PSI - Issue 2_B

7

Vaibhav Pandey et al. / Procedia Structural Integrity 2 (2016) 3288–3295 Author name / Structural Integr ty P o edi 00 (2016) 00 –000

3294

Fig. 7. LCF life for different USSPed conditions at total strain amplitude of Δε t /2= ±0.4%.

The fractographs of the un-USSPed and USSPed 60 specimens, tested in fatigue at strain amplitudes of ± 0.5% and ± 0.6% are shown in Fig. 8. Characteristic fatigue striations were observed in all the conditions. Some voids may also be seen resulting from the shearing/cracking of the coarse precipitates during cyclic loading. The number of crack initiation sites was found to be more in the USSPed samples and it may be due to increase in surface roughness which acted as active site for crack nucleation due to stress concentration. However, most of these cracks did not propagate due to associated compressive stresses and thus leads to increase in LCF life.

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Fig. 8. Fractographs of AA7075 of the specimens tested in different conditions (a) un-USSPed at strain amplitude ± 0.6%, (b) USSPed at strain amplitude ± 0.6%, (c) un-USSPed at strain amplitude ± 0.5%, (d) USSPed at strain amplitude ± 0.5%.