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  • 1.
    Alfthan, Johan
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    A micromechanical model for mechanosorptive creep in paper2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 3, p. 98-104Article in journal (Refereed)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling, a phenomenon known as mechanosorptive creep or accelerated creep. In this paper stress created at bonds due to anisotropic swelling during absorption and desorption of moisture, in combination with nonlinear creep, are proposed to be the cause for mechanosorptive creep. Two simplifled models are first discussed in order to demonstrate the suggested mechanism. A three-dimensional fibre network model composed of elastic fibres and inelastic bonds is then studied by finite element calculations. The relative sliding in the bonds is described by a nonlinear creep model which, in combination with anisotropic hygroexpansion of the fibres results in accelerated creep of the network.

  • 2. Bankel, J.
    et al.
    Berggren, K. F.
    Engstrom, M.
    Wiklund, I.
    Crawley, E. F.
    Söderholm, D.
    El Gaidi, K.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Benchmarking engineering curricula with the CDIO syllabus2005In: International journal of engineering education, ISSN 0949-149X, Vol. 21, no 1, p. 121-133Article in journal (Refereed)
    Abstract [en]

    Four internationally-renowned universities-Chalmers University of Technology, Linkoping University, Royal Institute of Technology (Sweden), and the Massachusetts Institute of Technology (USA)-developed a benchmark survey that may be used by any engineering school to benchmark curricula for teaching of personal, interpersonal and system building skills. These skills are enumerated in the CDIO Syllabus. Teaching activities were categorized as Introduce, Teach or Utilize, based on intent, time spent, and linkage to learning objectives, assignments and assessment criteria. Interviews were used to collect the data from instructors of the schools' engineering programs. The data was then reduced and analyzed to illuminate patterns of teaching. The results indicate that much effort is expended in covering these topics, but often in an inefficient, uncoordinated and unplanned manner. For example, there are often frequent repetitions of introducing a topic, without ever teaching it. In other instances, students are expected to utilize knowledge without having been taught it. The results of the benchmark survey indicate that a consistent and deliberately designed curriculum in this area could demand no additional resources, yet provide a much more effective education. The survey gives useful indications of how to begin such a curriculum redesign process.

  • 3.
    Bankel, Johan
    et al.
    Chalmers University of Technology.
    Berggren, Karl-Fredrik
    Linköping University.
    Blom, Karin
    KTH.
    Crawley, Edward F.
    Massachussetts Institute of Technology.
    Wiklund, Ingela
    Linköping University.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    The CDIO syllabus: a comparative study of expected student proficiency2003In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 28, no 3, p. 297-315Article in journal (Refereed)
    Abstract [en]

    Engineering students must graduate with command of a vast body of technical knowledge. They must possess personal, interpersonal and system-building skills to function in teams, and be prepared to produce products and systems. Their education must have been structured under a curriculum blending ability to combine technical expertise with ethical, innovative, philosophical and humanistic acumen. This paper describes a unique international collaboration among four universities to reform engineering education. The collaborators agreed to a statement of goals, which includes descriptions of knowledge, skills and attitudes vital to an effective education, and codifies proficiency levels expected of graduates. We developed and utilized unique stakeholder surveys both to validate our prototype and to determine desired proficiency levels. This collaboration resulted in The CDIO Syllabus, A Statement of Goals for Undergraduate Engineering Education. The syllabus is both a template and a process that can be used to customize the syllabus to others' programmes. It can define new educational initiatives/and be employed as the basis for rigorous assessment. This paper details how, with the input of industry, academia and others, we employed an engineering problem-solving paradigm to effect our redesign. It outlines the syllabus and the unique process employed to create it.

  • 4.
    Barbier, Christophe
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Experimental investigation of damage at folding of coated papers2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 1, p. 34-38Article in journal (Refereed)
    Abstract [en]

    An experimental investigation of damage occuring at folding of coated paper has been performed. For this purpose an experimental device was constructed in such a way that close resemblance with an industrial situation was achieved. During the experiments the influence on the damage levels in the coating from such features as delamination, humidity and paper thickness have been studied using an optical microscope. The behaviour of two different paper materials has been investigated. A stress (or strain) based fracture criterion is relevant for the present problem but biaxiality of stresses as well as in-plane anisotropy must be taken into account. It was observed that cracking of the coating would not lead to subsequent cracking of the paper substrate and that delamination occurred during folding, in the base stock and not at the paper/coating interface, but its quantitative influence as regards cracking could not be determined. The influence from sheet grammage was investigated and it was found that the only case when (visible) cracks did not appear was at low values. High humidity did not affect the cracking.

  • 5.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Numerical investigation of folding of coated papers2005In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 67, no 4, p. 383-394Article in journal (Refereed)
    Abstract [en]

    Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the numerical analysis, the basepaper is modelled as an anisotropic elastic-plastic material (both elastic and plastic anisotropy is accounted for) while the constitutive behaviour of the coating layers are approximated by classical (Mises) elastoplasticity. The numerical results suggest, among other things, that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. It is also shown that delamination buckling, in the present circumstances, will have a very small influence on the strain levels in the coating layer subjected to high tensile loading.

  • 6.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On dynamic effects at folding of coated papers2005In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 67, no 4, p. 395-402Article in journal (Refereed)
    Abstract [en]

    Folding of coated papers is examined numerically using the finite element method. The analysis is focused on the influence from dynamic effects on the folding process. In particular, the behaviour of field variables relevant for cracking of the coating layers are studied in some detail. The results presented indicate that dynamic effects are of little importance as regards maximum strain levels in the coating but will influence the stress and strain distributions. Accordingly, a quasi-static analysis of the problem will be sufficient in order to describe many of the important features related to cracking.

  • 7.
    Barbier, Christophe
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    On the effect of high anisotropy at folding of coated papers2004Report (Refereed)
  • 8.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On the effect of high anisotropy at folding of coated papers2006In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 72, no 3, p. 330-338Article in journal (Refereed)
    Abstract [en]

    A finite element procedure, developed in order to account for the effect of high anisotropy at folding of coated papers, is presented. The anisotropic behaviour (with very low stiffness in the thickness direction) is modelled using stiff structural elements (trusses and beams). The numerical results indicate that high elastic anisotropy leads to lower strain levels at folding than reported in previous analyses where this effect was not accounted for. High plastic anisotropy, on the other hand, will contradict this result.

  • 9.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Eklund, Johan
    DPC, MidSweden University.
    Folding of Printed Papers: Experiments and Numerical Analysis2003In: Preprints of the 2003 International Paper Physics Conference, 2003, p. 193-196Conference paper (Refereed)
  • 10.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Hallbäck, N.
    Karathanasis, M.
    On material characterization of paper coating materials by microindentation testing2005In: Journal of Coatings Technology Research, ISSN 1547-0091, Vol. 2, no 6, p. 463-471Article in journal (Refereed)
    Abstract [en]

    Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts arc, made to account for the influence from plasticity as well as from boundary effects.

  • 11.
    Berggren, Karl-Fredrik
    et al.
    Linköping University.
    Brodeur, Doris
    Massachusetts Institute of Technology.
    Crawley, Ed F.
    Massachusetts Institute of Technology.
    Ingemarsson, Ingemar
    Linköping University.
    Litant, William T. G.
    Massachusetts Institute of Technology.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    An International Initiative for Reforming Engineering Education2003In: World Transactions on Engineering and Technology Education, Vol. 2, no 1, p. 49-52Article in journal (Refereed)
  • 12. Crawley, E. F.
    et al.
    Malmqvist, J.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Brodeur, D. R.
    Overview2007In: Rethinking Engineering Education: The CDIO Approach, Springer-Verlag New York, 2007, p. 6-44Chapter in book (Refereed)
    Abstract [en]

    The objective of engineering education is to educate students who are ready to engineer, that is, broadly prepared with the pre-professional skills of engineering, and deeply knowledgeable of the technical fundamentals. It is the task of engineering educators to continuously improve the quality and nature of undergraduate engineering education in order to meet this objective. Over the past 25 years, many in industry, government, and university programs have addressed the need for reform of engineering education, often by stating the desired outcomes in terms of attributes of engineering graduates. By examining these views, we identified an underlying need: to educate students to understand how to Conceive-Design-Implement-Operate complex value-added engineering products, processes and systems in a modern, team-based environment.

  • 13.
    Crawley, E. F.
    et al.
    Massachusetts Institute of Technology.
    Malmqvist, J.
    Chalmers.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Brodeur, D. R.
    Massachusetts Institute of Technology.
    Edström, Kristina
    KTH, School of Education and Communication in Engineering Science (ECE), Learning.
    Rethinking engineering education: The CDIO approach, second edition2014Book (Other academic)
    Abstract [en]

    This book describes an approach to engineering education that integrates a comprehensive set of personal, interpersonal, and professional engineering skills with engineering disciplinary knowledge in order to prepare innovative and entrepreneurial engineers. The education of engineers is set in the context of engineering practice, that is, Conceiving, Designing, Implementing, and Operating (CDIO) through the entire lifecycle of engineering processes, products, and systems. The book is both a description of the development and implementation of the CDIO model and a guide to engineering programs worldwide that seek to improve the education of young engineers.

  • 14.
    Crawley, Edward F.
    et al.
    Massachusetts Institute of Technology.
    Malmqvist, JohanChalmers University of Technology.Östlund, SörenKTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).Brodeur, Doris R.Massachusetts Institute of Technology.
    Rethinking Engineering Education: The CDIO Approach2007Collection (editor) (Refereed)
    Abstract [en]

    In the past ten years, leaders in engineering industries have identified specific knowledge, skills, and attitudes required of their workforce if they want to be innovative and competitive in a global marketplace. Engineering education programs have kept pace with emerging disciplinary knowledge, research and technologies, but have been less successful in ensuring that their graduates acquire the knowledge, skills, and attitudes desired by industry. This book describes an approach to engineering education that integrates a comprehensive set of personal and interpersonal skills, and process, product, and system building skills with disciplinary knowledge. The education of engineers is set in the context of engineering practice, that is, Conceiving, Designing, Implementing, and Operating (CDIO) through the entire lifecycle of engineering processes, products, and processes. The CDIO approach and the topics in the book will be of increasing interest in the next five to ten years. At the start of the CDIO Initiative, four leading engineering programs in the United States and Sweden adopted the CDIO approach and collaborated in its development and implementation. In less than six years, the collaboration has grown to include more than twenty programs in nine different countries. This book will be both a description of the development and implementation of the CDIO approach, and a guide to engineering programs worldwide who seek to improve their programs. From the Foreword by Charles M. Vest, President Emeritus, MIT: The philosophy of the CDIO approach to engineering education captures these essential features of a modern engineering education -excitement about what engineers do, deep learning of the fundamentals, skills, and the knowledge of how engineers contribute to society.

  • 15.
    Crawley, Edward F.
    et al.
    Massachusetts Institute of Technology.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Edström, Kristina
    KTH, School of Education and Communication in Engineering Science (ECE), Lärande.
    Soderholm, Diane F.
    Massachusetts Institute of Technology.
    Curriculum Design based on the CDIO Syllabus2005In: 8TH UICEE ANNUAL CONFERENCE ON ENGINEERING EDUCATION, CONFERENCE PROCEEDINGS: BRINGING ENGINEERING EDUCATORS TOGETHER, UICEE , 2005, p. 313-317Conference paper (Refereed)
  • 16.
    Dominic, Chris A. S.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial marketing.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial marketing.
    Buffington, John
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial marketing.
    Masoud, Mian Muhammad
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial marketing.
    Towards a conceptual sustainable packaging development model: A corrugated box case study2015In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 28, no 5, p. 397-413Article in journal (Refereed)
    Abstract [en]

    Corrugated package designers are focused on balancing the need for product protection, material use efficiency and the packaging material's impact on the environment in the supply chain. The purpose of this paper is to develop a conceptual sustainable packaging model that integrates the variables of technical design, supply chain systems and environmental factors and then use the model to identify to improve upon corrugated container design. A model was developed, from the extant literature, and a case study was performed on a corrugated container. This is believed to be a unique integrated model of most relevant agents related to the design and implementation of a corrugated box through a supply chain from design to potential post-consumer reuse. From this study, we found opportunities to improve the environmental design of the corrugated container through four ex ante design stages, and two ex post facto supply chain stages. Further, research can evaluate and refine this model via a 'live supply chain' for use in guiding corrugated box material selection design and reuse/recycling. Integration of the design criterion for a unit load in the supply chain creates opportunity to observe the packaging system holistically. Waste in the manufacturing process and CO<inf>2</inf> emissions are traced along the material flow until the end of its useful life to provide an overall picture of the packaging system.

  • 17.
    Edström, Kristina
    et al.
    KTH, School of Education and Communication in Engineering Science (ECE), Department for Library services, Language and ARC, Learning Lab IKT.
    Gunnarsson, Svante
    Linköping University.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Integrated Curriculum Design2007In: Rethinking Engineering Education: The CDIO Approach / [ed] Crawley, E.F., Malmqvist, J., Östlund, S., & Brodeur, D.R., Springer, 2007Chapter in book (Refereed)
  • 18. Fellers, C.
    et al.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Mäkelä, P.
    Evaluation of the Scott bond test method2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 231-236Article in journal (Refereed)
    Abstract [en]

    The Scott bond test is the most commonly used test method for quantifying the delamination resistance of paper and board. The objective of this investigation was to validate the hypothesis that the Scott bond value would be dominated by the total energy under the force elongation curve in a z-directional tensile test. The investigation comprised three types of hand sheets with comparatively low strength values. Three test methods were used to obtain the energy for delamination: 1) Z-test, a z-directional tensile test, 2) Scott bond test, and 3) Simulated Scott bond test, a Scott bond type of test performed in a hydraulic tensile tester. The test data were expressed as a correlation between the failure energy obtained from the Z-test and the other two tests. The results showed that the Scott bond test gave slightly higher values than the Z-test for the weakest paper, but that the value tended to be much higher for the stronger papers. On the other hand the Simulated Scott bond test tended to give lower values than the Z-test. High speed photography was used to reveal several energy consuming mechanisms in the Scott bond test that can explain why this test gave higher values than the Ztest. The lower values from the Simulated Scott bond values are more difficult to explain. At this stage we can suggest that the failure mechanism is different if the paper is delaminated by pure tension or by a gradual delamination as in the Scott bond test.

  • 19. Gamstedt, E. Kristofer
    et al.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Fatigue propagation of fibre-bridged cracks in unidirectional polymer-matrix composites2001In: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 8, no 6, p. 385-410Article in journal (Refereed)
    Abstract [en]

    In order to improve the fatigue resistance of polymer-matrix composites by materials design, or to conceive micromechanics based models for life predictions, the underlying micromechanisms must be understood. Experimental investigations have revealed fibre-bridged cracking as a toughening micromechanism that retards further fatigue crack growth in a unidirectional 0 degrees carbon-fibre-reinforced epoxy. The bridging fibres exert a closing traction on the crack surfaces, thereby reducing the driving force for crack growth. In this study, the growth of bridged cracks has been quantified by a surface replication technique. The da/dN-DeltaK curve defined in terms of nominal stress-intensity factors shows a crack retarding behaviour. The crack growth curve can be replotted in terms of the effective stress-intensity factor where the contribution of the cohesive crack surface forces from the bridging fibres are taken into account. This curve falls somewhat closer to that of the neat matrix material, but the difference is still considerable, and it shows a decelerating propagation. Therefore, there must be other active toughening mechanisms besides fibre bridging, that slow the crack propagation down, and account for the fatigue resistant behaviour of the tested material. Ways by microstructural design to promote the fatigue resistant mechanisms are discussed.

  • 20.
    Gimåker, Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Nygårds, Mikael
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Shear strength development between couched papers during dryingManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    The out-of-plane properties (e.g., out-of-plane shear strength) of paper materials are very important for their performance during converting and end use. There is, however, a lack of published data on how shear strength develops throughout the stages of paper manufacturing. The present study investigates how the shear strength developed between couched sheets during drying in a Rapid-Köthen laboratory sheet drier. The shear strength of sheets was measured, starting from sheets with a solids content of approximately 35% all the way to fully dry sheets. Shear strength development was examined between both never-dried and rewetted sheets made of unbeaten and beaten pulp. The results indicate that the shear strength increased with increasing solids content at all solids contents investigated. The shear strength was low (<120 kPa) up to a solids content of approximately 60–70%, after which it increased rapidly with increasing solids content, suggesting that interactions important for the shear strength of dry paper start to develop at this particular dry content.

  • 21.
    Gimåker, Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Magnus
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Influence of beating and chemical additives on residual stresses in paper2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 445-451Article in journal (Refereed)
    Abstract [en]

    Residual stresses are the stresses remaining in a material when all external forces are removed. Residual stresses in paper can influence the converting and end-use performance. There are well-established methods for determining residual stresses in paper, and some knowledge exists of how to control and tailor the residual stresses. However, there is an increasing demand to be able to tailor paper grades with respect to their mechanical properties. Pulp fibres are commonly beaten to improve the mechanical performance, but beating also increases the sheet density, de-watering resistance, and residual stresses of the paper produced. This work examines whether beating and the addition of chemical additives, i.e., a single layer of poly(allylamine) or a multilayer of poly(allylamine) and poly(acrylic acid), exert different effects on the build-up of residual stresses in paper. Both beating the fibres and adding polyelectrolytes increased the in-plane strength, stiffness, and residual stresses of the paper sheets prepared. The fact that the residual stresses did not scale linearly with the stiffness of the prepared sheets suggests that both beating and polyelectrolyte addition made the fibre/fibre joints transfer load at a lower solids content, such that stresses were transferred between fibre layers in the sheet earlier in the drying process, thus increasing the residual stresses. The fact that the strength gain when building polyelectrolyte multilayers induced less residual stresses than when the strength was increased by beating indicates the possibilities for producing paper with high strength but less residual stress.

  • 22. Girlanda, O.
    et al.
    Hallbäck, N.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Tryding, J.
    Defect sensitivity and strength of paperboard in out-of-plane tension and shear2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 2, p. 100-104Article in journal (Refereed)
    Abstract [en]

    This paper considers the effects of defects in the form of cracks on the failure properties in the thickness direction of multilayered board. The objective was to study how the peak stress value changes with various crack lengths under various load conditions. Specimens with manufactured cracks cut parallel to the machine-direction-cross-machine-direction plane were glued in the Arcan device and tested under pure tensile stress and mixed shear-tensile stress. The lower peak out-of-plane tensile stress measured in damaged samples indicates a defect sensitivity in multilayered board. The results for one type of board show that the loss in tensile strength is independent of the crack length. On the other hand, mixed shear and tensile stress behaviour does not appear to be influenced by the presence of cracks.

  • 23. Girlanda, Orlando
    et al.
    Tjahjanto, Denny D.
    Ostlund, Soren
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Schmidt, Lars E.
    On the transient out-of-plane behaviour of high-density cellulose-based fibre mats2016In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 51, no 17, p. 8131-8138Article in journal (Refereed)
    Abstract [en]

    High density cellulose-based materials have been widely used for electrical insulation and (interior) construction or structural material. Similar to typical paper/board materials, the microstructure of high-density fibre mats consists of a porous network of cellulose fibres, which contributes to its highly non-linear mechanical response. Such fibre mats exhibit strong anisotropic material behaviour as well as significant transient (time-or rate-dependent) behaviour. The present investigation is aimed at studying the transient behaviour of high-density cellulose fibre mats, particularly during out-of-plane compression. A viscoelastic-viscoplastic constitutive model dedicated for high-density cellulose-based materials has been used to simulate the responses of the high-density cellulose-based fibre mats upon two types of transient loading, i.e. compressive creep and stress relaxation. The predictions of the model are then compared to the corresponding experimental characterization results, which indicate that material densification mechanism plays a more critical role during out-of-plane compression creep than in stress relaxation.

  • 24. Girlanda, Orlando
    et al.
    Tjahjanto, Denny D.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Ask, Anna
    Forslin, Julia
    Schmidt, Lars E.
    Modeling and experimental validation of the mechanical behavior of pressboard2014In: Proceedings of the 2014 Electrical Insulation Conference, IEEE conference proceedings, 2014, p. 203-207Conference paper (Refereed)
    Abstract [en]

    High density (HD) pressboard is an essential element in power transformers combining good electrical insulation properties with effective mechanical characteristics that well suit design requirements of power transformers. In order to ensure a correctly functioning transformer, it is therefore very important to characterize and to understand the mechanical properties of pressboard under different operating conditions.

    Pressboard is composed of natural polymeric chains, whose mechanical properties are affected by moisture and temperature. Moreover, temperature and moisture conditions in power transformers vary throughout manufacturing process and service/operation life-time. An accurate definition of the mechanical properties is, therefore, necessary.

    The present article focuses on the effect of different combinations of temperature/moisture and mechanical load on the deformation behavior of HD pressboard samples. A mechanical constitutive model is developed for finite element (FEM) simulation based on a viscoelastic–viscoplastic material description. Special attention is given on the complex through-thickness deformation behavior of HD pressboard. Thorough analyses are performed based on the comparisons between the results of experimental characterization and FEM modeling and simulations. The good agreement between experimental and modeling results shows a great potential for application in mechanical design of transformer insulation.

  • 25.
    Girlanda, Orlando
    et al.
    ABB Corporate Research.
    Tjahjanto, Denny
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Wei, Kun
    ABB Corporate Research.
    Schmidt, Lars
    ABB Corporate Research.
    Characterization and Modelling of the Mechanical Properties of Pressboard2013In: 2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE , 2013, p. 563-566Conference paper (Refereed)
    Abstract [en]

    Cellulose-based components constitute the bulk of the current insulation for transformers. Cellulose is an organic polymer material which combines excellent electrical properties and good mechanical performance. As a polymeric material, cellulose is very sensitive to moisture and temperature. These factors can influence the electrical and mechanical performance of a transformer throughout its lifetime. In order to ensure the quality of the product during transformer manufacturing, as well as during transformer life-time services, adequate models for predicting the physical properties of its constituents are needed. The present investigation tackles the mechanical description of pressboard. For this purpose, a three dimensional mechanical model is developed for simulating the in-plane and out-of-plane behavior of the pressboard material. The model is based on an anisotropic viscoelastic-viscoplastic constitutive law, which includes features that are particular for cellulose-based materials, e.g. the peculiar double nature of fiber-network-based and porous material. The material is orthotropic by nature, i.e. the in-plane mechanical properties markedly differ from the out-of-plane ones. Particular regard is taken when considering the effect of out-of-plane stresses which both cause viscous deformation and permanent compaction. The analyses on the mechanical behavior of pressboard are performed by comparing the experimental data on pressboard and the results of model simulations.

  • 26.
    Gudmundson, Peter
    et al.
    Swedish Institute of Composites.
    Östlund, Sören
    Swedish Institute of Composites.
    First Order Analysis of Stiffness Reduction Due to Matrix Cracking.1992In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 26, no 7, p. 1009-1030Article in journal (Refereed)
    Abstract [en]

    In this paper the reduction in effective elastic constants of composite lami nates due to matrix cracking is considered. A general easily applicable theory valid for two- and three-dimensional analysis of thin as well as thick laminates is presented. The theory is based on the change of elastic energy in a laminate at the appearance of a matrix crack in one layer. This information combined with a dilute approximation , i.e., different matrix cracks are considered not to interact with each other, is utilized to estimate the re duction of elastic constants for a certain crack density. The theory is asymptotically exact for nk « 1, where nk is the number of cracks per unit thickness of the cracked ply and a correct value of the slope of the stiffness reduction crack density curve is obtained at nk = 0.

  • 27.
    Gudmundson, Peter
    et al.
    SWEDISH INST. COMPOSITES.
    Östlund, Sören
    SWEDISH INST. COMPOSITES.
    Numerical verification of a procedure for calculation of elastic-constants in microcracking composite laminates.1992In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 26, no 17, p. 2480-2492Article in journal (Refereed)
    Abstract [en]

    In two recent papers Gudmundson and Ostlund have presented a simple to use theory for calculation of reduced thermoelastic constants in composite laminates with matrix cracks. The theory is valid for two- and three-dimensional laminates of arbitrary layups and is asymptotically exact for dilute and infinite microcrack densities. Furthermore, the theory is based solely on ply property data and matrix crack densities. No experimentally determined or unknown theoretical parameters are required. The theory predicts changes in all coefficients of the elastic stiffness and thermal expansion coefficient tensors. In previous papers the accuracy of the present theory has been investigated for cross ply laminates by comparisons to experimental results from the literature and two-dimensional finite element calculations. However, in order to become a powerful tool in the analysis of cracked composite laminates the theory must be verified at intermediate crack densities also for angle ply laminates. Unfortunately no useful experimental results for such laminates have been found in the literature and numerical methods must be considered for the verification. In the present paper the approximate theory is compared with three-dimensional finite element calculations of cracked thick [THETA, - THETA]M glass fiber reinforced epoxy laminates for a wide range of different matrix crack densities. The finite element calculations can be considered as exact for all crack densities within the present formulation, and errors are due only to the numerical algorithm. It is found that the dilute theory in combination with the theory for infinite crack densities to a surprisingly good accuracy cover all ranges of crack densities.

  • 28.
    Gudmundson, Peter
    et al.
    SWEDISH INST. COMPOSITE.
    Östlund, Sören
    SWEDISH INST. COMPOSITE.
    Prediction Of Thermoelastic Properties Of Composite Laminates With Matrix Cracks.1992In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 44, no 2, p. 95-105Article in journal (Refereed)
    Abstract [en]

    A theory is presented for the determination of changes in the elastic compliance tensor and the thermal expansion coefficients due to matrix cracking. Effects of residual stresses are taken into account. The theory is valid for two- or three-dimensional laminates of arbitrary lay-ups and is asymptotically exact for dilute micro-crack densities. For large micro-crack densities an alternative model is described which is asymptotically exact for large crack densities. Combined, the two models cover to a good approximation the whole range of micro-crack densities. The theory is applied to a micro-cracking cross-ply GFRP laminate for which the stress/strain curve is calculated. Data are also presented for changes in thermomechanical properties of angle ply laminates as functions of the lay-up angle.

  • 29.
    Gudmundson, Peter
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Stress Singularity At The Free-Surface Of A Dynamically Growing Crack.1990In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 57, no 1, p. 112-116Article in journal (Refereed)
    Abstract [en]

    The stress singularity at the intersection between the crack front and the free surface of a dynamically growing crack in a linear elastic isotropic material has been numerically evaluated by an especially developed finite element program. The singularity parameter (), defined by ~ R−1, is presented as a function of the crack-tip velocity and the angle (ß)between the crack front and the free surface. The angle (ß) at which the singularity () equals 0.5 was found to be 101 deg almost independently of the crack-tip velocity.

  • 30.
    Hagman, Anton
    et al.
    RISE BioEconomy.
    Timmerman, Brita
    Iggesund Paperboard.
    Nygårds, Mikael
    RISE BioEconomy.
    Lundin, Andreas
    Barbier, Christophe
    BillerudKorsnäs AB.
    Fredlund, Mats
    Stora Enso.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Experimental and numerical verification of 3D-forming2017In: ADVANCES INPULP AND PAPERRESEARCH,OXFORD 2017: Transactions of the 16th Fundamental Research Symposium, Pembroke College, Oxford, England, September 3-8, 2017 / [ed] Warren Batchelor and Daniel Söderberg, 2017, Vol. 1, p. 3-26Conference paper (Refereed)
    Abstract [en]

    Motivated by sustainability arguments there is a recent interest informing of advanced structures in paper and paperboard. Therefore,in this paper, hydro-forming of papers and the effect of different fibreraw materials, beating, strength additives (PVAm), grammage andwet and dry papers have been investigated experimentally andnumerically.The experiments were carried out in laboratory hydro-formingdevice. Softwood sheets performed better than hardwood sheets,since they had higher strain at break. The ability of paper to withstandhydro-forming successfully was primarily dependent of the strain atbreak of the paper in relation to the straining required to fill the mould.Forming of wet sheets were also investigated; overall the wet sheetsformed better than the dry sheets, which was due to higher strain atbreak and lower elastic energy. Since the forming was displacementcontrolled, there was no significant difference in the effects of beating,amount of PVAm or grammage.

    Finite element modelling was performed to identify local strainsand predict problematic regions. Simulations were also performed todetermine how anisotropic sheets would behave, as well as to comparethe process of hydro-forming with press-forming. The papers couldbe strained to higher strain levels than the measured strain at breakbecause the paper is supported by the membrane and mould duringthe forming operation. The maximum strain a paper can withstandcan be increased if the paper can slide into the mould, i.e. by havinga lower coefficient of friction between the steel mould and thepaperboard.During hydro-forming the paper is supported by a rubber membrane,which gives lower strain levels than the corresponding press-formingoperation due to the difference in how the paper is deformed. Pressformingtherefore required paper with higher strain at break. Higherfriction results in more paper being pulled into the mould, whichcontributes to wrinkling of the paper. Simulation of tray forming of acreased sample was performed, which showed that high friction orcompliant creases decreased the circumferential compression.

  • 31.
    Hirn, Ulrich
    et al.
    Graz University of Technology, Austria.
    Schennach, R.
    Graz University of Technology, Austria.
    Ganser, C.
    Montanuniversität, Leoben, Austria.
    Magnusson, Mikael S.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Teichert, C.
    Montanuniversität, Leoben, Austria.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    The Area of Molecular Contact in Fiber-Fiber Bonds2013In: Advances in Pulp and Paper Reserach, Cambridge 2013: Transactions of the 15th Fundamental Research Symposium / [ed] S.J. I'Anson, 2013, p. 201-223Conference paper (Refereed)
    Abstract [en]

    We are presenting a coherent theoretical concept as well as empirical evidence suggesting that there is a high degree of molecular contact in fiberfiber bonds, the surfaces might even be in full contact.

    Fundamental theoretical relations from contact mechanics governing the area in molecular contact between surfaces are reviewed and proposed for the quantitative analysis of the area in molecular contact in fiber-fiber bonds.

    The key parameters determining the degree of molecular contact according to the theory are indentation hardness and elastic modulus of the wet pulp fibers, surface roughness of the wet fibers and the pressure applied to the fiber bonds during bond formation.

    We provide results for fiber indentation hardness and effective elastic modulus from nanoindentation measurements of fiber surfaces at varying relative humidity and in water. The fiber surface properties have been determined with an atomic force microscopy technique specifically designed to measure soft, viscoelastic materials. Also, surface roughness has been measured in the wet and dry state.

    Experiments with individual fiber-fiber joints show that the breaking strength of these joints is independent from the pressure during bond formation indicating that the surfaces in fiber-fiber bonds are in a high degree of molecular contact, maybe even full contact. This is the case even if they are formed without external pressure. Computer simulations of the degree of mechanical contact of fiber surfaces during drying were performed indicating that capillary adhesion is pulling the fiber surfaces into a high degree of molecular contact. These findings are discussed with respect to the literature considering FRET microscopy and Transmission Electron Microscopy of fiber-fiber bonds.

  • 32.
    Huang, Hui
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Nygårds, Mikael
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Numerical analysis and experiments for increased understanding of cartonboard creasing and folding2012In: Verarbeitungsmaschinen und Verpackungstechnik 2012, 2012, p. 295-313Conference paper (Other academic)
    Abstract [en]

    Creasing and folding are vital processes in manufacturing of liquid and cartonboard packages. The quality of the crease and the subsequent folding is essential for good runnability and aesthetic appearance. The out-of-plane mechanical properties of cartonboard are particularly import in these processes. In this paper, recent advances in analysis of creasing and folding, using numerical simulations by means of the finite element method and the through-thickness shear strength profile of cartonboard, are presented.

    Existing methods to determine the out-of-plane shear strength of paper materials only give the strength in the weakest layer. In order to capture the through-thickness variation in shear strength the laminated notched shear test was introduced.

    In the simulations, the cartonboard was represented by a combination of continuum and cohesive models in order to capture the bulk and delamination properties, respectively. The continuum model was calibrated for each ply by testing individual plies that were isolated by grinding, and the cohesive model was calibrated using shear strength data from laminated notched shear tests.

    Results from the simulations are compared with creasing and folding experiments and the agreement is excellent considering the relative simplicity of the analysis. Finally, practical implications for trouble-shooting creasing and folding problems will be discussed.

  • 33. Isaksson, P.
    et al.
    Gradin, P.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    A Simplified Treatise of the Scott Bond Testing Method2010In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 50, no 6, p. 745-751Article in journal (Refereed)
    Abstract [en]

    The Scott bond test method has been used extensively in the paper industry over the years as a means to assess the bond strength of paper. The method has been a subject of some controversy lately since it does not always correlate to the sensitivity of the material to fracture by delamination. To gain some further insight into which parameters govern the fracture process in a Scott bond test a simplified approach has been chosen in order to formulate an analytical mathematical/mechanical model of the test. The model is dynamic in the sense that inertia effects are included. The material model utilised is a simple cohesive theory that assumes a linear behaviour between stress and crack opening when the material has started to degrade. This choice of material model makes the mathematical model very nonlinear. In fact, a system of three coupled nonlinear second order partial differential equations have to be solved and adjusted to the correct initial conditions. The material parameters needed for the model are the elastic modulus in the thickness direction, the transverse shear (elastic) modulus, the tensile strength (in the thickness direction) and the fracture work (per unit area) for a delamination crack. To investigate the ability of the model, a Scott bond testing apparatus have been equipped with a piezoelectric load sensor. The load cell was mounted on the apparatus' pendulum so that the load acting on the sample holder could be recorded during the whole impact stage. This was done for a number of different initial velocities of the pendulum and it is found that the model gives a fair prediction of the contact load.

  • 34.
    Isaksson, Per
    et al.
    Mid Sweden University.
    Gradin, Per
    Mid Sweden University.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A simplified treatise of the Scott-bond testing method2007In: 2007 International Paper Physics Conference, 2007, p. 1-6Conference paper (Other academic)
  • 35. Jamialahmadi, A.
    et al.
    Trost, T.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Dynamic performance of corrugated boxes2008In: Proceedings of the 16th IAPRI World Conference on Packaging, IAPRI , 2008Conference paper (Other academic)
    Abstract [en]

    This paper summarizes dynamic analysis of the interaction of corrugated boxes in transport using a pressure-mapping system. The dynamic contact forces on the contact area between boxes in both vertical and horizontal directions were measured and the position of the instantaneous Centre of Force (COF) was traced from which the pitch motion of boxes relative to each other was studied. The level-crossing diagrams of the contact forces show a Rayleigh distribution for the vertical contact and a Gaussian distribution for horizontal contacts. The contact force and acceleration power spectral density from accelerometers and pressure-mapping system were compared.

    The results show that a pressure mapping system is an interesting tool for analysis of the dynamic performance of systems of corrugated boxes under different stacking and loading conditions.

  • 36. Jamialahmadi, Arsalan
    et al.
    Trost, Thomas
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A Proposed Tool to Determine Dynamic Load Distribution between Corrugated Boxes2011In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 24, no 6, p. 317-329Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the dynamic analysis of the interaction of corrugated boxes in transport using a pressure-mapping system. The dynamic contact forces on the contact area between boxes in both vertical and horizontal directions were measured, and the position of the instantaneous centre of force was traced, from which the pitch motion of boxes relative to each other was studied. The level-crossing diagrams of the contact forces show a Rayleigh distribution for the vertical contact and a Gaussian distribution for the horizontal contacts. The contact force and acceleration power spectral density from accelerometers and pressure-mapping system were compared. The results show that a pressure-mapping system is an interesting tool for the analysis of the dynamic performance of systems of corrugated boxes under different stacking and loading conditions.

  • 37.
    Jangmalm, Anders
    et al.
    STFI, Swedish Pulp and Paper Research Institute, Stockholm, Sweden.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Modelling of curled fibres in two-dimensional networks1995In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 10, no 3, p. 156-161Article in journal (Refereed)
    Abstract [en]

    A two-dimensional micromechanical model for fibre networks constructed of curled fibres is presented. In the model, which allows for a general statistical description of parameters such as fibre length, fibre orientation and curl factors, the fibres are modelled as circle segments. By varying the radius of the circle anything from almost straight to half circle shaped fibres can be modelled. The mechanical response of the network model is obtained by finite element analysis. The fibres are modelled with beam elements having linear elastic material properties and a cross sectional area corresponding to that of an idealized circular fibre. The model is used to investigate the influence of fibre curl, fibre length and percentage of bonded fibre crossings on the mechanical behaviour of paper sheets of low to medium basis weight. The tensile stiffness index for different fibre curl is qualitatively compared with experimental data. The results from the present model show a less pronounced influence of the fibre curl compared to the experimental data and several possible reasons for this discrepancy are discussed. Large deformation analyses allowing for applied strains up to 5% results in a non-linear relation between the tensile stiffness index and the strain for curled fibres. For straight fibres the non-linear relation is less pronounced, although the difference is small. This result indicates that the ability of the fibre to carry load depends on the curl factor.

  • 38.
    Larsson, Per A.
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Linvill, Eric
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Lo Re, Giada
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Wågberg, Lars
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Ductile and thermoplastic cellulose with novel application and design opportunities2018In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 39. Lif, J.
    et al.
    Östlund, Sören
    Fellers, C.
    In-plane hygro-viscoelasticity of paper at small deformations2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 139-149Article in journal (Refereed)
    Abstract [en]

    A classic hygro-viscoelastic constitutive model applicable for the analysis of time and humidity-dependent stresses of paper structures using the finite element method (FEM) was investigated. For the evaluation of the parameters required to model two-dimensional behaviour, a procedure based on the interconversion of experimental creep source data at different moisture ratios is described. The procedure enables the selection of parameters for stable performance of the constitutive model to promote convergence of FEM simulations with combined mechanical and moisture boundary conditions such as prescribed tractions, displacements and moisture ratios. In order to account for the dependence of the moisture ratio of paper, an internal variable was used to shift the continuous spectral components of the relaxance matrix. Despite the assumption of orthotropic symmetry, a minor asymmetric behaviour was found on the transverse response during model validation of paperboard behaviour at uniaxial tensile testing conditions and constant levels of moisture ratio between 0.07 and 0.15. This phenomenon was found to be present when the time-dependent behaviour of the in-plane viscoelastic components differed. At higher strain levels (> 0.15% strain) and beyond the operating window of the model, the experimental findings show more profound asymmetry of the transverse response: this was probably caused by inelastic material behaviour. The model response to strain histories included some hereditary effects of the stress, which was found to agree well with the experimental results at small deformations. A numerical scheme was derived and used during implementation of the constitutive model in commercial FEM software. The solutions converged rapidly for the conditions investigated. After imposing higher moisture ratio at a given strain level, the stress levels were reduced and stress relaxation was shown during short-term simulations. Residual stress states were shown in the numerical simulations after unloading and changed moisture ratios, when hygroexpansion and the effect of clamped test pieces were included.

  • 40. Lif, Jan O.
    et al.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Fellers, Christer
    Applicability of Anisotropic Viscoelasticity of Paper at Small Deformations1999In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 2, no 3, p. 245-267Article in journal (Refereed)
    Abstract [en]

    In this paper the applicability of two-dimensional phenomenlogical linear viscoelastic modelling aimed at printing applications is presented. An iterative algorithm is used to find model parameters evaluated from dynamic mechanical testing at stationary conditions. Experiments are performed in the time domain with different load stimuli in either displacement or force control. The experiments are compared to model predictions.The results show that only small deviations were found on model parameters from the algorithm used on either the loss or the storage properties of paper. This was illustrated by converting line spectra from storage compliances to loss compliances within the frequency domain. The harmonic properties were obtained at conditions with nonlinear material behaviour. Despite this, the two-dimensional linear viscoelastic model described well the behaviour of paper at different states of stress and strain at levels adequate for web-fed printing. The usefulness of the relation between retardances and relaxances was examined by comparing model predictions with different driving stimuli resulting in either creep or relaxation. The time-dependent transverse strain of machine-made paper due to either longitudinal stress relaxation or creep was demonstrated. Finally, extensions of the present model including inelastic material behaviour were discussed.

  • 41.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Larsson, Per A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Advanced three-dimensional paper structures: Mechanical characterization and forming of sheets made from modified cellulose fibers2017In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 128, p. 231-240Article in journal (Refereed)
    Abstract [en]

    Cellulose partially converted to dialcohol cellulose has been identified as a potential breakthrough material for the production of bio-based, complex, double-curved surfaces due to its extensive strain-at-break characteristics (reaching as great as 80% in tensile loading). Tensile testing of handsheets made from modified cellulose fibers was conducted from 50 to 90% relative humidity (RH) and from 23 to 150 °C. Strain-at-break of the handsheets ranged from 35 to 80% over this humidity and temperature range, which is significantly greater than typical cellulose-based materials. The combined effect of moisture and temperature was further investigated by dynamic mechanical thermal analysis, which was utilized to determine the glass-transition temperature of the handsheets as a function of relative humidity. Based on the tensile test results and verified by the three-dimensional (3-D) forming and simulation, a forming limit diagram (strain-based failure surface which describes and illustrates the formability of the material) for the handsheets was generated. This forming limit illustrates significant extent to which this bio-based material can be 3-D formed into advanced structures. Furthermore, temperature was identified as the best, quickest, and most controllable method of improving extensibility of this material during 3-D forming.

  • 42.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Biofibre Materials Centre, BiMaC.
    Larsson, Per
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. TU Dresden, Fakultät Maschinenwissen, Institut für Verarbeitungsmaschinen und Mobile Arbeitsmaschinen .
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Advanced Three-Dimensional Paper Structures: Mechanical Characterization and Forming of Sheets Made from Modied Cellulose Fibers2017Report (Other academic)
  • 43.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Larsson, Per
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Dynamic Mechanical Thermal Analysis Data of Sheets Made from Wood-Based Cellulose Fibers Partially Converted to Dialcohol Cellulose2017In: Data in Brief, ISSN 2352-3409, Vol. 14, p. 504-506Article in journal (Refereed)
    Abstract [en]

    This data article contains the dynamic mechanical thermal analysis (DMTA) results for sheets made from cellulose fibers partially converted to dialcohol cellulose as presented in “Advanced Three-Dimensional Paper Structures: Mechanical Characterization and Forming of Sheets Made from Modified Cellulose Fibers” by Linvill et al. [1]. See Larsson and Wågberg [2] for a description and characterization of the material as well as how the material is produced. The DMTA tests were conducted at four different relative humidity levels: 0, 50, 60, and 70% RH, and the temperature was swept between 10 and 113 °C. The DMTA results enable the understanding of the elastic, viscoelastic, and viscoplastic mechanical properties of this material at a wide range of temperature and relative humidity combinations.

  • 44.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Wallmeier, Malte
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A constitutive model for paperboard including wrinkle prediction and post-wrinkle behavior applied to deep drawing2017In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 117, p. 143-158Article in journal (Refereed)
    Abstract [en]

    A simple, one-dimensional model for perfectly plastic hinges, utilizing a hinge yield strength, was applied to wrinkled paperboard and validated. The hinge model was incorporated into a three-dimensional constitutive model of paperboard including wrinkle initiation, wrinkle compression, as well as tensile reloading of wrinkled paperboard. The constitutive model enables the explicit finite element simulation of the deep drawing of a non-creased paperboard blank, including spring-back after the forming process. The results of the simulated deep-drawing process were validated against experimental deep-drawn paperboard cups, and parametric studies were conducted to investigate the effects of process and material parameters on three different quality measures (spring-back magnitude, asymmetry, and punch force). In addition to aiding the development of the simulation of paperboard deep drawing, the hinge yield strength was also found to be the only studied material property which could simultaneously improve all three quality measures.

  • 45.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Biofibre Materials Centre, BiMaC.
    Wallmeier, Malte
    TU Dresden, Fakultät Maschinenwissen, Institut für Verarbeitungsmaschinen und Mobile Arbeitsmaschinen .
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A Constitutive Model for Paperboard Including Wrinkle Prediction and Post-Wrinkle Behavior Applied to Deep Drawing2017Report (Other academic)
  • 46.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Biaxial (In-Plane) Failure and Yield of Paperboard2016In: / [ed] Samuel Schabel, 2016Conference paper (Other academic)
    Abstract [en]

    Understanding the biaxial (in-plane) failure behavior of paperboard is crucial to understand the limits of 3-D forming of paper materials, because the biaxial strain failure limit determines the extent to which paperboard can be formed in different conditions.

    A traditional cruciform biaxial specimen has been redesigned and modified with the help of laser engraving. By the use of laser engraving, 90 % of the effective thickness of the specimen in the center of the cruciform was removed, thus making the cruciform specimen more likely to fail in the center than at the edges. A variety of strain ratios were utilized to test the specimens with a biaxial testing machine, and the strain field was measured utilizing digital image correlation.

    The results of the biaxial testing were analyzed in order to determine both the strain-based yield and failure surfaces. Additionally, the stresses in the center of the specimen were estimated based on the forces measured during the test. Based on these estimated stresses, stress-based yield and failure surfaces were also constructed. Furthermore, various models for the strain- and stress-based yield surfaces were applied to the data and compared.

  • 47.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Biaxial In-Plane Yield and Failure of Paperboard2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 4, p. 659-667Article in journal (Refereed)
    Abstract [en]

    Paperboard is oftentimes subjected to biaxial in-plane stress and strain states, although very few experimental studies of the biaxial in-plane yield and failure of paperboard have been conducted. A new biaxial testing method to determine the in-plane stress- and strain-based yield and failure surface of paperboard was proposed and implemented. The method utilized cruciform specimens containing a reduced-thickness region (prepared by laser engraver) to increase probability of failure in that region, and digital image correlation was utilized to measure strain. The obtained stress-based failure surface was similar to previously reported results in the literature, but the obtained strain-based failure surface differed from the one previously reported strain-based failure surface. The obtained yield and failure surfaces had similar shape, providing confidence in both results due to the related deformation and failure mechanisms in paperboard. Furthermore, the overall shape of the stress- and strain-based yield surfaces was unaffected by the definition of the yield point. The obtained strain-based failure surface revealed the forming limits and therefore strengths and limitations of various 3-D forming methods for paperboard.

  • 48.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Explicit Finite Element Simulation of 3D Forming Processes for Paperboard2015Conference paper (Other academic)
  • 49.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Biofibre Materials Centre, BiMaC.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Parametric Study of Hydroforming of Paper Materials using the Explicit Finite Element Method with a Moisture-and Temperature-Dependent Constitutive Model2015Report (Other academic)
  • 50.
    Linvill, Eric
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Chemical Science and Engineering (CHE), Centres, Biofibre Materials Centre, BiMaC.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Parametric Study of Hydroforming of Paper Materials Using the Explicit Finite Element Method with a Moisture-dependent and Temperature-dependent Constitutive Model2016In: Packaging technology & science, ISSN 0894-3214, E-ISSN 1099-1522, Vol. 29, no 3, p. 145-160Article in journal (Refereed)
    Abstract [en]

    A moisture-dependent and temperature-dependent constitutive model for paper materials was proposed and implemented into a finite element model of the paper hydroforming process. Experimental hydroforming was conducted at temperatures of 23°C and 110 °C and moisture contents of 6.9 and 10.6 (respectively corresponding to 50 and 80% relative humidity). The proposed model, which also included the effects of drying, captured the extent of forming of all experimental results within reasonable accuracy. For the moisture content and temperature conditions in this study, the phenomenon of drying was found to be the reason why the application of temperature had a much greater effect on the degree of forming than hydroforming at various moisture contents. A simulation-based parametric study was conducted in order to identify the importance of various process and material parameters. This parametric study confirmed many previous empirical findings and was capable of quantifying the extent to which these process and material parameters affect the three-dimensional formability of paper. The coefficient of friction was identified as one of the most important factors when determining the extent of forming.

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