PSI - Issue 54

R.F. Fernandes et al. / Procedia Structural Integrity 54 (2024) 300–306 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results 3.1. Hardness and Monotonic tensile properties

Table 2 presents the hardness and monotonic tensile properties of the material, for the as built (AB) and stress relief (SR) series. It is possible to understand that the heat treatment has significantly influenced the mechanical behavior of the material. The AB series shown an average hardness of 165.6 HV, whereas the stress relief has a hardness of 114.4 HV, representing a 30% reduction.

Table 2. Hardness and monotonic tensile properties. Series HV 0.1 σ UTS (MPa)

σ YS (MPa)

ε f (%)

E (GPa)

AB SR

165.6 114.4

435 380

250 210

4.1 5.6

72 72

The decrease in hardness resulted in a reduction in monotonic tensile properties. Specifically, the ultimate tensile strength and yield strength of the SR series have decreased 13% and 16%, respectively. On the other hand, the SR ductility has increased 37% compared with the AB series. 3.2. Fatigue results The fatigue results for both the unnotched and notched specimens are displayed in Figure 2 for the AB and SR series. In general, it is evident that the SR series exhibits a higher fatigue strength in all cases. Figure 2a) specifically shows the fatigue results of the unnotched specimens for the AB and SR series. Upon closer analysis, it is evident that the SR series had a higher fatigue strength than the AB series. Comparing the results for a life of 10 5 cycles, the SR series increased by 11%. If a longer fatigue life is considered, the improvement can reach up to 15%. In Figure 3a), a comparison of semicircular notched specimens is presented for the AB and SR series. Some scattering was noted, mainly in the AB series. From this analysis it can be concluded that the SR series also had a higher fatigue strength. However, for a shorter fatigue life, both the AB and SR series exhibited similar behaviors. When framing 10 5 cycles, it is possible to conclude that the SR series has an increase of 7% in fatigue strength.

150 125 175 200

AB

SR

100

Ds [MPa]

75

10 4

10 5

10 6

10 7

Number of cycles to failure, N f

Fig. 2. Fatigue results for unnotched specimens for both as built (AB) and stress relief (SR) series.