Low cycle stress strain curves and fatigue under tension-compression and torsion

Abstract

The presented paper analyses low cycle fatigue of the grade 45 steel under stress and strain controlled low cycle tension-compression and torsion.
It was determined, that analysed material is cycli-cally stable, in both the tension-compression and torsion cases, because the parameter α = 0. The shape of the stress strain diagrams for both the analysed loading cases is simi-lar, as parameters A are similar for the tension-compression and the torsion. During the cyclic torsion, under stress lim-ited loading, the accumulation of plastic strain is not observed, i.e. quasistatic damage does not occur. The analyti-cal dependences applied for the fatigue damage calculation showed good agreement with the cyclic torsion data, since the theoretical fatigue curve for cyclic torsion showed good agreement with the experimental curve for the stress limited case – and is close to the theoretical fatigue curve under stress limited cyclic tension-compression loading, when estimating only fatigue damage.
This shows, that under cyclic torsion, the durabil-ity (in σi – Nc coordinates) is higher than the durability under cyclic tension-compression, because in this case the plastic strain is not accumulated, i.e. the quasistatic dam-age does not occur.