PSI - Issue 53

R.F. Fernandes et al. / Procedia Structural Integrity 53 (2024) 144–150 Author name / Structural Integrity Procedia 00 (2019) 000–000

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However, the results for a shorter fatigue life, characterized by higher levels of deformation, exhibit remarkable similarity between both notched and unnotched specimens for both the AB and SR series. This aspect is discussed in the following section. 3.3. Residual stresses The residual stresses were measured in the transversal direction of the samples cross-section with an average X ray penetration depth of 11 μ m. Figure 4 displays the results of residual stresses for a total thickness of 500 μ m. It is possible to observe that the as-built series exhibit an increasing behavior, while SR series has induced a decrease and stabilization of residual stress values. The homogenization observed in the SR series resulted in residual stress values three times lower than those in the AB series, considering a depth of 500 μ m. Moreover, the residual stresses in the AB series could be attributed to the high thermal gradients generated during the manufacturing process.

Fig. 3. Residual stresses gradient comparison between As-built (AB) and Stress relief (SR).

The increase in the fatigue strength mentioned above is justified by the heat treatment homogenization of the residual stresses throughout the material depth. It is important to note that the similar values in the shorter fatigue life between the series for both notched and unnotched specimens can be attributed to the higher values of deformation that reduces the residual stresses (Zhu et al., 2021). This effect is amplified in the case of notched specimens due to the higher levels of deformation caused by stress concentration at the notches. 3.4. Fatigue life predictions Fatigue life predictions were calculated using the constant amplitude fatigue results (R=0) from a previous study and by applying the SWT criteria, as described in Eq. (1) (Smith, 1970), to consider the stress ratio effect: �� �� � � ��� , (1)