| 1. |
|
|
| 2. |
- Huber, Johannes Albert Josef, PhD, 1989-, et al.
(författare)
-
Evaluation of Knots and Fibre Orientation by Gradient Analysis in X-ray Computed Tomography Images of Wood
- 2023
-
Ingår i: CompWood2023: Computational Methods in Wood Mechanics. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 9788412322279 ; , s. 143-144
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The mechanical properties of wood are governed by growth-dependent structures on themicro- and macroscopic level, which are subject to natural variation. Numerical modelsof wood on a scale of individual pieces of sawn timber may need to account e.g. for thegrowth ring orientation or the presence of knots and their effects on the local materialorientation, i.e. the variation of the fibre coordinate system (FCS). The FCS is composedof the mutually orthogonal longitudinal (l), radial (r) and tangential (t) directions. Agrowth surface represents a region of equal age, i.e. a former growth front of the tree,and at each point on a growth surface, the r direction consequently represents the surfacenormal. Growth surfaces surrounding a knot are usually approximated by analyticalsurfaces, onto which the l direction is modelled by hydrodynamic flow fields in lateral andby polynomials in the vertical direction, like in [1].A data-driven method used for detecting the location of knots and eliciting the in-planeprojection of the l direction on the surface of sawn timber is optical scanning combinedwith laser tracheid scanning [2]. A disadvantage of this method is that the internalstructure of the scanned timber remains unknown and needs to be extrapolated, againbased on assumptions of growth in wood. X-ray computed tomography (CT) of woodprovides images of the internal density distribution from which features like the pith, thegrowth rings, knots and defects can be extracted by image analysis.In a recent study [3], the local FCSs around knots were reconstructed by density gradientanalysis in CT images, on which finite element models were based for predicting thebending behaviour of sawn timber. Growth surfaces in wood represent regions of nearlyconstant density and can therefore be analysed in CT images by gradient-based methods.The goal of the present study was therefore to study how the gradient of the density fieldderived from CT images of wood can be used to determine growth surfaces, the region ofknots, the border between dead and live knot, and the locally varying FCSs.The material studied was comprised of small log sections of Scots pine (pinus sylvestris)(approximate diameters of 50 mm - 300 mm and length 250 mm) containing knot whorls,which were dried to fibre saturation. CT scans were acquired at a voxel size of 0.5 × 0.5 ×0.5 mm3 yielding a 3D image J(x, y, z). After scanning, the sections were cut throughthe centrelines of the knots and manual measurements were conducted of the dead knotborder, i.e. the position along the boundary of a knot after which a knot died off. At this border, the diameter of the knot stops increasing and the surrounding fibres grow aroundthe knot rather than merging with it. As the tree continues to grow, this will eventuallylead to bark being encased around the knot inside the tree.A purely data-driven analysis was performed based on the partial derivatives Jx , Jy , Jz ,from which the gradient structure tensor (GST) was constructed, see equation 1, where wσ is a Gaussian convolutional kernel. The eigenvalues and eigenvectors of the GSTwere extracted for each voxel and the resulting vector field was used in the subsequentanalyses. Equivalently, second order derivatives were studied to study curvature.The results indicate that gradient-based analyses on CT images of wood can be usedto approximate the locally varying FCSs around knots, see Figure 1 and that they mayfacilitate the determination of the region of dead and live knots.
|
|
| 3. |
|
|
| 4. |
- Maharjan, Rajan, 1985-, et al.
(författare)
-
Substructure modelling of full size timber modules
- 2023
-
Ingår i: Computational Methods in Wood Mechanics. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788412322279 ; , s. 48-
-
Konferensbidrag (refereegranskat)abstract
- From an environmental sustainability point of view, modern construction practices increasingly favorcarbon neutral buildings including those made from timber. Prefabricated timber modules havebecome popular due to their efficient in-house production followed by systematic and rapid on-siteinstallation. Construction companies often use these lightweight modules for residential buildings upto six story when feasible. While several studies are available that simulate stiffness and strength ofshear walls, a major component of the module responsible for transferring shear load and acting asa load bearing wall for vertical loads, e.g [1] and [2] for the EC5 design principles, relatively little workhas been done to analyze the structural performance of entire modules. This is likely due to limitedtime span the construction type has been common practice, practical challenges associated withexperimental tests and numerically demanding simulations of large structures. However, there aresome exceptions, e.g [3].This study introduces the concept of “super elements”, which are developed by condensing theinternal degrees of freedom (DOF:s) of a whole timber module to specified parts of its boundary. Theaim of this study is to reduce the number of DOF:s by using substructuring so that an entire structurecan be analyzed while subjected to external loading. Substructuring is a method of dividing a wholemodel into user defined parts (super elements) and coupling these together to create a global model[4]. The internal DOF:s of the super elements are “condensed” using static condensation, and thesuper elements are then connected to the rest of the model along selected restrained DOF:s [5].Figure 1(a) shows an example of a building with timber modules, while Figure 1(b) illustrates partsof a full-size timber module. Figure 1(c) represents a super element of the module. A simple, linearFE super element is developed for analyzing a part of a whole timber structure and it is coupled tothe rest of the structure only at designated pre-selected nodes. The model is then used to analyzethe response during various load cases applied to the whole structure.
|
|
| 5. |
- Penvern, H., et al.
(författare)
-
3D fibre orientation reconstruction around a knot in Douglas fir
- 2023
-
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
-
Konferensbidrag (refereegranskat)
|
|
