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Size Effect on the Strength of Ceramic Catalyst Supports
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Abstract
The typical ceramic catalyst support for automotive application has a total volume of 1640 cm3. Approximately 10% of this volume is subjected to tensile thermal stresses due to a radial temperature gradient in service [1]*. These stresses are kept below 50% of the substrate strength to minimize fatigue degradation and to ensure long-term durability [2]. However, the tensile strength measurements are carried out in 4-point bending using 2.5 cm wide x 1.2 cm thick x 10 cm long modulus of rupture bars in which the specimen volume subjected to tensile stress is merely 3.2 cm3 or 0.2% of the total substrate volume [3]. Thus, a large specimen population is often necessary (50 specimens or more) to obtain the strength distribution representative of full substrate. This is particularly true for large frontal area substrates for diesel catalyst supports with an order of magnitude larger stressed volume.
In this paper, the modulus of rupture data are obtained as function of specimen size. For example, in addition to the conventional 2.5 cm wide x 1.2 cm thick x 10 cm long specimens, the MOR data for ten different specimen sizes are presented. The stressed volume in these latter specimens is one to two orders of magnitude larger and hence representative of stressed volume in both the automotive and diesel catalyst supports in service. The new data show that the strength values are relatively insensitive to stressed volume indicating that the traditional specimen size for strength measurement is optimum in terms of specimen preparation, specimen testing and converter design. Only a large specimen population is necessary to obtain the complete strength distribution and to arrive at a safe design stress for long-term durability. In this manner, the high temperature fatigue data [4] based on 2.5 cm wide x 1.2 cm thick x 10 cm long specimens can also be used for estimating the allowable service stress to meet the required converter life. The present study shows that the measured strength can be significantly lower if shear deformation is a significant fraction of total deformation during bending as in the case of thick specimens. In such cases, a correction factor is necessary for obtaining the true strength from measured values.
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Authors
Citation
Gulati, S. and Reddy, K., "Size Effect on the Strength of Ceramic Catalyst Supports," SAE Technical Paper 922333, 1992, https://doi.org/10.4271/922333.Also In
References
- Gulati S.T. “Thermal Stresses in Ceramic Wall-Flow Diesel Filters,” SAE Paper No. 830079 February 1983
- Gulati S.T. “Long-Term Durability of Ceramic Honeycombs for Automotive Emissions Control,” SAE Paper No. 850130 February 1985
- Gulati S.T. et al. “Optimization of Substrate/Washcoat Interaction for Improved Catalyst Durability,” SAE Paper No. 910372 February 1991
- Helfinstine J.D. Gulati S.T. “High Temperature Fatigue in Ceramic Honeycomb Catalyst Supports,” SAE Paper No. 852100 October 1985
- Gulati S.T. “Design Considerations for Diesel Flow-Through Converters,” SAE Paper No. 920145 February 1992
- Griffith A.A. “The Phenomena of Rupture and Flow in Solids,” Phil. Trans. Royal Soc . London A221 1920
- Timoshenko S.P. Goodier J.N. Theory of Elasticity 2nd McGraw-Hill New York 1951
- Weibull W. “A Statistical Distribution Function of Wide Applicability,” J. App. Mech 18 1951
- Gulati S.T. Summers J.C. Linden D.G. White J.J. “Improvements in Converter Durability and Activity via Catalyst Formulation,” SAE Paper No. 890796 February 1989
- Gulati S.T. Sweet R.D. “Strength and Deformation Behavior of Cordierite Substrates from 70° to 2550°F;” SAE Paper No. 900268 February 1990
- Gulati S.T. Maret D. Lambert D.W. Zink U. “Systems Durability of a Ceramic Racetrack Converter,” SAE Paper No. 912371 October 1991
- Gulati S.T. “Physical Durability of Catalyst Supports in Harsh Environments,” 25th ISATA Conference Florence, Italy June 1992