Experimental and Theoretical Study on Stress-Strain Fatigue Properties of High-Strength Steel Bars

In order to compare the fatigue characteristics of high-strength steel bars with that of HRB400 steel bars, the allowable stress amplitudes of HRB600E and HRB500E steel bars were obtained through stress and strain fatigue tests, and the effects of diameters of steel bars and fatigue loading frequencies on the allowable stress amplitudes were analyzed; the stress-strain cycling properties of high-strength steel bars under constant-amplitude strain fatigue were studied and Coffin-Manson and Hollomon formulas and three-parameter fatigue formulas were established. Energy dissipation toughness was used for the first time to evaluate the capability of steel bars to dissipate seismic energy during strain fatigue (or repeated earthquake action). The test showed that the low cycle fatigue life of strain and cycle toughness of HRB500E steel bars produced by V-N microalloying were better than those of HRB500E steel bars produced by V-N-N_b method; high-strength steel bars were of benefit to improving their fatigue lifes, allowable stress amplitudes and total energy dissipation toughness. The total energy-consuming toughness was related to the strain amplitudes, increasing the strain amplitude decreased the total energy-consuming toughness; the fatigue life of T63E high strength steel bars was longer than that of HRB400 steel bars under the same strain amplitude. Finally, the relation between the total strain amplitude and the loss coefficient of strength or the plastic strain range was established.