A Microstructure-Based Time-Dependent Crack Growth Model for Life and Reliability Prediction of Turbopropulsion Systems
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HOT-SECTION components in advanced turbopropulsion systems are expected to operate at higher heat dwell conditions for longer time durations than those in current service conditions. Under high heat dwell environments, advanced Ni-based superalloys intended for engine disk applications may be susceptible to the occurrence of concurrent time-dependent damage modes such as creep, stress corrosion, and stress rupture in additional to cycle-dependent fatigue crack initiation and growth, which often manifest synergetic interaction effects on crack growth rates. Current life-prediction methodologies, however, generally do not treat synergetic interactions of multiple damage modes on component life reliability. Thus, there is a need to develop a probabilistic time-dependent fracture mechanics analysis capability for treating multiple damage modes in advanced Ni-based alloys for operations with long duration at high temperatures where time-dependent degradation mechanisms such as creep, oxidation, corrosion, and stress rupture may compete with timeKWAI S. CHAN, Institute Scientist, MICHAEL P. ENRIGHT, Staff Engineer, and JONATHAN MOODY, Research Engineer, are with the Southwest Research Institute, San Antonio, TX 78238. Contact e-mail: [email protected] SIMEON H.K. FITCH, Director, is with the Elder Research Inc., Charlottesville, VA 22903. Manuscript submitted April 1, 2013. Article published online September 5, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
independent fatigue crack growth as the component lifelimiting mechanism. To address this technology need, Elder Research Inc. (Elder), Charlottesville, VA, and Southwest Research Institute (SwRI), San Antonio, TX, conducted a methodology development program,[1] which focused on modeling the effects of competing time-dependent damage modes including creep, stress corrosion, and stress rupture on long-term performance and reliability of engine disks made from Ni-based superalloys that could exhibit location-specific microstructures, microstructural variability or evolution of microstructures after thermal exposures at elevated temperatures for extended time periods. One particular damage mode of interest was stress corrosion in the form of environmentally-enhanced crack growth, schematically shown in Figure 1, caused by ingress of oxygen and material degradation by oxide formation along grain boundaries. A generic fracture algorithm for treating time-dependent crack growth (TDCG) was integrated with a commercial probabilistic life-prediction code, called DARWIN,[2] to complement a suite of existing capabilities including finite element analysis tools, fracture mechanics analysis tools, and reliability analysis tools. This enhancement was utilized to demonstrate the potential use of such an analysis tool for estimating part life and reliability of a turbo engine subjected to aggressive mission profiles that contain long durations at high peak and dwell temperatures, which could lead to time-dependent damage modes such as creep, corrosion, and stress rupture. VOLUME
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