Mandar Chati

Cumulative Damage Modeling for Nickel-Based Superalloys Under Creep and Fatigue Loading

Turbine blades operating in aircraft engines are subjected to complex thermomechanical conditions that include a combination of very high temperatures, high stresses and aggressive oxidizing environments. As a result, such components can simultaneously experience damage from creep-, fatigueand oxidation-related mechanisms. Selected literature models were evaluated in their capability to predict the performance of single crystal nickel-based superalloys over a wide range of test conditions. Because existing models were not sufficiently accurate for commonly used superalloys such as Rene N5, a new cumulative damage model (CDM) was developed to account for the broad range of complex stress conditions and mission strain-temperature histories that can be experienced. The predictive capability of CDM has been assessed with solid and tubular specimens tested under both simple and complex thermal-mechanical conditions. The new modeling approach was also validated on test plans designed to be representative of a cooled, thin walled component loaded under engine-simulative conditions.

Fretting Fatigue Modeling and Repair Evaluation for Generator Rotors

Generator Rotor Tooth Cracks have been recently observed on some long service generator rotors. The purpose of this paper is to document the root cause analysis as well as a repair methodology that was developed in support of one of these cracked units. The paper discusses the development of a finite element model to understand the operating modes and failure mechanisms that caused the initiation of these cracks. The results of the analysis agreed very well with field observations on cracked units and with some limited repair options that have been successfully used in the past. An experimental fretting fatigue testing program is currently underway to substantiate and extend the results reported in this paper.Copyright