Abstract:

ESDU 04022 introduces the basic equations of low-cycle fatigue analysis, and some of the limitations of their usage. Both the strain-life relationship (otherwise known as the Coffin-Manson equation) and the cyclic stress-plastic strain equation are derived. The effects of mean stress on the strain-life relationship and the methods of correcting for these proposed by Morrow, Manson and Halford are discussed, as are the transition fatigue life and the Bauschinger effect. The cyclic hardening and softening behaviour of metallic materials during cycling and their stress and strain response at different test temperatures (including the effects of oxidation, creep-fatigue interaction, dynamic strain ageing, cold creep or "time-dependent plasticity", and martensite transformation during cycling) are also considered. The Data Item includes a section on low-cycle fatigue testing procedures and the pit-falls and uncertainties encountered during such testing. Procedures to determine the onset of failure and guidance on the design of LCF test pieces are presented with reference to contemporary standards. In addition, the Item discusses methods of estimating low-cycle fatigue properties that can be used when limited data are available; two comprehensive examples which illustrate the use of these methods are provided.