PSI - Issue 17

J.P. Pascon et al. / Procedia Structural Integrity 17 (2019) 411–418 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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In order to the show the plastic deformation evolution along the last load cycle (2 a = 15 mm), the plots of the equivalent plastic strain ( κ ) versus the x -coordinate are provided in Figure 6. As in Figure 5, the values are higher near the crack tip and for the load ratio R = -1. Moreover, the differences between the maximum load ( F = 20.5 kN) and the unloading ( F = 0) are higher for the load ratio R = 0. For the load ratio R = -1, one can see some differences near the crack tip comparing the maximum compressive load ( F = -20.5 kN) and the end of the cycle ( F = 0). Again, it is shown that the compressive part of the cycle contributes to the increase in the plastic strain.

Fig. 6. Equivalent plastic strain ( κ ) along the crack line (coordinate x as given in Fig. 2). The depicted values correspond to the nodes with coordinates y = 0 (bottom) and z = 4.8 mm (surface).

4. Conclusion

In this work, a numerical model for the stress-strain state ahead of a fatigue crack considering elastoplastic material with isotropic hardening governed by Swift’s law was presented. The analysed centre-cracked plate simulated a M(T) specimen made of 6005-T6 aluminum alloy. Numerical simulations were performed comparing two cyclic loadings having the same peak load and distinct ratios, R = 0 and R = -1. The results showed no significant variation in terms of the equivalent stress ( σ eq ), but considerable differences in the equivalent plastic strain ( κ ). Therefore, the compressive phase in the specimen under R = -1 also contributes to increase the equivalent plastic strain, which means that the level of yielding becomes higher even when the specimen is compressed. This result is in accordance to experimental data showing a deleterious effect of the compressive portion of the cyclic loading on the fatigue crack growth resistance.

Acknowledgements

The authors are thankful to CNPq (proc. 456808/2014-0 and 310074/2017-7) for supporting this research.