No abstract

This paper discusses a design procedure for structural components subjected to proportional and nonproportional low cycle fatigue damage. Strain multiaxiality and nonproportional factor were introduced for discussing the procedure. The applicability of the multiaxial proportional and nonproportional parameters was examined for the accurate prediction of proportional and nonproportional fatigue lives. A design flow was presented that indicates judging method to use uniaxial, multiaxial proportional or nonproportional damage law. The necessary data for the judgment were the exponent of Coffin-Manson law, a constant that expresses the amount of additional hardening and strain history.

In non-proportional multiaxial fatigue, principal directions of strains and stresses change during a cycle. In such a case, strain and stress ranges and mean strain and stress cannot be easily determined. Developing an appropriate method of determining the ranges and mean values are needed for the design of pressure vessels. This paper proposes a method for calculating the strain and stress ranges and mean values in non-proportional multiaxial loading. Based on the method proposed, non-proportional strain and stress ranges are derived and the accuracy of life prediction method using the ranges is discussed for type 304 stainless steel fatigued under 14 non-proportional strain paths.