Modelling transient behavior during stress relaxation

Stress relaxation test is widely used to estimate activation parameters during plastic deformation. The one-dimensional theoretical models used to predict the stress relaxation behavior uses the Orowan rate equation to derive the stress drop as a function of time. Classical models assume that the average mobile dislocation density and internal stress remain invariant during the test. Although subsequent works have extended the original models, the treatment is still incomplete. In the present work, two of the existing stress relaxation models, power law model and logarithmic model are analyzed using the experimental data obtained from SS 316. The models are modified based on the understanding of mechanics of deformation mechanism during stress relaxation. The modified power law model was found to be inconsistent mathematically whereas the modified logarithmic model was found to improve the accuracy of prediction.