PSI - Issue 66

Davide D’Andrea et al. / Procedia Structural Integrity 66 (2024) 449–458 D’Andrea et al./ Structural Integrity Procedia 00 (2025) 000–000

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Fig. 5. Temperature evolution during static tensile tests-

The other two static tensile tests exhibit the same temperature behavior. The average value of the limit stress for the PA12 obtained by MJF is equal to σ lim = 30.2±1.4 MPa. 4.3. Fatigue limit estimation by Risitano’s Thermographic Method To verify the results obtained by the STM a single stepwise fatigue test has been performed on the same PA12 specimen geometry. The stress level has been increased of 2 MPa every 3000 cycles up to the specimen failure starting from 24 MPa. In Fig. 6a are reported the maximum temperature values measured on the ROI vs. the number of cycles for each load step. Generally, the higher the applied stress level, the higher the stabilization temperature. The last stress level (σ a = 34.88 MPa) present a stabilization temperature of 4.8 K then, at 1800 cycles, temperature experiences a higher temperature increment with the failure of the specimen. The different recorded stabilization temperature can be reported vs. the applied stress level (Fig. 6b) and, according to RTM, stress levels below the fatigue limit (squares) have lower stabilization temperatures respect stress levels above the fatigue limit (dots). The fatigue limit can be identified in the knee region of the temperature-stress graph. It is possible to perform two linear regression and assess the fatigue limit as the intersection point. The fatigue limit assessed by RTM is equal to σ 0 RTM = 31.8 MPa.