Effect of non-metallic inclusions on AISI 4140 fatigue strength

In the present paper, a procedure for fatigue strength assessment of high strength steel (AISI 4140) containing non-metallic inclusions (NMIs) is proposed. Such a procedure implements: (i) a defect content analysis, (ii) the root area-parameter model, and (iii) the multiaxial critical plane-based criterion by Carpinteri at al. According to the defect content analysis, the distribution of NMIs is determined in two cross-sections perpendicular to the maximum principal stress directions under normal and shear uniaxial cyclic loadings. The return periods, obtained optimising the accuracy of the procedure in terms of fatigue strength estimation, are determined by taking into account five different prediction volumes. The results achieved through the proposed procedure are compared with both the experimental data and the results obtained employing the Carpinteri et al. criterion without optimisation.