visible and was due to significant slip between the glulam beams, which was successfully simulated.Read More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29BE.1943-5592.0000595

  • 249. Eklund, Urban
    et al.
    Grönlund, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Mesurement of cant feeding disturbances during sawing1999In: IWMS 14: 14e Séminaire international sur l'usinage du bois, 12-19 septembre 1999, Paris, Épinal, Cluny, France : actes du séminaire, Montpellier: CIRAD , 1999, p. 193-202Conference paper (Refereed)
  • 250.
    Eliasson, Lars
    et al.
    Linneaus University.
    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.
    Some aspects on the more efficient use of wood in the industrial manufacture of single-fammily timber houses2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 418-425Article in journal (Refereed)
2345678 201 - 250 of 915
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