PSI - Issue 17

C.A.R.P. Baptista et al. / Procedia Structural Integrity 17 (2019) 324–330 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Conclusion

In this work, aluminum alloy 2024-T3 C(T) specimens (4.5 mm thick) were treated by LSPwC technique using a pulsed (9 ns) Nd:YAG laser operating in the second harmonic (  = 532 nm) and pulse energy of about 0.26 J. The power density was estimated to be 5.2 GW/cm 2 . The overlapping rates of 50% and 75% were adopted for the laser treatments. The surface analyses showed that both hardness and roughness increased due to LSPwC treatment. As for the XRD measurements, despite their high scattering, a slight increase in the surface residual stresses compared to untreated specimen was also achieved. No significant effect due to the overlapping rate was observed in the surface analyses. Constant amplitude FCG tests were performed with two distinct load ratios: R = 0.2 and R = 0.5. A small increase in the crack closure loads (P cl  1.1-1.2 P min ) was evinced for the samples tested at R = 0.2 compared to the untreated ones, whereas negligible effect (P cl < 1.05 P min ) was observed in the R = 0.5 results. With regard to the number of cycles for crack growth, the three laser treated samples tested at R = 0.2 presented an increased number of cycles compared to both of the untreated specimens, whereas no gain was verified for the treated samples tested at R = 0.5; on the contrary, a decrease in the number of cycles was observed. It seems that for the higher R tests, where no crack closure occurs, a deleterious effect of laser treatment prevails, possibly due to surface damage. The presented results indicate that the increase in overlapping rate is not effective for the adopted LSPwC conditions. In further efforts it is intended to use higher pulse energy laser in order to achieve superior peening effect aiming to improve the FCG behavior of LSPwC treated samples.

Acknowledgements

The authors are thankful to Institute of Aeronautics and Space (IAE/DCTA) for conducting the fatigue crack growth tests. C.A.R.P. Baptista also acknowledges CNPq (proc. 456808/2014-0 and 310074/2017-7) for supporting this research.

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