Analytical over-energy with numerical investigation on fatigue small crack and the performance of multiaxial criterion linked to the threshold stress

The first part is dedicated to analyze an over-energy under rotating bending. An Asymptotic approach transformed over-energy in biquadratic function predict the threshold stress σ*. The database of 30NCD16 steel studied by Dubar are used for fatigue assessement. These stresses σ* are shears and lower than the endurance limit σ -1 . The threshold stress is expressed by nominal stress based on Mises criteria. Hence, the small crack and shear stress reproduces well the Kitagawa plot. We show also that this Kitagawa plot is bounded by the Bazant low. The second part is intending to validate the new multiaxial fatigue criterion. The previous expression of an over-energy under rotating bending-torsion and the triaxiality function suggested by De Leiris are formulated our criterion. The analysis of the fatigue defects uses both global and critical plane approaches. The data tests refer to the experimental tables in fatigue for S65A steel by Gough. The Dong Van2 and Robert’s criteria appears to be the most efficient. The quality of this study is to inform the reader on the steps of analyzing fatigue resistance with initiating small crack in order to prove the applicability of threshold stress methods. Further investigations will aim to validate these results by experimental test.