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Calibrations relating back-face strain (BFS) to crack length in precracked flexure specimens were developed for different strain gage sizes. The functions were verified via experimental compliance measurements of notched and precracked ceramic beams. Good agreement between the functions and experiments occurred, and fracture toughness was calculated using several operational methods: maximum test load and optically measured precrack length; load at 2% crack extension and optical precrack length; and maximum load and BFS crack length. All the methods gave comparable results. The initiation toughness, KIi, was also estimated from the initial compliance and load. The results demonstrate that the stability of precracked ceramic specimens tested in four-point flexure is a common occurrence, and that methods such as remotely monitored load-point displacement are only adequate for detecting stable extension of relatively deep cracks. [ABSTRACT FROM AUTHOR]

Reliable engine-weight estimation at the conceptual design stage is critical to the development of new aircraft engines. It helps to identify the best engine concept amongst several candidates. In this paper, the major enhancements to NASA's engine-weight estimate computer code (WATE) are described. These enhancements include the incorporation of improved weight-calculation routines for the compressor and turbine disks using the finite difference technique. Furthermore, the stress distribution for various disk geometries was also incorporated, for a life-prediction module to calculate disk life. A material database, consisting of the material data of most of the commonly used aerospace materials, has also been incorporated into WATE. Collectively, these enhancements provide a more realistic and systematic way to calculate the engine weight. They also provide additional insight into the design tradeoff between engine life and engine weight. To demonstrate the new capabilities, the enhanced WATE code is used to perform an engine weight/life tradeoff assessment on a production aircraft engine. [ABSTRACT FROM AUTHOR]