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  • 1.
    Altgen, Michael
    et al.
    Aalto Univ, Finland.
    Willems, Wim
    FirmoLin Technol BV, Netherlands.
    Hosseinpourpia, Reza
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT).
    Rautkari, Lauri
    Aalto Univ, Finland.
    Hydroxyl accessibility and dimensional changes of Scots pine sapwood affected by alterations in the cell wall ultrastructure during heattreatment2018Ingår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 152, s. 244-252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is a complex link between the water sorption behavior and the presence of accessible hydroxyl groups in the wood cell wall, which can be altered by heat-treatment (HT). This study analyses the effect of changes in the cell wall ultrastructure caused by two HT techniques on the hydroxyl accessibility, water vapor sorption and dimensional changes of Scots pine (Pinus sylvestris L.) sapwood. HT of wood in pressurized hot water at 120-170 °C was applied to cause the preferential bond cleavage, whereas HT of wood in oven-dry state in superheated steam at 180-240 °C was performed to create additional covalent cross-links within the cell wall matrix. Removal of cell wall polymers by HT and water leaching reduced the oven-dry dimensions of wood and enhanced the cellulose aggregation during drying. Cellulose aggregation restricted the cell wall shrinkage in circumferential direction, resulting in inhomogeneous shrinkage of the cell wall with only little changes in lumen volume by HT. Cellulose aggregation also reduced the water-saturated dimensions, but a decrease in swelling was only achieved when additional cross-links were formed by HT in dry state. Additional cross-links in the cell wall matrix also resulted in an additional reduction in water sorption at 25 °C and 93% RH. However, this was not caused by a further reduction in the hydroxyl accessibility. Instead, cross-linking was shown to reduce the amount of accessible OH groups that are simultaneously active in sorption, which was explained based on the concept of sorption of water dimers at hydroxyl group pairs at high RH levels.

  • 2.
    Anuar Bahari, Shahril
    et al.
    Universiti Teknologi MARA (UiTM), Malaysia.
    Nazarudin Zakaria, Mohd
    Universiti Teknologi MARA (UiTM), Malaysia.
    Osman, Syaiful
    Universiti Teknologi MARA (UiTM), Malaysia.
    Abu, Falah
    Universiti Teknologi MARA (UiTM), Malaysia.
    Jani Saad, Mohamad
    Malaysian Agricultural Research and Development Institute (MARDI), Malaysia.
    Hosseinpourpia, Reza
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT). Linnéuniversitetet, Kunskapsmiljöer Linné, Avancerade material. Linnéuniversitetet, Kunskapsmiljöer Linné, Grön hållbar utveckling.
    Strength Performance and Microstructure Characteristic of Naturally-Bonded Fiberboard Composite from Malaysian Bamboo (Bambusa vulgaris)2022Ingår i: Journal of Renewable Materials, ISSN 2164-6325, E-ISSN 2164-6341, Vol. 10, nr 10, s. 2581-2591Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study investigated the mechanical properties and microstructural characteristics of fiberboard composite produced by naturally-bonded Malaysian bamboo fiber (Bambusa vulgaris). The components that obtained through soda pulping of bamboo culms such as fiber and black liquor, were used for the preparation of high-density fibreboard composite at two target densities of 850 and 950 kg/m3. The bamboo fiberboard composite (BFC) were then produced at 200°C and two pressing parameters of 125 and 175 s/mm. The mechanical properties, e.g., flexural strength and internal bonding (IB) of BFC samples were evaluated according to BS EN 310: 1993 and BS EN 319: 1993, respectively. It was found that the mechanical performance of the composite with 850 kg/m3 density was significantly higher than 950 kg/m3 ones, especially for the samples with 125 s/mm pressing parameter. Microstructure characteristic of the BFC samples illustrated that the fiber linkages were cracked in the composites with higher density, e.g., the composite with the density of 950 kg/m3 and also black liquor were slightly degraded at longer pressing time, which led to the reduction in mechanical properties, especially in IB strength.

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  • 3.
    Elmukashf, Elsiddig
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Numerical analysis of dynamic crack propagation in rubber2012Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 177, nr 2, s. 163-178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present paper, dynamic crack propagation in rubber is analyzed numerically using the finite element method. The problem of a suddenly initiated crack at the center of stretched sheet is studied under plane stress conditions. A nonlinear finite element analysis using implicit time integration scheme is used. The bulk material behavior is described by finite-viscoelasticity theory and the fracture separation process is characterized using a cohesive zone model with a bilinear traction-separation law. Hence, the numerical model is able to model and predict the different contributions to the fracture toughness, i.e. the surface energy, viscoelastic dissipation, and inertia effects. The separation work per unit area and the strength of the cohesive zone have been parameterized, and their influence on the separation process has been investigated. A steadily propagating crack is obtained and the corresponding crack tip position and velocity history as well as the steady crack propagation velocity are evaluated and compared with experimental data. A minimum threshold stretch of 3.0 is required for crack propagation. The numerical model is able to predict the dynamic crack growth. It appears that the strength and the surface energy vary with the crack speed. Finally, the maximum principal stretch and stress distribution around steadily propagation crack tip suggest that crystallization and cavity formation may take place.

  • 4.
    Elmukashfi, Elsiddig
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Numerical analysis of dynamic crack propagation in biaxially strained rubber sheets2014Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 124/125, s. 1-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper proposes a computational framework for dynamic crack propagation in rubber in which a nonlinear finite element analysis using cohesive zone modeling approach is used. A suddenly initiated crack at the center of biaxially stretched sheet problem is studied under plane stress conditions. A transient dynamic analysis using implicit time integration scheme is performed. In the constitutive modeling, the continuum is characterized by finite-viscoelasticity theory and coupled with the fracture processes using a cohesive zone model. This computational framework was introduced previously by the present authors (Elmukashfi and Kroon, 2012). In the current work, the use of a rate-dependent cohesive model is examined in addition to investigation of generalized biaxial loading cases. A Kelvin–Voigt element is used to describe the rate-dependent cohesive model wherein the spring is described by a bilinear law and dashpot with a constant viscosity is adopted. An explicit integration is used to incorporate the rate-dependent cohesive model in the finite element environment. A parametric study over the cohesive viscosity is performed and the steady crack propagation velocity is evaluated and compared with experimental data. It appears that the viscosity varies with the crack speed. Further, the total work of fracture is estimated using rate-independent cohesive law such that the strength of the cohesive zone is assumed to be constant and the separation work per unit area is determined form the experimental data. The results show that fracture-related processes, i.e. creation of new surfaces, cavitation and crystallization; contribute to the total work of fracture in a contradictory manner.

  • 5.
    Ghavidel, Amir
    et al.
    University of Iasi, Romania.
    Hosseinpourpia, Reza
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT). Linnéuniversitetet, Kunskapsmiljöer Linné, Avancerade material.
    Militz, Holger
    University of Göttingen, Germany.
    Vasilache, Viorica
    University of Iasi, Romania.
    Sandu, Ion
    Academy of Romanian Scientists (AOSR), Romania;Romanian Inventors Forum, Romania.
    Characterization of Archaeological European White Elm (Ulmus laevis P.) and Black Poplar(Populus nigra L.)2020Ingår i: Forests, ISSN 1999-4907, E-ISSN 1999-4907, Vol. 11, nr 12, s. 1-13, artikel-id 1329Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study aims at characterization of freshly-cut and archaeological European white elm and poplar. The archaeological elm sample was buried at a depth of 8–10 m inside of soil with age approximation of ~1800–2000 years old, and the archaeological poplar sample was apart of a boat in a freshwater lake or river with age estimation of ~1000–1200 years. Alteration in the chemical structure of the elm and poplar samples due to the ageing process were confirmed by X-ray photoelectron spectroscopy (XPS). Both archaeological wood (AW) samples illustrated considerably lower cellulose crystallinity than the fresh samples as determined by X-ray diffraction. The sorption behavior of AW and fresh wood (FW) samples were evaluated by means of dynamic vapor sorption (DVS) analysis. Results exhibited a higher equilibrium moisture content (EMC) and sorption hysteresis values in archaeological elm and poplar as compared with the fresh samples. Higher hydrophilicity of the AW samples than the FW ones is attributed to their higher amorphous structure. The extensive degradation of AW samples were also confirmed by scanning electron microscopy (SEM) micrographs.

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  • 6.
    Ghavidel, Amir
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT).
    Jorbandian, Amin
    University of Tehran, Iran.
    Bak, Miklós
    University of Sopron, Hungary.
    Gelbrich, Jana
    Leibniz-IWT, Germany.
    Morrell, Jeffrey J.
    University of the Sunshine Coast, Australia.
    Sandu, Ion
    Academy of Romanian Scientists (AOSR), Romania;Romanian Inventors Forum, Romania.
    Hosseinpourpia, Reza
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT). Linnéuniversitetet, Kunskapsmiljöer Linné, Avancerade material. Linnéuniversitetet, Kunskapsmiljöer Linné, Grön hållbar utveckling. Michigan Technological University , USA.
    Degradation assessment of archaeological oak (Quercus spp.) buried under oxygen-limited condition2023Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 77, nr 3, s. 198-207Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The biological deterioration of archaeological wood under oxygen-limited conditions varies due to the limited activities of microorganisms. It is essential to expand the knowledge of the degradation types and the status of archaeological monuments for selecting the proper consolidates. The physical, chemical, and anatomical properties of approximately 600–650 year old archaeological oak collected from an archaeological site in Iasi-Romania were analysed to assess the quality and to identify the degradation types. The results were compared with similar tests on recently-cut oak. X-ray photoelectron spectroscopy (XPS) revealed the presence of more lignin-related peaks in the archaeological oak, which likely reflected the degradation of the wood carbohydrates as evidenced by the decreased oxygen-to-carbon ratio Cox/Cnon-ox. The differences in cellulose crystallinity were not significant suggesting that any cellulose degradation occurred in the amorphous regions. This was also reflected in the dynamic water vapor sorption analysis where the differences in sorption isotherms and hysteresis of archaeological and recently-cut oaks were marginal. Microscopic analysis of the oak cells illustrated bacterial degradation patterns, while the field emission scanning electron microscopy (FESEM) showed the presence of erosion bacteria in the archaeological oak collected from the site with low oxygen conditions.

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  • 7.
    Hosseinpourpia, Reza
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT). Linnéuniversitetet, Kunskapsmiljöer Linné, Avancerade material.
    Adamopoulos, Stergios
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT).
    Eceiza, Arantxa
    University of the Basque Country UPV/EHU, Spain.
    Thermal stability and water vapor sorption of wheat starch modified with isocyanate functional groups2019Ingår i: 7th International Conference on Biobased and Biodegradable Polymers (BIOPOL), 17-19th June 2019, Stockholm, Sweden, KTH , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wheat starch polymer was modified through the unequal reactivity of isocyanate groups in isophorone diisocyanate (IPDI) monomer. Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C NMR) confirmed the presence of both urethane and isocyanate functionalities in the modified polymer. Thermal stability and water vapor sorption properties of the modified polymer were evaluated by means of thermogravimetric analysis (TGA) and auto-dynamic vapor sorption (AVS) method, respectively. The results indicated that the modified starch polymer showed a better thermal stability (e.g. higher temperature at maximum weight loss) compared to the unmodified one. Water vapor sorption of starch polymer was considerably reduced after modification with IPDI monomer.

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  • 8.
    Huang, Tianxiao
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT).
    Hydrophobic Coating on Cellulosic Textile Material by Betulin and a Betulin Based Polymer2016Självständigt arbete på avancerad nivå (masterexamen), 80 poäng / 120 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Betulin is a naturally abundant compound in the outer bark of birch and can be easily

    obtained by solvent extraction. Herein, solutions of betulin were used to treat cellulosic

    textile fibers and improve their water repellency. Cotton fabrics impregnated in a 7.5 g

    L-1 solution of betulin in ethanol showed the highest water contact angle of about 153°

    while the impregnation in a 3.75 g L-1 solution resulted in a close effect. A terephthaloyl

    chloride-betulin copolymer was synthesized and dissolved in tetrahydrofuran to afford a

    solution with a concentration of 3.75 g L-1. The cotton fabric impregnated in this

    solution showed a water contact angle of 150°. Changes in morphology of the cellulose

    fibers before and after the treatment were observed by scanning electron microscopy,

    and the water repellency was measured by a standard spray test. The marketing strategy

    of the potential product, which will be developed based on this technique, was discussed.

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  • 9.
    Jin, Min
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Determination of fracture mechanics behavior of polyethylene sheets2017Självständigt arbete på avancerad nivå (magisterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Polyethylene is a widely-used material in package industries. The fracture behavior of this material has not been studied in the plastic region in many years. In this thesis work, the J-Integral which is one material property used to represent the plastic material strength is calculated through the numerical analysis. To build a correct numerical model, the material behavior is summarized from previous uniaxial tensile test. The result from the fracture experiment for variable initial crack length is used to validate the reliability of the numerical model. The numerical analysis is done by the software ABAQUS which has the function to get the value of J-Integral directly. The final result contains the comparison between experiments and numerical analysis and the value of J-Integral at the crack initiation. 

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  • 10.
    Karlsson, Emil
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Anja, Pettersson
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Modifierad konstruktion av plastkapsyl för förbättrad tätning2021Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    För att motverka att innehållet i en behållare läcker ut krävs det att förslutningen är tät. För att förhindra läckage används någon form av tätning. På kapsyler i plast integreras ofta tätande element direkt i kapsylen i form av läppar eller kanter som pressar mot flaskan.Studien berör den inbyggda tätningen på en ”push-on”-kapsyl i Polypropencopolymer. Kapsylen tillverkas av Emballator Växjöplast AB och kallas DLM (dropless medicine) då den i de flesta fall monteras på glas- eller plastflaska som innehåller medicin. Kapsylens underdel pressas på flaskan permanent och den tvådelade kapsylen fungerar genom att en separat överdel skruvas på underdelen.Studien innehåller produktutvecklingssteg för att ta fram en uppdaterad konstruktion som ska klara av de problem som flaskans profil medför. Studien är upplagd som en DRM-studie och försöker svara på vad som påverkar tätningsförmågan hos en kapsyl och hur de tätande elementen kan konstrueras för att neutralisera flaskans form. Problemen uppstår främst när kapsylen är monterad på glasflaskan och roteras, då flaskan i vissa fall har en något oval profil. Det är när flaskan roteras som tätningen inte anpassar sig tillräckligt fort för att bli tät igen. Genom arbetets gång har man insett att i stället för att forma tätningen så att den följer behållarens form fortare, och riskera plastisk deformation på grund av relaxation hos materialet, väljer man att placera ytterligare en tätning på toppen. Ytan på toppen av flaskan utnyttjas, eftersom det är en ledig yta på både kapsyl och flaska,för att tätningarna ska komplettera varandra. Det görs för att kunna ha kvar den nuvarande tätningen och endast addera en topptätning som är mindre känslig för ovalitet hos flaskan. Studiens resultat bör ses som underlag för framtagning av prototyper och testning, då det inte går att garantera konstruktionens duglighet utan fortsatt testning

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  • 11.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A constitutive framework for modelling thin incompressible viscoelastic materials under plane stress in the finite strain regime2011Ingår i: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 15, nr 4, s. 389-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material.

  • 12.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    A constitutive model for strain-crystallising rubber-like materials2010Ingår i: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 42, nr 9, s. 873-885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present paper, a constitutive model for strain-crystallising rubber is proposed. The constitutive behaviour is formulated in terms of a strain energy function, where the full network approach is adopted. The Arrhenius equation provides the basis for the crystallite nucleation law. The full network approach allows for the development of an anisotropic crystal structure. The model was applied to experimental results from uniaxial tensile tests. Strain-crystallisation causes a hysteresis in the stress–stretch relation, but according to the model predictions, the effect of crystallisation is not sufficient to explain the mechanical hysteresis observed in the tensile tests. Hence, additional viscoelasticity associated with amorphous polymer chains must be included. The model was fully able to predict both the stress vs. stretch relations and the crystallinity vs. stretch relations from the experiments.

  • 13.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    An 8-chain model for rubber-like materials accounting for non-affine chain deformations and topological constraints2011Ingår i: Journal of elasticity, ISSN 0374-3535, E-ISSN 1573-2681, Vol. 102, nr 2, s. 99-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several industrial applications involve rubber and rubber-like materials, and it is important to be able to predict the constitutive response of these materials. In the present paper, a new constitutive model for rubber-like solids is proposed. The model is based on the 8-chain concept introduced by Arruda and Boyce (J. Mech. Phys. Solids 41, 389–412, 1993) to which two new components are added. Real polymer networks do not deform affinely, and in the proposed model this is accounted for by the inclusion of an elastic spring, acting in series with the representative polymer chain. Furthermore, real polymer chains are not completely free to move, which is modelled by imposing a topological constraint on the transverse motions of the representative polymer chain. The model contains five model parameters and these need to be determined on the basis of experimental data. Three experimental studies from the literature were used to assess the proposed model. The model was able to reproduce experimental data performed under conditions of uniaxial tension, generalised plane deformation, and biaxial tension with an excellent accuracy. The strong predictive abilities together with the numerically efficient structure of the model make it suitable for implementation in a finite element context.

  • 14.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    An asymptotic analysis of dynamic crack growth in rubber2011Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, nr 17, s. 3111-3122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks are important for several reasons. For example, they facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. The present study focuses on the asymptotic fields in front of a crack that propagates dynamically in rubber. Static analyses of this type of problem have been made in previous studies. In order to be able to compare the present results with these earlier studies, the constitutive model from Knowles and Sternberg (J. Elast. 3:67–107, 1973) was adopted. It is assumed that viscoelastic stresses become negligible compared with the singular elastic stresses close to the crack tip. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. However, for a neoHookean type of model, inertia comes into play and causes a maximum theoretical crack speed that equals the shear wave speed.

  • 15. Kroon, Martin
    Analysis of dynamic crack propagation in rubber2012Ingår i: Presented at 10th World Congress on Computational Mechanics, 8-13 July, 2012, 2012Konferensbidrag (Refereegranskat)
  • 16.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Asymptotic mechanical fields at the tip of a mode I crack in rubber-like solids2014Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 10, s. 1923-1930Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth and failure. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. In the present work, we perform an asymptotic analysis of the mechanical fields in the vicinity of a propagating mode I crack in rubber. Plane deformation is assumed, and the material model is based on the Langevin function, which accounts for the finite extensibility of polymer chains. The Langevin function is approximated by a polynomial, and only the term of the highest order contributes to the asymptotic solution. The crack is predicted to adopt a wedge-like shape, i.e. the crack faces will be straight lines. The angle of the wedge and the order of the stress singularity depend on the hardening of the strain energy function. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. Hence, there is no upper theoretical limit to the crack speed.

  • 17.
    Kroon, Martin
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Dynamic Crack propagation in Rubber2016Ingår i: Presented at 24th International Congress of Theoretical and Applied Mechanics (ICTAM), Montreal, Canada, August 21-26, 2016, 2016Konferensbidrag (Refereegranskat)
  • 18.
    Kroon, Martin
    Malmö University.
    Dynamic Energy Release Rates in Rubber2016Ingår i: Presented at European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS), Crete, Greece, June 5-10, 2016, 2016Konferensbidrag (Refereegranskat)
  • 19.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Dynamic steady-state analysis of crack propagation in rubber-like solids using an extended finite element method2012Ingår i: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 49, nr 1, s. 73-86Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, ). The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.

  • 20. Kroon, Martin
    Dynamic steady-state crack propagation in rubber-like solids2011Konferensbidrag (Refereegranskat)
  • 21.
    Kroon, Martin
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Energy release rates in rubber during dynamic crack propagation2015Ingår i: Presented at ASME Applied Mechanics and Material Conference, July 25-29, 2015, 2015Konferensbidrag (Refereegranskat)
  • 22.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Energy release rates in rubber during dynamic crack propagation2014Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, nr 25-26, s. 4419-4426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The theoretical understanding of the fracture mechanics of rubber is not as well developed as for other engineering materials, such as metals. The present study is intended to further the understanding of the dissipative processes that take place in rubber in the vicinity of a propagating crack tip. This dissipation contributes significantly to the total fracture toughness of the rubber and is therefore of great interest from a fracture mechanics point of view. To study this, a computational framework for analysing high-speed crack growth in a biaxially stretched rubber under plane stress is therefore formulated. The main purpose is to investigate the energy release rates required for crack propagation under different modes of biaxial stretching. The results show, that inertia comes into play when the crack speed exceeds about 50 m/s. The total work of fracture by far exceeds the surface energy consumed at the very crack tip, and the difference must be attributed to dissipative damage processes in the vicinity of the crack tip. The size of this damage/dissipation zone is expected to be a few millimetres.

  • 23.
    Kroon, Martin
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Experimental measurement of energy release rate in polyethylene2017Ingår i: ICF 2017 - 14th International Conference on Fracture, Volume 2, International Conference on Fracture , 2017, Vol. 2, s. 618-619Konferensbidrag (Refereegranskat)
    Abstract [en]

    Semi-crystalline polymers are widely used in industrial applications, e.g. in beverage containers, plastic bags, etc. In many applications, the fracture mechanics properties are of great interest, e.g. in the opening procedure of beverage containers. The present work focuses on experimental measurement of the energy release rate in these polymers. A fairly simple multi-specimen experimental method is proposed that makes use of the stored elastic energy in the structure. By use of this method, the energy release rate is estimated to about 1.6 kJ/m2 for the polymer in question. 

  • 24. Kroon, Martin
    Numerical analysis of steady-state crack growth in rubber2012Ingår i: Presented at 10th World Congress on Computational Mechanics, 8-13 July, 2012, 2012Konferensbidrag (Refereegranskat)
  • 25. Kroon, Martin
    Numerical analysis of steady-state crack growth in rubber-like solids2011Ingår i: Presented at US National Congress on Computational Mechanics, 24-28 July, 2011, 2011Konferensbidrag (Refereegranskat)
  • 26.
    Kroon, Martin
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Rate-Dependent Crack Propagation in Polyethylene2019Ingår i: Proceedings of the First International Conference on Theoretical, Applied and Experimental Mechanics / [ed] Gdoutos, E E, Springer, 2019, s. 194-198Konferensbidrag (Refereegranskat)
    Abstract [en]

    Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. Crack growth was modelled using a rate-dependent cohesive zone. The problem was analyzed using Abaqus, and the crack growth experiments were simulated. The experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

  • 27. Kroon, Martin
    Some aspects of crack propagation in rubber2015Ingår i: Presented at 5th B. Broberg Symposium, August 24-25, 2015, 2015Konferensbidrag (Refereegranskat)
  • 28.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Steady-state Crack Growth in Rubber-like Solids2011Ingår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 169, nr 1, s. 49-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fracture toughness of rubber-like materials depends on several factors. First there is the surface energy required to create new crack surface at the crack tip. Second, a significant amount of energy is dissipated through viscoelastic processes in the bulk material around the crack tip. Third, if the crack propagates very rapidly, inertia effects will come into play and contribute to the fracture toughness. In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to study the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. In addition, the predicted distributions of stress and dissipation around the propagating crack tip are presented.

  • 29.
    Kroon, Martin
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Andreasson, E.
    Tetra Pak, Sweden;Blekinge Institute of Technology, Sweden.
    Persson Jutemar, E.
    Tetra Pak, Sweden.
    Petersson, V.
    Tetra Pak, Sweden.
    Persson, L.
    Tetra Pak, Sweden.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Olsson, P.A.T.
    Malmö University, Sweden.
    Anisotropic elastic-viscoplastic properties of at finite strains of of injection-moulded low-density polyethylene2018Ingår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 58, nr 1, s. 75-86Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.

  • 30.
    Kroon, Martin
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Andreasson, Eskil
    Tetra Pak.
    Modeling of damage and crack growth in semi-crystalline polymers2017Ingår i: Proceedings of NSCM 30: The 30th Nordic Seminar on Computational Mechanics, 25-27 October, 2017 / [ed] J. Høgsberg. N.L. Pedersen, DTU Mechanical Engineering , 2017, s. 108-108Konferensbidrag (Refereegranskat)
    Abstract [en]

    t. Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subroutine in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

  • 31.
    Kroon, Martin
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Andreasson, Eskil
    Tetra Pak.
    Olsson, Pär
    Malmö University.
    Assessment of fracture energy of polyethylene2017Ingår i: Svenska mekanikdagar 2017 Uppsala 12-13 juni, Uppsala universitet, 2017, s. 49-49Konferensbidrag (Refereegranskat)
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  • 32.
    Kroon, Martin
    et al.
    Malmö University.
    Faleskog, Jonas
    A J2-J3-dependent constitutive model for porous plasticity2016Ingår i: Presented at International Symposium on Plasticity, Big Island, Hawaii, January 3-9, 2016, 2016Konferensbidrag (Refereegranskat)
  • 33.
    Kroon, Martin
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Gortz, Jakob
    Blekinge Institute of Technology, Sweden.
    Islam, Shafiqul
    Blekinge Institute of Technology, Sweden.
    Andreasson, Eskil
    Tetra Pak, Sweden.
    Petersson, Viktor
    Tetra Pak, Sweden.
    Jutemar, Elin Persson
    Tetra Pak, Sweden.
    Experimental and theoretical study of stress relaxation in high-density polyethylene2024Ingår i: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stress relaxation of high-density polyethylene is addressed both experimentally and theoretically. Two types of stress relaxation testing are carried out: uniaxial tensile testing at constant test specimen length and compression testing of a 3D structure producing inhomogeneous deformation fields and relaxation. A constitutive model for isotropic, semi-crystalline polymers is also proposed. The model has the ability to model stress relaxation at different time scales. The developed model was implemented as a user subroutine in Abaqus (UMAT). The implicit integration scheme including an algorithmic tangent modulus is described in detail. The material model is calibrated by use of the uniaxial tensile tests, and the model is then validated by simulating the compression tests of the 3D structure. The model is able to describe the uniaxial tension tests well, and the comparison between the simulations and experimental testing of the 3D structure shows very good agreement.

  • 34.
    Kroon, Martin
    et al.
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för maskinteknik (MT).
    Olsson, P.
    Malmö University.
    Andreasson, E.
    Tetra Pak.
    Petersson, V.
    Estimation of the essential work of fracture of for an LDPE material2017Ingår i: The 8th International Conference on Fracture of Polymers, Composites and Adhesives, Les Diablerets, Schwitzerland, 10-14 September, 2017, 2017Konferensbidrag (Refereegranskat)
  • 35.
    Nicklisch, Felix
    et al.
    Technische Universität Dresden, Germany.
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Weller, Bernhard
    Technische Universität Dresden, Germany.
    Serrano, Erik
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för byggteknik (BY).
    Joint study on material properties of adhesives to be used in load-bearing timber-glass composite elements2014Ingår i: Glass | Facade | Energy / [ed] Jens Schneider, Bernhard Weller, Technische Uni Dresden , 2014, s. 271-280Konferensbidrag (Refereegranskat)
    Abstract [en]

    Beyond its transparency, glass offers a large potential to fulfill load-bearing functions. Timber-glass composite elements take advantage of the high stiffness and strength of glass. At the same time the post-breakage behavior of the composite element increases significantly compared to the brittle failure of a pure glass. The current study relates to timber-glass composites where the composite action is obtained via a linear bondline connecting the glass pane to a timber frame. The full potential of these composite elements arises from the use of adhesives of medium and high stiffness which exhibit rather small deformations compared to e.g. structural silicones. A central objective of the research is the assessment and the optimization of the bondline properties with respect to stiffness of the adhesive. The paper summarizes the results of an in-depth study on commercially available adhesives and evaluates their general suitability in timber-glass composites.

    The material properties of the adhesives were determined by thorough mechanical testing of the bulk material in the first place under varying conditions, typically encountered in façades. The potential use in glass-timber composites was then evaluated using small bonded specimens comprising birch plywood or massive pine wood in combination with soda-lime glass. Failure modes were categorized in order to ascertain the influence of the timber strength on the load-bearing capacity.

    In order to guarantee reliable results from various sources, parts of the tests were executed repeatedly at different laboratories. Results were compared and validated throughout the project. Hence the results of this study provide a reliable basis for material models used in e.g. numerical analysis and engineered design solutions. The study presented here is part of the WoodWisdomNet project “LBTGC - Load Bearing Timber Glass Composites”

  • 36.
    Nivrén, Linnéa
    Linnéuniversitetet, Fakulteten för konst och humaniora (FKH), Institutionen för design (DE).
    Fertile Wear: Underwear in relation to manufacturing toxicity, the ecosphere and our reproductive zones2021Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Every artifact in this consumerism world is connected to Earth’s four ecological layers. Everything around us, air, organism, water, and soil/rock also known by the names; atmosphere, biosphere, hydrosphere, and lithosphere. All together form the ecosphere, the place that contains all materials and resources that we use when creating artifacts. 

    »Every material that we use comes from the ecosphere and eventually goes back to it.« - Ann Thorpe

    The way humans use, extract, manufacture and dispose of materials has concerned me for many years, long before I started this design program. It has formed my way of making as a designer, and because of my love for textiles, I have been applying it in that field of practise. I want to design textiles that function and can be used frequently, with a purpose and in the end, decompose before I do.

    The aim of this conducted design project is to, in a playful way, break down the barrier between maker and user. Combined with unfolding the hidden truths about garments, how they are manufactured and where those textile components originate from. This would enable me to broaden my knowledge in the field and in return I will have the opportunity to share my insights with the public. Within this project I will also put the emphasis on the impact textiles have on our bodies, reproductive health and surrounding ecosystems.  Designing with the intention to highlight topics like this, the whole life cycle of garments, creates a stronger bond between user and maker. This is something I as a designer and maker want to build my foundation on.  In order to do this I needed to pin down where this conducted design project could take place and what sustainable possibilities of change it could embed for the future.

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  • 37.
    Osman, Syaiful
    et al.
    Universiti Teknologi MARA, Malaysia.
    Ahmad, Mansur
    Universiti Teknologi MARA, Malaysia.
    Zakaria, Mohd Nazarudin
    Universiti Teknologi MARA, Malaysia.
    Bakar, Balkis Fatomer A.
    Universiti Putra Malaysia Serdang, Malaysia.
    Abu, Falah
    Universiti Teknologi MARA, Malaysia.
    Kamarudin, Siti Hasnah
    Universiti Teknologi MARA, Malaysia.
    Bahari, Shahril Anuar
    Universiti Teknologi MARA, Malaysia.
    Hosseinpourpia, Reza
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för skog och träteknik (SOT). Linnéuniversitetet, Kunskapsmiljöer Linné, Avancerade material. Linnéuniversitetet, Kunskapsmiljöer Linné, Grön hållbar utveckling.
    Variation of chemical properties, crystalline structure and calorific values of native Malaysian bamboo species2022Ingår i: Wood and Fiber Science, ISSN 0735-6161, Vol. 54, nr 3, s. 173-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The chemical properties of four common Malaysian bamboo species locally known as Beting (Gigantochloa levis), Semantan (Gigantochloa scortechinii), Lemang (Schizostachyum brachyladum) and Akar (Bambusa vulgaris) were studied. Chemical analysis shows that the alkaline extractive content for Malaysian bamboo species studied was within 24.4% to 25.6%, ethanol-toluene extractive content for Malaysian bamboo species was within 4.0% to 7.2% and water extractive content was within 10.4% to 12.8%. The average value of holocellulose content for Malaysian bamboo was between 64.5% to 70.67%, Klason lignin within 25.3% to 28.4%, cellulose content was between 28.5% to 33.8% and α-cellulose content for all bamboo species was within the range of 40.7% to 47.9%. The crystallinity of bamboo samples was between 42.0 to 44.4%, indicating their semi-crystalline structure.  Heating value of bamboo ranged between 17.0 MJ/kg to 18.1 MJ/kg with G. scortechinii having the highest heating value.. The Inductive Couple Plasma Atomic Emission Spectroscopy (ICP-ES) analysis showed that Potassium (K) and Calcium (C) were the major elements in the ash of all bamboo samples. This study demonstrates the potential of native bamboo species as an alternative sustainable raw material to wood for a wide range of applications.

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