PSI - Issue 21

Mehmet F. Yaren et al. / Procedia Structural Integrity 21 (2019) 31–37 Yaren M. F. et al / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Results Single overload and its effect on fatigue crack growth life are investigated by experime nt in this study. It’s known that single overload retards crack growth because of plasticity on crack tip and the magnitude of overload is very important for this phenomenon. Finite element simulations and fracture toughness tests show that the maximum load for the used Al-7075 specimens with 27-28 mm crack lengths is nearly 15 kN. Therefore, single overload ratios ranged from 9kN/7kN to 14kN/7kN. The effect of overload magnitude on crack growth life is shown in Fig. 1. As seen from the figure, total crack growth life increases with magnitudes of overload ratios. The longest crack growth life is obtained in the case of 14kN/7kN as expected. In the case 9kN/7kN, retardation effect cannot be seen very clearly, as the overload ratio is very small.

Fig. 3. Effect of single overload magnitude on fatigue crack growth life.

Some crack growth retardation models are used for life prediction and results are compared with experimental part of this study. Results are plotted for each overload ratio and all comparisons are given in Fig. 4. As seen in the figure, all models are in agreement with experimental results except a few models in the case high overload ratios. It can be seen in Fig 4 c and d that Willenborg and models with its modifications underestimate crack growth life in the region after the overload.