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

Gorash, Yevgen and Mackenzie, Donald (2014) Cyclic yield strength in definition of design limits for fatigue and creep. Proceedings in Applied Mathematics and Mechanics, PAMM, 14 (1). pp. 365-366. ISSN 1617-7061

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    Abstract

    This study proposes a cyclic yield strength (CYS, σc ) 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, σm ) is defined on a monotonic stress-strain curve. Both values of σc and σm are identified using a 2-steps fitting procedure of the experimental stress-strain curves using Ramberg-Osgood and Chaboche material models. Comparison of σc and fatigue endurance limit σf 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 σc . A typical creep rupture curve in time-to-failure approach for creep analysis has 2 inflections corresponding to the σc and σm . 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 σc . These assumptions are confirmed for several structural low- and high-alloy steels for normal and high-temperature applications.