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- Itemstress generation modulus as a counterpart of the stress relaxation modulus(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Brückner, Rolf; Hessenkemper, Heiko; Habeck, Andreas; Yue, YuanzhengIn order to measure the time dependence of the stress relaxation modulus, E, a stress-strain deformation has to precede which induces a stress within the viscoelastic sample from which the sample relaxes. The generation of stress is characterized by a strain rate-dependent and relaxation rate-dependent portion which exhibits a maximum value, E_max, which is called "stress generation modulus". E_max was called the "maximum stress relaxation modulus" in earlier papers. Meanwhile, however, it turned out that a better verbal distinction should be made in future by the new term "stress generation modulus" because E_max is about one order of magnitude larger than E.
- ItemInfluence of oxygen partial pressure on crystallization behaviour and high-temperature stability of stone wool fibres(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2005) Kaasgaard, Martin; Jacobsen, Peter A. L.; Yue, YuanzhengThe influence of oxygen partial pressure on the redox State of the iron in stone wool is studied using thermogravimetry (TG). The thermal response of the stone wool is measured using differential scanning calorimetry (DSC). The high-temperature stability of stone wool depending on the oxygen partial pressure is observed using scanning electron microscopy (SEM). It is confirmed that the oxidation of Fe2+ to Fe3+ is responsible for the high-temperature stability of stone wool. Even a minor increase in oxygen partial pressure can considerably alter the crystallization behaviour and enhance the high-temperature stability of the stone wool. The origin for that is discussed.
- ItemNon-Newtonian flow behaviour of a phosphate glass melt at a viscosity close to the working point(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Yue, Yuanzheng; deClaville Christiansen, JesperThe dependence of both the shear and the extensional viscosity of the glass melt, namely, NaPoLi melt (Na2O ∙ Li2O ∙ 2P2O5), on the shear and extensional rate, respectively, was studied by means of a capillary method at a low shear viscosity near the working point at ηs = 10^3 Pa s. To accurately calculate shear viscosities, the Bagley end correction was made by determining the pressure drop at the entrance of the capillary. The extensional viscosity was estimated using the Cogswell model. It was found that a dilatant flow behaviour occurred at low shear rates, whereas a shear-thinning flow behaviour did at high shear rates. At the same time, an extension-thinning flow took place, which onsets at a very low extensional rate and then gradually tends to a constant value. With increasing the extensional rate, the Trouton ratio strongly deviates from the value of pure inelastic and isotropic fluids, i.e. 3. Αll the observed phenomena imply that the NaPoLi glass melt during extrusion is an anisotropic and viscoelastic fluid.
- ItemRheological properties of calcium metaphosphate melts during extrusion(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Yue, Yuanzheng; Carl, Gunter; Rüssel, ChristianAn extrusion method to determine viscosities is described. Here, different stages of the response on the load applied are observed and the viscous heating efFect caused by the mechanical deformation work is taken into account. The method enables the determination of viscosities in the ränge of 10⁶ to 10^(8.5) dPa s. The values obtained are in good agreement with interpolated ones determined by beam bending and cylinder rotation. During extruding of calcium metaphosphate melts, the viscositiy decreases with increasing shear rate. This shear-thinning efFect (or non-Newtonian behaviour) is attributed to the orientation of flow units of the dynamic melt network. It is found that both Newtonian and non-Newtonian flow behaviour of calcium metaphosphate melts was largely influenced by adding a small amount of SiO₂. However, the introduction of a small amount of SiO₂ into calcium metaphosphate melts is beneficial to study the flow behaviour, since by that the crystallization of melts is avoided, which hinders the continuation of extruding processes.
- ItemRheological properties and isochomal workability of lead Silicate glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Yue, Yuanzheng; Brückner, RolfFour different industrial lead Silicate glass melts were investigated by means of the cylinder compression method with respect to the flow and stress generation behaviour, the critical deformation rate hc, and the high-temperature tensile strength, σ_ts. Increasing PbO concentration has usually a large influence on t he Newtonian viscosity, it makes the melt "shorter" (more modernly speaking: more "fragile"). On the other hand, the influence on the non-Newtonian flow and stress generation behaviour and therefore, on the brittleness is very small, however, the high-temperature tensile strength is markedly negatively influenced. At low viscosities the melts with large P bO content show larger critical deformation rates and therefore, a better isochomal workability than those with smaller P bO contents. As compared with soda lime Silicate glass melts the lead Silicate melts reach clearly smaller hc and σ_ts values at comparable degrees of deformation and therefore, they have a worse isochomal workability This unexpected behaviour is discussed under structural aspects.
- ItemOn the different descriptions of the non-Newtonian viscosity (shear-thinning effect) of glass melts with respect to heat dissipation(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Yue, Yuanzheng; Brückner, RolfThe range of non-Newtonian viscosity is usually connected with high strain rates or/and stresses. Therefore, the effect of heat dissipation (or viscous heating) cannot be neglected. In order to regard this effect various correlations were given in former papers, which will be analyzed and discussed in the present paper. It turns out that through the exact thermal elimination of viscous headng one can easily obtain the quantity of the pure, realistic and exclusively structurally determined non-Newtonian viscosity, ηnN, which may be normalized by the Newtonian viscosity, η0, to yield the form, ηnΝ/η0- At small amounts of strain and stress other expressions, such as η/η0,Tmax and η/η0,Tnet, may describe the non-Newtonian flow behaviour approximately where the thermal elimination is not made for the as-measured non-Newtonian viscosity, η, but for the Newtonian values, ηο. (η0,Tmax Stands for the adiabatically corrected Newtonian viscosity, due to the maximum temperature of viscous heating by the total deformation work; η0,Tnet Stands for t h e nonadiabadcally corrected Newtonian viscosity due to the gross temperature of viscous heating, regarding also the heat flow out of t he glass sample.) In contrast to these more or less pure non-Newtonian normalized viscosities the so-called normalized non-Newtonian gross viscisity, η/η0, is that viscosity which involves the viscosity decrease due to the pure non-Newtonian flow, determined by structural orientation, as well as the viscosity decrease due to the viscous heating. The various relationschips are analyzed and discussed with the help of recently developed rheological equations.
- ItemInfluence of non-homologous substitutions of chemical components on rheological properties and on isochomal workability of Silicate glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Yue, Yuanzheng; Brückner, RolfThe glass melts of a non-homologous series were investigated with respect to flow behaviour and stress generadon behaviour as well as to workability by means of the cylinder compression method. The results show that the competition between the gross viscosity effect and the bonding strength of the dynamic glass melt structure extremely deterrnines the high-temperature tensile strength, σ_ts, the critical deformation rate hc, and by that the isochomal workability. The larger hc values are not always connected to a larger non-Newtonian flow effect or to a larger gross viscosity effect as it is usually the case for homologous series. However, the rule for homologous series that smaller Emax moduli, i.e. smaller stiffness and brittleness of a glass melt, are coupled to a better isochomal workability is also vahd for non-homologous series. The special connections between σ_ts, hc and deformation, Δh/h0, are analyzed.
- ItemWhich rheological parameters control the isochomal workability of glass melts from the Container glass industry?(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Yue, Yuanzheng; Brückner, RolfTwo species of brown glass which were characterized by industrial workability and quality criteria as "good" and " bad ", respectively, were investigated by the cylinder compression method and by the Christiansen method. Significant differences between the two species were found by means of the two methods in such a manner that the "good" brown glass samples indicate a better homogeneity and the corresponding melts a larger critical deformation rate, hc and therefore, a better isochomal workability than the " bad " brown glasses and melts. Additionally, the former ones show a larger ratio Fe²⁺/F_total with the consequence that they have a lower Newtonian viscosity at the same temperature. In contrast to the brown glass melts no clear differences in the rheological properties and isochomal workability could be detected between white Container glass melts which have also been characterized as "good" or as "bad". The white Container glass melts are classified to be less workable at equal viscosities than the brown glass melts. The stress generation modulus, E_max, and the normalized non-Newtonian viscosity, η/η0T, are less sensitive properties with respect to the redox State of the melts and to the homogeneity than the hc values. With the results of this study the limits of the sensitivity of the various properties resulting from the cylinder compression method were reached.
- ItemIsothermal and isochomal workability of glass melts - Influence of melting history: Minor composition changes of redox State and hydroxyl content - Αstudy of the sensitivity of the cylinder compression method(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Brückner, Rolf; Yue, YuanzhengThe influence of redox State and hydroxyl concentration on the pure non-Newtonian flow behaviour, on the gross non-Newtonian viscosity, on the stress generation modulus, brittleness, high-temperature tensile strength and on the critical deformation rate of an iron oxide-containing laboratory glass melt with two different melting histories, but with the same main chemical composition, is investigated by means of the cylinder compression method. The comparison of these properties between the oxidized and the reduced glass melt is made not only at equal temperatures but also at equal viscosities in order to distinguish between isothermal and isochomal workability and to examine how sensitive the applied method is. The result is that the reduced melt with a somewhat larger Fe²⁺/F_total ratio and with a larger hydroxyl content has a smaller stiffness and brittleness and therefore, a somewhat better isothermal workability than the oxidized melt. This is valid only for the comparison at equal temperatures. When the comparison is made at equal viscosities, however, the workability - or better the isochomal workability - of the two melts is the same. The reason is that a shift of the Newtonian viscosity is produced by the redox shift and hydroxyl content of the reduced melt to lower values which diminishes with increasing temperature. It is possible to construct master curves with respect to the measured properdes at four temperatures, by which a transfer to the low viscosity range is possible, i.e., one can get the isothermal workability of the glass melts over the whole working range. The measured values of the above-mentioned properties are represented by fitting with recently developed relations which give rise to interesting practical and theoretical conclusions about industrial production optimization and about some structural aspects of stressed melts.
- ItemDetermination of the rheological properties of high-viscous glass melts by the cylinder compression method(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Brückner, Rolf; Yue, Yuanzheng; Habeck, AndreasA detailed description of the cylinder compression method and its application on the viscoelastic behaviour of glass melts is given with the help of closed solutions and equations in contrast to algorithmic methods, like e.g. the finite element method. Special attention is paid to the system deformation and system deformation rate of the testing equipment and to the dissipation of mechanical energy within the specimen and the heat flow from the specimen. The limits of this treatment are discussed with respect to the applicability of the theoretical basis (Gent and Nadai equation) and with respect to the experimental determination of the rheological properties of glass melts. On this basis the pure non-Newtonian viscosity, ηnN, can be determined. If very small differences have to be ascertained in the rheological behaviour of glass melts due to small differences in composition or in melting history (e.g. redox condition or bad/good workability), the same conditions concerning the mechanical and thermal equipment and even the same geometry of the glass specimens have to be strictly maintained. Comparison between different glass melts should be made rather on the basis of equal (Newtonian) equilibrium viscosity, η₀, (isochomal conditions) and not on equal temperature. Owing to large thermal effects, the slope of the viscosity-temperature curve at η₀ plays a certain role, particularly for the forming process.