Fatigue of a highly prestrained dual-phase sheet steel

The effect of prestraining by 15-30% and ageing on the fatigue properties of a cold-rolled high-strength dual phase sheet steel was investigated. Prestraining was performed before machining the fatigue specimens and was carried out in uniaxial as well as biaxial tension. Fatigue testing was carried out under fully reversed strain control and both the cyclic stress-strain behaviour and the fatigue lives were recorded. Significant fatigue strength improvements by up to 50% were noted for the prestrained material as compared to the as-received condition. During fatigue testing in uniaxially prestrained conditions, the occurrence of mean stresses was noted. These mean stresses were persistent when testing at levels corresponding to longer fatigue lives. Taking into account an estimation of these mean stresses and the increase of monotonic strength, modelling of fatigue resistance for the prestrained materials shows fairly good correlation with experimental results.