| 1. |
- Guo, Xiaolei, et al.
(författare)
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Cutting forces and cutting quality in the up-milling of solid wood using ceramic cutting tools
- 2021
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 114:5-6, s. 1575-1584
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Tidskriftsartikel (refereegranskat)abstract
- Although many studies have focused on the cutting performance of ceramic blades in processing different materials, few have reported on their application in wood processing. Thus, it is necessary to explore the cutting performance of ceramic tools in solid wood machining. The aims of this paper were to evaluate the cutting performance of Al2O3 and Si3N4 ceramic tools in the process of machining Manchurian ash (Fraxinus mandshurica Rupr.) and Chinese fir (Cunninghamia lanceolata) by means of analysing cutting force and surface roughness and to provide guidelines for factories for applying ceramic tools in the manufacture of solid wood furniture. Up-milling tests were conducted for each combination of cutting speed, tool material, and workpiece material, and each combination was replicated five times. Results showed that (1) cutting force and surface roughness decreased with increase of cutting speed and (2) cutting force and surface roughness resulting from using Al2O3 ceramic cutting tools were larger than those of Si3N4 ceramic cutting tools, especially when cutting Manchurian ash with its extractives. Overall, ceramic tools can be used in high-speed cutting of solid wood. Compared with Al2O3 ceramic cutting tools, Si3N4 ceramic cutting tools are more suitable for cutting solid wood, especially those with extractives. Si3N4 ceramic tools provided not only chemical stability, but improved final product quality.
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| 2. |
- Huber, Johannes Albert Josef, 1989-, et al.
(författare)
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3D Quasi-Continuum and Finite Element Models Based on CT Scans of Timber Boards to Predict Stiffness and Strength
- 2021
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Ingår i: ICCSE1 1st International Conference on Computations for Science and Engineering.
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Konferensbidrag (refereegranskat)abstract
- Engineered wood products of today's construction industry require predictable mechanical properties of the used structural timber. At sawmills, automated strength grading is used to assess the stiffness and strength of sawn and dried timber boards. This process can be based on various technologies, e.g. surface scanning, dynamic excitation, flat-wise bending, which are used to derive so-called indicating properties, i.e. simplified numerical values. Heuristically derived statistical models can then be used to predict the stiffness and strength based on indicating properties. However, statistical strength grading can only exploit a small fraction of the potential strength of a single board, since it assesses the properties of a board in relation to its population. A growing number of sawmills in Sweden use computed tomography (CT) scanners to assess the incoming logs to optimise their positioning prior to sawing. CT scans provide high-quality data of the cross-sectional density distribution along the length of a log, which could also be used to derive continuum mechanical models of the yet unsawn boards and with that assess their mechanical properties. If the stiffness and strength of a virtual board can be predicted before it is sawn, then it could be pre-classified into a strength class or its specific use as a specific construction part could be predetermined already at the log stage, which would lead to a more efficient material usage. Additionally, the predictive power of the existing statistical strength grading processes could be improved for the final boards.The goals of this study were to i) derive 3D quasi-continuum and finite element (FE) models of CT scanned timber boards using different material laws for local stiffness based on measured density and ii) compare their capabilities for predicting stiffness and strength of the boards.The experimental material consisted of dried softwood boards (12% moisture content) of nominal cross-sectional dimensions 50x100mm with different lengths, scanned with a medical high-resolution CT scanner. The boards underwent an eigenfrequency measurement by dynamic excitation and were tested until failure in a four-point bending test, where both the local and global displacement were recorded.A previously developed algorithm was used to derive 3D quasi-continuum reconstructions from the CT scans and subsequently finite element (FE) models. The algorithm reconstructed the board geometry, pith, knots and local fibre directions (material coordinate system) on a volume grid of material points spaced 0.68mm apart. The stiffness tensor in each material point was made locally dependent on the measured density by different mathematical laws, e.g. constant, linear or power laws. Furthermore, material laws which scaled the stiffness tensor based on the ratio between the simulated and measured eigenfrequency were tested for comparison. The bending stiffness profile was calculated for each board along its length and different indicating properties for predicting stiffness and strength were derived and compared with respect to the experimental results. With the FE model, strain distributions in the cross-sections were studied and local stress states around the experimentally observed points of initial failure were investigated to determine whether similar dominant failure stress states existed among boards.The results showed high coefficients of determination between predicted stiffness and strength for material laws based on power laws and low values for linear laws. Nevertheless, the four-point bending tests only provided point-wise data (mid points) that could be used to validate the numerical model. It is therefore recommended to use field-based evaluations in the future, e.g. the surface strain obtained with DIC under four-point testing.
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| 3. |
- Huber, Johannes Albert Josef, 1989-, et al.
(författare)
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Finite Element Modelling Of Alternative Load Paths after a Wall Removal in a Platform CLT Building
- 2021
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Ingår i: World Conference on Timber Engineering 2021: Book of abstracts. - : Curran Associates, Inc.. ; , s. 1867-1873
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Konferensbidrag (refereegranskat)abstract
- Tall buildings with a high occupancy need to resist disproportionate collapse caused by unforeseen exposures, e.g. terrorism or accidents. If a damage has occurred in a building, the damage propagation can be halted if the structure is robust, i.e. it provides alternative load paths (ALPs). The ALPs of platform-type cross-laminated timber buildings have not been studied in detail on the component level. The goals of this paper are thus to elicit which ALPs may develop on single storeys in a corner bay of a platform-type cross-laminated timber building, and to study how the various building components contribute to the ALPs. For this purpose, a non-linear quasi-static pushdown analysis was conducted in a finite element model of an 8-storey building after a wall removal. Friction, fastener failure, timber failure and large displacements were accounted for. Four different ALPs were identified at various storeys and their mechanisms were described. The results could be used to improve the capacity of the ALPs and make platform-type cross-laminated timber buildings more robust in the future.
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| 4. |
- Huber, Johannes Albert Josef, 1989-, et al.
(författare)
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Finite Element Modelling of Catenary Action in a Cross-Laminated Timber Floor System
- 2021
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Ingår i: World Conference on Timber Engineering 2021: Book of abstracts. - : Curran Associates, Inc.. ; , s. 3018-3025
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Konferensbidrag (refereegranskat)abstract
- Buildings taller than four storeys require the designer to mitigate consequences of unexpected events, e.g. terrorism or accidents, such that a disproportionate collapse can be avoided after initial damage. One approach to halt damage propagation is using structural robustness, i.e. by providing alternative load paths. For platform-type cross-laminated timber (CLT) buildings, catenary action as an alternative load path is not fully understood. The goal of the research presented in this paper is to numerically study catenary action as a resistance mechanism for floor panels after internal load-bearing wall removal, and to identify the governing parameters of this mechanism. For this purpose, a non-linear high-fidelity finite element model was constructed and calibrated against test results. All components and connections were individually modelled, to account for failure in the connectors and the timber components. A parameter study evaluated the impact of the floor span, the storey location, the connection type and the tie level on the development of catenary action. It was shown that in specific the connection, the storey location and the tie level had significant effects on catenary action. The results provide insight into how CLT floor systems can be detailed to trigger catenary action following internal wall removal.
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| 5. |
- Huber, Johannes A. J., 1989-
(författare)
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Numerical Modelling of Timber Building Components to Prevent Disproportionate Collapse
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An increasing number of multi-storey buildings are being constructed with engineered wood products, such as glulam or cross-laminated timber (CLT). Multi-storey timber buildings can be safely designed for foreseeable loads, but knowledge is limited concerning their ability to survive unforeseeable events, e.g. accidents, natural disasters or terrorism. Multi-storey buildings with many occupants are required to be able to resist a disproportionate collapse due to an unexpected event. Collapse resistance consists of three lines of defence: I) decreasing the probability of the event, II) decreasing the structural vulnerability and III) increasing the structural robustness. The focus of the present thesis is on defence lines II and III, since they can be affected by engineering considerations.Robustness requires the availability of alternative load paths (ALPs) after an initial structural damage, e.g. the removal of an element. The activation of an ALP, e.g. catenary action, usually happens as the result of a larger displacement than that for which the components are designed, and with the participation of the surrounding structure. Physical tests of removal scenarios are expensive and they are often unable to represent realistic building situations. Numerical models can replace physical tests, e.g. by introducing parameter variations or changed boundary conditions, and can deliver an insight into the underlying mechanisms. Vulnerability depends on the ability of individual components of the structure to withstand loads greater than their intended design loads. To reduce vulnerability, so-called key elements can be be made overly strong. If the uncertainty concerning the material properties is high, e.g. for timber, both nominally stronger and larger amounts of material are required, resulting in inefficient material utilisation. Automated strength grading of sawn timber can narrow the uncertainty, but, even with the current technologies, the variations in the graded material remain large.The predictive power of computerised models for sawn timber offers a great potential for integration with traditional strength grading based on testing combined with statistical models. So far, surface data of sawn timber has been used for numerical models, but X-ray computed tomography (CT) scanning equipment now being installed in sawmills has made it possible to measure the inner structure of logs. Using CT data could make it possible to develop high-fidelity numerical models for predicting the mechanical properties of sawn timber, possibly even before sawing, and this could reduce the uncertainty for structural components and enable the production of high-strength timber. However, attempts to develop CT-based models for timber have been scarce.The objective of the work presented herein was to advance the research front regarding the prevention of disproportionate collapse in multi-storey timber buildings. The work has focused on numerical modelling aspects and on subsystems and components, rather than on entire buildings. The goals were: 1) to describe the state of the art regarding the prevention of disproportionate collapse and its application in timber buildings, 2) to develop models to identify and quantify the ALPs in subsystems and components of CLT buildings, and 3) to develop models of sawn timber based on X-ray CT scanning data, to reduce the uncertainty regarding the mechanical properties of the timber.For goal 1, the literature was reviewed and a survey was conducted among practitioners and researchers in the field. The results provided an extensive overview of the topic and the status quo in the industry, and identified a scarcity of guidelines for multi-storey CLT buildings.For goal 2, non-linear finite element (FE) models were developed for quasi-static pushdown analyses. A study of a platform joint first validated some modelling assumptions. The ALPs in single storeys in a corner bay of an 8-storey CLT building were then studied after the removal of bottom-storey walls. In subsequent parameter variations, the full bay was studied in dynamic analyses. The results identified six different ALPs, which were dependent on the connection capacities and the shear capacity of the floor panels, and indicated that collapse was likely after a double wall removal, but unlikely after a single wall removal. Furthermore, the ALPs in a platform-type CLT floor system were studied in parameter variations of calibrated FE models. The results showed how three different ALPs can develop, depending on the storey, the floor geometry and the connectors.For goal 3, a method was developed for the generation of continuum and FE models from CT scanning data of sawn timber, in which the knots, pith and local fibre orientations were reconstructed. The models gave realistic impressions and they could predict the bending stiffness, strength and initial failure location for Norway spruce sawn timber. The predictions improved, if the eigenfrequency of the sawn timber was also considered for modelling.
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| 6. |
- Huber, Johannes Albert Josef, 1989-, et al.
(författare)
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Using Computed Tomography Data for Finite Element Models of Wood Boards
- 2021
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Ingår i: 14th World Congress on Computational Mechanics (WCCM) ECCOMAS Congress 2020. - : Computational Structural Mechanics Association.
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Konferensbidrag (refereegranskat)abstract
- A procedure is presented to generate 3D FE models of timber boards based on CT scans. Theboards were tested in four-point bending tests until failure and the local displacement in the pure bendingzone was recorded. The CT scans were treated as 3D images and image processing methods were usedto reconstruct the board, the knots and the pith. A new procedure to reconstruct the fibre deviationsaround knots by accounting for image gradient information was used. A quadratic tetrahedral mesh wasgenerated for the region of the board which was under pure bending in the tests. The fibre directions andthe stiffness tensor, scaled by the local density, were transferred into each integration point of the meshand the bending test was replicated. Preliminary results show that the procedure is able to realisticallypredict the observed local stiffness of the boards. Further development of the procedure is required toaccount for dead knots and to extend the procedure for indicating strength and predicting failure.
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| 7. |
- Meulenberg, Vanessa, 1993-, et al.
(författare)
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Thin kerf cutting forces of frozen and non-frozen Norway spruce and Scots pine wood
- 2021
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 16:6, s. 414-420
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Tidskriftsartikel (refereegranskat)abstract
- Reducing the kerf width in bandsawing has potential in reducing waste while optimising the yield. To be able to reduce the kerf width, understanding the cutting forces becomes critical. In this work, nine cutting teeth with varying band-body thicknesses and side clearances were tested by cutting both heartwood and sapwood of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in frozen and non-frozen conditions. Single cutting teeth were moved into rotating wood samples in the 90–90° cutting direction, with chip thicknesses of 0.9 mm per cut. The main and normal cutting forces were measured. Scots pine had a higher density than Norway spruce and, therefore, a higher main cutting force. Non-frozen sapwood, non-frozen heartwood and frozen heartwood resulted in similar main cutting forces, but frozen sapwood resulted in significantly higher main cutting forces. Reducing the cutting width by about 45% resulted in an approximately 40% reduction in the main cutting force. The normal forces were not significantly affected by the species or cutting width. Frozen heartwood, non-frozen heartwood and non-frozen sapwood had similar normal cutting forces. Frozen sapwood had negative normal forces, and thus self-feeding was observed.
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| 8. |
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| 9. |
- Sharifi, Jonas, 1991-, et al.
(författare)
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Diaphragm shear and diagonal compression testing of cross-laminated timber
- 2021
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Ingår i: SN Applied Sciences. - : Springer. - 2523-3963 .- 2523-3971. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- To learn the characteristics of a cross-laminated timber (CLT) panel, it is crucial to perform experimental tests. This study presents two experimental test methods to measure the in-plane shear modulus of CLT panels. This characteristic can be measured by multiple methods such as the picture frame test, the diagonal compression test, and the diaphragm shear test. In this study, the same CLT panels are tested and evaluated in the diaphragm shear test and the diagonal compression test to see if more reliable results can be achieved from the diaphragm shear test. This evaluation is done by experimental tests and finite element simulations. The theoretical pure shear simulation is used as a reference case. Finite element simulations are made for both edge glued and non-edge glued CLT panels. Nine CLT panels are tested in the diaphragm shear test and the diagonal compression test. During ideal conditions (uniform material properties and contact conditions), all three simulated methods result in an almost equal shear modulus. During the experimental testing, the diagonal compression test gives more coherent results with the expected shear modulus based on finite element simulations. Based on the diaphragm shear test results, the CLT panels behave like edge glued, but this situation is dismissed. However, during ideal conditions, the diaphragm shear test is seen as a more reliable method due to the higher proportion of shear in the measured area.
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| 10. |
- Sharifi, Jonas, 1991-
(författare)
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In-Plane Shear Modulus of Cross-Laminated Timber
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cross-laminated timber (CLT) is a building component used in walls, floors, roofs, or beams in a building. The advantages of using CLT as a building component are, among others, its high load-carrying capability and the possibility of pre-fabrication. The in-plane shear properties of a CLT panel are the in-plane shear modulus and in-plane shear load carrying capacity. This thesis is solely about the in-plane shear modulus and is intended to increase the understanding about the in-plane shear modulus of CLT panels. The in-plane shear modulus is important and there is a need to better understand and estimate its value. The objective of this work was to contribute to the need of finding a suitable test method to measure the in-plane shear modulus of CLT panels and to find factors affecting the in-plane shear modulus. Three different methods: the picture frame test, the diagonal compression test and the diaphragm shear test, were used in practice and compared to a theoretical test method, the pure shear test. The three methods were compared by conducting experimental tests and by simulating the methods using finite element (FE). Based on the FE simulations, an equation to calculate the shear modulus was created for each test method. Results from the FE analyses showed that the picture frame test gave results similar to the theoretical pure shear test models. The reason for this result was that the picture frame test is a biaxial testing method. The diagonal compression test and the diaphragm shear test are uniaxial test method. It was also concluded that the picture frame test has a pure shear state in the measured region. The mean error for the in-plane shear modulus equations was estimated, by comparing results from practical testing and FE simulations, to be -2.5%, +12.6% and +11.8% for the picture frame test, diagonal compression test and diaphragm shear test, respectively. The diagonal compression test was the preferred method to use with respect to its simplicity.The factors having an impact on the in-plane shear modulus were found by comparing multiple FE simulations. The results showed that it is possible to increase the in-plane shear modulus by: increasing the odd numbered layers width-to-thickness ratio; decreasing the odd layers thickness ratio of the CLT panels thickness; increasing the number of layers; reducing the gaps between boards; and using alternative main laminate directions.
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