A model to predict S–N curves for surface and subsurface crack initiations in different environmental media

• Fatigue strength in environmental media is significantly decreased.
• Formation of different fractographies is attributed to different crack driving forces.
• Subsurface crack initiation is observed at nonmetallic inclusions in 3.5% NaCl solution.
• A model is proposed to study the relationship between fatigue life and material property.
• The model prediction is in good agreement with experimental observations.

The influence of environmental media on crack propagation of a structural steel at high-cycle and very-high-cycle fatigue (VHCF) regimes was investigated with the fatigue tests in air, water and 3.5% NaCl aqueous solution. The fatigue strength in water and 3.5% NaCl solution is significantly decreased and the cracking morphology due to different driving forces is presented. A model is proposed to explain the influence of environmental media on fatigue life, which reflects the variation of fatigue life with applied stress, grain size, inclusion size and material yield stress. The model prediction is in good agreement with experimental observations.