Influence of asymmetric cyclic loading on substructure formation and ratcheting fatigue behaviour of AISI 304LN stainless steel

Abstract: The aim of this report is to examine the nature of accumulation of ratcheting strain (ɛ r) vis-à-vis in situ substructural and microstructural variations in 304LN stainless steel under varied asymmetric cyclic loading (ACL) conditions. For this purpose, a series of ACL experiments have been carried out on cylindrical tensile specimens under different combinations of mean stress (σ m) and stress amplitude (σ a). In one set of experiments, σ m has been varied between 50 and 150MPa keeping σ a constant, while in a second set σ m has been kept constant and σ a is varied between 300 and 400MPa. From the results it can be inferred that ɛ r increases from cycle to cycle for ACL tests and the phenomenon is considered to be governed by the associated mechanics and mechanisms of deformation. Fatigue life of a specimen can either increase or decrease depending upon the test condition, which induces different variations in dislocation density, sub-grain size or micro-damage formation. [ABSTRACT FROM AUTHOR]