| 1. |
- Buck, Dietrich, 1990-
(författare)
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Mechanics of Cross-Laminated Timber
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing awareness of sustainable building materials has led to interest in enhancing the structural performance of engineered wood products. Wood is a sustainable, renewable material, and the increasing use of wood in construction contributes to its sustainability. Multi-layer wooden panels are one type of engineered wood product used in construction.There are various techniques to assemble multi-layer wooden panels into prefabricated, load-bearing construction elements. Assembly techniques considered in the earliest stages of this research work were laminating, nailing, stapling, screwing, stress laminating, doweling, dovetailing, and wood welding. Cross-laminated timber (CLT) was found to offer some advantages over these other techniques. It is cost-effective, not patented, offers freedom of choice regarding the visibility of surfaces, provides the possibility of using different timber quality in the same panel at different points of its thickness, and is the most well-established assembly technique currently used in the industrial market.Building upon that foundational work, the operational capabilities of CLT were further evaluated by creating panels with different layer orientations. The mechanical properties of CLT panels constructed with layers angled in an alternative configuration produced on a modified industrial CLT production line were evaluated. Timber lamellae were adhesively bonded in a single-step press procedure to form CLT panels. Transverse layers were laid at a 45° angle instead of the conventional 90° angle with respect to the longitudinal layers’ 0° angle.Tests were carried out on 40 five-layered CLT panels, each with either a ±45° or a 90° configuration. Half of these panels were evaluated under bending: out-of-plane loading was applied in the principal orientation of the panels via four-point bending. The other twenty were evaluated under compression: an in-plane uniaxial compressive loading was applied in the principal orientation of the panels. Quasi-static loading conditions were used for both in- and out-of-plane testing to determine the extent to which the load-bearing capacity of such panels could be enhanced under the current load case. Modified CLT showed higher stiffness, strength, and fifth-percentile characteristics, values that indicate the load-bearing capacity of these panels as a construction material. Failure modes under in- and out-of-plane loading for each panel type were also assessed.Data from out-of-plane loading were further analysed. A non-contact full-field measurement and analysis technique based on digital image correlation (DIC) was utilised for analysis at global and local scales. DIC evaluation of 100 CLT layers showed that a considerable part of the stiffness of conventional CLT is reduced by the shear resistance of its transverse layers. The presence of heterogeneous features, such as knots, has the desirable effect of reducing the propagation of shear fraction along the layers. These results call into question the current grading criteria in the CLT standard. It is suggested that the lower timber grading limit be adjusted for increased value-yield.The overall experimental results suggest the use of CLT panels with a ±45°-layered configuration for construction. They also motivate the use of alternatively angled layered panels for more construction design freedom, especially in areas that demand shear resistance. In addition, the design possibility that such 45°-configured CLT can carry a given load while using less material than conventional CLT suggests the potential to use such panels in a wider range of structural applications. The results of test production revealed that 45°-configured CLT can be industrially produced without using more material than is required for construction of conventional 90°-configured panels. Based on these results, CLT should be further explored as a suitable product for use in more wooden-panel construction.
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| 2. |
- Berg, Sven, et al.
(författare)
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Finite element analysis of bending stiffness for cross-laminated timber with varying board width
- 2019
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 14:6, s. 392-403
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Tidskriftsartikel (refereegranskat)abstract
- Cross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.
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| 3. |
- Berg, Sven, et al.
(författare)
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In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test
- 2019
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Ingår i: BioResources. - : NC State University. - 1930-2126 .- 1930-2126. ; 14:3, s. 5559-5572
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Tidskriftsartikel (refereegranskat)abstract
- Cross-laminated timber (CLT) is an engineered wood material that is used in the construction industry, e.g., for floors, walls, and beams. In cases where CLT-elements are used as shear walls, the in-plane-stiffness is an important property. For non-edge glued CLT, in-plane shear stiffness is lower than for edge-glued CLT. To evaluate the non-edge glued CLT panel’s in-plane shear modulus, the diagonal compression test and finite element (FE) simulation was used. FE-models with both isotropic and orthotropic material models were used to calculate the shear stiffness. The FE models using pure shear loads were used as a reference to determine the correct value of the shear modulus. To verify the FE simulations, diagonal compression tests were conducted on 30 CLT samples. A calibration formula was derived using the least square method for calculation of shear modulus. The formula gave accurate results. The results showed that FE simulations can reproduce the same shear stiffness as tests of non-edge glued 3-layer and 5-layer CLT panels.
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| 4. |
- Cao, Pingxiang, et al.
(författare)
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Effect of rake angle on cutting performance during machining of stone-plastic composite material with polycrystalline diamond cutters
- 2019
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Ingår i: Journal of Mechanical Science and Technology. - : Springer. - 1738-494X .- 1976-3824. ; 33:1, s. 351-356
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the effect of rake angle on cutting performance during machining of stone-plastic composite material with diamond cutters. To that end, an orthogonal cutting experiment was designed, in which stone-plastic composite material was planed by a polycrystalline diamond (PCD) cutter to produce chips. The features studied include cutting forces, cutting heat, chip formation and cutting quality. The conclusions are as follows: Firstly, increased rake angle causes frictional force and resulting force to decrease, promoting an increase in normal force. Secondly, during planing, cutting heat is primarily distributed in the chips, with less retained in the cutting edge, and the least retained in the machined surface. The temperatures of both cutting edge and chip decline with an increase in rake angle. Thirdly, as rake angle increases, chip morphology changes from segmental to curved and then to particle chips, with chip-breaking lengths first increasing and then decreasing. Finally, an increased rake angle leads a more stable cutting process and improved cutting quality. Therefore, with the precondition of blade strength, a diamond cutter with a larger rake angle can be used to machine stone-plastic composite to improve production quality by forming a smoother machined surface.
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| 5. |
- Ekevad, Mats, 1956-, et al.
(författare)
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Mechanics of stress-laminated timber bridges with butt end joints
- 2017
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Konferensbidrag (refereegranskat)abstract
- A number of variants of single span and three-span stress-laminated timber bridge decks have been studied via finite element simulations and experiments. Glulam beams in the decks were in general shorter than the total length of span which means that there were butt end joints in the decks. The butt end of each beam in a joint was not connected to the other beam which means that each butt end joint reduced the strength and stiffness of the whole of the deck. Results for deflection and stresses were examined for the studied variants in the form of reduction factors for strength and stiffness relative to a deck without butt end joints.Factors are shown in diagrams as function of ratio butt end distance/beam width and also butt end distance/span width. Comparison of achieved results with existing Eurocode rules shows that Eurocode rules are not totally appropriate.
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| 6. |
- Ekevad, Mats, 1956-, et al.
(författare)
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Potential Yield Increase with Reduced Saw Kerf Deviations when Curve Sawing
- 2017
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Konferensbidrag (refereegranskat)abstract
- Curve sawing with circular saw blades introduces saw kerf deviations due to the combination of the flat sawblade and the curvature of the saw kerf in log or cant direction. Deviations for a double arbor resaw used for curve sawing, are that the saw kerf becomes wider at top and bottom and that the desired rectangular cross sections of the boards become distorted. The yield loss due to the saw kerf deviation in practice for a sawmill was of interest in this study. Earlier and very approximate guesses and simple estimates have been indicating that the loss of income for a sawmill in Sweden producing 200’ m3 of sawn timber may be about 2 MSEK/year (0.22 Meuro/year). In this study calculations were based on true log data and assumed sawing conditions for a sawmill. A true mixed input log assortment (78458 spruce and pine logs taken into the log yard of a sawmill in northern part of Sweden) was used as basis. Individual curvature of these logs was taken into consideration but the calculation was still approximate because not all facts about sawing patterns, log classes etc. for an actual sawmill were known. Instead one single sawing class was used for the calculation of saw kerf deviation. Results show that the direct yield loss given the assumed input data was 0.61 %-units. This corresponds roughly to the income loss 0.2 Meuro/year mentioned above. Besides from the yield increase there are other advantages gained if the saw kerf deviation can be reduced.
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| 7. |
- 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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| 8. |
- Guo, Xiaolei, et al.
(författare)
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Evaluation of physical and mechanical properties of fiber-reinforced poplar scrimber
- 2017
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Ingår i: BioResources. - : NC State University. - 1930-2126 .- 1930-2126. ; 12:1, s. 43-55
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of poplar scrimber reinforced with glass fiber mesh were investigated. The influence of the different structures and densities were studied with respect to the modulus of rupture (MOR), modulus of elasticity (MOE), and impact toughness (IT). The glass fiber improved the mechanical properties of poplar scrimber. The MOR, MOE, and IT of the scrimber had an obvious dependence on the number of glass fiber layers. When the layers of glass fiber meshes were increased, the MOR, MOE, and IT were increased compared to the control group (scrimber without glass fiber reinforcement). The MOR, MOE, and IT of single-layer glass fiber reinforced scrimber increased a lot compared to the control group. The MOR, MOE, and IT of double-layer glass fiber reinforced scrimber (DGRS) were increased, but the amplitude of the increase was smaller than that of SGRS. Compared to the MOR, MOE, and IT of DGRS, the MOR, MOE, and IT of triple-layer glass fiber reinforced scrimber (TGRS) decreased slightly. When the density was increased, the increasing rate of the MOR, MOE, and IT of the glass fiber reinforced scrimber showed a downward trend, and the glass fiber had better strengthen effects on the scrimber at low density (0.6 g/cm3 and 0.7 g/cm3).
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| 9. |
- Guo, Xiaolei, et al.
(författare)
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The cutting performance of Al2O3 and Si3N4 ceramic cutting tools in the milling plywood
- 2018
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Ingår i: Advances in Applied Ceramics. - : Taylor & Francis. - 1743-6753 .- 1743-6761. ; 117:1, s. 16-22
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Tidskriftsartikel (refereegranskat)abstract
- This research focuses on the cutting performance of Al2O3 and Si3N4 ceramic cutting tools in upmillingplywood, the results of which are as follows. First, whether the tool material is Al2O3 orSi3N4 ceramic, the cutting forces at low-speed cutting were less than those at high-speedcutting, and the machining quality at low-speed cutting was greater than that at high-speedcutting. Then, whether at low- or high-speed cutting, the cutting forces of Al2O3 cutting toolswere higher than those of Si3N4 cutting tools, and the machining quality of plywood milledby Al2O3 ceramic cutting tools was poorer than that milled by Si3N4 ceramic cutting tools.Finally, Si3N4 ceramic cutting tools were more suitable to machine the wooden productionswith much glue content than Al2O3 ceramic cutting tools for the better machined quality.
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| 10. |
- Huang, Liangliang, et al.
(författare)
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Study on continuous cold-pressing technology of engineered wood flooring with EPI adhesive
- 2018
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Ingår i: Wood research. - : Statny Drevarsky Vyskumny Ustav. - 1336-4561. ; 63:2, s. 335-342
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Tidskriftsartikel (refereegranskat)abstract
- The effects of process parameters (adhesive spread, press time, and applied pressure) on the gluing performance of engineered wood flooring bonded with emulsion-polymer-isocyanate (EPI) adhesive were studied. The results showed (shear strength and aging test) that the major factors were adhesive spread and press time. The optimized parameters for best gluing performance of engineered wood flooring were 160 g.m-2, 14 s, and 60 s for adhesive spread, heat time, and press time, respectively, within certain ranges
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