On Using Stress Relaxation Tests to Characterize Material Behavior

Abstract

Stress relaxation tests, in which the gage length of the specimen was maintained constant by servocontrol, were performed on 2618-T61 aluminum. The test results, which were independent of the stiffness of the testing machine, were converted into a relation between stress and inelastic strain rate. It was found that the contribution by the anelastic component to the total stress relaxation was significant only in the initial stage. The validity of using the obtained stress versus inelastic-strain-rate relation to characterize the material behavior is also discussed. Results do not substantiate the concept of a “hardness” flow curve, but data were well predicted from the creep data by theory based on strain hardening and viscoelasticity.