PSI - Issue 57

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"Author name" / Structural Integrity Procedia 00 (2019) 000 – 000

Guillaume THOQUENNE et al. / Procedia Structural Integrity 57 (2024) 191–198

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b

Fig. 3. TE74 specimen geometry. a/ Crowned specimen – b/ Cylindrical specimen.

4. Specimen sizing The objective of specimen sizing is to assure a fatigue crack initiation in the heat treatment transition zone preventing core material plastic strain. Two parameters are considered: specimen geometry, which leads the Hertz stresses profile, and induction hardening depth which allows to place the transition zone at the right depth considering the shear stresses profile. As the fatigue crack initiation is induced by the shear stresses and the plastic strain due to the main stresses, we consider in this section the two fields separately. 4.1. Conditions of calculation Finite element calculations are performed with Abaqus software using the contact solver. The following specimen geometry is considered: • Diameter: 70 mm. • Radius of curvature: 300 mm. We thus calculated the complete stress field to extract the shear stresses and the Von Mises equivalent stresses ( = √ 1 2 √( 1 − 2 ) 2 +( 1 − 3 ) 2 +( 2 − 3 ) 2 ) which allow us to consider independently the plastic strain issue and the fatigue crack initiation respectively. 4.2. Material characteristics For this study, the chosen material is a typical induction hardened steel: 42CrMo4. Considering a typical induction hardening heat treatment on a 42CrMo4 steel, we took into account expected surface and core hardness, respectively 660 HV and 330 HV and a transition zone depth = 0.1 x IHD. From those properties we computed the Ultimate Tensile Stress (UTS) profile, based on the ISO 18265:2013 [2] standard Hardness-UTS conversion table and the Yield strength (YS) profile derived by the UTS profile, considering YS = 0.9 x UTS. We then considered the Cetim database [3] and obtained the torsional limit fatigue for 10 7 cycles (  D = 0.35 x UTS, see Table 1). The mechanical properties considered for the computation are presented in the Table 2 here after.