LIPS (LIFE PREDICTION SOFTWARE) is a computer program for predicting the life of an object that is made of a unidirectional-fiber/metal-matrix composite (MMC) material and that is subjected to mechanical loading along the fiber direction. The program is derived from a theory formulated to be consistent with the experimental observation that progressive fiber fracture (more precisely, successive fractures of different fibers) is a dominant damage mechanism that leads to failure in MMCs. This theory is fundamentally different from other theories in which the effects of broken fibers are represented by artificially reducing the moduli of the fibers. In the present theory, progressive fiber fracture is addressed via a fiber-fracture criterion based on a statistical distribution of fiber strength.

The fiber material is assumed to be isotropic and linearly elastic at all temperatures. For the matrix material, one can use any constitutive model of elastic-viscoplastic, creep, or viscoplastic behavior. In the special case of a composite material in which all the fibers are intact and the inelastic-strain rate of the matrix material can be expressed in a simple power-law form, the theory yields a closed-form expression for the strain in the composite material

LIPS is a Windows™-based application program designed for convenience of use by engineers. It affords considerable flexibility for selection of input and for interpretation of output.

LIPS consists of three modules — denoted the material data-base, analysis, and postprocessor modules. The data-base module contains tables of temperature-dependent properties of fiber and matrix materials. Drop-down-menu controls enable the user to classify a material as elastic, elastic-plastic, or elastic-viscoplastic. The user can select or modify properties of materials already in the data base, and can define new materials for the data base and specify their properties. The user can gain access to the material data-base module both before and after entering the analysis module.

The analysis module enables the user to provide the input data necessary for using the progressive-fiber-break model implemented by the program. The analysis module also provides access to the postprocessor module.

The postprocessor module affords basic capabilities for displaying the results of computations in graphical form and for printing the results in graphical or textual form. This module provides a postprocessing window, within which there are several pull-down menus that enable the user to select data for plotting, change a previously generated graph, and/or print a graph. The user can also open two results-of-computation or experimental-data files at the same time and compare the results on the same plot.

This work was done by Jalees Ahmad of Research Applications, Inc., for Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Materials category.

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,
Cleveland, Ohio 44135.

Refer to LEW-16835.


NASA Tech Briefs Magazine

This article first appeared in the March, 2000 issue of NASA Tech Briefs Magazine.

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