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  • 1. Johansson, Jimmy
    et al.
    Blom, Åsa
    Dvinskikh, Sergey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    NMR-measurements for determination of local moisture content of coated wood2013In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 10, no 5, p. 601-607Article in journal (Refereed)
    Abstract [en]

    Local increased moisture content (MC) in wood constructions may result in different kinds of mechanical and, especially, biological degrading problems. Therefore, it is of great importance to control the MC of the material. However, there is at present no appropriate method for determining local MC in wood without destroying the product itself. Nondestructive measurements of local MC in wood is significant for the possibility of, for instance, monitoring the in situ MC in wood constructions over time, and thereby predicting potential problems. The nuclear magnetic resonance (NMR) technique has been shown to be valuable for the measurement of MC in wood. In this study, the possibility of utilizing this technique for local MC measurement in wood has been tested on wood samples exposed to water absorption for 72 h. The samples came from three different wood species treated with paint systems available on the market. In the wood samples an artificial "crack" had been created in the paint to introduce an area where the water could easily gain access to the wood. The results show the possibility of using the NMR technique for local MC measurements in wood. The measurement area, however, must be related to the properties of the material. In the case of wood, the measurement spot must be related to the early/latewood proportions. Further, a calibration of the NMR measurement must be made in relation to the expected density variations of the material.

  • 2.
    Pourmand, Payam
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Wang, Lin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Assessment of moisture protective properties of wood coatings by a portable NMR sensor2011In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 8, no 5, p. 649-654Article in journal (Refereed)
    Abstract [en]

    We have evaluated the potential of nuclear magnetic resonance (NMR) spectroscopy based on small portable magnets for in situ assessment of moisture protective properties of wood coatings. Low field (1)H NMR with a unilateral permanent magnet was used to monitor and map the local moisture content (MC) of wood specimens uncoated or coated with various types of commercial paint systems. The MC beneath a coating layer was measured with a penetration depth up to 5 mm and with a depth resolution of 0.2 mm. The method is quick, noninvasive, simple to perform, and does not require removing wooden parts from the structure.

  • 3.
    Ståhlberg, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Properties of Powder Coatings in Load Carrying Construction2005In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 2, no 6, p. 473-481Article in journal (Refereed)
    Abstract [en]

    The present study describes the mechanical behavior of powder coatings used under very high compressive loads in clamping force joints. Carboxyl functional polyester powder coatings cured with hydroxyl functional β- hydroxyalkylamides, with variations in coating thickness and amount and type of filler, have been studied. The coatings were subjected to conventional tests for coatings and polymers and also to specially designed tests developed to study the behavior of powder coatings in clamping force joints. The specially designed tests were used to study the coatings under compressive loads, and the relation between the results from these test methods and from conventional tests is discussed. The results show the importance of coating thickness in order to achieve the desired mechanical properties of a coating when used under high compressive loads. These loads put high demands on the stability of the coating, and the defects must be kept to a minimum. Increased thickness will give rise to more defects in the coating, especially voids and blisters due to the evaporation of water formed during the curing of the polyester powder coating. The surface roughness of the coating is also affected by the coating thickness, but the main influence originates from the type and amount of filler used. A rough surface will give rise to stress concentrations and increased plastic deformations in the coating, impairing the properties of the clamping force joint.

  • 4.
    Tammisola, Outi
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Hellstrom, Georg
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Lagerstedt, Torgny
    Spin coating of Blu-Ray disks: modeling, experiments, limitations, and manipulation2010In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 7, no 3, p. 315-323Article in journal (Refereed)
    Abstract [en]

    A major challenge in the production of Blu-Ray Disks (BDs) is making the cover layer over the information area. The layer has to be both thick enough to protect the information and even enough for the information to be read through it optically. Furthermore, it is preferred not to cover the hole in the center of the disk. Spin coating is a candidate method for the production of these layers in a rapid reproduction process. When dispensing is performed off-center (in order not to cover the hole), a new complication appears, namely the formation of a slope toward the inner rim of the liquid film. Here, fundamental limitations for achieving even films in this system and ways to overcome the difficulties by manipulation of the process are studied. A mathematical model for this particular case of spin coating is obtained and validated by comparison with experiments made in industrial equipment aiming at producing BDs. The model agrees well with the experimental data. The model is then used to show that cover layers that fulfil the Blu-Ray specification are very difficult to produce with the spin-coating technique. Manipulation by inline curing and surface shear is added to the model and the results show that it is considerably easier to meet the BD specification when utilizing the manipulation.

  • 5.
    Wredenberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    On the stability of delamination growth at scratching of thin film structures2011In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 8, no 6, p. 707-717Article in journal (Refereed)
    Abstract [en]

    Scratching of thin film/substrate structures is studied theoretically and numerically. The results are discussed in connection to delamination initiation and in particular subsequent growth at scratching. The material behavior of the film is described by classical elastoplasticity accounting for large deformations. The deformation of the substrate is neglected indicating that the results are pertinent to soft thin films. The numerical investigation is performed using the finite element method (FEM) and the numerical strategy is discussed in some detail. The results from this study show that delamination growth at thin film scratching is a stable feature with crack arrest occurring at a decreasing load.

  • 6.
    Wredenberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On scratch testing of pressure-sensitive polymeric coatings2010In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 7, no 3, p. 279-290Article in journal (Refereed)
    Abstract [en]

    Scratching of polymeric coatings on hard substrates is studied experimentally and numerically from a mechanical point of view. In particular, the behavior of local and global mechanical properties, as well as the delamination behavior, at scratching due to pressure-sensitive effects is of interest. The numerical investigation is performed using the finite element method (FEM) where pressure sensitivity is modeled using the classical Drucker-Prager plasticity model (Drucker, Prager, Q. Appl. Math., 10 157-165 (1952)) while the adhesion of the coating to the substrate is modeled as a cohesive zone where relevant model parameters are determined experimentally using the double cantilever beam test with uneven bending moments (DCB-UBM). Good correlation between experimental and numerical results were achieved and the most important finding concerns the fact that the dependence of pressure sensitivity proved to be different for different mechanical quantities.

  • 7.
    Wredenberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On the stress distribution at scratching of thin film structures2010In: JCT Research, ISSN 1547-0091, E-ISSN 2168-8028, Vol. 7, no 5, p. 623-635Article in journal (Refereed)
    Abstract [en]

    Scratching of thin film/substrate structures is studied theoretically and numerically. In most cases, the material behavior of the film as well as the substrate is described by classical elastoplasticity accounting for large deformations; further, pressure-sensitive flow models are considered. The main efforts are devoted toward an understanding of the influence from the film/substrate boundary on the stress distribution at scratching but for comparative reasons, scratching of homogeneous materials are also studied and pertinent results presented. Among other things, the results are discussed in relation to delamination initiation and growth at scratching. The numerical investigation is performed using the finite element method, and the numerical strategy is discussed in some detail. The most important finding given by the present study is that high shear stresses are the main driving force for delamination initiation and growth along the film/substrate interface. It was also noted that the influence from pressure-sensitive flow on the stress fields related to delamination initiation is small, both quantitatively and qualitatively.

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