Effect of Pre-strain and Pre-corrosion on Ratcheting Behavior of ASTM A668 Class D Steel

Abstract

Ratcheting can be considered as one of the serious problems as this phenomenon causes premature failure of structural components. Ratcheting deformation can be regarded as the stress controlled low cycle fatigue (LCF) response of a material which occurs due to accumulation of plastic strain during asymmetric cyclic loading. Ratcheting is dependant on various parameters like material chemistry, stress states and environmental issues. The aim of this investigation was to study the effect of pre-strain (0%, 2%, 4% and 8%) on ratcheting in different heat treated conditions (normalized and hardened-tempered). The effect of pre-corrosion (7, 14 and 21 days in 3.5% NaCl solution) on the nature and extent of strain accumulation was also studied. Ratcheting tests were carried out at room temperature on cylindrical specimens having 12.5 mm gauge length and 6 mm gauge diameter. The results include reduced strain accumulation with increasing pre-strain strain level due to work hardening of the pre-strained samples. Further cyclic hardening takes place during ratcheting deformation. Pre-corroded samples showed more amount of strain accumulation compared to the samples without corrosion. Post ratcheting tensile strength increases in all the tested samples owing to cyclic hardening during ratcheting. The factographic studies indicated typical dimple features.