Towards the optimisation of the shot peening process in terms of fatigue resistance of the 2024-T351 and 7150-T651 aluminium alloys

The effect of the shot peening process on the surface changes occurring in the 2024-T351 and 7150-T651 aluminium alloys are examined using a design of experiments approach. Shot size, incidence angle, intensity and coverage were considered to be the main control factors. A mathematical method of obtaining the peening intensity at saturation point, from Almen strips peened for different length of time, was developed. Coverage results, determined experimentally, using image analysis, are shown to be consistent with predictions obtained using the Avrami and Holdgate theoretical methods. The important material parameters affected by shot peening, which are associated with changes in fatigue resistance, are the residual stress (RS), the surface roughness (SR) and the work hardening (WH). Design of experiment analysis was applied to obtain the best and worst expected combinations of RS, SR, and WH for fatigue life. The result of the fatigue tests using these combinations will be discussed in terms of current fatigue approaches.