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  • 1.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Hu, Min
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology. Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Evaluation of three dimensional fibre orientation in Norway spruce using a laboratory laser scanner2016In: WCTE 2016: World Conference on Timber Engineering, Vienna: Vienna University of Technology , 2016Conference paper (Refereed)
    Abstract [en]

    This paper addresses laser scanning and utilization of the tracheid effect for determination of local fibre orientation, which is decisive for strength and stiffness of timber. A newly developed laboratory laser scanner that can be used for high resolution and high precision scanning of wood surfaces is used for in-depth assessment of a single Norway spruce specimen that contains a knot. It is assumed that the specimen has a plane of symmetry, through the knot, and by splitting the specimen in two parts it is possible to determine fibre orientation on orthogonal planes. Hence, by relying on the assumption of symmetry, the fibre orientation in 3D space can also be determined. The results are used to evaluate the possibility of utilizing the tracheid effect for determination of the out-of-plane fibre angle of an investigated surface. Furthermore, the results are used for verification of a theoretical fibre orientation model that has often been used by researchers.

  • 2.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Hu, Min
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Tracheid effect scanning and evaluation of in-plane and out-of-plane fibre direction in Norway spruce using2018In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 4, p. 411-429Article in journal (Refereed)
    Abstract [en]

    Local fiber direction is decisive for both strength and stiffness in timber. In-plane fiber direction on surfaces of timber can be determined using the so-called tracheid effect which is frequently used in both research and industry applications. However, a similar established method does not exist for measuring the out-of-plane angle, also known as diving angle. The purposes of this article were to evaluate if the tracheid effect can also be used to determine, with reasonable accuracy, the out-of-plane angle in Norway spruce and to verify an existing mathematical model used to calculate the fiber direction in the vicinity of knots. A newly developed laboratory laser scanner was applied for assessment of fiber directions in a single Norway spruce specimen containing a knot. It was assumed that the specimen had a plane of symmetry through the center of the knot, and by splitting the specimen through this plane into two parts, it was possible to make measurements on orthogonal planes. The results showed that the out-of-plane angle could not be determined with very high accuracy and the difficulties related to this objective were analyzed. Regarding the mathematical model of fiber direction in the vicinity of a knot, fiber directions calculated on the basis of this model agreed well with experimentally obtained fiber directions, but successful application of the model requires that the geometry of the knot is known in detail.

  • 3.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modelling 3D orientation of knots in timber on the basis of dot laser scanning and the tracheid effect2015In: / [ed] Josef Eberhardsteiner and Michael Kaliske, 2015Conference paper (Refereed)
    Abstract [en]

    Ongoing research concerns the possibility of determining the 3D orientation of wood fibres within the entire volume of a wooden board using surface information from laser scanning. Previous research, Olsson and Oscarsson [1], has shown that the fibre orientation of side boards can be determined on the basis of such information. The present research is extended to also comprise boards cut from the centre of the log and a first step in this work is to establish 3D models of knots in boards on the basis of information from dot laser scanning of surfaces.

    In comparison with other approaches aiming at 3D models of knots and wood fibre orientation, e.g. Guindos and Guaita[2] and Hackspiel et al. [3], the present model relies to a larger extent on the actual fibre orientation measured on each individual board, rather than on general assumption and mathematical models of typical fibre orientation alone.  

    The fact that all data needed for the model can be sampled in sawmill production speed means that developed models could be used as a basis for advanced strength grading methods, for grading with respect to shape stability and for other purposes of industrial interest.

  • 4.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Three dimensional knot models based on surface laser scanning2015In: Proceedings 19th International Nondestructive Testing and Evaluation of Wood Symposium Rio de Janeiro, Brazil, 23-25 September, 2015. / [ed] Ross, Robert J.; Gonçalves, Raquel; Wang, Xiping,, Madison, USA: USDA, Forest Service, Forest Products Laboratory , 2015, Vol. 19, p. 83-90Conference paper (Refereed)
    Abstract [en]

    Most machine strength grading methods of today result in limited grading accuracy and poor yield in higher strength classes. A new and more accurate grading method utilizing laser scanning technique to determine the in-plane fibre directions on board surfaces was recently approved for the European market. In this, however, no consideration is taken to the out-of-plane direction of the fibres. A first step towards scanning-based 3D models of the fibre orientation is the establishment of 3D knot models. In this investigation laser scanning was used to identify knot surfaces on longitudinal board surfaces. By means of developed algorithms knot surfaces that belonged to the same physical knot visible on different sides of the board were identified. All knots with surface areas larger than 100 mm2 were correctly identified and modeled in 3D. This is a promising starting point for further development of the new grading method based on laser scanning.

  • 5.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Three-dimensional modelling of knots and pith location in Norway spruce boards using tracheid-effect scanning2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 5, p. 725-739Article in journal (Refereed)
    Abstract [en]

    Knots and the orientation of fibres in timber are decisive for the stiffness and strength of boards. Due to large property variations between members, strength grading is necessary. High resolution information of the orientation of fibres, both on surfaces and within members, would enable development of more accurate grading methods than those available today. A step towards three-dimensional (3D) models of the fibre orientation of the entire board volume is the establishment of 3D knot models based on scanning. The light from a dot laser illuminating the surface of a softwood board will, due to the tracheid effect, spread more along the fibres than across resulting in the dot entering an elliptical shape. In this investigation both the shape of the ellipse and the direction of its major axis were used to estimate the 3D fibre orientation on board surfaces. Knot surfaces were identified where the angle between the estimated 3D fibre direction and an approximated direction of the board’s pith exceeded a threshold value. By means of algorithms based on polar coordinates, knot surfaces which belonged to the same physical knot visible on different sides of the board were identified and as a result the position, orientation and volume of each knot were determined. Based on this information, a more accurate position of the board’s pith along the board was calculated. The established models showed good agreement with physical boards. The models constitute a promising starting point for further development of strength grading methods based on tracheid-effect scanning.

  • 6.
    Habite, Tadios
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Automatic detection of pith location along boards of Norway spruce on the basis of data from optical scanning of longitudinal surfaces2019In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019, Växjö: Lnu Press , 2019, p. 64-64Conference paper (Refereed)
    Abstract [en]

    Different mechanical and physical properties of wood are related to the location of pith. Norway spruce wood from the centre of logs, close to the pith, is characterized by lower longitudinal MOE, larger spiral grain angle, and larger longitudinal shrinkage coefficient than what wood farther away from the pith is [1]. Thus, knowledge of pith location along timber boards may play an important role in both appearance grading and in assessment of mechanical properties such as strength [2]. The current work aims to develop an algorithm which is capable of automatically estimating the pith location of Norway spruce boards, along the boards’ length direction, by utilizing optical scanning of longitudinal surfaces. The initial step of the algorithm is to identify defect free sections along the timber board. This is done by utilizing data from tracheid effect scanning of the four sides of the timber board. Thereafter, a continuous wavelet transform (CWT), similar to fast Fourier transform, is applied on grey scale images from scanning, to analyse the variation of light intensity across the four surfaces at selected positions along the board. Obtained local frequencies correspond to the local annular ring pattern on surfaces. Then, assuming that annular growth rings are concentric circles with the pith in the centre, detected local annular ring wavelengths (using CWT) and artificial annual ring wavelengths corresponding to different hypothetical locations of pith are compared, and an optimization procedure is used to identify the location of pith that minimizes the discrepancy between the detected and artificial sets of annular ring wavelengths. Figure 1 shows grey scale images of short segments of longitudinal surfaces, graphs of the detected local annual ring widths, and a photograph of the board cross section where the determined location of pith is marked out. Preliminary results reveal that data from optical scanners and the suggested method allow for accurate detection of annular ring width and location of pith along boards.

  • 7.
    Habite, Tadios
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Detection of Pith Location of Norway Spruce Timber Boards on the Basis of Optical Scanning2019In: Proceedings, 21st international nondestructive testing and evaluation of wood symposium: Freiburg, Germany / [ed] Xiping Wang; Udo H. Sauter; Robert J. Ross, Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory , 2019, p. 268-275Conference paper (Refereed)
    Abstract [en]

    Optical scanners are used in the woodworking industry to detect various defects, such as dead and live knots, cracks, and fibre distortions, which are important for the visual appearance grading of wood. Data from scanning is also used to assess mechanical properties such as bending and tensile strength, for the purpose of machine strength grading of sawn timbers. Knowledge of annular ring width and location of pith in relation to board cross-sections, and how these properties vary in the longitudinal direction of boards, is relevant for many purposes, such as assessment of shape stability and mechanical properties of timber. Therefore, the purpose of the present research is to evaluate possibilities to determine annular ring width and location of pith on the basis of scanning of surfaces parallel to the longitudinal board direction. The first step of this novel method is to identify clear wood sections, free of defects along boards. Then time-frequency analysis is applied to assess the variation of light intensity over surfaces of these sections, such that local wavelengths, related to the annular ring width patterns are detected on all four surfaces around the board. Finally, the location of pith is calculated by comparing annular ring width distributions on the different surfaces, and assuming that annular rings are concentric circles with the pith in the centre. Results indicate that optical scanners and the suggested method allow for accurate detection of annular ring width and location of pith along boards.

  • 8.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Growth layer and fibre orientation around knots in Norway spruce: a laboratory investigation2018In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 1, p. 7-27Article in journal (Refereed)
    Abstract [en]

    The strength of structural timber largely depends on the occurrence of knots and on the local material directions in the surroundings of such knots. There is, however, a lack of methods for establishing a full dataset of the local material directions. The present research aims at the development and application of a laboratory method to assess the geometry of growth layers and the orientation of fibres in a high-resolution 3D grid within wood specimens containing knots. The laboratory method was based on optical flatbed scanning and laser scanning, the former resulting in surface images and the latter, utilizing the tracheid effect, resulting in in-plane fibre angles determined in high-resolution grids on scanned surfaces. A rectangular solid wood specimen containing a single knot was cut from a tree in such a way that it could be assumed that a plane of symmetry existed in the specimen. By splitting the specimen through this plane through the centre line of the knot, two new specimens with assumed identical but mirrored properties were achieved. On one of the new specimens, the longitudinal-radial plane was subsequently scanned, and the longitudinal–tangential plane was scanned on the other. Then, by repeatedly planing off material on both specimens followed by scanning of the new surfaces that gradually appeared, 3D coordinate positions along different growth layers and 3D orientation of fibres in a 3D grid were obtained. Comparisons between detected fibre orientation and growth layer geometry were used for the assessment of the accuracy obtained regarding 3D fibre orientation. It was shown that the suggested method is well suited to capture growth layer surfaces and that it provides reliable information on 3D fibre orientation close to knots. Such knowledge is of great importance for understanding the properties of timber including knots. The quantitative data obtained are also useful for calibration of model parameters of general models on fibre orientation close to knots.

  • 9.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology. Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Three dimensional growth layer geometry and fibre orientation around knots: a laboratory investigation2016In: Proceedings of WCTE 2016 World Conference on Timber Engineering / [ed] Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna: Vienna University of Technology , 2016Conference paper (Refereed)
  • 10.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    SP Tech Res Inst Sweden, SP Wood Technol, Växjö.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation2015In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 1, p. 17-27Article in journal (Refereed)
    Abstract [en]

    During the last decade, the utilization of non-contact deformation measurement systems based on digital image correlation (DIC) has increased in wood related research. By measuring deformations with DIC systems, surface strain fields can be calculated. The first aim of this study concerns the possibility to detect detailed strain fields along the entire length of a wooden board subjected to pure bending and the potential of using such strain fields to determine a bending modulus of elasticity (MOE) profile along a board. Displacements were measured over 12 subareas along a flat surface of the board. For each such area, a separate local coordinate system was defined. After the transformation of locally measured coordinates to a global system, high resolution strain fields and a corresponding bending MOE profile were calculated. A second method in establishing bending MOE profiles is to use fibre angle information obtained from laser scanning and a calculation model based on integration of bending stiffness over board cross sections. Such profiles have recently been utilized for accurate strength grading. A second aim of this study was to investigate the accuracy of the bending MOE profiles determined using the latter method involving fibre angle information. Bending MOE profiles determined using the two described methods agree rather well. However, for some patterns of knot clusters, the local bending MOE, calculated on the basis of fibre angles and integration of bending stiffness, is overestimated. Hence, this research adds knowledge that may be utilized to improve the newly suggested strength grading method.

  • 11.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    An Application of 3D Fiber Angles Identified through Laser Scanning Based on Tracheid Effect2015Conference paper (Refereed)
  • 12.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology. Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Modelling local bending stiffness based on fibre orientation in sawn timber2018In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 6, p. 1605-1621Article in journal (Refereed)
    Abstract [en]

    Strength of structural timber depends to a high degree on the occurrence of knots and on the local fibre deviation around such defects. Knowledge of local fibre orientation, obtained by laser scanning, has been utilized in a previously developed machine strength grading method, but rather crude assumptions regarding the fibre orientation in the interior of boards and a mechanical model that does not capture the full compliance of knotty sections were adopted. The purpose of the present study was to suggest and verify a model with which local bending stiffness can be predicted with high accuracy. This study included development of a model of fibre orientation in the interior of boards, and application of a three-dimensional finite element model that is able to capture the compliance of the board. Verification included bending of boards in the laboratory and application of digital image correlation to obtain strain fields comparable to those obtained by finite element simulation. Results presented comprise strain fields of boards subjected to bending and calculated bending stiffness profiles along boards. Comparisons of results indicated that the model suggested here was sufficient to capture the variation of local bending stiffness along boards with very high accuracy.

  • 13.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Serrano, Erik
    Lund University.
    Assessment of a Three-Dimensional Fiber Orientation Model for Timber2016In: Wood and Fiber Science, ISSN 0735-6161, Vol. 48, no 4, p. 271-290Article in journal (Refereed)
    Abstract [en]

    Wood is an orthotropic material with very different properties along and across fibers, and every board has its own pattern of knots and fiber deviations. Therefore, detailed knowledge of the three-dimensional (3D) fiber orientation of individual boards would enable more accurate assessment of properties such as stiffness, strength, and shape stability. This paper presents a method for modeling 3D fiber orientation of side boards of Norway spruce. The method is based on dot laser scanning and utilization of the tracheid effect, and it is verified by a comparison between strain fields calculated on the basis of the fiber orientation model and corresponding strains determined using digital image correlation (DIC) technique. By means of the method, it is possible to identify knots and to reproduce the fiber orientation in clear wood in the vicinity of knots. Fiber orientation models of side boards including traversing edge knots were established and integrated in finite element models of boards used for simulation of four-point bending tests. The same boards were also tested in laboratory and displacement fields of the wide faces were recorded at different load levels using DIC technique. Comparisons of strain fields from measurements and simulations showed close agreement, regarding both strain patterns and strain levels. Local strain concentrations caused by very small defects were detected using the models and also found from the laboratory test results. The modeling approach may be used both to achieve improved accuracy of existing machine strength grading methods and, after further development, also for more advanced analysis of eg crack propagation and strength of timber.

  • 14.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Oscarsson, Jan
    SP Sveriges Tekniska Forskningsinstitut.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Nytt paradigm för hållfasthetssortering av konstruktionsvirke: Projektrapport ett2013Report (Other academic)
    Abstract [sv]

    Den undersökning som redovisas i denna rapport har genomförts under hösten 2012 och våren 2013 inom projektet "Nytt paradigm för hållfasthetssortering av konstruktionsvirke". Projektet som kommer att pågå under perioden december 2011 till juni 2014 går ut på att för industriellt bruk utveckla en nyligen föreslagen metod för hållfasthetssortering av konstruktionsvirke, vilken baseras på laserskanning i kombination med dynamisk excitering och densitetsbestämning av virke. Projektet finansieras till 50 % av VINNOVA och till 50 % av de företag som medverkar i projektet, nämligen Innovativ Vision AB (IV), Vida Vislanda AB, Södra Timber AB, Derome Timber AB och Dynalyse AB. Linnéuniversitetet (Lnu) och SP Sveriges Tekniska Forskningsinstitut AB (SP) samverkar med nämnda företag i utförandet av forskningen.

    Syftet med undersökningen är i först hand att utvärdera alternativa sätt för att bestämma densitet för virke och att verifiera implementeringen av programvara för industriellt bruk. Syftet är också att ta fram ett utökat material för att bedöma vilken precision den nya sorteringsmetoden kan erbjuda och för att bedöma hur känslig den är för olika typer förändringar och störningar som kan uppkomma. Undersökningen bygger på ett begränsat material och en mer omfattande undersökning planeras för genomförande under senare delar av projektet.

  • 15.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology. SP Sveriges Tekniska Forskningsinstitut.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Nytt paradigm för hållfasthetssortering av konstruktionsvirke: Projektrapport två2014Report (Other academic)
    Abstract [sv]

    Undersökningen som redovisas i denna rapport har genomförts under hösten 2013 och våren 2014 inom projektet "Nytt paradigm för hållfasthetssortering av konstruktionsvirke". Projektet, som pågår under perioden december 2011 till juni 2014, går ut på att för industriellt bruk utveckla en nyligen föreslagen metod för hållfasthetssortering av konstruktionsvirke, vilken baseras på laserskanning i kombination med dynamisk excitering och densitetsbestämning av virke. Projektet finansieras till 50 % av VINNOVA och till 50 % av de företag som medverkar i projektet, nämligen Innovativ Vision AB (IV), Vida Vislanda AB, Södra Timber AB, Derome Timber AB och Dynalyse AB. Linnéuniversitetet (Lnu) och SP Sveriges Tekniska Forskningsinstitut AB (SP) samverkar med nämnda företag i utförandet av forskningen.

    Ett syfte med undersökningen är att på ett stort material bestående av många olika virkesdimensioner verifiera de starka statistiska samband som sedan tidigare påvisats för ett begränsat antal plankor och dimensioner, mellan å ena sidan indikerande egenskaper som baseras på mätningar och beräkningar och å andra sidan böjstyrka, elasticitetsmodul och densitet. Ett annat syfte med undersökningen är att visa att nödvändig data kan samlas in av samma utrustning och under samma förhållanden som kommer att gälla vid framtida hållfasthetssortering baserad på den aktuella metoden. Slutligen är ett syfte att samla in och dokumentera data som kan användas för forskning och utveckling både inom och efter det att det aktuella projektet har avslutats.

  • 16.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Strength grading based on high resolution laser scanning: performance of a procedure newly approved for the European market2015In: Proceedings of the 19th International Nondestructive Testing and Evaluation of Wood Symposium / [ed] Ross, Robert J.; Goncalves, Raquel; Wang, Xiping, Madison, USA: USDA, United States Department of Agriculture, Forest Service, Forest Products Laboratory , 2015, Vol. 19, p. 232-240Conference paper (Refereed)
    Abstract [en]

    Strength grading of timber is necessary to ensure sufficient structural performance of the material, and machines based on different types of non-destructive measurements are available on the market. The purpose of this paper is to present results on an investigation of a new method and procedure for machine strength grading that is based on laser scanning and utilization of the tracheid effect, in combination with dynamic excitation and weighing. The investigated sample comprised more than 900 pieces of timber of Norway spruce (Picea abies) from Sweden, Norway and Finland. The coefficient of determination between the indicating property (IP) to bending strength and the measured bending strength was as high as R2 = 0.69, while the coefficient of determination between dynamic MOE and measured bending strength was R2 = 0.53. A comparison of the performance with what have been presented for machines that are based on X-ray in combination with dynamic excitation indicates that the new method/procedure will surpass such machines. 

  • 17.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Strength grading on the basis of high resolution laser scanning and dynamic excitation: a full scale investigation of performance2017In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 75, no 1, p. 17-31Article in journal (Refereed)
    Abstract [en]

    Effective utilization of structural timber requires grading and indicating properties (IPs) that are able to predict strength with high accuracy, and machines that are able to measure the underlying board properties at a speed that corresponds to the production speed of sawmills. The aim of this research is to assess the performance of a new machine strength grading method/procedure which was recently approved for the European market and to compare the performance of it with the performance of other available techniques. The novel method is based on laser scanning utilizing the tracheid effect, in combination with data from dynamic excitation and weighing. Applied indicating properties are defined in detail and results presented include assessment of the repeatability, coefficients of determination between IPs and grade determining properties, and examples of the yield achieved in different strength classes and combinations of strength classes. The investigated sample comprised more than 900 pieces of timber of Norway spruce (Picea abies) from Sweden, Norway and Finland. For this sample the coefficient of determination between the IP to bending strength and the measured bending strength was as high as R2 = 0.69, while the coefficient of determination between dynamic modulus of elasticity (MOE) and measured bending strength was R2 = 0.53. The yield in high strength classes, C35 and above, become about twice as high using the new method/procedure compared to machines using dynamic MOE as IP. A comparison of the performance with what have been presented for machines that are based on X-ray in combination with dynamic excitation indicates that the new method/procedure will surpass such machines as well. 

  • 18.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    SP Technical Research Institute of Sweden, Sweden.
    Three dimensional fibre orientation models for wood based on laser scanning utilizing the tracheid effect2014In: Proceedings of the 2014 World Conference on Timber Engineering (WCTE), Quebec City, Canada, August 10−14, 2014, 2014Conference paper (Refereed)
    Abstract [en]

    Recentresearch has shown that machine strength grading based on tracheid effectscanning of fibre directions projected on board surfaces can provide moreaccurate strength predictions than today’s grading methods. Scanning techniquesin which 3D fibre orientations can be taken into account would most likelyimprove the strength grading results even further. In this investigation thepossibility of determining such 3D orientations by dot laser scanning wasinvestigated. For a set of 20 side boards, scanning data was used to calculatetraversing knot directions which were in turn applied to determine pithlocation and root end of original logs. By means of the shape of laser dots,which due to the tracheid effect are turned elliptic on board surfaces, and thedetermined pith location, the size and direction of the diving angle of thefibres was calculated. The research showed that this angle can be accuratelydetermined in the vicinity of knots.

  • 19.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Dynamic excitation and higher bending modes for prediction oftimber bending strength2010In: Proceedings of the final conference of COST action E53, 2010Conference paper (Other academic)
    Abstract [en]

    The potential of utilizing eigenfrequencies corresponding to edgewise bending modes for predicting the bending strength of timber is investigated. The research includes measurements of axial and transversal resonance frequencies, laboratory assessment of density, static bending stiffness and bending strength of 105 boards of Norway spruce of dimensions 45×145×3600 mm. It is shown that Eb,1, (MOE based on the eigenfrequency of the first bending mode) gives a higher coefficient of determination to the bending strength than what Ea,1 (MOE based on the first axial eigenfrequency) does. It is also shown that eigenfrequencies corresponding to higher bending modes can be used in the definition of a new prediction variable, the modulus of inhomogeneity (MOI). This is a scalar value representing the lack of fit between the true, measured eigenfrequencies and the expected (assuming homogeneity) eigenfrequencies of a board. The results show that using the MOI as a third prediction variable, in addition to Eb,1 and density, increases the coefficient of determination with respect to bending strength from R2 = 0.69 to R2 = 0.75.

  • 20.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    SP Technical Research Institute of Sweden, Videum Science Park, 351 96, Växjö, Sweden.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Prediction of timber bending strength on basis of bending stiffness and material homogeneity assessed from dynamic excitation2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 4, p. 667-683Article in journal (Refereed)
    Abstract [en]

    The potential of utilizing resonance frequencies corresponding to edgewise bending modes for predicting the bending strength of timber is investigated. The research includes measurements of axial and transversal resonance frequencies, laboratory assessment of density, static bending stiffness and bending strength of 105 boards of Norway spruce of dimensions 45×145×3600 mm. It is shown that Eb,1, (MOE based on the resonance frequency of the first bending mode) gives a higher coefficient of determination to the bending strength than what Ea,1 (MOE based on the first axial resonance frequency) does. It is also shown that resonance frequencies corresponding to higher bending modes can be used in the definition of a new indicating property, the measure of inhomogeneity (MOI). This is a scalar value representing the lack of fit between the true, measured resonance frequencies and the expected (assuming homogeneity) resonance frequencies of a board. The results show that using the MOI as a third indicating property, in addition to Eb,1 and density, increases the coefficient of determination with respect to bending strength from R2=0.69 to R2=0.75.

  • 21.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Prediction of timber bending strength using dynamic excitation of bending modes2010In: Proceedings of the 11th World Conference on Timber Engineering / [ed] Ario Ceccotti, 2010Conference paper (Refereed)
    Abstract [en]

    The potential of utilizing eigenfrequencies corresponding to edgewise bending modes for predicting the bending strength of timber is investigated. The research includes measurements of axial and transversal resonance frequencies, laboratory assessment of density, static bending stiffness and bending strength of 105 boards of Norway spruce of dimensions 45×145×3600 mm. It is shown that Eb,1, (MOE based on the eigenfrequency of the first bending mode) gives a higher coefficient of determination to the bending strength than what Ea,1 (MOE based on the first axial eigenfrequency) does. It is also shown that eigenfrequencies corresponding to higher bending modes can be used in the definition of a new prediction variable, the modulus of inhomogeneity (MOI). This is a scalar value representing the lack of fit between the true, measured eigenfrequencies and the expected (assuming homogeneity) eigenfrequencies of a board. The results show that using the MOI as a third prediction variable, in addition to Eb,1 and density, increases the coefficient of determination with respect to bending strength from R2 = 0.69 to R2 = 0.75.

  • 22.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology. SP Technical Research Institute of Sweden.
    Serrano, Erik
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Prediction of timber bending strength and in-member cross-sectional stiffness vartiation on basis of local wood fibre orientation2013In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 71, no 3, p. 319-333Article in journal (Refereed)
    Abstract [en]

    Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3600 mm, a coefficient of determination as high as 0.68-0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles.

  • 23.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Pot, Guillaume
    LaBoMaP, France.
    Viguier, Joffrey
    LaBoMaP, France.
    Faydi, Younes
    LaBoMaP, France.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Performance of strength grading methods based on fibre orientation and axial resonance frequency applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.)2018In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 75, no 4, article id 102Article in journal (Refereed)
    Abstract [en]

    Key messageMachine strength grading of sawn timber is an important value adding process for the sawmilling industry. By utilizing data of local fibre orientation on timber surfaces, obtained from laser scanning, more accurate prediction of bending strength can be obtained compared to if only axial vibratory measurements are performed. However, the degree of improvement depends on wood species and on board dimensions. It is shown that a model based on a combination of fibre orientation scanning and axial vibratory measurement is very effective for Norway spruce (Picea abiesL.) and Douglas fir (Pseudotsuga menziesii(Mirb.) Franco). For European oak (Quercus petraea(Matt.) Liebl./Quercus roburL.) boards of narrow dimensions, axial vibratory measurements are ineffective whereas satisfactory results are achieved using a model based on fibre orientation.ContextMachine strength grading of sawn timber is an important value adding process for the sawmilling industry.AimsThe purpose of this paper has been to compare the accuracy of several indicating properties (IPs) to bending strength when applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.).MethodsThe IPs were determined for a set of data comprising scanned high-resolution information of fibre orientation on board surfaces, axial resonance frequency, mass and board dimensions.ResultsWhereas dynamic axial modulus of elasticity (MoE) gave good prediction of bending strength of Norway spruce (R-2=0.58) and Douglas fir (R-2=0.47), it did not for narrow dimension boards of oak (R-2=0.22). An IP based on fibre orientation gave, however, good prediction of bending strength for all three species and an IP considering both dynamic axial MoE and local fibre orientation for prediction of bending strength gave very good accuracy for all species (Norway spruce R-2=0.72, Douglas fir R-2=0.62, oak R-2=0.59). Comparisons of results also showed that scanning of fibre orientation on all four sides of boards resulted in more accurate grading compared to when only the two wide faces were scanned.ConclusionData of local fibre orientation on wood surfaces give basis for accurate machine strength grading. For structural size timber of Norway spruce and Douglas fir, excellent grading accuracy was achieved combining such data with data from vibratory measurements. The improvements achieved enable substantial increase of yield in high-strength classes.

  • 24.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Serrano, Erik
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Förfarande och anordning för utvärdering av en bräda av trä2014Patent (Other (popular science, discussion, etc.))
    Abstract [sv]

    Föreliggande redogörelse avser en metod och en anordning för utvärdering av en bräda av trä med en ländriktning. Data som indikerar fiberorienteringen över brädans yta inhämtas och för ett antal underpartier hos brädan bestäms en nominell, lokal elasticitetsmodul, MOE, på basis av nämnda fiberorienteringsdata och en nominell materialparameter. En nominell global MOE i längdriktningen för träbrädan i sin helhet genereras och jämförs med en sekundär global MOE. På basis av nämnda fiberorienteringsdata och denna jämförelse genereras en uppskattad lokal elasticitetsmodul, MOE, i nämnda längdriktning för ett flertal underpartier. Dessa data kan användas för exempelvis tillförlitlig hållfasthetsgradering av träbrädor.

  • 25.
    Oscarsson, Jan
    SP Wood Technology, SP Technical Research Institute of Sweden, Videum Science Park, SE-351 96 Växjö.
    Strength grading of structural timber and EWP laminations of Norway spruce - Development potentials and industrial applications2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Machine strength grading of structural timber is a sawmill process by which considerable value is added to sawn products. The principle of such grading is that the strength of a timber member is predicted on the basis of a so called indicating property (IP) which, in general, represents an averaged value of the modulus of elasticity (MOE) measured over a board length of about one meter or more.

    A limitation of today’s grading methods is that the accuracy of strength predictions is often rather poor, which results in a low degree of utilization as regards structural potential of sawn timber. However, it has for many years been well known to researchers that much better strength predictions can be made by using localized MOE values, determined over a very short length, as IP. Still, the determination of such values in a sawmill production environment has been technically very difficult to achieve.

    In the research presented in this thesis, dot laser scanning with high resolution was utilized for detection of local fibre orientation on the surfaces of timber members. Since wood is an orthotropic material with superior structural performance in the longitudinal fibre direction, information about fibre orientation was, in combination with beam theory and measured wood material properties, used to determine the bending MOE variation along boards. By application of an IP defined as the lowest MOE found along a board, more accurate strength predictions than what is obtained by common commercial grading techniques was attained.

    The thesis also involves flatwise wet gluing of Norway spruce side boards into laminated beams. As side boards, being cut from the outer parts of a log, have excellent structural properties it was not surprising to find that the beams had high strength and stiffness, even when laminations of sawfalling quality were used. The possibility of grading boards in a wet state by means of axial dynamic excitation was investigated with a positive result and application of simple grading rules resulted in considerable improvement of beam bending strength. Finally, bending MOE variation determined on the basis of laser scanned fibre directions was used for identification of weak sections in laminations. Elimination of such sections by means of finger jointing showed that average lamination strength of a board sample could be improved by more than 35 percent.

  • 26.
    Oscarsson, Jan
    SP Sveriges Tekniska Forskningsinstitut.
    Strength grading of structural timber and EWP laminations of Norway spruce: Development potentials2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Strength grading of structural timber is a process by which value is added to sawn products. It is to the greater part carried out using machine grading based on statistical relationships between so called indicating properties and bending strength. The most frequently applied indicating property (IP) on the European market is the stiffness in terms of average modulus of elasticity (MOE) of a timber piece, although MOE is a material property that varies within timber.

    A major limitation of today’s grading methods is that the described relationships are relatively poor, which means that there is a potential for more accurate techniques. The main purpose of this research has been to initiate development of more accurate and efficient machine grading methods.

    Strength of timber is dependent on the occurrence of knots. At the same time, knot measures applied as indicating properties until today have shown to be poor predictors of strength. However, results from this research, and from previous research, has shown that not only size and position of knots but also fibre deviations in surrounding clear wood are of great importance for local stiffness and development of fracture under loading. Thus, development of new indicating properties which take account of knots as well as properties of surrounding fibres, determined on a very local scale, was considered as a possible path towards better strength grading.

    In the research, results from contact-free deformation measurements were utilized for analysis of structural behaviour of timber on both local and global level. Laser scanning was used for detection of local fibre directions projected on surfaces of pieces. Scanned information, combined with measures of density and average axial dynamic MOE, was applied for calculation of the variation of local MOE in the longitudinal board direction. By integration over cross-sections along a piece, a stiffness profile in edgewise bending was determined and a new IP was defined as the lowest bending MOE along the piece.

    For a sample of Norway spruce planks, a coefficient of determination of 0.68 was achieved between the new IP and bending strength. For narrow side boards to be used as laminations in wet-glued glulam beams, the relationship between IP and tensile strength was as high as 0.77. Since the intended use of the narrow boards was as laminations in wet-glued beams, the possibility of grading them in a wet state was also investigated. Grading based on axial dynamic excitation and weighing gave just as good results in a wet state as when the same grading procedure was applied after drying.

    It was also found that the relationship between the new IP and strength was dependent on what scale the IP was determined. Optimum was reached for moving average MOE calculated over lengths corresponding with approximately half the width of investigated pieces.

    Implementation of the new IP will result in grading that is more accurate than what is achieved by the great majority of today’s grading machines. The new method will probably also be particularly favourable for development of engineered wood products made of narrow laminations.

  • 27.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Determination of tensile strain fields in narrow Norway spruce side boards as a basis for verification of new machine strength grading methodsManuscript (preprint) (Other academic)
    Abstract [en]

    Today’s methods for machine strength grading of structural timber result, in general, in strength predictions with a rather low accuracy. A need for development of more precise methods has been identified. Application of stiffness in terms of locally determined MOE as indicating property is an evident starting point for such a process. Development of new grading procedures and models require laboratory verification, and this research investigates the possibility of using contact-free deformation measurement technique based on white-light digital image correlation (DIC) for this purpose. A sample of nine Norway spruce (Picea abies) side boards of narrow dimensions was tested in tension according to the European Standard EN 408. Simultaneously, deformations along the entire length of one of the flatwise surfaces of each board were measured using two master-slave connected DIC systems. Strain fields were subsequently calculated. To evaluate the accuracy of the measurement technique, local MOE determined traditionally, i.e. on the basis of elongations measured in accordance with EN 408, was compared with corresponding MOE values calculated on the basis of DIC deformation measurements. Acceptable agreement between compared MOEs were achieved and the accuracy of MOE values determined on the basis of the DIC technique was on the same level as requirements laid down in EN 408. However, the resolution of the information supplied by the DIC technique can, in contrast to elongations measured traditionally, be used to gain detailed knowledge regarding local MOE in evaluated boards. Therefore, based upon achieved results, in combination with certain identified potentials for measurement improvements, it is concluded that DIC technique can be used as a tool for development and laboratory verification of new strength grading methods.

  • 28.
    Oscarsson, Jan
    et al.
    SP Technical Research, Institute of Sweden, Växjö.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Improving Strength of Glulam Laminations of Norway Spruce Side Boards by Removal of Weak Sections Using Optimized Finger Jointing2014In: Materials and Joints in Timber Structures: Recent Developments of Technology / [ed] Simon Aicher; H.-W. Reinhardt ;Harald Garrecht, Springer, 2014, p. 801-811Conference paper (Refereed)
    Abstract [en]

    Recent research has shown that glulam laminations of Norway spruce side boards possess excellent structural properties. This investigation concerns the possibility of improving the performance of such laminations through elimination of weak board sections by means of finger jointing. Sections to be removed were identified using profiles of edgewise bending stiffness determined on the basis of scanned fibre angle fields on board surfaces. The difference in average tension strength and average tension stiffness, respectively, between a group of finger jointed boards and a reference group of non-jointed boards was evaluated. Joints were inserted in the first group with an average distance of 2.4 m. It was found that the finger jointing gave a considerable increase of strength (36 %), whereas the stiffness improvement was not as evident. Based upon the results, it can be assumed that application of finger jointed side board laminations will result in glulam beams with very high strength.

  • 29.
    Oscarsson, Jan
    et al.
    SP Technical Research Institute of Sweden, Sweden.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Localized modulus of elasticity in timber and its significance for the accuracy of machine strength grading2014In: Wood and Fiber Science, ISSN 0735-6161, Vol. 46, no 4, p. 489-501Article in journal (Refereed)
    Abstract [en]

    From previous research, it is well known that a localized modulus of elasticity (MOE) is a better indicating property (IP) of strength than an MOE averaged across a longer span. In this study, it was investigated to what extent the relationship, in terms of coefficient of determination (R2), between strength and localized MOE was dependent on the length across which the MOE was determined. Localized MOE was calculated with MOE profiles based on dot laser scanning of fiber directions, axial dynamic excitation, and a scheme of integration across a board's cross-section. Two board samples were investigated. Maximum R2 values, which were as high as 0.68 and 0.77, respectively, were obtained for localized MOE determined across lengths corresponding to about half the depth of the investigated boards. Consequently, application of a highly localized bending MOE as an IP will result in very competitive grading.

  • 30.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology. SP Technical Research Institute of Sweden.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Optimization of machine strength grading of structural timber by means of bending MOE profiles with high resolution2013In: Proceedings of the 18th International Nondestructive Testing and Evaluation of Wood Symposium, Madison, Wisconsin, USA, September 24−27, 2013, Madison: USDA (United States Department of Agriculture), Forest Service, Forest Products Laboratory , 2013, p. 396-403Conference paper (Refereed)
    Abstract [en]

    Most machine strength grading methods are based on rather poor statistical relationships between edgewise bending strength and modulus of elasticity (MOE), the latter determined either as flatwise bending MOE measured over a length of about one meter, or as global axial dynamic MOE. Furthermore, European Standards stipulate that local MOE in both edgewise bending and tension shall be determined at a critical section and over a length of five times the depth of the piece. However, a study of tensile strain fields determined on side board surfaces using contact-free measurement technique showed that stiffness reduction occurs very locally. This characteristic was used for development of a new indicating property (IP) defined as local edgewise bending MOE and determined by means of scanned fibre direction fields and stiffness integration over cross-sections. A maximum coefficient of determination equal to 0.77 was obtained between strength and such an IP determined over a length of about the member’s half depth.

  • 31.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Strain fields around a traversing edge knot in a spruce specimen exposed to tensile forces2010In: Proceedings of the 2010 World Conference on Timber Engineering / [ed] Ario Ceccotti, 2010Conference paper (Refereed)
    Abstract [en]

    Two-dimensional strain fields around a traversing edge knot in a spruce specimen subjected to tensile loading were measured using a contact-free measuring tchnique based on digital image correlation. The strain fields were measured by consecutive load tests in which one side of the specimen was studied during each test. The objectives were to examine to what extent the strain fields could be detected, to investigate the correlation between strain fields measured on different sides of the specimen and to analyse the strain distribution around the knot. The results show that the applied technique is very useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Both clear wood defects that could not have been identified by neither visual inspection nor scanning and the release of internal stresses were identified. The correlation between strain fields on different sides of the specimen was very good. The measurement results were compared with finite element calculations and the degree of correspondence was surprisingly good, considering the fact that the used model was fairly simple.

  • 32.
    Oscarsson, Jan
    et al.
    SP Technical Research Institute of Sweden, Videum Science Park, 351 96, Växjö, Sweden .
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Strain fields around knots in Norway spruce specimens exposed to tensile forces2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 4, p. 593-610Article in journal (Refereed)
    Abstract [en]

    Two-dimensional strain fields around knots in two Norway spruce specimens subjected to tension loading were detected using a contact-free measuring technique based on white-light digital image correlation. The first specimen included a traversing edge knot and the second one a centric knot. The development of strain fields as function of load level were measured by consecutive cyclic load tests in which one side of a specimen was studied during each test. The objectives were to examine to what extent the strain fields could be detected, to investigate the correlation between strain fields measured on different sides of a specimen, and to analyse the strain distributions around the knots. The results show that the applied technique is very useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Clear wood defects that could not have been detected by neither visual inspection nor scanning were observed and conclusions could be drawn regarding release of internal stresses. The correlations between strain fields on different sides of the specimens were excellent and the correspondence between measurement results and comparative finite element calculations was surprisingly good, considering the fact that the employed FE models were fairly simple.

  • 33.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Tensile strain fields around an edge knot in a spruce specimen2010In: Proceeedings of the Final Conference of COST Action E53, 4−7 May, Edinburgh, Scotland, 2010, 2010Conference paper (Other academic)
    Abstract [en]

    Strain fields around a traversing edge knot in a spruce specimen subjected to tensile loading were measured using a contact-free measuring technique based on digital image correlation. The strain fields were measured by consecutive load tests in which one side of the specimen was studied during each test. The objectives were to examine 1. to what extent the strain fields could be detected, 2. the correlation between strain fields on different sides of the specimen, and 3. the strain distribution around the knot. It was shown that the applied technique is very useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Both clear wood defects that could not have been detected by visual inspection or scanning and the release of internal stresses were identified. The correlation between strain fields on different sides of the specimen was very good. The correspondence between measurement results and comparative finite element calculations was surprisingly good, considering the fact that the used model was fairly simple.

  • 34.
    Oscarsson, Jan
    et al.
    SP Sveriges Tekniska Forskningsinstitut.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Determination of tensile strain fields in Norway spruce side boards using two master-slave connected contact-free measurement systems based on digital image correlation.2011In: Proceedings (Poster session) of the 17th International Nondestructive Testing and Evaluation of Wood Symposium, Sopron, Hungary, September 14-16, 2011., 2011Conference paper (Refereed)
    Abstract [en]

    A sample of nine Norway spruce side boards of narrow dimensions were tested in tension according to the standard EN 408. Strain fields were simultaneously measured using two master-slave connected measurement systems based on digital image correlation (DIC). Each system performed a separate measurement project measuring about 50% of the measurable length of each board and the results were combined, visualized and evaluated as one project using specific DIC software. The objectives were to investigate the possibility of measuring strain fields by use of multi-system measurements, to analyze the strain field distribution and to investigate the possibility of determining local modulus of elasticity (MOE) using strain field measurements. The results show that longitudinal strain fields were useful for identification of areas with reduced stiffness, that lateral board displacements, measured by the DIC systems, can be applied for identification of local defects, and that strain fields can be used for local MOE determination.

  • 35.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering. SP Technical Research Institute of Sweden.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Determining tensile strain fields in Norway spruce side boards using two master-slave connected digital image correlation systems2012Report (Other academic)
    Abstract [en]

    Machine strength grading of structural timber is in general based upon statistical relationships between bending strength and other timber properties (so called indicating properties). The overall aim of the research presented in this report was to investigate the possibility of obtaining a better understanding of such relationships using a contact-free deformation measurement technique based on digital image correlation (DIC). A sample of nine Norway spruce (Picea abies) side boards of narrow dimensions was tested in tension according to the European Standard EN 408. Deformations and strain fields along flatwise board surfaces were simultaneously determined using two master-slave connected DIC measurement systems. Each system performed a separate measurement project measuring slightly more than 50 % of the measurable length of each board and the results were combined, visualized and evaluated as one project using specific DIC software. The objectives were to investigate the possibility of identifying strain fields on timber pieces of narrow dimensions by use of multi-system measurements, to analyze the strain field distribution, and to investigate the possibility of determining local modulus of elasticity (MOE) using deformations and strain fields occurring on board surfaces. The results show that longitudinal strain fields can be useful for identification of areas with reduced stiffness and that lateral board displacements, measured by the DIC systems, can be applied for identification of local defects. Promising results were also achieved as regards local MOE determination on the basis of strain field measurements.

  • 36.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Strength grading of narrow dimension Norway spruce side boards in the wet state using first axial resonance frequency2011In: International Wood Products Journal, ISSN 2042-6445, Vol. 2, no 2, p. 108-114Article in journal (Refereed)
    Abstract [en]

    Strength grading of Norway spruce (Picea abies (L.) Karst.) side boards in the wet state was investigated. For a sample of 58 boards, density and dynamic modulus of elasticity in the axial direction, MOEdyn, were determined in the wet state. The boards were then split into two parts and the procedure of determining MOEdyn was repeated both before and after the boards were dried to a target moisture content of 12 %. Finally, tensile strength of the split boards was measured and its relationship to MOEdyn for both wet and dried split boards determined. The investigation also included an evaluation of a so called reversed lamination effect on the stiffness caused by the splitting of boards into two parts. The results show that strength grading of split boards in the wet state can give just as good results as grading performed after drying. The reversed lamination effect on the stiffness of split boards was found to be of lower order.

  • 37.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Strength grading of wet Norway spruce side boards by use of axial dynamic excitation2010In: Proceedings of the 2010 World Conference on Timber Engineering, Riva del Garda, Trento, Italy, June 20-24 / [ed] Ario Ceccotti, 2010Conference paper (Refereed)
    Abstract [en]

    Strength grading of Norway spruce side boards in the wet state was investigated. For a batch of 58 boards, densities and dynamic modulus of elasticity in the axial direction, MOEdyn, were determined in the wet state. The boards were then split into two parts and the procedure of determining MOEdyn was repeated both before and after the boards were dried to a target moisture content of 12 %. Tensile strength of the split boards was measured and its relation to MOEdyn for both split and unsplit boards determined. A so called reversed lamination effect on the stiffness caused by the splitting of boards into two parts was also evaluated. The results show that strength grading of split boards in the wet state could give just as good results as grading performed after drying. The reversed lamination effect on the stiffness of split boards was found to be of lower order.

  • 38.
    Oscarsson, Jan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Serrano, Erik
    Strength grading of wet Norway spruce side boards for use as laminations in wet-glued laminated beams2010In: Proceedings of the final conference of COST action E53, 4-7 May 2010, Edinburgh, Scotland, 2010., 2010Conference paper (Other academic)
    Abstract [en]

    Strength grading of Norway spruce side boards in the wet state was investigated. For a sample of 58 boards of dimensions 25×120×3000 mm3, density and dynamic modulus of elasticity in the axial direction, MOEdyn, were determined in the wet state. The boards were then split into two parts and the procedure of determining MOEdyn was repeated both before and after the boards were dried to a target moisture content of 12 %. Tensile strength of the split boards was finally measured and its relation to MOEdyn for both split and unsplit boards determined. The investigation also included an evaluation of a so called reversed lamination effect on the stiffness caused by the splitting of boards into two parts. The results show that strength grading of split boards in the wet state could give just as good results as grading performed after drying. The coefficient of determination between MOEdyn in wet and dried states was as high as R2=0.92, and the relation between MOEdyn in the wet state and tensile strength in the dried state, σt, was of the same order (R2=0.55) as the relation between MOEdyn in the dried state and σt (R2=0.52). Regarding the reversed lamination effect on the stiffness of split boards, it was found to be of low order.

  • 39.
    Oscarsson, Jan
    et al.
    SP Technical Research Institute of Sweden, Sweden.
    Serrano, Erik
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Identification of weak sections in glulam beams using calculated stiffness profiles based on lamination surface scanning2014In: Proceedings of the 2014 World Conference on Timber Engineering, Quebec, Canada, 10-14 August, Université Laval , 2014Conference paper (Refereed)
    Abstract [en]

    Models for estimation of structural properties of glued laminated timber (glulam) are generally based on the relationship between properties of the individual laminations and the properties of the glulam. In this investigation, a recently presented machine strength grading method based on laser scanning of fibre direction fields was applied for determination of axial modulus of elasticity (MOE) profiles along glulam laminations. These profiles were then used to calculate edgewise bending MOE (EB) profiles of glulam beams. The objectives were to investigate the relationship between position of bending failure and position of lowest EB value along investigated beams, and the relationship between the mentioned EB value and bending strength of the beams. It was found that both relationships were rather weak, whereas local bending MOE determined in accordance with EN408 was predicted with high accuracy on the basis of EB profiles.

  • 40.
    Petersson, Hans
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Bengtsson, Tomas
    Blixt, Johan
    Enquist, Bertil
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Källsner, Bo
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Serrano, Erik
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Sterley, Magdalena
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Oscarsson, Jan
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Högre värdeutbyte genom våt- och torrlimning av sågade sidobrädor till egenskapsoptimerade träprodukter för byggmarknaden2009Report (Other (popular science, discussion, etc.))
    Abstract [en]

    The purpose of this project was to investigate the possibilities to manufacture wet-glued laminated beams for load bearing applications from Norway spruce side board lamellae and by that achieve products that are difficult to obtain from the centre yield of a log and also contribute to increased profitability in the sawmill industry.

     

    Properties such as shape stability, strength and stiffness of wet glued beams with crosssectional dimensions 50×300 mm2 and lengths 4850 and 5200 mm were analysed and compared with corresponding dry glued products. The results obtained are very promising. espite the fact that the beams were produced from a batch of unsorted boards, the performed tests showed that the product has the necessary qualities to be competitive in relation to both glued laminated timber of grade L40 and structural strength graded timber of grade C35. Requirements concerning limitations for geometrical characteristics as expressed in a proposal for a new harmonised glulam standard are also met.

     

    The bond line of the wet glued beams was analysed regarding mechanical properties such as fracture energy, local strength and wood failure percentage after cyclic boiling and drying treatments. The results showed that the bonds are able to comply with requirements concerning bond lines to be used in indoor as well as outdoor constructions for structural pplications.

     

    To be able to improve the quality of boards for use as lamellae in wet glued beams, a method for scanning the slope of grain and disturbance of grain on board surfaces was also further developed and implemented.

  • 41.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Blixt, Johan
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Sterley, Magdalena
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Petersson, Hans
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Wet glued laminated beams using side boards of Norway spruce2011Report (Other academic)
    Abstract [en]

    In a previous research project, carried out during the years 2006-2008, the possibility to manufacture wet glued laminated beams using ungraded laminations of Norway spruce side boards was investigated with very promising results.

    In the project presented in this report, the performance of the wet glued beams has been further investigated and developed as regards grading of side board laminations, bond line properties and lamination finger jointing. The possibility to use scanning equipment for measurement of fibre angles and prediction of strength and stiffness of boards and beams has been studied and the procedures for technical approval and CE marking have been probed into. Studies concerning market and economy for the beams and layouts for a pilot plant and a full capacity plant, respectively, for production of such beams have also been carried out.

    The possibility to grade side boards in the wet state using axial dynamic excitation was investigated with a positive result. From such excitation, a board’s stiffness (modulus of elasticity) could be determined. Accordingly, grading criteria regarding axial stiffness, and knot size, was applied to grade side board laminations into two classes; outer and inner laminations. Strength and stiffness tests of beams manufactured from such graded laminations showed that the beams actually could challenge first rate glulam and LVL products available on the market.

    Regarding beam shape and shape stability, cross section cupping may need further attention. Even if this deformation was small, it was still visible to the naked eye. The problem could probably be overcome if the beams are dried to a moisture content of 12-14% before planing.

    Results of shear tests show that green glued bond lines can fulfil strength requirements for glulam. However, delamination requirements for service class 3 (outdoors) were not fully met. From small scale tensile testing of glued bonds it was concluded that green glued bonds with high density wood have the same tensile strength and fracture energy as dry glued bonds. For bonds with low density wood and/or small amount of adhesive, the tensile strength could be lower than for dry glued bonds, whereas the fracture energy was on a similar level.

    Strength testing of wet and dry glued finger joints demonstrated that joints glued from high density wood was significantly stronger than low density joints and that there was no significant difference between the strength of green glued joints and joints glued after drying. From X-ray measurement it was shown that the glue penetration into the wood fibres is much deeper in a green glued joint than in a joint that is glued in the dried state.

    From scanning algorithms developed within the scope of this project it is possible to obtain reasonably accurate predictions of grain-angle distributions on board surfaces as well as rather accurate descriptions of knot locations and of fibre-angle disturbances around knots. From scanning of board ends, cross section characteristics with respect to radial and tangential directions and of annual ring widths could also be determined. Finally, both board and beam stiffness were predicted from this data, with an accuracy that is comparable with the one obtained from well-reputed commercial grading systems.

  • 42.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Sterley, Magdalena
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Petersson, Hans
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Green-glued laminated beams: High performance and added value2010In: World Conference on Timber Engineering, 2010Conference paper (Refereed)
    Abstract [en]

    The work presented in this paper deals with the use of green gluing (also known as wet gluing) as a mean to overcome the difficulties in making use of side boards for structural applications. By manufacturing laminated beams from unseasoned side boards several advantages are obtained. Beams were manufactured from side boards of approximately 25 mm thickness. The board width was 120 mm. The boards were glued together with a 1-component polyurethane adhesive to form a beam cross-section of approximately 120×315 mm2. After curing, the beams were split into two halves, each approximately 55 mm wide. These 55×315 mm2 beams were then dried in a conventional kiln dryer. Finally, the beams were planed to target size, 50×300 mm2. Tests performed included beam bending tests for strength and stiffness, tests of the shape stability of the beams, tests of the integrity of the adhesive bond lines (delamination) and tests on the strength and fracture energy of the adhesive bond lines. The main results obtained show that there is a potential for the production of green-glued laminated beams with good technical performance.

  • 43.
    Serrano, Erik
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology. SP Technical Research Institute of Sweden, Borås.
    Oscarsson, Jan
    SP Technical Research Institute of Sweden, Borås.
    Sterley, Magdalena
    SP Technical Research Institute of Sweden, Borås.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Green-Glued Products for Structural Applications2014In: Materials and Joints in Timber Structures: Recent Developments of Technology, Springer, 2014, p. 45-55Conference paper (Refereed)
    Abstract [en]

    The results from bending tests on 107 laminated, green-glued, beams manufactured from Norway spruce side boards are presented. The beams were made by face gluing 21-25 mm thick boards using a commercial one-component moisture curing polyurethane adhesive. In addition to the bending test results, results from shape stability measurements after climatic cycling and bond line strength and durability test results are also presented. The results from the bending tests show that, by applying very simple grading rules, it is possible to obtain beams with high bending strength (with a 5%-percentile characteristic value of 40,1 MPa) and substantial stiffness (mean value of 14360 MPa). Also the shape stability of the beams and the strength and the durability of the interlaminar bonds were found to be satisfactory.

  • 44.
    van Blokland, Joran
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Bending properties and strain fields around knots in thermally modified timber2018In: / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge, 2018Conference paper (Refereed)
    Abstract [en]

    Thirty-two (32) boards of Norway spruce with cross-sectional dimensions of 145×45 mm2 were first tested non-destructively in a four-point static bending test, were then thermally modified according to the ThermoWood® process, and were finally tested destructively in the mentioned test set up. For one of these boards, the 2D strain fields occurring due to pure bending were recorded, both before and after thermal modification, over the surface of a knotty part of the board using a non-contact optical deformation measurement system. The objectives were to get more insight into the static bending behaviour of thermally modified timber (TMT), specifically with regard to the local and global modulus of elasticity (MOE) and their respective relationship to bending strength, and the strain development around a cluster of knots. The bending strength was significantly reduced by thermal treatment, whereas the effect on the MOEs was limited. Linear regression analyses demonstrated that bending strength of TMT can be predicted by employing stiffness as indicating property. Strain field measurements showed that at the examined levels of loading the quantity and distribution of strains in a knotty area were not influenced by thermal modification. It was therefore suggested that the influence of thermal modification on global stiffness, as well as on local stiffness around knots, is limited.

  • 45.
    van Blokland, Joran
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Källander, Björn
    Swedish Wood, Sweden.
    Evaluation of non-destructive test methods to predict bending properties of thermally modified timber2018In: 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea, World Conference on Timber Engineering (WCTE) , 2018, p. 8-Conference paper (Refereed)
    Abstract [en]

    Thermally modified wood is available through a number of manufacturers in Europe on today’s market for interior and exterior building products. Thermal modification of wood allows for improvement of dimensional stability and durability, but a considerable decrease in strength properties occurs. Despite this loss in strength, thermally modified wood shows potential to be further exploited in structures exposed to loading. For such applications, accurate prediction of its static bending behaviour is essential. This paper studies the applicability of two different non-destructive test (NDT) techniques in estimating the bending properties of thermally modified timber (TMT). The study was done on 100 Norway spruce logs. One hundred (100) boards (i.e. one from each log) were thermally modified and the mirrored 100 boards were used as controls. After modification, resonance-based and time-of-flight measurements of axial wave velocity were carried out. Subsequently, all 200 boards were bent to failure following European standard EN408. This study shows that although TMT has a lower bending strength than unmodified timber, predictions of bending strength and stiffness using the NDT techniques are possible and with sufficient accuracy. The resonance-based method gave better predictions of the bending properties of TMT in respect to time-of-flight method.

  • 46.
    van Blokland, Joran
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction2019In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 3, p. 327-340Article in journal (Refereed)
    Abstract [en]

    The market share of thermally modified wood (TMW) has increased in Europe during the past few years as an environmentally friendly and durable building product. However, TMW products of today are not permitted for use in structural applications, because the reduction in strength that is caused by thermal treatment cannot be accounted for. The purpose of this paper was to investigate the bending properties of thermally modified timber (TMT) of Norway spruce, and to explore possibilities to predict the bending properties of TMT. A sample of 100 boards from a 2X-log sawing pattern of 100 logs was thermally modified according to the ThermoWood® process, while the mirror 100 boards served as an unmodified control sample. Two non-destructive methods were employed: (1) a novel method based on scanning of fibre directions to obtain the lowest edgewise bending modulus of elasticity (MOE) along a board, and (2) a conventional excitation method to determine the first axial resonance frequency used to calculate the axial dynamic MOE. Finally, the boards were bent to failure according to European standard EN 408. Despite the fact that bending strength was reduced by 42% due to thermal treatment, the type and location of failure in TMT remained related to the presence of knots. Prediction of bending strength based on local fibre direction and axial dynamic MOE, gave coefficients of determination of 0.51 for the thermally modified boards and 0.69 for the control boards, whereas axial dynamic MOE alone gave 0.46 and 0.57, respectively. These results indicate that although Norway spruce TMT has lower bending strength compared to unmodified timber, predictions of the bending strength can be made with good accuracy.

1 - 46 of 46
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