Detailed Assessment of Fatigue Life: A Critical Review

For the construction, design and operation of technical components and systems the appropriate technical codes and standards provide detailed stress analysis procedures, material data and a design philosophy which guarantees a reliable behaviour of the structural components throughout the specified lifetime. Especially for cyclic stress evaluation the different codes and standards provide different fatigue analyses procedures to be performed considering the various (specified or measured) loading histories (of mechanical and thermal origin) and geometric complexities of the components. In order to fully understand the background of the fatigue analysis included in the codes and standards as well as of the fatigue design curves used as a limiting criteria (to determine the fatigue life usage factor), it is important to understand the history and the methodologies which are available for the design engineers. In the paper the different fatigue analysis procedures in the technical codes and standards (e.g. ASME-III, KAT 3201.2, prEN 13445-18) are discussed in detail. The most important parameters influencing the fatigue analysis, like plastification factor K_e, the correction factors with respect to mean stress, to surface finish, to tempeature, to the environment and to unwelded and welded components are verified on the basis of experimental results. Thus safety margins relevant for the assessment of fatigue life are shown and compared with the safety factors implemented in the different technical codes and standards.