Fatigue Prediction using Critical Plane Methods
Research on fatigue started in the 19th century, initiated following failing railroad axles that caused train accidents. In a rotating axle, stress varies from tension to compression and back to tension in one revolution. The load history is simple because it is uniaxial and proportional. Fatigue can then be evaluated with the S-N curve, also known as the Wöhler curve, which relates stress amplitude to a component’s life. In many applications we deal with multiaxiality and non-proportional loading. In this instance, the S-N curve is insufficient for fatigue prediction. Critical plane models examine stress state in different orientations in space and can therefore incorporate some effects of multiaxiality and non-proportionality. Because they can accurately predict the fatigue failure phenomena for many structural applications, they have gained a wide acceptance among the engineering community.