INFLUENCE OF DEFECTS AND SHARP NOTCHES ON AXIAL FATIGUE STRENGTH OF ADDITIVELY MANUFACTURED MARAGING STEEL SPECIMENS

In recent papers the authors investigated the fatigue strength of additively manufactured (AMed) maraging steel specimens, where the effects of building orientation and ageing heat treatment were analysed. Then, the defect influence on fatigue behaviour was studied on the basis of the √("area" ) parameter to calculate the stress intensity factor of the killer defects, which were examined by SEM observations of the fracture surfaces. In the present paper, new axial fatigue test results on AMed maraging steel produced by two different AM system (EOS Gmbh and SISMA SpA) are presented. Furthermore, axial fatigue tests were carried out on wrought maraging steel specimens both in annealed and in aged condition. A stress intensity factor-based design curve for the untreated specimens produced by SISMA were obtained taking into account the short crack effect by means of the El-Haddad-Smith-Topper model. The relevant material length parameter has been calibrated by matching this model with Murakami’s expression of the threshold range of mechanically short cracks. The advantage of the adopted engineering approach is that only Vickers hardness of the material is necessary. Eventually, the stress intensity factor-based design curve was adopted to estimate the fatigue strength of sharp V-shaped notches characterised by a reduced notch opening angle.