Thermo-mechanical characterization of cellular ceramics in high

Thermo-mechanical characterization of cellular
ceramics in high-temperature environments
Ehsan Rezaei1,2, Alberto Ortona2, Sophia Haussener1
1Institute of Mechanical Engineering, EPFL, 1015 Lausanne, Switzerland
2ICIMSI-SUPSI, 6928, Manno, Switzerland
Introduction
Mechanical testing
Cellular ceramics are attracting materials for high temperature applications such as
thermal energy storage systems, thermal protection systems, porous burners,
reformers, and volumetric solar radiation absorbers.[1-3] These material structures
are able to withstand oxidative environments at high temperatures and are
particularly resistant to thermal shock. This work presents our recent studies on
thermal and mechanical behavior of Si-SiC porous ceramics including both
numerical and experimental approaches.
Solar radiation absorber
Catalyst support
Structured heat exchanger
Porous burner
Flexural tests have been conducted on both
random and lattice structures in order to better
understand their mechanical behavior.[8]
Acoustical Emission (AE) and Electrical
Resistance (ER) were recorded during the tests
to gain more information on the fracture of
samples. Data were processed using Weibull
statistics. AE and ER monitoring techniques
show to be very practical means to detect the
crack initiation in these foams. AE and ER
monitoring techniques show to be very practical Weibull distribution for bending strength,
σ, of three different random foam. S
means to detect the crack initiation in these
represents the probability of survival.
foams.
An increased amount of Si in the material resulted in higher strength, favouring SiSiC foams, especially if passive oxidation conditions are met and therefore excess
silicon oxidation is mitigated at high temperatures.
Sandwich structures
Manufacturing Si-SiC foams
Si-SiC open-cell foams are produced by EngiCer,
Switzerland. A Replica technique followed by Si
infiltration is used.
In the case of lattice structures the polymeric
template is designed using a parametric MATLAB
code and then manufactured using a 3D printer.
The final product is a macro-porous reticulated
ceramic, microscopically made of reaction bonded
β-SiC, α-SiC powders, Si, and a low amount of
residual carbon.
3D surface rendering of a 5 PPI SiSiC foam(rel. density 0.15) using
structural data obtained by X-ray
computed tomography with
resolution of 30 μm.
AE and ER measurements in complete correlation with load cell results.
Thermal conductivity
Numerical simulations show the influence of cell
morphology on thermal conductivity and
mechanical properties of reticulated ceramic
foams. We used tetrakaidecahedron cells to
approximate the real foam structures.[4-5]
Effective thermal conductivity, effective elastic
modulus and stress concentration factor are
calculated using a parametric study considering
foams with different porosities, cell inclination
angle, and ligament tapering. [6-7]
DAQ
Mechanical and thermal simulations
Heater
Power
Supply
CONTROLLER
From left to right in order, CAD model of lattice structure, 3D
printed and final Si-SiC lattice.
Effective thermal conductivity of lattices and foams are measured using a custommade experimental set-up. Cubic specimen are placed between two plates held at
constant temperatures. The thermal conductivity is measured after the system
reaches steady state. The results show good agreement with the numerical analysis.
Chiller
Test set-up to measure effective thermal
conductivity in lattices and foams
Influence of cell inclination angle, ϴ
on effective elastic modulus, Eeff,
for different relative densities, d.
Thermal conductivity of foam samples
after oxidation in 1600⁰C in air.
Conclusions
Si-SiC porous ceramics are special materials with unique properties that find
applications in very high temperatures (above 1000°C).[2] However due to their
complex geometry, new methods must be developed to give the possibility of a fully
coupled thermo-mechanical analysis.
Acknowledgement
Real foam structures are often modeled by
tetrakaidecahedron cells. Left: One cell of the real foam.
Right: Tetrakaidecahedron cell.
Influence of cell inclination angle, ϴ,
on effective thermal conductivity Ke,
for different porosities, ɛ.
In cooperation with CTI Swiss Competence Centers for Energy Research (SCCER Heat
and Electricity Storage). We thank EngiCer for technical assistance and for
manufacturing the specimen.
References:
[1] A. Ortona, T. Fend, H. W. Yu, K. Raju, P. Fitriani, D.H. Yoon, Solar Energy Materials and Solar Cells, 132, 123-130 (2015)
[2] S. Gianella, D. Gaia, A. Ortona. Advanced Engineering Materials 14 (12): 1074–81. (2012)
[3] T. Fend, Thomas. Optica Applicata 40.2 , 271-284. (2010)
[4] Zhu, H. X., J. F. Knott, and N. J. Mills. Journal of the Mechanics and Physics of Solids 45.3, 319-343. (1997)
[5] Van der Burg, M. W. D., Shulmeister, V., Van der Geissen, E., Marissen, Journal of Cellular Plastics, 33(1), 31-54 (1997)
[6] C. D’Angelo, A. Ortona, P. Colombo. Acta Materialia 61 (14): 5525–34. (2013)
[7] C. D’Angelo, A. Ortona, P. Colombo. Acta Materialia 60 (19): 6692–6702. (2012)
[8] E. Rezaei, G. Bianchi, S. Gianella, A. Ortona. Journal of the European Ceramic Society, 34(10), 2133-2141.

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