| 1. |
- Gimåker, Magnus, et al.
(författare)
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Influence of beating and chemical additives on residual stresses in paper
- 2011
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 26:4, s. 445-451
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Marin, Gustav, et al.
(författare)
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Stiffness and strength properties of five paperboards and their moisture dependency
- 2019
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Ingår i: Paper Conference and Trade Show, PaperCon 2019. - : TAPPI Press. - 9781510893948 ; , s. 1193-1208
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Konferensbidrag (refereegranskat)abstract
- Five folding box boards made on the same paperboard machine have been analyzed. The paperboards were from the same product series but had different grammage (235, 255, 270, 315, 340 g/m2) and different bending stiffness. The paperboards are normally used to make packages, and since the bending stiffness and grammage varies the packages performance will be different. Finite element simulations can be used to predict these differences. However, the stiffness and strength properties then need to be known. For efficient determination of the three-dimensional properties in MD, CD and ZD, it is proposed that the whole paperboard should be characterized with the following tests: in-plane tension, ZD tension, shear strength profiles and two-point bending. The stiffness and strength properties have with the proposed setups been determined at different relative humidity (20, 50, 70 and 90 % RH), and the mechanical properties have been evaluated as function of moisture ratio. The results showed a linear relation between mechanical properties and moisture ratio for each paperboard. The data was then normalized with data for the standard climate (50 % RH) and investigated as a function of moisture ratio. The results indicated that the normalized mechanical properties for all paperboards coincided along one single line and could therefore be expressed as a linear function of moisture ratio and two constants. Consequently, the study indicates that it is possible to obtain the mechanical properties of a paperboard, by knowing the structural properties for the preferred level of RH and the mechanical property for the standard climate (50 % RH and 23 °C).
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| 3. |
- Östlund, Magnus, et al.
(författare)
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Experimental determination of residual stresses in paperboard
- 2005
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Ingår i: Experimental mechanics. - 0014-4851 .- 1741-2765. ; 45:6, s. 493-497
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Tidskriftsartikel (refereegranskat)abstract
- A method for the experimental determination of the through-thickness residual stress distribution in paper-board is presented.The successive removal of thin layers from strips of board through surface grinding changes the stress-state and the bending stiffness resulting in a changed curvature, which is measurable. From tests of strips in both in-plane directions, stress distributions can then be evaluated using the Treuting-Read method. Geometrically nonlinear effects at the large deformations taking place are avoided through a proper choice of strip dimensions. Typical results are presented and factors influencing the accuracy of the determination are thoroughly discussed.
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| 4. |
- Östlund, Magnus, et al.
(författare)
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Influence of Paperboard Structure and Processing Conditions on Forming of Complex Paperboard Structures
- 2011
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Ingår i: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 24:6, s. 331-341
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Tidskriftsartikel (refereegranskat)abstract
- Experiments were made with a laboratory apparatus for forming paper sheets into double-curved structures. The purpose was to learn more about the design criteria for forming of paper materials into complex shapes. The influence of forming parameters such as moisture and temperature was studied, and the performance of some common pulps as raw materials for the paper sheets was evaluated. Papers made from short hardwood fibres performed worse than papers from other pulps, and the method of moisture application was more important than the amount of moisture that was applied.
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| 5. |
- Östlund, Magnus, 1974-
(författare)
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Residual stresses in paperboard and the influence of drying conditions
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The drying sequence in the manufacturing process for paperboard involves evaporation of water, primarily from within the fibres. The vapour is then transported out of the web by pressure or concentration gradients. As the moisture transport from the paper web to the ambient is quicker than the moisture transport within the fibre network to the surfaces of the web, moisture gradients develop through the thickness of the web. This work concerns effects on the mechanics of paper drying from the variation in moisture through the relatively thin structures of paper and paperboard.Distributions of inplane residual stresses through paper materials in the unloaded state after drying are believed to be caused by the varying moisture through the thickness during drying. The distributions in general exhibit compressive stress near the board surfaces and tensile stress in the interior of the board. This may be modified after drying and is also affected by structural variation in the material between different plies of multi-ply paperboards.The stress development during drying is important because it influences the resulting material properties of the paper and because it can lead to curl, which is a quality problem. The residual stresses themselves are an error source in simulation or evaluation of the mechanical behaviour of paper.In this work, residual stress distributions in paperboard were determined experimentally, to clarify the mechanisms of residual stress build-up. An experimental method for such tests was also developed. Based on the experimental findings, the mechanics of paper drying was modelled and the stress build-up simulated. Simulation offers a way of studying how the properties of paper develop during drying of wet paper webs.
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| 6. |
- Östlund, Magnus, et al.
(författare)
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Residual stresses in paperboard through the manufacturing process
- 2005
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 31:4, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- The residual stresses in a machine-made multi-ply board with chemical pulp in all plies were monitored as the board progressed after the initial drying through calendering, moisture treatments and coating. After drying, the stresses were compressive near the surfaces. In the coated board at the end of the machine, the stress state was reversed to a large extent with tensile stresses in the outermost layers. The various moisture applications on the board in the post-processing steps are regarded to have caused the change in the residual stress state. In another machine-made board, with mechanical pulp in the middle plies, the stresses after drying were limited to the surface plies made from chemical pulp, but were again compressive at the surfaces. This stress state was largely unaffected by post-processing. The possibility for stress reversal and the implications on in-plane and out-of-plane dimensional stability of the boards are discussed.
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| 7. |
- Östlund, Magnus, et al.
(författare)
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The influence of drying conditions on residual stress build-up in paperboard
- 2004
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 30:11, s. 312-316
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Tidskriftsartikel (refereegranskat)abstract
- The through-thickness distributions of in-plane residual stress have been determined for some laboratory-made paperboards. The effects of drying variables such as temperature, moisture flow resistance at the surfaces and thickness of the boards on residual stresses were studied. The drying rate was shown to influence residual stresses only for relatively slow drying. Residual stresses correlate well with the moisture gradient during drying for various drying methods. Some effects of the drying conditions on paper tensile stiffness are discussed. One-sided heating for curl control is also discussed.
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| 8. |
- Östlund, Magnus, et al.
(författare)
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The influence of drying restraints and beating degree on residual stress build-up in paperboard
- 2004
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 30:11, s. 289-293
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Tidskriftsartikel (refereegranskat)abstract
- The through-thickness distribution of in-plane residual stress has been determined for laboratory-made paperboards, to study the causes of these stresses. The degree of restraint during drying is shown not to influence the residual stresses in a significant way. However, a higher level of beating of the pulp leads to higher residual stresses. The drying gradient through the sheet combined with the shrinkage of paper as moisture content decreases is suggested as the main reason for residual stress build-up. No effect an free shrinkage was seen when attempting to limit the drying gradients by decreasing the grammage.
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| 9. |
- Östlund, Magnus, et al.
(författare)
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The influence of through-thickness variation on the mechanics of paper drying
- 2005
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Ingår i: ADVANCES IN PAPER SCIENCE AND TECHNOLOGY. - 9780954527235 ; , s. 213-240
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Konferensbidrag (refereegranskat)abstract
- A material model for drying paper is presented. Moisture-dependent material parameters, hygroscopic shrinkage, the elastic and the time-dependent responses of the material to load, and the effect of unloading at a higher stiffness than the load was applied at are modelled. The model is used to determine the effects of a varying moisture ratio through the paper during drying on free shrinkage development and stiffness development at free drying. Simulation results for the stress development during drying and the state of residual stress immediately after drying are also presented. The model predicts a variation of in-plane elastic moduli through the paper, a prediction that is studied by experiments.
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| 10. |
- Alfthan, Johan, et al.
(författare)
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A micromechanical model for mechanosorptive creep in paper
- 2002
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 28:3, s. 98-104
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Alzweighi, Mossab
(författare)
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Modelling Fiber Network Materials:Micromechanics, Constitutive Behaviour and AI
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on understanding the mechanical behavior of fiber-based materials by utilizing various modeling approaches. Particular emphasis is placed on their structural variability, anisotropic properties, and damage behavior. Furthermore, the study explores moisture diffusion phenomena within these materials, leveraging machine learning techniques. The research employs a blend of multiscale modeling, experimental investigation, machine learning, and continuum modeling to enhance the predictive capabilities for modelling fiber-based materials.In Paper I, the work investigates the impact of stochastic variations in the structural properties of thin fiber networks on their mechanical performance. A multiscale approach that includes modeling, numerical simulation, and experimental measurements is proposed to assess this relationship. The research also considers the influence of drying conditions during production on fiber properties. The study finds that spatial variability in density has a significant impact on local strain fields, while fiber orientation angle with respect to drying restraints is a key influencer of the mechanical response. In Paper II, the research delves into the investigation of anisotropic properties and pressure sensitivity of fiber network materials. It draws a comparison between the Hoffman yield criterion and the Xia model, which are widely utilized for simulating the mechanical response in fiber-based materials. The study performs a detailed analysis of these models under bi-axial loading conditions, assessing their numerical stability and calibration flexibility. Further supporting the research community, the paper provides open-source access to the user material implementations of both models and introduces a calibration tool specifically for the Xia model, thereby promoting ease of usage and facilitating further research in this domain. In Paper III a novel thermodynamically consistent continuum damage model for fiber-based materials is introduced. Through the integration of elastoplasticity and damage mechanisms, the model employs non-quadratic surfaces comprised of multi sub-surfaces, augmented with an enhanced gradient damage approach. The model’s capability is demonstrated by predicting the nonlinear mechanical behavior under in-plane loading. This study provides valuable insights into the damage behavior of fiber-based materials, showcasing a range of failure modes from brittle-like to ductile. In Paper IV, the study examines moisture penetration in fiber-based materials and the resultant out-of-plane deformation, known as curl deformation, using a combination of traditional experiments, machine learning techniques, and continuum modeling. The paper compares the effectiveness of two machine learning models, a Feedforward Neural Network (FNN) and a Recurrent Neural Network (RNN), in predicting the gradient of the moisture profile history. The study finds that the RNN model, which accounts for temporal dependencies, provides superior accuracy. The predicted gradient moisture profile enables simulating the curl response, offering a deeper understanding of the relationship between moisture penetration and paper curling.
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| 12. |
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| 13. |
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| 14. |
- Bankel, Johan, 1959, et al.
(författare)
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Benchmarking engineering curricula with the CDIO syllabus
- 2005
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Ingår i: International Journal of Engineering Education. - 0949-149X. ; 21:1, s. 121-133
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 15. |
- Bankel, Johan, et al.
(författare)
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The CDIO syllabus: a comparative study of expected student proficiency
- 2003
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Ingår i: European Journal of Engineering Education. - : Taylor & Francis. - 0304-3797 .- 1469-5898. ; 28:3, s. 297-315
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
- Barbier, Christophe, et al.
(författare)
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Experimental investigation of damage at folding of coated papers
- 2002
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:1, s. 34-38
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 17. |
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| 18. |
- Barbier, Christophe, et al.
(författare)
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Numerical investigation of folding of coated papers
- 2005
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Ingår i: Composite Structures. - : Elsevier. ; 67:4, s. 383-394
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Tidskriftsartikel (refereegranskat)abstract
- 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 elasticplastic 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
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| 19. |
- Barbier, Christophe, et al.
(författare)
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On dynamic effects at folding of coated papers
- 2005
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Ingår i: Composite structures. - : Elsevier BV. - 0263-8223 .- 1879-1085. ; 67:4, s. 395-402
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Barbier, Christophe, 1974-, et al.
(författare)
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On material characterization of paper coating materials by microindentation testing
- 2005
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Ingår i: JCT. - Boston : Springer. - 0361-8773. ; 2:6, s. 463-471
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Tidskriftsartikel (refereegranskat)abstract
- 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 are made to account for the influence from plasticity as well as from boundary effects
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| 21. |
- Barbier, Christophe, 1974-, et al.
(författare)
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On the effect of high anisotropy at folding of coated papers
- 2007
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 72:3, s. 330-338
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 22. |
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| 23. |
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| 24. |
- Borodulina, Svetlana, et al.
(författare)
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Digital Analysis of Deformed Corrugated Boxes Using 3D Speckles
- 2010
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Konferensbidrag (refereegranskat)abstract
- During transportation from the manufacturer to the retailer packages are affected by vibrations, shocks, staticand dynamic loads, as well as by changes in temperature and humidity. In order to improve the quality of the packaging towithstand stresses during transportation it is important to know the parameters that characterize the deformation state inthe package. Corrugated boxes are affected by a phenomenon known as mechanosorptive creep, the basics of which arestill not well understood. That is why it is interesting to know how changes in moisture content affect corrugated boxesand how it is possible to prolong the lifetime of transportation packages. This paper presents an attempt to use the whitelight digital photography method for a three-dimensional analysis of the deformation states near collapse of a corrugatedbox during varying humidity, and attempts to obtain characteristic parameters that can be used to describe deformationstates close to collapse. A series of tests using an optical non-destructive testing method are reported and the results fordifferent test configurations are presented. Comparison is made between tests performed at different load levels andclimate conditions. The optical deformation measurement system used for analysis was ARAMIS® (GOM mbH,Braunschweig, Germany). Advantages and disadvantages of working with this system are also described and suggestionsfor future work are discussed.
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| 25. |
- Borodulina, Svetlana
(författare)
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Micromechanics of Fiber Networks
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current trends in papermaking involve, but are not limited to, maintaining the dry strength of paper material at a reduced cost. Since any small changes in the process affect several factors at once, it is difficult to relate the exact impact of these changes promptly. Hence, the detailed models of the network level of a dry sheet have to be studied extensively in order to attain the infinitesimal changes in the final product.In Paper A, we have investigated a relation between micromechanical processes and the stress–strain curve of a dry fiber network during tensile loading. The impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds, is discussed. In Paper B, we studied the impact of the chemical composition of the fiber cell wall, as well as its geometrical properties, on the fiber mechanical properties using the three-dimensional model of a fiber with helical orientation of microfibrils at a range of different microfibril angles (MFA). In order to accurately characterize the fiber and bond properties inside the network, via statistical distributions, microtomography studies on the handsheets have been carried out. This work is divided into two parts: Paper C, which describes the methods of data acquisition and Paper D, where we discuss the extracted data. Here, all measurements were performed at a fiber level, providing data on the fiber width distribution, width-to-height ratio of isotropically oriented fibers and contact density. In the last paper, we utilize data thus obtained in conjunction with fiber morphology data from Papers C and D to update the network generation algorithm in order to produce more realistic fiber networks. We also successfully verified the models with the help of experimental results from dry sheets tested under uniaxial tensile tests. We carry out numerical simulations on these networks to ascertain the influence of fiber and bond parameters on the network strength properties.
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| 26. |
- Brandberg, August, 1990-
(författare)
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Insights in paper and paperboard performance by fiber network micromechanics
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fiber networks are ubiquitous due to their low cost and high ratio of mechanical performance to weight. Fiber networks made of cellulose fibers from trees are used as information carriers (paper) and as packaging (board). Often the ideal product is both mechanically sturdy and possible to print on. This thesis investigates the underlying reasons for the mechanical performance of paper and board through the discretization and direct simulation of every fiber in the network.In Paper A the effect of fiber-fiber bond geometry on sheet stiffness is investigated. Many packaging products seek to maximize the bending stiffness by employing stiff outer layers and a bulkier layer in the middle. In bulky sheets, the fibers are frequently uncollapsed resulting in a more compliant bonded segment. Because all the loads in the network are transferred via the bonds, such compliance can cause unexpectedly large decreases in mechanical performance. Although many models have been presented which aim to predict the tensile stiffness of a sheet, these predictions tend to overestimate the resulting stiffness. One reason is that the bonds are generally considered rigid. By finite element simulations, we demonstrated the effect of the lumina configuration on the stiffness of the bonded segment on the scale of single fiber-to-fiber bonds, and that the average state of the fiber lumen has a marked effect on the macroscopic response of fiber networks when the network is bulky, has few bonds, or has a low grammage.Compression strength is central in many industrial applications. In paper B we recreated the short span compression test in a simulation setting. The networks considered are fully three-dimensional and have a grammage of 80 to 400 gsm, which is the industrially relevant range. By modeling compression strength at the level of individual fibers and bonds, we showed that fiber level buckling or bifurcation phenomena are unlikely to appear at the loads at which the macroscopic sheet fails.In paper C, we developed a micromechanical model to study the creation of curl in paper sheets subjected to a moisture gradient through the sheet. A moisture gradient is always created during the printing process, which may lead to out-of-plane dimensional instability. We showed that the swelling anisotropy of individual fibers bonded at non-parallel angles causes an additional contribution to the curl observed on the sheet level.
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| 27. |
- Brandberg, August, 1990-
(författare)
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Micro-mechanical characterization and modeling of paper and paperboard
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fiber networks made of cellulose fibers from trees are used as information carriers (paper) and as packaging (paperboard). This thesis investigates the mechanical performance of paper and paperboard via micro-mechanical modeling and presents new methods for the mechanical characterization of the micro scale, necessary in such models. In Paper A the effect of the fiber-fiber bond geometry on the sheet stiffness is investigated. In thick, low density sheets, the fiber lumen remains open resulting in a more compliant bonded segment. By finite element simulations, we demonstrate the effect of the lumen configuration on the stiffness of the bonded segment. Most important for the stiffness of the segment is the average state of the fiber lumen which has a marked effect on the macroscopic response of fiber networks when the network is sparse. Compression strength is central in many industrial applications. In Paper B we recreated the short span compression test in a simulation setting. The networks considered are three-dimensional and have a grammage of 80--400 gm^-2. By modeling compression strength at the level of individual fibers and bonds, we show that widespread fiber level buckling is unlikely to appear at the loads at which the macroscopic sheet fails. In Paper C we develop a micro-mechanical model to study the creation of curl in paper sheets subjected to a moisture gradient through the thickness of a sheet. A moisture gradient is created during the printing process if the ink is water based, which may lead to out-of-plane deformations (curl). The effect of transverse fiber shrinkage is captured using a multiscale model where the fiber-fiber bond is modeled with volume elements. We show how the swelling anisotropy of individual fibers contributes to the curl of the sheet in such settings. In Paper D we present how to uniquely and compactly describe the distribution of fiber shapes (length, width, wall thickness, curl) used in network simulations. Using a canonical vine structure, fiber shapes measured using an optical image analyzer are used to construct a multivariate distribution function. New fiber geometries can then be generated by sampling from this distribution. Having access to such a complete description with both the distribution of fiber properties and the dependence between properties is shown to be superior to previously presented methods using micro-mechanical simulations of thermo-mechanical (TMP) long fiber sheets. In Paper E we compare sheet testing, micro-mechanical tensile testing, and nanoindentation as methods to extract the elastic material properties of individual pulp fibers. Nanoindentations are performed parallel to and orthogonal to the axis of the fiber after it has gone through all steps of papermaking, and indentation moduli are extracted. By relating the indentation modulus to the components of the anisotropic stiffness tensor, the longitudinal and transverse elastic modulus can be determined via an iterative error minimization scheme. We show that nanoindentation is an alternative to traditional methods with the advantage of yielding the transverse modulus and enabling measurement of the fiber properties after papermaking.
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| 28. |
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| 29. |
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| 30. |
- Crawley, Edward F., et al.
(författare)
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Curriculum Design based on the CDIO Syllabus
- 2005
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Ingår i: 8TH UICEE ANNUAL CONFERENCE ON ENGINEERING EDUCATION, CONFERENCE PROCEEDINGS. - : UICEE. ; , s. 313-317
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Konferensbidrag (refereegranskat)
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| 31. |
- Crawley, E. F., et al.
(författare)
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Overview
- 2007
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Ingår i: Rethinking Engineering Education. - Boston, MA : Springer-Verlag New York. - 9780387382876 ; , s. 6-44
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Bokkapitel (refereegranskat)abstract
- 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.
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| 32. |
- Crawley, Edward F, et al.
(författare)
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Rethinking engineering education - The CDIO approach, 2nd ed
- 2014
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- © Springer International Publishing Switzerland 2007, 2014. 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.
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| 33. |
- Dominic, Chris A. S., et al.
(författare)
-
Towards a conceptual sustainable packaging development model : A corrugated box case study
- 2015
-
Ingår i: Packaging technology & science. - New York : Wiley. - 0894-3214 .- 1099-1522. ; 28:5, s. 397-413
-
Tidskriftsartikel (refereegranskat)abstract
- 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 CO2 emissions are traced along the material flow until the end of its useful life to provide an overall picture of the packaging system.
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| 34. |
- Edström, Kristina, 1963-, et al.
(författare)
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Integrated Curriculum Design
- 2007
-
Ingår i: Rethinking Engineering Education: The CDIO Approach. - : Springer.
-
Bokkapitel (refereegranskat)
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| 35. |
- Eriksson, Daniel, 1987-
(författare)
-
Getting to grips with cartons : Interactions of carbonboard packages with an artificial finger
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Packaging is an important part of most products in our modern world. It produces waste, but it also enables products to reach consumers safely and efficiently. Hence, the proper design of packaging is becoming increasingly important. Historically, cartonboard packages were designed for box compression strength. While this remains important, there are other types of loads that are important to consider. One such type of load arises from manual handling. As packages as moved and used, consumers need to exert forces on the package. These forces deform and can damage the package.Understanding these interactions can be challenging. By developing a method for quantifying the deformation due to manual handling, it becomes possible to measure and compare a redesigned package with the original to see if the performance has changed. This can aid packaging designers, but it can also be used for product control. The converting process is complex and deviations from specification can be introduced at many points along the production process.In this work, a method for quantifying interactions similar to those in manual handling is presented and evaluated. The method is then applied to study the effect of position and material properties on the mechanics of the interaction. The method is shown to have low variability and be robust to modifications in packaging and experimental design. It was seen that increasing the size of packages from 82 mm to 98 mm corresponded to decreasing the grammage by 10-20%. The method also showed the stiffening effect of corners and flaps, suggesting that the strategic placement of these design elements could help maintain the desired mechanical properties of the package at the point of interaction, provided the most likely point can be predicted.
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| 36. |
- Esteves, Claudia, et al.
(författare)
-
Differences and similarities between kraft and oxygen delignification of softwood fibers : effects on mechanical properties
- 2021
-
Ingår i: Cellulose. - : Springer Science and Business Media B.V.. - 0969-0239 .- 1572-882X. ; 28, s. 3775-3788
-
Tidskriftsartikel (refereegranskat)abstract
- Charged groups in pulp have been shown to enhance the tensile strength of the paper produced from the pulp. Oxygen delignification introduces charged groups and it is of interest to determine how the delignification should be distributed between the cooking and the oxygen stage with respect to mechanical properties. A number of unbleached kraft cooked and oxygen delignified pulps within a wide kappa number range were produced and refined, and the effects of the refining on the morphology and mechanical properties were studied. The WRV correlated with the fiber charge and at a given fiber charge, kraft cooked and oxygen delignified pulps had the same WRV development in refining, although they had significantly different kappa numbers. The tensile strength development during refining depends on the fiber rigidity which is affected by the lignin content, the fiber charge and the chemical and mechanical processes used. Refining increased the curl of the kraft cooked pulps and decreased the curl of oxygen delignified pulps, irrespective of kappa number. A greater increase in tensile strength was seen for the pulps with a higher fiber charge and WRV, probably because of the greater degree of fibrillation achieved in the beating process. Despite the greater fiber deformation in the oxygen delignified pulps, the strength can be increased by a larger amount of charged groups and a greater swelling of the fibers. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
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| 37. |
- Esteves, Claudia, et al.
(författare)
-
Differences and similarities between kraft and oxygen delignification of softwood fibers : effects on chemical and physical properties
- 2021
-
Ingår i: Cellulose. - : Springer Science and Business Media B.V.. - 0969-0239 .- 1572-882X. ; 28:5, s. 3149-3167
-
Tidskriftsartikel (refereegranskat)abstract
- The fiber properties after oxygen delignification and kraft pulping were studied by looking into the chemical characteristics and morphology. The effect of the two processes on the fibers was evaluated and compared over a wider kappa number range (from 62 down to15). Wide-angle X-ray scattering, nuclear magnetic resonance and fiber saturation point were used to characterize the fiber network structure. Fiber morphology and fiber dislocations were evaluated by an optical image analysis. The total and surface fiber charges were studied by conductometric and polyelectrolyte titrations. The fiber wall supramolecular structure, such as crystallinity, size of fibril aggregates, pore size and pore volume, were similar for the two processes. The selectivity, in terms of carbohydrate yield, was equal for kraft cooking and oxygen delignification, but the selectivity in terms of viscosity loss per amount of delignification is poorer for oxygen delignification. Clearly more fiber deformations (2–6% units in curl index) in the fibers after oxygen delignification were seen. Introduction of curl depended on the physical state of the fibers, i.e. liberated or in wood matrix. In the pulping stage, the fiber continue to be supported by neighboring fibers, as the delignified chips maintain their form. However, in the subsequent oxygen stage the fibers enter in the form of pulp (liberated fibers), which makes them more susceptible to changes in fiber form. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
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| 38. |
- Esteves, Claudia, 1989-
(författare)
-
Pulp strength enhancement by oxygen delignification
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oxygen delignification is widely used in the pulp and paper industry as a part of delignification process between the kraft cook and bleaching. However, its potential has not been fully utilized. Rather than an intermediate process between cooking and bleaching, oxygen delignification is a strong oxidizing agent with powerful effects on the pulp properties. In this work, the hypothesis that oxygen delignification has the potential to improve the pulp mechanical properties was investigated. Several pulps were produced by either kraft cooking or kraft cooking combined with a subsequent oxygen delignification stage to a similar kappa number and their properties were analyzed and compared. This methodology assessed the real oxidative potential of oxygen on the final fiber properties. Total fiber charge, pulp mechanical properties, fiber morphology, swellability and fiber nanostructure, were studied.The major part of this research investigated the relationship between the carboxylic acid groups, seen as total fiber charge, and the mechanical strength of the paper. The total fiber charge was evaluated by conductometric titration and correlated with the pulp swellability and mechanical properties. It was demonstrated that oxygen delignification could significantly increase the charge content and the swelling of the pulp when an extended oxygen delignification (i.e, higher delignification degree) was used. In addition, the tensile index of the sheets increased when the fiber charge after oxygen delignification was sufficiently high. The swelling of the different pulps was investigated by Schopper-Riegler degree (SR°), water retention value (WRV) and fiber saturation point (FSP). It was determined that the higher the fiber charge, the higher the swelling ability, regardless of the lignin content. High alkali impregnation was utilized in this study due to its potential to increase cooking yield. The yield was compared to kraft pulp cooked with standard and high alkali impregnation, followed by oxygen delignification and bleaching. It was observed that the increase in yield was preserved in both unit processes, i.e., after oxygen delignification and after bleaching. During this work, pulp properties such as fiber morphology and fiber nanostructure were also important properties that were studied following each unit process and refining step. Oxygen-delignified pulps presented higher fiber deformation when compared to the kraft-cooked pulps. However, even with higher fiber deformation, oxygen-delignified pulps showed higher mechanical strength, contradicting previous reports that claimed lower pulp strength for oxygen-delignified pulps, due to fiber deformation. Additionally, it was found that fiber deformation tends to increase with PFI-refining for kraft-cooked pulps, while for oxygen and bleached pulps it tends to decrease. Fiber nanostructure was additionally studied by X-ray scattering, and the results obtained from pulp delignification by kraft and kraft followed by oxygen delignification were compared. This thesis highlights the benefits of increasing fiber charge by performing an extended oxygen delignification after a reduced kraft cooking. The results indicate that when oxygen-delignified pulps achieve 80 % higher fiber charge than kraft-cooked pulps at a similar kappa number, the pulp tensile index can be improved by up to 18 %. The oxidation reactions that occur during the oxygen delignification lead to a significant increase in the carboxylic acid groups in the fibers which increases the fiber's swelling ability and improves the refining process efficiency. The combination of those effects results in a higher tensile index and lower refining energy required. However, to obtain mechanical improvement, the oxygen delignification must be sufficiently long (extended). Therefore, it is believed that an extended oxygen delignification will yield a more uniform distribution of the charged groups in the fibers, which will increase the fiber swelling and fiber flexibility leading to a more efficient refining process and stronger fiber bonding structure in the paper.
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| 39. |
- Esteves, Cláudia S. V. G., 1989-, et al.
(författare)
-
Evaluating the Potential to Modify Pulp and Paper Properties through Oxygen Delignification
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:23, s. 13703-13711
-
Tidskriftsartikel (refereegranskat)abstract
- The potential to modify pulp and paper properties by oxygen delignification was assessed by looking beyond the ordinary purpose of oxygen delignification. Pulps with the same kappa number were obtained by both pulping and the combination of pulping and oxygen delignification, and the mechanical and chemical properties were compared. The oxidation of pulp components leads to an increase in carboxylic acid groups in the fibers, resulting in a large influence on fiber swelling, seen as an increase in the water retention value and fiber saturation point. The introduction of charged groups appears to replace some of the morphological changes caused by refining and enhance the strength of fiber–fiber joints, generating pulps with better refinability and higher tensile strength. Oxygen delignification was able to improve the tensile index with 6% at the same sheet density and less refining energy, when the amount of total fiber charges was higher than 140 μekv/g.
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| 40. |
- Esteves, Claudia, et al.
(författare)
-
The effects of high alkali impregnation and oxygen delignification of softwood kraft pulps on the yield and mechanical properties
- 2022
-
Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 37:2, s. 223-231
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated whether the yield improvement after high alkali impregnation (HAI) is maintained after oxygen delignification and whether the potential of oxygen delignification to increase the mechanical properties is affected by high alkali impregnation. The yield improvement achieved by high alkali impregnation (1 %) was preserved after oxygen delignification, particularly of glucomannan. The total fiber charge and swelling increased after oxygen delignification regardless of the type of impregnation in the cooking step. The tensile index improvement obtained by oxygen delignification was retained if this was preceded by high alkali impregnation. The stiffness index was higher and elongation slightly lower after HAI impregnation than after a standard (REF) impregnation. Fibers obtained through high alkali impregnation seem to be slightly less deformed and slightly wider than fibers obtained after a standard impregnation.
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| 41. |
- Esteves, Claudia, et al.
(författare)
-
The impact of bleaching on the yield of softwood kraft pulps obtained by high alkali impregnation : Bleaching and high alkali impregnation impact
- 2022
-
Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 37:4, s. 593-608
-
Tidskriftsartikel (refereegranskat)abstract
- High alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition, viscosity, brightness, mechanical and morphological properties were studied. Compared to cooking after standard impregnation the yield improvement achieved by HAI was preserved in both types of bleaching sequences (2 % units for chlorine dioxide and 4 % units for hydrogen peroxide). The introduction of charged groups into the cellulose fibers was higher with hydrogen peroxide bleaching than with chlorine dioxide however, no significant impact was seen on the swelling or mechanical properties. The brightness was higher for the pulps bleached with chlorine dioxide compared with hydrogen peroxide. Hydrogen peroxide bleaching resulted in similar brightness development for both standard and HAI. Fibers bleached with chlorine dioxide had the highest curl index (16-17 %) compared to the fibers bleached with hydrogen peroxide (15 %). © 2022 the author(s)
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| 42. |
- Fellers, C., et al.
(författare)
-
Evaluation of the Scott bond test method
- 2012
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 231-236
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 43. |
- Gamstedt, E. Kristofer, et al.
(författare)
-
Fatigue propagation of fibre-bridged cracks in unidirectional polymer-matrix composites
- 2001
-
Ingår i: Applied Composite Materials. - 0929-189X .- 1573-4897. ; 8:6, s. 385-410
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 44. |
- Gard Timmerfors, Jessica, 1989-
(författare)
-
Wood chips for kraft and sulfite pulping : evaluation of novel forest-industrial drum-chipping technology
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood chipping and the supply of high-quality wood chips are of critical importance for most forest-industrial processes. The quality of wood chips affects product yield, product quality, and processability. Wood chips from a novel type of forest-industrial drum chipper, with a large drum and specially designed wood-chip channels, were evaluated with regard to wood chips for the Kraft and sulfite processes. Wood chips from a full-scale demonstration version of the drum chipper and from a conventional disc chipper at a Kraft mill were compared. The average bulk density and the fractions of oversized and overthick wood chips were similar, but the demonstration drum chipper produced 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. A pilot-scale drum chipper based on the new technology was used to produce short wood chips designed for acidic processes. When the drum velocity was 30-34 m/s and the average wood-chip length 21-22 mm, the fraction of pin chips and fines was 4.2% and the fraction of total accept was 89-90%. When the average wood-chip length was decreased to 17 mm, the fraction of pin chips and fines increased to 8.5% and the fraction of total accept decreased to 80-82%. The pilot drum chipper was used to investigate the influence of using different tree species (aspen, birch, pine, and spruce), processing of wood with different moisture content, and frozen wood. For hardwood (aspen and birch), the fraction of total accept reached ~90% when the average wood chip length was 17 mm. The pilot drum chipper was also used to generate wood chips of heartwood of pine for a comparison of 15 sulfite-process reaction conditions that differed with regard to impregnation and cooking procedures. The analyses included absorption of liquid in a specially designed impregnation reactor, pulp yield, reject, viscosity, kappa number, brightness, fiber properties, and chemical composition as determined using compositional analysis based on two-step hydrolysis with sulfuric acid and pyrolysis-gas chromatography/mass spectrometry. The results reveal in detail how the individual wood constituents were affected by the different treatments, and demonstrate the benefits of using a pressurized impregnation step prior to sulfite cooking.
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| 45. |
- Gimåker, Magnus, 1980-
(författare)
-
Influence of fibre modification on moisture sorption and the mechanical properties of paper
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibre modification might be a way to improve the performance of paper, to increase its cost competiveness and enable new paper-based products to be developed. Therefore, the influence of fibre modification (with polyelectrolytes or by fibre cross-linking) on the mechanical properties of special importance for packaging paper grades was studied. Creep deformation under varying humidity conditions (i.e. mechano-sorptive creep) is of outmost importance for the stacking life of paper-based boxes. The influence on creep behaviour of adsorbing polyallylamine (a cationic polyelectrolyte) to fibre surfaces or throughout the fibre walls was studied. Adsorption to fibre surfaces reduced the creep at constant humidity. The mechano-sorptive creep was not however influenced. The use of polyelectrolytes did not thus appear to be a feasible strategy for reducing mechano-sorptive creep. Polyelectrolytes can however be efficient in improving other mechanical properties. The use of multilayers consisting of polyallylamine (PAH) and polyacrylic acid (PAA) was for example shown to significantly increase the strength of paper with much less densification and build-up of residual stress than is obtained by beating. Cross-linking by oxidation with periodate radically decreased the mechano-sorptive creep of sheets made from the oxidised fibres. The basic mechanism behind the reduction in mechano-sorptive with cross-linking was found to be that the cross-linking slowed down the moisture sorption kinetics. A lower sorption rate led to smaller moisture content variations during the mechano-sorptive creep testing, and thus less sorption-induced swelling and stress concentrations at fibre/fibre joints. However, for cross-linking to be a practical way to reduce creep, the large problem of embrittlement must be solved. The shear strength of couched sheets was measured to study the interaction between the sheets at different solids content. The shear strength was low until a solids content of approximately 60−70% was reached, which suggests that interactions important for the strength at complete dryness start to develop at this solids content. The effect of different fibre modifications and additives on how the fibres interact during the consolidation process is not always well understood. The method of shear strength determination could in the future be applied to modified fibres to hopefully increase the understanding of how different modifications influence the fibre/fibre interactions. A deeper understanding might reduce the time for the development of new and improved fibre modifications.
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| 46. |
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| 47. |
- Gimåker, Magnus, et al.
(författare)
-
Shear strength development between couched papers during drying
-
Annan publikation (populärvet., debatt m.m.)abstract
- 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.
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| 48. |
- Girlanda, Orlando, et al.
(författare)
-
Characterization and Modelling of the Mechanical Properties of Pressboard
- 2013
-
Ingår i: 2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP). - : IEEE. - 9781479925964 ; , s. 563-566
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 49. |
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| 50. |
- Girlanda, O., et al.
(författare)
-
Defect sensitivity and strength of paperboard in out-of-plane tension and shear
- 2005
-
Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 31:2, s. 100-104
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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