| 1. |
- Berndt, Sonja I., et al.
(författare)
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Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
- 2013
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:5, s. 501-U69
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Tidskriftsartikel (refereegranskat)abstract
- Approaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups.
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| 2. |
- Benrick, Anna, 1979, et al.
(författare)
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Autonomic nervous system activation mediates the increase in whole-body glucose uptake in response to electroacupuncture
- 2017
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Ingår i: Faseb Journal. - : Federation of American Societies for Experimental Biology. - 0892-6638 .- 1530-6860. ; 31:8, s. 3288-3297
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Tidskriftsartikel (refereegranskat)abstract
- A single bout of low-frequency electroacupuncture (EA) causing muscle contractions increases whole-body glucose uptake in insulin-resistant rats. We explored the underlying mechanism of this finding and whether it can be translated into clinical settings. Changes in glucose infusion rate (GIR) were measured by euglycemic-hyperinsulinemic clamp during and after 45 min of low-frequency EA in 21 overweight/obese women with polycystic ovary syndrome (PCOS) and 21 controls matched for age, weight, and body mass index (experiment 1) and in rats receiving autonomic receptor blockers (experiment 2). GIR was higher after EA in controls and women with PCOS. Plasma serotonin levels and homovanillic acid, markers of vagal activity, decreased in both controls and patients with PCOS. Adipose tissue expression of pro-nerve growth factor (proNGF) decreased, and the mature NGF/proNGF ratio increased after EA in PCOS, but not in controls, suggesting increased sympathetic-driven adipose tissue metabolism. Administration of alpha-/beta-adrenergic receptor blockers in rats blocked the increase in GIR in response to EA. Muscarinic and dopamine receptor antagonist also blocked the response but with slower onset. In conclusion, a single bout of EA increases whole-body glucose uptake by activation of the sympathetic and partly the parasympathetic nervous systems, which could have important clinical implications for the treatment of insulin resistance.
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| 3. |
- Briggert, Andreas, 1984-, et al.
(författare)
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Evaluation of three dimensional fibre orientation in Norway spruce using a laboratory laser scanner
- 2016
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Ingår i: WCTE 2016. - Vienna : Vienna University of Technology. - 9783903039001
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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.
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| 4. |
- 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
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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.
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| 5. |
- Fornes, R., et al.
(författare)
-
The effect of androgen excess on maternal metabolism, placental function and fetal growth in obese dams
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Pregnant women with polycystic ovary syndrome (PCOS) are often overweight or obese. To study the effects of maternal androgen excess in obese dams on metabolism, placental function and fetal growth, female C57Bl6J mice were fed a control (CD) or a high fat/high sucrose (HF/HS) diet for 4-10 weeks, and then mated. On gestational day (GD) 15.5-17.5, dams were injected with dihydrotestosterone (CD-DHT, HF/HS-DHT) or a vehicle (CD-Veh, HF/HS-Veh). HF/HS dams had higher fat content, both before mating and on GD18.5, with no difference in glucose homeostasis, whereas the insulin sensitivity was higher in DHT-exposed dams. Compared to the CD groups, the livers from HF/HS dams weighed more on GD18.5, the triglyceride content was higher, and there was a dysregulation of liver enzymes related to lipogenesis and higher mRNA expression of Fitm1. Fetuses from HF/HS-Veh dams had lower liver triglyceride content and mRNA expression of Srebf1c. Maternal DHT exposure, regardless of diet, decreased fetal liver Pparg mRNA expression and increased placental androgen receptor protein expression. Maternal diet-induced obesity, together with androgen excess, affects maternal and fetal liver function as demonstrated by increased triglyceride content and dysfunctional expression of enzymes and transcription factors involved in de novo lipogenesis and fat storage.
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| 6. |
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| 7. |
- Hu, Min, 1979-, et al.
(författare)
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Assessment of a Three-Dimensional Fiber Orientation Model for Timber
- 2016
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Ingår i: Wood and Fiber Science. - 0735-6161. ; 48:4, s. 271-290
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Hu, Min, 1979-, et al.
(författare)
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Comparison of local variation of modulus of elasticity determined on basis of scanned fiber angles and full strain field measurements
- 2013
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Ingår i: The 18th International Nondestructive Testing and Evaluation of Wood Symposium. - Madison, WI, USA.
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Konferensbidrag (refereegranskat)abstract
- Strength grading methods are normally based on relationships between one measured value of modulus of elasticity (MOE), regarded as being valid for the whole board, and bending strength. Studies have shown, however, that with a detailed knowledge of local variation of MOE within boards, a highter coefficient of determination (R2) with respect to bending strength can be obtained. Measurements of fiber angles from laser scanning has shown to be a powerful tool to establish MOE profile along boards in a speed that cooresponds to the production speed at a sawmill. The present study aims at investigating the accuracy of the local MOE profile determined on basis of fiber angles from laser scanning. The study was carried out on a board of Norway spruce of dimension 50 by 150 by 3,900 mm. First the fiber angles on all four surfaces were identified using a WoodEye scanner and on the basis of these measurements, a MOE profile was calculated. Thereafter, the board was subjected to a constant bending moment and suring loading an image correlation system, Aramis, was employed for detection of the strain field with high resolution along the whole board. This strain field was then used to estanlish a 'true' MOE profile along the board. The MOE profiles determined in two different ways were compared and they show a close compliance. However, some difference were found and these were used for calibration of the method for MOE determination on the basis of scanning results. The present research thus contributes further improvement of a newly suggested grading method.
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| 9. |
- Hu, Min, 1979-, et al.
(författare)
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Fibre directions at a branch-stem junction in Norway spruce : a microscale investigation using X-ray computed tomography
- 2022
-
Ingår i: Wood Science and Technology. - : Springer Nature. - 0043-7719 .- 1432-5225. ; 56, s. 147-169
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Tidskriftsartikel (refereegranskat)abstract
- The connection between branch and trunk in a tree must be strong enough to transfer all loads acting on the branch, and it is well known that such branch-stem connections are indeed very strong. In this paper, X-ray computer tomography is employed to investigate the local fibre orientation in the close surrounding of a knot in a Norway spruce specimen to better understand the origins of the mechanical strength of the branch-trunk connection. First, a wood specimen containing an entire knot from pith to bark was imaged with a voxel size of 52 mu m. Subsequently, smaller specimens were cut from this original specimen and imaged again with increasingly higher resolution over four levels. With the highest resolution level (2.6 mu m voxel size), the tracheids with smallest lumen were successfully traced. The results revealed how the direction of the fibre paths that start below the knot curve around it as the paths progress upwards to the region just above the knot, where the paths divide into two: one set of paths integrating with the knot on its top side and the other set continuing up along the trunk. Fibres that integrate with the knot at its top follow paths just before they continue into the knot, with a radius of curvature of only about 1 mm in both vertical and horizontal directions. No abrupt change of fibre pattern between latewood and earlywood is observed; rather, a continuous change of fibre direction across annual layers can be seen. The detailed characterisation of the local fibre structure around the knot provides new data that can explain the remarkable strength of the branch-trunk connection.
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| 10. |
- Hu, Min, 1979-, et al.
(författare)
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Grading of sawn timber using the vibration technique : locating imperfections based on flexural mode shapes
- 2011
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Ingår i: 17th international nondestructive testing and evaluation of wood symposium. - Sopron, Hungary : University of West Hungary. - 9789639883819 ; , s. 269-276
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Konferensbidrag (refereegranskat)abstract
- The present study aims at investigating the potential of using mode shape or mode shape curvature (MSC) for detecting defects in wooden beams. It includes modal analysis, Finite Element (FE) modeling and visual scanning. An FE model was created to investigate the effect of defects of different size and location on the mode shape/MSC. The mode shape/MSC showed a good potential to be used for finding defects. An experimental study on 17 boards of Norway spruce, dimensions of 50×150×3900 mm, was conducted using experimental modal analysis. The findings reveal that: (1) the mode shape/MSC studied in the FE-model could be used to locate defects, (2) the method is very sensitive to measurement noise and it requires an accurately measured mode shape, (3) an error analysis shows that it is not possible to achieve the accuracy needed using accelerometers.
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| 11. |
- Hu, Min, 1979-, et al.
(författare)
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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
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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.
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| 12. |
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| 13. |
- Hu, Min, 1979-
(författare)
-
Local variation in bending stiffness in structural timber of Norway spruce : for the purpose of strength grading
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most strength grading machines on the European market use an averagemodulus of elasticity (MOE), estimated on a relatively large distance along awood member, as the indicating property (IP) to bending strength. Theaccuracy of such grading machines in terms of coefficient of determination israther low at R2 ≈ 0.5. This research is motivated by a desire to increase theaccuracy of the strength grading in the industry today. The aim of the presentstudy is to contribute knowledge of local variation in bending stiffness/MOEwith high resolution and thus locate weak sections due to stiffness reducingfeatures (the most important is knots) for structural timber.The present study introduces three methods that involve structural dynamics,classical beam theory and optical measurement to assess local wood stiffness.Specifically:The dynamic method, in which a wood member is treated as an ordinaryphysical structure and the local stiffness is studied by exploring itsdynamic properties.In Method II, a bending MOE profile is established based on local fibre angle information. The local fibre orientation is detected through highresolution laser scanning based on the tracheid effect. For Method III, a bending MOE profile is established using surfacestrain information under four-point bending. A high resolution strainfield is obtained using the digital image correlation (DIC) technique.From the present study, the two latter methods are more favourable inevaluating the local stiffness within a piece of structural timber. Moreover, thestudy reveals that the established bending MOE profiles using the two lattermethods, i.e. based on information of the local fibre angle and surface strain,agree reasonably well. However, for some patterns of knot clusters, the localbending MOE, calculated on the basis of fibre angles, is significantly higherthan the local bending MOE estimated on the basis of surface strain.
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| 14. |
- Hu, Min, et al.
(författare)
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Maternal testosterone exposure increases anxiety-like behavior and impacts the limbic system in the offspring.
- 2015
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490. ; 112:46, s. 14348-53
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Tidskriftsartikel (refereegranskat)abstract
- During pregnancy, women with polycystic ovary syndrome (PCOS) display high circulating androgen levels that may affect the fetus and increase the risk of mood disorders in offspring. This study investigated whether maternal androgen excess causes anxiety-like behavior in offspring mimicking anxiety disorders in PCOS. The PCOS phenotype was induced in rats following prenatal androgen (PNA) exposure. PNA offspring displayed anxiety-like behavior in the elevated plus maze, which was reversed by flutamide [androgen receptor (AR) blocker] and tamoxifen [selective estrogen receptor (ER) modulator]. Circulating sex steroids did not differ between groups at adult age. The expression of serotonergic and GABAergic genes associated with emotional regulation in the amygdala was consistent with anxiety-like behavior in female, and partly in male PNA offspring. Furthermore, AR expression in amygdala was reduced in female PNA offspring and also in females exposed to testosterone in adult age. To determine whether AR activation in amygdala affects anxiety-like behavior, female rats were given testosterone microinjections into amygdala, which resulted in anxiety-like behavior. Together, these data describe the anxiety-like behavior in PNA offspring and adult females with androgen excess, an impact that seems to occur during fetal life, and is mediated via AR in amygdala, together with changes in ERα, serotonergic, and GABAergic genes in amygdala and hippocampus. The anxiety-like behavior following testosterone microinjections into amygdala demonstrates a key role for AR activation in this brain area. These results suggest that maternal androgen excess may underpin the risk of developing anxiety disorders in daughters and sons of PCOS mothers.
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| 15. |
- Hu, Min, 1979-, et al.
(författare)
-
Modelling local bending stiffness based on fibre orientation in sawn timber
- 2018
-
Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 76:6, s. 1605-1621
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 16. |
- Hu, Min, 1979-, et al.
(författare)
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Modelling local bending stiffness of Norway spruce sawn timber using scanned fibre orientation
- 2018
-
Ingår i: <em>Proceedings</em>, 2018, ICEM 2018. - : MDPI.
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Konferensbidrag (refereegranskat)abstract
- 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, have been utilized in a previously developed machine strength grading method. However, that method was based on 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. The purpose of the present study was to suggest and verify a model by 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 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 variation along boards. Comparisons of results indicated that models suggested herein were sufficient to capture the variation of local bending stiffness along boards with very high accuracy.
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| 17. |
- Hu, Min, 1979-
(författare)
-
Studies of the fibre direction and local bending stiffness of Norway spruce timber : for application on machine strength grading
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 18. |
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| 19. |
- Lukacevic, Markus, et al.
(författare)
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A 3D model for knots and related fiber deviations in sawn timber for prediction of mechanical properties of boards
- 2019
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 166, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Olsson, Anders, 1973-, et al.
(författare)
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Performance of timber board models for prediction of local bending stiffness and strength-with application on douglas fir sawn timber
- 2022
-
Ingår i: Wood and Fiber Science. - : Society of Wood Science Technology. - 0735-6161. ; 54:4, s. 226-245
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Tidskriftsartikel (refereegranskat)abstract
- Efficient utilization of structural timber requires accurate methods for machine strength grad-ing. One of the most accurate methods presented this far is based on data of local fiber orientation on board surfaces, obtained from laser scanning. In this paper, two potential improvements of this method are exam-ined. The first one consists of replacing a model based on simple integration over cross sections of boards for calculation of local bending stiffness by a 3D solid finite element (FE) model from which local bending stiffness is derived. The second improvement concerns replacement of a simple model for the fiber orienta-tion in the interior of board by a more advanced one taking location of pith and growth direction of knots into account. Application of the alternative models on a sample of more than 200 Douglas fir boards, size 40 mm x 100 mm x 3000 mm, cut from large logs, show that each of the evaluated model improvements contributes to improved grading accuracy. When local bending stiffness is calculated utilizing the herein suggested FE model in combination with the improved model of fiber orientation in the interior of boards, a coefficient of determination to bending strength as high as 0.76 is obtained. For comparison, a coefficient of determination of 0.71 is obtain using the simpler original models.
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| 21. |
- Penvern, H., et al.
(författare)
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3D fibre orientation reconstruction around a knot in Douglas fir
- 2023
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Ingår i: 3rd ECCOMAS Thematic Conference on Computational Methods in Wood Mechanics (CompWood 2023), September 5-8, 2023, Dresden, Germany. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788412322279 ; , s. 137-138
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Konferensbidrag (refereegranskat)
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| 22. |
- Penvern, Helene, et al.
(författare)
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A laboratory method to determine 3D fibre orientation around knots in sawn timber : case study on a Douglas fir specimen
- 2024
-
Ingår i: Wood Science and Technology. - : Springer. - 0043-7719 .- 1432-5225.
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of structural timber largely depend on the occurrence of knots and on fbre deviation in their vicinities. In recent strength grading machines, lasers and cameras are used to detect surface characteristics such as the size and position of knots and local fbre orientation. Since laser dot scanning only gives reliable information about the fbre orientation in the plane of board surfaces, simple assumptions are usually made to defne the inner fbre orientation to model timber boards. Those models would be improved by better insight into real fbre deviation around knots. In the present work, a laboratory method is developed to evaluate growth layers geometries and fbre orientation, solely based on the fact that the fbers are parallel to the tree rings and without any further assumptions. The method simply relies on color scans and laser dot scans of Douglas fr (Pseudotsuga menziesii) timber specimen sections revealed by successive planing. The proposed method provides data on fbre orientation in 3D with an accuracy that is relevant for the calibration of detailed models.
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