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Hu, Min
Publications (10 of 14) 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
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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: 2019-08-29Bibliographically 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: 2019-08-29Bibliographically 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: 2019-08-29Bibliographically approved
Hu, M. (2018). Studies of the fibre direction and local bending stiffness of Norway spruce timber: for application on machine strength grading. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Studies of the fibre direction and local bending stiffness of Norway spruce timber: for application on machine strength grading
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Machine strength grading is a production process in the sawmill industry used to grade sawn timber boards into different strength classes with specific characteristic values of the bending strength, modulus of elasticity (MOE) and density. These properties are called grade determining properties. Each of these is predicted on the basis of a statistical relationship between the property and a so-called indicating property (IP), which is based on non-destructively assessed board properties. In most cases, the prediction of strength is crucial for the grading. The majority of commercial grading machines rely on a statistical relationship of strength to an IP, which is either a global dynamic MOE or an averaged flatwise bending MOE measured over a board length of about one meter. The problem of today’s machine strength grading is that the accuracy of the strength prediction is rather poor with a coefficient of determination of about R2 ≈ 0.5 − 0.6. One consequence of this is that much of the strength potential of timber is unused.

The intention of this research is to contribute to a long-term goal, which is development of a method for prediction of bending strength that is more accurate than the methods available today. The research relies on three hypotheses. First, accurate prediction of bending strength can be achieved using an IP that is a localized MOE value (determined over a short length) that represents the lowest local bending stiffness of a board. Second, knowledge of the local bending stiffness with high resolution along a board’s longitudinal direction can be established on the basis of fibre direction within the board in combination with dynamic MOE. Third, fibre directions in the interior of a board can be determined by application of fibre angle models utilizing data of fibre directions on the board’s surfaces obtained from tracheid effect scanning. Following these hypotheses, this work has included laboratory investigations of local material directions, and development of models for fibre directions of the interior of boards. The work also included application of one-dimensional (1D) analytical models and three-dimensional (3D) finite element models of individual boards for the mechanical behaviour, analysis of mechanical response of boards based on experiments and based on the suggested models. Lastly, the suggested models were evaluated by comparisons of calculated and experimentally determined local bending stiffness along boards, and of predicted and experimentally determined bending strength.

The research contributes with in-depth knowledge on local fibre directions close to knots, and detailed information on variation of the local bending stiffness in boards. Moreover, fibre angle models for fibre directions in the interior of boards are presented. By application of the fibre angle models in the 3D model of the whole board, the local bending stiffness along timber boards can be determined over a very short length (l < 50 mm). A comparison with results determined on an experimental basis show a very close similarity implying that the applied models are sufficient to capture the variation of local bending stiffness, caused by knots and fibre distortions, with very high accuracy. Furthermore, it is found that by means of IPs derived using the suggested models, bending strength can be predicted with high accuracy. For a timber sample comprising 402 boards, such IPs results in coefficient of determination as high as R2 = 0.73. However, using IPs based on the 3D finite element model did not improve the R2 value achieved when using the IPs based on the 1D model.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2018
Series
Linnaeus University Dissertations ; 307/2018
Keywords
digital image correlation, diving angle, fibre angle, grain angle, indicating property, laser scanning, modulus of elasticity, tracheid effect
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-69636 (URN)978-91-88761-13-2 (ISBN)978-91-88761-14-9 (ISBN)
Public defence
2018-02-01, N1017, Hus N, Växjö, 10:00
Opponent
Supervisors
Available from: 2018-01-10 Created: 2018-01-09 Last updated: 2018-01-17Bibliographically 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 Science and Technology, 2018
Keywords
Diving angle, fiber direction, knots, laser scanning, Norway spruce, tracheid effect
National Category
Wood Science
Identifiers
urn:nbn:se:lnu:diva-69632 (URN)000448771800005 ()2-s2.0-85055887329 (Scopus ID)
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-07-09Bibliographically approved
Hu, M., Olsson, A., Johansson, M., Oscarsson, J. & Serrano, E. (2016). Assessment of a Three-Dimensional Fiber Orientation Model for Timber. Wood and Fiber Science, 48(4), 271-290
Open this publication in new window or tab >>Assessment of a Three-Dimensional Fiber Orientation Model for Timber
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2016 (English)In: Wood and Fiber Science, ISSN 0735-6161, Vol. 48, no 4, p. 271-290Article in journal (Refereed) Published
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.

National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-57467 (URN)000388430500006 ()
Available from: 2016-10-19 Created: 2016-10-19 Last updated: 2018-01-09Bibliographically approved
Briggert, A., Hu, M., Olsson, A. & Oscarsson, J. (2016). Evaluation of three dimensional fibre orientation in Norway spruce using a laboratory laser scanner. In: WCTE 2016: World Conference on Timber Engineering. Paper presented at World Conference on Timber Engineering (WCTE), Vienna, August 22-25, 2016. Vienna: Vienna University of Technology
Open this publication in new window or tab >>Evaluation of three dimensional fibre orientation in Norway spruce using a laboratory laser scanner
2016 (English)In: WCTE 2016: World Conference on Timber Engineering, Vienna: Vienna University of Technology , 2016Conference paper, Published 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.

Place, publisher, year, edition, pages
Vienna: Vienna University of Technology, 2016
Keywords
Fibre orientation, knots, laser scanning, Norway spruce, tracheid effect
National Category
Other Civil Engineering
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-74996 (URN)2-s2.0-85010988868 (Scopus ID)9783903039001 (ISBN)
Conference
World Conference on Timber Engineering (WCTE), Vienna, August 22-25, 2016
Available from: 2018-06-04 Created: 2018-06-04 Last updated: 2019-08-12Bibliographically approved
Hu, M., Briggert, A., Olsson, A., Johansson, M., Oscarsson, J. & Säll, H. (2016). Three dimensional growth layer geometry and fibre orientation around knots: a laboratory investigation. In: Eberhardsteiner, W. Winter, A. Fadai, M. Pöll (Ed.), Proceedings of WCTE 2016 World Conference on Timber Engineering: . Paper presented at World Conference on Timber Engineering (WCTE 2016), August 22-25, 2016, Vienna, Austria. Vienna: Vienna University of Technology
Open this publication in new window or tab >>Three dimensional growth layer geometry and fibre orientation around knots: a laboratory investigation
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2016 (English)In: Proceedings of WCTE 2016 World Conference on Timber Engineering / [ed] Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna: Vienna University of Technology , 2016Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Vienna: Vienna University of Technology, 2016
National Category
Building Technologies Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-74977 (URN)2-s2.0-85010934380 (Scopus ID)
Conference
World Conference on Timber Engineering (WCTE 2016), August 22-25, 2016, Vienna, Austria
Available from: 2018-06-04 Created: 2018-06-04 Last updated: 2019-08-13Bibliographically approved
Hu, M., Olsson, A., Johansson, M. & Oscarsson, J. (2015). An Application of 3D Fiber Angles Identified through Laser Scanning Based on Tracheid Effect. In: : . Paper presented at 19th international nondestructive testing and evaluation of wood symposium. Rio de Janeiro, Brazil, 22-25 Sept. USDA Forest Service, Forest Products Laboratory
Open this publication in new window or tab >>An Application of 3D Fiber Angles Identified through Laser Scanning Based on Tracheid Effect
2015 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
USDA Forest Service, Forest Products Laboratory, 2015
Series
General Technical Report ; FPL-GTR-239
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-50649 (URN)
Conference
19th international nondestructive testing and evaluation of wood symposium. Rio de Janeiro, Brazil, 22-25 Sept
Note

Ej belagd 20160408

Available from: 2016-03-12 Created: 2016-03-12 Last updated: 2016-12-15Bibliographically approved
Hu, M., Johansson, M., Olsson, A., Oscarsson, J. & Enquist, B. (2015). Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation. European Journal of Wood and Wood Products, 73(1), 17-27
Open this publication in new window or tab >>Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation
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2015 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 1, p. 17-27Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2015
National Category
Construction Management
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-38089 (URN)10.1007/s00107-014-0851-3 (DOI)000347688100002 ()2-s2.0-84920552031 (Scopus ID)
Available from: 2014-11-07 Created: 2014-11-07 Last updated: 2018-01-09Bibliographically approved
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