Practical And Technical Challenges Of The Exhaust System Fatigue Life Assessment Process At Elevated Temperature

Download or read book Practical and Technical Challenges of the Exhaust System Fatigue Life Assessment Process at Elevated Temperature written by Mark T. Seitz and published by . This book was released on 2017 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exhaust system durability and reliability assessments are challenging due to the inherent complexities of mechanical, thermal, and chemical interactions, and the variability associated with material properties, loading, and environment. The traditional methodology for predicting exhaust system durability and reliability was developed to provide a pragmatic, conservative, and economically viable solution--hence, the predominance of fatigue life approximations in cold or ambient conditions. Through the definition of target loading using measured field data collection, and determination of component durability capability through simple uniaxial or biaxial oscillating load bench tests, system level life assessment is possible. Exhaust system durability and reliability estimates conducted in cold conditions require that the life prediction method include a level of conservatism to account for actual field usage thermal conditions. The ability to bypass the engine out hot exhaust gas has become increasingly difficult due to the elimination of standard exhaust manifold designs. Some designs require the converter inlet pipes to be directly attached to the engine head without any exhaust manifold present. The natural progression in exhaust system durability assessment is to conduct all measurements inclusive of engine out elevated temperature conditions and to conduct component oscillating load bench testing at elevated temperatures. There are many challenges associated with the development of a robust life assessment methodology encompassing actual vehicle usage environmental conditions of an exhaust system. In this paper, work conducted to evaluate new process integration, encompassing high-temperature life assessment, is introduced. Oscillating load bench tests are conducted to develop allowable load-life curves, the methods of strain calibration for hot gages explored, and the method for conversion of load-life curves to local hot strain life curves conducted. The critical aspects of the assessment process, such as the determination of the thermal modification factor and the procedure for transforming a loading profile into a damage equivalent form at an equivalent temperature for rainflow counting, are explored. The assumptions, limitations, and viability to integrate these into the standard design and development process are evaluated.