| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Huber, Johannes Albert Josef, 1989-, et al.
(författare)
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Review of Robustness in Timber Buildings
- 2017
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Konferensbidrag (refereegranskat)abstract
- Timber buildings today aim for taller and larger dimensions to accommodate increased numbers of occupants. In tall buildings, more human lives are at risk if large portions of the structure collapse progressively during catastrophic failure events. To safeguard timber structures from disproportionate collapse due to localised failures, the aspect of robustness in particular needs to be considered. In the literature about building structures the term robustness seems to be contemplated in diverse ways. Several possible approaches to define and analyse this property can be found. However, certain consensus as to what characterises a robust structure seems to exist. A review of the concept of robustness for building structures in general and timber structures in specific is presented in this paper. Certain commonly applied terminology and definitions in the context of robustness are analysed. In the literature, risk-based, reliability-based and performance-based concepts for robustness appear to be established. The first two concepts are briefly summarised. The performance-based concept is treated in greater detail to highlight different procedures of deterministic robustness analyses. Common general characteristics of robust buildings which seem to be agreed upon are summarised. Robustness provisions for timber buildings in specific are described and compared to provisions in other building materials such as steel and concrete. The development of alternate load paths during local failure seems to play an essential role in preventing progressive collapse in buildings. The literature about robustness seems to be comprehensive concerning general considerations and concerning structures built in concrete or steel but appears to be rather limited in regards to timber structures. Evaluations of robustness in timber structures seem to be focused on risk-based and reliability-based concepts in literature.
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| 5. |
- Lhate, Inacio, et al.
(författare)
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Machining properties of lesser used wood species from Mozambique
- 2017
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Ingår i: Wood research. - : Statny Drevarsky Vyskumny Ustav. - 1336-4561. ; 62:4, s. 635-644
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Tidskriftsartikel (refereegranskat)abstract
- The present study was aiming at measuring cutting forces for wood of lesser used species from Mozambique such as Acacia nigrescens Oliv (namuno), Pericopsis angolensis Meeweven (muanga), Pseudolachnostylis maprounaefolia Pax (ntholo) and Sterculia appendiculata K. Schum (metil). Another aim was to use an expeditious method to compare performance of the species when cut. A machinability index calculated using Digraph and Matrix Methods was used for ranking the performance of the species when cut. Two different cutting tools 20o and 30o rake angle were used. Main cutting force in 90°-90° and 90°-0°cutting directions were measured by piezoelectric gauge. The results of the experiments showed that cutting forces followed normal trends to increase with density and decrease with increasing rake angle. The ratio between wood density and cutting forces in cutting directions 90°-90° and 90°-0° were 7 s2m-4 and 17.3 s2m-4, respectively. The most difficult species to be machined was Namuno, whereas the easiest species to be machined was Metil.
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| 6. |
- Li, Rongrong, et al.
(författare)
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Non-standard test method for glue line shear strength
- 2017
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Ingår i: Wood research. - : Statny Drevarsky Vyskumny Ustav. - 1336-4561. ; 62:5, s. 825-830
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Tidskriftsartikel (refereegranskat)abstract
- The relevant standards for glueline shear strength testing were summarized and analyzed in this paper. Depending on these existing test standards, the resulting stress in glueline is not pure shear stress, but a combination of shear and normal stresses. In order to overcome this deficiency, a symmetrical structure was proposed for making samples. Some comparative testing was accomplished by using these symmetrical samples, the results showed that the normal stress could be avoided during testing. These results were also confirmed by finite element method (FEM), the simulation results showed that the shear stress in glueline was uniform
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| 7. |
- Li, Rongrong, et al.
(författare)
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Prediction of cutting force during gypsum fiber composite milling process using response surface methodology
- 2017
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Ingår i: Wood and Fiber Science. - : Society of Wood Science and Technology. - 0735-6161. ; 49:4, s. 453-460
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Tidskriftsartikel (refereegranskat)abstract
- Gypsum fiber composite (GFC) is a kind of building material widely used in interior decoration. Milling is the most commonly used machining process for GFC. Cutting force as an important cutting characteristic parameter has significant influence on the quality of machined surface, power consumption, and tools wear. The tangential force (Fx) and normal force (Fy) were measured and analyzed to find out the effects of milling parameters on these cutting forces. Milling parameters considered were spindle speed, feed rate, and depth of cut. The response surface methodology (RSM) was selected to develop mathematical models and optimize milling parameters. The results showed that with the increase of feed rate and depth of cut, the Fx and Fy increased. But the cutting forces decreased with the increase of spindle speed. The optimization results indicated that high spindle speed, low feed rate, and small depth of cut are preferable for milling of GFC to obtain the best result.
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| 8. |
- Marklund, Birger, et al.
(författare)
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Influence of Tool Geometry on Self-feeding when Sawing Frozen Wood
- 2017
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Konferensbidrag (refereegranskat)abstract
- Sawing during the cold winter period is a problem for sawmills operating in the northern parts of the world and is becoming an increasingly important economic factor. One common effect of processing frozen timber is poor barking leading to increased tool wear and decreased pulp-chip quality, which implies lower chip value. Other common effects in the conversion steps of a sawmill are sawdust attached to the surface of the sawn timber (sawdust gluing), knot rupture, tool breakdown, and self-feeding, i.e. the sawblade feeds the wood to be sawn more or less independent of the feeding equipment. This study deals with the self-feeding phenomenon and how this problem can be reduced by adapting tool parameters to the properties of the frozen wood material. The results show that the amount of sapwood in the sawn timber has a great influence on the amount of self-feeding and that the effect can be reduced by adapting the rake angle of the tool to the conditions of frozen timber. A bevel at the edges of the cutting teeth reduced self-feeding forces, but increased main cutting forces.
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| 9. |
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| 10. |
- Rudak, Pavel, et al.
(författare)
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Motion of chips when leaving the cutting zone during chipboard plane milling
- 2017
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126 .- 1930-2126. ; 13:1, s. 646-661
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Tidskriftsartikel (refereegranskat)abstract
- Mathematical equations were established and the following regularities of the plane milling process of wood materials were analyzed: the effect of the cutting edge inclination angle on the chip exit angle, influence of the cutting edge inclination angle on the speed of chip movement along the blade and exit speed of the chips from the cutting zone, the dependence of the chip exit angle on the friction coefficients of the chips on the processed material surface and along the blade surface (the friction coefficients were determined from the results of the experimental measurements), and influence of the mill rotation frequency on the chip exit angle. The milling of the chipboards with various mill designs was performed at different cutting conditions (diameter = 7 mm to 24 mm, number of cutting elements = 1 to 3, cutting edge inclination angle = -5° to 20°, frequency of the mill rotation = 3000 min-1 to 24000 min-1, feed per tooth = 0.1 mm to 1.5 mm). The process of chip exit from the cutting zone was photographed, and the chip exit angles were measured. A comparison of the values of the chip exit angles obtained from the experiments with those from the calculations based on the developed mathematical equations showed a high convergence.
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