Some Studies on the Stress Relaxation Behavior of Prestressed Wire

Abstract

This paper presents the experimental results of the relaxation behavior of three types of prestressed wires under various testing conditions including variations of the initial stress, temperature, stressing time prestretching. Also presented are brief discussions on the mechanism of stress relaxation of the steel and the application of the metallurgical theory to the relaxation behavior of the prestressed wire under actual conditions.
The mechanism responsible for the decrease of stress relaxation loss in the prestressed wire the reduction of the number of mobile dislocations by either the realignment of dislocation due to cell formation or the strain aging due to free carbon and nitrogen atoms.
In practice, the low stressing rate and long prestretching time give smaller relaxation loss than the other conditions because the number of mobile dislocations decreases. When the strain fluctuates, the apparent relaxation loss is smaller than the pure relaxation loss under a constant strain. It is, therefore, necessary to take into consideration the decrease of the mobile dislocations during the stress relaxation under a constant strain before the strain start to fluctuate.