Cyclic yield strength in definition of design limits for fatigue and creep

This study proposes a cyclic yield strength (CYS, σ c y ) as a key characteristic for the definition of safe design for engineering structures operating under fatigue and creep conditions. CYS is defined on a cyclic stress‐strain curve, while monotonic yield strength (MYS, σ m y ) is defined on a monotonic stress‐strain curve. Both values of σ c y and σ m y are identified using a 2‐steps fitting procedure of the experimental stress‐strain curves using Ramberg‐Osgood and Chaboche material models. Comparison of σ c y and fatigue endurance limit σ f lim on the S‐N fatigue curve reveals that they are approximately equal. Hence, basically safe fatigue design is guaranteed in purely elastic domain defined by the σ c y . A typical creep rupture curve in time‐to‐failure approach for creep analysis has 2 inflections corresponding to the σ c y and σ m y . These stresses separate 3 sections on the creep rupture curve, which are characterised by 3 different creep fracture modes and 3 creep deformation mechanisms. Thus, basically safe creep design is guaranteed in linear creep domain with brittle failure mode defined by the σ c y . These assumptions are confirmed for several structural low‐ and high‐alloy steels for normal and high‐temperature applications. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)