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Prediction of bending strength of thermally modified timber using high-resolution scanning of fibre direction
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. (GoFP)ORCID iD: 0000-0001-6756-3682
Linnaeus University, Faculty of Technology, Department of Building Technology.ORCID iD: 0000-0002-6410-1017
Linnaeus University, Faculty of Technology, Department of Building Technology.ORCID iD: 0000-0002-8513-0394
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. (GoFP)ORCID iD: 0000-0002-6909-2025
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. Vol. 77, no 3, p. 327-340
Keywords [en]
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: urn:nbn:se:lnu:diva-80374DOI: 10.1007/s00107-019-01388-wISI: 000463863700001Scopus ID: 2-s2.0-85064163799OAI: oai:DiVA.org:lnu-80374DiVA, id: diva2:1287601
Funder
Swedish Research Council Formas, 942-2015-722Stora EnsoAvailable from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-10-17Bibliographically approved

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van Blokland, JoranOlsson, AndersOscarsson, JanAdamopoulos, Stergios

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van Blokland, JoranOlsson, AndersOscarsson, JanAdamopoulos, Stergios
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Department of Forestry and Wood TechnologyDepartment of Building Technology
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European Journal of Wood and Wood Products
Building TechnologiesWood Science

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