lnu.sePublications
Change search
Link to record
Permanent link

Direct link
BETA
Olsson, Anders
Publications (10 of 68) Show all publications
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
Show others...
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 ()
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-02-22Bibliographically 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)
Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-04-17Bibliographically 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
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-03-21
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). National Institute of Forest Science (NIFoS)
Open this publication in new window or tab >>Evaluation of non-destructive test methods to predict bending properties of thermally modified timber
Show others...
2018 (English)In: 2018 World Conference on Timber Engineering (WCTE),August 20-23, 2018, Seoul, Republic of Korea, National Institute of Forest Science (NIFoS) , 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
National Institute of Forest Science (NIFoS), 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)
Conference
2018 World Conference on Timber Engineering (WCTE),August 20-23, 2018, Seoul, Republic of Korea
Note

Ej belagd 181022

Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-03-18Bibliographically 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
Show others...
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 ()
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-01-18Bibliographically 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 ()
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-12-12Bibliographically approved
Olsson, A., Pot, G., Viguier, J., Faydi, Y. & Oscarsson, J. (2018). 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.). Annals of Forest Science, 75(4), Article ID 102.
Open this publication in new window or tab >>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.)
Show others...
2018 (English)In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 75, no 4, article id 102Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Grain angle, Fibre direction, Tracheid effect, Structural timber, Longitudinal vibrations, Grade determining property
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-79603 (URN)10.1007/s13595-018-0781-z (DOI)000451958200001 ()
Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-01-18Bibliographically approved
Briggert, A., Hu, M., Olsson, A. & Oscarsson, J. (2018). Tracheid effect scanning and evaluation of in-plane and out-of-plane fiber direction in norway spruce timber. Wood and Fiber Science, 50(4), 411-429
Open this publication in new window or tab >>Tracheid effect scanning and evaluation of in-plane and out-of-plane fiber direction in norway spruce timber
2018 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 4, p. 411-429Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Society of Wood Science Technology, 2018
Keywords
Diving angle, fiber direction, knots, laser scanning, Norway spruce, tracheid effect
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-78841 (URN)000448771800005 ()
Available from: 2018-11-15 Created: 2018-11-15 Last updated: 2018-11-15Bibliographically approved
Briggert, A., Hu, M., Olsson, A. & Oscarsson, J. (2018). Tracheid effect scanning and evaluation of in-plane and out-of-plane fibre direction in Norway spruce using. Wood and Fiber Science, 50(4), 411-429
Open this publication in new window or tab >>Tracheid effect scanning and evaluation of in-plane and out-of-plane fibre direction in Norway spruce using
2018 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, no 4, p. 411-429Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Society of Wood Socience and Technology, 2018
National Category
Wood Science
Identifiers
urn:nbn:se:lnu:diva-69632 (URN)
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-04-17Bibliographically approved
Olsson, A. & Oscarsson, J. (2017). Strength grading on the basis of high resolution laser scanning and dynamic excitation: a full scale investigation of performance. European Journal of Wood and Wood Products, 75(1), 17-31
Open this publication in new window or tab >>Strength grading on the basis of high resolution laser scanning and dynamic excitation: a full scale investigation of performance
2017 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 75, no 1, p. 17-31Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
Springer, 2017
National Category
Construction Management Wood Science
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-59045 (URN)10.1007/s00107-016-1102-6 (DOI)000392318500002 ()
Available from: 2016-12-16 Created: 2016-12-16 Last updated: 2017-11-29Bibliographically approved
Organisations

Search in DiVA

Show all publications