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Lukacevic, M., Kandler, G., Hu, M., Olsson, A. & Füssl, J. (2019). A 3D model for knots and related fiber deviations in sawn timber for prediction of mechanical properties of boards. Materials & design, 166, 1-18, Article ID 107617.
Open this publication in new window or tab >>A 3D model for knots and related fiber deviations in sawn timber for prediction of mechanical properties of boards
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2019 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 166, p. 1-18, article id 107617Article in journal (Refereed) Published
Abstract [en]

Increased use of wood has led to complex timber constructions and new types of engineered wood products. In simulations, however, mainly simplified models are used to describe this material with its strongly varying properties. Therefore, reliable prediction tools for mechanical properties of wooden boards are needed. Those varying properties mainly originate from knots and fiber deviations. Thus, we use fiber directions on board surfaces to reconstruct knots within boards. Combined with a fiber deviation model we assess our model with experiments on different levels: fiber directions on surfaces, strain fields and bending stiffness profiles.

This model now better describes fiber patterns near knots and knot clusters. Also, we showed that accurate modeling of the pith is important to avoid large regions of incorrect fiber deviations. Furthermore, modified knot stiffness properties were successfully used to consider pre-cracked knots. Finally, we obtained multiple bending stiffness profiles, where we showed that even local effects can be simulated accurately.

We anticipate our tool to be a starting point for improving strength grading models, where effects of knot configurations can be studied more easily than with experiments alone. Furthermore, the presented improvements will render the simulation of realistic failure mechanisms in wooden boards more likely.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-80009 (URN)10.1016/j.matdes.2019.107617 (DOI)000458260700015 ()2-s2.0-85060758980 (Scopus ID)
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-10-17Bibliographically approved
Habite, T., Olsson, A. & Oscarsson, J. (2019). Automatic detection of pith location along boards of Norway spruce on the basis of data from optical scanning of longitudinal surfaces. In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019 (pp. 64-64). Växjö: Lnu Press
Open this publication in new window or tab >>Automatic detection of pith location along boards of Norway spruce on the basis of data from optical scanning of longitudinal surfaces
2019 (English)In: 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, Oral presentation with published abstract (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.

Place, publisher, year, edition, pages
Växjö: Lnu Press, 2019
Keywords
Fibre orientation - modeling and grading of wood
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering); Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89351 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from material properties to Timber Structures, Växjö, Sweden, June 17-19, 2019
Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-10-17Bibliographically approved
Habite, T., Olsson, A. & Oscarsson, J. (2019). Detection of Pith Location of Norway Spruce Timber Boards on the Basis of Optical Scanning. In: Xiping Wang; Udo H. Sauter; Robert J. Ross (Ed.), Proceedings, 21st international nondestructive testing and evaluation of wood symposium: Freiburg, Germany. Paper presented at 21st International Nondestructive Testing and Evaluation of Wood Symposium, Freiburg, Germany, September 24-27, 2019 (pp. 268-275). Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory
Open this publication in new window or tab >>Detection of Pith Location of Norway Spruce Timber Boards on the Basis of Optical Scanning
2019 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
Madison, U.S.A: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, 2019
Series
General Technical Report ; FPL-GTR-272
Keywords
pith location, annual ring width, continuous wavelet transform
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering); Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89385 (URN)
Conference
21st International Nondestructive Testing and Evaluation of Wood Symposium, Freiburg, Germany, September 24-27, 2019
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2019-10-17Bibliographically approved
Olsson, A., Briggert, A. & Oscarsson, J. (2019). Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect. European Journal of Wood and Wood Products, 77(6), 1063-1077
Open this publication in new window or tab >>Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect
2019 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 6, p. 1063-1077Article in journal (Refereed) Published
Abstract [en]

Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow forre-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certainmargins are required between knots and a finger joint in structural timber, which means that a considerable amount of clearwood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducingthe quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) applicationof methods of colour scanning and tracheid effect scanning to detect knots and grain disturbance on board surfaces, and (2)interpretation of the requirements of EN 15497 regarding where finger joints may be placed. The standard’s requirementwhen producing finger joints is that the minimum distance between a knot and a finger joint is three times the knot diameter.The standard allows for the minimum distance between a knot and a finger joint to be shortened to 1.5 times the diameterwhen the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect partsof members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledgeof fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increasethe quality of finger joints.

Place, publisher, year, edition, pages
Springer, 2019
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-89702 (URN)10.1007/s00107-019-01465-0 (DOI)000490859500002 ()
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-12-06
Gečys, T., Bader, T. K., Olsson, A. & Kajėnasa, S. (2019). Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections. Construction and Building Materials, 228, Article ID 116702.
Open this publication in new window or tab >>Influence of the rope effect on the slip curve of laterally loaded, nailed and screwed timber-to-timber connections
2019 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 228, article id 116702Article in journal (Refereed) Published
Abstract [en]

Timber-to-timber connections with different types of screws and nails were experimentally investigated with the aim to quantify the contribution of their axial resistance to their slip and their lateral load bearing capacity, which is the so-called rope effect in dowel-type timber connections. Five different types of screws, including partly threaded and double-threaded screws, as well as three types of nails, including smooth round nails, twisted square-sectioned and grooved nails, were used in the experimental investigations in order to cover a broad range of axial resistance of fasteners. Their behavior was tested in single shear and double shear timber-to-timber connections. In addition to connection testing, system and material properties were experimentally determined. This gave input to design equations and allowed for a comparison of the mechanical model in the European design standard for timber structures, Eurocode 5, with experiments. Experiments indicate that the initial slip modulus in the quasi-elastic domain is not influenced by withdrawal capacity of the fastener, while it shows pronounced influence on load-carrying capacity and the nonlinear shape of the slip curve of the connection at larger deformations. Rope effect strongly depends on fastener properties. High axial resistance of fasteners leads to highly non-linear slip curves and design equations tended to underestimate strength including the rope effect up to a displacement limit of 15 mm. Experimentally observed failure modes were well in line with the theoretical failure modes predicted by the design model. The provided experimental results are motivation for improvement of design models and development of analytical and numerical models that account for nonlinear effects in the complex load transfer mechanism.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Rope effect; Dowel-type connection; Nonlinear slip; Ductility; Stiffness
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89192 (URN)10.1016/j.conbuildmat.2019.116702 (DOI)
Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-10-17Bibliographically approved
van Blokland, J., Olsson, A., Oscarsson, J. & Adamopoulos, S. (2019). Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction. European Journal of Wood and Wood Products, 77(3), 327-340
Open this publication in new window or tab >>Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction
2019 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 3, p. 327-340Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
axial dynamic excitation, fibre angle, four-point bending, grade determining properties, machine strength grading, ThermoWood®, tracheid effect
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-80374 (URN)10.1007/s00107-019-01388-w (DOI)000463863700001 ()2-s2.0-85064163799 (Scopus ID)
Funder
Swedish Research Council Formas, 942-2015-722Stora Enso
Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-10-17Bibliographically approved
van Blokland, J., Adamopoulos, S., Olsson, A. & Oscarsson, J. (2018). Bending properties and strain fields around knots in thermally modified timber. In: Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge (Ed.), : . Paper presented at 9th European Conference on Wood Modification (ECWM), 17-18 September 2018, Bugers’ Zoo, Arnhem, The Netherlands.
Open this publication in new window or tab >>Bending properties and strain fields around knots in thermally modified timber
2018 (English)In: / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge, 2018Conference paper, Published 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.

Keywords
four-point bending, modulus of elasticity, Norway spruce, strain measurement, strength prediction, ThermoWood®
National Category
Wood Science Building Technologies
Identifiers
urn:nbn:se:lnu:diva-77974 (URN)
Conference
9th European Conference on Wood Modification (ECWM), 17-18 September 2018, Bugers’ Zoo, Arnhem, The Netherlands
Note

Ej belagd 190524

Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-10-17Bibliographically approved
van Blokland, J., Adamopoulos, S., Olsson, A., Oscarsson, J. & Källander, B. (2018). Evaluation of non-destructive test methods to predict bending properties of thermally modified timber. In: 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea: . Paper presented at 2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea (pp. 8). World Conference on Timber Engineering (WCTE)
Open this publication in new window or tab >>Evaluation of non-destructive test methods to predict bending properties of thermally modified timber
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2018 (English)In: 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, Published 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.

Place, publisher, year, edition, pages
World Conference on Timber Engineering (WCTE), 2018
Keywords
ThermoWood®, resonance method, time-of-flight method, four-point bending, Norway spruce
National Category
Wood Science Building Technologies
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-77976 (URN)2-s2.0-85058158034 (Scopus ID)
Conference
2018 World Conference on Timber Engineering (WCTE), August 20-23, 2018, Seoul, Republic of Korea
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-10-17Bibliographically approved
Hu, M., Briggert, A., Olsson, A., Johansson, M., Oscarsson, J. & Säll, H. (2018). Growth layer and fibre orientation around knots in Norway spruce: a laboratory investigation. Wood Science and Technology, 52(1), 7-27
Open this publication in new window or tab >>Growth layer and fibre orientation around knots in Norway spruce: a laboratory investigation
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2018 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 1, p. 7-27Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-69631 (URN)10.1007/s00226-017-0952-3 (DOI)000419587400001 ()2-s2.0-85028777374 (Scopus ID)
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-10-17Bibliographically approved
Hu, M., Olsson, A., Johansson, M. & Oscarsson, J. (2018). Modelling local bending stiffness based on fibre orientation in sawn timber. European Journal of Wood and Wood Products, 76(6), 1605-1621
Open this publication in new window or tab >>Modelling local bending stiffness based on fibre orientation in sawn timber
2018 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 6, p. 1605-1621Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering; Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-69634 (URN)10.1007/s00107-018-1348-2 (DOI)000447204700004 ()2-s2.0-85053440591 (Scopus ID)
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-10-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6410-1017

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