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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: 2019-08-29Bibliographically 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: 2019-05-24Bibliographically 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: 2019-05-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6756-3682

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