An algorithm for the geometric reconstruction of knots within timber boards based on fibre angle measurements

Kandler, Georg; Lukacevic, Markus; Füssl, Josef

doi:10.1016/j.conbuildmat.2016.08.001

Cited by 42 publications

(15 citation statements)

References 29 publications

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“…A threshold was set for the angle between the determined local fibre direction and the longitudinal direction of the board such that positions on the wood surface where the determined angle exceeded a threshold of 56° (Briggert et al 2016) were regarded as being within a knot. In both studies (Briggert et al 2016 andKandler et al 2016), knots were identified on surfaces with reasonable but not excellent accuracy with respect to size and shape of knots. The reasons for the limited accuracy being (1) the limited spatial resolution of the laser dot grid and (2) the uncertainty of the relationship between the roundness of the laser dots and the assessed diving angle.…”

Section: Detection Of Knots On the Basis Of Tracheid Effect Scanningmentioning

confidence: 94%

“…The shape of a dot of light, which on a surface of an isotropic material would have been circular in shape, becomes, on a softwood surface, stretched out in the direction of the fibres and the major axis of the thus stretched, elliptically shaped spot indicates the local in-plane fibre direction. Attempts to detect knots on the basis of data from tracheid effect scanning have been presented both by Briggert et al (2016) and by Kandler et al (2016). In both studies, light dots on the wood surfaces from a laser source were assessed both with respect to the main direction of the elliptically shaped light spots, from which the in-plane fibre directions were obtained, and with respect to the roundness of the light spots.…”

Section: Detection Of Knots On the Basis Of Tracheid Effect Scanningmentioning

confidence: 99%

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Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect

2019

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Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow for re-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certain margins are required between knots and a finger joint in structural timber, which means that a considerable amount of clear wood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducing the quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) application of 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 requirement when 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 diameter when the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4 to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect parts of members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledge of fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increase the quality of finger joints.

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Section: Detection Of Knots On the Basis Of Tracheid Effect Scanningmentioning

confidence: 94%

Section: Detection Of Knots On the Basis Of Tracheid Effect Scanningmentioning

confidence: 99%

Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect

2019

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“…In the work presented by Lukacevic and Füssl (2014), knot positions and knot geometries were detected by digital image processing of images of the board surfaces. Further attempts and algorithms to model knots in 3D within boards, based on the detection of knots on wood surfaces, have been presented by Briggert et al (2016a) and Kandler et al (2016). The results obtained were in both cases quite accurate regarding size and position of knots but not regarding the precise shape of the knots.…”

Section: Models For Fibre Orientation In the Vicinity Of Knotsmentioning

confidence: 99%

Modelling local bending stiffness based on fibre orientation in sawn timber

Olsson

Johansson

et al. 2018

Eur. J. Wood Prod.

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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.

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“…For determining the mechanical properties of individual timber boards, data acquired through laser scanning is used [4]. Based on the obtained data, the 3D knot geometry is reconstructed automatically [5]. For this, knot areas are identified based on measured fibre angles and are grouped to knot groups.…”

Section: Materials Model For Timber Boardsmentioning

confidence: 99%

Stochastic engineering framework for timber structural elements

Kandler

Lukacevic

Wolff

et al. 2018

Beton und Stahlbetonbau

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Due to the natural growth process of trees, the resulting wooden boards show a high amount of random fluctuation in their mechanical properties. In this work, a framework able to consider the impact of random stiffness fluctuations of wooden boards on the performance of glued laminated timber (GLT) is presented. A 2D finite element model is employed to depict the interactions between individual laminations and is integrated into a commercial robustness analysis and optimisation software package. The mechanical properties of each board are obtained during the grading process and are condensed into so‐called stiffness and strength profiles. Based thereon, a probabilistic material model is developed for the random generation of an arbitrary number of stiffness and strength profiles. On basis of the probabilistic material model and the mechanical FE model, the sensitivity to changes in the design can be explored. Subsequently, the optimal design parameters of the user‐defined structure are identified. An exemplary application scenario shows the workflow for determining the optimum hole dimensions and location in a GLT beam. The material model indicates large scatter in the mechanical properties, leading to conservative results. Nonetheless, the example shows the strengths of the employed workflow from sensitivity analysis to best designs.

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An algorithm for the geometric reconstruction of knots within timber boards based on fibre angle measurements

Cited by 42 publications

References 29 publications

Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect

Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect

Modelling local bending stiffness based on fibre orientation in sawn timber

Stochastic engineering framework for timber structural elements

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