Advanced Structural Analysis/Part I - Theory/Failure Modes/Fatigue/Crack Initiation/Loading/Influence of Mean Stress/Algebraic Models

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The effect of mean stress, ,can be modeled by the following relations:

  • Soderberg: ;
    which is conservative for most engineering alloys
  • Modified Goodman: ;
    which is nonconservative when . It is however, a good approximation for brittle materials and conservative for ductile alloys, when
  • Gerber: ;
    which is only valid when , as a result of the quadratic term. It is a good approximation for ductile alloys