The Influence Of Strain Path On Mechanical Behaviors Of Steel 907A

Mechanical behaviors of steel 907A under monotonic tension, monotonic torsion, torsion-tension, tension-torsion, tension-torsion-tension strain paths were studied by standard cylinder specimen in this paper.The results indicate that the shear yield stress of the steel derived according to GB10128-88 in torsion test was not in accordance with either Mises or Tresca yield criterions, and the relative error was separately 30% and 50%. In this paper, a new method of determining yield torque of idealized elastic-plastic material was made out, the shear yield stress of the steel determined by which was well consistent with these two yield criterions, and the relative error was only 2.6% and 12.4%.When effective stress-effective strain coordinate axis was used, stress level of monotonic tension was higher than that of monotonic torsion. Multiple n behavior was observed in not only S-ecurve but also r-ycurve of the steel when used double logarithmic coordinate axis. In addition, the second hardening stage of T-y curve came later than that of 5-ecurve.Under torsion-tension and tension-torsion-tension strain paths, in the final tension stage, the true stress-strain curves would not longer accord with Hollomon equation because of the inhomogeneous strain hardening level in the cross section caused by pre-torsion. A method of calculating the hardening curve in the subsequent tension stage after homogeneous pre-shear strain in solid cylinder specimen was made out in this paper.Under torsion-tension and tension-torsion-tension strain paths, in the subsequent tension stage, both yield stress and ultimate tensile strength increased, especially the latter strain path, while ductility decreased with the increase of pre-straining value. In torsion-tension experiments, there was a pronounced loss in the ductility for the final tension stage when transition strain was higher. When prestrain reached a critical value, fracture type would change from plastic to brittle.In this paper, total plasticity was used to characterize the sum of the plasticity exhausted under every one of strain path. There was a maximum value in the total plasticity-prestrain curve of the steel not only in torsion-tension but also in tension-torsion-tension cases. Both maximum values of total plasticity in the cases were higher than the plasticity under monotonic loading strain path.The tension-torsion experiment led to an initially increased flow stress in the final torsion stage, as compared to the fully monotonic torsion experiment. Then, the flow curve of the subsequent torsion stage tends to that of the monotonic torsion. After a strain of about 0.22, torsion strain eliminated the previous tension effects.