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  • 201.
    Doroudgarian, Newsha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Moisture uptake and resulting mechanical response of biobased composites:: II. Composites2015Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 36, nr 8, s. 1510-1519Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The durability of entirely bio-based composites with respect to the exposure to elevated humidity was evaluated. Different combinations of bio-based resins (Tribest, EpoBioX, Envirez) and cellulosic fibers (flax and regenerated cellulose fiber rovings and fabrics) were used to manufacture unidirectional and cross-ply composite laminates. Water absorption experiments were performed at various humidity levels (41%, 70%, and 98%) to measure apparent diffusion coefficient and moisture content at saturation. Effect of chemical treatment (alkali and silane) of fibers as protection against moisture was also studied. However, fiber treatment did not show any significant improvement and in some cases the performance of the composites with treated fibers was lower than those with untreated reinforcement. The comparison of results for neat resins and composites showed that moisture uptake in the studied composites is primarily due to cellulosic reinforcement. Tensile properties of composites as received (RH = 24%) and conditioned (RH = 41%, 70%, and 98%) were measured in order to estimate the influence of humidity on behavior of these materials. Results were compared with data for glass fiber reinforced composite, as a reference material. Previous results from study of unreinforced polymers showed that resins were resistant to moisture uptake. Knowing that moisture sorption is primarily dominated by natural fibers, the results showed that some of the composites with bio-based resins performed very well and have comparable properties with composites of synthetic epoxy, even at elevated humidity.

  • 202.
    Doroudgarian, Newsha
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pupure, Liva
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sensivity to moisture and its effect on mechanical behavior of bio-based resins reinforced with cellulosic fibers2013Inngår i: 21st anniversary of the bio-environmental polymer society, 2013Konferansepaper (Fagfellevurdert)
  • 203.
    Dyakov, Sergey
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO. Trinity College Dublin.
    Baldycheva, A.
    Perova, T. S.
    Li, G. V.
    Astrova, E. V.
    Gippius, N. A.
    Tikhodeev, S. G.
    Surface states in the optical spectra of two-dimensional photonic crystals with various surface terminations2012Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, nr 11, s. 115126-1151268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reflection and transmission spectra of two-dimensional photonic crystal slabs, fabricated by photoelectrochemical etching of deep macropores and trenches in Si, are investigated theoretically and experimentally. It is shown that the presence of an unstructured silicon interfacial layer between the air and the photonic crystal structure can give rise to surface (Tamm) states within the TE and TM photonic stop bands. In the presence of roughness of inner surfaces of air pores, the surface states show up as dips within the stop bands in the reflection spectrum. The calculated electromagnetic near-field distribution demonstrates the vortices between the upper pores at the frequency of the surface mode. The experimental reflection and transmission spectra are in a good agreement with theoretical calculations performed by the Fourier modal method in the scattering matrix form.

  • 204.
    Dyakov, Sergey
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO. Trinity College Dublin.
    Perova, T. S.
    Miao, C. Q.
    Xie, Y. -H
    Cherevkov, S. A.
    Baranov, A. V.
    Influence of the buffer layer properties on the intensity of Raman scattering of graphene2013Inngår i: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, nr 6, s. 803-809Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using a model of oscillating dipoles, we simulate the intensity of the G-band in the Raman signal from structures consisting of graphene, separated by an arbitrary buffer layer from a substrate. It is found that a structure with an optimized buffer layer refractive index and thickness exhibits a Raman signal which is nearly 50 times more intense than that from the same structure with a non-optimized buffer layer. The theoretical simulations are verified by Raman measurements on structures consisting of a layer of graphene on SiO2 and Al2O3 buffer layers. The optical contrast of the single graphene layer is calculated for an arbitrary buffer layer. It was found that both the Raman intensity and optical contrast can be maximized by varying the buffer layer thickness.

  • 205.
    Dyakov, Sergey
    et al.
    Department of Electronic and Electrical Engineering, Trinity College Dublin, Ireland.
    Zhigunov, D.M.
    Hartel, A.
    Zacharias, M.
    Perova, T.S.
    Timoshenko, V.Y.
    Enhancement of photoluminescence signal from ultrathin layers with silicon nanocrystals2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 6, s. 061908-1-061908-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the model of oscillating dipoles, we simulated the photoluminescence intensity of a triple-layered structure where the silicon nanocrystals layer was enclosed by buffer and capping silicon dioxide layers. It was found that a structure with an optimized buffer layer thickness exhibited photoluminescence which was approximately 20 times more intense than that from the structure without a buffer layer. Theoretical simulations were verified by photoluminescence measurements for the corresponding structures with silicon nanocrystals fabricated by plasma enhanced chemical vapour deposition.

  • 206.
    Edgren, Fredrik
    et al.
    Swerea SICOMP AB, Mölndal.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Determination of strength parameters for NCF composites2006Inngår i: Proceedings of the 3rd International Conference on Composites Testing and Model Identification: CompTest 2006, Faculty of Engineering, University of Porto, Portugal , 2006, s. 66-67Konferansepaper (Annet vitenskapelig)
  • 207.
    Edgren, Fredrik
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Asp, Leif
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Failure of NCF composites subjected to combined compression and shear loading2006Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 66, nr 15, s. 2865-2877Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier studies have shown that formation of kink bands is the mechanism that is likely to govern failure of compression loaded non-crimp fabric (NCF) composite laminates. Because of this, a failure criterion for prediction of failure caused by kinking under multiaxial (axial compression and shear) loading has been adapted to a NCF composite system. The criterion has been validated for compression tests of quasi-isotropic laminates tested in uniaxial compression. By performing compression tests of the laminate at different off-axis angles, it was possible to vary the ratio of compressive axial stress/shear stress in the specimens. The test results proved that the criterion works well for predictions of kinking governed failure for the present material system. Detailed fractographic studies confirmed that formation of kink bands was the mechanism responsible for specimen failure. Kink bands were also found to develop at loads significantly lower than load at specimen failure.

  • 208. Edgren, Fredrik
    et al.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sjögren, A.
    Compression after impact strength predictions for NCF composite structures2004Inngår i: From nano-scale interactions to engineering structures: ECCM 11, 11th European Conference on Composite Materials ; May 31 - June 3, 2004, Rhodes, Greece / [ed] Costas Galiotis, Rhodos: European Society for Composite Materials , 2004Konferansepaper (Fagfellevurdert)
  • 209.
    Edgren, Fredrik
    et al.
    SICOMP AB, Swedish Institute of Composites.
    Mattsson, David
    Asp, Leif
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Formation of damage and its effects on non-crimp fabric reinforced composites loaded in tension2004Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, nr 5, s. 675-692Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Non-crimp fabric (NCF) composites, manufactured by resin infusion techniques are one of the most promising next generation composite materials. They offer large potential for application in primary structures as they give excellent performance at low production costs. However, before NCF composites will be efficiently used in design, detailed understanding of governing micro mechanisms must be accumulated and described by predictive models. In the present study, NCF cross-ply laminates have been tested in tension. Intralaminar cracks caused in the 90° fibre bundle layers and their effect on laminate mechanical properties have been monitored. Occurrence of ‘novel' type of cracks propagating in the load direction (longitudinal cracks) is explained by a thorough FE analysis using an Representative Volume Element (RVE) approach, revealing stress concentrations caused by 0° fibre bundle waviness. Effects of damage on mechanical properties are modelled using modified micro mechanical models developed for analysis of conventional laminated composites. The analysis reveals mechanical degradation to be ruled by the crack opening displacement (COD). However, unlike traditional composites, transverse cracks do not generally extend through the entire thickness of the 90° layer, but are rather contained in single fibre bundles, limiting the COD

  • 210.
    Edgren, Fredrik
    et al.
    Swerea SICOMP AB, Mölndal.
    Soutis, C.
    University of Sheffield.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Damage tolerance analysis of NCF composite sandwich panels2008Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 68, nr 13, s. 2635-2645Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper concerns development and validation of impact damage representations in carbon fibre non-crimp fabric reinforced face sheets for damage tolerance analysis of sandwich panels loaded in compression. For this purpose, experimental data accompanied by fractographic observations have been employed to scrutinize numerical predictions by state-of-the-art notch strength models. As a result, equivalent hole representations of visible impact damage (VID) and, more surprisingly, of the subtle barely visible impact damage (BVID) are recommended for reliable damage tolerance prediction of the compression after impact (CAI) load case for the investigated panels. This recommendation relies on the identification of the mechanisms controlling failure resulting in reliable damage tolerance predictions employing a linear cohesive zone model.

  • 211.
    Egertz, David
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Novel Safety Requirements and Crash Test Standards for Light- Weight Urban Vehicles2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In recent years the interest for smaller, cheaper and more energy efficient vehicles hasincreased significantly. These vehicles are intended to be used in urban areas, where theactual need of large heavy cars is generally minor. The travelled distance is on average lessthan 56km during a day and most often there is only one person travelling in the vehicle. Manyof the established car manufacturers have recently started to take interest into this marketsegment, but the majority of these small vehicles are still manufactured by smaller companiesat a low cost and with little or no research done on vehicle traffic safety. This may be becausethere are still no legal requirements on crash testing of this type of vehicles.This report will examine road safety for Urban Light-weight Vehicle (ULV) to find criticalcrash scenarios from which future crash testing methods for urban vehicles can be derived.The term ULV is specific to this report and is the title for all engine powered three- and fourwheeledvehicles categorized by the European Commission. Other attributes than the wheelgeometry is engine power and the vehicles unladen mass. The maximum allowed weight for athree-wheeled ULV is 1 000kg and 400kg for a four-wheeled one.By studying current crash test methods used in Europe by Euro NCAP it has beenconcluded that these tests are a good way of assessing car safety. For light-weight urbanvehicles it has been concluded that some of these tests need to be changed and that some newtest scenarios should be added when assessing road safety. The main reasons for this is linkedto that vehicle’s with a weight difference of more than 150kg cannot be compared withcurrent test methods, and that crash tests are performed with crash objects with similar orequal mass in current safety assessment programs. This correlates poorly to the trafficsituation for light-weight urban vehicles since it would most likely collide with a far heaviervehicle than itself in an accident event.To verify the actual traffic situation in urban areas, accident statistics have beenexamined closely. The research has shown that there are large differences between rural andurban areas. For instance; 66% of all severe and fatal traffic accident occurs in rural areaseven though they are less populated. Even the distribution of accident categories has showndifferent in rural and urban areas. The United Nations Economic Commission for Europe(UNECE) has defined accident categories in their database which is widely used within theEuropean Union. By comparing each accident category’s occurrence, injury and fatality rate,the most critical urban accident categories were found in the following order.

    1. Collision due to crossing or turning

    2. Vehicle and pedestrian collision

    3. Rear-end collision

    4. Single-vehicle accident

    5. Other collisions

    6. Head-on collision

    Statistics also show that of all fatally injured crash victims in urban trafficapproximately; one third is travelling by car; one third by motorcycle, moped or pedal-cycle;and one third are pedestrians. This means that unprotected road travelers correspond to twothirds of all fatal urban traffic accidents, a fact that has to be taken into account in future crashtesting of urban vehicles. With all the information gathered a total of four new crash testscenarios for light-weight urban vehicles have been presented:

    • Vehicle-to-vehicle side impact at 40km/h with a 1 300kg striking vehicle to evaluate theoccupant protection level of the light-weight vehicle.

    • Vehicle-to-motorcycle side impact at 40km/h with motorcycle rider protection evaluation.

    • Pedestrian protection assessment at 40km/h over the whole vehicle front and roof area.

    • Rigid barrier impact at 40km/h corresponding to an urban single vehicle accident with aroad side object or a collision with a heavier or similar sized vehicle.

  • 212. Eita, M.
    et al.
    Arwin, H.
    Granberg, Hjalmar
    RISE., Innventia.
    Wågberg, L.
    Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films2011Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, nr 2, s. 566-572Artikkel i tidsskrift (Fagfellevurdert)
  • 213.
    Eitelberger, Johannes
    et al.
    Vienna University of Technology, Austria.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    de Borst, Karin
    Vienna University of Technology, Austria.
    Jäger, Andreas
    Vienna University of Technology, Austria.
    Multiscale prediction of viscoelastic properties of softwood under constant climatic conditions2012Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 55, s. 303-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper covers the development and validation of a multiscale homogenization model for linear viscoelastic properties of wood. Starting point is the intrinsic structural hierarchy of wood, which is accounted for by several homogenization steps. Using the correspondence principle, an existing homogenization model for the prediction of elastic properties of wood is adapted herein for upscaling of viscoelastic characteristics. Accordingly, self-consistent, Mori–Tanaka, and unit-cell-based techniques are employed, leading to pointwise defined tensorial creep and relaxation functions in the Laplace-Carson domain. Subsequently, these functions are back-transformed into the time domain by means of the Gaver-Stehfest algorithm. With this procedure the orthotropic macroscopic creep behavior of wood can be derived from the isotropic shear behavior of the lignin-hemicellulose phase. A comparison of model predictions for viscoelastic properties of softwood with corresponding experimentally derived values yields very promising results and confirms the suitability of the model.

  • 214.
    Eitzenberger, Johannes
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mechanics of microdamage development and stiffness degradation in fiber composites2007Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Damage in composites reduces its performance and durability and thus its usefulness. The common subject in all papers presented in the licentiate thesis is distributed microdamage, and the materials of interest are a Hemp/Lignin natural composite and glass/carbon fiber reinforced plastics composites. The focus is on how the damage affects the performance in terms of creep strain and stiffness. In Paper A a nonlinear viscoelastic viscoplastic model of a Hemp/Lignin composite is generalized by including stiffness reduction, and thus the degree of microdamage, in the composite (when loaded in the axial direction). Schapery's model is used to model the nonlinear viscoelasticity whereas the viscoplastic strain is described by a nonlinear function presented by Zapas and Crissman. In order to include stiffness reduction due to damage, Schapery's model is modified by incorporating a maximum strain-state dependent function reflecting the elastic modulus reduction with increasing strain measured in tensile tests. The model successfully describes the main features for the investigated material and shows good accuracy within the considered stress range. In Paper B the stiffness reduction of a unidirectional (UD) composite containing fiber breaks with partial interface debonding is analyzed. The analysis is performed by studying how the average crack opening displacement (COD) depends on fiber and matrix properties, fiber content and debond length. The COD is normalized with respect to the size of the fiber crack and to the far field stress in the fiber. In contrast to other performed analysis an analytical relationship is developed which links the entire stiffness matrix of the damaged UD composite with the COD and the crack sliding displacement (CSD). However, the CSD is excluded from the analysis since it is found by parametric inspection that it does not affect the longitudinal stiffness. Some trends regarding the COD dependence on the different properties can be extracted from available approximate analytical stress transfer models. To obtain more reliable results, in the current analysis these dependences are extracted from extensive FEM based parametric analysis performed on a model consisting of three concentric cylinders: a) broken fiber; b) matrix cylinder around it; c) large effective composite cylinder surrounding them. This model is used since it is more adequate than unit cell models considering only fiber and matrix. The cracks, which are only in the fibers, are distributed in such a way that they are non-interactive. It is shown that the parameters that affect the COD the most are the ratio of the longitudinal fiber modulus and matrix modulus, the fiber content and the debond length. These relationships are described by simple fitting functions which excellently fit the numerical results. These simple functions are merged into one relationship describing the COD's dependence on the relevant parameters. Simulations performed for carbon and glass fiber polymer composites show that the relative longitudinal stiffness reduction in the carbon fiber composite is slightly larger than in the glass fiber composite. This trend holds for all considered debond lengths and is related to higher longitudinal fiber and matrix modulus ratio in the carbon fiber composite leading to larger crack openings and larger stress perturbation zones. It is shown that the stiffness reduction depends on the debond length. In Paper C the analysis performed in Paper B is continued by studying how the COD is affected when the cracks are interactive. It is shown that the effect on the COD in the glass fiber composite is negligible. However, the effect on the COD in the carbon fiber composite is significant. This difference is related to higher longitudinal fiber and matrix modulus ratio for the carbon fiber composite. In Paper D the same model is used to analyse the strain energy release rate related to the debond crack growth along the fiber. The energy release rate is calculated using the virtual crack closure technique applied to displacement and stress field in the vicinity of the debond crack tip calculated using refined FE model. It is shown that the energy release rate is larger for very short debonds. It reduces to a constant value indicating a stable debond crack growth after its initiation. It is shown that the strain energy release rate in the plateau region also can be calculated using a simple analytical model based on the self-similar crack growth assumption. When the stress state perturbations related to debonds at both fiber ends start to interact, the energy release rate decreases. In a future work the obtained relationships for the energy release rate will be incorporated in a microdamage evolution model describing the statistics of fiber breaks and debond growth in fatigue loading conditions.

  • 215.
    Eitzenberger, Johannes
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Sprickstorlekens (COD) beroende av blandningsförhållande och elastiska egenskaper hos fiber och matris i kontinuerliga och enhetsriktade (UD) kolfiberkompositer2007Inngår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 29-Konferansepaper (Annet vitenskapelig)
  • 216. Eitzenberger, Johannes
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Debond crack growth in fatigue along fiber in UD composite with broken fibers2008Inngår i: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Assuming that Paris law is applicable for individual debond crack propagation along the fiber/matrix interface, the related strain energy release rate in a unidirectional composite is analysed using FEM and also using simple analytical considerations based on self-similar debond crack propagation. Model with axial symmetry consisting of three concentric cylinders is used: partially debonded broken fiber in the middle is surrounded by matrix cylinder which is embedded in a large block of effective composite with properties calculated using rule of mixtures and Halpin-Tsai expressions. It is shown for pure mechanical loading that the fiber elastic properties have a huge effect on the released energy, whereas fiber content in the composite in the considered realistic range has effect only for short debonds. The interaction between debonds approaching from both fiber fragment ends is investigated and related to material properties and geometrical parameters. It is shown that the self-similar debond propagation model gives slightly overestimated values of the strain energy release rate which may be related to interaction effects not included in the analytical model.

  • 217.
    Eivazihollagh, Alireza
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Bäckström, Joakim
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Dahlström, Christina
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Carlsson, Fredrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Ibrahem, Ismail
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Lindman, Björn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Edlund, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    One-pot synthesis of cellulose-templated copper nanoparticles with antibacterial properties2017Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 187, s. 170-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a facile in situ synthesis of spherical copper nanoparticles (NPs) templated by a gelled cellulose II matrix under alkaline aqueous reaction conditions. In under 20 min, the hybrid material could be obtained in a one-pot reaction. Field-emission scanning electron microscopy (FE-SEM) revealed that the polycrystalline NPs of 200–500 nm were well distributed in the regenerated cellulose matrix. The average Cu crystallite size was of the order of 20 nm, as estimated from both X-ray diffraction (XRD) and FE-SEM. XRD data also indicated that the composite contained up to approximately 20% Cu2O. In suspensions containing the hybrid material, growth of Escerichia coli and Staphylococcus aureus strains was inhibited by 80% and 95%, respectively, after 72 h. The synthesis procedure offers a general approach to designing various low-cost hybrid materials of almost any shape, and the concept could be extended to utilization areas such as catalysis, functional textiles, and food packaging as well as to electronic applications.

  • 218.
    Ekstedt, Sofia
    et al.
    Swerea SICOMP AB.
    Wysocki, Maciej
    Swerea SICOMP AB.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structural batteries made from fibre reinforced composites2009Inngår i: ICCM 17, Edinburgh: 17th International Conference on Composite Materials ; 27 Jul 2009 - 31 Jul 2009, Edinburgh International Convention Centre, Edinburgh, UK, London: IOM Communications , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Structural, fibre reinforced, battery prototypes with two types of electrolyte matrix material, a gel and a solid polymer, have been manufactured. This was to confirm the concept of using carbon fibres as current collector in the anode as well as providing a mechanical load-carrying functionality. As a result, functioning batteries with gel electrolyte have been produced and their properties have been characterised.

  • 219.
    Ekstedt, Sofia
    et al.
    Swerea SICOMP AB.
    Wysocki, Maciej
    Swerea SICOMP AB.
    Asp, Leif
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Structural batteries made from fibre reinforced composites2010Inngår i: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 39, nr 3-5, s. 148-150Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural, fibre reinforced, battery prototypes with two types of electrolyte matrix material (a gel and a solid polymer) have been manufactured. This was to confirm the concept of using carbon fibres as current collector in the anode as well as providing a mechanical load-carrying functionality. As a result, functioning batteries with gel electrolyte have been produced and their properties have been characterised.

  • 220.
    Elnekhaily, Sarah A.
    et al.
    Department of Materials Science and Engineering, Texas A&M University, College Station TX; Department of Metallurgical and Materials Eng., Faculty of Petroleum and Mining Eng., Suez University, Suez, Egypt.
    Talreja, Ramesh
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, Texas A&M University, College Station, TX; Department of Aerospace Engineering, Texas A&M University, College Station, TX .
    Damage initiation in unidirectional fiber composites with different degrees of nonuniform fiber distribution2018Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 155, s. 22-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports a study of the initiation of the first failure event in unidirectional composites subjected to transverse tension. Two energy based point failure criteria – critical dilatational energy density and critical distortional energy density – are considered. The manufacturing induced disorder in the fiber distribution in the composite cross section is described in terms of the degree of nonuniformity, which is quantified and for which an algorithm is developed. The nonuniformity is captured in a representative volume element (RVE) whose minimum size is determined based on statistics of nearest fiber distance distribution. Several realizations of the RVE for three fiber volume fractions and three degrees of nonuniformity are analyzed using a finite element model. A parametric study of the effect of matrix/fiber stiffness ratio on the damage initiation is also conducted. Significant effects of the fiber distribution nonuniformity on the strain to onset of damage are found.

  • 221.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Effect of light power density variation on dental light-cure resin composites2001Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Dental resin based composites are tooth-colored filling materials composed of synthetic resins and particulate ceramic reinforcing filler particles. The resin system also contains molecules that promote and/or modify the polymerisation reaction of the dimethacrylate resin monomers. The filler is bonded to the cured polymer with a film of silane coupling agent covering the filler particles. That silane film is also bonded to the reinforcing filler particles. Dental composites have been used as restorative materials for anterior applications since the 60s. Their tooth matching ability, ability to bond to tooth tissues and their lack of mercury have also promoted them as an alternative to dental amalgam for use in posterior teeth. Favourable results from long-term clinical trails demonstrate that when placed correctly, composites can produce esthetical posterior restorations with acceptable longevity ( el-Mowafy et al., 1994: Taylor et al., 1994 ), although not yet comparable to amalgams (Mjor). Significant problems still remain to be solved and limit their usefulness in the routine practice of dentistry. One of the most significant problems today relates to large material contraction during intra-oral polymerisation of composites. The hardening of composites is the result of polymerisation reactions involving dimethacrylate monomers. A rigid and heavily cross-linked polymer network is produced which surrounds the inert filler particles. The extent of this reaction, the degree of conversion, dictates many of the physical and mechanical properties of the composites. The degree of cure is influenced by many factors, including the light energy used to activate the reaction (Rueggeberg and Jordan, 1993). A reduction in volume, here termed shrinkage, occurs when the monomer polymerises. That shrinkage, which is more than 10-20 times higher in microns than what occurs when an amalgam sets, is caused by a change from van der Waal bonding to covalent bond formation. During that reaction, the monomer molecules rearrange and move closer together (Oleinik, 1986). The magnitude of the shrinkage is dictated by the extent of the reaction, as well as by the nature of the monomers. Research program In the currently ongoing study we are studying the effect of light intensity on polymerisation-induced strain, degree of conversion, volumetric changes and modulus of elasticity of two commercial dental composites. The objective is to test the hypothesis that low light intensity and increased curing time can be used to cure composites with better performance than high intensity cured composites. The benefits with the low intensity long time cure could be improved marginal integrity without loss of mechanical and physical properties. MethodsPolymerisation strain: Small ring shape samples were prepared and cured with three different light intensities (800, 450 and 200 mW/cm2). The polymerisation strain was measured by strain gages. The temperature increase was also measured. The sources of increased temperature are heat generated from the lamp as well as exothermal heat from curing. Volumetric shrinkage: The overall volumetric shrinkage was measured using water and mercury displacement methods. Degree of conversion: The effect of light intensity irradiation time on degree of conversion was measured by spectroscopy (FT- Raman). Modulus of Elasticity: One important factor influencing residual stresses is the stiffness of the dental composite. A miniature tensile machine for small sample size was used to measure the Young's modulus for two materials cured with different light intensities. ResultsA decrease in light intensity decreased the residual strain for the different material systems being evaluated. As long as the lower light intensity was compensated with an increased curing time, degree of conversion, Young's modulus and volumetric shrinkage were compared to high intensity cure for shorter time. The temperature increase, though, was lower for the low intensity cure than for the high intensity cure, even if longer time was used for the low intensity cure. DiscussionThe above results support the proposed hypothesis. A lower light intensity delays gelation, allowing the material to flow more initially. Such flow decreases the induced strain. Another important factor is the lower increase in temperature, which also decreases the thermal shrinkage that occurs during cooling back to room temperature. Differences between the two materials can also be related to differences in molecular structures between the two composites. An important conclusion is that for these materials, the polymerisation reaction is controlled by the total light energy supplied to the dental composite.

  • 222.
    Emami, Nazanin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Variables affecting stress development and resin conversion in light-cured dental composites2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The general aim of this dissertation was to identify and investigate factors that can be used to minimize stress development in light cured dental resins without compromising the conversion level of the polymer. Modulus of elasticity, polymerization contraction strain, degree of conversion and shrinkage of light-cure dental composites were determined after curing with three different light power densities where total irradiated energy (J/cm2) kept constant. FT-Raman spectroscopy was employed to determine the degree of conversion. The cure kinetic of light cured resins was studied by use of photocalorimetry (photo-DSC). Dynamic mechanical thermal (DMTA) analysis was used to investigate how different light curing methods affected glass transition and tangent delta of light curable dental resins when the temperature changed from 0 to 200°C. Optical properties of dental composites were studied. Three different filler types, two different surface treatments and eight different filler fractions per filler type and surface treatment were investigated. Light transmission was measured for the different composite compositions at sample thicknesses of 1 to 5 mm by use of a universal power meter. As long as the total light energy remained the same, the modulus of elasticity remained constant for each composite, even though the power density differed. Composite thickness, irradiance time, composition of the light cure composite and irradiation value had significant impact on degree of conversion. The irradiance value did not significantly affect on the transition temperature value. Initiator, co-initiators and light irradiance value had all significant impact on cure behavior. Different filler types and filler surface treatments had significant effects on light absorption. In general, light absorption increased linearly with filler fraction and sample thickness of the cured composites. Conclusion: Low rather than high light irradiance values decrease stress levels in composites, and comparable conversion levels are reached as long as the total light energy value remains the same for low versus high irradiance. By increasing the composite thickness above 2 mm but not exceeding 6 mm, energy levels exceeding 30 J are needed to achieve acceptable levels of degree of conversion. Different irradiance values do not affect the final Tg of tested composites as long as the total light energy remains the same. By using appropriate photo initiator/co-initiator combination and soft-start curing it is possible to achieve slow curing and high DC within a 40 s. As expected, different filler particle properties have significant effects on light absorption during curing making it important to consider these differences when one tries to develop a general light curing strategy for light curable dental resins.

  • 223.
    Emami, Nazanin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Söderholm, Karl-Johan M.
    Department of Dental Biomaterials, University of Florida.
    Dynamic mechanical thermal analysis of two light-cured dental composites2005Inngår i: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 21, nr 10, s. 977-983Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ObjectivesClinical observations suggest that some composite resins are more often linked to post-operative sensitivity than others. These differences may relate to differences in modulus of elasticity and polymerization rates among materials. The aim of this study was to identify viscoelastic behavior of two light curable composites and determine whether significant differences in viscoelastic behavior exist between the two materials when light cured at each of three different irradiance values.MethodsTwo composites (Z100 and Z250 by 3M ESPE) were evaluated. Six specimens per composite and irradiance value (250, 500 and 850 mW/cm2) were made. The curing times were chosen to produce a fixed energy value of 30 J/cm2 independent of irradiation value. Dynamic mechanical thermal analysis (DMTA) was performed in single cantilever clamped mode.ResultsThere were significant differences in transition temperatures between the two materials and the three frequencies at their glass transition temperatures, while significant differences did not exist at the lower transitions. The glass transition of Z250 was lower and narrower than that of Z100. Z250 exhibited lower storage modulus values. The irradiance values did not affect any of the transition temperatures significantly.SignificanceThe lower and more distinct Tg of Z250 suggests that Z250 cures more efficiently than Z100. The lower storage modulus of Z250 suggests that Z250 develops less stress in the tooth than Z100 during curing if shrinkage is the same for the two materials. The findings suggest that the material chosen, rather than irradiance, determines the stress level developed during light curing.

  • 224.
    Emami, Nazanin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Söderholm, Karl-Johan M.
    Department of Dental Biomaterials, University of Florida.
    Influence of light-curing procedures and photo-initiator/co-initiator composition on the degree of conversion of light-curing resins2005Inngår i: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 16, nr 1, s. 47-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: The hypothesis that the degree and rate of conversion can be modified favourably by using different light-curing procedures and different photo initiator/co-initiator combinations was tested.Method: A photo-initiator (0.02 mM/g resin); either camphorquinone (CQ) or 1-phenyl-1,2-propanedione (PPD), was mixed with bisGMA:TEGDMA (50:50 by weight). In addition, a co-initiator (0.04 mM/g resin); either N,N-dimethyl-p-aminobenzoic acid ethylester (DABE), N,N-cyanoethylmethylaniline (CEMA), or 2-dimethylaminoethyl methacrylate (DMAEMA), was added. These six combinations were subjected to three curing conditions (standard curing, soft-start curing or LED curing). The conversion levels (DC) were determined with differential scanning calorimetry (DSC). The DSC results were analysed using a general linear model (GLM) and Duncans multiple range test and regular t-test.Results: The fastest conversion initially was obtained by standard curing, followed by LED curing and soft-start curing. After 40 s of curing, conventional curing and soft-start curing produced a higher DC than LED curing. However, strong interactions occurred between the different variables (curing method, initiator and co-initiator). Initially, CQ was more efficient than PPD, but after 40 s, this difference was insignificant.Conclusion: By using soft-start curing and an appropriate photo initiator/co-initiator combination it is possible to achieve slow curing and a high DC at within a curing time of 40 s.

  • 225.
    Emami, Nazanin
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Söderholm, Karl-Johan M.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Effect of light power density variations on bulk curing properties of dental composites2003Inngår i: Journal of Dentistry, ISSN 0300-5712, E-ISSN 1879-176X, Vol. 31, nr 3, s. 189-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective. The hypothesis that low light intensity and long but sufficient curing time can produce composites with volumetric shrinkage, degree of conversion (DC%) and Young's modulus (E-modulus) comparable to those of high light intensity cured composite was tested, when the contraction strain and heat generation were lower with low light intensity curing. Methods. Dental composites (Z100 and Z250, 3M ESPE) were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm2 for 140, 60 and 35 s from a distance of 7 mm. Strain-gages were used for contraction strain measurements. DC% was measured at the top and the bottom of 4 mm thick samples using FT-Raman spectroscopy. Volumetric polymerization shrinkage was determined using a water displacement method. E-modulus was determined in tension on composite specimens. Results. The results were analyzed using ANOVA and Duncan's multiple range tests and regular t-test. Polymerization stress level decreased significantly (p<0.05) when cured with 200 mW/cm2 rather than with 800 mW/cm2. Temperature rises were significantly different (p<0.05) for different composites and light intensity values. Reduction in light intensity did not decrease the DC% values significantly at the top surfaces. The most dramatic differences existed between top and bottom surfaces (p<0.05) rather than among curing groups. Measured E-modulus and volumetric shrinkage values were not significantly different (p>0.05) between different light intensity groups. Conclusion. DC%, E-modulus and the volumetric shrinkage values in cured composites were not affected by low light intensity, however, the contraction strain and polymerization's exotherm were decreased. Thus our results support the proposed hypothesis.

  • 226.
    Engkvist, Gustav
    et al.
    Högskolan i Halmstad.
    Hansson, Sebastian
    Högskolan i Halmstad.
    FE-modellering av hjullast på sandwichpanel2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    This bachelor thesis in mechanical engineering was performed during the spring2015 in collaboration with Composite Consulting Group in Laholm. TheComposites Consulting Group works mainly with design and details of differentcomposite projects, their main area is FE-calculations, 3D-modelling andmechanical tests with composite materials.The aim of this bachelor thesis was to simplify the calculation process of solidmechanics for sandwich panels by simulation with computer software. The goalwas to decrease the time for the design and calculation process of the constructionand the cost of the practical tests. Our task was to build a static three dimensionalmodel with the computer software Abaqus, where the result should correspondwith the practical pressure tests in laboratory.The project started with collection of material data from Composites ConsultingGroup and by learning the software Abaqus, simultaneously a specification wasdeveloped in corporation with the company. Later on, a static wheel pressuremodel in the software Abaqus was produced which simulated the behavior of thesandwich panel during static wheel-pressure by a pallet truck. The results from thewheel-pressure model were verified with the practical tests.The project led to a static three dimensional wheel- contact model with thesoftware Abaqus to calculate complex wheel-contact problems on sandwichpanels. The wheel-contact model corresponded to the practical test results. Thecontact model with Abaqus enabled faster and more efficient design anddevelopment process of new sandwich panels. It also provided better analysis ofthe sandwich panels’ behavior during wheel- contact loading.

  • 227.
    Englund, F.
    et al.
    Technical Research Institute of Sweden.
    Bryne, Lars Elof
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Ernstsson, M.
    Institute for Surface Chemistry, Stockholm, Sweden.
    Lausmaa, J.
    SP Technical Research Institute of Sweden.
    Wålinder, Magnus E. P.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Spectroscopic studies of surface chemical composition and wettability of modified wood2009Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 4, nr 1-2, s. 80-85Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent advances in spectroscopic methods used in the surface science field may provide new valuable information about the surface chemical composition of engineering materials. Such methods, combined with wettability analyses, have been applied in the development of well-designed adhesives and coating systems for newly developed and commercially available modified wood materials. The main objective of this paper is to demonstrate and present some aspects on the application of two different state-of-the-art spectroscopic methods for surface chemical composition studies of a complex material such as modified wood. The methods are X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the former generating more quantitative data and the latter more qualitative data. The spectroscopic data are also combined with wettability data obtained from contact angle measurements using the Wilhelmy method. Modified wood samples were prepared from pilot plant or commercially produced acetylated, furfurylated and thermally modified wood. Effects of wood surface ageing, i.e. the time after machining, on the surface chemical composition and wettability were also studied. Results clearly indicate a hydrophobization process due to ageing of the unmodified and certain modified wood, probably mainly related to a migration and reformation of extractives in the surface. The surface composition and wettability of acetylated wood was not appreciably affected by the ageing process. Such findings could be quantified by the XPS measurements, which is further discussed and related to the different wood modification routes. ToF- SIMS is a powerful tool and complementary to XPS for identification of, for example, specific hydrophobic substances in the wood surfaces. In addition, this method provides ion images, mapping the lateral distribution of selected secondary ions signals within an analysed wood surface area.

  • 228.
    Englund, F.
    et al.
    Technical Research Institute of Sweden.
    Bryne, Lars-Elof
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Ernstsson, Marie
    Institute for Surface Chemistry, Stockholm, Sweden.
    Lausmaa, J
    SP Technical Research Institute of Sweden.
    Wålinder, M. E. P.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggnadsmaterial.
    Some Aspects on the Determination of Surface Chemical Composition and Wettability of Modified Wood2009Inngår i: Proceedings of the Fourth European Conference on Wood Modification / [ed] F. Englund, C.A.S. Hill, H. Militz and B.K. Segerholm, Stockholm: SP Technical Research Institute of Sweden , 2009, s. 553-560Konferansepaper (Fagfellevurdert)
  • 229.
    Engstrom, Jonas
    et al.
    Swerea SICOMP AB.
    Joffe, Roberts
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fernberg, Patrik
    Swerea SICOMP AB.
    Characterization of carbon nanotube doped carbon fiber prepreg laminate2012Inngår i: Proceedings of the 15th European Conference on Composite Materials / [ed] Marino Quaresimin; Laszlo Kollar; Leif Asp, Venice, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The current paper reports results from a preliminary study on PREGCYL™ NC R2HM-01 which is a carbon nanotube doped prepreg produced by Nanocyl. The work consisted of sample manufacturing in autoclave, microcopy analysis with XHR-SEM and mechanical testing. The mechanical testing consisted of tensile tests of unidirectional (in longitudinal direction) and cross-ply laminates. Test of unidirectional laminates showed that stiffness of the PREGCYL material is slightly higher than that of MTM55 composites (111GPa vs 102GPa). The results from tests of cross-ply laminates indicated that damage (transverse cracks) initiation is delayed in PREGCYL composites compare to the MTM55 material. Damage accumulation also seems to be slower in nano-doped composites.

  • 230.
    Eric, Jacques
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kjell, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Impact of the mechanical loading on the electrochemical capacity of carbon fibres for use in energy storage composite materials2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Reducing system mass for improvements in system performance has become a priority for future applications such as mobile phones or electric vehicles which require load bearing components and electrical energy storage devices. Structure and energy storage are usually subsystems with the highest mass contributions but energy storage components are structurally parasitic. A novel solution is a multifunctional lightweight design combining these two functions in a single material entity able to simultaneously bear mechanical loads as a carbon fiber composite component and store electrochemical energy as a lithium-ion battery.

  • 231.
    Ericson, Mats L.
    Luleå tekniska universitet.
    Engineering properties of glass mat reinforced thermoplastics (GMT): a review1995Rapport (Annet vitenskapelig)
  • 232.
    Ericson, Mats L.
    et al.
    Luleå tekniska universitet.
    Berglund, Lars
    Luleå tekniska universitet.
    Deformation and fracture of glass-mat-reinforced polypropylene1992Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 43, nr 3, s. 269-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical properties of glass-mat-reinforced thermoplastics, GMT, can be varied within wide limits through the choice of glass mat, fibre content, and thermoplastic matrix. A great variety of fibre configurations and fibre contents is commercially available. In order to understand how the fibre structure of GMT materials controls the mechanical properties, two structurally different GMT materials were studied. Several grades with different fibre contents were used for each material. One material had short fibres (12 mm long), discretely dispersed with in-plane random orientation. The other material had in-plane continuous looped bundles of fibres. The deformation and fracture of these materials have been studied as a function of fibre content. The present work shows that the material with discretely dispersed fibres has higher values of tensile creep modulus, tensile strength, elongation at fracture, and work of fracture (area under the stress/strain curve). The results are discussed and related to the structural differences between the two materials.

  • 233.
    Ericson, Mats L.
    et al.
    Luleå tekniska universitet.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Processing and mechanical properties of orientated preformed glass-mat-reinforced thermoplastics1993Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 49, nr 2, s. 121-130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stiffness and strength of moulded, glass-mat-reinforced thermoplastics (GMT) components would be increased by the presence of highly orientated fibres at critical locations. A previously described method to produce preformed GMT materials was therefore further developed to make orientation of the fibres in the preform possible. Two ‘orientation plates' were used to orientate the fibres during spray-up of a glass-fibre/polyethylene preform. The preform was then heated by hot gas and compression moulded. The ratio of the highest and lowest stiffnesses of a given plate was in the range of 27 to 38. Micromechanics equations were used with classical lamination theory to design a model laminate with stiffness properties in close agreement with experimental data. Reasons for the relatively wide fibre orientation distribution and low fibre length efficiency factor obtained for the model laminate are discussed and improvements suggested.

  • 234.
    Ericson, Mats L.
    et al.
    Luleå tekniska universitet.
    Berglund, Lars A.
    Luleå tekniska universitet.
    The effect of microstructure on the elastic modulus and strength of performed and commercial GMTs2003Inngår i: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 14, nr 1, s. 35-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique was used to fabricate performed glass fiber/polypropylene GMTs. The method utilizes thermoplastic powder and fiber roving in a spray-up procedure in which a porous perform in fabricated, heated and molded. The objective was to compare the properties of various preformed GMT composition with two commercial GMTs and to relate the mechanical properties to the microstructure of the materials. Preformed GMTs were fabricated with various fiber lengths and with or without a fiber/matrix adhesion promotor. Processing observation, microstructure, tensile creep modulus, and tensile strength of these preformed GMTs are reported. Fiber length and the addition of a fiber/matrix adhesion promotor had generally little effect on the modulus and strength of the preformed GMT. Comparisons with two structurally different commercial GMTs also showed negligible effects on modulus and strength. The major reason for this is suggested to be the inhomogeneities of the materials. The mechanical properties are controlled by local inhomogeneities rather than by the general microstructure of the material. These inhomogeneities arise from the fiber arrangement in the semi-finished sheet or perform. Since the microstructure of preformed GMT can be controlled, this material is well suited for future studies on the effect of better fiber dispersion.

  • 235.
    Ericson, Mats L.
    et al.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Design and potential of instrumented ultramicrotomy1997Inngår i: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 38, nr 17, s. 4485-4489Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultramicrotomes are generally used for preparation of very thin sections for transmission electron microscopy. Recently it has been shown that when the sample holder of the ultramicrotome is instrumented with a force transducer, it is possible to measure the very small sectioning force during sectioning, and calculate the energy dissipated. In the present work, the instrumentation is further improved. The new sample holder, which uses two piezo-electric force transducers can measure two force components simultaneously. It is not only robust and stiff, but it also shows high sensitivity and reproducibility. It is possible to detect sectioning forces lower than 0.1 mN. The method is demonstrated on two amorphous polymers, poly(methyl methacrylate) and epoxy. Fracture energies in the same order of magnitude as theoretical predictions from chemical bond fracture only are recorded. It is therefore suggested that the method of instrumented ultramicrotomy is a useful tool when information on covalent bond density is needed. Potential future applications are identified including research on nano-scale fracture, characterization of molecular anisotropy and developments of the ultramicrotome

  • 236.
    Ericson, M.L.
    et al.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Method of measuring energy dissipation during crack propagation in polymers with an instrumented ultramicrotome1996Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 13, nr 3, s. 655-662Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to characterize very local energy dissipation during crack propagation in polymers, an ultramicrotome was instrumented to measure the energy dissipated during sectioning. The work to section per unit area, W s, was measured for five different amorphous polymers [polymethyl methacrylate (PMMA), polystyerene (PS), polycarbonate (PC) and two epoxy resins] in the glassy state. When the section thickness was varied between 60 and 250 nm, W s varied between 15 and 100 Jm-2, depending on the material and section thickness. The method and the results are compared with other methods used for determining the energy dissipation at a local level as well as at a macroscopic level in polymers. The differences between different polymers were found to be contradictory to macroscopic fracture toughness, G lc, measurements. The material that showed the highest W s had the lowest G lc values reported. Possible mechanisms for energy dissipation during sectioning are also discussed.

  • 237.
    Eriksson, Carl-Johan
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap.
    Erlingsson, Jonas
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap.
    FRP i brokonstruktion: -varför används FRP inte i Sverige2015Independent thesis Basic level (university diploma), 10 poäng / 15 hpOppgave
    Abstract [en]

    FRP stands for Fiber Reinforced Polymer. FRP materials have yet to be introduced inbridge construction in Sweden. Composite materials can through combined componentsand manufacturing processes be tailored to fit advanced bridge designs. FRP materials arestrong, durable and of low weight. FRP materials give the superstructure reduced weightand are therefore a suitable alternative for industrial prefabrication. This report shows thatFRP materials are possible to use in bridge construction. With the introduction of a specificEurocode we are confident that FRP materials will become a competitive alternative inbridge construction in Sweden in the future.

  • 238.
    Eriksson, Daniel
    et al.
    Swedish University of Agricultural Sciences, Vindeln Experimental Forest, Vindeln, Sweden.
    Lindberg, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bergsten, Urban
    Swedish University of Agricultural Sciences, Department of Silviculture, Umeå, Sweden.
    Influence of silvicultural regime on wood structure characteristics and mechanical properties of clear wood in Pinus sylvestris2006Inngår i: Silva Fennica, ISSN 0037-5330, E-ISSN 2242-4075, Vol. 40, nr 4, s. 743-762Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The objective of the study presented here was to evaluate the influence of two contrasting silvicultural regimes on the structural characteristics and mechanical properties of different wood tissue types at different heights in Scots pine (Pinus sylvestris L.) trees, and reasons for these differences. Wood samples were taken from two stands (a dense 85-year-old stand established by direct seeding and a 56-year-old widely spaced stand established by planting, designated SDR and PWR, respectively in the boreal zone of Sweden). The wood properties associated with the examined silvicultural regimes differed, in terms of both structural characteristics (with up to fivefold differences between SDR and PWR) and mechanical properties (with up to almost threefold differences between SDR and PWR). Differences between the regimes were highest for stiffness, followed by strength and hardness properties and lowest for relative stiffness after 1000 h of loading (creep) (with higher parameter values for SDR than for PWR in each case). The rankings could be explained by differences among the mechanical properties in their sensitivity to maturation of wood characteristics. In conclusion, silvicultural regimes have great potential to regulate wood structural characteristics and mechanical properties, apparently due to the influences of the green crown and growth rate on the vascular cambium, the strength of which vary throughout the rotation period. A silvicultural regime could therefore be seen as a tool that can be used to select material qualities and to make wood a more homogenous material for engineers

  • 239. Eriksson, Jerry
    et al.
    Ludvigsson, Mikael
    Dorn, Michael
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för bygg- och energiteknik (BE).
    Serrano, Erik
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för bygg- och energiteknik (BE).
    Enquist, Bertil
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för bygg- och energiteknik (BE).
    Load bearing timber glass composites: A WoodWisdom-Netproject for innovative building system2013Inngår i: COST Action TU0905 Mid-term Conference on Structural Glass / [ed] Jan Belis; Christian Louter; Danijel Mocibob, Boca Raton, Fla: CRC Press, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this three year project, which is part of the WoodWisdom-Net researchprogram, is to develop an innovative load bearing building system composed of timberglasscomposites. The structural loads applied onto these composites will be transferred to, andsupported by, the glass component, in contrary to today’s traditional solutions where glass elementsonly function as an environmental shield. Using such structural elements will make itpossible to largely increase the glass surface in buildings, allowing the presence of more naturallight in personal homes and office buildings.

    Timber-glass shear walls and beams will be developed taking into consideration long-term behaviorand seismic performance. Design concepts, feasibility studies and performance assessmentsof these components will be performed in order to improve the overall performance. Theproject also includes the development of new design calculations as well as the optimization ofmanufacturing methods.

    Material properties of timber, glass and adhesives will be determined from small and large scaleexperimental investigations, and will be used as input for theoretical calculations and modelingwork. The projects industrial partners will function as expertise and take part in the developmentand construction of demonstration objects.

    The project consortium is composed of academic and industrial partners from Austria, Sweden,Germany, Turkey, Slovenia, Chile, and Brazil. This paper presents material specifications andresults from small scale testing performed by the Swedish project partners.

  • 240.
    Esmaeili, Nima
    et al.
    University of Bolton.
    Jahandideh, Arash
    South Dakota State University.
    Muthukumarappan, Kasiviswanathan
    South Dakota State University.
    Åkesson, Dan
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Skrifvars, Mikael
    Högskolan i Borås, Akademin för textil, teknik och ekonomi.
    Synthesis and characterization of methacrylated star-shaped poly(lactic acid) emplying core moilecules with different hydroxyl groups2017Inngår i: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 134, nr 39, artikkel-id 45341Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A set of novel bio-based star-shaped thermoset resins was synthesized via ring-opening polymerization of lactide and employing different multi-hydroxyl core molecules, including ethylene glycol, glycerol, and erythritol. The branches were end-functionalized with methacrylic anhydride. The effect of the core molecule on the melt viscosity, the curing behavior of the thermosets and also, the thermomechanical properties of the cured resins were investigated. Resins were characterized by Fourier-transform infrared spectroscopy, 13C-NMR, and 1H-NMR to confirm the chemical structure. Rheological analysis and differential scanning calorimetry analysis were performed to obtain the melt viscosity and the curing behavior of the studied star-shaped resins. Thermomechanical properties of the cured resins were also measured by dynamic mechanical analysis. The erythritol-based resin had superior thermomechanical properties compared to the other resins and also, lower melt viscosity compared to the glycerol-based resin. These are of desired characteristics for a resin, intended to be used as a matrix for the structural composites. Thermomechanical properties of the cured resins were also compared to a commercial unsaturated polyester resin and the experimental results indicated that erythritol-based resin with 82% bio-based content has superior thermomechanical properties, compared to the commercial polyester resin. Results of this study indicated that although core molecule with higher number of hydroxyl groups results in resins with better thermomechanical properties, number of hydroxyl groups is not the only governing factor for average molecular weight and melt viscosity of the uncured S-LA resins.

  • 241.
    Espadas-Escalante, Juan José
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    van Dijk, Nico P.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    A study on the influence of boundary conditions in computational homogenization of periodic structures with application to woven composites2017Inngår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 160, s. 529-537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of boundary conditions (BCs) in the estimation of elastic properties of periodic structures is investigated using computational homogenization with special focus on planar structures. Uniform displacement, uniform traction, periodic, in-plane periodic and a proposed mix of periodic and traction BCs are used. First, the effect of the BCs is demonstrated in structures with one-, two- and three-dimensional periodicity. Mixed BCs are shown to most accurately represent the behavior of layered structures with a small number of repeating unit cells. Then, BCs are imposed on a twill woven composite architecture. Special attention is devoted to investigate the sensitivity of the estimated properties with respect to the BCs and to show differences when considering a single lamina or a laminate. High sensitivity of the in-plane extensional modulus and Poisson's ratio with respect to the type of BCs is found. Moreover, it is shown that the mix of BCs and in-plane periodic BCs are capable to represent an experimental strain field.

  • 242.
    Eva, Marra
    KTH, Skolan för kemivetenskap (CHE).
    Synthesis and Characterization of GDC-NiO Nanopowder2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    A composite of Cerium Gadolinium Oxide (GDC) and Nickel Oxide (NiO) was prepared by the co-precipitation method. The synthesized powder is the precursor of Ni-GDC which is a potential anode material for a Solid Oxide Fuel Cell (SOFC). X-ray diffraction results confirm the formation of GDC and NiO, as well as the nanometric dimensions of these formed phases. Mesoporous domains and high surface area are evidenced by the results of Nitrogen physisorption. The crystallinity of the powder and its agglomerated structure are graphically shown in the images obtained by the Scanning Electron Microscopy (SEM) and Transmission Scanning Microscopy (TEM). All these results indicate that co-precipitation is a suitable method for obtaining the GDC-NiO composite.

  • 243.
    Fall, Andreas
    RISE - Research Institutes of Sweden, Bioekonomi, Bioraffinaderi och energi.
    Nanocellulose and graphene: promising hybrid materials2018Inngår i: Recent advances in cellulose nanotechnology research: production, characterization and applications, Trondheim: RISE PFI , 2018Konferansepaper (Fagfellevurdert)
  • 244.
    Fallqvist, B.
    et al.
    Royal Institute of Technology, (KTH).
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Constitutive modelling of composite biopolymer networks2016Inngår i: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 395, s. 51-61Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical behaviour of biopolymer networks is to a large extent determined at a microstructural level where the characteristics of individual filaments and the interactions between them determine the response at a macroscopic level. Phenomena such as viscoelasticity and strain-hardening followed by strain-softening are observed experimentally in these networks, often due to microstructural changes (such as filament sliding, rupture and cross-link debonding). Further, composite structures can also be formed with vastly different mechanical properties as compared to the individual networks. In this present paper, we present a constitutive model presented in a continuum framework aimed at capturing these effects. Special care is taken to formulate thermodynamically consistent evolution laws for dissipative effects. This model, incorporating possible anisotropic network properties, is based on a strain energy function, split into an isochoric and a volumetric part. Generalisation to three dimensions is performed by numerical integration over the unit sphere. Model predictions indicate that the constitutive model is well able to predict the elastic and viscoelastic response of biological networks, and to an extent also composite structures.

  • 245.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Development and characterization of functional composite materials for advanced energy conversion technologies2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The solid oxide fuel cell (SOFC) is a potential high efficient electrochemical device for vehicles, auxiliary power units and large-scale stationary power plants combined heat and power application. The main challenges of this technology for market acceptance are associated with cost and lifetime due to the high temperature (700-1000 oC) operation and complex cell structure, i.e. the conventional membrane electrode assemblies. Therefore, it has become a top R&D goal to develop SOFCs for lower temperatures, preferably below 600 oC. To address those above problems, within the framework of this thesis, two kinds of innovative approaches are adopted. One is developing functional composite materials with desirable electrical properties at the reduced temperature, which results of the research on ceria-based composite based low temperature ceramic fuel cell (LTCFC). The other one is discovering novel energy conversion technology - Single-component/ electrolyte-free fuel cell (EFFC), in which the electrolyte layer of conventional SOFC is physically removed while this device still exhibits the fuel cell function. Thus, the focus of this thesis is then put on the characterization of materials physical and electrochemical properties for those advanced energy conversion applications. The major scientific content and contribution to this challenging field are divided into four aspects except the Introduction, Experiments and Conclusions parts. They are:

    1. Continuous developments and optimizations of advanced electrolyte materials, ceria-carbonate composite, for LTCFC. An electrolysis study has been carried out on ceria-carbonate composite based LTCFC with cheap Ni-based electrodes. Both oxygen ion and proton conductance in electrolysis mode are observed. High current outputs have been achieved at the given electrolysis voltage below 600 oC. This study also provides alternative manner for high efficient hydrogen production.
    2.  Compatible and high active electrode development for ceria-carbonate composite electrolyte based LTCFC. A symmetrical fuel cell configuration is intentionally employed. The electro-catalytic activities of novel symmetrical transition metal oxide composite electrode toward hydrogen oxidation reaction and oxygen reduction reaction have been experimentally investigated. In addition, the origin of high activity of transition metal oxide composite electrode is studied, which is believed to relate to the hydration effect of the composite oxide.
    3. A novel all-nanocomposite fuel cell (ANFC) concept proposal and feasibility demonstration. The ANFC is successfully constructed by Ni/Fe-SDC anode, SDC-carbonate electrolyte and lithiated NiO/ZnO cathode at an extremely low in-situ sintering temperature, 600 oC. The ANFC manifests excellent fuel cell performance (over 550 mWcm-2 at 600 oC) and a good short-term operation as well as thermo-cycling stability. All results demonstrated its feasibility and potential for energy conversion.
    4. Fundamental study results on breakthrough research Single-Component/Electrolyte-Free Fuel Cell (EFFC) based on above nanocomposite materials (ion and semi-conductive composite) research activities. This is also the key innovation point of this thesis. Compared with classic three-layer fuel cells, EFFC with an electrolyte layer shows a much simpler but more efficient way for energy conversion. The physical-electrical properties of composite, the effects of cell configuration and parameters on cell performance, materials composition and cell fabrication process optimization, micro electrochemical reaction process and possible working principle were systematically investigated and discussed. Besides, the EFFC, joining solar cell and fuel cell working principle, is suggested to provide a research platform for integrating multi-energy-related device and technology application, such as fuel cell, electrolysis, solar cell and micro-reactor etc.

    This thesis provides a new methodology for materials and system innovation for the fuel cell community, which is expected to accelerate the wide implementation of this high efficient and green fuel cell technology and open new horizons for other related research fields.

  • 246.
    Fang, Mei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Belova, Lyuba
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. Venkat
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Thermal anealing effects on Ag/TiO2 thin films prepared by ink-jet printingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The effects of heat treatment on both the phase structure and the electronic band structure were studied for Ag/TiO2 composite films prepared by inkjet printing. Ag nanoparticles can form ‘metal-bridge’ to link TiO2 particles in the mesoporous structured films and improve the transport properties of the films. The distribution of Ag in the composite films shows dependence on the annealing conditions: Ag clusters were observed at high annealing temperature (>600 °C), and they can be annihilated by a longer time annealing. Comparing with pure TiO2 films, the decreased intensity of the photoluminescence (PL) emission spectra of Ag/TiO2 composite films indicates that the doped Ag atoms could act as traps to capture electron and inhabit the recombination of electron-hole pairs. From the identifiable PL emission peaks, the band structure of the films is deduced.

  • 247.
    Farge, L.
    et al.
    Laboratoire de Science et Génie des Surfaces, EEIGM.
    Ayadi, Z.
    Laboratoire de Science et Génie des Surfaces, EEIGM.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Optically measured full-field displacements on the edge of a cracked composite laminate2008Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 39, nr 8, s. 1245-1252Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The main objectives of this study are to visualize the displacement field on the edge of a [0, 554, -554]s GF/EP laminate specimen with multiple transverse cracks and to analyze the crack opening displacement dependence on the applied mechanical load. The specimen full-field displacement measurement was carried out using ESPI (Electronic Speckle Pattern Interferometry) and phase-shifting. ESPI is an optical technique that provides the displacement for every point on a surface. The measurement resolution is roughly 20 nm. The displacement measurement is along the tensile axis and takes place on the specimen edge. Using the displacement map, it is possible to obtain the displacement profiles along the tensile-axis. The different profiles were drawn along the specimen edge at several distances from the mid-plane corresponding to the different plies. Studies of the displacement discontinuities make it possible to carry out a measurement of the crack opening displacements corresponding to the cracks in the measurement field. The experimental results are in a good agreement with idealized straight crack model in low stress region and much larger in the high stress region, which is attributed to development of local inter-ply delaminations.

  • 248.
    Farge, L.
    et al.
    Nancy Université-INPL.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Z.
    Nancy Université-INPL.
    Damage characterization of a cross-ply carbon fiber/epoxy laminate by an optical measurement of the displacement field2010Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 70, nr 1, s. 94-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using Electronic Speckle Pattern Interferometry (ESPI), full-field displacement measurement was performed on the edge of a cracked cross-ply graphite/epoxy laminate subjected to a tensile loading. The displacement jumps corresponding to cracks are clearly visible and can be used to determine the Crack Opening Displacement (COD) values along the cracks. The main objective of this study is to determine if the application of successive loads of increasing magnitude may have modified the existing cracks and thereby changed the COD dependence on the applied stress. Moreover, we have tested the applicability of the assumed linear elastic COD behavior in the presence of very high stress concentration at the crack tips. The profile of the opening along the crack was also studied.

  • 249. Farge, L.
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Z.
    Study of the displacement field on the edge of cracked laminated composites2008Inngår i: 13th European Conference on Composite Materials: 2-5 June 2008, Stockholm, Sweden, 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Using Electronic Speckle Pattern Interferometry (ESPI), the full-field displacement measurement was obtained on the edge of a cracked laminate subjected to a tensile loading. The displacement jumps corresponding to cracks are clearly visible and can be used to determine the Crack Opening Displacement (COD) values along the cracks. The main objective of this study is to determine if the application of high load may have modified the existing cracks and consequently changed the COD dependence on the applied stress. The profile of the opening was also studied.

  • 250.
    Farge, Laurent
    et al.
    Laboratoire d’Energètique et de Mécanique Théorique et Appliquee, Vandoeuvre Lés Nancy Cedex.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Ayadi, Zoubir
    Institut Jean Lamour, Nancy Cedex.
    Use of full-field measurements to evaluate analytical models for laminates with intralaminar cracks2012Inngår i: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 46, nr 21, s. 2739-2752Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Full-field displacement measurements between intralaminar cracks in cross-ply laminates were performed to evaluate the accuracy of shear lag models and Hashin’s model. The dependence of the average crack opening displacement on the crack density was measured and compared with model predictions. It was found that Hashin’s model overestimates the average COD by at least 25%. The value of the shear lag parameter was back-calculated by fitting. With the same goal the strain in the middle between two cracks was measured rendering shear lag parameter which was only 1% different. The found value does not agree with any of the used shear lag models. Measurement shows nonzero intralaminar shear zones in both layers covering a part of the ply thickness.

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