The effect of 5% tensile pre-straining on the low cycle fatigue (LCF) behaviour of Inconel-718 (IN718) superalloy was studied at ambient temperature using fully reversed total strain controlled fatigue tests. For comparison, LCF tests were also carried out on the alloy in unstrained (baseline) condition. Tension-compression cyclic tests were carried out with strain ratio R = 1 and at a constant strain rate of 0.01s-1. The total strain amplitude varied from ±0.4 to ±1.2%. The low cycle fatigue results were analyzed to determine the cyclic stress-strain curves. The cyclic strain hardening parameters were evaluated from the cyclic stress–strain curves. Important fatigue parameters, namely fatigue ductility coefficient, fatigue ductility exponent, and fatigue strength coefficient, were evaluated for both cases. Analysis and comparison of the experimental results showed that the 5% tensile pre-strain causes significant reduction (almost ~50 %) in the fatigue life of the material. For both the baseline and 5% pre-strained material, the plastic strain amplitude in relation to fatigue-life plots exhibited a bilinear relationship. The geometry of hysteresis loops and the occurrence of Masing behavior were analyzed and it was found that the alloy in peak-aged condition exhibited a tendency towards Masing behavior.
Manikandan et al. (Wed,) studied this question.