| 1. |
- Afshar, R., et al.
(author)
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A micro-CT investigation of densification in pressboard due to compression
- 2023
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In: Strain. - : John Wiley & Sons. - 0039-2103 .- 1475-1305. ; 59:4
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Journal article (peer-reviewed)abstract
- As a non-destructive inspection method, micro-computed tomography has been employed for determining local properties of a cellulose-based product, specifically pressboard. Furthermore, by utilizing the determined properties in a detailed numerical model, by means of a finite element analysis, we demonstrate a continuum anisotropic viscoelastic-viscoplastic model. Through such a combination of non-invasive experiments with accurate computations in mechanics, we attain a better understanding of materials and its structural integrity at a pre-production stage increasing the success of the first prototype. In detail, this combination of micro-computed tomography and finite element analysis improves accuracy in predicting materials response by taking into account the local material variations. Specifically, we have performed indentation tests and scanned the internal structure of the specimen for analysing the densification patterns within the material. Subsequently, we have used a developed material model for predicting the response of material to indentation. We have computed the indentation test itself by simulating the mechanical response of high-density cellulose-based materials. In the end, we have observed that pressboard, having initially a heterogeneous density distribution through the thickness, shows a shift in the densification to the more porous part after indentation. The densification maps of the simulated results are presented by comparing with the experimental results. A reasonable agreement is observed between the experimental and the simulated densifications patterns, which suggests that the proposed methodology can be used to predict densification also for other fibre-based materials during manufacturing or in service loading.
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| 2. |
- Girlanda, O., et al.
(author)
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Defect sensitivity and strength of paperboard in out-of-plane tension and shear
- 2005
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In: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 31:2, s. 100-104
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Journal article (peer-reviewed)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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| 3. |
- Girlanda, O., et al.
(author)
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Delamination position in multiply paperboard achieved by different testing methods
- 2008
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In: Appita journal. - 1038-6807. ; 61:2, s. 107-112
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Journal article (peer-reviewed)abstract
- The determination properties of nine commercial multiply board grades, both coated and uncoated, were measured using four testing methods, the Z-Directional Tensile Strength test (ZDTS), the Scott Bond Test (SBT), the Wheel Delamination Test (WDT), and the IGT method. The positions of delamination failure in the thickness direction were then recorded and compared. For the IGT tests, failure profiles and the final failure positions were evaluated. The results showed that the failures in the ZDTS, WDT and SBT tests mainly occur in the middle ply, whereas failure in the IGT tests occurs in the top plies as well as in the middle ply. Some boards presented also more than one failure position for the same type of test. The correlations between the different delamination resistances were also investigated. The WDT and SBT method showed a good correlation, whereas no correlation could be found between the other methods.
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| 4. |
- Girlanda, O., et al.
(author)
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Modelling of delamination in paperboard during sheet offset printing
- 2008
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In: Appita journal. - 1038-6807. ; 61:2, s. 113-119
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Journal article (peer-reviewed)abstract
- Delamination of multiply paperboard during offset printing is caused by the ink tack induced forces applied on the surface of the board. The purpose of this investigation was to analyze the influence of mechanical properties of the plies and interface resistance on the delamination behaviour of the paperboard. Paperboard was modelled as a four-ply sandwich structure. A user-defined interface model described the mechanical behaviour of the interfaces between the plies. The results in terms of critical ink tack length and stress conditions in the interfaces at delamination initiation were defined for different ply structures. The delamination process in multiply paperboard was highly dependent on the stress concentration caused by the ink tack. The delamination always occurred in the interface between top and middle ply. The main stress component causing delamination was tensile stress in the thickness direction, whereas the interlaminar shear was less relevant. Bending stiffness and in-plane tensile stiffness influenced the critical ink tack length, but did not affect the stress situation at the delamination point.
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| 5. |
- Tjahjanto, Denny D., et al.
(author)
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Anisotropic viscoelastic-viscoplastic continuum model for high-density cellulose-based materials
- 2015
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In: Journal of the mechanics and physics of solids. - : Elsevier BV. - 0022-5096 .- 1873-4782. ; 84, s. 1-20
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Journal article (peer-reviewed)abstract
- A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress-strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media. Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.
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