Stress relaxation properties of prestressed steel wires

In this study, stress relaxation phenomenon has been examined generally. Experiments were carried out on carbon steel wires with diameter 8 mm which are particularly used in prestressed concrete composites. Thermomechanically heat treatment was also carried out on this wire in order to relieve the residual stresses accumulated after the cold work. The heat treatment temperature and the stretch ratio, which are the parameters of thermomechanical heat treatment, were changed. Thermomechanical heat treatment experiments have been performed under two separate groups. In one of the groups, stretch ratios were changed at a constant temperature of 350 °C. In the other group, the heat treatment temperature was changed while the strain ratio was constant at 40%. The optimum thermomechanical heat treatment conditions have been determined by changing the heat treatment temperature and stretch ratio and by observing the effect of these changes of tensile stress and stress relaxation behaviour of the cold drawn steel wires. It is not always feasible to perform stress relaxation experiments in long periods of time as 1000 h. The general conditions of the laboratories are not suitable to permit this period of time. In this study, the results of the relaxation experiments are emphasised with empirical formulas.