The Features of Fatigue Resistance of Critical Members Steels under High Stress Ratio

ENG: From the standpoint of risk analysis and the concept of safety, the authors propose a new interpretation of critical members. Their performance determines the level of losses during the operation of mechanical systems. Therefore, it is advantageous to make critical members from high-strength steels that are sensitive to most influencing factors. Elements made of high-strength steels suffer from cyclic load with high stress ratio. In this aspect, cylindrical samples of heat-treated 09Cr16Ni4Nb and 13Cr15Ni4Мо3 steels were tested for tensile fatigue. The test results were presented in the form of a lifetime equation. Smith diagrams in coordinates were obtained by simple transformations from lifetime equation. These graphs showed a slightly anomalous concave shape instead of the expected convex shape. This indicates a loss of sensitivity to mean stress at high stress ratio. The authors explain this phenomenon from the standpoint of the merging of fatigue and fracture mechanics concept. Interestingly, a similar form was obtained for the graph of the dependence of the critical cyclical SIF on stress ratio. That is, the sensitivity of cyclic toughness to the value of the stress ratio decreases as it increases.

ENG: From the standpoint of risk analysis and the concept of safety, the authors propose a new interpretation of critical members. Their performance determines the level of losses during the operation of mechanical systems. Therefore, it is advantageous to make critical members from high-strength steels that are sensitive to most influencing factors. Elements made of high-strength steels suffer from cyclic load with high stress ratio. In this aspect, cylindrical samples of heat-treated 09Cr16Ni4Nb and 13Cr15Ni4Мо3 steels were tested for tensile fatigue. The test results were presented in the form of a lifetime equation. Smith diagrams in coordinates were obtained by simple transformations from lifetime equation. These graphs showed a slightly anomalous concave shape instead of the expected convex shape. This indicates a loss of sensitivity to mean stress at high stress ratio. The authors explain this phenomenon from the standpoint of the merging of fatigue and fracture mechanics concept. Interestingly, a similar form was obtained for the graph of the dependence of the critical cyclical SIF on stress ratio. That is, the sensitivity of cyclic toughness to the value of the stress ratio decreases as it increases.