Mechanical properties of prestressing strands and how they tend to change under thermo-mechanical treatment

This paper examines the mechanical properties of high-strength (1,770 MPa) 7-wire prestressing strands and how they tend to change under thermo-mechanical treatment involving short-term induction tempering under high tension. The change dynamics of the following properties was monitored for 12.5 mm strands: tensile strength, yield strength, full elongation at maximum tension force and modulus of elasticity in the temperature range from 360 to 400 °С, the process speed range from 50 to 65 m/min, and at the tension force of 64 kN. The authors found a quantitative increase of the mechanical properties of prestressing strands for all the studied regimes of thermo-mechanical treatment. Thermo-mechanical treatment resulted in a significant growth in yield strength — from 28 to 36%, and in full elongation at maximum tension force, which demonstrated a higher than double growth. The paper shows how the temperature and rate of thermo-mechanical processing influence the mechanical properties of prestressing strands and their change dynamics.