lnu.sePublications
Change search
Refine search result
12 1 - 50 of 94
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vercruysse, Adrien
    Stenberg, Sarah
    Vibration Distribution Due to Continous, Intermittent or Half Embedded Elastomer Connections in Wooden Constructions2016In: Proceeding of the 2016 World Conference on Timber Engineering (WCTE), August 22-25, 2016 Vienna / [ed] Josef Eberhardsteiner, Wolfgang Winter, Alireza Fadai, Martina Pöll, Vienna: TU-MV Media Verlag , 2016, 2912-2920 p.Conference paper (Other academic)
    Abstract [en]

    Elastomers are commonly used to decrease the sound transmission between apartments in timber framed houses. In previous studies, different types of elastomers have been evaluated experimentally. The wooden assemblies, in which elastomers were used in the connections, showed that elastomers cause the vibrations to increase in the direction perpendicular to the applied load within the low frequency span.

    In this study, the effects on acceleration, depending on how the elastomers are placed are studied. The cases having the elastomer continuous, placed as intermittent pieces or positioned half embedded in the junctions are evaluated.

    The frequency dependent properties of the elastomers are needed in order to model the dynamic behaviour and thereby be able to predict sound- and vibration transmission in wooden houses. Here, the properties of a wooden construction having different elastomers connections are studied to enable simulations of the behaviour of the elastomers in a FE model in the future.

  • 2.
    Carlsson, Peter
    et al.
    Mid Sweden University.
    Esping, Björn
    Mid Sweden University.
    Dahlblom, Ola
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Söderström, Ove
    Royal Institute of Technology.
    Optimization, a tool with which to create an effective drying schedule1998In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 52, no 5, 530-540 p.Article in journal (Refereed)
    Abstract [en]

    A method for defining effective schedules for kiln drying of wood is presented. The method is designed in such a way that it proposes an optimized variation of temperature and humidity which yields the minimum total drying time , with the condition that the moisture content and the deformation not exceed specified limits after the drying and that the stress not exceeds a specified level at any time during the drying process in order to avoid crack development. To demonstrate the capability of the optimization method numerical results are presented. It should be noted that ill this first approach, drying starts from moisture content corresponding to the fibre-saturation point, i.e. approximate to 30%).

  • 3.
    Crocetti, Roberto
    et al.
    Lund University.
    Gustafsson, Per Johan
    Lund University.
    Danielsson, Henrik
    Lund University.
    Emilsson, Arne
    Limträtenik AB.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Experimental and numerical investigation on the shear strength of glulam2010In: International Council for Research and Innovation in Building and Construction: Working Commission W18 ‑ Timber Structures — 2010, Nelson: University of Canterbury , 2010Conference paper (Refereed)
    Abstract [en]

    According to EC5, the shear resistance of a structural timber element should be determined on the basis of the characteristic shear strength of the material, along with classical beam theory. For glulam, the characteristic strength values are given by the European standard EN 1194 [3], which assumes a direct relationship between tensile strength and shear strength of the lamination. As an example, the characteristic shear strength of glulam class GL28c, consisting of inner laminations with characteristic tensile strength ft,0,k = 14.5 MPa, would  be fv,k = 0.32·(14.5)^0.8 = 2.9 MPa. However, recent investigations both on glulam members [4] and on timber members [5] have shown that the shear strength of spruce is higher than the shear strength obtained by means of the model proposed by EN1194. Moreover, the studies show that the shear strength is nearly constant, regardless the strength class of the timber material.

  • 4.
    Dahlblom, O.
    et al.
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Petersson, H.
    Lund University.
    Simulation of wood deformation processes in drying and other types of environmental loading1996In: Annales des Sciences Forestieres, ISSN 0003-4312, Vol. 53, no 4, 857-866 p.Article in journal (Refereed)
    Abstract [en]

    Deformation processes in wood exposed to drying and other types of environmental loading are simulated by use of the finite element method. In the material model applied, the orthotropic structure of the wood material is considered. The differences of properties in the longitudinal, radial and tangential directions for stiffness parameters as well as for moisture shrinkage parameters are taken into account. As an illustration of possible application areas, the deformation development of boards during drying is simulated. In the analyses, the influence of spiral grain and the variation of wood properties with the distance from the pith are considered. The simulation yields information about unfavourable deformations that develop during the drying process., Le processus de déformation du bois exposé au séchage et autres types de charges environnementales est simulé par la méthode des éléments finis. La structure orthotropique du bois est prise en considération sur le modèle de matériel utilisé. Les différences existant au niveau des propriétés des directions longitudinales, radiales et tangentielles sont prises en compte pour les paramètres de rigidité et de contraction par humidité. Une des possibilités du champ d'applications est illustrée par le fait que l'évolution de la déformation des planches pendant le séchage est simulée. À l'échelon des analyses, l'influence du grain spiral et la variation des propriétés du bois avec la distance depuis la moelle sont pris en compte. La simulation permet d'obtenir des informations concernant l'évolution des déformations défavorables pendant le processus de séchage.

  • 5. Dahlblom, Ola
    et al.
    Lindemann, Jonas
    Ormarsson, Sigurdur
    Software for Numerical Simulation of Drying Induced Deformation of Wooden Products2003In: 8th International IUFRO Wood Drying Conference, TRANSILVANIA University of Brasov, Faculty of Wood Industry , 2003, 45-50 p.Conference paper (Refereed)
    Abstract [en]

    A previously developed computational model for 3D finite element simulations of wood during moisture changes is in the present work provided with a special-purpose graphical user interface. The software is designed to use a personal computer for the graphical user interface and to have possibility to use distributed computational resources for the simulation.

  • 6. Dahlblom, Ola
    et al.
    Ormarsson, Sigurdur
    Petersson, Hans
    Prediction of deformations by an extended two-dimensional formulation1996In: Quality wood drying through process modelling and novel technologies / [ed] Alain Cloutier, Yves Fortin, 1996, 69-76 p.Conference paper (Refereed)
  • 7.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Experimental investigation of basic wood properties with respect to spatial variation in stem1997In: International Conference on Wood-Water relations, Department of Structural Engineering and Materials, Technical University of Denmark / [ed] P. Hoffmeyer,, 1997, 197-212 p.Conference paper (Refereed)
  • 8.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Stiffness and shape stability analysis of sawn timber based on experimentally found variations of wood properties1999In: Connection between Silviculture and Wood Quality through Modelling Approaches and Simulation Softwares, 1999Conference paper (Refereed)
  • 9.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology, Sweden.
    Persson, Kent
    Lund Institute of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Investigation of variation of engineering properties of spruce1999In: Wood Drying Research & Technology for Sustainable Forestry Beyond 2000, 1999Conference paper (Refereed)
  • 10.
    Dahlblom, Ola
    et al.
    Lund Institute of Technology.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Full 3-D FEM-Simulations of Drying Distortion in Spruce Boards based on Experimental Studies2001In: 7th International IUFRO Wood Drying Conference, 2001Conference paper (Refereed)
  • 11.
    Dahlblom, Ola
    et al.
    Lund University, Sweden.
    Petersson, Hans
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Stiffness, strength and shape stability grading analysis of sawn timber based on experimentally found growth characteristics2000In: World Conference on Timber Engineering, 2000Conference paper (Refereed)
    Abstract [en]

    Stiffness, strength and shape stability analysis of sawn timber should be based on how the material properties vary in the stem due to different growth conditions. As part of an EU study, results from investigations of the modulus of elasticity, shrinkage coefficient and spiral grain angle of spruce are presented. The variation in properties with the position in the stem has been investigated. The specimens were sawn from 274 stems in 29 stands in five countries of the European Union. A total of about 7000 small specimens were tested. Results from the modelling of stiffness and moisture-induced deformations of battens are presented. The simulations were based on material data obtained from measurements performed on specimens sawn from the same logs as the battens. The simulation results are compared with experimental results and are of interest for the development of new grading procedures for sawn timber.

  • 12. Dahlblom, Ola
    et al.
    Petersson, Hans
    Persson, Kent
    Ormarsson, Sigurdur
    Experimental investigation of basic properties of spruce1998In: World Conference on Timber Engineering, 1998Conference paper (Refereed)
  • 13. Eriksson, John
    et al.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Adaptive Finite Element Analysis of Non-linear Moisture Flow and Associated Distortion Behaviour in Wood2003In: ADMOS Conference on Adaptive Modelling and Simulation, 2003Conference paper (Refereed)
  • 14.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    An experimental and numerical study of the shape stability in glued columns2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 6, 423-429 p.Article in journal (Refereed)
    Abstract [en]

    The study concerns the question of how the shape stability features of laminated columns of Norway spruce can be improved in terms of twist through optimal orientation of the individual laminates. Both experimental testing and numerical simulations were employed for evaluating twist stability. In all the columns studied, deformations were measured experimentally at different moisture content levels. A number of columns were also selected for numerical analysis in order to obtain a more thorough understanding of the twist behavior involved, their geometries and material properties of interest being determined. The experimental results showed the twist stability of the columns to be highly dependant upon the internal orientation of the individual laminates. It was also found that high quality columns in terms of shape stability could be manufactured, even when the center-core material has a strong twist tendency. The numerical simulations performed were in close agreement with the experimental results.

  • 15.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Chalmers University of Technology.
    Experimental study of shape stability in glued boards2004In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 62, no 3, 225-232 p.Article in journal (Refereed)
    Abstract [en]

    An experimental study of shape stability in wooden glued boards was performed to verify certain results of particular interest obtained earlier in numerical simulations. Possibilities for achieving products of good shape stability by gluing boards together in an optimal way are discussed. Since twist is often the most serious form of distortion defects for the user, it was the main type of board deformation considered. Three types of glued products were tested. The experiments show clearly that glued boards can be produced that remain stable in shape when exposed to extreme variations in moisture. The results agree well with the numerical simulations performed earlier. It was found that initial twist could be reduced by proper application of pressure during gluing and that through gluing the occurrence of cracking defects on visible surfaces could be substantially reduced.

  • 16.
    Eriksson, John
    et al.
    Chalmers University of Technology .
    Ormarsson, Sigurdur
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Chalmers University of Technology .
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Finite element analysis of coupled nonlinear heat and moisture transfer in wood2006In: Numerical Heat Transfer, Part A Applications, ISSN 1040-7782, E-ISSN 1521-0634, Vol. 50, no 9, 851-864 p.Article in journal (Refereed)
    Abstract [en]

    A nonlinear model for analysing heat and moisture flow in wood during drying below the fiber saturation point is presented. The model used considers wood at a macro level without taking the various moisture transports mechanisms at the microscopic level into account. Based on the finite-element method, a coupled system of equations resulting from the adopted heat and moisture transfer equations is established and an iterative scheme is proposed. The numerical procedure is verified by a test example. In a two-dimensional analysis, the influence of the coupling on the combined heat and moisture transfer is studied for a board subjected to a typical kiln-drying condition. How well the results agree with those obtained by introducing a commonly applied simplification is discussed.

  • 17.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    The effect of initial green state moisture gradients on stresses in timber boards during drying2016In: Eccomas 2016 Proceedings, 2016Conference paper (Refereed)
  • 18.
    Florisson, Sara
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    The effect of surface emission, diffusion and initial moisture profiles on stress development in timber boards2017In: CompWood 2017 : Computational Methods in Wood Mechanics – from Material Properties to Timber: Programme & book of abstract, TU Verlag , 2017Conference paper (Refereed)
  • 19.
    Gustafsson, Per Johan
    et al.
    Lund University.
    Emilsson, Arne
    Lund University.
    Crocetti, Roberto
    Lund University.
    Ormarsson, Sigurdur
    Lund University.
    Provningar av limträs skjuvhållfasthet hösten 20092010Report (Other academic)
  • 20.
    Johansson, Marie
    et al.
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Effect of residual stresses on performance of sawn timber: Experiments2005In: Fifth IUFRO Workshop on Connection between Forest Resources and Wood Quality : Modelling Approaches and Simulation Software, 2005Conference paper (Refereed)
  • 21.
    Johansson, Marie
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Technical University of Denmark.
    Influence of growth stresses and material properties on distortion of sawn timber – Numerical investigation.2009In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 66, no 6, 604Article in journal (Refereed)
  • 22.
    Kliger, Robert
    et al.
    Chalmers University of Technology, Sweden.
    Johansson, Marie
    Chalmers University of Technology, Sweden.
    Ormarsson, Sigurdur
    Chalmers University of Technology, Sweden.
    Bäckström, Magnus
    Chalmers University of Technology, Sweden.
    The Builders'€™ View on Drying Quality and its Consequences2004In: Proceedings of COST E15 - Drying timber for value-added products, Athens, Greece, 22-24 April. 01/01/2004, 2004Conference paper (Refereed)
  • 23. Larsen, Finn
    et al.
    Ormarsson, Sigurdur
    A numerical and experimental study of stress and crack development in kiln-dried wood2012In: Proceedings of World Conference on Timber Engineering 2012, 2012Conference paper (Refereed)
    Abstract [en]

    Numerical and experimental investigations were carried out on well defined log-disc samples of Norway spruce consisting of both heartwood and sapwood, with the aim of gaining more adequate knowledge of stress and fracture generation during the drying process. Use of thin discs enabled a well-controlled and simplified drying history of the samples to be obtained. Experiments supported by the numerical model showed the heartwood to dry below the fibre saturation point, much earlier than the sapwood, and thus to start shrinking at a much earlier stage.

  • 24.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs2014In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 1, 133-140 p.Article in journal (Refereed)
    Abstract [en]

    Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) concerning the TSt and fracture behavior of Norway spruce under various climatic conditions. Thin log disc specimens were studied to simplify the description of the moisture flow in the samples. The specimens designed for TS were acclimatized to a moisture content (MC) of 18% before TSt tests at 20°C, 60°C, and 90°C were carried out. The maximum stress results of the disc simulations by FEM were compared with the experimental strength results at the same temperature levels. There is a rather good agreement between the results of modeling and experiments. The results also illustrate the strong decrease of TSt with increasing temperature at a constant MC level.

  • 25.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Numerical and experimental study of moisture-induced stress and strain field developments in timber logs2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 4, 837-852 p.Article in journal (Refereed)
    Abstract [en]

    When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.

  • 26.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Olesen, John Forbes
    Technical University of Denmark, Denmark.
    Experimental Investigation of Moisture Driven Fracture in Solid Wood2010In: WCTE - World Conference on Timber Engineering 2010: Conference Proceeding, Riva del Garda: Trees and Timber Institute , 2010, 449-450 p.Conference paper (Refereed)
    Abstract [en]

    Solid timber products, containing both heartwood and sapwood, often have a high tendency to crack during the drying process. This can cause severe loss of material for the saw-mills, especially for products with large cross sectional dimensions. The cracks (e.g. end-cracks) arise, in some cases, early in the drying process and close again later in the process. It can be difficult to see the closed cracks with visual grading. This may result in too high grading of the damaged material which may cause problems for customers such as building and furniture industries. Moisture content (MC) in green wood varies within the cross section of a timber log. The MC of heartwood, for example, is considerable lower than the MC of sapwood. Shrinkage starts at different times within different parts of the cross section, which results in a complex state of strains and stresses. The moisture related crack pattern in wood often becomes quite complex because of the annual ring structure and the different MC levels within heartwood and sapwood. The focus of this work represents the cross sectional behaviour of a timber log. The main aim is to accumulate experimental results and data for the development of a finite element model to evaluate the various couplings in the hygro-mechanical problem that govern moisture driven cracking in wood.

  • 27.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Olesen, John Forbes
    Technical University of Denmark, Denmark.
    Experimental study of moisture-driven distortion and fracture in solid wood2010In: 11th International IUFRO Wood Drying Conference : Recent Advances in the Field of Wood Drying, Luleå: Luleå tekniska universitet, 2010, 137-144 p.Conference paper (Refereed)
    Abstract [en]

    Moisture-induced fracture and lack of shape stability in solid wood products are well known problems to the saw-milling and building industries. Cracks that initiate during the drying process may cause severe material losses and the building industry may be forced to use alternative building materials. The cracking caused by kiln-drying of solid timber (and round wood) is extremely difficult to predict due to the strong orthotropic and non-homogeneous characteristics of the material in combination with considerable amounts of microscopic defects which may act as crack initiators. An experimental study has been performed to reveal the cracking behaviour of Norway spruce during drying from green moisture content down to equilibrium moisture content (EMC) at a temperature of 22-24°C and a RH of 64%. The moisture related strains and crack widths were measured with a digital image correlation system (ARAMIS) on thin discs cut from a timber log. The history of the strain field over the entire cross section of the discs was measured throughout the drying period. The results showed that the thicker discs (30 mm) cracked very early during the drying process. They also cracked significantly more than the thinner ones (15 mm) and the crack patterns developed differently. For the thicker discs the early cracks which may partly be caused by the moisture gradient in the longitudinal direction of the log, closed and became invisible later during the drying process. This indicates that sealing of timber log ends in the green moisture state could significantly reduce the development of end-cracks. It was also recognized that the initial moisture content and the shrinkage properties vary significantly from pith to bark. Based on this experimental finding it can be concluded that modelling of crack propagation in solid wood must take the material inhomogeneities into account.

  • 28.
    Larsen, Finn
    et al.
    University of Denmark.
    Ormarsson, Sigurdur
    University of Denmark.
    Olesen, John Forbes
    University of Denmark.
    Moisture-driven fracture in solid wood2011In: Wood Material Science & Engineering, ISSN 1748-0272, Vol. 6, no 1-2, 49-57 p.Article in journal (Refereed)
    Abstract [en]

    Moisture-induced fractures in solid timber create considerable problems for both building industries and sawmills. Cracks caused by kiln-drying of solid timber are extremely difficult to predict. This paper reports on experiments concerned with methods of reducing cracks in wood and with the cracking behaviour of Norway spruce discs. The spruce was dried from green moisture content down to equilibrium moisture content at 23°C and 64% relative humidity. Moisture-related strains and crack development were measured using a digital image correlation system, Aramis. The moisture gradient in the longitudinal direction had a major influence on crack behaviour and was quite pronounced in discs more than 30 mm thick, but much more limited in discs only 15 mm thick. Although the thicker discs often cracked very early in the drying process, many of these cracks became invisible later on in the drying process, suggesting that sealing the ends of timber logs while in the green moisture state could considerably reduce the development of end-cracks. The initial moisture content and the shrinkage properties of the wood varied markedly from pith to bark. The importance of taking material inhomogeneities into account when modelling crack propagation in solid wood is emphasized. © 2011 Taylor & Francis.

  • 29.
    Lindemann, Jonas
    et al.
    Lund Institute of Technology, Sweden.
    Ormarsson, Sigurdur
    Dahlblom, Ola
    Sandberg, Göran
    Enabling Access to Distributed Resources in a Software for Simulating Drying Induced Deformation of Wood2003In: 16th Nordic Seminar on Computational Mechanic, 2003Conference paper (Refereed)
  • 30.
    Nilsson, Jonaz
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Moisture-related distortion and damage of lightweight wood panels: experimental and numerical study2017In: Journal of the Indian Academy of Wood Science, ISSN 0972-172XArticle in journal (Refereed)
    Abstract [en]

    This study was conducted to increase the knowledge of moisture-related distortion and damage in the field of wood-based lightweight panels. By increasing the possibilities of predicting moisture-related distortion and damage, the possibilities of using lightweight wood materials could increase. The study was performed through experiments and modelling work on a wooden panel product with numerous struts and two thin outer-face sheets of beech-wood glued tightly onto the struts, as well as reference panels of solid wood. During the testing period the results showed the density of the studied lightweight panels to vary from 170 to 290 kg/m3. These panels shrunk and swelled less than the solid wood panels and reacted faster to changes of surrounding humidity and temperature. Moisture related distortions such as twist and bow were not inferior compared to the solid wood panels. Shrinkage or swelling produced moisture related stresses. This may mean that the panel will have a risk of serious damage in the form of cracks or glue release between the outer face sheet and the struts when it is exposed to intense drying. The experimental tests also followed how various damages arose in the panels. Until the damage occurred, the deformation results showed a strong agreement between the experimental and the model findings. Better knowledge of how this type of panel reacts to climate variations is important for the further design and development of this type of product.

  • 31.
    Ormarsson, Sigurdur
    Lund University.
    A Finite Element Study of the Shape Stability of Sawn Timber Subjected to Moisture Variations1995Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Shape instability in timber products exposed to moisture variation is a serious problem since it can make wood products unsuitable for construction purposes. In this thesis the finite element method has been used to simulate deformations during the drying process

    .…

    .…

    .…

    To investigate the influence of different parameters on drying deformations a parameter study was performed, the influence of different material parameters and of different constitutive models being studied. In addition, the influence of the spiral grain angle, the conical angle, the orientation of the growth rings, the cross section dimension and the drying profile was examined.

  • 32.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Moisture-induced stresses in curved statically indeterminate timber structures2015In: Theoretical, Numerical, and Experimental Analyses in Wood Mechanics, 2015Conference paper (Refereed)
  • 33.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Numerical Analysis of Moisture-Related Distortion in Sawn Timber1999Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A 3D theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate, the mechano-sorption strain rate and the creep strain rate. The 3D theory used for analyzing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of boards during drying was simulated. .....

  • 34.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark, Denmark.
    Blond, Mette
    COWI A/S, Denmark.
    An improved method for calculating force distributions in moment-stiff timber connections2012In: Proceedings of World Conference on Timber Engineering 2012, 2012Conference paper (Refereed)
    Abstract [en]

    An improved method for calculating force distributions in moment-stiff multi-dowel timber connections is presented, a method based on use of three-dimensional finite element simulations of timber connections subjected to moment action. The study that was carried out aimed at determining how the slip modulus varies with the angle between the direction of the dowel forces and the fibres in question, as well as how the orthotropic stiffness behaviour of the wood material affects the direction and the size of the forces. It was assumed that the force distribution generated by the moment action taking place strives to minimize the slip rotation between the separate members of a given timber connection. The results of modified hand calculations and of the corresponding finite element calculations that were performed were found to agree rather closely, and to differ remarkably from the results of conventional hand calculations.

  • 35. Ormarsson, Sigurdur
    et al.
    Cown, Dave
    Wood Quality and Solid Wood Products Forest Research.
    Moisture-Related Distortion of Boards and Wooden Products of Radiata Pine: Comparison with Norway Spruce2003In: IUFRO – All Division 5 Conference, Forest products research – providing for sustainable choices, 2003Conference paper (Refereed)
  • 36.
    Ormarsson, Sigurdur
    et al.
    Chalmers University of Technology.
    Cown, Dave
    Forest Res, Wood Qual & Solid Wood Prod, New Zealand.
    Moisture-Related Distortion of Timber Boards of Radiata Pine: Comparison with Norway Spruce2005In: Wood and Fiber Science, ISSN 0735-6161, Vol. 37, no 3, 424-436 p.Article in journal (Refereed)
    Abstract [en]

    Based on material data obtained by several researchers at Forest Research in New Zealand, with respect to variations in the main material properties from pith to bark, the distortion model developed earlier for Norway spruce has been further modified for radiata pine. Numerical simulations were performed for both pine and spruce to investigate how different sawn pattern options affect the shape stability of individual boards. Results for spruce presented earlier have shown clearly that warping of the timber products is strongly influenced by the annual ring patterns within the individual boards. Comparisons between the two species were performed to study how the radial variations in the basic properties such as shrinkage parameters, stiffness parameters, and spiral grain have influence on the warping. Generally, the intrinsic patterns of variation in wood properties within stems were similar, and both species show a tendency to distort with changing moisture environment. There are strong indications that intelligent re-combination of material in glued products may overcome many of the inherent problems in using biological material with predictable variation in material properties. Keyword: Finite element simulations, Pinus radiata, shrinkage, spiral grain, distortions, wood, timber boards

  • 37. Ormarsson, Sigurdur
    et al.
    Cown, Dave
    Wood Quality and Solid Wood Products Forest Research.
    Dahlblom, Ola
    Lund Institute of Technology, Sweden.
    Finite Element Simulations of Moisture Related Distortion in Laminated Timber Products of Norway Spruce and Radiata Pine2003In: 8th International IUFRO Wood Drying Conference, 2003Conference paper (Refereed)
    Abstract [en]

    A three dimensional finite element model has been used to analyse distortion in different laminated products of Norway spruce and Radiata pine such as laminated boards, panels and windows. The results show that twist of the products is strongly influenced by the radial variation in material data (spiral grain, shrinkage coefficients etc), original location of the separate pieces within the log and how they are oriented in the products. The results also indicate that the twist pattern for both the spices are quite similar but the twist values of Radiata pine are significantly higher because of its high spiral grain angle. The shape stability of laminated engineering products of wood can be much improved by combining the material knowledge and simulation technique to find the optimal choice and orientation of the individual pieces in the products.

  • 38. Ormarsson, Sigurdur
    et al.
    Dahlblom, O.
    Nygaard, M. J.
    Finite Element Simulation of Mechanical and Moisture-Related Stresses in Laterally Loaded Multi-Dowel Timber Connections2010In: WCTE - World Conference on Timber Engineering 2010, Riva del Garda: Trees and Timber Institute , 2010Conference paper (Refereed)
    Abstract [en]

    Numerical simulations of stress distribution within a moment stiff timber frame corner have been performed. The frame corner is a multi-dowel connection with two slotted-in steel plates. The interaction between the fasteners and the wood material is modelled as a full contact interaction based on penalty formulation. The wood material is assumed to be an orthotropic material in reference to elastic and shrinkage behaviours. Both mechanical loading (from snow and wind) and moisture loading have been studied. Model adaptivity was used to reduce the computer time and to find suitable coupling conditions between beam and solid elements. The simulation results have been compared with typical hand calculations. The conclusion is that the hand calculations diverge quite a lot from the simulation results and relatively small moisture changes can cause significant stresses in areas adjoining the fasteners.

  • 39.
    Ormarsson, Sigurdur
    et al.
    Lund University,.
    Dahlblom, O.
    Lund University.
    Petersson, H.
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 1: Theory1998In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 32, no 5, 325-334 p.Article in journal (Refereed)
    Abstract [en]

    A three-dimensional theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed, assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate and the mechano-sorption strain rate. Wood is assumed to be an orthotropic material with large differences between the longitudinal, radial and tangential directions in the properties found. The influence of the growth rings, the spiral grain and the conical shape of the log on the orthotropic directions in the wood is taken account of in the model. A finite element formulation is used to describe the deformation process and the stress development during drying.

  • 40. Ormarsson, Sigurdur
    et al.
    Dahlblom, O.
    Lund Institute of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Shape stability of wooden products: Influence of radial variations of basic properties and spiral grain1996In: Connection Between Silviculture and Wood Quality Through Modelling Approaches and Simulation Softwares — 1996, 1996Conference paper (Refereed)
  • 41.
    Ormarsson, Sigurdur
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Dahlblom, Ola
    An extended beam model for simulation of hygro-mechanical and visco elastic deformations in inhomogeneous timber structures2014In: 11th World Congress on Computational Mechanics - 2014, Barcelona: Spanish Association for Numerical Methods in Engineering , 2014Conference paper (Refereed)
    Abstract [en]

    Due to numbers of failures of large glue laminated (glulam) timber structures there seems to be a need for better design tools for wood applications. In EC5 and in many textbooks on timber design it is stated that the moisture sensitivity of the wood material needs to be taken into account in the design process. But the fact is that in stress calculations associated with ordinary timber design, these matters are not dealt with properly. The problem is that it is very difficult to predict the variation of moisture-related stresses during the service life of the timber structure as a whole. A proper prediction requires that material inhomogeneity, mechano-sorption effect and visco-elastic behaviour are taken into account. The paper presents a finite element implementation of a new beam element able to simulate hygro-mechanical and visco-elastic behaviours in inhomogeneous timber structures.

  • 42.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark, Denmark.
    Dahlblom, Ola
    Lund University.
    Finite element modelling of moisture related and visco-elasticdeformations in inhomogeneous timber beams2013In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 49, 182-189 p.Article in journal (Refereed)
    Abstract [en]

    Wood is a hygro-mechanical, non-isotropic and inhomogeneous material concerning both modulus ofelasticity (MOE) and shrinkage properties. In stress calculations associated with ordinary timber design,these matters are often not dealt with properly. The main reason for this is that stress distributions ininhomogeneous glued laminated members (glulam) and in composite beams exposed to combinedmechanical action and variable climate conditions are extremely difficult to predict by hand. Severalexperimental studies of Norway spruce have shown that the longitudinal modulus of elasticity and thelongitudinal shrinkage coefficient vary considerably from pith to bark. The question is how much thesevariations affect the stress distribution in wooden structures exposed to variable moisture climate. Thepaper presents a finite element implementation of a beam element with the aim of studying how woodencomposites behave during both mechanical and environmental load action. The beam element is exposedto both axial and lateral deformation. The material model employed concerns the elastic, shrinkage, mechano-sorption and visco-elastic behaviour of the wood material. It is used here to simulate the behaviourof several simply-supported and continuous composite beams subjected to both mechanical and environmentalloading to illustrate the advantages this can provide. The results indicate clearly both the inhomogeneityof the material and the variable moisture action occurring to have had a significant effecton the stress distribution within the cross-section of the products that were studied.

  • 43.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark, Denmark.
    Dahlblom, Ola
    Lund University, Sweden.
    Modelling of growth stress generation and timber distortions related to log sawing and forced drying2008In: 8th World Congress on Computational Mechanics and 5th European Congress on Computational Methods in Applied Sciences and Engineering, 2008Conference paper (Refereed)
    Abstract [en]

    Growth stresses can cause fibre collapse in living trees (often in combination with strong wind loading), internal checking resulting in end-splitting of logs, and instantaneous board distortions when the log is split into timber. How much the growth rate and growth stresses affect the final shape stability of solid timber products is not fully understood. For trees with abnormal growth conditions resulting in eccentric growth and generation of reaction wood, it is very complicated to estimate how timber products made of such material will behave during moisture variation. To study this behaviour a finite element analysis in which stress formation during normal and abnormal tree growth was simulated with the aim of better understanding of the growth stress formation.

    The model for progressive growth stress generation in trees with normal growth conditions is formulated as a one dimensional axisymmetric general plane strain model of the tree stem. The trunk is considered as a very long solid cone with zero shear stresses. In the model, each new (and stress free) annual ring is progressively added to the stem during the analysis. Thereafter the cell maturation is assumed to start, i.e. the crystallization of the cellulose leads to longitudinal shrinkage of the new annual ring whereas the lignification process results in transversal expansion of the fibres. Since the maturing annual ring is attached to the old and already matured rings, a strain constraint develops in the stem. The new annual ring becomes stretched longitudinally and compressed tangentially, whereas the matured rings are exposed to the opposite stress conditions. The material model used is based on the assumption of small strains and the biological maturation strains are used as a driving force for the growth stress evolutions. The aim here is also to take into account viscous effects of the wood material. ......

  • 44.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark.
    Dahlblom, Ola
    Johansson, Marie
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Finite element study of growth stress formation in wood and related distortion of sawn timber2009In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 43, 387-403 p.Article in journal (Refereed)
    Abstract [en]

    Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.

  • 45.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark.
    Dahlblom, Ola
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Numerical study of how creep and stiffness evolution affect the growth stress formation in trees2010In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 24, no 1, 105-115 p.Article in journal (Refereed)
    Abstract [en]

    It is not fully understood how much growth stresses affect the final quality of solid timber products in terms of e.g. shape stability. It is for example difficult to predict the internal growth stress field within the tree stem. Growth stresses are progressively generated during the tree growth and they are highly influenced by climate, biologic and material related factors. To increase the knowledge of the stress formation a finite element model was created to study how the growth stresses develop during the tree growth. The model is an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The material model used is based on the theory of small strains (where strains refer to the undeformed configuration which is good approximation for strains less than 4%) where so-called biological maturation strains (growth-related strains that form in the wood fibres during their maturation) are used as a driver for the stress generation. It is formulated as an incremental material model that takes into account elastic strain, maturation strain, viscoelastic strain and progressive stiffening of the wood material. The results clearly show how the growth stresses are progressively generated during the tree growth. The inner core becomes more and more compressed whereas the outer sapwood is subjected to slightly increased tension. The parametric study shows that the growth stresses are highly influenced by the creep behaviour and evolution of parameters such as modulus of elasticity, micro fibril angle and maturation strain.

  • 46.
    Ormarsson, Sigurdur
    et al.
    Lund University.
    Dahlblom, Ola
    Lund University.
    Petersson, Hans
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 2: Simulation of drying board1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 5, 407-423 p.Article in journal (Refereed)
    Abstract [en]

    A theory for analysing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of a board during drying was simulated. The simulation yields information about unfavourable deformations and stresses during the drying process. To investigate factors that influence drying deformations, a parameter study was performed in which the influence of different constitutive models and different material parameters was studied. In addition, the influence of the spiral grain angle was examined.

  • 47.
    Ormarsson, Sigurdur
    et al.
    Chalmers University of Technology.
    Dahlblom, Ola
    Lund University.
    Petersson, Hans
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 3: Influence of annual ring orientation2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 3, 207-219 p.Article in journal (Refereed)
    Abstract [en]

    Numerical simulations were performed to investigate how the annual ring orientation affects the shape stability of sawn timber. The influence of radial variations in the basic properties and the spiral grain is also studied. The knowledge obtained can contribute to more effective use of the raw material through allowing boards having properties that would yield bad shape stability to be sorted out. Possibilities for improving shape stability through gluing pieces of wood together are examined as well.

  • 48.
    Ormarsson, Sigurdur
    et al.
    Chalmers University of Technology, Sweden.
    Dahlblom, Ola
    Lund University, Sweden.
    Petersson, Hans
    Chalmers University of Technology, Sweden.
    Computer simulations of varying growth characteristics on stiffness grading properties of structural timber1999In: RILEM Symposium on Timber Engineering, Rilem publications, 1999, 549-559 p.Conference paper (Refereed)
    Abstract [en]

    In order to investigate stiffness and strength properties of sawn timber, it is common practice to load the specimens and measure the deflection. The results obtained from measurements are strongly influenced by grain deviation with respect to the longitudinal direction and by variation of material properties with position in the log. Effects of this type are often explained by the presence of juvenile wood and compression wood. In addition to being influenced by fibre misalignment and variation in properties, the grading procedure is often disturbed by twist deformations of the board caused by spiral grain.

  • 49. Ormarsson, Sigurdur
    et al.
    Dahlblom, Ola
    Lund Institute of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Influence of annual ring orientation on shape stability of sawn timber1996In: Quality Wood Drying Through Process Modelling and Novel Technologies / [ed] A. Cloutier, Y. Fortin, and R. Gosselin, 1996, 427-436 p.Conference paper (Refereed)
  • 50. Ormarsson, Sigurdur
    et al.
    Dahlblom, Ola
    Lund Institute of Technology, Sweden.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Influence of spiral grain on stiffness grading of structural timber1999In: Proceedings of Pacific Timber Engineering Conference PTEC 99, 1999, 63-69 p.Conference paper (Refereed)
12 1 - 50 of 94
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf