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An improved z-directional fibre orientation measurement method has been developed that combines favourable methods for sheet splitting, layer imaging and image processing. The method enables uneven sheet splitting to be corrected arithmetically, thus providing a better reproduction of the true three-dimensional (3D) layered fibre orientation. The n...
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... the laminating method for sheet splitting was introduced by Knotzer [1,19,20]. The paper sample (grey) is sandwiched between two laminating foils and inserted in the laminator, where moving rolls transport the sandwich through the device, see Figure 1. On its way, the sample is heated, hot melt glue applied to the inner part of the laminating foils melts and firmly attaches the transparent plastic film to the paper surface. ...
Citations
... The disadvantage of the tomography-based method for detecting fibre orientation and anisotropy profiles is the limited size of the specimen, which may not always be representative of a given material. The alternative methods are based on sheetsplitting [21]. With this technique, the fibre network is delaminated in thin layers and each layer is analysed using optical methods through identifying the fibres in planar images. ...
Thin fibre networks are characterised by a certain degree of randomness in their mechanical response. This randomness can be seen as one of the main reasons for unexplained occasional failures that cannot be predicted by deterministic materials models. Direct fibre-level mechanical simulations can provide insights into the role of the constitutive components of such networks as well as capture the mechanisms of failure. However, these direct simulations are limited to small fibre networks due to overwhelming computational costs and cannot be employed for product development. Therefore, a stochastic multiscale approach for predicting the random mechanical response for thin fibre networks of arbitrary size is necessary. In such a model, the randomness in the network is mathematically described by spatial fields of material properties characterised using stochastic volume elements. In this book chapter, the steps involved in three-dimensional (3D)-fibre network characterisation, random generation, and finite-element simulation are described. This is followed by a description of the stochastic continuum modelling approach with a quantitative comparison to direct numerical simulation with respect to mechanical response and strain localisation pattern. The mathematical preliminaries and advanced topics related to stochastic continuum modelling using spatial field representations are presented in detail.
... These include x-ray diffraction (Prud'homme et al., 1975), micro-computed tomography (μCT) (Sharma et al., 2014;Tsarouchas and Markaki, 2011) and optical measurements (Rigdahl et al., 1983;Finger and Majewski, 1954;O. Kallmes, 1969;Hirn and Bauer, 2007;Yang et al., 1987). ...
Tensile testing was used to measure the mechanical properties of paper at various orientations relative to the machine direction of paper. New, artificially aged, and naturally aged paper were shown to behave as orthotropic materials, as shown by the orientation dependence of the Young's modulus, E. The Young's modulus data could be fit to a simplified equation, indicating the shear modulus is relatively insensitive to the specific orientation. The shear modulus as measured by ultrasonic measurements was similar to that measured by fitting the modulus vs orientation data obtained by tensile testing to the orthotropic equation. The inelastic tensile strength could also be described by a simple non-linear equation, and there was more deviation of the data from this prediction for brittle papers than for non-brittle papers. The extent of fiber orientation (Ex/Ey) could be inferred by either the Young's modulus or the tensile strength, TS, i.e. Ex/Ey ≈ TSx/TSy. The measured strains were lowest for brittle paper. All brittle papers gave a strain to failure <1% whereas the non-brittle papers gave a strain to failure >1%.
... The local fiber orientation was measured with a sheet splitting method [37] . Each specimen was split in the thickness direction into 14-20 layers and subsequently scanning the layers by an optical scanner with a resolution of 13 μm/pixel. ...
The stochastic variations in the structural properties of thin fiber networks govern to a great extent their mechanical performance. To assess the influence of local structural variability on the local strain and mechanical response of the network, we propose a multiscale approach combining modeling, numerical simulation and experimental measurements. Based on micro-mechanical fiber network simulations, a continuum model describing the response at the mesoscale level is first developed. Experimentally measured spatial fields of thickness, density, fiber orientation and anisotropy are thereafter used as input to a macroscale finite-element model. The latter is used to simulate the impact of spatial variability of each of the studied structural properties. In addition, this work brings novelty by including the influence of the drying condition during the production process on the fiber properties. The proposed approach is experimentally validated by comparison to measured strain fields and uniaxial responses. The results suggest that the spatial variability in density presents the highest impact on the local strain field followed by thickness and fiber orientation. Meanwhile, for the mechanical response, the fiber orientation angle with respect to the drying restraints is the key influencer and its contribution to the anisotropy of the mechanical properties is greater than the contribution of the fiber anisotropy developed during the fiber sheet-making.
... The local fiber orientation was measured with a sheet splitting method [37] . Each specimen was split in the thickness direction into 14-20 layers and subsequently scanning the layers by an optical scanner with a resolution of 13 μm/pixel. ...
The stochastic variations in the structural properties of thin fiber networks govern to a great extent their mechanical performance. To assess the influence of local structural variability on the local strain and mechanical response of the network, we propose a multiscale approach combining modeling, numerical simulation and experimental measurements. Based on micro-mechanical fiber network simulations, a continuum model describing the response at the mesoscale level is first developed. Experimentally measured spatial fields of thickness, density, fiber orientation and anisotropy are thereafter used as input to a macroscale finite-element model. The latter is used to simulate the impact of spatial variability of each of the studied structural properties. In addition, this work brings novelty by including the influence of the drying condition during the production process on the fiber properties. The proposed approach is experimentally validated by comparison to measured strain fields and uniaxial responses. The results suggest that the spatial variability in density presents the highest impact on the local strain field followed by thickness and fiber orientation. Meanwhile, for the mechanical response, the fiber orientation angle with respect to the drying restraints is the key influencer and its contribution to the anisotropy of the mechanical properties is greater than the contribution of the fiber anisotropy developed during the fiber sheet-making.
... The local FO was measured with a sheet splitting method described in detail by Hirn and Bauer (2007). As it is a destructive method, the determination of local FO was the last measurement step. ...
Measured local paper structure—i.e. local basis weight, local thickness, local density and local fiber orientation—has been linked to local strain and local material failure (local temperature increase due to energy dissipation upon fiber–fiber bond failure) measured during tensile testing. The data has been spatially linked through data map registration delivering several thousand 1×1mm2 paper regions, each containing all measured properties. The relation between local paper structure and resulting local deformation and failure is studied with regression models. Multiple linear regression modeling was used to identify the paper structure related drivers for local concentrations of strain under load and local concentrations of material failure, which are both starting to occur considerably before rupture of the paper. Analyzing the development of local strain in paper we found that regions with higher basis weight and higher fiber orientation in load direction tend to exhibit considerably lower strain during tensile testing. Furthermore, the relation between local strain and local grammage can be predicted with the statistical theory of elasticity. Also regions with higher density have lower local strain, but not as pronounced. The findings for local fiber–fiber bond failure of paper are similar but not equivalent. The strongest correlation exists with local grammage. Local density and local fiber orientation show in turn weaker correlation with local bond failure. Local variations in paper thickness were not relevant in any case. These findings are highlighting the relevance of local fiber orientation and local density variations as structural mechanisms governing paper failure. In the past the focus has been mostly on paper formation. Together with local grammage (formation) they are responsible for the weak spots in paper, and thus cause local concentrations of paper strain and the initiation of failure under tensile load.
... Both measurements are based on sheet splitting. The measurement for z-directional fibre orientation has been described elsewhere [43]. For z-directional fibre length distribution, the paper was laminated in a commercial hot laminator and subsequently split by hand. ...
A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects of the dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects on the through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.
... Both measurements are based on sheet splitting. The measurement for z-directional fibre orientation has been described elsewhere [43]. For z-directional fibre length distribution, the paper was laminated in a commercial hot laminator and subsequently split by hand. ...
A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects of the dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects on the through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.
The scope of the Progress in Paper Physics Seminar is to discuss the broad scope of physical properties of paper, paperboard and new cellulose containing materialas. The program contain presentations reporting on the latest experimental, theoretical and computational developments. The three invited plenary speakers aim at bringing industry and academia together for in-depth discussions on selected topics in paper physics the potential impact on industry. The selected 37 oral presentations and 12 poster presentations provide opportunity to improve scientific knowledge and explore the latest outcomes and trends in the field.
Fibre orientation influences many important properties of fibre-based materials, for example, strength and stiffness. Fibre
orientation and the orientation anisotropy in paper and other wood fibre-based materials have previously been estimated using
two-dimensional images. Recently, we presented a method for estimating the three-dimensional fibre orientation in volume images
based on local orientation estimates. Here, we present an evaluation of the method with respect to scale and noise sensitivity.
The evaluation is performed for both tubular and solid fibres. We also present a new method for automatic scale selection
for solid fibres. The method is based on a segmentation of the fibres that also provides an estimate of the fibre dimension
distribution in an image. The results show that the fibre orientation estimation performs well both in noisy images and at
different scales. The presented results can be used as a guide to select appropriate parameters for the method when it is
applied to real data. The applicability of the fibre orientation estimation to fibre-based materials with solid fibres is
demonstrated for a volume image of a press felt acquired with X-ray microtomography.
