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  • 1.
    Hagman, Anton
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Influence of inhomogeneities on the tensile and compressive mechanical properties of paperboard2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Egenskaperna hos ett kartongark kan grovt delas upp i två kategorier: i-planet egenskaper och ut-ur-planet egenskaper. I-planet egenskaperna har länge varit ett område som pappersmekanister och andra pappersforskare visat intresse för. Anledningen till detta är att de är avgörande för hur väl det går att konvertera kartongen till färdiga förpackningar, samt hur väl de förpackningarna klarar sin uppgift. Dragegenskaperna prövas när kartongen dras genom tryck- och konverteringsmaskiner i hög hastighet. Tryckegenskaperna spelar stor roll för hur väl en förpackning klarar att staplas och hålla sitt innehåll intakt. Inhomogeniteter påverkar både drag och tryckegenskaper. Papprets naturliga variation påverkar dragegenskaperna hos kartongen och kan orsaka problem för kartongmakarna. Särskilt när utvecklingen går mot mer avancerade kartong utseenden. Å andra sidan så använder sig kartongmakare flitigt av egenskapsvariationer genom tjockleken på kartongen, när dom vill åstadkomma böjstyva kartonger utan att slösa med fibrer. I detta fall är det intressant att veta hur de lokala kompressionsegenskaperna påverkas av kartongens ut-ur-planet profil. Det första två uppsatserna i denna avhandling, A och B, handlar om just detta. Uppsatserna C, D och E avhandlar hur i-planet variationer påverkar kartongens egenskaper.

    I Artikel A undersöks vilka skademekanismer som aktiveras under ett kortspannskompressionstest (SCT). Tre flerskiktskartonger undersöktes. De hade valts så att de hade distinkt olika skjuvstyrkeprofiler. Kartongerna karakteriserades och datan användes som materialdata i en finit element modell av SCT-testet. Modellen bestod av skikt, betraktade som kontinuum, mellan vilka det fanns kohesiva ytor. Huvudmekanismen i SCT var att kartongen delaminerade på grund av skjuvskador.

    Den andra uppsatsen, Artikel B, var en fortsättning på den första. Denna gång undersöktes fem flerskiktskartonger framtagna så att de hade olika skjuvstyrka beroende på positionen i tjockleksled. Det konstaterades att kompressionsegenskaperna lokalt styrs av skjuvstyrkeprofilen och styvhetsgradienter. Vidare konstaterades det att mekanismerna innan kartongen delaminerar är, i huvudsak, elastiska.

    Den tredje artikeln, Artikel C, fokuserade på hur dragprov på kartong påverkas av provstorleken och töjningsvariationen. Tre olika flerskiktskartonger användes som provmaterial och provbitar med olika storlek analyserades. Förutom dragprov så användes digital image correlation (DIC) för analysen. Det visade sig att den globala töjbarheten varierade med storleken på provet beroende på kvoten mellan längd och bredd. DIC visade att detta i sin tur berodde på att zoner med hög töjbarhet aktiverades i provet. Dessa zoner hade samma storlek oberoende av provstorlek och påverkade därför den totala töjbarheten olika mycket.

    Artikel D undersöker töjningszonerna som sågs i Artikel C samt hur de påverkas av kreppning. Vidare undersöktes pappersproverna med hjälp av termografi. Termografin visade att varma zoner uppstod i proven när det töjdes. Zonerna blev synliga när provet töjdes plastiskt. Termografi kördes parallellt med DIC på några prover. Det visade sig att de varma zonerna överenstämde med zoner med hög lokal töjning. Vidare kunde det visas att dessa zoner övenstämde med papperets mikrostruktur, formationen. En finit element analys av hur papper med olika formation töjs gjordes. Delar av provningen gjordes på kreppade papper som har högre töjbarhet. Det visades sig att någon form av skada hade överlagrats på papprets mikrostruktur under kreppningen, och att den deformationen återtogs när pappret töjdes.

    I den sista artikeln, Artikel E, behandlas hur VFM (Virtual Field Method) kan användas på DIC-data från kartong. DIC-datan som användes hämtades från Artikel C. Detta gjordes för att visa på hur olika VFM-formuleringar kan användas för att karakterisera styvhetsvariationen hos kartong. Provet delades upp i tre subregioner baserat på den axiella töjningsgraden. VFM-analysen visade att dessa subregioners styvhet och tvärkontraktionstal sjönk monotont, men att skillnaden mellan regionerna ökade med ökande spänning. även om endast ett prov undersöktes, så indikerade resultaten att områden med hög styvhet endast förbättrar de mekaniska egenskaperna marginellt. Analysen visade också att även om subregionerna inte är sammanhängande, så har dom liknande mekaniska egenskaper.

  • 2.
    Hagman, Anton
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Investigations of In-Plane Properties of Paperboard2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In-plane properties of paperboard have always been of interest to paper mechanical researchers. The reason for this is that they play a large role for the usability of the paperboard throughout its lifespan.  Tensile properties are crucial when the board is fed through printing and converting machines at high speeds in the beginning of its life. While compressive properties are essential in the later use of e.g. packages. In this thesis some methods for evaluating in-plane properties are reinvestigated.

    In Paper A the tensile test was investigated with focus on sample size and strain distributions. Three different multiply paperboards were examined with varying sample sizes using speckle photography. Different strain behaviour was found for different sample sizes. This difference was dependent on the length to width ratio of the sample and was caused by the activation of strain zones in the sample. These zones were of a constant size and therefore occupied different amounts of the total sample area.

    Paper B investigates the mechanism that causes failure in the short span compression test (SCT). Three different multiply paperboards were examined, this time chosen to have distinctly different through-thickness profiles. The boards were characterized and the data was used to simulate a SCT test with the three different boards. The simulation was conducted with a finite element model consisting of layers of continuum elements with cohesive interfaces in-between. From the model it was concluded that the main mechanism for failure in SCT is delamination that was caused by shear damage. 

  • 3.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Considine, J. M.
    Nygårds, M.
    Stiffness heterogeneity of multiply paperboard examined with VFM2017Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series, Springer, 2017, s. 151-159Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mechanical heterogeneity of a multiply paperboard was characterized in uniaxial tension using DIC and VFM. The specimen was divided into three subregions based on axial strain magnitude. VFM analysis showed that the subregions had stiffnesses and Poisson’s ratio’s that varied in a monotonically decreasing fashion, but with the stiffness differences between subregions increasing with applied tensile stress. An Equilibrium Gap analysis showed improved local equilibrium when comparing a homogeneous analysis with the subregion analysis. Although only a single specimen was examined, results suggest that high stiffness regions provide only marginal improvement of mechanical behavior. The analysis also showed that even though the subregions themselves were non-contiguous, their mechanical behavior was similar. © The Society for Experimental Mechanics, Inc. 2017.

  • 4. Hagman, Anton
    et al.
    Considine, John
    Nygårds, Mikael
    Stiffness Heterogeneity of Multiply Paperboard Examined with VFM2016Konferensbidrag (Övrigt vetenskapligt)
  • 5.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Huang, Hui
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Investigation of shear induced failure during SCT loading of paperboards2013Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, nr 3, s. 415-429Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In-plane compression has been analyzed experimentally and numerically using three machine made multiply paperboards. The paperboards had different shear strength profiles. Both short span compression (SCT) and long span compression (LCT) were performed. A finite element model of the SCT setup was developed, and the experimental results in MD and CD could be well predicted by the model. Using the model we could identify that the SCT failure was initiated by shearing of the interfaces in combination with the onset of plasticity in the loading direction. The model was used to make a parameter study. It showed that increased SCT values can be achieved by increasing the stiffness of the board or increase the failure displacement. The increase of stiffness was associated with ply properties, while the failure displacement was associated with interface properties.

  • 6.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Nygards, Mikael
    Short compression testing of multi-ply paperboard, influence from shear strength2016Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, nr 1, s. 123-134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of the through-thickness shear strength profiles on the short span compression test was examined. This was done both with experiments and finite element simulations on five industrial produced paperboards. It was concluded that the short span compression test is governed by in-plane stiffness and through thickness delamination The delamination damage was in turn dependent on the local transverse shear strength and in-plane stiffness gradients. Furthermore, it was concluded that the pre-delamination mechanisms were elastic. Finally it was possible to alter the results from the test by altering the shear strength of the paperboard; this should be done uniformly over the entire middle ply of the board if an increased SCT value was what was sought after.

  • 7.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Nygårds, M.
    Thermographical Analysis of Paper During Tensile Testing and Comparison to Digital Image Correlation2017Ingår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 57, nr 2, s. 325-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thermal response in paper has been studied by thermography. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Because of its fibrous network structure, paper has an inhomogeneous micro-structure, which is called formation. It could be shown that the formation was the cause of the inhomogeneous deformations in paper. Finite element simulations was used to show how papers with different degrees of heterogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid compaction of the paper was created during the creping process. During tensile testing this was recovered as the paper network structure was strained.

  • 8.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation. KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation. KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Investigation of sample-size effects on in-plane tensile testing of paperboard2012Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 2, s. 295-304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of sample size on in-plane strain behavior in paperboard was investigated, with the aim to explore the differences between local and global properties in paperboard, and try to pinpoint the mechanisms behind such differences. The local properties are of interest in converting as well as for future 3D forming of paperboard. It is important to identify differences in behavior between local and global properties since most paperboards are evaluated against the latter. The methods used for evaluation were tensile tests in controlled environment and speckle photography. The results show that there is a difference in strain behavior that is dependent of the length to width ratio of the sample, that this behavior cannot be predicted by standard tensile tests and that it depends on the board composition. The speckle analysis revealed that the behavior is a result of the activation of strain zones in the sample. These zones are relatively constant in size and therefore contribute differently to total strain in samples of different size.

  • 9.
    Hagman, Anton
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Investigation of shear induced failure during SCT loading of paperboards2013Rapport (Övrigt vetenskapligt)
  • 10. Hagman, Anton
    et al.
    Nygårds, Mikael
    Thermographical analysis of paper during tensile testing and comparison to digital image correlation2016Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The thermal response in paper has been studied using thermography. It was observed that an inhomogenous deformation pattern arose in the paper samples during tensile testing. In the plastic regime a pattern of warmer streaks could be observed in the samples. On the same samples digital image correlation (DIC) was used to study local strain fields. It was concluded that the heat patterns observed by thermography coincided with the deformation patterns observed by DIC. Due to the fibrous network structure paper has an inhomogenous microstructure, called formation. It could be shown that the formation was the cause of the inhomogenous deformations in paper. Finite element simulations were used to show how papers with different amount of homogeneity would deform. Creped papers, where the strain at break has been increased, were analysed. For these paper it was seen that an overlaid permanent damage was created during the creping process. During tensile testing this was recovered as the paper network structure was strained.

  • 11.
    Huang, Hui
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Hagman, Anton
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Quasi static analysis of creasing and folding for three paperboards2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The creasing and folding behavior of three paperboards have been studied both experimentally and numerically. Creasing and folding studies were performed on strips in both the machine direction and the cross machine direction. A finite element model that mimicked the experimental creasing and folding setup was developed, and the creasing and folding behavior could be well predicted for all three paperboards.

    An experimental characterization scheme consisting of three experiments was proposed, and was shown to be sufficient to predict the creasing and folding behavior. For the whole paperboard the shear strength profiles in the through thickness direction was determined with the notched shear test. Each ply was laid free by grinding, and density measurements and in-plane tension tests were performed on the bottom, middle and top plies of each paperboard. Instead of assuming uniform properties in each ply, the shear strength profiles were used to map the measured properties in the through thickness direction.

    Numerical simulations were performed when the ply and interface properties of the paperboards were altered to follow different shear strength profiles. This was done in order to mimic different production strategies. It was shown that the interface strengths mainly influenced the folding behavior. Whereas altered the ply properties affected the creasing force needed.

  • 12.
    Huang, Hui
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Hagman, Anton
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Nygårds, Mikael
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellens Centrum BiMaC Innovation.
    Quasi static analysis of creasing and folding for three paperboards2014Ingår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 69, nr 1, s. 11-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The creasing and folding behavior of three paperboards have been studied both experimentally and numerically. Creasing and folding studies were performed on strips in both the machine direction and the cross machine direction. A finite element model that mimicked the experimental creasing and folding setup was developed, and the creasing and folding behavior could be well predicted for all three paperboards. An experimental characterization scheme consisting of three experiments was proposed, and was shown to be sufficient to predict the creasing and folding behavior. For the whole paperboard the shear strength profiles in the through thickness direction was determined with the notched shear test. Each ply was laid free by grinding, and density measurements and in-plane tension tests were performed on the bottom, middle and top plies of each paperboard. Instead of assuming uniform properties in each ply, the shear strength profiles were used to map the measured properties in the through thickness direction. Numerical simulations were performed when the ply and interface properties of the paperboards were altered to follow different shear strength profiles. This was done in order to mimic different production strategies. It was shown that the interface strengths mainly influenced the folding behavior. Whereas altered the ply properties affected the creasing force needed.

  • 13. Jeong, S. H.
    et al.
    Hagman, Anton
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Hjort, K.
    Jobs, M.
    Sundqvist, J.
    Wu, Z.
    Liquid alloy printing of microfluidic stretchable electronics2012Ingår i: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 12, nr 22, s. 4657-4664Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, microfluidic stretchable electronics has attracted great interest from academia since conductive liquids allow for larger cross-sections when stretched and hence low resistance at longer lengths. However, as a serial process it has suffered from low throughput, and a parallel processing technology is needed for more complex systems and production at low costs. In this work, we demonstrate such a technology to implement microfluidic electronics by stencil printing of a liquid alloy onto a semi-cured polydimethylsiloxane (PDMS) substrate, assembly of rigid active components, encapsulation by pouring uncured PDMS on-top and subsequent curing. The printing showed resolution of 200 μm and linear resistance increase of the liquid conductors when elongated up to 60%. No significant change of resistance was shown for a circuit with one LED after 1000 times of cycling between a 0% and an elongation of 60% every 2 s. A radio frequency identity (RFID) tag was demonstrated using the developed technology, showing that good performance could be maintained well into the radio frequency (RF) range.

1 - 13 av 13
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