Continuous fiber ceramic composite materials (CFCCs) are being considered for an increasing number of commercial applications. They provide the potential for lighter, stronger, more corrosion-resistant components that can perform at higher temperature for long periods of time. Global competitiveness demands a shortening of the time for CFCC commercialization. Thus, considerable efforts has been expended to develop and improve the materials, and to a lesser extent, to develop component design methods and data bases of engineering properties. To shorten the time to commercialization, project efforts must be integrated, while balancing project resources between material development and engineering design. Currently a good balance does not exist for most materials development projects. To rectify this imbalance, improvements in engineering design and development technologies must be supported and accelerated, with a focus on component issues. This will require project managers to give increasing emphasis to component design needs in addition to their current focus on material development.
The need for improved performance in high temperature environments is prompting industry to consider the use of structural ceramic materials in heat exchanger tubes and other high temperature components. In recognition of this need, the U. S. Department of Energy has supported work for the development of nondestructive methods for evaluating flaws in monolithic ceramic components, and the associated establishment of criteria for the acceptance of flawed components. Under this development of flaw assessment criteria, DOE supported the work being presented in this paper.
The approach to developing the life prediction model combines finite element predictions, considering creep behavior, with continuum damage mechanics and Weibull reliability statistics. ABAQUS is used to predict time dependent creep response of the component based on experimental creep data. A continuity parameter is then calculated at each time step following continuum damage mechanics methods. Finally, Weibull statistics are used with the resulting continuity parameter to predict the reliability at each time step, through the use of the NASA-Lewis computer program CARES, interfaced to ABAQUS with ABACARES.
There is very limited data available to characterize the creep, continuum damage and reliability behavior of the material. For the life prediction model reported, it is assumed that the material damages isotropically. Directional effects of the damage can be added as material databases improve.
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