Considerations of Allowable Stress of Corrosion Fatigue (Focused on the Influence of Pitting)

Long life corrosion fatigue behaviour is discussed. The importance of (i) quantification of corrosion pit depth (or surface roughness caused by corrosion) as a function of service period and (ii) corrosion pit modelling is emphasized. Extreme value statistics is useful for corrosion pit depth quantification. It is demonstrated that a corrosion pit can be treated as an elliptical crack with the same depth and surface length as a pit. From these considerations, a method for determination of a reasonable allowable stress in corrosion fatigue is proposed. Finally, an example of an allowable stress is given, i.e. the allowable stresses of a real machine component under rotating bending stress are determined from estimation curves of pit depth together with corrosion fatigue crack growth data.