| 1. |
- Andrä, Heiko, et al.
(författare)
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Micromechanical network model for the evaluation of quality controls of paper
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 49-55
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Konferensbidrag (refereegranskat)abstract
- In this paper, we discuss the challenges in modelling and simulating infinitesimal and large deformations of cellulose fiber networks, mainly in the context of the prediction of quality controls for paper.Understanding the influence and sensitivity of macroscopic production parameters like grammage and thickness of paperboard and understanding the influence of the fiber suspension on the quality of paper is important for the development of better papers and for preserving raw materials and energy.The new simulation framework consists of the virtual stochastic paper structure generator PaperGeo, that was integrated in the GeoDict 1 software suite, and the finite element solver FeelMath (Finite Elements for Elastic Materials and Homogenization) for solving the equations of elasticity. The fibers and the contacts are modelled by using geometrically exact beams of Simo-type [1].The microstructural model and the fiber network model are validated against standard measurements of existing papers in the following way: At first we perform tensile and bending tests to measure the macroscopic stress-strain relations. In the next step we apply a representative macroscopic stress or strain onto the boundaries of realizations of the stochastic fiber network model and compute by homogenization the effective (stiffness) coefficients. Finally we compare the numerical results with the measurements.This procedure can also be used for an identification of elastic parameters on the microscale and to study the sensitivity of the effective (macroscopic) stiffness with regard to the parameters of the microstructure
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| 2. |
- Fredlund, Kerstin, 1954, et al.
(författare)
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Absorption of zinc and retention of calcium: dose-dependent inhibition by phytate
- 2006
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Ingår i: Journal of Trace Elements in Medicine and Biology. - : Elsevier BV. - 0946-672X. ; 20:1, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- The dose-dependent inhibitory effect of sodium phytate (myo-inositol-hexaphosphate) on absorption of zinc and retention of calcium was studied in man. No systematic study of this dose-response effect has been reported to this time. Forty subjects were served meals containing white wheat rolls without/with additions of phytate. Ten subjects were given test meals containing one or two of the studied levels of phytate and in addition all subjects were served meals to which no phytate was added. The zinc content was 3.1 mg (47 mu mol) and the calcium content 266 mg (6.6 mmol). The rolls were labelled extrinsically with radioisotopes, Zn-65 and Ca-47, and whole-body retention of both minerals was measured. Totally 105 meals were served, 36 meals in which no phytate was added and 9-10 meals on each level of phytate. The zinc absorption in meals to which either 0, 25, 50, 75, 100, 140, 175 or 250 mg of phytate-P (0, 134, 269, 403, 538, 753, 941 or 1344 mu mol phytate) had been added was 22%, 16%, 14%, 11%, 7%, 7%, 7% and 6%, respectively (mean values). The addition of 50 mg phytate-P or more significantly decreased zinc absorption (p = 0.01) as compared to absorption from the test meals with no added phytate. The calcium retention at day 7 in the same meals was 31%, 28%, 27%, 26%, 22%, 19%, 14% and 11% (mean values). The addition of 100 mg phytate-P or more significantly decreased calcium retention (p = 0.03) compared to the test meals with no added phytate. It was concluded that the inhibitory effect of phytate on the absorption of zinc and the retention of calcium was dose dependent.
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| 5. |
- Görtz, Morgan, 1994, et al.
(författare)
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Iterative method for large-scale Timoshenko beam models assessed on commercial-grade paperboard
- 2024
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Ingår i: Computational Mechanics. - 1432-0924 .- 0178-7675. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale structural simulations based on micro-mechanical models of paper products require extensive numerical resources and time. In such models, the fibrous material is often represented by connected beams. Whereas previous micro-mechanical simulations have been restricted to smaller sample problems, large-scale micro-mechanical models are considered here. These large-scale simulations are possible on a non-specialized desktop computer with 128GB of RAM using an iterative method developed for network models and based on domain decomposition. Moreover, this method is parallelizable and is also well-suited for computational clusters. In this work, the proposed memory-efficient iterative method is numerically validated for linear systems resulting from large networks of Timoshenko beams. Tensile stiffness and out-of-plane bending stiffness are simulated and validated for various commercial-grade three-ply paperboards consisting of layers composed of two different types of paper fibers. The results of these simulations show that a linear network model produces results consistent with theory and published experimental data
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| 6. |
- Hagman, Anton, et al.
(författare)
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Experimental and numerical verification of 3D-forming
- 2017
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Ingår i: ADVANCES INPULP AND PAPERRESEARCH,OXFORD 2017. - 9780992616335 ; , s. 3-26
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Johnson, Tomas, 1979, et al.
(författare)
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A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
- 2015
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
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Tidskriftsartikel (refereegranskat)abstract
- When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to a mixture of water and hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry as well as to packaging manufacturers. In this paper an extended multi-scale model of edge wicking in multi-ply paperboard is presented. The geometric and physical properties of the paperboard are modeled on the micro-scale, and include fillers and fines. The absolute air permeabilities and pore size distributions are validated with experimental and tomographic values. On the macro-scale random porosity and sizing distributions, time and sizing dependent contact angles, and inter-ply dependence are modeled. Arbitrary shapes of the paperboard are handled through an unstructured 3D surface mesh. Stationary and transient edge wicking simulations are validated against experiments with excellent agreement. The simulations show that the diffusive menisci between the liquid and air phases together with the two-ply model is necessary to achieve good agreement with the transient edge wicking experiments.
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| 10. |
- Kettil, Gustav, 1990, et al.
(författare)
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A Multiscale Method for Discrete Fiber Network Models
- 2018
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Ingår i: 6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems). 7th European Conference on Computational Fluid Dynamics, 11-15 June 2018, Glasgow, UK.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The mechanics of paper depends on the properties of its fibers and bonds. Modeling paper as a network [1] will include effects of single fibers and bonds, capturing heterogeneous properties. In the ISOP (Innovative Simulation of Paper) project at Fraunhofer-Chalmers Centre, the forming process is simulated [2, 3]. To investigate the mechanical properties of the resulting simulated paper sheets a network approach is utilized. Numerical investigation of fiber networks is demanding due to the large number of fibers and bonds, fluctuation of their properties, and the non-regular network structure. Multiscale methods are useful tools to circumvent such problems. In this work a multi-scale approach for fiber networks is developed, based on a FEM-method for continua [4]. Consider a fiber network governed by a model resulting in an equation Kx = F, where K describes the network properties, x are node displacements, and F are applied forces. The idea of the multi-scale method is to consider a subset of all nodes, denoted coarse nodes, which in turn represents a coarse grid. At each coarse node a basis function is defined similarly as in the finite element method. By solving a system including the coarse nodes an approximation would be attained, however this approximation would leave out the fine scale effects of the heterogeneous network. Instead the coarse basis functions are modified by solving a local system at each coarse node, including surrounding fine nodes. These modified basis functions are thereafter used when solving the global system, resulting in an approximation of the network displacements now including effects from the fine scale.
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