Browsing by Author "Berg, Gunnar"

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    Hardness and flow behaviour of glass in the nanometre range - An Interpretation of the load dependence of the hardness
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Meinhard, Holger; Grau, Peter; Berg, Gunnar; Mosch, Susan
    The flow behaviour of glass was investigated by Vickers hardness indentation technique with Variation of the deformation rate by six Orders of magnitude. The hardness tests were carried out on commercial sheet glass with three different loading regimes. A general flow equation in form of a power law was used to describe the deformation behaviour of the materials. The influences of loading mode and deformation rate on the parameters of this law were investigated. An essential result of this work is that the load and Penetration depth dependence of the hardness, respectively, the so-called indentation size effect, is an inevitability of the special methodology of the indentation technique during deformation of strain rate-sensitive materials.
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    Load dependence of the hardness of silicate glasses - Not just due to indenter tip defects
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Grau, Peter; Berg, Gunnar; Fränzel, Wolfgang; Schinker, Martin
    The real contact area of Berkovich indenters with typical indenter tip defects is calculated as a function of the penetration depth in a general form and compared with literature results for Vickers indenters. The influence of the tip defects on the load dependence of hardness is treated for both types of indenters, taking into account possible purely elastic deformation at the beginning of contact. Using the example of recording microhardness measurements on glass made using a Berkovich indenter, it is shown that a linear dependence exists between load and depth of penetration in the millinewton load region which can be explained by a rounded indenter tip. However, the resulting corrections for the real contact area are not sufficient to compensate for the load dependence of the hardness in the entire load region. A method is proposed for showing definitely that the load dependence of the hardness is caused not just by indenter tip defects but also by material properties. This method is tested on extensive measurements of the authors, as well as on results of Frischat and the Oak Ridge group.
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    Low-temperature tensile deformation of flat glass containing metal particles to generate dichroism
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1998) Borek, Reinhard; Berg, Klaus-Jürgen; Berg, Gunnar
    Uniformly oriented metal particles shaped like prolate spheroids are produced by tensile deformation of flat glasses, containing small spherical particles of some 10 nm in diameters. The deformation is performed at temperatures only slightly above Tg. High tensile stresses up to 200 N/mm² and low velocities of deformation characterize the special conditions of this process. The method has been improved such as to exceed the previous limitation to relatively small values of the cross section of the specimens. A unidimensional hydromechanical model including the conservation equations for momentum, mass and energy describes the glass deformation. The model has been solved numerically A good agreement has been attained between experimental and theoretical results.