Fatigue- Ratcheting Interaction Behavior of AISI 4340 Steel

Divya Bharathi, K (2015) Fatigue- Ratcheting Interaction Behavior of AISI 4340 Steel. MTech by Research thesis.



Ratcheting is known as accumulation of plastic strain during asymmetric cyclic loading of materials under non-zero mean stress. This study intends to investigate the ratcheting behavior in AISI 4340 steel which is mainly used for designing of railway wheel sets, axles, shafts, aircraft components etc. The effect of stress ratio on the ratcheting behavior in both annealed and normalised conditions, effect of previous low cycle fatigue deformation on ratcheting behavior and vice versa were investigated for investigated steel. Ratcheting tests were done at different stress ratios of -0.4, -0.6 and -0.8 and strain controlled low cycle fatigue tests were done at strain amplitudes of ±0.50 and ±0.75. The results showed that cyclic hardening takes place during ratcheting deformation while strain accumulation increases with increasing stress ratio. Prior fatigue deformation induces more ratcheting strain in the material under same magnitudes of stress ratios. Post ratcheted samples showed increase in tensile strength and hardness which increases with increasing stress ratio and these variations in tensile properties are correlated with the induced cyclic hardening. The X-ray diffraction profile analysis using the modified Williamson–Hall equation has been carried out in order to estimate the dislocation densities in the specimens subjected to both ratcheting and low cycle fatigue. Increase in strain accumulation has been explained by increase in dislocation densities in the specimens and a correlation between the strain produced by ratcheting deformation and the estimated dislocation density has been established.

Item Type:Thesis (MTech by Research)
Uncontrolled Keywords:Low cycle fatigue, Ratcheting, hardening behavior, optical microscopy, X-ray diffraction profile analysis, dislocation density
Subjects:Engineering and Technology > Metallurgical and Materials Science
Divisions: Engineering and Technology > Department of Metallurgical and Materials Engineering
ID Code:6912
Deposited By:Mr. Sanat Kumar Behera
Deposited On:11 Jan 2016 15:56
Last Modified:11 Jan 2016 15:56
Supervisor(s):Dutta, K

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