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Journal of Ceramic Science and Technology 2/2016
Vol. 7, No. 2 · June 2016
Microscale-Motivated Continuum Damage Simulations of Brittle Ceramics under Thermomechanical Loading
J. Gundlach, D. Henneberg, J. Scheel, A. Ricoeur
Pages 145-154 · DOI: 10.4416/JCST2016-00012
Two approaches towards modeling damage in a brittle material caused by thermomechanical loading are presented. Both rely on microcrack growth, in the first case in a homogeneous matrix, in the second one at grain boundaries. Two-scale simulations e.g. of thermal shocks applied to single-phase or layered structures are performed in connection with the finite element method. Damage and crack patterns are predicted just as quantities like residual strength or critical temperature jumps.
Thermal Shock and Thermo-Mechanical Behavior of Carbon-Reduced and Carbon-Free Refractories
A. Böhm, S. Dudczig, J. Fruhstorfer, A. Mertke, C.G. Aneziris, J. Malzbender
Pages 155-164 · DOI: 10.4416/JCST2015-00081
The thermal shock behaviour of novel carbon-reduced refractories with maximum grain size of 1 mm was investigated. A wedge splitting test for small specimen geometries (max. 40 × 40 × 20 mm3) was successfully implemented with different loading configurations to determine "work of fracture" and thermal shock parameters. Additionally, heating-up thermal shock tests were performed with an electron beam facility. The addition of 2.5 wt% ZrO2 and TiO2 to Al2O3 refractories appears to improve their thermal shock resistance due to microstructural changes that reduce brittleness and inhibit critical c …
Estimation of Damage in Refractory Materials after Progressive Thermal Shocks with Resonant Frequency Damping Analysis
N. Traon, T. Tonnesen, R. Telle
Pages 165-172 · DOI: 10.4416/JCST2015-00080
This work correlates damping measurements and the microstructural changes in refractory castables after these have been exposed to thermal shocks in air. In accordance with DIN EN 993 – 11, refractory samples based on tabular alumina with the addition of partially stabilized zirconia (PSZ) were progressively subjected to thermal shocks in air at different temperatures (750, 850, 950 and 1050 °C). White fused alumina samples were also exposed to the same thermal shocks at 950 °C. Evaluation of the thermal shock damage to the high-alumina refractory castables was based on the dynamic Young's mod …
Thermal Shock Performance of Refractories for Application in Steel Ingot Casting
J. Fruhstorfer, S. Schafföner, J. Werner, T. Wetzig, L. Schöttler, C.G. Aneziris
Pages 173-182 · DOI: 10.4416/JCST2016-00010
This study investigates the thermal shock performance of carbon-free and low-carbon-containing refractories, with and without nanoscale additives, based on alumina, mullite, and alumina doped with zirconia and titania (AZT). For this purpose, the porosity and cold modulus of rupture of the refractories before and after a single thermal shock by compressed air were determined. The mullite-matrix materials exhibited the highest porosities owing to restrained densification during sintering, but exhibited the lowest strength losses of the carbon-free materials. In general, the carbon-containing ma …
Prediction of Effective Thermal Conductivity of Refractory Materials at High Temperatures based on Synthetic Geometry Generation
C. Demuth, J. Hubálková, M.A.A. Mendes, M.A.A. Mendes, F. Ballani, D. Trimis, D. Trimis, S. Ray
Pages 183-192 · DOI: 10.4416/JCST2016-00006
In the present article, the numerical prediction of the effective thermal conductivity (keff) of low-carbon refractory materials at high temperatures is investigated. The employed numerical methodology consists of computational geometry generation by a modified random sequential adsorption (RSA) algorithm and solution of a heat conduction problem in the generated material sample by the finite volume method (FVM). The probability distributions, employed for modelling the grain sizes, are reexamined. Several aspects are recognised as crucial for reasonable predictions of keff in the considered r …
Mechanical Characterisation of Carbon-Bonded Magnesia at Temperatures up to 1400 °C
J. Solarek, C.G. Aneziris, H. Biermann
Pages 193-202 · DOI: 10.4416/JCST2016-00017
The mechanical properties of carbon-bonded magnesia were investigated from room temperature to 1400 °C in tension, compression and bending. For this purpose, quasi-static, static and cyclic tests were conducted on two testing machines, equipped with inert atmosphere chambers and inductive heating devices. Characterisation of the microstructure was performed with scanning electron microscopy (SEM) and optical microscopy (OM). Porosity and density were measured with the Archimedes principle and pycnometry. From the creep tests, activation energies and Norton exponents for high-temperature creep …
Influence of Interfaces on Crack Propagation through a Layered Refractory Loaded by Thermal Shock
J. Hein, O. El Khatib, M. Kuna
Pages 203-208 · DOI: 10.4416/JCST2016-00004
Layered structures have been suggested to improve the thermal shock resistance of refractories. Owing to the fast temperature increase of the outer surface, high thermal tensile stresses occur inside the refractory. Depending on the intensity of thermal shock and the material, cracks may arise and grow through and between the layers. To study the behavior of such a crack system and the influence of interfaces on it, a symmetrically layered strip is considered. The cracks through the layers and along the interfaces are modeled using cohesive zones. Systematic changes of the cohesive parameters …
Carbon-Bonded Alumina Refractories with Reduced Carbon Content due to the Addition of Semi-Conductive Silicon and/or Nanoparticles
N. Brachhold, J. Fruhstorfer, A. Mertke, C.G. Aneziris
Pages 209-222 · DOI: 10.4416/JCST2016-00024
This study investigated the combined effect of nanoscaled additives (carbon nanotubes and nanoscaled alumina) and semi-conductive silicon on carbon-bonded alumina with a reduced primary carbon content of 20 wt%. It focused on the initial cold modulus of rupture and its evolution on exposure to thermal shock. The use of the single additive groups or their combination yielded an increased initial strength compared to the reference without additives. It was shown that the combination of the additives resulted in a material that exhibited no statistically significant decrease of the cold modulus o …
