Probabilistic Ceramic Matrix Composite Analyzer (PCEMCAN) is a user-friendly computer program that predicts uncertainties in the mechanical and thermal properties of ceramic-matrix composite (CMC) materials. These materials are candidates for fabrication of structural components that will be required to withstand loads at high temperatures in advanced aircraft engines. PCEMCAN is intended to help researchers develop improved CMCs for aircraft-engine components and to help engineers assess reliability and assure long operational lifetimes for those components.
PCEMCAN is an integrated computer code that embodies a combination of:
- the formal probabilistic methodology of CEMCAN [reported in "CEMCAN - Ceramic Matrix Composites Analyzer" (LEW-16327), NASA Tech Briefs, Vol. 21, No. 5 (May 1997), page 32]; and
- the fast probability integration (FPI) technique [reported in "Probabilistic Analysis of Composite-Material Structures" (LEW-16092), NASA Tech Briefs, Vol. 21, No. 2 (February 1997), page 58].
Micromechanical and macromechanical theories as implemented in CEMCAN are used to predict the strengths and other properties of CMCs. Uncertainties in primitive variables are provided as input to PCEMCAN in the form of means, standard deviations, and types of probability distributions that characterize those uncertainties. The types of probability distributions available in PCEMCAN include normal, Weibull, and log-normal.
The probabilistic integration of random primitive variables is performed by use of the FPI technique. Fewer computational simulations are needed to determine the scatter in response variables (e.g., properties of plies and laminates) when using the FPI technique than when using the Monte Carlo technique. PCEMCAN expresses the scatter in the response variables in the form of cumulative probability distribution functions (CDFs), which are useful for probabilistic analyses of structures and assessments of degrees of reliability of components. PCEMCAN also quantifies the sensitivities of the response variables to the random primitive variables.
More specifically, for given scatter of properties of fibers, properties of matrix and interphase materials, fiber volume ratio, ply thickness, and other primitive variables, the response variables (properties of the composite material) for which CDFs can be computed include the modulus of elasticity, Poisson's ratio, coefficients of thermal expansion, thermal conductivity, and laminate failure strength. PCEMCAN also computes the means, medians, and standard deviations of response variables.
These results can be used in probabilistic structural analysis to compute the reliability of a component or to asses the life of the component for a desired reliability. Sensitivity information can be used to increase reliability and to improve manufacturing processes and quality control. Finally, the probabilistic approach of PCEMCAN is beneficial in reducing the number of experiments needed, reducing (relative to the deterministic approach) the degree of conservatism in the design of a component, and making material-development and design processes more cost-effective.
This work was done by Pappu L. N. Murthy of Glenn Research Center, Ashwin R. Shah of Sest, Inc., and Subodh K. Mital of the University of Toledo.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 - 8
21000 Brookpark Road
Refer to LEW-16653