Some Considerations in Using Strain-Life Approach in Fatigue Design

The use of the strain-life technique in designing for finite fatigue life is discussed. The difference in mathematical form of the cyclic stress-strain curve and hysteresis loops is explained. Examples are given to illustrate that stronger materials are not necessarily better for fatigue resistance. The importance of the knowledge of actual operating conditions of components and structures in designing for finite life is emphasized. Conditions under which the strain-life and K_f-Δs methods yield the same results are derived. A list of materials which satisfy these conditions is included.