Combined Axial Stress Fatigue Reliability for AISI 4130 and 4340 Steels

The failure-governing strength distributions of round specimens are determined. These are subjected to a mean tensile axial stress onto which alternating tensile and compressive axial stresses are superimposed. The AISI 4340 steel specimens are tested for a life of 10⁶ cycles and the AISI 4130 steel specimens for 2 × 10⁶ cycles. Distributional Goodman diagrams are developed and various combined-stress theories are compared with the experimental results. The application of the probabilistic “Design-for-Reliability” methodology utilizing these design data is illustrated by two examples. This methodology leads to improved design and to the determination of the reliability of mechanical parts and components subjected to such combined axial fatigue loads.