| 1. |
- Nordin, Lars-Olof, et al.
(författare)
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Structure and mechanical properties of wood-based composites
- 2002
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Ingår i: FRC 2002. - : Conference Design Consultants. - 954045920 ; , s. 112-118
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Konferensbidrag (refereegranskat)abstract
- Wood-based paper fiber composites are of interest due to favorable mechanical properties of the fibers. Wood fibers were separated from sapwood of spruce by a sulfite cooking procedure with 2, 3, 4 and 5 hrs cooking times. Oriented fiber mats were manufactured from these fibers, which were mildly treated as compared with commercial paper fibers. Composites were produced with fiber volume fractions in the range 17.6-19.5%. Scanning electron microscopy, mechanical testing and micromechanics modeling of composites modulus were methods used. Mechanical property data from the literature were compiled and compared with the present results. Young's modulus and strength were 6.4-8.4 GPa and 59-115 MPa respectively. Differences were mainly attributed to differences in fiber orientation distribution, but advantages were noted with longer cooking time fibers separated into individual wood cells. If the low fiber content is taken into account, this material has high stiffness and strength compared to results found in the literature.
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| 2. |
- Persson, Per, et al.
(författare)
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Comparison of the adsorption of o-phthalate on boehmite (γ-AlOOH), aged γ-Al2O3, and goethite (α-FeOOH)
- 1988
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 206:1, s. 252-266
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Tidskriftsartikel (refereegranskat)abstract
- This work is concerned with the adsorption of o-phthalate (1,2-benzenedicarboxylate) at the water-metal (hydr)oxide interface. Previously published infrared spectroscopic, potentiometric, and adsorption data characterizing the boehmite (gamma-AlOOH) system are compared with new data collected for o-phthalate adsorption on aged gamma-Al2O3 and goethite (alpha-FeOOH). The study focuses on identifying bonding mechanisms, stoichiometries, and stabilities of the formed complexes, and comparing these among the three systems. Furthermore, the effects of ionic strength and composition of the ionic medium are investigated. The infrared spectroscopic data provided direct, molecular-level evidence for the existence of two dominating surface complexes on all three solids. One was shown to be a deprotonated outer-sphere species and the other was an inner-sphere surface complex. The inner-sphere complexes on the three solids were structurally related, and they were tentatively assigned to a mononuclear, chelating structure involving both carboxylate groups. The outer-sphere complexes were shown to increase in relative importance at high pH and low ionic strengths, while low pH and high ionic strengths favored the inner-sphere complexes. The information gained from the infrared spectroscopic investigations was used as qualitative input in the formulation of the surface complexation models. New models, based on the extended constant capacitance approach, were presented for the o-phthalate/aged gamma-Al2O3 and o-phthalate/goethite systems.
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| 3. |
- Brozovic, Danilo, 1979-
(författare)
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Service Provider Flexibility : A Strategic Perspective
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about service provider flexibility and how provider flexibility facilitates customer value creation in contexts where customer processes and activities change. Provider flexibility is delineated as a mechanism of value creation and defined as the ability of the service provider to respond to changes or to bring about changes that support its customers’ value creation. Although provider flexibility has been implied as a relevant factor in value creation, previous studies focusing on some kind of provider flexibility would benefit from a deeper understanding of the strategic role that service provider flexibility plays in value creation.The purpose of this study is to provide a framework that explicates the strategic role of provider flexibility in value creation. The role of provider flexibility in the adjustment of the provider’s processes and activities and the development of opportunities based on insights from customer interactions are thus emphasized. Moreover, while these insights from customer interactions can offer valuable development opportunities for the service provider, these opportunities yield returns only with the transfer of the insights back to the service provider’s organization.The research process evolves along five research articles that develop the understanding of the strategic role of provider flexibility in value creation. The study builds on the empirical data from five service organizations of large industrial firms. The empirical insights from the articles are expanded and their conclusions further developed by iteratively and abductively substantiating the research model. The discussion explicates how exercising provider flexibility—in the form of organizational flexibility in the provider sphere, interaction flexibility in the joint sphere, and flexibility in use in the customer sphere—contributes to value creation. Moreover, findings show that the provider and the customer are entwined in a service system surrounding their service relationship. Provider flexibility in this aspect functions not merely as a mechanism of value creation, but also as a carrier of knowledge and information about the customer. Having this dynamics in mind, the provider continues to use provider flexibility to reinvent itself and constantly evolve the organization.This thesis contributes to the literature by providing a framework that explicates the strategic role of provider flexibility in value creation. More specifically, the contributions are: 1) an increased understanding of how provider flexibility in value creation is exercised, placing provider flexibility at the core of the encompassing process of value creation, and thus explicating the manner in which the encompassing process of value creation can unfold; and 2) an increased understanding of the strategic role of the work of part-time marketers by delineating the process of provider flexibility in value creation where different aspects of provider flexibility in value creation are linked.
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| 4. |
- Giannadakis, Konstantinos
(författare)
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Mechanisms of inelastic behavior of fiber reinforced polymer composites
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present thesis, the sources of linear/non-linear viscoelastic and viscoplastic behaviour in polymer composite materials are under study. The significance of this work is related to the nature of all composite materials. All polymer composites tend to indicate a time-dependent behaviour. This behaviour can be either linear or nonlinear. No matter what it is, is very important to be taken into account in the analysis, since it is related to strain rate effects, microdamage induced to the structure of the composite and/or irreversible plastic strains.This microdamage is usually caused due to the application of high stresses or high strain. For that reason additional stiffness degradation experiments were performed. In these tests, samples were subjected to high stress levels. Such high stress levels are also responsible for irreversible phenomena that were mentioned before. Then, a material model was used to study the viscoelastic and viscoplastic behaviour. This model assumes that the viscoelastic and viscoplastic responses may be decoupled; the micro-damage influenced viscoelastic strain response can be separated from viscoplastic response which is also affected by damage. In this thesis, three materials were studied, each one corresponding to a submitted/published scientific article. The first paper entitled "Time dependent nonlinear behaviour of recycled PolyPropylene (rPP) in high tensile stress loading" studied the behaviour of recycled polypropylene and recycled polypropylene with the addition of Maleic Anhydride grafted PolyPropylene (MAPP). The time dependent response was decomposed into nonlinear viscoelastic and viscoplastic parts and each of them was quantified. It was found that the elastic properties did not degrade due to high loading. The addition of MAPP did not change the mechanical properties of the rPP. Then the material model was applied and the involved parameters were identified.In the second article, entitled "Mechanical properties of a recycled carbon fibre reinforced MAPP modified polypropylene composite", the previously studied rPP/MAPP matrix was used to form a composite by using recycled carbon fibres. It was found that in creep tests, the time and stress dependence of viscoplastic strains follows a power law, which makes the determination of the parameters in the viscoplasticity model relatively simple. What is more, the viscoelastic response of the composite was found to be linear in the investigated stress domain. The material model was validated in constant stress rate tensile tests. Finally, in the third article, entitled "The sources of inelastic behaviour of GF/VE NCF [45/-45]s laminates" a glass fibre non-crimp fabric laminate was studied. The viscoelastic and viscoplastic material model parameters were calculated and it was found that the material indicates no linear region. This fact was also attributed to the fibre orientation. Loading the fibres in an off-axis direction caused shear stresses, which are responsible for microdamage (related to the fibre-matrix interface and intralaminal cracks) which is considered to be an important source of non-linearity.
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| 5. |
- Grubb, Anders, et al.
(författare)
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Generation of a new cystatin C-based estimating equation for glomerular filtration rate by use of 7 assays standardized to the international calibrator
- 2014
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Ingår i: Clinical Chemistry. - : Oxford University Press (OUP). - 0009-9147 .- 1530-8561. ; 60:7, s. 974-986
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND:Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays.METHODS:Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR.RESULTS:We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C.CONCLUSIONS:A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
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| 6. |
- Jonsson, Carrie
(författare)
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Deposit formation in the grate-kiln process
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Deposit formation in the grate-kiln process is a challenge for the iron ore pellet production industry. The deposits cause disturbances that affect the production capacity of the pelletizing plant. To prevent or mitigate these occurrences, it is important to understand the deposit formation mechanism during the process, which is the overall goal of this work. The results from this work can be used to enhance the understanding of deposit formation in the iron ore pelletizing industry.In this work, particle and deposit formations were studied both in a full-scale grate-kiln plant (40 MW) and in a pilot-scale pulverised coal-fired furnace (400 kW). The sampled particles and deposits were characterized with scanning electron microscopy equipped with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), laser diffraction (CILAS) and X-ray fluorescence (XRF).In the first part of this work, the initiating step in deposit formation— i.e. particle formation mechanisms— was investigated. Particles were sampled from the transfer chute in a full-scale grate-kiln production plant during combustion of oil and coal in separate firings. The results showed that particles in the flue gas consisted principally of fragments from iron ore pellets and minor ashes from heavy fuel oil and pulverised coal combustion. Three categories of particle modes were identified: (1) a submicron mode consisting of condensed products from vaporized species that had relatively high concentrations of Na and K for both combustion cases, with high concentrations of Cl and S during heavy fuel oil combustion, and high concentrations of Si, Fe and minor P, Ca and Al during coal combustion (2) a first fragmentation mode consisting of both iron ore pellet fines and fly ash particles with a significant amount of Fe (>65 wt %) for both combustion cases, with high concentrations of Ca and Si during heavy fuel oil combustion and high concentrations of Si and Al during coal combustion (3) a second fragmentation mode consisting almost entirely of coarse iron ore pellet fines, predominantly Fe (~90 wt %). The particles in the flue gas were dominated by iron ore fines within the second fragmentation mode, which contributed >96 wt % of the total mass of collected particles.In the second part of this work, short-term deposits were collected at the same location in the grate-kiln as the collection of particles. They were characterized by their chemical composition and microstructure in order to obtain information about the deposit formation. Deposit sampling was carried out during separate combustion firings of oil and coal. A significant difference in the deposition behaviour was observed: deposition during oil firing was negligible compared with coal firing. The deposits from coal firing were mainly fine-grained iron oxide particles embedded in a molten (bonding) phase that comprised mainly of Si, Al, Fe, Ca and O. Moreover, it was found that the prevailing flue gas direction determines the formation of the deposits on the probe and that inertial impaction controls the deposition rate. However, this rate can also be affected significantly by the amount of entrained particles that were present in the kiln.In the third part of this work, two different coals were combusted both in a full-scale grate-kiln plant and in a pilot-scale pulverized coal-fired furnace (ECF). The ECF is designed as a scaled-down grate-kiln for combustion testing. Particle and short-term deposit samplings were carried out in both appliances. Dust originating from iron ore pellets was only present in the grate-kiln as there was no flow of iron ore pellets in the ECF. The results showed that Na, K and Cl contents in submicron mode were higher in the grate-kiln than in the ECF, due to alkali circulation in the grate-kiln. The coarse mode particles (2.6-4.2 μm) sampled from the grate-kiln contained significantly more Fe, which originated from the iron ore pellets. The presence of coarse particles (>6 μm) was substantial (>96 wt % of the total particle mass) in the grate-kiln but insignificant in the ECF. The short-term deposits from the grate-kiln consisted of a variety of particles from both iron ore pellets and coal ash particles embedded in an iron-rich silicate molten phase. Short-term deposits from the grate-kiln were harder and denser compared to the shortterm deposits from the ECF. Short-term deposits from the ECF were porous and consisted of coal ash particles embedded in a silicate molten phase. The molten phase in short-term deposits from the gratekiln had a higher Fe content and a higher CaO/(SiO2+Al2O3) ratio than the molten phase from the ECF short-term deposits. Thermochemical calculations showed that the molten phase in the short-term deposits from the grate-kiln had a lower viscosity compared to the molten phase in short-term deposits from the ECF.
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| 7. |
- Nordin, Lars-Olof, et al.
(författare)
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Mechanical response of thermoset polymers under high compressive loads, 2
- 2005
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Ingår i: Macromolecular materials and engineering. - : Wiley. - 1438-7492 .- 1439-2054. ; 290:11, s. 1073-1082
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Tidskriftsartikel (refereegranskat)abstract
- A nonlinear viscoelastic material model was used to describe the experimental behaviour of thin vinyl ester specimens subjected to compression in thickness direction. The stress-dependent material functions in the model were found in creep and strain recovery tests on thick cylindrical specimens. The elastic and creep response of thin thermoset polymer specimens subjected to compressive loads was simulated while varying the geometry of the test set samples. The calculated increase in the apparent elastic modulus and decrease of the creep-strain rate due to reduced thickness-to-width ratio is in a good qualitative correlation with experimental results for corresponding geometries. The constraint due to friction and interaction with the material outside the loaded surface area were identified as the cause for high apparent stiffness, which converges with decreasing thickness to an asymptotic value dependent on the modulus and Poisson's ratio of the material.
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| 8. |
- Nordin, Lars-Olof, et al.
(författare)
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Methodology for parameter identification in nonlinear viscoelastic material model
- 2005
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Ingår i: Mechanics of time-dependant materials. - : Springer Science and Business Media LLC. - 1385-2000 .- 1573-2738. ; 9:4, s. 259-280
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Tidskriftsartikel (refereegranskat)abstract
- Two methodologies for identification of material functions in Schapery's nonlinear viscoelastic material model are compared in context to their ability to deal with deviations from Heaviside stepwise load application and unloading in real test conditions where the time intervals for load increase to plateau value and to unloading to zero are finite. In the first method the description of the whole loading, creep, unloading and recovery process is given by one-step load application and one-step unloading whereas in the second method the load increase and decrease intervals are approximated by two-step load application with 0.5 of the load applied in the increase region. Vinyl ester with known viscoelastic properties and incremental form of Schapery's constitutive equation is used to simulate "experimental data" for several length of load application and unloading. The two data reduction methodologies are applied to these "data" and the accuracy of identified material functions is compared with the true values (input data).
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| 9. |
- Nordin, Lars-Olof, et al.
(författare)
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Nonlinear viscoelastic behavior of paper fiber composites
- 2005
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 65:10, s. 1609-1625
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic material model for composites made from phenol-formaldehyde impregnated paper is developed starting from Schapery's nonlinear viscoelastic and nonlinear viscoplastic constitutive law derived from thermodynamics. Methodology for determination of the included stress-dependent functions has been developed and used to determine properties of two composites in two directions related to material symmetry. Creep with following strain recovery tests have been performed at several levels of stress. Data reduction is based on two-step load application methodology to include effect of finite time of load increase to the plateau value and its removal. No stiffness reducing micro damage was detected and the plastic deformations were considered negligible or accounted for in a simplified manner. The material model was used to simulate a constant stress rate loading and unloading test. Model is validated comparing simulations with results from test.
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| 10. |
- Nordin, Lars-Olof, et al.
(författare)
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Nonlinear viscoplastic and nonlinear viscoelastic material model for paper fiber composites in compression
- 2006
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 37:2, s. 344-355
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Tidskriftsartikel (refereegranskat)abstract
- Compressive behavior of phenol-formaldehyde impregnated paper composites is studied in creep and strain recovery tests observing large nonlinear viscoelastic strains and irreversible strains, describing the latter as viscoplasticity. Stiffness reduction was not observed in experiments and therefore is not included in the material model. Schapery's nonlinear viscoelastic and nonlinear viscoplastic constitutive law is used as a material model and the stress dependent non-linearity functions are determined. First, the time and stress dependence of viscoplastic strains is described by Zapas et al. model and identified measuring the irreversible strains after creep tests of different length at the same stress and doing the same for creep tests of a fixed length but at different stress. Then, the determination of nonlinear viscoelastic stress dependent parameters is performed.
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