Cumulative Fatigue damage of AA7075-T6 under Shot Peening and Ultrasonic Surface Treatments

Marwa S. Mahammed; Hussain J. Alalkawi; Saad T. Faris

doi:10.24237/djes.2021.14101

Authors

Marwa S. Mahammed
eng_grand-mech022@gmail.com
Department of Mechanical Engineering, College of Engineering, University of Diyala, 32001 Diyala, Iraq
Hussain J. Alalkawi Department of Mechanical Engineering, College of Engineering, University of Diyala, 32001 Diyala, Iraq
Saad T. Faris Department of Mechanical Engineering, College of Engineering, University of Diyala, 32001 Diyala, Iraq

Keywords:

AA7075, Cumulative fatigue damage, UIT, sp, Life improving

Abstract

One of the important aspects of mechanical design is improving fatigue life.; In this work, the effect of Ultrasonic impact treatment (UIP) and shot peening (SP)on constant cumulative fatigue life and fatigue strength of AA7075-T6 were studied; The sample group was machined and primed, and some specimens were treated using ultrasonic impact therapy (UIT) with one line of peening. Fatigue experiments were conducted under constant and variable amplitude (R=-1) at ambient temperature to determine the fatigue life of the S-N curve and fatigue strength during treatment 3.46% and 8.57% at 107 cycles for (UIT) and (SP). Cumulative fatigue damage testing was carried out for two steps loading it is observed that the fatigue life for SP and UIP treated specimens was improved compared to the unpeeled results. The fatigue endurance limit was enhanced by 35% for UIT and 54% for SP. The fatigue life for both treatments was much improved compared to as-received metal. These results also show a strong tendency of increasing fatigue strength after application of (UIT) and (SP) with an increase in mechanical properties of the material used.

Conclusion

The constant fatigue properties are considerably enhanced by (UIT) and (SP) techniques. The fatigue strength at 107 cycles is improved by 3.46% and 8.57% for UIT and SP respectively.
Cumulative fatigue life was increased by 13.9 percent and 12.6 percent for low-high and high-low loading by UIT, respectively, while 36.6 percent and 22.3 percent were increased for low-high and high-low loading by SP, respectively, and fatigue life was improved by 36 percent and 54 percent for UIT and SP.
The (UIT) and (SP) techniques are a suitable method for hardening the surface of metals due to the formation of a hard layer by increasing compressive residual stresses.
The Miner theory does not follow the conservative and detailed prediction of the life of certain fatigue specimens

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