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On the nonlinear behavior of Young's modulus of carbon‐bonded alumina at high temperatures
Author(s) -
Luchini Bruno,
Grabenhorst Joern,
Fruhstorfer Jens,
Pandolfelli Victor C.,
Aneziris Christos G.
Publication year - 2018
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.15575
Subject(s) - materials science , composite material , thermal expansion , modulus , microstructure , graphite , thermogravimetric analysis , carbon fibers , young's modulus , porosity , scanning electron microscope , anisotropy , chemical engineering , physics , quantum mechanics , composite number , engineering
The origin of the nonlinear behavior of the Young's modulus ( E ) of carbon‐bonded alumina at high temperatures was addressed, based on the microstructural changes observed during processing and their thermo‐mechanical properties. Impulse excitation technique, thermogravimetric analysis, porosity measurement, and scanning electron microscopy were conducted in order to highlight and explain the E behavior. The finite element model of a virtual microstructure was simulated and the results attained are in good agreement with the experimental data. The tests revealed that the Young's modulus of a cured sample heated from room temperature up to 500°C was governed by the release of volatiles. Above this temperature, the thermal expansion mismatch among alumina, graphite, and the carbon matrix is dominant resulting in an increase in the effective Young's modulus. During cooling, crack networks and gaps between alumina particles and the carbon matrix were developed. The former were induced by volatile release and by the graphite's highly anisotropic thermal expansion. The latter was derived by the thermal expansion mismatch between the alumina and the carbon matrix. The closure of the gaps and cracks governed the expansion behavior during the second heating cycle and a nonlinear effective Young's modulus increase as a function of temperature was observed.