Competitive giga-fatigue life analysis owing to surface defect and internal inclusion for FV520B-I

• An experiment for FV520B-I was carried out to investigate the competitive character of FV520B-I.
• Both surface and internal fatigue life models were obtained to investigate the yardstick of the fatigue competition.
• An empirical fatigue competition model for FV520B-I was established to analysis the competitive fatigue failure.
• The potential study on the competitive fatigue failure for FV520B-I was proposed.

Research of material giga-cycle fatigue shows that fatigue failure is caused by a comprehensive effect of the competition between surface defect and internal inclusion, and the competition is more significant with high strength steal FV520B-I. A clear understanding of fatigue failure mechanism can improve the accuracy of the fatigue life prediction for FV520B-I. There is currently no available fatigue-life model that describes the competition mechanism of giga cycle behavior for FV520B-I. In this paper, ultrasonic fatigue experiment is presented, which revealed the existence of the competition during the giga-cycle process. The giga-fatigue life prediction models for FV520B-I are established with the consideration of surface defect and internal inclusion. Based on fracture mechanics, the surface roughness is correlated to surface defect. The competition analysis is carried out on the basics of fatigue strength to obtain the critical defect value. The critical defect value is the direct criterion in practical engineering and the primary factor of final failure is determined by comparing the actual defect with the critical value. Then the competitive giga-fatigue model for FV520B-I is established and the actual fatigue life is calculated by substituting the actual defect value into the corresponding fatigue life model.

The primary factor of the fatigue failure is determined by the competition between the surface defect and internal inclusion. Fatigue life models and life curves are established with the ultrasonic experimental data. In the competition region, the failure caused by internal inclusion and the failure caused by surface defect have the equal opportunity to occur. Fatigue failure prefers the location with low fatigue strength, so the fatigue strength is chosen as the theatrical analysis criteria of the competition and the defect value is the direct analysis criterion in the practical engineering. In critical state, the fatigue strength affected by internal inclusion and the strength affected by surface defect are equal, then the critical defect value is calculated. By comparing the actual defect value with the critical defect value, the primary factor of final fatigue failure is determined. Then the competitive giga-fatigue model is established and the actual fatigue life is calculated by substituting the actual defect value into the corresponding fatigue life model.Figure optionsDownload as PowerPoint slide