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This paper presents a semi-graphical approach for finding the first critical speed of a stepped shaft with finite bearing stiffness. The method is particularly applicable to high-speed turbine rotors with journal bearings. Using Rayleigh's Method and the exact solution for whirling of a uniform shaft with variable support stiffness, estimates of the lowest critical speed are easily obtained which are useful in the design stage. First critical speeds determined by this method show good agreement with values computed by the Prohl Method for the normal range of bearing stiffness. A criterion is also established for determining if the criticals are "bearing critical speeds" or "bending critical speeds," which is of importance in design. Discusser E. G. Baker

The intent of this paper is to explain the basic theory and steps involved in performing a Weibull analysis of gas turbine component data. It is also to illustrate through practical examples, the application of the theory discussed and to demonstrate the versatility of performing Weibull analysis. Real-world applications will include using Weibull analysis to identify batch problems in fuel nozzle support housings and a method to determine if the thrust bearing wear rate is best fit with a three-parameter Weibull or a lognormal distribution. Also, a special technique will be described to determine if Weibull distributions for blade path and flashback thermocouple failures are significantly different failure modes.