PSI - Issue 76

R. Fernandes et al. / Procedia Structural Integrity 76 (2026) 43–49

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specimen, the first two overloads resulted in similar reductions comparable to those of the stress-relieved specimen. However, the third overload resulted in the fracture of the specimen. The parameter U was obtained and is presented in Fig. 4. Both figures demonstrate similar behavior, with the second and third overloads contributing to the activation of the crack closure phenomena in specimens that did not fracture under the overload conditions. Contrary, the first overloads exhibit no effect on crack closure across all cases. Current behavior is quite similar to that observed by the authors, Jesus et al. (2022), in which refers that overloads applied at lower ΔK values had no impact on crack closure levels due to insufficient plasticity at the crack tip. The as-built specimen exhibited a minimum load ratio parameter of 0.82 for the second overload. The stress relieved specimen exhibited a minimum load ratio parameter of 0.83 and 0.73 for the second and third overload, respectively. Shot peening slight increases the parameter U in transient regime, after second and third overloads.

Fig. 4. Parameter U against the stress intensity factor range for transient regime: a) No shot-peened; b) Shot-peened.

Figure 5 shows the fatigue crack growth rates curves for shot-peened and non-shot-peened specimens under an overload ratio of 2.0. It is observed that the four specimens’ conditions exhibit similar behavior under the same overload conditions. However, at t he higher stress intensity factor range (ΔKOL = 9 MPa√m), the as -built (AB) specimen fractured when the overload was applied.