Survey about effects of shot peening conditions on fatigue performances of Ti–6Al–4V mechanical specimens featured by different cross-section geometries

The present article provides a technical survey of the effects of shot peening conditions on the fatigue performance of Ti–6Al–4V specimens representative of the material (and the surface treatment) used in helicopter rotor hubs. As the effects of shot peening on non-plain surfaces have been fairly neglected in the scientific literature, the present work attempts to define the effects of shot peening on different specimens, featuring specific cross-section geometries, namely smooth and sharp edged specimens. Experimental tests also include measurements of the residual stress field caused by shot peening and the definition of the fatigue limit (by means of the ‘staircase method’) for all the tested specimen configurations. The present study proceeds with an optical and scanning electron microscopic investigation of the dynamics and causes of the different fatigue limits associated with the geometrical features. The present study conveys a strong correlation between specimen geometry and shot peening microstructural effects, resulting in different fatigue performances. The present work concludes that, whenever surface treatment is involved in the manufacturing process, the component's design must be included, in addition to the required geometrical features for the operative conditions, an evaluation of how these provided features might affect the surface treatment outcome.