| 1. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Evaluation of three dimensional fibre orientation in Norway spruce using a laboratory laser scanner
- 2016
-
Ingår i: WCTE 2016. - Vienna : Vienna University of Technology. - 9783903039001
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
|
| 2. |
- Briggert, Andreas, 1984-
(författare)
-
Modelling and strength grading of structural timber and glulam lamellae on the basis of optical scanning and dynamic excitation
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Machine strength grading of sawn timber is a sawmill process in which density, modulus of elasticity (MOE) and bending or tensile strength are predicted such that the timber can be assigned to strength classes. The predictions of these properties are performed using one or several so-called indicating properties (IPs), which represent a board property, or combination of board properties, measured non-destructively. A limitation of today’s strength grading is that the IPs applied in the industry for prediction of strength, in general, are based on rather weak statistical relationships between IPs and strength properties, which in turn results in poor material utilisation. It is well known that the strength of sawn timber is associated with the presence of knots and their surrounding fibre disorientations. Local fibre direction at surfaces of softwood can be determined by means of the light scattering that occur when a wood surface is illuminated by a dot-laser, i.e. by application of the so-called tracheid effect. Lately, IPs based on such measurements have been developed, and some of the suggested IPs have a strong statistical relationship to bending strength. The purposes of the research presented in this thesis are to contribute with knowledge of possibilities and limitations of the tracheid effect and of data of fibre directions in the vicinity of knots, to evaluate if information of fibre directions at surfaces of Norway spruce sawn timber can be used to achieve a better material utilisation of glulam lamellae and finger-jointed timber, and to provide insight regarding the grading regulations in Europe. Results presented herein show that knots and fibre direction within the interior of boards can be modelled on the basis of data obtained by means of the tracheid effect, but also that a previously proposed method to determine out-of-plane fibre angles gives poor accuracy. As regards grading of glulam lamellae, an IP based on fibre directions and dynamic MOE is proposed for prediction of tensile strength. The latter is used when grading glulam lamellae. Application of the proposed IP resulted in substantially increased yield in strength classes. It is also shown that this IP is applicable for boards with sawn as well as with planed surface finish. Regarding current regulations for machine strength grading in Europe, results indicate that grading based on global board properties give higher yield than what is appropriate.
|
|
| 3. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Predicting tensile strength in sawn timber using in plane fibre directions and dynamic modulus of elasticity
- 2019
-
Ingår i: Proceedings. - Madison, WI : U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. ; , s. 242-249
-
Konferensbidrag (refereegranskat)abstract
- Machine strength grading of sawn timber is based on the relationship between indicating properties (IPs) and so-called grade determining properties (GDPs). The former are calculated using board properties measured non-destructively whereas the latter are determined by destructive tests. For T-classes, applied GDPs are tensile strength, density and modulus of elasticity in tension. Efficient utilisation of sawn timber thus require IPs predicting the GDPs with high accuracy. This study aims at deriving an IP for tensile strength in the board direction using multiple linear regression based on board properties and at applying this new IP in a grading method and calculating corresponding yield in T-classes. The nondestructive and destructive testing were performed for more than 900 boards of Norway spruce originating from Finland, Norway and Sweden. Board properties necessary for calculating this new IP were density, axial resonance frequency and in-plane fibre directions at the board’s longitudinal surfaces, and these properties were determined using X-ray scanning, dynamic excitation and optical scanning, respectively. A high coefficient of determination between IP and tensile strength was obtained, implying that this new IP predicts tensile strength better than IPs used in industry today. Furthermore, since only a part of the board is destructively tested, settings can be determined using either IPs calculated for the tested part of the boards or IPs calculated for the entire length of the boards. Employing the latter resulted in higher yields but lower coefficients of determination. Several grading machines on the market are based on this approach.
|
|
| 4. |
|
|
| 5. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Prediction of tensile strength of sawn timber : models for calculation of yield in strength classes
- 2020
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 53:3, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- In Europe, strength classes for structural timber and glulam lamellae are defined by minimum requirements of characteristic values of the grade determining properties (GDPs). To fulfill these minimum requirements of characteristic values in the daily production at sawmills, indicating properties (IPs) to GDPs are calculated for each board and based on predetermined limits of the IPs (settings) boards are assigned to the graded class, or rejected. The aims of this paper is to address and discuss two different grading procedures/models that can be applied when settings for IPs that reflects a local board property are derived and to show how the yield in different T-classes depend on the model applied. It is not always that a board’s weakest cross-section is evaluated in a destructive test. An IP representing a local board property can therefore be determined either as the lowest property of the tested part of the board or as the lowest property along the whole board when applied to derive settings. Results presented in this paper show that too low settings and too large yields are obtained when the latter IP is employed. Similarly, IPs reflecting a global board property, like axial dynamic MOE, also give too low settings and too high yield in strength classes. This paper is the second and closing part of a series of two paper on prediction of GDPs and procedures for grading sawn timber into T-classes.
|
|
| 6. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Prediction of tensile strength of sawn timber : definitions and performance of indicating properties based on surface laser scanning and dynamic excitation
- 2020
-
Ingår i: Materials and Structures. - : Springer. - 1359-5997 .- 1871-6873. ; 53:3, s. 1-20
-
Tidskriftsartikel (refereegranskat)abstract
- The presence of wood irregularities such as knots are decisive for the mechanical properties of sawn timber, and efficient utilisation of timber requires methods by which grade determining properties can be predicted with high accuracy. In the glulam and sawmilling industries today, there is a potential and a need for more accurate prediction methods. This paper concerns the performance of a set of indicating properties calculated by means of data from surface laser scanning, dynamic excitation and X-ray scanning, the latter used to obtain boards’ average density. A total number of 967 boards of Norway spruce originating from Finland, Norway and Sweden were used to determine statistical relationships between the indicating properties and the grade determining properties used to grade sawn timber into T-classes. Results show that the indicating properties give coefficients of determination to tensile strength as high as 0.70. Furthermore, results also show that laser scanning of boards with sawn surface finish give basis for almost as accurate grading as what scanning of planed boards do. The results imply that more accurate grading of timber into T-classes is possible by application of a new set of indicating properties. This paper is part one of a series of two papers. In the second paper, two models to derive settings and calculate yield in different strength classes using the indicating properties presented herein are compared and discussed.
|
|
| 7. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Three dimensional knot models based on surface laser scanning
- 2015
-
Ingår i: Proceedings 19th International Nondestructive Testing and Evaluation of Wood Symposium Rio de Janeiro, Brazil, 23-25 September, 2015.. - Madison, USA : USDA, Forest Service, Forest Products Laboratory. ; , s. 83-90, s. 83-90
-
Konferensbidrag (refereegranskat)abstract
- Most machine strength grading methods of today result in limited grading accuracy and poor yield in higher strength classes. A new and more accurate grading method utilizing laser scanning technique to determine the in-plane fibre directions on board surfaces was recently approved for the European market. In this, however, no consideration is taken to the out-of-plane direction of the fibres. A first step towards scanning-based 3D models of the fibre orientation is the establishment of 3D knot models. In this investigation laser scanning was used to identify knot surfaces on longitudinal board surfaces. By means of developed algorithms knot surfaces that belonged to the same physical knot visible on different sides of the board were identified. All knots with surface areas larger than 100 mm2 were correctly identified and modeled in 3D. This is a promising starting point for further development of the new grading method based on laser scanning.
|
|
| 8. |
- Briggert, Andreas, 1984-, et al.
(författare)
-
Tracheid effect scanning and evaluation of in-plane and out-of-plane fibre direction in Norway spruce using
- 2018
-
Ingår i: Wood and Fiber Science. - : Society of Wood Science and Technology. - 0735-6161. ; 50:4, s. 411-429
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 9. |
- Hu, Min, 1979-, et al.
(författare)
-
Growth layer and fibre orientation around knots in Norway spruce : a laboratory investigation
- 2018
-
Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225. ; 52:1, s. 7-27
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 10. |
|
|
| 11. |
- Lemke, Ulf, et al.
(författare)
-
New Criteria For Visual Strength Grading of Sawn Timber From Birch Grown In Sweden
- 2023
-
Ingår i: World Conference on Timber Engineering (WCTE 2023). - : World Conference on Timber Engineering (WCTE). - 9781713873273 ; , s. 740-749
-
Konferensbidrag (refereegranskat)abstract
- Today there is no standard for strength grading and CE-marking sawn timber of Birch grown in Sweden, which makes it impossible to use this material as structural timber. Internationally, there are standards for visual grading of hardwood in several European countries. However, these standards may not be used to classify Birch timber grown in Sweden without having been tested and verified to meet the standard's requirements. In a project (BizWOOD) run by RISE, 600 pieces of sawn birch wood from Sweden is visually graded and strength tested. The project aims to result in grading rules for birch, either by using international standards or where international standards will be used as references for the identification of defects that will be included in the grading model. This paper summarizes parts of the BizWOOD project and includes 1) description of sampling and timber origin, 2) visual grading according to international standards, 3) strength testing of the material, 4) evaluation of mechanical characteristics, 5) evaluation of grading techniques.
|
|
| 12. |
- Olsson, Anders, 1973-, et al.
(författare)
-
Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect
- 2019
-
Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 77:6, s. 1063-1077
-
Tidskriftsartikel (refereegranskat)abstract
- Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow forre-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certainmargins are required between knots and a finger joint in structural timber, which means that a considerable amount of clearwood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducingthe quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) applicationof 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 requirementwhen 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 diameterwhen the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect partsof members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledgeof fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increasethe quality of finger joints.
|
|
