Analysis of the coefficient of normal stress effect in chosen multiaxial fatigue criteria

The paper undertakes a comparison of the experimental and calculated fatigue lives by using criteria formulated by Findley, Matake and Dang Van for S355J2WP, S355J2G3 and 30CrNiMo8 steels. The considered criteria include the coefficient k (the coefficient of material sensitivity to the normal or hydrostatic stresses) which originally is related to the fatigue limits. It is shown that the value of k coefficient depends on the number of cycles to failure and better results are obtained using the proposed idea of calculating the k value for number of cycles specified for analysed steels than using the original concept of the fatigue limits. Analysis of the criteria consisted in comparison of the experimental and calculated results obtained for different values of the k coefficient determined for different number of cycles. The results of calculations were compared with the experimental results for cyclic bending, torsion and proportional combination of bending with torsion.