Efficient and Accurate Methods for Probabilistic Analysis of Titanium Rotors

Abstract

Fan and compressor rotors and disks in aircraft jet engines use titanium alloys. Hard alpha (HA) anomalies, which may occur during the manufacturing process, can reduce rotor structural integrity and in rare cases cause catastrophic failures. To address this low-probability but high-consequence design issue, a methodology and a computer program, DARWIN 1 (Design Assessment of Reliability With INspection), have been developed to compute the probability-of-fracture as a function of flight cycles. It considers random HA defect occurrence and location, random inspection schedules, and several other random variables. This paper summarizes the probabilistic methods developed for DARWIN. DARWIN Probabilistic Analysis Methodology To increase aircraft safety, the FAA, working closely with the engine industry, has developed supplemental design and lifing methods that have formed the basis for an ongoing TRMD (Turbine Rotor Material Design) research program [Leverant et. al., 1999 & McClung et. el., 1999]. One of the objectives of TRMD is to develop a damage tolerance based probabilistic design code which integrates finite element stress analysis, fracture mechanics analysis, non-destructive inspection simulation, and probabilistic analysis to assess the risk of rotor fracture with in-service inspection. Given an initial hard alpha (HA) anomaly in a disk, the defect size and the stress intensity factor K will increase as a function of flight cycles. Failure occurs when the maximum K exceeds the fracture toughness K C , i.e., gt =