Thermomechanical Property Data Base Developed for Ceramic Fibers

For application conditions under which the fibers display time-dependent mechanical behavior, tests measured fiber creep, rupture, and stress relaxation properties under constant temperature and stress (or strain) for up to ~100 hr (ref. 1). Because of the many test variables in such studies, mechanism-based analytical models (ref. 2) were developed for these properties. Such models not only allow accurate interpolation of time, temperature, and stress effects within the data set, but also permit prediction of fiber behavior outside the data set (see figure). This modeling capability is particularly important for the time variable because fiber test times are generally much shorter than the service lives required for some advanced heat engine components (>10^4 hr).

Currently, the thermomechanical property data base and models for a variety of ceramic fibers are publicly available in numerous reports, publications, and review papers (refs. 3 and 4). For component developmental programs outside and within NASA (Enabling Propulsion Materials (EPM) and the Advanced High Temperature Engine Materials Technology Program (HITEMP)), these results are being used by composite designers and fabricators to select the optimum fiber for each application and also by the fiber manufacturers to understand and improve fiber performance. Research at Lewis is continuing in order to expand the data base and improve the property models, particularly for those fiber types with the most technical potential.

Creep and rupture strengths of Hi-Nicalon silicon carbide fibers for service lives of 10^2 and 10^4 hr. Symbols indicate actual data points and lines indicate predictions from property models.

References

1. DiCarlo, J.A.: Property Goals and Test Methods for High Temperature Ceramic Fiber Reinforcement. Adv. Sci. Tech. 1995, vol. 7, 1995.

2. DiCarlo, J.A., et al.: Models for the Thermostructural Properties of SiC Fibers. High Temperature Ceramic-Matrix Composites I, A.G. Evans and R. Naslain, eds. Ceramic Trans., vol. 57, American Ceramic Society, 1995, pp. 343-348.

3. Tressler, R.E.; and DiCarlo, J.A.: Creep and Rupture of Advanced Ceramic Reinforcements. High Temperature Ceramic-Matrix Composites II, A.G. Evans and R. Naslain, eds. Ceramic Transactions, vol. 57, American Ceramic Society, 1995, pp. 141-155.

4. DiCarlo, J.A.; and Dutta, S: Continuous Ceramic Fibers for Ceramic Composites. Handbook on Continuous Fiber-Reinforced Ceramic Matrix Composites, chapter 4, R.L. Lehman, S.K. El-Rahaiby, and J.B. Wachtman, eds. Purdue University (West Lafayette, IN), 1995.