Preeti Verma

Influence of Heat Treatment on Ratcheting Fatigue Behavior and Post Ratcheting Tensile Properties of Commercial Aluminum

The objective of this work is the study of ratcheting fatigue behavior and post fatigue tensile properties of the commercial aluminum via heat treatment like annealing and normalizing. In view of this, stress controlled fatigue tests carried out at room temperature up to 150 cycles under different combinations of mean stress and stress amplitude using a servo-hydraulic testing machine. It is found that in both annealed and normalized conditions, accumulation of ratcheting strain increases with increasing stress parameters. Strain accumulation in normalized condition is less due to increased dislocation density during asymmetric cyclic loading. In normalized, the saturation in strain accumulation was also achieved earlier as compared to annealed due to attainment of stable dislocation configuration. It has been noticed that the Post fatigue tensile strength enhances while the ductility decreases with increasing stress parameters because of cyclic hardening. Fractographic studies have demonstrated that dimple size decreases with increasing strain accumulation.

Cyclic Deformation Behavior of Modified 9Cr–1Mo Steel at Elevated Temperatures

Modified 9Cr–1Mo steel exhibited dynamic strain ageing (DSA) in the temperature range from 523 to 673 K and it was established on the basis of plateau/peak in yield and tensile strength, minima in ductility and serrations in stress–strain curve. High density of dislocations and typical features like dislocation debris, kinks and bowing of dislocations was observed in the regime of DSA. This steel exhibited cyclic softening irrespective of the strain amplitude, strain rate, and temperature. The observed cyclic softening is associated with many factors like cell formation at room temperature and additionally annihilation of array of dislocations at 573 K, in addition to coarsening of carbides at 873 K.