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  • 1.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ekevad, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Crack influence on load-bearing capacity of glued laminated timber using extended finite element modelling2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 335-343Article in journal (Refereed)
    Abstract [en]

    Most of the cracks are caused by changes in temperature and relative humidity which lead to shrinkage and swelling of the wood and thereby induce stresses in the structure. How these cracks influence the strength of the wooden structure, especially the shear strength, is not well understood. However, it is reasonable to expect that cracks have an impact on the shear strength as they preferably run along the beams in the direction of grain and bond lines. The purpose of this study was to investigate the load-bearing capacity of cracked glulam beams and to find a model that could predict the failure load of the beams due to the cracks. Three-point bending tests were used on glulam beams of different sizes with pre-manufactured cracks. An orthotropic elastic model and extended finite element method was used to model the behaviour of the cracked beams and to estimate the load-bearing capacity. The conclusions were validated by numerical simulations of the mechanical behaviour of three-point bending of glulam beams with different crack locations. The crack initiation load was recorded as the failure load and compared to the experimental failure load. The results of the compaction simulations agree well with the experimental results.

  • 2.
    Mansouri, Hamid
    et al.
    ENSTIB-UHP, Epinal.
    Pizzi, Antonio
    ENSTIB-UHP, Epinal.
    Leban, Jean-Michel
    INRA, Campenoux.
    Delmotte, L.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Causes for the improved water resistance in pine wood linear welded joints2011In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, no 16, p. 1987-1995Article in journal (Refereed)
    Abstract [en]

    Linear vibration welding of good quality pine (Pinus sylvestris) wood from Sweden containing a small proportion of a native mixture of terpenoic acids, known under the collective name of rosin, has been shown to yield joints of much upgraded water resistance. This has been shown to be due to the protecting influence the molten rosin from the wood itself has on the welded interphase, because of the water repellency of rosin. Joints of unusually high percentage wood failure but modest strength were obtained, rosin apparently reinforcing the welded interphase to yield weldline strengths always much higher than the strength of the surrounding wood.

  • 3.
    Sandberg, Dick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Vaziri, MojganLuleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Final Cost Action FP0904 Conference: “Recent Advances in the Field of TH and THM Wood Treatment” : May 19-21, 2014, Skellefteå, Sweden : book of abstracts2014Conference proceedings (editor) (Refereed)
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  • 4.
    Sandberg, Dick
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Trischler, Johann
    Linnæus University, Forestry and Wood Technology.
    Öhman, Micael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The role of the wood mechanical industry in the Swedish forest industry cluster2014In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 29, no 4, p. 352-359Article in journal (Refereed)
    Abstract [en]

    The forest and forest products form one of the most important basis for the transfer to a biobased economy in Sweden. About 75% of the area covered by forest in Sweden is used industrially to produce raw material for the wood-refining industries. Every year, this cluster uses 75 million m3 of roundwood and has an export value of € 12 billion. This review paper is devoted to the wood mechanical industry, i.e. the industry which turns the forest into sawn timber, packaging, construction wood, furniture and interior fittings. The sawmills consume about half of the volume of softwood which is felled, and about two thirds of the sawn timber goes to export without any further refining within the country. Nevertheless, in spite of the relatively low degree of refinement in the sawmill and the fact that the sawmills in general over time have a very low profitability, they are responsible for 70–80% of the forest owners' profits on the sale of timber. An increased upgrading of the sawn timber within the country is desirable from a national economic viewpoint – increased employment opportunities, increased export income etc. It should then in the first place be for products with a higher added value, such as furniture and fittings. Today, the refinement value is 15–20 times higher for products from joinery and furniture industries compared that of the sawn timber and the added value of the wood within the building industry is only about 1.5 times.

  • 5.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Water resistance of Scots pine joints produced by linear friction welding2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wood welding is a mechanical friction process allowing the assembly of timber without any adhesives. The process consists of applying mechanical friction, under pressure, alternately to the two wood surfaces to be welded. This process can be applied to weld two flat pieces of timber, originating from the same or different tree species, and can be used in the manufacture of furniture and wood joinery. The only limitation is that the joint is not exterior-grade, but only suitable for interior joints. Exterior use, or use in an environment with varying humidity demands water resistance of the welded joints. The main objective of this thesis is to study the water resistance of the welded wood. This is complemented with special attention to non-destructive test methods such as X-ray Computed Tomography (CT-) scanning and Magnetic Resolution Imaging (MRI). The influence of welding parameters and wood properties on crack formation and crack propagation in the weldline was investigated. The influence of these parameters on weldline density and water absorption in the weldline were also studied. Investigations in this thesis are based on welded samples of Scots pine (Pinus sylvestris) of the dimensions 200 mm × 20 mm × 40 mm which were cut in the longitudinal direction of the wood grain. The tensile-shear strength of the welded Scots pine samples were determined using European standard EN 205. Different non-destructive methods such as X-ray Computed Tomography (CT-) scanning to study crack formation and propagation, and magnetic Resolution Imaging (MRI) to characterize water penetration and the distribution mechanism in welded wood were used. Solid state CPMAS 13C NMR spectrometry and X-ray microdensitometry investigations were carried out to study the mechanism of adhesion in Scots pine. These various non-destructive methods offer the advantage of non-invasive analysis and the elimination of any artifacts present due to preparation and sectioning. The most important results are summarized as follows: •X-ray Computed Tomography (CT-) scanning and Magnetic Resolution Imaging (MRI) are versatile research methods applicable to investigations of welded woods. •Water resistance of welded Scots pine can be increased using heartwood, a welding pressure of 1.3 MPa, and a welding time of 1.5 s. •Optimization tests showed that the tensile-shear strength of Scots pine was more sensitive to welding time changes than holding time and could be optimized to more than 9.7 MPa using 1.3 MPa welding pressure, > 3.5 s welding time, and < 60 s holding time. •Changing welding parameters and wood properties can increase water resistance of welded wood to some extent, but treating the weldline with certain natural and environmentally-friendly water repellents is still necessary. •Welded Scots pine shows unusually high water resistance and tensile-shear strength. This may be explained by there being more extractives compounds in Scots pine. •MRI experiments showed that the origin of the joint failure in welded beech is poor water resistance of the weldline, while swelling and shrinkage of wood are the main reasons for joint failure of welded Scots pine. •Extractives in Scots pine dramatically improve water resistance of the welded joint, but not to a level to classify the joint as an unprotected exterior grade. However, it can qualify as a joint for protected semi-exterior application.

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  • 6.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Abrahamsson, Lars
    Vattenfall AB, BU Fuel, Engineering & Projects, Solna, Sweden.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Welding of wood in the presence of wollastonite2020In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 15, no 1, p. 1617-1628Article in journal (Refereed)
    Abstract [en]

    The use of wollastonite as a natural additive for the welding of Scots pine improved the water resistance and shear strength of the welded joint. The X-ray computed tomography images revealed that the welding of Scots pine with wollastonite could postpone crack formation in the welded joints. The specimens welded for a longer time (5 s) had a more uniform distribution of wollastonite particles in welded joints. The microstructure of the wood and the thickness of the wood cell walls also had a great influence on the thickness and strength of the welded joints. Water immersion tests showed that the use of wollastonite in wood joints was able to meet the requirement of resistance to frequent short-term and long-term exposure to water.

  • 7.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Three-dimensional finite element modelling of heat transfer for linear friction welding of Scots pine2014In: Final Cost Action FP0904 Conference: “Recent Advances in the Field of TH and THM Wood Treatment” : May 19-21, 2014, Skellefteå, Sweden : book of abstracts / [ed] Mojgan Vaziri; Dick Sandberg, Skellefteå: Luleå tekniska universitet, 2014, p. 45-46Conference paper (Refereed)
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  • 8.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Gheinani, Iman Tavakoli
    Department of Mechanical Engineering, ENSTIB-LERMAB, University of Lorraine, Epinal, France.
    Three-dimensional finite element modelling of heat transfer for linear friction welding of Scots pine2014In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, no 2, p. 102-109Article in journal (Refereed)
    Abstract [en]

    Finite element numerical analyses were performed to determine three-dimensional heat flux generated by friction to wood pieces during linear friction welding. The objective was to develop a computational model to explain the thermal behaviour of welded wood material rather than experimental methods, which are usually expensive and time consuming. This model serves as a prediction tool for welding parameters, leading to optimal thermo-mechanical performance of welded joints. The energy produced by the friction welding of small wood specimens of Scots pine (Pinus sylvestris L.) was determined by thermocouples and used as input data in the model. The model is based on anisotropic elasticity and the thermal properties were modelled as isotropic. This numerical simulation gave information on the distribution of the temperature in the welding interface during the entire welding process. A good agreement between the simulation and experimental results showed the appropriateness of the model for planning welded wood manufacture and prediction of thermal behaviour of wood during other mechanically induced vibration processes. The specimens presented in this model required a heat flux of 11 kW/m2 to achieve a satisfactory welding joint.

  • 9.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Gheinani, Iman Tavakoli
    ENSTIB-LERMAB, University of Lorraine, Mechanical Engineering, 27 rue Philippe Seguin, Epinal, France.
    Wood modification through mechanically induced wood fusion welding: 3-D finite element modelling of heat transfer.2014In: The seventh European Conference on Wood Modification (ECWM7: Book of Abstracts / [ed] Lina Nunes; Dennis Jones; Callum Hill; Holger Militz, Lissabon, 2014, p. 43-44Conference paper (Refereed)
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  • 10.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Dreimol, Christopher
    Wood Materials Science, Institute for Building Materials, ETH Zürich, 8093 Zürich, Switzerland; Cellulose & Wood Materials Laboratory, Empa, 8600 Dübendorf, Switzerland.
    Abrahamsson, Lars
    Vattenfall AB, BU Fuel, Engineering & Projects, Evenemangsgatan 13, 169 79 Solna, Sweden.
    Niemz, Peter
    Wood Materials Science, Institute for Building Materials, ETH Zürich, 8093 Zürich, Switzerland.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Parameter estimation and model selection for water vapour sorption of welded bond-line of European beech and Scots pine2023In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 77, no 7, p. 515-526Article in journal (Refereed)
    Abstract [en]

    The single exponential kinetics (SEK) and parallel exponential kinetics (PEK) models were fitted to kinetic sorption data of welded and unwelded Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.). Furthermore, diffusion coefficients of water vapour in wood were determined using two different Fickian diffusion solutions. The objective was to identify how well these models could represent the moisture contents of the specimens and to characterize differences between the sorption behaviour of welded and unwelded wood. This knowledge can be used to enhance the moisture resistance of welded wood, develop drying schedules, and improve the quality of timbers. The PEK and SEK models provided the most precise and the second most precise fits to the sorption kinetic data, respectively. The two Fickian models are equivalent when both the infinite series are truncated at n = 10. The Fickian models also exhibited the highest discrepancy with the experimental data. Nevertheless, the Fickian models fit relatively better to the sorption data of the welded wood than to that of the unwelded wood. This behaviour may be due to the rigid and less-swelling structure of the welded bond line.

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  • 11.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Dreimol, Christopher
    Wood Materials Science, Institute for Building Materials, ETH Zürich, 8093 Zürich, Switzerland; Cellulose & Wood Materials Laboratory, Empa, 8600 Dübendorf, Switzerland.
    Abrahamsson, Lars
    Vattenfall AB, BU Fuel, Engineering & Projects, Evenemangsgatan 13, 169 79 Solna, Sweden.
    Niemz, Peter
    Wood Materials Science, Institute for Building Materials, ETH Zürich, 8093 Zürich, Switzerland.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Water-vapour sorption of welded bond-line of European beech and Scots pine2023In: Holzforschung, ISSN 1437-434X, Vol. 77, no 7, p. 500-514Article in journal (Refereed)
    Abstract [en]

    The wood–water interactions of welded bond-lines of European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were in this paper studied for the first time with dynamic vapour sorption equipment. The aim of this study was to characterize the water sorption in the welded bond-line and to define to which extent it deviates from water sorption of the unwelded wood. The objective was to provide deepened knowledge about water sorption of the welded bond-line, which could be used to improve the moisture resistance of welded wood in the future. The welded wood generally had lower equilibrium moisture contents than the unwelded wood. The welded bond-lines of beech and pine showed greater hysteresis than the unwelded wood from 0 to 55 % relative humidity. All specimens showed faster adsorption than desorption. However, the welded wood showed slower adsorption but faster desorption than unwelded wood. The time to complete half of the fractional change in moisture content (E(t) = 0.5) increased as the moisture content increased. The adsorption diffusion coefficients of beech and welded beech were higher than those of pine and welded pine up to 50 % and 40 % RH, respectively. In desorption, pine had a higher diffusion coefficient than beech in the whole range of 85–0 % RH. Analogously, welded pine had a higher diffusion coefficient than welded beech in the range of 85–5 % RH. In contrast to the desorption, the welded wood always had lower adsorption diffusion coefficients than the corresponding unwelded wood. The diffusion coefficients showed irregular patterns in some ranges of the RH. Therefore, it was hard to make a clear conclusion about the water-sorption behaviour of the specimens based on the defined diffusion coefficients.

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  • 12.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    du Plessis, Anton
    Department of Forest & Wood Science, Stellenbosch University, Stellenbosch, South Africa.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Berg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Nano X-ray tomography analysis of the cell-wall density of welded beech joints.2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 4, p. 368-372Article in journal (Refereed)
    Abstract [en]

    This paper reports the results of a novel approach using nano X-ray computed tomography (CT) for the non-invasive determination of the weld-line density profile of welded wood joints. As a case study, wood samples with a dimension of 2 mm × 2 mm × 20 mm were cut from a board of welded beech (Fagus sylvatica L.). The spatial resolution of the X-ray scan was 500 nm. Densitometry results showed that welding was accompanied by a considerable increase in the bulk density and a decrease in the cell-wall density at the weld-line. The cell-wall density in the weld-line was almost 33% less than that of the unaffected wood. As an additional application of nano computed tomography, the 3D imaging also revealed details of the internal structure of the welded sample. This study showed that nano-CT is a powerful tool for the descriptive and quantitative study of welded wood.

  • 13.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Abrahamsson, Lars
    Vattenfall AB, BA Generation, BU Fuel, Engineering & Projects, Solna, Sweden.
    Lin, Chia-Feng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wettability of welded wood-joints investigated by the Wilhelmy method: part 1. Determination of apparent contact angles, swelling, and water sorption.2021In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 75, no 1, p. 65-74Article in journal (Refereed)
    Abstract [en]

    This study presents a novel application of the Wilhelmy plate method on welded joints of Scots pine sapwood and beech. Welding resulted in an increase in the contact angle (increased hydrophobicity) as well as a decrease in the water uptake and swelling of the welded pine-joint compared to non-welded pine. When the welding time was extended from 4 to 5 s, these properties were further pronounced. Welding of beech, on the other hand, led to an increase in the contact angle and a decrease in the water uptake, but an increase in the swelling.

    Fourier Transform Infrared spectroscopy showed that welding increased the aliphatic C-H and unsaturated C=C stretching absorption bands in pine and beech. Scanning electron microscopy showed a dense structure at the welded joints of the both species, giving evidence of a lower porosity that leads to a lower permeability as a result of the welding.

  • 14.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Abrahamsson, Lars
    Vattenfall AB, BA Generation, BU Fuel, Engineering & Projects, Solna, Sweden.
    Moghaddam, M.S
    Rise Research Institutes of Sweden Ab, Stockholm, Sweden.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wettability of welded wood-joints investigated by the Wilhelmy method: part 2. Effect of wollastonite additive2021In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 75, no 1, p. 79-86Article in journal (Refereed)
    Abstract [en]

    The effect of wollastonite on the wetting properties of welded Scots pine-joints was studied using the multicycle Wilhelmy plate method and by observation of the chemical composition of the welded joints. Welding pine with wollastonite for 5 s resulted in a decrease in the water uptake and the swelling, and an increase in the contact angle of the welded joint compared to welded wood without wollastonite. High-performance liquid chromatography and gas chromatography/mass spectrometry showed the presence of dehydration products such as furfural, 5-hydroxymethylfurfural, and levoglucosan in methanol extracts from welded joints of specimens welded with and without wollastonite. Phenols were also found by analysis using the Folin-Ciocalteu method and High-performance liquid chromatography. The importance of such compounds in relation to the wetting properties of the welded joint is discussed.

  • 15.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pizzi, A.
    ENSTIB-LERMAB, Université Henri Poincaré - Nancy.
    Mansouri, H.R.
    ENSTIB-LERMAB, Université Henri Poincaré - Nancy.
    Moisture sensitivity of Scots pine joints produced by linear frictional welding2010In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 24, no 8, p. 1515-1527Article in journal (Refereed)
    Abstract [en]

    The industrial application range of welded wood so far has been limited to interior use because of its poor moisture resistance. Influences of some welding and wood parameters such as welding pressure, welding time, and heartwood/sapwood on water resistance of Scots pine (Pinus sylvestris) were investigated. An X-ray Computed Tomography scanner was used to monitor density change in weldlines during water absorption-desorption. Axial samples measuring 200 mm × 20 mm × 20 mm from Scots pine were welded and placed standing in 5-mm-deep tap water. Then they were taken out of the water one at a time and scanned at 10-min intervals until the first crack appeared in the weldline where the two parts of each specimen made connection. Results showed that the X-ray Computed Tomography can be used as an effective tool to study welded wood. Welding pressure, welding time, and heartwood/sapwood showed significant effect on length and location of the crack in the welded zone. Data evaluation showed that combination of 1.3 MPa welding pressure, 1.5 s welding time and using heartwood led to highest moisture resistance, which produced only a very short crack in the beginning of the weldline

  • 16.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pizzi, Antonio
    ENSTIB-UHP, Epinal.
    Influence of machine setting and wood parameters on crack formation in Scots pine joints produced by linear friction welding2012In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 26, no 18-19, p. 2189-2197Article in journal (Refereed)
    Abstract [en]

    Previous investigations on linear welded woods have shown that the connections are not sufficiently resistant to water for use in outdoor conditions. Therefore, they are utilized mainly for non-structural use, with only short time exposure to varying humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood or sapwood on crack formation in the weldline of Scots pine (Pinus sylvestris) were investigated. Axial samples measuring 200 mm×20 mm×20 mm from Scots pine were welded, placed vertically in 5-mm-deep tap water and were taken out of the water one at a time after each 10 min of water absorption. Then they were scanned and put back into water until the first crack appeared in the weldline. An X-ray Computer Tomography (CT-) scanner was used to monitor water movement and density change in the weldlines during water absorption–desorption. CT-scanning enabled to detect the cracks as they formed in the weldline and could be used in wood welding studies. Data evaluation showed that all the three studied parameters had significant effects on crack formation and that crack occurrence could be postponed by using heartwood samples with 1.3 MPa welding pressure and 1.5 s welding time.

  • 17.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pizzi, Antonio
    ENSTIB-LERMAB, Université Henri Poincaré - Nancy.
    Influence of welding parameters and wood properties on the water absorption in Scots pine joints induced by linear welding2011In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, no 15, p. 1839-1847Article in journal (Refereed)
    Abstract [en]

    Wood welding is an environmentally-friendly and very quick technique to yield wood joints in just a few minutes and without using any adhesives. The only limitation of welded wood is that the joint is suitable only for interior use. Exterior use, or use in an environment with varying humidity requires water resistance of the welded joints. An investigation was performed to determine the effects of welding parameters and wood properties on water absorption in the weldline and how to reduce it through controlling the production parameters. The influences of welding pressure, welding time, and heartwood/sapwood on water absorption in the weldline of Scots pine (Pinus sylvestris) joints were investigated. Specimens composed of two pieces of heartwood or sapwood, each of dimensions 200 mm × 20 mm × 20 mm, were welded together to form specimens of dimensions 200 mm × 20 mm × 40 mm. The specimens were allowed to stand in 5-mm-deep tap water and then they were taken out of the water one at a time and scanned in 10-min intervals until the first crack appeared in the weldline. An X-ray Computerized Tomography scanner was employed to monitor water movement and density change in weldlines during water absorption-desorption. All three evaluated parameters showed significant effect on water absorption. Samples of heartwood welded by 1.3 MPa welding pressure and 1.5 s welding time showed the lowest water absorption

  • 18.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pizzi, Antonio
    ENSTIB-LERMAB, Université Henri Poincaré - Nancy.
    Influence of weldling parameters on weldline density and its relation to crack formation in welded Scots pine joints2011In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, no 15, p. 1819-1828Article in journal (Refereed)
    Abstract [en]

    Exterior use of welded wood laminates without further treatment is not recommended. Frictional welded joints have poor resistance to moisture variation, especially to drying. Therefore, application of welded woods is limited to interior use without exposure to highly variable air humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood/sapwood on weldline density of Scots pine (Pinus sylvestris) joints were investigated. Interdependence between density and water resistance of weldline (in terms of crack time) was also studied by comparing the results of this investigation with those of the earlier studies. Specimens composed of two wood pieces, each measuring 20 mm x 20 mm x 200 mm, were welded together to form a specimen measuring 40 mm x 20 mm x 200 mm by a vibration movement of one wood surface against another at a frequency of 150 Hz. An X-ray Computerized Tomography scanner was used to measure weldline density. Weldlines of sapwood produced by 1.3 MPa welding pressure and 1.5 s welding time showed the highest density. No correlation between weldline density and crack time was evident.

  • 19. Vaziri, Mojgan
    et al.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pizzi, Antonio
    ENSTIB-UHP, Epinal.
    Optimization of tensile-shear strength for linear welded Scots pine2012In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 26, no 1-3, p. 109-119Article in journal (Refereed)
    Abstract [en]

    The mechanical performance of welded wood has a decisive role in its applications. This study was performed to determine the welding conditions that optimized the tensile-shear strength of welded Scots pine (Pinus sylvestris). Tensile-shear strength as a function of welding pressure, welding time and holding time1 was measured according to European standard EN 205. Maximum tensile-shear strength of welded sample was 9.3 MPa that was obtained using 1.3 MPa welding pressure, 2.8 s welding time and 70 s holding time. This tensile-shear strength was about two times that of PVAc-glued samples. According to data evaluation tensile-shear strength could be optimized to 9.7 MPa by increasing the welding time to 3.5 s and decreasing the holding time to 60 s.

  • 20.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Orädd, Greger
    Department of Radiation Sciences, Umeå University.
    Lindgren, Owe
    Pizzi, Antonio
    ENSTIB-UHP, Epinal.
    Magnetic resonance imaging of water distribution in welded woods2011In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, no 16, p. 1997-2003Article in journal (Refereed)
    Abstract [en]

    This study was performed for a better understanding of water effect on welded wood and improving its water resistance. In this article, we have also attempted to demonstrate the feasibility of using Magnetic Resonance Imaging technology to study water movement in welded woods. Water distribution in welded woods of Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) was investigated by Magnetic Resonance Imaging. Axial specimens were cut from beech and sapwood of Scots pine in longitudinal direction of wood grain. Two pieces of each wood species were welded together by a linear vibration machine. Sub-samples measuring 30 mm × 20 mm × 100 mm were cut from the welded specimens for Magnetic Resonance Imaging. The results showed that weldline of Scots pine was more resistant to water than weldline of beech. Pine joint was still holding after 40 h immersion in water, while a rapid wetting of the beech joint resulted in breakage of the joint in even less than an hour. This preliminary study also showed that MRI is a powerful tool to measure water distribution in welded woods and highlighted the potential of this technique to enhance understanding of wood welding

  • 21.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Rogaume, Caroline
    ENSTIB-LERMAB, University of Lorraine, France.
    Masson, Eric
    CRITT Bois, France.
    Pizzi, Antonio
    ENSTIB-LERMAB, University of Lorraine, France.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    VOC emissions from linear vibration2015In: Proceedings of the 1st COST Action FP1407 Conference: Life Cycle Assessment, EPDs and Modified Wood, Koper, Slovenia, August 25-26 / [ed] A. Kutnar; M. Burnard; M. Schwarzkopf ; A. Simmons, Koper, Slovenia: University of Primorska, Scence and Research Centre of Koper , 2015, p. 26-27Conference paper (Refereed)
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  • 22.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Water resistance of welded pine2019In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 15, no 4, p. 200-205Article in journal (Refereed)
    Abstract [en]

    Wood welding is a novel technology to join wood elements based on friction between two wood surfaces. The crack formation in the welded joint was visualized and studied using X-ray Computed Tomography. Increasing the welding time from 4 s to 5 s could either make no difference or decrease the cracking time i.e. the time from water exposure of the specimen to the crack appearance in the welded joint, whereas increasing the welding time could improve the water resistance and shear strength of the welded joint. The incompatibility between the CT-scanning results with immersion test and the shear strength results lead to the idea that the cracking time may not be an indicator of durability and strength of the welded wood

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    fulltext
  • 23.
    Vaziri, Mojgan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Welding of thermally modified wood and thermal modification of the welded wood: Effects on the shear strength under climatic conditions2021In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 16, no 2, p. 3224-3234Article in journal (Refereed)
    Abstract [en]

    This work investigated how thermal modification affects the shear strength of welded joints under different climatic conditions. The order of the thermal modification, before or after the welding, was investigated for its effect on the shear strength of the welded wood. Two groups of thermally modified specimens were prepared in a laboratory kiln under controlled conditions, one thermally modified before welding and the other after welding of the specimens. The shear strength of the specimens were measured at four different moisture contents of 10%, 12%, 16%, and 18%, and the results for the two different approaches were compared. Moreover, observations of the X-ray computed tomography scanning and digital microscopy were used to study the density profile and the structural details of the welded joints. The results showed that thermal treatment of the wood either before or after welding had a negative influence on the shear strength, and the modes of failure of the joints in mechanical tests were in most cases brittle. In the weld interface of the wood modified before welding, a rigid material similar to charcoal was produced as a result of the further degradation of wood by welding pressure and frictional motion. Welding of wood before thermal modification, however, yielded thicker and more densified joints with less susceptibility to higher moisture variations than the joints obtained by welding the thermally modified wood.

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    fulltext
  • 24.
    Zor, Mustafa
    et al.
    Bülent Ecevit University, Caycuma Vocational School, Department of Design, Zonguldak, Turke.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Shear strength of welded birch wood produced by linear friction2019In: III. International Mediterranean Forest And Environment Symposium: Full-paper proceedings / [ed] Turgay Dindaroğlu, Turkey: Kahramanmaras Sutcu Imam University, Faculty of Forestry , 2019, p. 109-112Conference paper (Refereed)
    Abstract [en]

    Friction welding of wood is a joining technique that has the advantage of being a fast process that does not require the utilization of additional material such as mechanical fastener or synthetic adhesives. The water resistance, as well as shear strength of the welded joints of birch (Betula pendula) at 24 and 48 hours water-soaking time were investigated. Additionally, an X-ray Computed Tomography (CT) scanning was used to monitor the density profile of the welded bond-line. The LT-surfaces of specimens measuring 200 × 20 × 20 mm (L × T × R) were welded two-by-two. The results showed that the shear strength decreased slightly with increasing immersion time. The reduction of the shear strength caused by immersion in water for 24h and 48h compared to non-soaked specimens, were 60% and 79%, respectively. The X-ray CT-scanning results revealed that the average density of the Birch (530 kg/m3) increased to 700 kg/m3 in the welded bond line, i.e. the wood also undergo densification during the welding process.

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    fulltext
  • 25.
    Zor, Mustafa
    et al.
    Bülent Ecevi̇t Üni̇versi̇tes, Turkey.
    Vaziri, Mojgan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Water Resistance of Welded Birch Wood Produced by Linear Friction2020In: Kastamonu University Journal of Forestry Faculty, ISSN 1303-2399, Vol. 20, no 3, p. 266-271Article in journal (Refereed)
    Abstract [en]

    Aim of study: In this study, it was aimed to determine the shear strength after water immersion and observe bond-line density of the welded birch wood.

    Material and methods: 24 welded samples of dimensions 200x20x20 mm3 (LxTxR) were prepared from sapwood of birch wood (Betula pendula). Shear strength of welded birch at 24h and 48h water soaking were investigated.X-Ray CT-scanning was used to monitor the density profile of welded bond-line.

    Main results: The results showed that shear strength decreased slightly with increasing water immersion time. The decreasing of the average shear strength, caused by immersion for 24h and 48h were 60.25% and 78.9%, respectively, compared to control sample. With the welding process, a significant change in density was observed in the welding bond-line. As a result, the X-Ray CT scanner shows that it works effectively on wood material.

    Highlights: The results of this research revealed the applicability of a new method alternative to traditional mechanical fasteners (nail, screw etc.) or gluing. The availability of welding combining method in the field of wood engineering should be explored widely and more studies are recommended for appropriate parameters.

1 - 25 of 25
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