PSI - Issue 59

Jesús Toribio et al. / Procedia Structural Integrity 59 (2024) 90–97 Jesús Toribio / Procedia Structural Integrity 00 ( 2024) 000 – 000

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In order to complete the analysis, Fig. 6 shows the evolution of K H against the TTS zone aspect ratio for the four fatigue pre-cracking loading regimes considered in the study (Table 3). Again a decrease of K H is observed when the value of the aspect ratio a H /b H increases, reaching a minimal value in the case of a semicircular TTS region ( a H /b H =1). According to this result, the values of the critical SIF in harsh environment are higher when an intense fatigue pre-cracking loading regime is applied. A final point should be emphasized. According to Figs. 4 and 6, the values of the critical SIF K H in samples subjected to high fatigue pre-cracking loads with a small TTS zone aspect ratio are higher than unity. However, the fracture surfaces observed experimentally in prestressing steels wires (Fig. 1) have a fatigue pre-crack ( a O /b O ) with a semi-elliptic shape and aspect ratio of 0.78 (Athanassiadis et al., 1981; Caspers et al., 1986). Therefore, it is reasonable to consider that the value of the crack aspect ratio of the TTS zone after fatigue pre-crack ( a H /b H ), lower than a O /b O , can be placed near to 0.6-0.7 (Fig. 3). Therefore, in this interval of values, K H never reaches the fracture toughness of the material ( K O ), as shown in Fig. 6.

Fig. 4. Critical SIF in hydrogenating environment K H as a function of the fatigue pre-cracking intensity K max .

Fig. 5. Evolution of the slope of critical SIF in harsh environment K H against K max with the aspect ratio a H / b H of the semi-elliptical TTS region.

Fig. 6. Critical SIF in hydrogen environment K H versus semi-elliptical TTS region aspect ratio a H / b H for different fatigue pre-cracking level K max .